Characterization of activity in the primary somatosensory cortex during active behavior and sleep

Although many studies have examined the activity patterns of barrel cortex neurons in immobilized or anesthetized rats, few have examined activity patterns in freely behaving rats. In my thesis work I characterized the activity patterns of barrel cortex neurons in freely behaving animals. Studies have shown that in anesthetized or immobilized rats, barrel cortex neurons fire well below 1 Hz during spontaneous activity and in response to vibrissa stimulation. During periods of sensory-cue interaction and during periods of non-stimulus-related activity, the majority of neurons fired at rates significantly greater than 1 Hz. During slow wave sleep (SWS), firing rates were lower, but were still significantly greater than 1 Hz. I also found that more than 80% of neurons were either up-modulated (experienced a 20% or greater increase in firing rate) or down-modulated (experienced a 20% or greater decrease in firing rate) during cue interaction. These data contradict the view that low firing rates typify the output of the barrel cortex during awake activity and during sleep and suggest that a large fraction of neurons are modulated by a stimulus. To examine the spatio-temporal characteristics of the spiking activity of barrel cortex neurons, the spiking activity of each cell recorded was modeled, using the Generalized Linear Model (GLM). The direction of modulation experienced by a neuron could be predicted by its activity patterns during awake behavior in the absence of a tactile cue and during sleep. During maze running in the region of the maze that did not possess the tactile cue, up modulated cells showed greater burst incidence and had shorter relative refractory periods than down modulated cells. During SWS, the down modulated cells showed greater burst incidence and had lower firing rates than up modulated cells. GLM analysis also showed that the firing patterns of many barrel cortex cells during maze running were similar to those reported in anesthetized rats. Specifically, spiking activity was followed by a relative refractory period, which was often followed by a period of rebound excitation. These studies shed light on how the barrel cortex processes information during awake behavior and sleep.