Thalamic microcircuitry: neurons, synapses, and circuit motifs in receptive field structure and sensory processing

Our perception of the world is first shaped by the thalamus, a structure composed of many nuclei in the center of our brains. Different nuclei hold different responsibilities - vision (dorsal lateral genicular nucleus; dLGN), audition (medial geniculate nucleus; MGN), somatosensation (ventro-basal nuclei; VB), though many properties across these sensory modalities appear to be universal. In this thesis, we completed a comprehensive characterization of the neurons, connections, and microcircuitries within the rodent VB thalamus. Our most prominent finding is the confirmation of the existence of local interneurons in the VB and the discovery of their profoundly active and diverse role in thalamic processes. Thus, we have observed that the fundamental excitatory and inhibitory neurons of dLGN and VB nuclei and their intrinsic circuit motifs are indistinguishable. Only a few notable differences are, however, present. (1), Principal excitatory neurons of the VB, the thalamocortical (TC) relays, have morphological types that appear to be distributed heteroge-neously throughout the VB whereas dLGN TC morphological types have regional preferences. (2), VB inhibitory local interneurons represent a smaller proportion of the total neuronal popula-tion compared to their dLGN counterparts. The similarities between these thalamic regions great-ly outnumber the differences. It then introduces new questions of how different vision and soma-tosensation of the physical world are when these senses are ultimately represented as binary sig-nals and are processed in similar manners in the thalamus. Following these questions may lead to new therapeutic solutions for retinally blind patients, tactile prostheses, or neurological disorders of sensory perception like schizophrenia.