Interneuroner

Interneurons are neurons that connect other neurons within the same region of the central nervous system, rather than projecting to distant targets. They form local circuits that regulate the flow of information, contribute to processing within neural networks, and influence the timing and synchronization of neuronal activity.

In the brain, interneurons are highly diverse. Many are inhibitory, using GABA as their primary neurotransmitter, while some are excitatory. They are abundant in the cerebral cortex, hippocampus, and spinal cord, where they modulate the activity of principal neurons. Functional classes are often defined by molecular markers and connectivity, such as parvalbumin-positive, somatostatin-positive, and VIP-positive interneurons, each with characteristic targets and firing patterns. Interneurons can target the soma, dendrites, or axon initial segments of other neurons, enabling precise control of excitation and inhibition within circuits. They can act as local circuit neurons with short axons or participate in longer-range associations within a region.

Developmentally, most cortical interneurons originate in the ventral forebrain, particularly the medial and caudal ganglionic eminences, and migrate tangentially into the cortex. Their diversity arises from transcriptional programs and activity-dependent refinement that shape synaptic connections and functional roles in mature circuits.

Dysfunction of interneurons has been linked to several neurological and psychiatric disorders, including epilepsy, schizophrenia, autism spectrum disorders, and Rett syndrome. Studying interneurons helps explain how disruption of the balance between excitation and inhibition can impact cognition, behavior, and motor control.

Interneurons are a broad category found throughout the central nervous system, including the spinal cord, where they participate in reflex circuits and locomotor networks, emphasizing their role in shaping motor and sensory processing.