Figure 5.

(A) Shows the average synaptic weight of synapses from the group of neurons representing S₁ (green) and every synapse in the network (blue) for the first hour of the experiment. Randomly selected stimuli S_k are delivered to the network (black arrows), separated by random intervals of between 100 and 300 ms. These are visible in the synchronous spikes in (B,C). Every time S₁ is chosen, dopamine is delivered to the network (dashed line). Raster plot (B) depicts the first 1 s of network activity when S₁ was delivered to the network; and (C) illustrates 1 s of activity after 1 h of simulation, showing how the neurons stimulated by S₁ have learned to respond more strongly. Note that in (A), the average of all the weights is increasing because, additionally to S₁ always being rewarded, some stimuli S_k ≠ S₁ also randomly get picked up soon before or after reward is delivered to the network.