A contribution to neuromorphic engineering: neuromodulation implemented through photochromic compounds maintained out of equilibrium by UV–visible radiation

Neuromodulation is the alteration of neuronal and synaptic properties in the context of neuronal circuits. It allows anatomicallydefined circuits to produce multiple outputs reconfiguring networks into different functional circuits. In this work, neuromodulationis mimicked using a solution of two direct photochromic compounds, a naphthopyran and a spirooxazine, whichare models of phasic excitable neurons, sensitive to UV radiation. When the system, constituted by the two photochromic compounds, receives a UV signal, it behaves as a recurrent network with mutual inhibitory actions. The network responds to different UV wavelengths by changing its photo-excitability, synaptic strength, wiring of the circuit, and dynamics. These results contribute to the development of neuromorphic engineering. They will promote the design of artificial neural networks with a larger number of nodes, communicating through optical signals. These networks will be the essential ingredients ofthe new-generation brain-like computing machines complementing current electronic computers.