Figure 6.

Development of the asymmetric circuit through STDP. A, Initial circuit with symmetric connections. Arrow in each circle represents direction selectivity of the cell. Line thickness represents synaptic strength (the weakest connections are shown in gray). B, Simulated spatiotemporal spike patterns in the circuit evoked by a small object (top) moving rightward (left column) or leftward (right column) across the visual field. Each red or blue dot represents a spike of a presynaptic neuron (indexed 1-143, from left to right) with the corresponding color. Black dots represent spikes of the target neuron. C, Mature circuit after extensive exposure to motion stimuli in both directions, during which the connections underwent spike-timing-dependent modification. Line thickness is proportional to the synaptic strength after 800 simulated motion sweeps in each direction. The velocity of motion in each direction followed a Gaussian distribution (mean: 60°/sec; SD: 20°/sec).