The ocular dominance and receptive field properties of visual cortex cells of cats following long-term transection of the optic chiasm and monocular deprivation during adulthood

Visual hemispheric dominance induced in split brain cats during development: a model of deficient interhemispheric transfer derived from physiological evidence in single visual cortex cells

The effects of cancellation of both interhemispheric callosal transfer and interocular interactions, were studied in early monocularly deprived cats. The main purpose of this study was therefore to prove whether unilateral hemispheric dominance would result under these conditions and to what extent each hemisphere will be functionally independent. Secondly, we have attempted to establish such an experimental model physiologically, on the single cell level. Interhemispheric transfer was surgically canceled by sagittal transection of the corpus callosum. In addition, the ocular projections were separated by sagittal transection of the optic chiasm in the transbuccal approach. This condition had practically induced visual split brain condition in these cats. These manipulations were carried out concurrently with monocular deprivation (SBDK group) which was surgically done by eye closure during the critical period of development of the visual system. Thus, the hemisphere ipsilaterally to the visually deprived eye had developed under conditions of deficient visual experience while the hemisphere ipsilaterally to the normal eye had developed under conditions of unaltered visual experience. A group of cats (SBK) similarly operated but equally binocularly exposed during development was served as controls. In addition, adult cats similarly operated during adulthood either chronically or acutely were studied to evaluate the effects of interhemispheric and interocular separation. Other groups of cats were also studied for comparison, and included sham operated and normal adult cats. At adulthood, electrophysiological studies were done on these cats, in which action potentials were extracellularly recorded from single cells in the visual cortex (area 17-18 boundary) following anesthesia and paralysis. Stimulation was carried out manually and by a computer driven optical system, presenting on a tangent screen light bars at various spatial positions, orientations and directions. Receptive fields were thus mapped for all neurons and their dimensions and eccentricities were measured. The responsiveness, ocular dominance and other parameters were also studied for these cells. The results in the early deprived cats and in their controls, had shown a full separation between the two hemispheres, as reflected in the almost absolute ipsilateral eye responsiveness (> 97.0% cells). In comparison, in the sham operated and in the normal control cats only minor proportions of cells (13.0-18.7%) have been found as ipsilaterally and monocularly driven, showing almost full interhemispheric and interocular interaction. The main difference, however, in the results between the early monocularly deprived cats and their controls is that in the first group the two hemispheres were asymmetric concerning the amount of visual activation and in the second one they were very symmetric.(ABSTRACT TRUNCATED AT 400 WORDS)

Binocularity and excitability loss in visual cortex cells of corpus callosum transected kittens and cats

The contribution of the corpus callosum to binocularity of visual cortex cells and to their responsiveness was studied in cats. Electrophysiological recordings of the responses of single cells to visual stimulation was performed in the callosal projection zone, visual cortex area 17-18 boundary in callosotomized cats. Callosotomy was carried out by transection of the visual segment of the corpus callosum in 6-7-week-old kittens and in acute and chronic adult cats (postoperative recovery time: 11 days-39 months). While in our normal cats the common proportion of binocularly driven cells (79.8%) was found (66.3% in the sham controls), a remarkable diminution (29.7%) was found in the callosotomized kittens, in the acute (39.7%) and in the chronic (50.6%)-operated cats. We have also found a change in the amount of binocularity as function of postoperative recovery time. While the proportion of binocular cells was conceivable (60.7%) in the short- and intermediate-term callosotomized cats (postoperative time: 0.3-5.5 months), it was diminished (36.9%) in the long-term (6.5-39 months) chronic cats. As to the responsiveness level, it was found that visual responsive cells constituted 88% of the cells in the normal and 80.3% in the sham controls. In comparison, they constituted 69.2% in the acute, 54.4% in the chronic and 52.8% in the callosotomized kittens. Furthermore, callosal transection had produced a symmetric effect in the two hemispheres, regarding binocularity and responsiveness. It has been thus concluded that the corpus callosum is essential for the mediation of binocular functions between the two hemispheres; in addition, cortical excitability has been also found to depend on callosal integrity.