Date on Master's Thesis/Doctoral Dissertation

12-2012

Document Type

Master's Thesis

Degree Name

M.S.

Department

Anatomical Sciences and Neurobiology

Committee Chair

Bickford, Martha E.

Author's Keywords

Cortex; vision; pulvinar; thalamus; striate; extrastriate

Subject

Visual cortex; Visual pathways

Abstract

The secondary visual pathway, from the retina through the superior colliculus and pulvinar nucleus has been linked to spatial attention (Snow et aI., 2009; Arend et aI., 2008) movement planning and motor response to visual stimuli (Wilke et aI. 2010; Grieve et aI. 2000). The tree shrew temporal cortex receives input from the tecto-recipient pulvinar nucleus, composed of the dorsal (PD) and central (PC) subdivisions (Lyon et al. 2003a). We looked at the projections from this pathway to the temporal cortex and compared them to the VI projections to the temporal cortex in the tree shrew. Our focus was to determine if there are differences in these projections that could further define their functional relationships. The characteristics we compared are the layers of termination, the axon and bouton density, the axon arbor shape and branching, axon caliber, bouton size, type and clustering. In order to clearly identify the target temporal lobe areas of projections from VI and the pulvinar, we mapped the architectonic features of the areas on a model brain using a computerized microscope system onto which we then mapped the VI and pulvinar nucleus projections. Our research found that the area to which the axons project defines the morphological characteristics of projections to that target area more than the source of the projection does. This is contrary to existing model of cortical areas receiving "driver" and "modulator" projections that have distinct morphological characteristics. We found three projection "zones" within the TP and TD areas, TP representing the upper peripheral visual field, caudal TD representing the central visual field and rostral TD representing the lower peripheral visual field. Projections to each of these target zones had different morphological characteristics. This evidence would indicate that there are three functions represented in these cortical areas that combine the input of the primary and the secondary visual pathways. The V I and pulvinar nucleus tecto-recipient zone projections to the temporal cortex were thin, dense and moderately to heavily branched. The boutons were mostly small and numerous. V I axons projecting to TP (V 1-TP) and PD axons projecting to TP (PD-TP) have wide arbors of thin axons with extensive branching and many small boutons of mixed boutons en passant and terminal bouton type. V 1 to TP axons are sparser than PO to TP axons and are more likely to give rise to boutons en passant. Pulvinar nucleus projections to caudal ID (PO-TO, PC-cID) also result in wide arbors. These are dense and extensively branched with mixed thin and thick axons and many small to medium sized boutons. VI projections to TD (VI-TD) and pulvinar nucleus projections to rostral TO (PC-rTD) are organized in narrow local arbors of mixed thin and thick caliber axons with sparse to moderate density and branching. Boutons are small to medium sized. V I-TD axon branching is more sparse than PC-rTD axon branching. VI-TD axons have slightly more boutons than PC-rTD axons.

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