| dc.description.abstract | Pulvinar is the largest thalamic nucleus in primates, with extensive connections with visual cortical areas. In simian species, two retinotopic maps have been reported in the lateral (PL) and inferior (PI) pulvinar subdivisions. The maps connect with the primary visual cortex (V1). The medial inferior pulvinar (PIm), medial to these maps, have heavy connections with the middle temporal area (MT), a motion processing area in the early visual system.
In this thesis I examine the structure of these areas and how they modulate cortical vision processing. I electrophysiologically examined the organization of the two retinotopic maps and PIm in bush baby (Otolemur garnettii), a prosimian primate close to the common ancestor of primates, and found it to be approximately homographic with the different pulvinar maps reported in New World and Old World simians. The projections from the retinotopic maps to V1 have recently been shown to have strong excitatory control on V1 output, despite being long considered a part of feedback modulation. We examined the axonal and synaptic morphology of pulvinar projections to V1 to reveal the anatomical basis of this strong control. The PL axon terminals in V1 appear to only end in layer 1a, synapse directly on distal dendrites of local pyramidal neurons, and not recruit local inhibitory networks that may amplify the signal. We investigated the functional effect of PIm projections to MT by recording in MT while pharmacologically manipulating PIm activity . The pulvinar showed a net excitatory effect on MT output, but this effect required a V1 relay. The direct pulvinar to MT projections appeared to be inhibitory.
In summary, we expanded our understanding of structure and function of the primate pulvinar, by revealing a common pattern in its functional organization, and identifying the effect of its modulation on early visual cortices such as V1 and MT, as well as the anatomical basis underlying one of these projections. | |
