Part of the human brain, the basal forebrain structures are located in the

forebrain In the anatomy of the brain of vertebrates, the forebrain or prosencephalon is the rostral (forward-most) portion of the brain. The forebrain (prosencephalon), the midbrain (mesencephalon), and hindbrain (rhombencephalon) are the three prima ...

to the front of and below the

striatum The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (a cluster of neurons) in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives glutamate ...

. They include the ventral basal ganglia (including

nucleus accumbens The nucleus accumbens (NAc or NAcc; also known as the accumbens nucleus, or formerly as the ''nucleus accumbens septi'', Latin for "nucleus adjacent to the septum") is a region in the basal forebrain rostral to the preoptic area of the hypot ...

and ventral pallidum), nucleus basalis,

diagonal band of Broca The diagonal band of Broca is one of the basal forebrain structures that are derived from the ventral telencephalon during development. This structure forms the medial margin of the anterior perforated substance. This brain region was described ...

, substantia innominata, and the medial septal nucleus. These structures are important in the production of

acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Par ...

, which is then distributed widely throughout the brain. The basal forebrain is considered to be the major

cholinergic Cholinergic agents are compounds which mimic the action of acetylcholine and/or butyrylcholine. In general, the word "choline" describes the various quaternary ammonium salts containing the ''N'',''N'',''N''-trimethylethanolammonium cation. ...

output of the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...

(CNS) centred on the output of the nucleus basalis. The presence of non-cholinergic neurons projecting to the cortex have been found to act with the cholinergic neurons to dynamically modulate activity in the cortex.

Function

Acetylcholine is known to promote wakefulness in the basal forebrain. Stimulating the basal forebrain gives rise to acetylcholine release, which induces

wakefulness Wakefulness is a daily recurring brain state and state of consciousness in which an individual is conscious and engages in coherent cognitive and behavioral responses to the external world. Being awake is the opposite of being asleep, in which m ...

and

REM sleep Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream vi ...

, whereas inhibition of acetylcholine release in the basal forebrain by adenosine causes slow wave sleep. The nucleus basalis is the main neuromodulator of the basal forebrain and gives widespread

projections to the neocortex. The nucleus basalis is an essential part of the neuromodulatory system that controls behaviour by regulating

arousal Arousal is the physiological and psychological state of being awoken or of sense organs stimulated to a point of perception. It involves activation of the ascending reticular activating system (ARAS) in the brain, which mediates wakefulness, th ...

and

attention Attention is the behavioral and cognitive process of selectively concentrating on a discrete aspect of information, whether considered subjective or objective, while ignoring other perceivable information. William James (1890) wrote that "Att ...

. The nucleus basalis is also seen to be a critical node in the memory circuit. The importance of non-cholinergic neurons in the basal forebrain structures has been shown in working together with the cholinergic neurons in a dynamically modulatory way. This is seen to play a significant role in cognitive functions.

Adenosine Adenosine (symbol A) is an organic compound that occurs widely in nature in the form of diverse derivatives. The molecule consists of an adenine attached to a ribose via a β-N9-glycosidic bond. Adenosine is one of the four nucleoside buildin ...

acts on A1 receptors of

neurons in the basal forebrain. This results in hyperpolarization of cholinergic neurons, which inhibits the release of

Nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its ...

production in the basal forebrain is both necessary and sufficient to produce

sleep Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited Perception, sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefuln ...

Clinical significance

Acetylcholine affects the ability of brain cells to transmit information to one another, and also encourages neuronal plasticity, or learning. Thus, damage to the basal forebrain can reduce the amount of acetylcholine in the brain and impair learning. This may be one reason why basal forebrain damage can result in memory impairments such as

amnesia Amnesia is a deficit in memory caused by brain damage or disease,Gazzaniga, M., Ivry, R., & Mangun, G. (2009) Cognitive Neuroscience: The biology of the mind. New York: W.W. Norton & Company. but it can also be caused temporarily by the use ...

and confabulation. One common cause of basal forebrain damage is an

aneurysm An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus ...

of the anterior communicating artery. It is thought that damage to the nucleus basalis and its cortical projections are implicated in forms of

dementia Dementia is a disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively affe ...

, notably Alzheimer's dementia and Parkinson's disease dementia. There have been studies on the use of

deep brain stimulation Deep brain stimulation (DBS) is a neurosurgical procedure involving the placement of a medical device called a neurostimulator, which sends electrical impulses, through implanted electrodes, to specific targets in the brain (the brain nucle ...

to the nucleus basalis, in the treatment of dementia, and while giving some positive results trials are still being undertaken.

References

{{Authority control Rostral basal ganglia and associated structures