Figure 1.

Network architecture. (A) Example of input configurations from a single stimulus-responsive input population. Each input population is represented by 20 cells, which output independent Poisson spike trains but correlated connections. The total number of independent sets of connections ranges from 2 to 20. Left: with two independent inputs per stimulus population, and low input connection probability (1/5 is shown) associative layer cells receive selective input. Right: with 10 independent inputs per stimulus population, and low input connection probability (1/5 is shown) associative layer cells receive more uniform, less correlated inputs. Poisson input groups randomly project to a sparse-random recurrent network of excitatory (red) and inhibitory (cells). Input projection probability ranges from 1/20 (sparse) to 1/2 (dense), with input connections selected independently between each set of independent input cells per input population. (B) Complete network structure (Bourjaily and Miller, 2011). Excitatory-to-excitatory connections (arrows) and inhibitory-to-excitatory connections (balls) are probabilistic and plastic. All-to-all inhibitory-to-inhibitory synapses are also present but not plastic. In the relevant simulations, STDP or triplet-STDP occurs at excitatory-to-excitatory and input-to-excitatory synapses, while LTPi occurs at inhibitory-to-excitatory synapses. Inhibition is feed forward only (i.e., the network does not include recurrent excitatory-to-inhibitory synapses). Excitatory cells from the Associative layer project all-to-all, with initially equal synaptic strength to excitatory cells in both the Hold and Release pools of the decision-making network. The decision-making network consists of two excitatory pools with strong intra-pool recurrent connections, which compete via cross-inhibition between pools (Wang, 2002). Strong intra-pool recurrent excitation ensures bistability for each pool, while the cross-inhibition generates winner-take-all (WTA) dynamics such that only one population can be active following the stimulus, resulting in one decision. Whether the motor output (based on the decision of hold versus release) is correct for the corresponding cue, determines the presence of Dopamine (DA) at the input synapses, according to the rules of the task in Figure 2.