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David Gaffan - One of the best experts on this subject based on the ideXlab platform.
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Differentiating the Roles of the Hippocampus and Perirhinal Cortex in Processes beyond Long-Term Declarative Memory: A Double Dissociation in Dementia
Journal of Neuroscience, 2006Co-Authors: Andy C. H. Lee, John R. Hodges, Mark J. Buckley, David Gaffan, Tina Emery, Kim S. GrahamAbstract:There is increasing evidence to suggest that the hippocampus and Perirhinal Cortex may mediate processes beyond long-term declarative memory. We assessed patients with Alzheimer's disease (AD) or semantic dementia (SD) on a visual oddity judgment task that did not place an explicit demand on long-term memory and is known to be sensitive to hippocampal and Perirhinal Cortex lesions. Importantly, within the medial temporal lobe, AD is associated with predominant hippocampal atrophy, whereas SD patients have greater Perirhinal Cortex damage. The AD group was selectively impaired in oddity judgment for scenes, whereas the SD patients demonstrated a deficit in face oddity judgment only. This compelling double dissociation supports the idea that the hippocampus and Perirhinal Cortex may be critical for the processing of scenes and objects, respectively, in the domain of perception or very short-term working memory.
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Perirhinal Cortex ablation impairs configural learning and paired-associate learning equally.
Neuropsychologia, 1998Co-Authors: Mark J. Buckley, David GaffanAbstract:Abstract Combined damage to the Perirhinal and entorhinal Cortex has been implicated in the formation of stimulus–stimulus associative memories. We show in this article that relative to three normal controls three cynomolgus monkeys with ablations restricted to the Perirhinal Cortex were impaired on a visual paired–associate learning task in which subjects had to learn which of two visual stimuli were associated with a cue stimulus. The subjects with Perirhinal Cortex ablations also showed an impairment of a similar magnitude on a visual configural learning task in which they had to learn which of two configurations of visual stimuli were associated with food-reward. The stimuli in both tasks were comprised of alphanumeric characters presented upon a touch-screen. Both groups made fewer errors on the configural learning task than on the paired–associate learning task. We suggest that performance on both tasks relies critically on the Perirhinal Cortex due to the specialization of the Perirhinal Cortex in processing knowledge about objects. We argue that the specializations of this system and of other memory systems such as the hippocampal-fornix spatial\episodic memory system, are conferred by the specialization of their anatomical connections to other structures. We reject the notion that there are specific memory processes such as the hippocampal based configural associative system that was proposed to be critical for configural associative learning.
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impairment of visual object discrimination learning after Perirhinal Cortex ablation
Behavioral Neuroscience, 1997Co-Authors: Mark J. Buckley, David GaffanAbstract:Eight cynomolgus monkeys learned preoperatively 20 concurrent visual discriminations between pairs of colored shapes presented on a touch screen with 24-hr intertrial intervals. Three then received bilateral Perirhinal Cortex ablation, and 5 remained controls. The ablated monkeys were severely impaired in reacquiring the preoperatively acquired set, whereas postoperative learning of 20 new discriminations was not significantly affected. The task was then made more difficult. First, the number of foils from which the stimulus had to be selected was increased to 2, 4, 7, and then 14. Second, larger sets of 40, 80, and 160 problems were presented. Both manipulations revealed some significant but relatively mild impairments in the monkeys with ablations. It is suggested that Perirhinal Cortex ablation impairs the monkey's capacity to identify individual objects, which leads to deficits in both visual-object recognition memory and discrimination learning.
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functional double dissociation between two inferior temporal cortical areas Perirhinal Cortex versus middle temporal gyrus
Journal of Neurophysiology, 1997Co-Authors: Mark J. Buckley, David Gaffan, Elisabeth A. MurrayAbstract:Buckley, M. J., D. Gaffan, and E. A. Murray. Functional double dissociation between two inferior temporal cortical areas: Perirhinal Cortex versus middle temporal gyrus. J. Neurophysiol. 77: 587–59...
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interaction of Perirhinal Cortex with the fornix fimbria memory for objects and object in place memory
The Journal of Neuroscience, 1996Co-Authors: David Gaffan, Amanda ParkerAbstract:Four monkeys ( Macaca mulatta ) were trained preoperatively in an automated object-in-place memory task in which they learned 20 new scenes in each daily session. In the object-in-place memory task, the correct, rewarded response in each scene is to a particular object of a pair, which always occupies a particular position in a unique background that has been generated using randomly chosen colors and shapes. Each animal then underwent two surgeries, with a period of testing after each. In the first, control surgery, each animal had either a unilateral lesion of the Perirhinal Cortex or unilateral fornix–fimbria transection, combined with section of the body and splenium of the corpus callosum and the anterior commissure (to prevent interhemispheric transfer of visual information). The disconnection was completed in the second surgery, after which all animals had a unilateral Perirhinal Cortex ablation in one hemisphere, unilateral fornix–fimbria transection in the contralateral hemisphere, and partial forebrain commissurotomy. The monkeys performance was compared for the learning of 200 scenes, preoperatively and after each surgery. After control surgery, the animals were mildly impaired on the object-in-place task. After disconnection, the animals showed a severe impairment in object-in-place memory. We conclude from this that, in episodic memory, the Perirhinal Cortex provides input of visual object information to the subiculum, hippocampus, and fornix.
Timothy J. Bussey - One of the best experts on this subject based on the ideXlab platform.
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nmda receptors and bdnf are necessary for discrimination of overlapping spatial and non spatial memories in Perirhinal Cortex and hippocampus
Neurobiology of Learning and Memory, 2018Co-Authors: Magdalena Miranda, Timothy J. Bussey, Brianne A Kent, Lisa M Saksida, Juan Facundo Morici, Francisco Tomas Gallo, Noelia V Weisstaub, Pedro BekinschteinAbstract:Successful memory involves not only remembering information over time but also keeping memories distinct and less confusable. Discrimination of overlapping representations has been investigated in the dentate gyrus (DG) of the hippocampus and largely in the Perirhinal Cortex (Prh). In particular, the DG was shown to be important for discrimination of overlapping spatial memories and Prh was shown to be important for discrimination of overlapping object memories. In the present study, we used both a DG-dependent and a Prh-dependent task and manipulated the load of similarity between either spatial or object stimuli during information encoding. We showed that N-methyl-D-aspartate-type glutamate receptors (NMDAr) and BDNF participate of the same cellular network during consolidation of both overlapping object and spatial memories in the Prh and DG, respectively. This argues in favor of conserved cellular mechanisms across regions despite anatomical differences.
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depletion of perineuronal nets enhances recognition memory and long term depression in the Perirhinal Cortex
The Journal of Neuroscience, 2013Co-Authors: Carola Romberg, Timothy J. Bussey, Sujeong Yang, Riccardo Melani, Melissa R Andrews, Alexa E Horner, Maria Grazia Spillantini, James W Fawcett, Tommaso PizzorussoAbstract:Perineuronal nets (PNNs) are extracellular matrix structures surrounding cortical neuronal cell bodies and proximal dendrites and are involved in the control of brain plasticity and the closure of critical periods. Expression of the link protein Crtl1/Hapln1 in neurons has recently been identified as the key event triggering the formation of PNNs. Here we show that the genetic attenuation of PNNs in adult brain Crtl1 knock-out mice enhances long-term object recognition memory and facilitates long-term depression in the Perirhinal Cortex, a neural correlate of object recognition memory. Identical prolongation of memory follows localized digestion of PNNs with chondroitinase ABC, an enzyme that degrades the chondroitin sulfate proteoglycan components of PNNs. The memory-enhancing effect of chondroitinase ABC treatment attenuated over time, suggesting that the regeneration of PNNs gradually restored control plasticity levels. Our findings indicate that PNNs regulate both memory and experience-driven synaptic plasticity in adulthood.
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muscimol ap5 or scopolamine infused into Perirhinal Cortex impairs two choice visual discrimination learning in rats
Neurobiology of Learning and Memory, 2010Co-Authors: Boyer D. Winters, Susan J Bartko, Lisa M Saksida, Timothy J. BusseyAbstract:Abstract The Perirhinal Cortex (PRh) has been strongly implicated in object recognition memory and visual stimulus representation. Studies of object recognition have revealed evidence for the involvement of several neurotransmitter subsystems, including those involving NMDA (N-methyl- d -aspartic acid) and muscarinic cholinergic receptors. In the present study, we assessed the possible involvement of PRh and related receptor subsystems in two-choice visual discrimination learning by Lister Hooded rats tested in touchscreen-equipped operant boxes. In Experiment 1, daily pre-training inactivation of PRh with the GABAA receptor agonist muscimol (0.5 μg/hemisphere) significantly impaired acquisition of the two-choice visual discrimination. In Experiment 2, daily pre-training blockade of either NMDA or muscarinic receptors in PRh with AP5 (5.9 μg/hemisphere) or scopolamine (10 μg/hemisphere), respectively, impaired task acquisition. These results parallel the findings from object recognition studies and suggest a generality of neurotransmitter receptor involvement underlying the role of PRh in both object recognition memory and visual discrimination learning. The involvement of PRh in both types of tasks may be related to its role in complex visual stimulus representation.
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Perirhinal Cortex resolves feature ambiguity in configural object recognition and perceptual oddity tasks
Learning & Memory, 2007Co-Authors: Susan J Bartko, Rosemary A Cowell, Boyer D. Winters, Lisa M Saksida, Timothy J. BusseyAbstract:The Perirhinal Cortex (PRh) has a well-established role in object recognition memory. More recent studies suggest that PRh is also important for two-choice visual discrimination tasks. Specifically, it has been suggested that PRh contains conjunctive representations that help resolve feature ambiguity, which occurs when a task cannot easily be solved on the basis of features alone. However, no study has examined whether the ability of PRh to resolve configural feature ambiguity is related to its role in object recognition. Therefore, we examined whether bilateral excitotoxic lesions of PRh or PPRh (Perirhinal plus post-rhinal cortices) in the rat would cause deficits in a configural spontaneous object recognition task, and a configural simultaneous oddity discrimination task, in which the task could not be solved on the basis of features, but could only be solved using conjunctive representations. As predicted by simulations using a computational model, rats with PPRh lesions were impaired during a minimal-delay configural object recognition task. These same rats were impaired during a zero-delay configural object recognition task. Furthermore, rats with localized PRh lesions were impaired in a configural simultaneous oddity discrimination task. These findings support the idea that PRh contains conjunctive representations for the resolution of feature ambiguity and that these representations underlie a dual role for PRh in memory and perception.
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perceptual functions of Perirhinal Cortex in rats zero delay object recognition and simultaneous oddity discriminations
The Journal of Neuroscience, 2007Co-Authors: Susan J Bartko, Rosemary A Cowell, Boyer D. Winters, Lisa M Saksida, Timothy J. BusseyAbstract:The Perirhinal Cortex (PRh) is widely accepted as having an important role in object recognition memory in humans and animals. Contrary to claims that PRh mediates declarative memory exclusively, previous evidence suggests that PRh has a role in the perceptual processing of complex objects. In the present study, we conducted an examination of the possible role of PRh in perceptual function in rats. We examined whether bilateral excitotoxic lesions of PRh or PPRh (Perirhinal plus postrhinal cortices) in the rat would cause deficits in a zero-delay object-recognition task and a simultaneous oddity discrimination task. Both of these tasks measured spontaneous (untrained, unrewarded) behavior, and the stimuli in these experiments were manipulated to produce varying levels of perceptual difficulty. As predicted by simulations using a computational model, rats with PPRh lesions were impaired in object recognition when the stimuli to be discriminated were manipulated to share many features in common. Furthermore, rats with PPRh and PRh lesions were impaired in a simultaneous oddity discrimination task when the stimuli to be discriminated were manipulated explicitly to be more perceptually similar. These findings provide support for the idea that PRh in the rat is important for the perceptual processing of complex objects, in addition to its well established role in memory.
John Patrick Aggleton - One of the best experts on this subject based on the ideXlab platform.
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Medial temporal pathways for contextual learning: Network c-fos mapping in rats with or without Perirhinal Cortex lesions.
Brain and Neuroscience Advances, 2017Co-Authors: Lisa Kinnavane, Eman Amin, C.m. Olarte-sánchez, John Patrick AggletonAbstract:In the rat brain, context information is thought to engage network interactions between the postrhinal Cortex, medial entorhinal Cortex, and the hippocampus. In contrast, object information is thought to be more reliant on Perirhinal Cortex and lateral entorhinal Cortex interactions with the hippocampus. The ‘context network’ was explored by mapping expression of the immediate-early gene, c-fos, after exposure to a new spatial environment. Structural equation modelling of Fos counts produced networks of good fit that closely matched prior predictions based on anatomically-grounded functional models. These same models did not, however, fit the Fos data from home-cage controls nor did they fit the corresponding data from a previous study exploring object recognition. These additional analyses highlight the specificity of the context network. The home-cage controls, meanwhile, showed raised levels of inter-area Fos correlations between the many sites examined, i.e., their changes in Fos levels lacked anatomical specificity. Two additional groups of rats received Perirhinal Cortex lesions. While the loss of Perirhinal Cortex reduced lateral entorhinal c-fos activity, it did not affect mean levels of hippocampal c-fos expression. Likewise, overall c-fos expression in the prelimbic Cortex, retrosplenial Cortex and nucleus reuniens of the thalamus appeared unaffected by the Perirhinal Cortex lesions. Nevertheless, the Perirhinal Cortex lesions disrupted network interactions involving the medial entorhinal Cortex and the hippocampus, highlighting ways in which Perirhinal Cortex might affect specific aspects of context learning.
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differing time dependencies of object recognition memory impairments produced by nicotinic and muscarinic cholinergic antagonism in Perirhinal Cortex
Learning & Memory, 2011Co-Authors: Chris J Tinsley, Malcolm W. Brown, John Patrick Aggleton, Nadine S Fontainepalmer, Maria Vincent, Emma P E Endean, Clea E WarburtonAbstract:The roles of muscarinic and nicotinic cholinergic receptors in Perirhinal Cortex in object recognition memory were compared. Rats' discrimination of a novel object preference test (NOP) test was measured after either systemic or local infusion into the Perirhinal Cortex of the nicotinic receptor antagonist methyllycaconitine (MLA), which targets alpha-7 (α7) amongst other nicotinic receptors or the muscarinic receptor antagonists scopolamine, AFDX-384, and pirenzepine. Methyllycaconitine administered systemically or intraPerirhinally before acquisition impaired recognition memory tested after a 24-h, but not a 20-min delay. In contrast, all three muscarinic antagonists produced a similar, unusual pattern of impairment with amnesia after a 20-min delay, but remembrance after a 24-h delay. Thus, the amnesic effects of nicotinic and muscarinic antagonism were doubly dissociated across the 20-min and 24-h delays. The same pattern of shorter-term but not longer-term memory impairment was found for scopolamine whether the object preference test was carried out in a square arena or a Y-maze and whether rats of the Dark Agouti or Lister-hooded strains were used. Coinfusion of MLA and either scopolamine or AFDX-384 produced an impairment profile matching that for MLA. Hence, the antagonists did not act additively when coadministered. These findings establish an important role in recognition memory for both nicotinic and muscarinic cholinergic receptors in Perirhinal Cortex, and provide a challenge to simple ideas about the role of cholinergic processes in recognition memory: The effects of muscarinic and nicotinic antagonism are neither independent nor additive.
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suppression to visual auditory and gustatory stimuli habituates normally in rats with excitotoxic lesions of the Perirhinal Cortex
Behavioral Neuroscience, 2009Co-Authors: Jasper Robinson, John Patrick Aggleton, David J Sanderson, Trisha A JenkinsAbstract:In 3 habituation experiments, rats with excitotoxic lesions of the Perirhinal Cortex were found to be indistinguishable from control rats. Two of the habituation experiments examined the habituation of suppression of responding on an appetitive, instrumental baseline. One of those experiments used stimuli selected from the visual modality (lights), the other used auditory stimuli. The third experiment examined habituation of suppression of novel-flavored water consumption. In contrast to the null results on the habituation experiments, the Perirhinal lesions disrupted transfer performance on a configural, visual discrimination, indicating the behavioral effectiveness of the lesions. Implications for comparator theories of habituation are considered, and it is concluded that others' demonstrations of the sensitivity of object recognition to Perirhinal Cortex damage is not the result of standard habituation.
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recognition memory what are the roles of the Perirhinal Cortex and hippocampus
Nature Reviews Neuroscience, 2001Co-Authors: Malcolm W. Brown, John Patrick AggletonAbstract:The hallmark of medial temporal lobe amnesia is a loss of episodic memory such that patients fail to remember new events that are set in an autobiographical context (an episode). A further symptom is a loss of recognition memory. The relationship between these two features has recently become contentious. Here, we focus on the central issue in this dispute — the relative contributions of the hippocampus and the Perirhinal Cortex to recognition memory. A resolution is vital not only for uncovering the neural substrates of these key aspects of memory, but also for understanding the processes disrupted in medial temporal lobe amnesia and the validity of animal models of this syndrome.
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Different Contributions of the Hippocampus and Perirhinal Cortex to Recognition Memory
The Journal of Neuroscience, 1999Co-Authors: H Wan, John Patrick AggletonAbstract:Brain regions involved in visual recognition memory, including the hippocampus, have been investigated by measuring differential neuronal activation produced by novel and familiar pictures. Novel and familiar pictures were presented simultaneously, one to each eye, using a paired viewing procedure. Differential neuronal activation was determined using immunohistochemistry for the protein products of c-fos as an imaging technique. The results establish that the regions of the rat brain associated with discriminating the novelty or familiarity of an individual item (such as a single object) differ from those responding to a spatial array of items (such as a scene). Perirhinal Cortex and area TE of the temporal lobe are activated significantly more by pictures of novel than of familiar individual objects, but the hippocampus is not differentially activated. In contrast, pictures of novel arrangements of familiar items produce significantly greater activation than familiar arrangements of these items in postrhinal Cortex and subfield CA1 of the hippocampus but significantly less activation in the dentate gyrus and subiculum; Perirhinal Cortex and area TE are not differentially activated. Thus, the hippocampus is importantly involved in processing information essential to recognition memory concerning the relative familiarity of arrangements of items, as needed for episodic memory of scenes, whereas the Perirhinal Cortex processes such information for individual items.
Jocelyne Bachevalier - One of the best experts on this subject based on the ideXlab platform.
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memory for spatial location and object place associations are differently processed by the hippocampal formation parahippocampal areas th tf and Perirhinal Cortex
Hippocampus, 2008Co-Authors: Jocelyne Bachevalier, Sarah NemanicAbstract:To clarify the specific contribution of the medial temporal lobe structures in spatial memory, we tested monkeys (Macaca mulatta) with sham operations and with lesions of either the hippocampal formation, areas TH/TF or Perirhinal Cortex on two versions of the visual-paired comparison task, measuring Spatial Location, and Object-in-Place associations. In the Spatial Location version, the comparison was between two identical objects presented simultaneously in a familiar and a novel location. In the Object-in-Place version, the comparison was between an image consisting of five objects and another image showing the same five objects, but with the position of 2, 3, or 4 of the objects rearranged. Finally, a VPC-Control task was given to animals with hippocampal and Perirhinal lesions, in which the comparison was between an image consisting of five objects and another image showing four of the five familiar objects and a new one. Perirhinal lesions yielded no deficit in the Spatial Location task and a deficit in the Object-in-Place task associated with a deficit in the VPC-control task, suggesting that this cortical area does not participate in spatial memory unless the stimuli have overlapping features. Areas TH/TF lesions produced a deficit in both Spatial Location and Object-in-Place tasks, whereas the hippocampal lesions resulted in a deficit of Object-in-Place associations only. The data showed that the hippocampal formation, areas TH/TF, and Perirhinal Cortex appear to contribute interactively to object and spatial memory processes.
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memory for spatial location and object place associations are differently processed by the hippocampal formation parahippocampal areas th tf and Perirhinal Cortex
Hippocampus, 2008Co-Authors: Jocelyne Bachevalier, Sarah NemanicAbstract:To clarify the specific contribution of the medial temporal lobe structures in spatial memory, we tested monkeys (Macaca mulatta) with sham operations and with lesions of either the hippocampal formation, areas TH/TF or Perirhinal Cortex on two versions of the visual-paired comparison task, measuring Spatial Location, and Object-in-Place associations. In the Spatial Location version, the comparison was between two identical objects presented simultaneously in a familiar and a novel location. In the Object-in-Place version, the comparison was between an image consisting of five objects and another image showing the same five objects, but with the position of 2, 3, or 4 of the objects rearranged. Finally, a VPC-Control task was given to animals with hippocampal and Perirhinal lesions, in which the comparison was between an image consisting of five objects and another image showing four of the five familiar objects and a new one. Perirhinal lesions yielded no deficit in the Spatial Location task and a deficit in the Object-in-Place task associated with a deficit in the VPC-control task, suggesting that this cortical area does not participate in spatial memory unless the stimuli have overlapping features. Areas TH/TF lesions produced a deficit in both Spatial Location and Object-in-Place tasks, whereas the hippocampal lesions resulted in a deficit of Object-in-Place associations only. The data showed that the hippocampal formation, areas TH/TF, and Perirhinal Cortex appear to contribute interactively to object and spatial memory processes. © 2007 Wiley-Liss, Inc.
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effects on visual recognition of combined and separate ablations of the entorhinal and Perirhinal Cortex in rhesus monkeys
The Journal of Neuroscience, 1993Co-Authors: Martine Meunier, Mortimer Mishkin, Jocelyne Bachevalier, Elisabeth A. MurrayAbstract:Performance on visual delayed nonmatching-to-sample was assessed in rhesus monkeys with combined and separate ablations of the Perirhinal and entorhinal Cortex, as well as in unoperated controls. Combined (i.e., rhinal Cortex) lesions yielded a striking impairment on this task, one almost as severe as that seen after combined amygdalohippocampal removals that included some of this subjacent Cortex (Mishkin, 1978; Murray and Mishkin, 1984). Ablations of the Perirhinal Cortex alone produced a deficit nearly as severe as that found after rhinal Cortex lesions, whereas ablations of the entorhinal Cortex alone produced only a mild deficit. Contrary to the conclusion from an earlier study (Murray and Mishkin, 1986), the present results demonstrate not only that damage limited to the rhinal Cortex is sufficient to produce a severe loss in visual recognition, but also that such damage leads to a far greater loss than damage to any other single structure in the medial part of the temporal lobe.
David K. Bilkey - One of the best experts on this subject based on the ideXlab platform.
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changes in nos protein expression and activity in the rat hippocampus entorhinal and postrhinal cortices after unilateral electrolytic Perirhinal Cortex lesions
Hippocampus, 2003Co-Authors: Ping Liu, Yiwen Zheng, Paul F Smith, David K. BilkeyAbstract:The integrity of the Perirhinal Cortex is critical for certain types of learning and memory. One important issue relating to the function of this region is its interaction with other brain areas that play a role in memory processing. This study investigates the time course of changes in activity and protein expression of nitric oxide synthase (NOS), which transforms L-arginine into nitric oxide (NO) and citrulline, in the hippocampus and the entorhinal and postrhinal cortices after unilateral electrolytic lesions of the Perirhinal Cortex. Electrolytic lesions of the Perirhinal Cortex resulted in long lasting changes in NOS activity and protein expression in the entorhinal and postrhinal cortices (< or = 2 weeks post-lesion). In contrast, there was a small and transient decrease in nNOS expression (with no change in NOS activity) in the dorsal portion of the hippocampus. iNOS was not expressed in any region examined at any time point. These findings provide the first evidence that electrolytic lesions of the Perirhinal Cortex can result in long-term neurochemical changes in its anatomically related structures. Given that NO has been implicated in neuroplasticity processes, the interpretation of memory impairments induced by electrolytic lesions of the Perirhinal Cortex (and possibly, therefore, other brain regions) need to be considered with regard to these findings.
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intrinsic theta frequency membrane potential oscillations in layer iii v Perirhinal Cortex neurons of the rat
Hippocampus, 1999Co-Authors: David K. Bilkey, Uwe HeinemannAbstract:The firing of a proportion of neurons in the in vivo Perirhinal Cortex, a brain region involved in object recognition memory, has recently been shown to be synchronized with hippocampal theta activity. The purpose of the present study was to determine whether neurons located in Perirhinal Cortex have intrinsic properties that might encourage their participation in theta activity. To these ends, current clamp recordings were made from 98 neurons located in layer III/V of the in vitro rat Perirhinal Cortex. The intrinsic properties of these neurons were investigated, and a subset of 61 neurons were tested for the presence of membrane potential oscillations at threshold levels of depolarization. Thirty-nine percent of these neurons displayed a theta-frequency membrane potential oscillation (MPO; mean frequency = 8.6 Hz). When depolarized past spike threshold, these neurons tended to fire in clusters, with a within-cluster interspike interval close to the peak to peak interval of the MPOs. Neurons that did not generate MPOs generated nonaccomodating action potential trains with a frequency that spanned the theta range. Biocytin staining indicated that MPOs could be generated in cells with both pyramidal and nonpyramidal morphology. These findings demonstrate that a large proportion of Perirhinal neurons exhibit intrinsic properties that could assist in the entrainment and synchronization of theta-frequency oscillations. These properties may enhance the communication of information between the Perirhinal Cortex, entorhinal Cortex, and hippocampus. Hippocampus 1999;9:510–518. © 1999 Wiley-Liss, Inc.
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direct connection between Perirhinal Cortex and hippocampus is a major constituent of the lateral perforant path
Hippocampus, 1998Co-Authors: Ping Liu, David K. BilkeyAbstract:Single-pulse stimulation of the Perirhinal Cortex (PRC) evoked field responses in the dorsal hippocampal CA1 region in urethane-anesthetized rats. In depth profiles conducted by moving the PRC stimulating electrode, the largest amplitude hippocampal potential was generated when the stimulating electrode was located within the Perirhinal region. More dorsal (temporal Cortex) or more ventral (lateral entorhinal Cortex) stimulating sites elicited minimal hippocampal potentials. The hippocampal response was maintained during 100 Hz stimulation of the PRC, suggesting that it was monosynaptic, and high-frequency stimulation (400 Hz) of the PRC produced a significant potentiation of hippocampal CA1 field potentials (46.73 ± 4.14%). When the PRC and the lateral perforant path (LPP) were stimulated separately, the depth/amplitude profiles obtained from a roving recording electrode located within the dorsal hippocampus were similar. In order to determine if fibers from PRC project to the hippocampus via the LPP, the PRC-CA1 and LPP-CA1 potentials were recorded prior to and during procaine (20%, 0.5 μl) blockade of the LPP. A simultaneous loss of both potentials was observed immediately following procaine infusion, while a commissural control potential was unaffected. Both LPP and PRC potentials returned approximately 30–40 min later. Electrolytic lesions of PRC produced a significant decrease in the amplitude of LPP-hippocampal potentials when testing was conducted 4–5 days postlesion. Lesions of lateral entorhinal Cortex or temporal Cortex did not produce such effects. These data suggest that a direct pathway from Perirhinal Cortex to the dorsal hippocampal CA1 field can undergo long-term potentiation (LTP) and that this pathway makes a major contribution to the lateral perforant path. © 1996 Wiley-Liss, Inc.
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excitotoxic lesions centered on Perirhinal Cortex produce delay dependent deficits in a test of spatial memory
Behavioral Neuroscience, 1998Co-Authors: David K. BilkeyAbstract:: Rats with bilateral electrolytic or ibotenic acid lesions that were centred in Perirhinal Cortex displayed a significant delay-dependent deficit on a delayed nonmatch to position task in the T maze. Although the removal of prominent extramaze visual cues did not affect the performance of these rats, rotating the maze between the sample and test phases did, indicating that rats were using a spatial strategy. Interestingly, a further group of rats with hippocampal and Perirhinal damage displayed deficits that may reflect a dysfunction in the use of inertial cues. These results suggest that both electrolytic and excitotoxic lesions of Perirhinal Cortex produce spatial memory impairments but that these impairments are qualitatively different than those exhibited following hippocampal damage.
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lesions of rat Perirhinal Cortex exacerbate the memory deficit observed following damage to the fimbria fornix
Behavioral Neuroscience, 1995Co-Authors: Kjesten A. Wiig, David K. BilkeyAbstract:Rats that had received bilateral lesions of the Perirhinal Cortex, fimbria-fornix, combined lesions of both these structures, or sham operations were tested on an object-guided delayed non-match-to-sample task. Perirhinal lesioned and fimbria-fornix lesioned rats were moderately impaired when delay intervals of 30 s or more were introduced between the sample and test phases of the experiment. Animals with combined lesions displayed a considerably greater impairment than animals with lesions of either structure alone. The combined lesioned animals were severely impaired in the initial acquisition of the task and displayed a profound memory deficit at delay intervals of greater than 4 s. These results emphasize the importance of the Perirhinal Cortex to memory function and suggest that the Perirhinal Cortex and the hippocampal formation may function interactively in the execution of memory processes.
