In the

human brain The human brain is the central organ (anatomy), organ of the nervous system, and with the spinal cord, comprises the central nervous system. It consists of the cerebrum, the brainstem and the cerebellum. The brain controls most of the activi ...

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

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

s located mainly in the substantia innominata of the basal forebrain. 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 Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

acetylcholine Acetylcholine (ACh) is an organic compound 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 ...

, 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, ...

and other brain structures.

Structure

The nucleus basalis in humans is a somewhat diffuse collection of large cholinergic 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 nerve tract, 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 o ...

and the

globus pallidus The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a major component of the Cerebral cortex, subcortical basal ganglia in the brain. It consists of two adjacent segments, one external (or lateral), known in rodents simpl ...

, and lateral to the anterior

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

in an area known as the substantia innominata. 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 paired white matter structure, as a two-way nerve tract, tract, carrying afferent nerve fiber, ascending and efferent nerve fiber, descending axon, fibers, to and from the cerebral cortex. The internal capsule is situate ...

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 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 neurons, in the process known as neurodegeneration. Neuronal damage may also ultimately result in their death. Neurodegenerative diseases include amyotrophic lateral sclerosis, mul ...

such as

Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease and the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems wit ...

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor system, motor and non-motor systems. Symptoms typically develop gradually and non-motor issues become ...

, 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 syndrome associated with many neurodegenerative diseases, characterized by a general decline in cognitive abilities that affects a person's ability to perform activities of daily living, everyday activities. This typically invo ...

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 cholinergic function are limited.

History

The nucleus basalis is named after Theodor Meynert. Meynert originally called this group of cells the 'ganglion of the ansa peduncularis' (ganglion der Hirnschenkelschlinge), leading Albert von Kölliker in 1896 to recognize Meynert's contribution with the

eponym An eponym is a noun after which or for which someone or something is, or is believed to be, named. Adjectives derived from the word ''eponym'' include ''eponymous'' and ''eponymic''. Eponyms are commonly used for time periods, places, innovati ...

‘basal ganglion of Meynert’ (Meynert’sches Basalganglion). Later, in a pair of 1942 publications, Harald 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 subcortical nucleus (neuroanatomy), nucleus with a rounded structure, in the basal ganglia nuclear group. It is located at the base of the forebrain and above the midbrain. The putamen and c ...

- 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 (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

(0.05 millimeters).

References

External links

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