Figure 9. Hypothesized flow of sensory-evoked and spontaneous activity through auditory cortical circuits.

Each sheet represents a population of the corresponding layer, with cones and spheres representing PCs and INs, respectively. Colored symbols represent active neurons. For both types of activity, pyramidal cells exhibited dense and distributed activity in the deep layers, but sparse and localized activity in the superficial layers; interneurons show a pattern of activity similar to that of deep layer pyramidal cells. For sensory responses, earliest firing is seen in cells of the middle and deep layers, presumably reflecting the strongest afferent input onto these neurons. For spontaneous events, activity spread upward from the deep layers.