Figure 3.

Illustration of LTP contribution to the Clopath rule. A presynaptic neuron (A) and a postsynaptic neuron (B) emit a spike at t_sp,pre = 4 ms and t_sp,post = 6 ms, respectively. The presynaptic spike elicits a trace $s_j^{*}$ (gray) at the synapse. The excursion of the postsynaptic membrane potential V_i (B, blue) elevates the low-pass filtered potential ū₊ (green) so that both V_i and ū₊ exceed the respective thresholds θ₊ (dash-dotted, dark blue) and θ₋ (dash-dotted, dark green), cf. (13), between t₁ and t₂. Only within this period, shifted by d_s = 3 ms, which is for times t₁ + 3 ms < t < t₂ + 3 ms (B, red background), see section 3.2.3 for details, the LTP of the synaptic weight is non-vanishing because of the threshold-linear functions in equation (13). The shift by d_s = 3 ms does not apply to the spike trace (A, red background). The rectangular shape of the spikes is achieved by a clamping of the membrane potential to V_clamp = 33 mV for a period of t_clamp = 2 ms.