Fig. 6.

Time course of the model activity (black trace), connectivity (n, dashed line in bottom panel), average synaptic strength (s, dark gray solid line), and effective connectivity (n.s,dotted line). To mimic glutamatergic blockade,n was suddenly decreased (by 25% from 1.2 to 0.9 at thevertical dotted line; see bottom panel), which in turn decreasedn.s. Becausen.s, which represents the gain of the positive feedback in the circuit, is too small, activity stops. In the absence of activity, s recovers and reaches a higher level than in control (in other words, the level of depression in the network, 1 − s, has decreased). Whens is high enough to compensate for the decrease ofn, the product n.s reaches the control value, and the network becomes active again. Once the activity has recovered, the inter-episode intervals are longer, and the episode durations are slightly shorter than under control conditions.