Fig. 2. Emulation of the rate-based synaptic adaptation function using postsynaptic spikes in the Pt/WO_3−x/W memristors.

a, b Synaptic EPSC and PPF functions triggered by a presynaptic spike [2 V, 10 ms] and paired spikes. c Dependence of the EPSC amplitude on the rate of presynaptic spike trains (20, 50, and 100 Hz). Eight pulses [2 V, 10 ms] were used to stimulate the device. d Response of the synaptic weight (conductance G_c) to a group of postsynaptic spike trains with a frequency sequence (50 Hz → 10 Hz → 5 Hz → 10 Hz). The pulse [−2V, 10 ms] on the bottom electrode as the postsynaptic spike. e Sliding threshold effect of the history-dependent synaptic adaptation function with different G₀. Herein, the experienced G₀ was activated to three levels starting from a fixed initial conductance of G_i = 0.1µS. For the case of G₀ = 0.5 µS and 1.0 µS, the stimulation was conducted using a pulse amplitude of −2V and pulse width of 10 ms with postsynaptic spike rates of 20 Hz and 50 Hz, respectively. The peak of temporary conductance potentiation (G_peak) was collected to calculate ΔG_c = G_peak − G₀, which represents a type of short-term plasticity. f Biological BCM curve. The vertical and horizontal axes are the weight modification φ(c) and postsynaptic firing rate c, respectively. According to the BCM function of φ^BCM, the depression/potentiation of φ(c) occurs as the firing rate is lower/higher than modification threshold θ_m. In particular, the parameter θ_m is adaptive to the experienced activity: the synapse which experienced a period of inactivity would follow the blue curve with smaller θ_m, whereas the synapse that experienced a period of enhanced activity would follow the red curve. Reproduced with permission³². Copyright 2012, Nature Pub. Group. The red shaded area indicates an EDE of |ΔG_c| in the depression region, which was usually absent in previous memristor-based BCM studies.