Abstract
Neural circuit development is profoundly influenced by experience-dependent processes. The visual system serves as a robust model for understanding how experience affects sensory perception and the circuit mechanisms required for processing of the visual world. Decades of research have focused on cortical processing of visual receptive field properties and the early plasticity of cortical neurons, with less concentration on the contributing inputs to visual cortex. In this thesis I focus on the lateral geniculate nucleus of the thalamus and its contributing role to visual circuit development. I investigated the development of receptive field properties of individual lateral geniculate nucleus neurons and sought to understand how changes in neural responses with short-term experience could influence the development of motion processing. As this project evolved, we recognized that superior electrophysiological tools are required for charting discrete developmental changes in functioning neural circuits. This resulted in the simultaneous development of novel carbon fiber microelectrode arrays while still using multichannel commercial arrays to study the development of the ferret lateral geniculate nucleus.
In the first part of this thesis, I characterize the developmental changes in receptive field properties of ferret lateral geniculate nucleus neurons that occur with acute visual experience. My work established that there are no changes in lateral geniculate nucleus response properties with exposure the six hours of a moving stimuli. This set of stimuli has been shown to drive the rapid emergence of cortical direction selectivity but did not have any significant effect on direction selectivity in the lateral geniculate nucleus nor did it produce changes in response properties that could confer cortical direction selectivity. These data suggest that cortical mechanisms likely drive the development of direction selectivity in the visual cortex and that these changes can precede developmental changes in spatiotemporal properties of ferret lateral geniculate nucleus neurons.
In the second part of this thesis, I detail a protocol for constructing and implementing carbon fiber microelectrode arrays for use in in vivo electrophysiological recordings. In order to understand the precise mechanisms for the circuit computation of direction selectivity, the ideal experiment would employ dense simultaneous electrophysiological recordings of many of the thalamocortical cells that provide inputs to a single cortical neuron, enabling a complete characterization of the development of that circuit. However, such dense multichannel electrodes are not currently available commercially and so we developed new methods for building dense electrode arrays for acute cellular recordings.
Together, these projects allowed us to assess short-term changes in an in vivo model for the development of visual motion processing, suggesting that cortical mechanisms are responsible for the development of direction selectivity and have paved the way for precisely testing this hypothesis.