The Cholinergic Multicompartmental Basal Forebrain Microcircuit

The basal forebrain (BF) is composed of an affiliation of structures, including the medial septum, ventral pallidum (VP), vertical diagonal band (VDB) and horizontal diagonal band (HDB) nuclei, substantia innominata/extended amygdala (SI/EA), and peripallidal regions. Together, they constitute one of the most extensive multicompartmental microcircuits in the brain. A prominent feature of the mammalian BF is the presence of aggregated and nonaggregated, large, cholinergic neurons, which project to the cerebral cortex, the hippocampal complex, and the amygdala. This highly complex system has been implicated in cortical activation, attention, motivation, and memory, as well as neuropsychiatric disorders such as Alzheimer’s disease, Parkinson’s disease, schizophrenia, and drug abuse. Advances in modern tracing, genetic, and refined pharmacological techniques have dramatically increased the understanding of how the BF cholinergic system can support both phasic acetylcholine (ACh) release in attention, memory, and sensory processing and tonic ACh release over broad cortical areas as part of a general arousal effect.