Master's Theses

Date of Award

2012

Document Type

Thesis

Department

Biology

Keywords

NeuroSciences, Neuroanatomy, Cerebral Cortex

Abstract

The purpose of this thesis is to characterize the cortical inputs to area 18 of ferret visual cerebral cortex. Contrary to feedforward connections, feedback connections are presumed to have a modulatory influence on the responses of lower order neurons providing information already processed. Input from feedback connections can supposedly elicit changes in the response to stimuli within the receptive field and may be involved in the role of discriminating objects relative to the background. The aim of our set of experiments was to fully analyze and compare the anatomical characteristics of feedback connections to area 18 from extrastriate areas as opposed to the feedback connections to area 17 in visual cortex. In our analysis, we focus on the overall pattern of retrogradely labeled cells, the proportion of feedback label to area 18, the laminar distribution of these cells, their density and clustering tendencies, and their cortical extent. With this solid base of information we can then make further hypotheses regarding the influence and role extrastriate areas 19, 21, and Suprasylvian cortex provide in modulation. The mean proportion of total cortical input from area 17 is 19.9%, from area 18 (39.5%), from area 19 (27.5%), from area 21 (4%), and from Ssy area (17.1%), from cells undefined in the border covering area 17 and area 18 (3.6%), border cells between area 18 and area 19 (1.5%). The overall feedback proportions when data is pooled for area 19 is 57.2%, for area 21 (8.75%), Ssy area (26.1%), area 18/19 border (6.6%) and area 19/21 border (1.4%). Within each area, there is a significantly larger proportion of feedback connections arising from the infragranular layers (means range between 70 and 88%) than from the supragranular layers (means range between 8% and 25%). After pooling all of our cases together, we measure the grand median of the nearest neighbor distance for each cortical area providing connections to area 18 including area 17 (34.14μm), area 18 (39.48μm), area 19 upper layers (45.61μm), area 19 lower layers (39.55μm), area 21 lower layers (62.48μm), Ssy area upper layers (57.8μm), Ssy area lower layers (44.28μm), borders of area 17/18 (34.58μm), borders of area 18/19 (55.4μm), borders of area 19/21 (41.58μm), and lateral temporal areas (57.74μm). We find the characterization of inputs to area 18 in comparison to the feedback projections to area 17 vary in proportion, anatomical location and cortical extent, which suggest different retinotopic representation in the visual fields.

Included in

Biology Commons

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