Network activity encodes sequence information.

Network responses to 3 sequentially presented items with (A) and without synaptic augmentation (B). The bottom panel in (A) shows the level of synaptic augmentation in the corresponding synaptic populations. The presentation of an item is simulated by a 10-fold increase of the background input selectively to the corresponding neuronal population for 250ms (gray areas). The background input to the remaining populations is kept constant at its baseline level. Network parameters: P = 16, τ = 8ms, α = 1.5Hz, AEE = 6.0, AEI = 1.1, AIE = 1.75, Ibkg = 8.0Hz; Short-term plasticity parameters: U = 0.3, KA = 0.01, τD = 0.3s, τF = 1.5s, τA = 20s.

Replay of a novel sequence.

(A) Architecture of the memory and read-out network (see main text for details). (B) Top panel: Input to the read-out network from the memory network. Middle panel: Activation state of the item-selective populations in the read-out network, as determined by comparing the sum of the input from the memory network and of the background input to the threshold. Bottom panel: Time course of the background input to the read-out network. (C) Same as (B) for a different sequence. Note that the time course of the background input to the read-out network is the same in (B) and (C).

Fast-replay of a novel sequence.

The top panel shows the response of the network to the external inputs depicted in the bottom panel. After the presentation of the sequence, the background input is first decreased for 3 seconds and then increased for 250 milliseconds. The middle panel shows the resulting time course of Aux in the corresponding synaptic populations. Immediately before the background input is increased again, Aux ≃ AU.

Reactivation of an activity-silent memory.

The top panel shows the response of the network to the external inputs depicted in the bottom panel. 8 seconds after the presentation of the two items, the background input to the neuronal population selective to second item (red) is decreased for 8 seconds, and then restored to its original level, while decreasing the background input to the neuronal population selective to the first item (blue). The middle panel shows the resulting time course of the level of augmentation in the corresponding synaptic populations.