Figure 7. A Spike-Timing Model of Sensory-Motor Refinement.

(A) Schematic of the spike-timing dependent plasticity model. A motor neuron (grey) receives sensory input from homonymous (blue) and heteronymous (red) sensory afferent populations. The strength of the sensory-motor synapses is subject to STDP, resulting in a dependence on the phase relationship between the firing patterns of the sensory afferent and the motor neuron.

(B) Long-tailed STDP model. The horizontal axis is the difference t_pre-t_post in ms between the pre- and postsynaptic spike times. The vertical axis is the change in synaptic strength relative to the maximal strength produced by a single spike pair.

(C) Simulated motor neuron spike train. The neuron fires a burst of ~6 spikes twice per second.

(D) Distribution of sensory afferent firing phases relative to the phase of the simulated motor neuron activity. On each cycle, homonymous and heteronymous afferent activity was phase shifted relative to the motor oscillation by a random amount chosen from a zero-mean Gaussian distribution with a standard deviation of 10 or 15 degrees, respectively (n = 100 each). The distributions shown have been normalized to a peak value of 1.

(E) Sensory-motor synapse strengths shortly after application of STDP model (left), and following application of model over 200 minutes of simulated muscle contraction (right). Synaptic strengths are reported in units of the maximum allowed synaptic strength (1 nS), and all synapses were set to a relative strength of 1.0 at the beginning of the simulation.

(F) Percentage of sensory-motor synapses refined during a representative application of the STDP model.