Architecture and activity of the model network.

<p>(A) The primary auditory cortex is represented by a recurrent neural network divided into cortical columns. Columns are arranged tonotopically by their best frequencies (BFs), but the BFs of neurons within each column show some variability (BFs are represented by color). Arrows illustrate the connectivity of one column. (B) Upon sensory stimulation a column may generate a population spike (PS), shown here as a transient increase in the column’s mean firing-rate, <i>E</i> (top). The inhibitory population (mean firing-rate, <i>I</i>) lags behind the excitatory activity. A PS depletes the synaptic resources, which recover gradually (bottom; <i>x</i> is the mean fraction of available resources in excitatory synapses, <i>y</i> in inhibitory synapses). Stimulus duration shown in gray. (C) The threshold for PS generation. Left: Time course of responses for stimuli of varying amplitude. Response strength is displayed using a color scale. Right: Spike count (integrated from stimulus onset until 45 ms following offset; see <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1005437#sec019" target="_blank">Methods</a>) as a function of input amplitude, with (black) and without (cyan) feedback inhibition. (D) A PS that is initiated in one column (here, column 11) can propagate across the network. The color scales of (C) and (D) are identical. Stimulus duration in (C) and (D) is the same as in (B). (E) A low level of synaptic resources (x) may prevent subsequent stimuli from evoking a PS. Stimulus presentations are shown in gray. (F,G) Refractoriness of PS generation. Following a PS, a stimulus has to be stronger (F) or presented at a longer latency (G) in order to evoke a PS. Stimuli marked by black bars under the traces. In (F), the first stimulus has <i>A</i> = 5 Spikes/s, and values next to the traces specify the amplitude of the second stimulus. In (G), all stimuli are of the same amplitude, <i>A</i> = 5 Spikes/s. (H) The spike count for the second stimulus. The first stimulus was always presented with <i>A</i> = 5 Spikes/s. The second stimulus varied in amplitude (abscissa) and ISI (ordinate).