Neuronal organization within the mammalian dorsal lateral geniculate complex and adjacent pulvinar nuclei: a comparative approach

Abstract

This dissertation attempts to understand the organization of some of the nuclei which constitute the mammalian visual thalamus through an electrophysiological and histological investigation of the cat and rat aided by an evaluation of comparative neuro- anatomical and physiological literature.
The introduction initially reviews the anatomy and physiology of the cat's visual system. Later a review of comparative aspects provides a background for the evaluation of the experimental results in a comparative context.
Responses of cells in the cat's dorsal lateral geniculate complex, comprising the laminated lateral geniculate and medial interlaminar (MIN) nuclei, were investigated in paralysed cats, lightly anaesthetized with either pentobarbitone or N2O/O2 supplemented with pentobarbitone, Geniculate cells were initially classified as sustained or transient according to their response properties. This revealed a differential distribution of receptive field types within the LGNd complex, and evidence of laminar organization in the MIN.
Later cells were further classified as 'brisk' or 'sluggish', sustained or transient according to their response properties providing additional evidence for a differential distribution of 'brisk' and 'sluggish' cell types within the LGNd complex.
Responses of cells in the LGNd complex to textured 'visual noise' were also investigated. On-centre/off-centre and sustained/ transient cell types in the LGNd complex did not appear to be differentiated by their responses to visual noise as are simple and complex cells in the striate cortex.
A preliminary investigation of the response properties and vlsuotopic organization of cells in the feline extrageniculate visual thalamus was attempted. It was found that cytoarchitecturally defined thalamic regions do not essentially delineate functional (visuotopically organized) regions.
The response properties of cells in the rat's LGNd (with regard to the sustained/transient classification) and pulvinar were Investigated. These results were compared with the neuronal organization found in the cat.
In the discussion an overview of the experimental results is provided and the functional significance of the neuronal organization found in the mammalian LGNd complex and pulvinar-complex is discussed.