Douglas Harper's Etymology Dictionary
1939, from internuncial + neuron.
Wiktionary
a. Between neurons n. (context anatomy English) A multipolar neuron that connects afferent and efferent neurons
Wikipedia
An interneuron (also called relay neuron, association neuron, connector neuron, intermediate neuron or local circuit neuron) is one of the three classifications of neurons found in the human body. Interneurons create neural circuits, enabling communication between sensory or motor neurons and the central nervous system (CNS). They have been found to function in reflexes, neuronal oscillations, and neurogenesis in the adult mammalian brain. Interneurons can be further broken down into two groups: local interneurons, and relay interneurons. Local interneurons have short axons and form circuits with nearby neurons to analyze small pieces of information. Relay interneurons have long axons and connect circuits of neurons in one region of the brain with those in other regions. The interaction between interneurons allow the brain to perform complex functions such as learning, and decision-making.
Usage examples of "interneuron".
Aplysia motor neurons following sensory stimulation shows that they are responding both directly, monosynaptically, and polysynaptically, by way of interneurons.
The hidden layers of PDF models are intended to serve almost as such interneurons, and massively increase the power of the networks to learn, to generalize, to predict.