Fig 5. Spike timing dependent plasticity.

The post–synaptic neuron (red) spikes follow that of the pre–synaptic neuron (black), leading to an increase in the synaptic weight (facilitation) (Fig 5A top panel). The opposite temporal order (post–synaptic spikes occur before pre–synaptic spikes) leads to a decrease in synaptic weights (depression) (Fig 5A bottom panel). The increase/decrease in synaptic weight (Δw) is shown as a function of the time difference between the pre–and the post–synaptic spike (5b). When the presynaptic spike occurs before the post–synaptic spike is positive and otherwise negative. The distribution of synaptic weights of all KC-MBONs pairs evolves over time (c). In the left panel of (c) all the initial weights were set to 1.4. The system was then stimulated with different odors of varying concentrations. The weights were sampled at fixed intervals of time. The distribution of weights was plotted using a color map (see color bar for the frequency values). The mean synaptic weight was overlaid on the distribution (white trace). The right panel shows the temporal evolution of the synaptic weights when a low initial weight (0.6) was used.