The cerebral connexions of the visual system

• Main Author: Headon, Maurice P.
• Published: University of Oxford 1976
• Subjects: 617.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.458705

In the mammalian visual system the experimental investigation of the effect of sensory experience on the postnatal brain was facilitated by the detailed information that was already available on the structure and function of the normal adult and the relative ease with which the animal's visual environment could be modified by eyelid suture. When performed in young kittens this procedure produced a cellular atrophy in the lateral geniculate nucleus which resembled histologically the transneuronal degeneration studied in the same site after eye enucleation (Wiesel & Hubel 1963a). The physiological studies (Hubel & Wiesel 1965) pointed out the role of a process of competition between deprived and non-deprived visual inputs in the postnatal development of the visual pathways. This idea of competition was applied as a mechanism to explain the cellular atrophy in the lateral geniculate nucleus following lid suture in kittens after the observation that the degeneration was confined to the binocular segments of the geniculate (Guillery & Stelzner, 1970). It was postulated that cells in the binocular portion of the visual cortex may be regarded as receiving axons from 2 adjacent geniculate laminae and there may be a competition for synaptic space on the cortical cell with the neurons from the non-deprived laminae of the lateral geniculate nucleus forming greater axonal arborisations at the expense of those from the deprived laminae. This abnormally restricted cortical arborisation of the deprived geniculo-cortical cells could be reflected in a retrograde fashion in a smaller perikaryal size of the deprived cells than the non-deprived cells with a rich arborisation. Secondly the monocular segment of retina-geniculate-cortex pathway could be a site in which competition was not occurring so that the lack of degeneration here was a reflection of the absence of competition.