Interneuron

An interneuron is a neuron that carries information between other neurons within a particular region of the central nervous system, rather than projecting to distant targets. Interneurons thus form local circuits and are often the most numerous neuron type in the brain. They contrast with primary sensory neurons, which convey information from the periphery, and motor neurons, which project to muscles.

Most CNS interneurons are inhibitory or excitatory connectors within local networks. Many are inhibitory and use GABA as a neurotransmitter, though excitatory interneurons that use glutamate also exist. They regulate the activity of principal neurons, coordinate timing and gain, and contribute to pattern generation. They participate in reflexes, sensory integration, and various aspects of cognitive processing.

Anatomical and molecular diversity is a hallmark of interneurons. In the cortex, interneurons include subtypes such as parvalbumin-positive, somatostatin-positive, and VIP-positive cells, each contributing differently to network dynamics. They typically have short axons and dense local connectivity, and their morphology and firing patterns help classify them into functional types such as fast-spiking or regular-spiking.

Clinical significance: Dysfunction of interneuron networks is linked to several neurological and psychiatric disorders, including epilepsy, schizophrenia, and autism spectrum disorders. Interneurons therefore play a central role in shaping neural circuits and brain function.