Title

The Y visual pathway of the cat: Neural connectivity and response properties

Date of Completion

January 2006

Keywords

Biology, Neuroscience

Degree

Ph.D.

Abstract

In the cat, information encoded by Y retinal ganglion cells is widely distributed in early stages of visual processing. Y retinal afferents diverge to target two different layers (i.e. A and C) of the lateral geniculate nucleus (LGN), and Y geniculate afferents can project to up to three cortical areas (i.e. areas 17, 18 and 19, see Sherman, 1985 for review). While the functional significance of the large increase in spatial coverage within the Y pathway remains unclear, one possibility is that Y cells may diverge into separate channels in these early processing stages. In my dissertation, I tested this hypothesis by studying the response properties and connection specificity of Y geniculate cells and their cortical targets. Firstly, I asked whether Y cells in layer A (YA) and layer C (YC) of LGN were 'different enough' to be considered as two separate types. Secondly, I compared the response properties of YA and YC cells that shared a common retinal input. Thirdly, I studied the response properties of cortical cells that received monosynaptic input from YA or YC cells. ^ My results demonstrate that YA and YC cells with overlapping receptive fields differ significantly in several parameters including response latency, response transiency, receptive-field size, and linearity of spatial summation. In some of these parameters; the differences between YA and YC cells are as pronounced as the differences between X and Y cells in layer A, which are generally considered as two distinct cell types. Furthermore, I show that YA and YC cells sharing a common retinal input always have overlapping receptive fields (overlap ≥ 70%) of the same sign (both ON or both OFF) but they frequently differ in receptive-field size and response latency. Finally, my results provide further evidence indicating that YA and YC cells are likely to target cells with different receptive fields in the primary visual cortex. In summary, my results indicate that Y retinal ganglion cells diverge into separate channels at the early stages of the visual pathway.^