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|Title:||The lateral geniculate nucleus: Morphogenesis, functional specializations, and oculomotor feedback|
|Doctoral Committee Chair(s):||Malpeli, Joseph G.|
|Department / Program:||Neuroscience|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||As an effort to understand the functional significance of the laminar organization of the lateral geniculate nucleus (LGN), I developed the first computational model of LGN morphogenesis which reproduces the realistic global laminar patterns. In the rhesus LGN, a laminar transition from 6-layered to 4-layered regions coincides with small gaps (optic-disc gaps), representing the blindspot. A computer simulation of the model supports the hypothesis that the transition in laminar pattern is triggered by the optic-disc gaps, which act as a singularity in a developmental gradient. It suggests that some morphological features of the brain are indirectly determined by the dynamics of the system, instead of being directly specified by a genetic program.
In a second experiment, I tested the theory that the cat medial interlaminar nucleus (MIN, a subdivision of the LGN) is a structure specialized for scotopic vision, by comparing contrast sensitivity functions for cells in the MIN and other major divisions of the LGN (layers A and C) over a range of adaptation levels from mid-mesopic to absolute threshold. The results are consistent with the theory: the MIN is more sensitive for low spatial frequencies, especially at low luminance levels; layer A excels for high spatial frequency, but only for relatively high luminance levels; layer C is intermediate in this acuity-sensitivity tradeoff. These results suggest that one function of geniculate lamination is to expand the range of vision for low-contrast, dim stimuli by increasing the signal-to-noise ratio through central convergence.
In a third experiment, I examined the issue of visuo-oculomotor integration in the cat LGN. Three major findings were obtained: (1) most LGN neurons increase their spontaneous activity after saccades in the absence of any visual input; (2) the visual activity of most LGN neurons interacts with gaze direction; (3) there are transient changes in geniculate visual responses immediately after saccades. These results suggest that one function of centrifugal feedback to the LGN is to integrate oculomotor signals into the visual system.
|Rights Information:||Copyright 1995 Lee, Daeyeol|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9624409|