Fig. 4: Shunting inhibition and single-neuron implementation of XOR.

A A volatile Pt/GeSe₃/Ag device under a mixed mode operation. In the absence of light (yellow trace), electrical pulses applied to the device induce a switching event, while the presence of light inhibits device switching. B Sketch of a biological neuron. Shown is a single dendrite of the neuron possessing an excitatory synapse and, proximally to the neuron’s soma, a synapse capable of shunting inhibition. Each excitatory input generates an EPSP (red trace) that propagates, but its effect is gated by inhibitory inputs. An input to the shunting inhibitory synapse attenuates the EPSP (blue trace), but in the absence of excitation, it has no effect (not shown). A volatile type memristive device emulates this dendrite, with the excitatory and shunting inhibitory inputs applied by electrical and optical stimulation respectively. C A neuron (Z) comprising two distinct dendrites (D1 and D2) that receive inputs from neurons X and Y. Each dendrite has an excitatory and a shunting input synapse and functionally emulates the biological counterpart shown in B. D Results of Z’s output for different input pairs. Errorbars represent the mean of multiple measurements. Owing to the memristive dendrites, neuron Z realizes an XOR gate, a function that is impossible for a single layer of point neurons. The green plane defines the activation threshold of Z.