Fig. 1: Dual-excitatory PdSe₂ artificial synapse.

Schematic of biological synapse that can release two types of excitatory neurotransmitters, glutamate (red triangle), and dopamine (yellow circle), from a single presynaptic membrane; these neurotransmitters can interact with receptors on the postsynaptic membrane either independently or synergistically (top). Schematic of artificial synaptic device based on layered PdSe₂ (bottom). When the device received negative presynaptic spikes, the hole (red sphere) accumulate in the conduction channel and the increasing hole currents simulate the postsynaptic glutamate currents (bottom left); when device received positive presynaptic spikes after negative spikes, the electrons (yellow sphere) began to neutralize holes, and the decreasing hole currents simulate the decreasing postsynaptic glutamate currents induced by inhibitory effect between glutamate and dopamine interaction (bottom middle); when the device continued to receive positive presynaptic spikes, the electrons accumulated in the conduction channel and the increasing electron currents simulated the postsynaptic dopamine currents (bottom right).