The Structure of Functional Connectivity in Cat Primary Visual Cortex

The key to understanding how the brain works is to understand the computations it performs. The structure of anatomical and functional connectivity determines what the brain can compute and how it does so. Correlations have served as a tool for analysing connectivity for over five decades. The mammalian visual cortex has become the most intensively researched cortical area and is unmatched for our knowledge of its anatomical layout and, most importantly, stimulus selectivity. Furthermore, recent perspectives on correlations have arisen from information theory and network models of the brain. The purpose of this dissertation is to determine the precise structure of functional connectivity in cat primary visual cortex. We aim to contribute to and extend previous work by analysing the structure of neural responses and correlations during spontaneous activity, the presentation of artificial stimuli and the presentation of natural stimuli. We report on a comprehensive set of twenty functional and neurophysiological factors, and reveal how previously unexplored factors govern correlations in visual cortex in vivo. Furthermore we find novel functional relationships between factors governing the responses of neurons, and report on a set of properties which allow to distinguish narrow from broad spiking cells. Much attention is devoted to the precise functional dependency of correlations upon firing rate, with the development of methods to remove the firing rate modulation. We show that timescale is an important determinant of correlations, and that natural stimuli generate different correlations than artificial stimuli. We also show that during spontaneous activity, neurons are more likely to fire together if they are tuned to a similar orientation. These results emphasize that both spontaneous and stimulus driven cortical activity contain rich structure that is far from a decorrelated state