Hydrocephalus developed in cat: Physiology of visual cortex cells

We have studied whether the remarkable shrinkage of the cerebral structurs and the thinning of its mantle following dilatation of the ventricular system in cat with developmental hydrocephalus, affects physiological mechanisms in the visual cortex. Since the hydrocephalic cat functioned behaviourally normally, it was utilized as an analogous model for hydrocephalic children in which no major problem has been observed in processing visual information. We have studied electrophysiologically hydrocephalic and control cats which had undergone sagittal splitting of the optic chiasm during development, simultaneously with monocular lid suture. The cats were anesthetized, paralyzed and subjected to extracellular recording of action potentials from single cells in cortical visual areas 17 and 18. The responsiveness of these cells to visual stimulation and their receptive field properties were characterized. In the hydrocephalic cat the majority of the physiological parameters of the cells in the visual cortex were present, as expressed in their ocular dominance distribution, their receptive field organization and selectivity to the orientation and direction of the visual stimulus. Even the interocular competition has been found as taking place in the hydrocephalic brain. However, some degradation was found, as expressed in the receptive field quality and the general level of excitability in comparison to that of the control cats. It has been thus concluded that in the hydrocephalic cat processing of visual information is principally normal, despite the remarkable deformation found in the structural organization of the visual system.