Fig. 3: The demonstration of Triplet-STDP based on controllable photoconductance.

Schematic of the pulse schemes for the post-pre-post (a) and pre-post-pre (b) triplet spiking signals, along with the corresponding current changes, respectively. Note that two sets of triplet spiking configurations of pre-post-pre and post-pre-post are defined as electric-light-electric (E-L-E) and light-electric-light (L-E-L) schemes, respectively. The timing window pair (Δt₁, Δt₂) denotes the spiking intervals within each triplet signal. For the L-E-L triplet, the spiking pair corresponds to post-pre (Δt₁ < 0) and pre-post (Δt₂ > 0), whereas for the E-L-E triplet, it corresponds to pre-post (Δt₁ > 0) and post-pre (Δt₂ < 0). c The evolution of weight variation of the Triplet-STDP for the L-E-L and E-L-E branches with symmetrical spike timing (|Δt₁| = |Δt₂| ). d Weight variation of the Triplet-STDP as functions of Δt₁ and Δt₂ with asymmetrical values. For the L-E-L branch, Δt₁ = −50 ms and Δt₂ varies from 30 to 100 ms; for the E-L-E branch, Δt₁ = 50 ms and Δt₂ varies from −30 to −100 ms. e The weight variation evolution of the Triplet-STDP for the L-E-L scheme as a function of Δt₂ (discrete symbols). The fitted solid curves follow the Triplet-STDP equation. f Weight variation mapping of the Triplet-STDP as functions of Δt₁ and Δt₂, where potentiation or depression with different synaptic weight variations is obtained under different spike sequences with distinct timing intervals. The inset shows the schematic of the L-E-L and E-L-E sequences. Here, the background color gradients indicate the value of Δw.