Figure 2.

Active and passive memory mechanisms in the circuit model: (A-C) active match enhancement and suppression, (D-F) passive repetition suppression. (A,D) Spatio-temporal activity pattern in the WM, ME and MS populations in an ABBA task, where a sample (90°) is followed by two nonmatch test stimuli (270°) and then by the final match (90°). x-axis: time, y-axis: neurons labeled by their preferred directions, firing rate is color-coded. (A) Comparison neurons respond to their preferred stimuli, but the activity is higher in the ME cells than in the MS cells for the match, and vise versa for the nonmatch stimuli. (D) If the activity in the WM circuit is disrupted, passive repetition suppression prevails in the comparison neurons. (B,E) Firing rates of a neuron preferring the test stimulus on two trials: when the test appears as a match (orange line) and as a nonmatch (purple line). In the match condition, the sample is also the preferred stimulus for this neuron, and in the nonmatch condition the sample is the antipreferred stimulus. Note sample-selective persistent activity in the ME cell during the delay. (C,F) Average responses to the neuron's preferred stimulus appearing as a sample, match, nonmatch and repeated nonmatch. These model results account for the single-neuron activities recorded from behaving monkeys in Figures 1C,1D.