Dissertations, Theses, and Capstone Projects

Date of Degree

5-2015

Document Type

Dissertation

Degree Name

Ph.D.

Program

Psychology

Advisor

Joshua C. Brumberg

Subject Categories

Psychology

Keywords

Inverted; Neocortex; Pyramidal Cell

Abstract

Within the nervous system, the cortex is the area of the brain where higher order sensory, motor and cognitive processing occurs. The cortex contains a diverse array of cell types which form complicated and intricate circuits which gives rise to higher order sensory, motor and cognitive functions. The majority of neurons found in the cortex are pyramidal cells. While pyramidal cells differ based on soma size, dendrite span and cortical position, almost all share a noticeable defining characteristic: their apical dendrite extends toward the pial surface. However, there also exists a class of pyramidal cell where the apical dendrite extends in the opposite direction, toward the cortical white matter; these pyramidal cells appear to be upside down, or inverted. Utilizing physiological and histological techniques, inverted pyramidal cells (IPCs) within neocortex layer VI of the somatosensory cortex were examined and compared to the more common upright pyramidal cells (UPCs). This research produced a number of key findings: 1) the intrinsic physiology of IPCs differs from UPCs on a number of measures including input resistance, and action potential threshold and half-width; 2) IPCs, beyond the orientation of the apical dendrite, are morphologically dissimilar as compared to UPCs and 3) Stimulation of the underlying cortical white matter revealed IPCs are either integrated into different cortical circuits or process inputs differently. The main conclusions emphasize a need for further examination and classification of cortical neuronal cell types. These data are relevant to models of information processing through micro- and larger neocortical circuits and indicate that different cell types found within similar lamina can have different functional properties.

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