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E. Bui, C. Milleret; Asymmetry Of Visual Interhemispheric Integration In Unilateral Early Convergent Strabismus : An Electrophysiological Approach . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4306.
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Unilateral convergent squint significantly modifies interhemispheric transfer to areas 17 and 18 when activated through the stimulation of the non deviated eye. This was established in cats with surgically induced squint performed early after birth. It was shown that the location of transcallosally activated neurons of the visual areas 17 and 18 in the hemisphere ipsilateral to the deviated eye is not restricted to the 17/18 border (as in normal conditions) but expands to large portions of A17 an A18. It results of the stabilisation of exuberant juvenile callosals terminals
Interhemispheric transfer to areas 17 and 18 when activated through the stimulation of the deviated eye is not established, and it is discussed whether interhemispheric integration in case of convergent strabismus is symmetrical or not. Therefore, we have tried to investigate this matter in studying the transcallosal visual responses induced by the stimulation of the deviated eye of four anaesthetised and paralysed adult cats whose right eye had been surgically deviated on postnatal day 6. After acute section of the optic chiasm, single–unit activity was recorded from A17 and A18 of the left hemisphere while the right eye was visually stimulated.
A total of 70/278 units were transcallosaly activated. They were mainly located at the 17/18 border (n=61 ; 87,1%) and were rare in A17 (n=7 ; 10%) and A18 (n=2,9%). Numerous functional abnormal properties of the transcallosal neurons characterized the interhemispheric transfer activated through the stimulation of the deviated eye : decreased binocularity, reduced orientation selectivity, dense laminar distribution revealing a radial exuberance of the callosal terminals activated through the stimulation of the deviated eye.
If analysed tangentially to the cortex, this location was similar to the one present in normally reared cats ; however, it was clearly different to the one which characterised the interhemispheric transfer activated through the stimulation of the non deviated eye, where a tangential exuberance of callosal terminals is present. Transcallosal receptive fields were manifestly located within the hemifield ipsilateral to the explored cortex, alike the receptive fields which characterise the transfer in the other way, but they still had a contact to the central vertical meridian, as in normal conditions. An asymmetry in visual interhemispheric transfer to areas 17 and 18 in cats with convergent strabismus was therefore established.
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