Cortical Stimulation Mapping

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George A Ojemann - One of the best experts on this subject based on the ideXlab platform.

  • Cortical Stimulation Mapping and wada results demonstrate a normal variant of right hemisphere language organization
    Epilepsia, 2012
    Co-Authors: Daniel L Drane, George A Ojemann, Ettore Lettich, Jenny Rorabackcarson, Adam O Hebb, Tamir Y Hersonskey, Timothy H Lucas, Daniel L Silbergeld, John W Miller, Jeffrey G Ojemann
    Abstract:

    Purpose Exclusive right hemisphere language lateralization is rarely observed in the Wada angiography results of epilepsy surgery patients. Cortical Stimulation Mapping (CSM) is infrequently performed with such patients, as most undergo non-dominant left hemisphere resections, which are presumed not to pose any risk to language. Early language reorganization is typically assumed in such individuals, taking left hemisphere epileptiform activity as confirmation of change resulting from a pathological process. We present data from CSM and Wada studies demonstrating that right hemisphere language occurs in the absence of left hemisphere pathology, suggesting it can exist as a normal, but rare variant, in some individuals. Further, these data confirm the Wada test findings of atypical dominance.

  • Cortical Stimulation Mapping and wada results demonstrate a normal variant of right hemisphere language organization
    Epilepsia, 2012
    Co-Authors: Daniel L Drane, George A Ojemann, Ettore Lettich, Jenny Rorabackcarson, Adam O Hebb, Tamir Y Hersonskey, Timothy H Lucas, Daniel L Silbergeld, John W Miller, Jeffrey G Ojemann
    Abstract:

    Cortical Stimulation Mapping (CSM) involves inducing a localized electrical blockage of Cortical function, and has been used in neurosurgery to identify areas essential to language functioning since the pioneering work of Penfield and Roberts with epilepsy surgery patients during the mid-1950s (Penfield & Roberts, 1959). Identification of language cortex enables the surgeon to avoid language areas when formulating a surgical strategy and to expand the resection of epileptic regions with increased safety (Kim et al., 2009). CSM results have brought insight to the distribution of language, confirming the presence of the classical Broca’s and Wernicke’s areas and identifying nontraditional sites found elsewhere in the cortex (Ojemann et al 1989). These data have also validated the accuracy of the intracarotid amobarbital (Wada) procedure, confirming that essential language sites are present in patients that are left-hemisphere (LH) dominant for language. The Wada procedure has served as the gold-standard for determining language dominance in presurgical patients since the early days of epilepsy surgery. Nevertheless, little data have been published examining CSM in patients who are determined to be exclusively right-hemisphere (RH) dominant for speech. Such individuals are believed to be rare, and atypical language lateralization is thought to often develop in patients following an early life injury involving their left cerebral hemisphere (Moddel et al., 2009; Rasmussen & Milner, 1977). Surgical patients experiencing such pathological language reorganization may not undergo CSM, as neurosurgical intervention is more likely to involve the LH of these individuals. As the Regional Epilepsy Center at the University of Washington has over 30 years of data involving CSM and the Wada procedure, we sought to examine the frequency of RH language dominance, validate the Wada procedure in these cases, and determine how the CSM results of such patients compare to those of individuals with typical speech lateralization. Validation of the Wada Procedure The Wada procedure has traditionally been the primary method for determining language dominance in neurosurgical candidates, as it provides a means to assess each hemisphere’s contribution to language function independently (Loring et al., 1992). This procedure remains in use by most epilepsy centers for the presurgical evaluation, although increasing efforts have been made to employ a noninvasive alternative [e.g., fMRI] (Arora et al., 2009). The principle behind the Wada was demonstrated by W. James Gardner in 1941 (Gardner, 1941), who injected procaine directly into the cortex thought to potentially be involved in language. Juhn Wada more formally established this procedure in the area of epilepsy surgery, making separate injections of amobarbital into each internal carotid artery to produce hemispheric anesthesia (Wada, 1949). During this period of anesthesia, patients are asked to carry out tasks to evaluate language and memory. Anesthetizing the area renders it nonfunctional, causing the hemisphere with language representation to be revealed when language deficits appear during an injection. The validity of LH language dominance as predicted by the Wada procedure has been demonstrated in several group studies using CSM (Loring et al., 1992; Ojemann et al., 1989), yet validity data for RH language dominance in epilepsy have been restricted primarily to a handful of case studies with one or two subjects (Rosenbaum et al., 1989; Wyllie et al., 1990). Duffau and colleagues (2008) found RH language sites in a small series of tumor patients (n=9) who were all left-handed, but did not have Wada data on any of their patients (some percentage were likely bilateral language cases). One recent study examined CSM results in 15 neurosurgical patients (mostly tumor patients) that had exhibited either RH (n=7) or bilateral (n=8) language on the Wada (Chang et al., 2011). These researchers found language sites in the RH of all 15 patients, thoroughly delineated their neuroanatomical location, and noted that the pattern of language sites was consistent with findings from LH language dominant patients. There are also a few additional studies that demonstrate RH speech in a small number of patients identified as bilateral by the Wada (Jabbour et al., 2005; Loring et al., 1988). Prevalence of Atypical Language Lateralization Years of accumulated knowledge from the use of the Wada confirms that most neurosurgical candidates are LH dominant for language, with atypical language lateralization in a minority (Loring et al., 1990; Moddel et al., 2009). The prevalence of exclusive RH speech is believed to be infrequent, and right-sided surgery on such patients is believed to be rare. Most studies have suggested the prevalence of RH language representation to range from approximately 2 to 10% in epilepsy patients undergoing the Wada (Loring et al., 1990; Moddel et al., 2009), with the exception of a study by Rasmussen and Milner (1977) that estimated it to be as high as nearly 20%. These studies have estimated bilateral language representation to range from 5 to 25% in this population. Variability in reported prevalence rates is believed to primarily reflect differences in the implementation of the Wada across epilepsy centers, as many institutions have not routinely administered the Wada procedure to all individuals. Most centers select patients for the Wada based on the presumed clinical likelihood of atypical language occurrence. Variability in reported rates of atypical language may also be influenced by small sample sizes used in these studies, and general variability across Wada methodologies. Finally, while the Wada procedure is invasive and administered only to neurosurgical candidates, functional technologies (fMRI, functional transcranial Doppler sonography, MEG) have been used to estimate rates of atypical language prevalence in healthy subjects (Knecht et al., 2000; Szaflarski et al., 2002). These studies suggest that atypical language lateralization (RH or bilateral) will occur in 4 to 7.5% of right-handers and up to 22% of left-handers in the general population. Studies of “crossed-aphasia,” a term for the development of language impairment in normal right-handed individuals who sustained damage to the right hemisphere later in life, also provides evidence that atypical language lateralization may be a normal variant of language development (Hecaen & Albert 1978). Such studies suggest that atypical language may occur in .4% to 3% of healthy right handed adults (Marien et al 2004; Zangwill 1979), although most reports have not included the necessary functional imaging studies to determine whether this reflects bilateral or right only language (See Vandervliet et al 2008; Vitali et al 2011 for recent exceptions). More than two hundred cases appear in the research literature (Marien et al 2004); with more recent studies documenting similar aphasia types, lesion-behavior relationships, and recovery patterns as in uncrossed aphasia (Castro-Caldas & Confraria 1984; Coppens et al 2002; Yarnell 1981). The similarity of the resulting syndromes suggests that atypical language representation could parallel the more typical left-hemisphere variety. Right-hemisphere Speech Patients as Surgical Candidates Most neurosurgical patients found to have RH speech are undergoing surgical procedures involving their LH. This is because atypical lateralization of the neural language network appears to occur most frequently as a result of early childhood neuronal injuries leading to a shift of language functions from the left to the RH. A previous study from our Center (Miller et al., 2003) had also suggested that atypical speech lateralization may not occur in epilepsy patients with normal neurologic histories through the age of 15 years. In the current study, we retrospectively examined the CSM and Wada data of all patients found to have RH speech and who also underwent RH surgical procedures. This represents the largest published sample of epilepsy patients undergoing the Wada procedure, and is unique in that it is a near consecutive series requiring the obligatory completion of this study for all surgical candidates during the time span of the study regardless of hemisphere of seizure onset and the routine injection of both hemispheres. Additionally, the Wada procedure remained unchanged throughout the duration of the study. We predicted that CSM results for these RH patients would positively identify one or more essential language sites in each patient, providing validation for the sensitivity of the Wada procedure for detecting RH speech in a large, unselected sample of RH language patients. We also hypothesized that the general distribution of sites would be consistent with the patterns observed in neurosurgical patients with LH language dominance, as we believe that prior research suggests this group will predominantly reflect a sample of patients with an atypical yet normal variant of language organization.

  • analysis of naming errors during Cortical Stimulation Mapping implications for models of language representation
    Brain and Language, 2010
    Co-Authors: David P Corina, Brandon Conner Loudermilk, Landon T Detwiler, Richard F Martin, James F Brinkley, George A Ojemann
    Abstract:

    This study reports on the characteristics and distribution of naming errors of patients undergoing Cortical Stimulation Mapping (CSM). During the procedure, electrical Stimulation is used to induce temporary functional lesions and locate 'essential' language areas for preservation. Under Stimulation, patients are shown slides of common objects and asked to name them. Cortical Stimulation can lead to a variety of naming errors. In the present study, we aggregate errors across patients to examine the neuroanatomical correlates and linguistic characteristics of six common errors: semantic paraphasias, circumlocutions, phonological paraphasias, neologisms, performance errors, and no-response errors. Aiding analysis, we relied on a suite of web-based querying and imaging tools that enabled the summative Mapping of normalized Stimulation sites. Errors were visualized and analyzed by type and location. We provide descriptive statistics to characterize the commonality of errors across patients and location. The errors observed suggest a widely distributed and heterogeneous Cortical network that gives rise to differential patterning of paraphasic errors. Data are discussed in relation to emerging models of language representation that honor distinctions between frontal, parietal, and posterior temporal dorsal implementation systems and ventral-temporal lexical semantic and phonological storage and assembly regions; the latter of which may participate both in language comprehension and production.

  • category specific recognition and naming deficits following resection of a right anterior temporal lobe tumor in a patient with atypical language lateralization
    Cortex, 2009
    Co-Authors: Daniel L Drane, George A Ojemann, Jeffrey G Ojemann, Daniel L Silbergeld, John W Miller, Elizabeth H Aylward, Daniel Tranel
    Abstract:

    We present a patient with right-hemispheric speech lateralization who exhibited severe recognition and naming deficits for unique objects (famous faces and landmarks) and grossly normal recognition and naming performances for nonunique objects (animals and man-made objects) following an anterior right temporal lobe (TL) resection of a ganglioglioma. While recognition deficits have been reported for famous faces following right temporal pole lesions, and for landmarks and geographic regions following right TL damage in general, this is the first reported case of both recognition and naming deficits for these objects resulting from a single lesion. These results are consistent with research suggesting that the neuroanatomic substrates for the recognition and naming of unique objects lie in the anterior TL regions. Left temporal pole lesions have been associated with naming deficits for unique objects while right temporal pole lesions have been associated with recognition deficits for unique objects. However, these findings suggest that the substrates of naming can be located in homotopic regions of the right hemisphere when language lateralization is atypical. As various object categories appear to have different neuroanatomical representations in the TLs, we discuss the possible benefits of sampling a wider array of objects during Cortical Stimulation Mapping of language.

  • dissociation of action and object naming evidence from Cortical Stimulation Mapping
    Human Brain Mapping, 2005
    Co-Authors: David P Corina, Richard F Martin, James F Brinkley, Erin K Gibson, Andrew Poliakov, George A Ojemann
    Abstract:

    This Cortical Stimulation Mapping study investigates the neural representation of action and object naming. Data from 13 neurosurgical subjects undergoing awake Cortical Mapping is presented. Our findings indicate clear evidence of differential disruption of noun and verb naming in the context of this naming task. At the individual level, evidence was found for punctuate regions of perisylvian cortex subserving noun and verb function. Across subjects, however, the location of these sites varied. This finding may help explain discrepancies between lesion and functional imaging studies of noun and verb naming. In addition, an alternative coding of these data served to highlight the grammatical class vulnerability of the target response. The use of this coding scheme implicates a role for the supramarginal gyrus in verb-naming behavior. These data are discussed with respect to a functional-anatomical pathway underlying verb naming.

Jeffrey G Ojemann - One of the best experts on this subject based on the ideXlab platform.

  • Cortical cartography reveals political and physical maps
    Epilepsia, 2014
    Co-Authors: David W Loring, William D Gaillard, Susan Y Bookheimer, Kimford J Meador, Jeffrey G Ojemann
    Abstract:

    Advances in functional imaging have provided noninvasive techniques to probe brain organization of multiple constructs including language and memory. Because of high overall rates of agreements with older techniques, including Wada testing and Cortical Stimulation Mapping (CSM), some have proposed that those approaches should be largely abandoned because of their invasiveness, and replaced with noninvasive functional imaging methods. High overall agreement, however, is based largely on concordant language lateralization in series dominated by cases of typical cerebral dominance. Advocating a universal switch from Wada testing and Cortical Stimulation Mapping to functional magnetic resonance imaging (fMRI) or magnetoencephalography (MEG) ignores the differences in specific expertise across epilepsy centers, many of which often have greater skill with one approach rather than the other, and that Wada, CSM, fMRI, and MEG protocols vary across institutions resulting in different outcomes and reliability. Specific patient characteristics also affect whether Wada or CSM might influence surgical management, making it difficult to accept broad recommendations against currently useful clinical tools. Although the development of noninvasive techniques has diminished the frequency of more invasive approaches, advocating their use to replace Wada testing and CSM across all epilepsy surgery programs without consideration of the different skills, protocols, and expertise at any given center site is ill-advised.

  • Cortical Stimulation Mapping and wada results demonstrate a normal variant of right hemisphere language organization
    Epilepsia, 2012
    Co-Authors: Daniel L Drane, George A Ojemann, Ettore Lettich, Jenny Rorabackcarson, Adam O Hebb, Tamir Y Hersonskey, Timothy H Lucas, Daniel L Silbergeld, John W Miller, Jeffrey G Ojemann
    Abstract:

    Cortical Stimulation Mapping (CSM) involves inducing a localized electrical blockage of Cortical function, and has been used in neurosurgery to identify areas essential to language functioning since the pioneering work of Penfield and Roberts with epilepsy surgery patients during the mid-1950s (Penfield & Roberts, 1959). Identification of language cortex enables the surgeon to avoid language areas when formulating a surgical strategy and to expand the resection of epileptic regions with increased safety (Kim et al., 2009). CSM results have brought insight to the distribution of language, confirming the presence of the classical Broca’s and Wernicke’s areas and identifying nontraditional sites found elsewhere in the cortex (Ojemann et al 1989). These data have also validated the accuracy of the intracarotid amobarbital (Wada) procedure, confirming that essential language sites are present in patients that are left-hemisphere (LH) dominant for language. The Wada procedure has served as the gold-standard for determining language dominance in presurgical patients since the early days of epilepsy surgery. Nevertheless, little data have been published examining CSM in patients who are determined to be exclusively right-hemisphere (RH) dominant for speech. Such individuals are believed to be rare, and atypical language lateralization is thought to often develop in patients following an early life injury involving their left cerebral hemisphere (Moddel et al., 2009; Rasmussen & Milner, 1977). Surgical patients experiencing such pathological language reorganization may not undergo CSM, as neurosurgical intervention is more likely to involve the LH of these individuals. As the Regional Epilepsy Center at the University of Washington has over 30 years of data involving CSM and the Wada procedure, we sought to examine the frequency of RH language dominance, validate the Wada procedure in these cases, and determine how the CSM results of such patients compare to those of individuals with typical speech lateralization. Validation of the Wada Procedure The Wada procedure has traditionally been the primary method for determining language dominance in neurosurgical candidates, as it provides a means to assess each hemisphere’s contribution to language function independently (Loring et al., 1992). This procedure remains in use by most epilepsy centers for the presurgical evaluation, although increasing efforts have been made to employ a noninvasive alternative [e.g., fMRI] (Arora et al., 2009). The principle behind the Wada was demonstrated by W. James Gardner in 1941 (Gardner, 1941), who injected procaine directly into the cortex thought to potentially be involved in language. Juhn Wada more formally established this procedure in the area of epilepsy surgery, making separate injections of amobarbital into each internal carotid artery to produce hemispheric anesthesia (Wada, 1949). During this period of anesthesia, patients are asked to carry out tasks to evaluate language and memory. Anesthetizing the area renders it nonfunctional, causing the hemisphere with language representation to be revealed when language deficits appear during an injection. The validity of LH language dominance as predicted by the Wada procedure has been demonstrated in several group studies using CSM (Loring et al., 1992; Ojemann et al., 1989), yet validity data for RH language dominance in epilepsy have been restricted primarily to a handful of case studies with one or two subjects (Rosenbaum et al., 1989; Wyllie et al., 1990). Duffau and colleagues (2008) found RH language sites in a small series of tumor patients (n=9) who were all left-handed, but did not have Wada data on any of their patients (some percentage were likely bilateral language cases). One recent study examined CSM results in 15 neurosurgical patients (mostly tumor patients) that had exhibited either RH (n=7) or bilateral (n=8) language on the Wada (Chang et al., 2011). These researchers found language sites in the RH of all 15 patients, thoroughly delineated their neuroanatomical location, and noted that the pattern of language sites was consistent with findings from LH language dominant patients. There are also a few additional studies that demonstrate RH speech in a small number of patients identified as bilateral by the Wada (Jabbour et al., 2005; Loring et al., 1988). Prevalence of Atypical Language Lateralization Years of accumulated knowledge from the use of the Wada confirms that most neurosurgical candidates are LH dominant for language, with atypical language lateralization in a minority (Loring et al., 1990; Moddel et al., 2009). The prevalence of exclusive RH speech is believed to be infrequent, and right-sided surgery on such patients is believed to be rare. Most studies have suggested the prevalence of RH language representation to range from approximately 2 to 10% in epilepsy patients undergoing the Wada (Loring et al., 1990; Moddel et al., 2009), with the exception of a study by Rasmussen and Milner (1977) that estimated it to be as high as nearly 20%. These studies have estimated bilateral language representation to range from 5 to 25% in this population. Variability in reported prevalence rates is believed to primarily reflect differences in the implementation of the Wada across epilepsy centers, as many institutions have not routinely administered the Wada procedure to all individuals. Most centers select patients for the Wada based on the presumed clinical likelihood of atypical language occurrence. Variability in reported rates of atypical language may also be influenced by small sample sizes used in these studies, and general variability across Wada methodologies. Finally, while the Wada procedure is invasive and administered only to neurosurgical candidates, functional technologies (fMRI, functional transcranial Doppler sonography, MEG) have been used to estimate rates of atypical language prevalence in healthy subjects (Knecht et al., 2000; Szaflarski et al., 2002). These studies suggest that atypical language lateralization (RH or bilateral) will occur in 4 to 7.5% of right-handers and up to 22% of left-handers in the general population. Studies of “crossed-aphasia,” a term for the development of language impairment in normal right-handed individuals who sustained damage to the right hemisphere later in life, also provides evidence that atypical language lateralization may be a normal variant of language development (Hecaen & Albert 1978). Such studies suggest that atypical language may occur in .4% to 3% of healthy right handed adults (Marien et al 2004; Zangwill 1979), although most reports have not included the necessary functional imaging studies to determine whether this reflects bilateral or right only language (See Vandervliet et al 2008; Vitali et al 2011 for recent exceptions). More than two hundred cases appear in the research literature (Marien et al 2004); with more recent studies documenting similar aphasia types, lesion-behavior relationships, and recovery patterns as in uncrossed aphasia (Castro-Caldas & Confraria 1984; Coppens et al 2002; Yarnell 1981). The similarity of the resulting syndromes suggests that atypical language representation could parallel the more typical left-hemisphere variety. Right-hemisphere Speech Patients as Surgical Candidates Most neurosurgical patients found to have RH speech are undergoing surgical procedures involving their LH. This is because atypical lateralization of the neural language network appears to occur most frequently as a result of early childhood neuronal injuries leading to a shift of language functions from the left to the RH. A previous study from our Center (Miller et al., 2003) had also suggested that atypical speech lateralization may not occur in epilepsy patients with normal neurologic histories through the age of 15 years. In the current study, we retrospectively examined the CSM and Wada data of all patients found to have RH speech and who also underwent RH surgical procedures. This represents the largest published sample of epilepsy patients undergoing the Wada procedure, and is unique in that it is a near consecutive series requiring the obligatory completion of this study for all surgical candidates during the time span of the study regardless of hemisphere of seizure onset and the routine injection of both hemispheres. Additionally, the Wada procedure remained unchanged throughout the duration of the study. We predicted that CSM results for these RH patients would positively identify one or more essential language sites in each patient, providing validation for the sensitivity of the Wada procedure for detecting RH speech in a large, unselected sample of RH language patients. We also hypothesized that the general distribution of sites would be consistent with the patterns observed in neurosurgical patients with LH language dominance, as we believe that prior research suggests this group will predominantly reflect a sample of patients with an atypical yet normal variant of language organization.

  • Cortical Stimulation Mapping and wada results demonstrate a normal variant of right hemisphere language organization
    Epilepsia, 2012
    Co-Authors: Daniel L Drane, George A Ojemann, Ettore Lettich, Jenny Rorabackcarson, Adam O Hebb, Tamir Y Hersonskey, Timothy H Lucas, Daniel L Silbergeld, John W Miller, Jeffrey G Ojemann
    Abstract:

    Purpose Exclusive right hemisphere language lateralization is rarely observed in the Wada angiography results of epilepsy surgery patients. Cortical Stimulation Mapping (CSM) is infrequently performed with such patients, as most undergo non-dominant left hemisphere resections, which are presumed not to pose any risk to language. Early language reorganization is typically assumed in such individuals, taking left hemisphere epileptiform activity as confirmation of change resulting from a pathological process. We present data from CSM and Wada studies demonstrating that right hemisphere language occurs in the absence of left hemisphere pathology, suggesting it can exist as a normal, but rare variant, in some individuals. Further, these data confirm the Wada test findings of atypical dominance.

  • category specific recognition and naming deficits following resection of a right anterior temporal lobe tumor in a patient with atypical language lateralization
    Cortex, 2009
    Co-Authors: Daniel L Drane, George A Ojemann, Jeffrey G Ojemann, Daniel L Silbergeld, John W Miller, Elizabeth H Aylward, Daniel Tranel
    Abstract:

    We present a patient with right-hemispheric speech lateralization who exhibited severe recognition and naming deficits for unique objects (famous faces and landmarks) and grossly normal recognition and naming performances for nonunique objects (animals and man-made objects) following an anterior right temporal lobe (TL) resection of a ganglioglioma. While recognition deficits have been reported for famous faces following right temporal pole lesions, and for landmarks and geographic regions following right TL damage in general, this is the first reported case of both recognition and naming deficits for these objects resulting from a single lesion. These results are consistent with research suggesting that the neuroanatomic substrates for the recognition and naming of unique objects lie in the anterior TL regions. Left temporal pole lesions have been associated with naming deficits for unique objects while right temporal pole lesions have been associated with recognition deficits for unique objects. However, these findings suggest that the substrates of naming can be located in homotopic regions of the right hemisphere when language lateralization is atypical. As various object categories appear to have different neuroanatomical representations in the TLs, we discuss the possible benefits of sampling a wider array of objects during Cortical Stimulation Mapping of language.

  • Cortical Stimulation Mapping of language cortex by using a verb generation task effects of learning and comparison to Mapping based on object naming
    Journal of Neurosurgery, 2002
    Co-Authors: Jeffrey G Ojemann, George A Ojemann, Ettore Lettich
    Abstract:

    Object. Cortical Stimulation Mapping has traditionally relied on disruption of object naming to define essential language areas. In this study, the authors reviewed the use of a different language task, verb generation, in Mapping language. This task has greater use in brain imaging studies and may be used to test aspects of language different from those of object naming. Methods. In 14 patients, Cortical Stimulation Mapping performed using a verb generation task provided a map of language areas in the frontal and temporoparietal cortices. These verb generation maps often overlapped object naming ones and, in many patients, different areas of cortex were found to be involved in the two functions. In three patients, Stimulation Mapping was performed during the initial performance of the verb generation task and also during learned performance of the task. Parallel to findings of published neuroimaging studies, a larger area of stimulated cortex led to disruption of verb generation in response to stimulatio...

Daniel L Drane - One of the best experts on this subject based on the ideXlab platform.

  • knowledge of language function and underlying neural networks gained from focal seizures and epilepsy surgery
    Brain and Language, 2019
    Co-Authors: Daniel L Drane, Nigel P Pedersen
    Abstract:

    Abstract The effects of epilepsy and its treatments have contributed significantly to language models. The setting of epilepsy surgery, which allows for careful pre- and postsurgical evaluation of patients with cognitive testing and neuroimaging, has produced a wealth of language findings. Moreover, a new wave of surgical interventions, including stereotactic laser ablation and radio frequency ablation, have contributed new insights and corrections to language models as they can make extremely precise, focal lesions. This review covers the common language deficits observed in focal dyscognitive seizure syndromes. It also addresses the effects of surgical interventions on language, and highlights insights gained from unique epilepsy assessment methods (e.g., Cortical Stimulation Mapping, Wada evaluation). Emergent findings are covered including a lack of involvement of the hippocampus in confrontation word retrieval, possible roles for key white matter tracts in language, and the often-overlooked basal temporal language area. The relationship between language and semantic memory networks is also explored, with brief consideration given to the prevailing models of semantic processing, including the amodal Hub and distributed, multi-modal processing models.

  • Cortical Stimulation Mapping and wada results demonstrate a normal variant of right hemisphere language organization
    Epilepsia, 2012
    Co-Authors: Daniel L Drane, George A Ojemann, Ettore Lettich, Jenny Rorabackcarson, Adam O Hebb, Tamir Y Hersonskey, Timothy H Lucas, Daniel L Silbergeld, John W Miller, Jeffrey G Ojemann
    Abstract:

    Purpose Exclusive right hemisphere language lateralization is rarely observed in the Wada angiography results of epilepsy surgery patients. Cortical Stimulation Mapping (CSM) is infrequently performed with such patients, as most undergo non-dominant left hemisphere resections, which are presumed not to pose any risk to language. Early language reorganization is typically assumed in such individuals, taking left hemisphere epileptiform activity as confirmation of change resulting from a pathological process. We present data from CSM and Wada studies demonstrating that right hemisphere language occurs in the absence of left hemisphere pathology, suggesting it can exist as a normal, but rare variant, in some individuals. Further, these data confirm the Wada test findings of atypical dominance.

  • Cortical Stimulation Mapping and wada results demonstrate a normal variant of right hemisphere language organization
    Epilepsia, 2012
    Co-Authors: Daniel L Drane, George A Ojemann, Ettore Lettich, Jenny Rorabackcarson, Adam O Hebb, Tamir Y Hersonskey, Timothy H Lucas, Daniel L Silbergeld, John W Miller, Jeffrey G Ojemann
    Abstract:

    Cortical Stimulation Mapping (CSM) involves inducing a localized electrical blockage of Cortical function, and has been used in neurosurgery to identify areas essential to language functioning since the pioneering work of Penfield and Roberts with epilepsy surgery patients during the mid-1950s (Penfield & Roberts, 1959). Identification of language cortex enables the surgeon to avoid language areas when formulating a surgical strategy and to expand the resection of epileptic regions with increased safety (Kim et al., 2009). CSM results have brought insight to the distribution of language, confirming the presence of the classical Broca’s and Wernicke’s areas and identifying nontraditional sites found elsewhere in the cortex (Ojemann et al 1989). These data have also validated the accuracy of the intracarotid amobarbital (Wada) procedure, confirming that essential language sites are present in patients that are left-hemisphere (LH) dominant for language. The Wada procedure has served as the gold-standard for determining language dominance in presurgical patients since the early days of epilepsy surgery. Nevertheless, little data have been published examining CSM in patients who are determined to be exclusively right-hemisphere (RH) dominant for speech. Such individuals are believed to be rare, and atypical language lateralization is thought to often develop in patients following an early life injury involving their left cerebral hemisphere (Moddel et al., 2009; Rasmussen & Milner, 1977). Surgical patients experiencing such pathological language reorganization may not undergo CSM, as neurosurgical intervention is more likely to involve the LH of these individuals. As the Regional Epilepsy Center at the University of Washington has over 30 years of data involving CSM and the Wada procedure, we sought to examine the frequency of RH language dominance, validate the Wada procedure in these cases, and determine how the CSM results of such patients compare to those of individuals with typical speech lateralization. Validation of the Wada Procedure The Wada procedure has traditionally been the primary method for determining language dominance in neurosurgical candidates, as it provides a means to assess each hemisphere’s contribution to language function independently (Loring et al., 1992). This procedure remains in use by most epilepsy centers for the presurgical evaluation, although increasing efforts have been made to employ a noninvasive alternative [e.g., fMRI] (Arora et al., 2009). The principle behind the Wada was demonstrated by W. James Gardner in 1941 (Gardner, 1941), who injected procaine directly into the cortex thought to potentially be involved in language. Juhn Wada more formally established this procedure in the area of epilepsy surgery, making separate injections of amobarbital into each internal carotid artery to produce hemispheric anesthesia (Wada, 1949). During this period of anesthesia, patients are asked to carry out tasks to evaluate language and memory. Anesthetizing the area renders it nonfunctional, causing the hemisphere with language representation to be revealed when language deficits appear during an injection. The validity of LH language dominance as predicted by the Wada procedure has been demonstrated in several group studies using CSM (Loring et al., 1992; Ojemann et al., 1989), yet validity data for RH language dominance in epilepsy have been restricted primarily to a handful of case studies with one or two subjects (Rosenbaum et al., 1989; Wyllie et al., 1990). Duffau and colleagues (2008) found RH language sites in a small series of tumor patients (n=9) who were all left-handed, but did not have Wada data on any of their patients (some percentage were likely bilateral language cases). One recent study examined CSM results in 15 neurosurgical patients (mostly tumor patients) that had exhibited either RH (n=7) or bilateral (n=8) language on the Wada (Chang et al., 2011). These researchers found language sites in the RH of all 15 patients, thoroughly delineated their neuroanatomical location, and noted that the pattern of language sites was consistent with findings from LH language dominant patients. There are also a few additional studies that demonstrate RH speech in a small number of patients identified as bilateral by the Wada (Jabbour et al., 2005; Loring et al., 1988). Prevalence of Atypical Language Lateralization Years of accumulated knowledge from the use of the Wada confirms that most neurosurgical candidates are LH dominant for language, with atypical language lateralization in a minority (Loring et al., 1990; Moddel et al., 2009). The prevalence of exclusive RH speech is believed to be infrequent, and right-sided surgery on such patients is believed to be rare. Most studies have suggested the prevalence of RH language representation to range from approximately 2 to 10% in epilepsy patients undergoing the Wada (Loring et al., 1990; Moddel et al., 2009), with the exception of a study by Rasmussen and Milner (1977) that estimated it to be as high as nearly 20%. These studies have estimated bilateral language representation to range from 5 to 25% in this population. Variability in reported prevalence rates is believed to primarily reflect differences in the implementation of the Wada across epilepsy centers, as many institutions have not routinely administered the Wada procedure to all individuals. Most centers select patients for the Wada based on the presumed clinical likelihood of atypical language occurrence. Variability in reported rates of atypical language may also be influenced by small sample sizes used in these studies, and general variability across Wada methodologies. Finally, while the Wada procedure is invasive and administered only to neurosurgical candidates, functional technologies (fMRI, functional transcranial Doppler sonography, MEG) have been used to estimate rates of atypical language prevalence in healthy subjects (Knecht et al., 2000; Szaflarski et al., 2002). These studies suggest that atypical language lateralization (RH or bilateral) will occur in 4 to 7.5% of right-handers and up to 22% of left-handers in the general population. Studies of “crossed-aphasia,” a term for the development of language impairment in normal right-handed individuals who sustained damage to the right hemisphere later in life, also provides evidence that atypical language lateralization may be a normal variant of language development (Hecaen & Albert 1978). Such studies suggest that atypical language may occur in .4% to 3% of healthy right handed adults (Marien et al 2004; Zangwill 1979), although most reports have not included the necessary functional imaging studies to determine whether this reflects bilateral or right only language (See Vandervliet et al 2008; Vitali et al 2011 for recent exceptions). More than two hundred cases appear in the research literature (Marien et al 2004); with more recent studies documenting similar aphasia types, lesion-behavior relationships, and recovery patterns as in uncrossed aphasia (Castro-Caldas & Confraria 1984; Coppens et al 2002; Yarnell 1981). The similarity of the resulting syndromes suggests that atypical language representation could parallel the more typical left-hemisphere variety. Right-hemisphere Speech Patients as Surgical Candidates Most neurosurgical patients found to have RH speech are undergoing surgical procedures involving their LH. This is because atypical lateralization of the neural language network appears to occur most frequently as a result of early childhood neuronal injuries leading to a shift of language functions from the left to the RH. A previous study from our Center (Miller et al., 2003) had also suggested that atypical speech lateralization may not occur in epilepsy patients with normal neurologic histories through the age of 15 years. In the current study, we retrospectively examined the CSM and Wada data of all patients found to have RH speech and who also underwent RH surgical procedures. This represents the largest published sample of epilepsy patients undergoing the Wada procedure, and is unique in that it is a near consecutive series requiring the obligatory completion of this study for all surgical candidates during the time span of the study regardless of hemisphere of seizure onset and the routine injection of both hemispheres. Additionally, the Wada procedure remained unchanged throughout the duration of the study. We predicted that CSM results for these RH patients would positively identify one or more essential language sites in each patient, providing validation for the sensitivity of the Wada procedure for detecting RH speech in a large, unselected sample of RH language patients. We also hypothesized that the general distribution of sites would be consistent with the patterns observed in neurosurgical patients with LH language dominance, as we believe that prior research suggests this group will predominantly reflect a sample of patients with an atypical yet normal variant of language organization.

  • category specific recognition and naming deficits following resection of a right anterior temporal lobe tumor in a patient with atypical language lateralization
    Cortex, 2009
    Co-Authors: Daniel L Drane, George A Ojemann, Jeffrey G Ojemann, Daniel L Silbergeld, John W Miller, Elizabeth H Aylward, Daniel Tranel
    Abstract:

    We present a patient with right-hemispheric speech lateralization who exhibited severe recognition and naming deficits for unique objects (famous faces and landmarks) and grossly normal recognition and naming performances for nonunique objects (animals and man-made objects) following an anterior right temporal lobe (TL) resection of a ganglioglioma. While recognition deficits have been reported for famous faces following right temporal pole lesions, and for landmarks and geographic regions following right TL damage in general, this is the first reported case of both recognition and naming deficits for these objects resulting from a single lesion. These results are consistent with research suggesting that the neuroanatomic substrates for the recognition and naming of unique objects lie in the anterior TL regions. Left temporal pole lesions have been associated with naming deficits for unique objects while right temporal pole lesions have been associated with recognition deficits for unique objects. However, these findings suggest that the substrates of naming can be located in homotopic regions of the right hemisphere when language lateralization is atypical. As various object categories appear to have different neuroanatomical representations in the TLs, we discuss the possible benefits of sampling a wider array of objects during Cortical Stimulation Mapping of language.

Daniel L Silbergeld - One of the best experts on this subject based on the ideXlab platform.

  • Cortical Stimulation Mapping and wada results demonstrate a normal variant of right hemisphere language organization
    Epilepsia, 2012
    Co-Authors: Daniel L Drane, George A Ojemann, Ettore Lettich, Jenny Rorabackcarson, Adam O Hebb, Tamir Y Hersonskey, Timothy H Lucas, Daniel L Silbergeld, John W Miller, Jeffrey G Ojemann
    Abstract:

    Purpose Exclusive right hemisphere language lateralization is rarely observed in the Wada angiography results of epilepsy surgery patients. Cortical Stimulation Mapping (CSM) is infrequently performed with such patients, as most undergo non-dominant left hemisphere resections, which are presumed not to pose any risk to language. Early language reorganization is typically assumed in such individuals, taking left hemisphere epileptiform activity as confirmation of change resulting from a pathological process. We present data from CSM and Wada studies demonstrating that right hemisphere language occurs in the absence of left hemisphere pathology, suggesting it can exist as a normal, but rare variant, in some individuals. Further, these data confirm the Wada test findings of atypical dominance.

  • Cortical Stimulation Mapping and wada results demonstrate a normal variant of right hemisphere language organization
    Epilepsia, 2012
    Co-Authors: Daniel L Drane, George A Ojemann, Ettore Lettich, Jenny Rorabackcarson, Adam O Hebb, Tamir Y Hersonskey, Timothy H Lucas, Daniel L Silbergeld, John W Miller, Jeffrey G Ojemann
    Abstract:

    Cortical Stimulation Mapping (CSM) involves inducing a localized electrical blockage of Cortical function, and has been used in neurosurgery to identify areas essential to language functioning since the pioneering work of Penfield and Roberts with epilepsy surgery patients during the mid-1950s (Penfield & Roberts, 1959). Identification of language cortex enables the surgeon to avoid language areas when formulating a surgical strategy and to expand the resection of epileptic regions with increased safety (Kim et al., 2009). CSM results have brought insight to the distribution of language, confirming the presence of the classical Broca’s and Wernicke’s areas and identifying nontraditional sites found elsewhere in the cortex (Ojemann et al 1989). These data have also validated the accuracy of the intracarotid amobarbital (Wada) procedure, confirming that essential language sites are present in patients that are left-hemisphere (LH) dominant for language. The Wada procedure has served as the gold-standard for determining language dominance in presurgical patients since the early days of epilepsy surgery. Nevertheless, little data have been published examining CSM in patients who are determined to be exclusively right-hemisphere (RH) dominant for speech. Such individuals are believed to be rare, and atypical language lateralization is thought to often develop in patients following an early life injury involving their left cerebral hemisphere (Moddel et al., 2009; Rasmussen & Milner, 1977). Surgical patients experiencing such pathological language reorganization may not undergo CSM, as neurosurgical intervention is more likely to involve the LH of these individuals. As the Regional Epilepsy Center at the University of Washington has over 30 years of data involving CSM and the Wada procedure, we sought to examine the frequency of RH language dominance, validate the Wada procedure in these cases, and determine how the CSM results of such patients compare to those of individuals with typical speech lateralization. Validation of the Wada Procedure The Wada procedure has traditionally been the primary method for determining language dominance in neurosurgical candidates, as it provides a means to assess each hemisphere’s contribution to language function independently (Loring et al., 1992). This procedure remains in use by most epilepsy centers for the presurgical evaluation, although increasing efforts have been made to employ a noninvasive alternative [e.g., fMRI] (Arora et al., 2009). The principle behind the Wada was demonstrated by W. James Gardner in 1941 (Gardner, 1941), who injected procaine directly into the cortex thought to potentially be involved in language. Juhn Wada more formally established this procedure in the area of epilepsy surgery, making separate injections of amobarbital into each internal carotid artery to produce hemispheric anesthesia (Wada, 1949). During this period of anesthesia, patients are asked to carry out tasks to evaluate language and memory. Anesthetizing the area renders it nonfunctional, causing the hemisphere with language representation to be revealed when language deficits appear during an injection. The validity of LH language dominance as predicted by the Wada procedure has been demonstrated in several group studies using CSM (Loring et al., 1992; Ojemann et al., 1989), yet validity data for RH language dominance in epilepsy have been restricted primarily to a handful of case studies with one or two subjects (Rosenbaum et al., 1989; Wyllie et al., 1990). Duffau and colleagues (2008) found RH language sites in a small series of tumor patients (n=9) who were all left-handed, but did not have Wada data on any of their patients (some percentage were likely bilateral language cases). One recent study examined CSM results in 15 neurosurgical patients (mostly tumor patients) that had exhibited either RH (n=7) or bilateral (n=8) language on the Wada (Chang et al., 2011). These researchers found language sites in the RH of all 15 patients, thoroughly delineated their neuroanatomical location, and noted that the pattern of language sites was consistent with findings from LH language dominant patients. There are also a few additional studies that demonstrate RH speech in a small number of patients identified as bilateral by the Wada (Jabbour et al., 2005; Loring et al., 1988). Prevalence of Atypical Language Lateralization Years of accumulated knowledge from the use of the Wada confirms that most neurosurgical candidates are LH dominant for language, with atypical language lateralization in a minority (Loring et al., 1990; Moddel et al., 2009). The prevalence of exclusive RH speech is believed to be infrequent, and right-sided surgery on such patients is believed to be rare. Most studies have suggested the prevalence of RH language representation to range from approximately 2 to 10% in epilepsy patients undergoing the Wada (Loring et al., 1990; Moddel et al., 2009), with the exception of a study by Rasmussen and Milner (1977) that estimated it to be as high as nearly 20%. These studies have estimated bilateral language representation to range from 5 to 25% in this population. Variability in reported prevalence rates is believed to primarily reflect differences in the implementation of the Wada across epilepsy centers, as many institutions have not routinely administered the Wada procedure to all individuals. Most centers select patients for the Wada based on the presumed clinical likelihood of atypical language occurrence. Variability in reported rates of atypical language may also be influenced by small sample sizes used in these studies, and general variability across Wada methodologies. Finally, while the Wada procedure is invasive and administered only to neurosurgical candidates, functional technologies (fMRI, functional transcranial Doppler sonography, MEG) have been used to estimate rates of atypical language prevalence in healthy subjects (Knecht et al., 2000; Szaflarski et al., 2002). These studies suggest that atypical language lateralization (RH or bilateral) will occur in 4 to 7.5% of right-handers and up to 22% of left-handers in the general population. Studies of “crossed-aphasia,” a term for the development of language impairment in normal right-handed individuals who sustained damage to the right hemisphere later in life, also provides evidence that atypical language lateralization may be a normal variant of language development (Hecaen & Albert 1978). Such studies suggest that atypical language may occur in .4% to 3% of healthy right handed adults (Marien et al 2004; Zangwill 1979), although most reports have not included the necessary functional imaging studies to determine whether this reflects bilateral or right only language (See Vandervliet et al 2008; Vitali et al 2011 for recent exceptions). More than two hundred cases appear in the research literature (Marien et al 2004); with more recent studies documenting similar aphasia types, lesion-behavior relationships, and recovery patterns as in uncrossed aphasia (Castro-Caldas & Confraria 1984; Coppens et al 2002; Yarnell 1981). The similarity of the resulting syndromes suggests that atypical language representation could parallel the more typical left-hemisphere variety. Right-hemisphere Speech Patients as Surgical Candidates Most neurosurgical patients found to have RH speech are undergoing surgical procedures involving their LH. This is because atypical lateralization of the neural language network appears to occur most frequently as a result of early childhood neuronal injuries leading to a shift of language functions from the left to the RH. A previous study from our Center (Miller et al., 2003) had also suggested that atypical speech lateralization may not occur in epilepsy patients with normal neurologic histories through the age of 15 years. In the current study, we retrospectively examined the CSM and Wada data of all patients found to have RH speech and who also underwent RH surgical procedures. This represents the largest published sample of epilepsy patients undergoing the Wada procedure, and is unique in that it is a near consecutive series requiring the obligatory completion of this study for all surgical candidates during the time span of the study regardless of hemisphere of seizure onset and the routine injection of both hemispheres. Additionally, the Wada procedure remained unchanged throughout the duration of the study. We predicted that CSM results for these RH patients would positively identify one or more essential language sites in each patient, providing validation for the sensitivity of the Wada procedure for detecting RH speech in a large, unselected sample of RH language patients. We also hypothesized that the general distribution of sites would be consistent with the patterns observed in neurosurgical patients with LH language dominance, as we believe that prior research suggests this group will predominantly reflect a sample of patients with an atypical yet normal variant of language organization.

  • category specific recognition and naming deficits following resection of a right anterior temporal lobe tumor in a patient with atypical language lateralization
    Cortex, 2009
    Co-Authors: Daniel L Drane, George A Ojemann, Jeffrey G Ojemann, Daniel L Silbergeld, John W Miller, Elizabeth H Aylward, Daniel Tranel
    Abstract:

    We present a patient with right-hemispheric speech lateralization who exhibited severe recognition and naming deficits for unique objects (famous faces and landmarks) and grossly normal recognition and naming performances for nonunique objects (animals and man-made objects) following an anterior right temporal lobe (TL) resection of a ganglioglioma. While recognition deficits have been reported for famous faces following right temporal pole lesions, and for landmarks and geographic regions following right TL damage in general, this is the first reported case of both recognition and naming deficits for these objects resulting from a single lesion. These results are consistent with research suggesting that the neuroanatomic substrates for the recognition and naming of unique objects lie in the anterior TL regions. Left temporal pole lesions have been associated with naming deficits for unique objects while right temporal pole lesions have been associated with recognition deficits for unique objects. However, these findings suggest that the substrates of naming can be located in homotopic regions of the right hemisphere when language lateralization is atypical. As various object categories appear to have different neuroanatomical representations in the TLs, we discuss the possible benefits of sampling a wider array of objects during Cortical Stimulation Mapping of language.

  • Cortical Stimulation Mapping in a patient with foreign accent syndrome case report
    Clinical Neurology and Neurosurgery, 2009
    Co-Authors: Taylor J Abel, Adam O Hebb, Daniel L Silbergeld
    Abstract:

    Abstract Foreign accent syndrome is a rare language output disorder characterized by changes in various speech features leading to a perceived foreign accent. There are few cases reported in the literature. Due to the rarity of this condition, information regarding the functional neuroanatomy of FAS is lacking. We present the case of a 60-year-old woman with a left anterior parietal lobe breast carcinoma metastasis who developed foreign accent syndrome (FAS). This patient presented to the emergency room with right upper extremity weakness, facial weakness, and altered speech. Neurological examination revealed the patient’s speech to be dysarthric and accented, but otherwise appropriate. Brain magnetic resonance (MR) imaging demonstrated a 3 cm × 3 cm × 3 cm lesion in the left anterior parietal lobe. The patient underwent craniotomy for resection of the mass. Intra-operative Cortical Stimulation Mapping demonstrated the lesion to be confined to somatosensory cortex and gross total resection was performed. There were no new neurological deficits post-operatively. To our knowledge, this is a unique case of FAS due to breast carcinoma metastasis. Additionally, this is the first documented case of electroCortical function Stimulation Mapping of language and Rolandic cortex in a patient with FAS.

  • Cortical Stimulation Mapping of phantom limb rolandic cortex case report
    Journal of Neurosurgery, 1995
    Co-Authors: Jeffrey O Ojemann, Daniel L Silbergeld
    Abstract:

    ✓ Findings of intraoperative rolandic cortex Mapping during awake craniotomy for a tumor in a patient with a contralateral upper-extremity amputation are presented. This patient sustained a traumatic amputation at the mid-humerus 24 years previously. Initially he had experienced rare painless phantom limb sensations but none in the past 10 years. Functional Mapping during an awake craniotomy was performed to maximize safe tumor resection. Typical temporal and frontal speech areas were identified; motor representation of face and jaw extended more superiorly than sensory representation. Shoulder movements were evoked more laterally than usual at the superior aspect of the craniotomy. A small region of precentral gyrus, between the jaw and shoulder representations, elicited no detectable effect when stimulated. Somatosensory Mapping showed a similar topographical distribution of face and mouth cortex; however, posterior and inferior to the shoulder motor cortex, right arm and hand (phantom) sensations were ...

Ettore Lettich - One of the best experts on this subject based on the ideXlab platform.

  • Cortical Stimulation Mapping and wada results demonstrate a normal variant of right hemisphere language organization
    Epilepsia, 2012
    Co-Authors: Daniel L Drane, George A Ojemann, Ettore Lettich, Jenny Rorabackcarson, Adam O Hebb, Tamir Y Hersonskey, Timothy H Lucas, Daniel L Silbergeld, John W Miller, Jeffrey G Ojemann
    Abstract:

    Cortical Stimulation Mapping (CSM) involves inducing a localized electrical blockage of Cortical function, and has been used in neurosurgery to identify areas essential to language functioning since the pioneering work of Penfield and Roberts with epilepsy surgery patients during the mid-1950s (Penfield & Roberts, 1959). Identification of language cortex enables the surgeon to avoid language areas when formulating a surgical strategy and to expand the resection of epileptic regions with increased safety (Kim et al., 2009). CSM results have brought insight to the distribution of language, confirming the presence of the classical Broca’s and Wernicke’s areas and identifying nontraditional sites found elsewhere in the cortex (Ojemann et al 1989). These data have also validated the accuracy of the intracarotid amobarbital (Wada) procedure, confirming that essential language sites are present in patients that are left-hemisphere (LH) dominant for language. The Wada procedure has served as the gold-standard for determining language dominance in presurgical patients since the early days of epilepsy surgery. Nevertheless, little data have been published examining CSM in patients who are determined to be exclusively right-hemisphere (RH) dominant for speech. Such individuals are believed to be rare, and atypical language lateralization is thought to often develop in patients following an early life injury involving their left cerebral hemisphere (Moddel et al., 2009; Rasmussen & Milner, 1977). Surgical patients experiencing such pathological language reorganization may not undergo CSM, as neurosurgical intervention is more likely to involve the LH of these individuals. As the Regional Epilepsy Center at the University of Washington has over 30 years of data involving CSM and the Wada procedure, we sought to examine the frequency of RH language dominance, validate the Wada procedure in these cases, and determine how the CSM results of such patients compare to those of individuals with typical speech lateralization. Validation of the Wada Procedure The Wada procedure has traditionally been the primary method for determining language dominance in neurosurgical candidates, as it provides a means to assess each hemisphere’s contribution to language function independently (Loring et al., 1992). This procedure remains in use by most epilepsy centers for the presurgical evaluation, although increasing efforts have been made to employ a noninvasive alternative [e.g., fMRI] (Arora et al., 2009). The principle behind the Wada was demonstrated by W. James Gardner in 1941 (Gardner, 1941), who injected procaine directly into the cortex thought to potentially be involved in language. Juhn Wada more formally established this procedure in the area of epilepsy surgery, making separate injections of amobarbital into each internal carotid artery to produce hemispheric anesthesia (Wada, 1949). During this period of anesthesia, patients are asked to carry out tasks to evaluate language and memory. Anesthetizing the area renders it nonfunctional, causing the hemisphere with language representation to be revealed when language deficits appear during an injection. The validity of LH language dominance as predicted by the Wada procedure has been demonstrated in several group studies using CSM (Loring et al., 1992; Ojemann et al., 1989), yet validity data for RH language dominance in epilepsy have been restricted primarily to a handful of case studies with one or two subjects (Rosenbaum et al., 1989; Wyllie et al., 1990). Duffau and colleagues (2008) found RH language sites in a small series of tumor patients (n=9) who were all left-handed, but did not have Wada data on any of their patients (some percentage were likely bilateral language cases). One recent study examined CSM results in 15 neurosurgical patients (mostly tumor patients) that had exhibited either RH (n=7) or bilateral (n=8) language on the Wada (Chang et al., 2011). These researchers found language sites in the RH of all 15 patients, thoroughly delineated their neuroanatomical location, and noted that the pattern of language sites was consistent with findings from LH language dominant patients. There are also a few additional studies that demonstrate RH speech in a small number of patients identified as bilateral by the Wada (Jabbour et al., 2005; Loring et al., 1988). Prevalence of Atypical Language Lateralization Years of accumulated knowledge from the use of the Wada confirms that most neurosurgical candidates are LH dominant for language, with atypical language lateralization in a minority (Loring et al., 1990; Moddel et al., 2009). The prevalence of exclusive RH speech is believed to be infrequent, and right-sided surgery on such patients is believed to be rare. Most studies have suggested the prevalence of RH language representation to range from approximately 2 to 10% in epilepsy patients undergoing the Wada (Loring et al., 1990; Moddel et al., 2009), with the exception of a study by Rasmussen and Milner (1977) that estimated it to be as high as nearly 20%. These studies have estimated bilateral language representation to range from 5 to 25% in this population. Variability in reported prevalence rates is believed to primarily reflect differences in the implementation of the Wada across epilepsy centers, as many institutions have not routinely administered the Wada procedure to all individuals. Most centers select patients for the Wada based on the presumed clinical likelihood of atypical language occurrence. Variability in reported rates of atypical language may also be influenced by small sample sizes used in these studies, and general variability across Wada methodologies. Finally, while the Wada procedure is invasive and administered only to neurosurgical candidates, functional technologies (fMRI, functional transcranial Doppler sonography, MEG) have been used to estimate rates of atypical language prevalence in healthy subjects (Knecht et al., 2000; Szaflarski et al., 2002). These studies suggest that atypical language lateralization (RH or bilateral) will occur in 4 to 7.5% of right-handers and up to 22% of left-handers in the general population. Studies of “crossed-aphasia,” a term for the development of language impairment in normal right-handed individuals who sustained damage to the right hemisphere later in life, also provides evidence that atypical language lateralization may be a normal variant of language development (Hecaen & Albert 1978). Such studies suggest that atypical language may occur in .4% to 3% of healthy right handed adults (Marien et al 2004; Zangwill 1979), although most reports have not included the necessary functional imaging studies to determine whether this reflects bilateral or right only language (See Vandervliet et al 2008; Vitali et al 2011 for recent exceptions). More than two hundred cases appear in the research literature (Marien et al 2004); with more recent studies documenting similar aphasia types, lesion-behavior relationships, and recovery patterns as in uncrossed aphasia (Castro-Caldas & Confraria 1984; Coppens et al 2002; Yarnell 1981). The similarity of the resulting syndromes suggests that atypical language representation could parallel the more typical left-hemisphere variety. Right-hemisphere Speech Patients as Surgical Candidates Most neurosurgical patients found to have RH speech are undergoing surgical procedures involving their LH. This is because atypical lateralization of the neural language network appears to occur most frequently as a result of early childhood neuronal injuries leading to a shift of language functions from the left to the RH. A previous study from our Center (Miller et al., 2003) had also suggested that atypical speech lateralization may not occur in epilepsy patients with normal neurologic histories through the age of 15 years. In the current study, we retrospectively examined the CSM and Wada data of all patients found to have RH speech and who also underwent RH surgical procedures. This represents the largest published sample of epilepsy patients undergoing the Wada procedure, and is unique in that it is a near consecutive series requiring the obligatory completion of this study for all surgical candidates during the time span of the study regardless of hemisphere of seizure onset and the routine injection of both hemispheres. Additionally, the Wada procedure remained unchanged throughout the duration of the study. We predicted that CSM results for these RH patients would positively identify one or more essential language sites in each patient, providing validation for the sensitivity of the Wada procedure for detecting RH speech in a large, unselected sample of RH language patients. We also hypothesized that the general distribution of sites would be consistent with the patterns observed in neurosurgical patients with LH language dominance, as we believe that prior research suggests this group will predominantly reflect a sample of patients with an atypical yet normal variant of language organization.

  • Cortical Stimulation Mapping and wada results demonstrate a normal variant of right hemisphere language organization
    Epilepsia, 2012
    Co-Authors: Daniel L Drane, George A Ojemann, Ettore Lettich, Jenny Rorabackcarson, Adam O Hebb, Tamir Y Hersonskey, Timothy H Lucas, Daniel L Silbergeld, John W Miller, Jeffrey G Ojemann
    Abstract:

    Purpose Exclusive right hemisphere language lateralization is rarely observed in the Wada angiography results of epilepsy surgery patients. Cortical Stimulation Mapping (CSM) is infrequently performed with such patients, as most undergo non-dominant left hemisphere resections, which are presumed not to pose any risk to language. Early language reorganization is typically assumed in such individuals, taking left hemisphere epileptiform activity as confirmation of change resulting from a pathological process. We present data from CSM and Wada studies demonstrating that right hemisphere language occurs in the absence of left hemisphere pathology, suggesting it can exist as a normal, but rare variant, in some individuals. Further, these data confirm the Wada test findings of atypical dominance.

  • Cortical Stimulation Mapping of language cortex by using a verb generation task effects of learning and comparison to Mapping based on object naming
    Journal of Neurosurgery, 2002
    Co-Authors: Jeffrey G Ojemann, George A Ojemann, Ettore Lettich
    Abstract:

    Object. Cortical Stimulation Mapping has traditionally relied on disruption of object naming to define essential language areas. In this study, the authors reviewed the use of a different language task, verb generation, in Mapping language. This task has greater use in brain imaging studies and may be used to test aspects of language different from those of object naming. Methods. In 14 patients, Cortical Stimulation Mapping performed using a verb generation task provided a map of language areas in the frontal and temporoparietal cortices. These verb generation maps often overlapped object naming ones and, in many patients, different areas of cortex were found to be involved in the two functions. In three patients, Stimulation Mapping was performed during the initial performance of the verb generation task and also during learned performance of the task. Parallel to findings of published neuroimaging studies, a larger area of stimulated cortex led to disruption of verb generation in response to stimulatio...

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