Illustration of the mechanism that compresses the temporal sequence of spikes.

<p><b>a</b>) The weight of a connection between a pre- and post-synaptic neuron increases according to the STDP rule, even if the interval between pre- and post-synaptic spike exceeds the delay of the connection. However, when the connection is strong enough, the pre-synaptic neuron can directly cause the post-synaptic neuron to fire. Thereby, the temporal interval of both spikes becomes shortened. <b>b</b>) The same effect applies when timed spikes of several neurons are required. In this example, the neurons a-j are connected with neuron k and fire in a temporal sequence. Neuron i and j together can make neuron k spike. However, STDP also increases connection weights from neurons spiking earlier in time (e.g. h and g). After sufficient repetitions, neuron i can directly evoke the spike of the target neuron as the contribution of neuron h already increased the activity level of neuron k. Thereby, neuron k spikes earlier. This mechanism continuous for all preceding neurons.