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Kazuo Mukuno - One of the best experts on this subject based on the ideXlab platform.

  • representation of the visual field in the striate cortex comparison of mr findings with visual field deficits in organic mercury poisoning minamata disease
    American Journal of Neuroradiology, 1997
    Co-Authors: Yukunori Korogi, Toru Okajima, Ichiro Ikushima, Takeshi Sugahara, Mutsumasa Takahashi, Toshinori Hirai, Mika Kitajima, Yoshinori Shigematsu, Kazuo Mukuno
    Abstract:

    PURPOSE To compare MR imaging findings of the striate cortex with visual field deficits in patients with Minamata disease and to reestimate the classical Holmes retinotopic map by using the data obtained from comparing visual field abnormalities with degree of visual cortex atrophy. METHODS MR imaging was performed in eight patients with Minamata disease who had been given a full neuroophthalmic examination, including Goldmann dynamic perimetry. The atrophic portions of the Calcarine area were measured in the sagittal plane next to the midsagittal image and represented as a percentage of atrophy of the total length of the Calcarine Fissure. MR findings were compared with results of a visual field test. RESULTS The visual field test revealed moderate to severe concentric constriction of the visual fields, with central vision ranging from 7 degrees to 42 degrees (mean, 19 degrees). The ventral portion of the Calcarine sulcus was significantly dilated on MR images in all patients. A logarithmic correlation was found between the visual field defect and the extent of dilatation of the Calcarine Fissure. The central 10 degrees and 30 degrees of vision seemed to fill about 20% and 50% of the total surface area of the Calcarine cortex, respectively. CONCLUSION Visual field deficits in patients with Minamata disease correlated well with MR findings of the striate cortex. Our data were consistent with the classical Holmes retinotopic map.

  • Representation of the visual field in the striate cortex: comparison of MR findings with visual field deficits in organic mercury poisoning (Minamata disease).
    AJNR. American journal of neuroradiology, 1997
    Co-Authors: Yukunori Korogi, Toru Okajima, Ichiro Ikushima, Takeshi Sugahara, Mutsumasa Takahashi, Toshinori Hirai, Mika Kitajima, Yoshinori Shigematsu, Kazuo Mukuno
    Abstract:

    To compare MR imaging findings of the striate cortex with visual field deficits in patients with Minamata disease and to reestimate the classical Holmes retinotopic map by using the data obtained from comparing visual field abnormalities with degree of visual cortex atrophy. MR imaging was performed in eight patients with Minamata disease who had been given a full neuroophthalmic examination, including Goldmann dynamic perimetry. The atrophic portions of the Calcarine area were measured in the sagittal plane next to the midsagittal image and represented as a percentage of atrophy of the total length of the Calcarine Fissure. MR findings were compared with results of a visual field test. The visual field test revealed moderate to severe concentric constriction of the visual fields, with central vision ranging from 7 degrees to 42 degrees (mean, 19 degrees). The ventral portion of the Calcarine sulcus was significantly dilated on MR images in all patients. A logarithmic correlation was found between the visual field defect and the extent of dilatation of the Calcarine Fissure. The central 10 degrees and 30 degrees of vision seemed to fill about 20% and 50% of the total surface area of the Calcarine cortex, respectively. Visual field deficits in patients with Minamata disease correlated well with MR findings of the striate cortex. Our data were consistent with the classical Holmes retinotopic map.

Yukunori Korogi - One of the best experts on this subject based on the ideXlab platform.

  • MRI in occipital lobe infarcts: classification by involvement of the striate cortex
    Neuroradiology, 1998
    Co-Authors: Mika Kitajima, Yukunori Korogi, T. Kido, Osamu Ikeda, S. Morishita, M. Takahashi
    Abstract:

    We reviewed the MRI studies of 25 patients with occipital lobe infarcts to clarify the distribution of infarcts in the posterior cerebral arterial territory, focussing on their relationship to the striate cortex. Visual field defects and MRI findings were also correlated in 16 patients. On coronal and/or sagittal images, the distribution of the infarct and its relationship to the striate cortex were classified. Involvement of the cortex of both upper and lower lips of the Calcarine Fissure was observed in 10 patients, and involvement of the lower lip alone in 15. The upper cortical lesions were always accompanied by lower cortical lesions. The visual field defects were complete hemianopia in nine patients, superior quadrantanopia in six and hemianopia with a preserved temporal crescent in one. All patients with superior quadrantanopia had involvement of the lower cortex alone; there were no cases of inferior quadrantanopia. The characteristic vascular anatomy, and poor development of the collateral circulation in the lower cortical area, may explain the vulnerability of this area to infarcts.

  • representation of the visual field in the striate cortex comparison of mr findings with visual field deficits in organic mercury poisoning minamata disease
    American Journal of Neuroradiology, 1997
    Co-Authors: Yukunori Korogi, Toru Okajima, Ichiro Ikushima, Takeshi Sugahara, Mutsumasa Takahashi, Toshinori Hirai, Mika Kitajima, Yoshinori Shigematsu, Kazuo Mukuno
    Abstract:

    PURPOSE To compare MR imaging findings of the striate cortex with visual field deficits in patients with Minamata disease and to reestimate the classical Holmes retinotopic map by using the data obtained from comparing visual field abnormalities with degree of visual cortex atrophy. METHODS MR imaging was performed in eight patients with Minamata disease who had been given a full neuroophthalmic examination, including Goldmann dynamic perimetry. The atrophic portions of the Calcarine area were measured in the sagittal plane next to the midsagittal image and represented as a percentage of atrophy of the total length of the Calcarine Fissure. MR findings were compared with results of a visual field test. RESULTS The visual field test revealed moderate to severe concentric constriction of the visual fields, with central vision ranging from 7 degrees to 42 degrees (mean, 19 degrees). The ventral portion of the Calcarine sulcus was significantly dilated on MR images in all patients. A logarithmic correlation was found between the visual field defect and the extent of dilatation of the Calcarine Fissure. The central 10 degrees and 30 degrees of vision seemed to fill about 20% and 50% of the total surface area of the Calcarine cortex, respectively. CONCLUSION Visual field deficits in patients with Minamata disease correlated well with MR findings of the striate cortex. Our data were consistent with the classical Holmes retinotopic map.

  • Representation of the visual field in the striate cortex: comparison of MR findings with visual field deficits in organic mercury poisoning (Minamata disease).
    AJNR. American journal of neuroradiology, 1997
    Co-Authors: Yukunori Korogi, Toru Okajima, Ichiro Ikushima, Takeshi Sugahara, Mutsumasa Takahashi, Toshinori Hirai, Mika Kitajima, Yoshinori Shigematsu, Kazuo Mukuno
    Abstract:

    To compare MR imaging findings of the striate cortex with visual field deficits in patients with Minamata disease and to reestimate the classical Holmes retinotopic map by using the data obtained from comparing visual field abnormalities with degree of visual cortex atrophy. MR imaging was performed in eight patients with Minamata disease who had been given a full neuroophthalmic examination, including Goldmann dynamic perimetry. The atrophic portions of the Calcarine area were measured in the sagittal plane next to the midsagittal image and represented as a percentage of atrophy of the total length of the Calcarine Fissure. MR findings were compared with results of a visual field test. The visual field test revealed moderate to severe concentric constriction of the visual fields, with central vision ranging from 7 degrees to 42 degrees (mean, 19 degrees). The ventral portion of the Calcarine sulcus was significantly dilated on MR images in all patients. A logarithmic correlation was found between the visual field defect and the extent of dilatation of the Calcarine Fissure. The central 10 degrees and 30 degrees of vision seemed to fill about 20% and 50% of the total surface area of the Calcarine cortex, respectively. Visual field deficits in patients with Minamata disease correlated well with MR findings of the striate cortex. Our data were consistent with the classical Holmes retinotopic map.

  • MRI in Minamata disease (organic mercury poisoning): correlation with visual field abnormalities
    Proceedings of the XV Symposium Neuroradiologicum, 1995
    Co-Authors: T. Okuda, S. Hamatake, Ryuji Murakami, Mutsumasa Takahashi, Yukunori Korogi, Toshinori Hirai, Yuji Sakamoto, Toru Okajima
    Abstract:

    The purpose of this study was to review MRI findings in Minamata disease (MD), and to correlate these with visual field abnormalities. MRI at 1.5T and visual field tests were performed in 20 patients with a mild type of MD, 8 patients with typical MD, and 10 control subjects. The atrophic portions of the Calcarine areas were measured in the sagittal planes. In patients with constriction of the visual fields, the anterior portion of the Calcarine Fissure was significantly dilated, reflecting atrophy of the visual cortex. There was significant correlation between the degree of the temporal visual fields and the width of the Calcarine sulci (r = 0.753, P< 0.0001). MRI has proved to be useful in studying abnormalities of the Calcarine area due to methylmercury poisoning.

Riitta Hari - One of the best experts on this subject based on the ideXlab platform.

  • Stronger occipital cortical activation to lower than upper visual field stimuli. Neuromagnetic recordings.
    Experimental brain research, 1999
    Co-Authors: K. Portin, Simo Vanni, Veijo Virsu, Riitta Hari
    Abstract:

    We recorded whole-scalp magnetoencephalographic (MEG) responses to black-and-white checkerboards to study whether the human cortical responses are quantitatively similar to stimulation of the lower and upper visual field at small, 0–6°, eccentricities. All stimuli evoked strongoccipital responses peaking at 50–100 ms (mean 75 ms). The activation was modeled with a single equivalent current dipole in the contralateral occipital cortex, close to the Calcarine Fissure, agreeing with an activation of the V1/V2 cortex. The dipole was, on average, twice as strong to lower than to upper field stimuli. Responses to hemifield stimuli that extended to both lower and upper fields resembled the responses to lower field stimuli in source current direction and strength. These results agree with psychophysical data, which indicate lower visual field advantage in complex visual processing. Parieto-occipital responses in the putative V6 complex were similar to lower and upper field stimuli.

  • Comparison of human occipital cortical activation to lower and upper visual field stimuli
    Perception, 1997
    Co-Authors: K. Portin, Simo Vanni, Riitta Hari
    Abstract:

    We compared cortical responses to lower and upper quadrant and full hemifield stimuli (90° and 180° sectors of circular checkerboards) measured from 15 healthy subjects with a Neuromag-122™ whole-scalp neuromagnetometer. The 0.2 s stimuli were presented once every second, while the subjects fixated a black dot in the centre of the screen.The first evoked responses, peaking at 70 ms in the contralateral hemisphere, were stronger for lower than for upper field stimulation (13/15 subjects, LVF; 11/15 RVF). The sources of the evoked responses, modelled as equivalent current dipoles, clustered around the Calcarine Fissure, with a trend for stronger sources after lower than after upper field stimulation (on average 12% LVF; 40% RVF; ns).Attention-related visual processing may be enhanced in the lower compared with the upper visual field (Rubin et al, 1996 Science271 651 – 653). Although our data showed a strong tendency to larger responses for lower than for upper visual field stimuli, this difference was not s...

Richard A. Armstrong - One of the best experts on this subject based on the ideXlab platform.

  • Visual evoked electrical and magnetic response to half-field stimulation using pattern reversal stimulation.
    Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians (Optometrists), 2007
    Co-Authors: G F Harding, Richard A. Armstrong, B. Janday
    Abstract:

    The visual evoked magnetic response to half-field stimulation using pattern reversal was studied using a dc-SQUID coupled to a second-order gradiometer. The main component of the magnetic response consisted of a positive wave at around 100ms (P100M). At the same time this component was present the reponse to half-field stimulation consisted of an outgoing field contralateral and extending to the midline. When the left half-field was stimulates the outgoing field was over the posterior right visual cortex and when the right half field was stimulated it was over the left anterior visual cortex. These findings would correltly identify a source located in the contralateral visual cortex. The orientation of the dipoles was not that previously assumed to explain the paradoxical lateralization of the visual evoked potential. The results are discussed in terms of both electrical and magnetic models of the Calcarine Fissure.

  • Topographic mapping and source localization of the pattern reversal visual evoked magnetic response
    Brain Topography, 1991
    Co-Authors: G F Harding, B. Janday, Richard A. Armstrong
    Abstract:

    The topography of the visual evoked magnetic response (VEMR) to pattern reversal stimulation was studied in four normal subjects using a single channel BTI magnetometer. VEMRs were recorded from 20 locations over the occipital scalp and the topographic distribution of the most consistent component (P100M) studied. A single dipole in a sphere model was fitted to the data. Topographic maps were similar when recorded two months apart on the same subject to the same stimulus. Half field (HF) stimulation elicited responses from sources on the medial surface of the Calcarine Fissure mainly in the contralateral hemisphere as predicted by the cruciform model. The full field (FF) responses to large checks were approximately the sum of the HF responses. However, with small checks, FF stimulation appeared to activate a different combination of sources than the two HFs. In addition, HF topography was more consistent between subjects than FF for small check sizes. Topographic studies of the VEMR may help to explain the analogous visual evoked electrical response and will be essential to define optimal recording positions for clinical applications.

  • The visual evoked magnetic response to a pattern onset stimulus
    1991
    Co-Authors: C Degg, Richard A. Armstrong, A. Slaven, G F Harding
    Abstract:

    The topography of the visual evoked magnetic response to a pattern onset stimulus was studied in four normal subjects. The topography of th CIIm component was consistent when measured on the same subject nine months apart. Full field responses were more variable than half field responses. With decreasing check size, the field pattern changes from a simple distribution with one outgoing and one ingoing area of field to a more complex pattern with in and outgoing fields over each hemisphere of the brain. The source may originate at the pole or from within the Calcarine Fissure.

  • Topographic mapping and source localization of the pattern onset visual evoked magnetic response
    Brain topography, 1991
    Co-Authors: C Degg, A. Slaven, Richard A. Armstrong
    Abstract:

    The topography of the visual evoked magnetic response (VEMR) to pattern reversal stimulation was studied in four normal subjects using a single channel BTI magnetometer. VEMRs were recorded from 20 locations over the occipital scalp and the topographic distribution of the most consistent component (P100M) studied. A single dipole in a sphere model was fitted to the data. Topographic maps were similar when recorded two months apart on the same subject to the same stimulus. Half field (HF) stimulation elicited responses from sources on the medial surface of the Calcarine Fissure mainly in the contralateral hemisphere as predicted by the cruciform model. The full field (FF) responses to large checks were approximately the sum of the HF responses. However, with small checks, FF stimulation appeared to activate a different combination of sources than the two HFs. In addition, HF topography was more consistent between subjects than FF for small check sizes. Topographic studies of the VEMR may help to explain the analogous visual evoked electrical response and will be essential to define optimal recording positions for clinical applications.

Mika Kitajima - One of the best experts on this subject based on the ideXlab platform.

  • MRI in occipital lobe infarcts: classification by involvement of the striate cortex
    Neuroradiology, 1998
    Co-Authors: Mika Kitajima, Yukunori Korogi, T. Kido, Osamu Ikeda, S. Morishita, M. Takahashi
    Abstract:

    We reviewed the MRI studies of 25 patients with occipital lobe infarcts to clarify the distribution of infarcts in the posterior cerebral arterial territory, focussing on their relationship to the striate cortex. Visual field defects and MRI findings were also correlated in 16 patients. On coronal and/or sagittal images, the distribution of the infarct and its relationship to the striate cortex were classified. Involvement of the cortex of both upper and lower lips of the Calcarine Fissure was observed in 10 patients, and involvement of the lower lip alone in 15. The upper cortical lesions were always accompanied by lower cortical lesions. The visual field defects were complete hemianopia in nine patients, superior quadrantanopia in six and hemianopia with a preserved temporal crescent in one. All patients with superior quadrantanopia had involvement of the lower cortex alone; there were no cases of inferior quadrantanopia. The characteristic vascular anatomy, and poor development of the collateral circulation in the lower cortical area, may explain the vulnerability of this area to infarcts.

  • representation of the visual field in the striate cortex comparison of mr findings with visual field deficits in organic mercury poisoning minamata disease
    American Journal of Neuroradiology, 1997
    Co-Authors: Yukunori Korogi, Toru Okajima, Ichiro Ikushima, Takeshi Sugahara, Mutsumasa Takahashi, Toshinori Hirai, Mika Kitajima, Yoshinori Shigematsu, Kazuo Mukuno
    Abstract:

    PURPOSE To compare MR imaging findings of the striate cortex with visual field deficits in patients with Minamata disease and to reestimate the classical Holmes retinotopic map by using the data obtained from comparing visual field abnormalities with degree of visual cortex atrophy. METHODS MR imaging was performed in eight patients with Minamata disease who had been given a full neuroophthalmic examination, including Goldmann dynamic perimetry. The atrophic portions of the Calcarine area were measured in the sagittal plane next to the midsagittal image and represented as a percentage of atrophy of the total length of the Calcarine Fissure. MR findings were compared with results of a visual field test. RESULTS The visual field test revealed moderate to severe concentric constriction of the visual fields, with central vision ranging from 7 degrees to 42 degrees (mean, 19 degrees). The ventral portion of the Calcarine sulcus was significantly dilated on MR images in all patients. A logarithmic correlation was found between the visual field defect and the extent of dilatation of the Calcarine Fissure. The central 10 degrees and 30 degrees of vision seemed to fill about 20% and 50% of the total surface area of the Calcarine cortex, respectively. CONCLUSION Visual field deficits in patients with Minamata disease correlated well with MR findings of the striate cortex. Our data were consistent with the classical Holmes retinotopic map.

  • Representation of the visual field in the striate cortex: comparison of MR findings with visual field deficits in organic mercury poisoning (Minamata disease).
    AJNR. American journal of neuroradiology, 1997
    Co-Authors: Yukunori Korogi, Toru Okajima, Ichiro Ikushima, Takeshi Sugahara, Mutsumasa Takahashi, Toshinori Hirai, Mika Kitajima, Yoshinori Shigematsu, Kazuo Mukuno
    Abstract:

    To compare MR imaging findings of the striate cortex with visual field deficits in patients with Minamata disease and to reestimate the classical Holmes retinotopic map by using the data obtained from comparing visual field abnormalities with degree of visual cortex atrophy. MR imaging was performed in eight patients with Minamata disease who had been given a full neuroophthalmic examination, including Goldmann dynamic perimetry. The atrophic portions of the Calcarine area were measured in the sagittal plane next to the midsagittal image and represented as a percentage of atrophy of the total length of the Calcarine Fissure. MR findings were compared with results of a visual field test. The visual field test revealed moderate to severe concentric constriction of the visual fields, with central vision ranging from 7 degrees to 42 degrees (mean, 19 degrees). The ventral portion of the Calcarine sulcus was significantly dilated on MR images in all patients. A logarithmic correlation was found between the visual field defect and the extent of dilatation of the Calcarine Fissure. The central 10 degrees and 30 degrees of vision seemed to fill about 20% and 50% of the total surface area of the Calcarine cortex, respectively. Visual field deficits in patients with Minamata disease correlated well with MR findings of the striate cortex. Our data were consistent with the classical Holmes retinotopic map.