The nucleus basalis, also known as the nucleus basalis of Meynert or nucleus basalis magnocellularis, is a group of

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

s located mainly in the

substantia innominata The substantia innominata also innominate substance, or substantia innominata of Meynert (Latin for unnamed substance) is a series of layers in the human brain consisting partly of gray and partly of white matter, which lies below the anterior part ...

of the

basal forebrain Part of the human brain, the basal forebrain structures are located in the forebrain to the front of and below the striatum. They include the ventral basal ganglia (including nucleus accumbens and ventral pallidum), nucleus basalis, diagonal band ...

. Most neurons of the nucleus basalis are rich in the

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neuro ...

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 ...

, and they have widespread projections to the

neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, sp ...

and other brain structures.

Structure

The nucleus basalis in humans is a somewhat diffuse collection of large

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. F ...

neurons in the basal forebrain. The main body of the nucleus basalis lies inferior to the

anterior commissure The anterior commissure (also known as the precommissure) is a white matter tract (a bundle of axons) connecting the two temporal lobes of the cerebral hemispheres across the midline, and placed in front of the columns of the fornix. In most exist ...

and the

globus pallidus The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a subcortical structure of the brain. It consists of two adjacent segments, one external, known in rodents simply as the globus pallidus, and one internal, known in rod ...

, and lateral to the anterior

hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...

in an area known as the

. Rostrally, the nucleus basalis is continuous with the cholinergic neurons of the nucleus of the diagonal band of Broca. The nucleus basalis is thought to consist of several subdivisions based on the location of the cells and their projections to other brain regions. Occasional neurons belonging to the nucleus basalis can be found in nearby locations such as the internal laminae of the globus pallidus and the genu of the

internal capsule The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the g ...

Function

The widespread connections of the nucleus basalis with other parts of the brain indicate that it is likely to have an important modulatory influence on brain function. Studies of the firing patterns of nucleus basalis neurons in nonhuman primates indicate that the cells are associated with arousing stimuli, both positive (appetitive) and negative (aversive). There is also evidence that the nucleus basalis promotes sustained attention, and learning and recall in long term memory Cholinergic neurons of the nucleus basalis have been hypothesized to modulate the ratio of reality and virtual reality components of visual perception.Smythies, J. (2009) Philosophy, Perception and Neuroscience. Philosophy 38, 638–51. Experimental evidence has shown that normal visual perception has two components. The first (A) is a bottom-up component in which the input to the higher visual cortex (where conscious perception takes place) comes from the retina via the

lateral geniculate body In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral project ...

and V1. This carries information about what is actually outside. The second (B) is a top-down component in which the input to the higher visual cortex comes from other areas of the cortex. This carries information about what the brain computes is most probably outside. In normal vision, what is seen at the center of attention is carried by A, and material at the periphery of attention is carried mainly by B. When a new potentially important stimulus is received, the nucleus basalis is activated. The axons it sends to the visual cortex provide collaterals to pyramidal cells in layer IV (the input layer for retinal fibres) where they activate excitatory nicotinic receptors and thus potentiate retinal activation of V1. The cholinergic axons then proceed to layers I-II (the input layer for cortico-cortical fibers) where they activate inhibitory muscarinic receptors of pyramidal cells, and thus inhibit cortico-cortical conduction. In this way activation of nucleus basalis promotes (A) and inhibits (B), thus allowing full attention to be paid to the new stimulus. Goard and Dan, and Kuo et al. report similar findings. Gerrard Reopit, in 1984, confirmed the reported findings in his research. Merzenich and Kilgard, among others, have investigated the role of the nucleus basalis in sensory plasticity.

Clinical significance

Neurons of the nucleus basalis are particularly vulnerable in age-related

neurodegenerative diseases A neurodegenerative disease is caused by the progressive loss of structure or function of neurons, in the process known as neurodegeneration. Such neuronal damage may ultimately involve cell death. Neurodegenerative diseases include amyotrophic ...

such as

Alzheimer's disease Alzheimer's disease (AD) is a neurodegeneration, 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 short-term me ...

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms becom ...

, and several others. The resulting decrease in acetylcholine in the brain is thought to contribute to the decline in mental function of affected patients. For this reason, most currently available pharmacological treatments for

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 ...

focus on compensating for faltering function of the nucleus basalis through artificially increasing acetylcholine levels. Because many other systems also are compromised in neurodegenerative diseases, the benefits of selectively increasing

function are limited.

History

The nucleus basalis is named after

Theodor Meynert Theodor Hermann Meynert (15 June 1833 – 31 May 1892) was a German-Austrian psychiatrist, neuropathologist and anatomist born in Dresden. Meynert believed that disturbances in brain development could be a predisposition for psychiatric illness an ...

. Meynert originally called this group of cells the 'ganglion of the

ansa peduncularis Ansa (Latin for "handle") or ANSA may refer to: Organizations * Agenzia Nazionale Stampa Associata, Italian news agency ** Ansa Mediterranean or ANSAmed, section of the above * Applied Neuroscience Society of Australasia * Association of Norweg ...

' (ganglion der Hirnschenkelschlinge), leading Albert von Kölliker in 1896 to recognize Meynert's contribution with the

eponym An eponym is a person, a place, or a thing after whom or which someone or something is, or is believed to be, named. The adjectives which are derived from the word eponym include ''eponymous'' and ''eponymic''. Usage of the word The term ''epon ...

‘basal ganglion of Meynert’ (Meynert’sches Basalganglion). Later, in a pair of 1942 publications, Harold Brockhaus referred to the cells as the basal nucleus ). In these reports, he also emphasized the continuity of the nucleus basalis proper with the nucleus of the diagonal band of Broca, referring to the entire collection of large cells as the basal nucleus complex (Basalkernkomplex).

Additional images

File:Nucleus basalis of Meynert -l- very low mag.jpg, NBM in relation to the

and

putamen The putamen (; from Latin, meaning "nutshell") is a round structure located at the base of the forebrain (telencephalon). The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that compose the basal n ...

- very low magnification. File:Nucleus basalis of Meynert - very high mag.jpg, NBM - very high magnification. File:Cholinergic neurons of the nucleus basalis of Meynert.jpg, Micrograph of cholinergic neurons in the nucleus basalis of a rhesus monkey; Bar = 50

microns The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

(0.05 millimeters).

References

External links

{{DEFAULTSORT:Nucleus Basalis Of Meynert Alzheimer's disease Rostral basal ganglia and associated structures Acetylcholine