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 primary ...

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 The ventral pallidum (VP) is a structure within the basal ganglia of the brain. It is an output nucleus whose fibres project to thalamic nuclei, such as the ventral anterior nucleus, the ventral lateral nucleus, and the medial dorsal nucleus. The ...

nucleus basalis The nucleus basalis, also known as the nucleus basalis of Meynert or nucleus basalis magnocellularis, is a group of neurons located mainly in the substantia innominata of the basal forebrain. Most neurons of the nucleus basalis are rich in the ...

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 b ...

, substantia innominata, and the

medial septal nucleus The medial septal nucleus (MS) is one of the septal nuclei. Neurons in this nucleus give rise to the bulk of efferents from the septal nuclei. A major projection from the medial septal nucleus terminates in the hippocampal formation. It plays a ro ...

. 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. Part ...

, 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 cati ...

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 Human brain, brain state and state of consciousness in which an individual is conscious and engages in coherent cognition, cognitive and behavioral responses to the external world. Being awake is the opposite of ...

and REM sleep, whereas inhibition of acetylcholine release in the basal forebrain by adenosine causes

slow wave sleep Slow-wave sleep (SWS), often referred to as deep sleep, consists of stage three of non-rapid eye movement sleep. It usually lasts between 70 and 90 minutes and takes place during the first hours of the night. Initially, SWS consisted of both S ...

. The nucleus basalis is the main

neuromodulator Neuromodulation is the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. Neuromodulators typically bind to metabotropic, G-protein coupled receptors (GPCRs) to initiate a second ...

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 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 "Atte ...

. 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 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 che ...

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 sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...

Clinical significance

Acetylcholine affects the ability of brain cells to transmit information to one another, and also encourages

neuronal plasticity Neuroplasticity, also known as neural plasticity, or brain plasticity, is the ability of neural networks in the brain to change through growth and reorganization. It is when the brain is rewired to function in some way that differs from how it p ...

, 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 and

confabulation In psychology, confabulation is a memory error defined as the production of fabricated, distorted, or misinterpreted memories about oneself or the world. It is generally associated with certain types of brain damage (especially aneurysm in the an ...

. 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 (s ...

of the

anterior communicating artery In human anatomy, the anterior communicating artery is a blood vessel of the brain that connects the left and right anterior cerebral arteries. Anatomy The anterior communicating artery connects the two anterior cerebral arteries across the co ...

. 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 Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As t ...

and

Parkinson's disease dementia Parkinson's disease dementia (PDD) is dementia that is associated with Parkinson's disease (PD). Together with dementia with Lewy bodies (DLB), it is one of the Lewy body dementias characterized by abnormal deposits of Lewy bodies in the brain. ...

. 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 nucleus ...

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