Cortical Pyramidal Neuron Subtype Classification and Visual Response Diversity

Date of Award

Spring 5-15-2015

Author's School

Graduate School of Arts and Sciences

Author's Department


Degree Name

Doctor of Philosophy (PhD)

Degree Type



A detailed inventory of the cortex's constituent pieces is essential to effectively understand the principles underlying cortical signal processing and computation. The classification of pyramidal neurons into functional subtypes remains a crucial part of this survey since the subtype-specific division of labor creates a rich substrate for computation. However, the extreme integration of individual neurons into the collective cortex suggests that cellular individuality may represent a smaller component of computational role in the context of the larger network. This possibility raises an important question: is the computational function of a neuron determined by its individual type or by its circuit connections and network role?

Electrophysiological profiles were created from turtle pyramidal neurons in the primary visual cortex by measuring passive neuronal properties and responses to current injection using whole-cell patch-clamp recordings. A blind clustering algorithm exercised on the data revealed the presence of two principle classes of neurons.

To address functional profiles, we recorded visual responses of identified neurons to diffuse light flashes. Visual responses consist of a smooth early response and a more dominant and fluctuating late response. These response epochs are hypothesized to correspond to thalamic and intracortical inputs, respectively. Cluster analysis of the dominant late response does not support evidence for subtypes.

Our study shows that the answer to the posed question appears to be both yes and no. Visual responses to whole-field flashes show likely cell-type specific inputs from the lateral geniculate nucleus, but late responses mediated by intracortical inputs are similar for both types.


English (en)

Chair and Committee

Ralf Wessel

Committee Members

John Clark, Mark Alford, Anders Carlsson, Bruce Carlson, Michael Ariel


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