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A command neuron is a single
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. ...
(or small set of neurons) whose
stimulation Stimulation is the encouragement of development or the cause of activity generally. For example, "The press provides stimulation of political discourse." An interesting or fun activity can be described as "stimulating", regardless of its physic ...
results in the evocation of an
endogenous Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell. In contrast, exogenous substances and processes are those that originate from outside of an organism. For example, es ...
, specific, naturally occurring behavior pattern. Command neurons act as
neural In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...
decision making
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
; push buttons that can trigger a complete, coordinated
behavioral Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...
act and are often the sole determinant of whether an action is performed or not. Command neurons receive a convergence of integrative and sensory input and output to a multifarious group of pattern generating efferent cells. Stimulation of the command neuron triggers a lower level central pattern generator whose motorneurons and
interneuron Interneurons (also called internuncial neurons, relay neurons, association neurons, connector neurons, intermediate neurons or local circuit neurons) are neurons that connect two brain regions, i.e. not direct motor neurons or sensory neurons. In ...
s produce a particular
fixed action pattern A fixed action pattern is an ethological term describing an instinctive behavioral sequence that is highly stereotyped and species-characteristic. Fixed action patterns are said to be produced by the innate releasing mechanism, a "hard-wired" neural ...
.


History

The term command neuron first appeared in a 1964 paper titled "Interneurons Commanding Swimmeret Movements in the Crayfish", by CAG Wiersma and K Ikeda in volume 12 of ''Comparative Biochemistry and Physiology'' vol 12 on pp 509–525 Wiersma and Ikeda used the term to describe how a single action potential in any of the four giant fibers that run along the dorsal margin of the
crayfish Crayfish are freshwater crustaceans belonging to the clade Astacidea, which also contains lobsters. In some locations, they are also known as crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, mu ...
nerve cord caused the crayfish to execute a tail-flip
escape response Escape response, escape reaction, or escape behavior is a mechanism by which animals avoid potential predation. It consists of a rapid sequence of movements, or lack of movement, that position the animal in such a way that allows it to hide, freeze ...
. This concept came to epitomize the general
neurobiological Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, developme ...
principle that complex information can be encoded on the level of individual neurons. Soon, researchers were finding command neurons in multiple
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
and
vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
, including
crickets Crickets are orthopteran insects which are related to bush crickets, and, more distantly, to grasshoppers. In older literature, such as Imms,Imms AD, rev. Richards OW & Davies RG (1970) ''A General Textbook of Entomology'' 9th Ed. Methuen 8 ...
,
cockroaches Cockroaches (or roaches) are a paraphyletic group of insects belonging to Blattodea, containing all members of the group except termites. About 30 cockroach species out of 4,600 are associated with human habitats. Some species are well-known a ...
,
lobsters Lobsters are a family (biology), family (Nephropidae, Synonym (taxonomy), synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs ...
, and certain
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
.


Criticism

In 1978, Kupfermann and Weiss' "The Command Neuron Concept" proposed a more rigorous definition of the command neuron than had previously been used. They suggested that for any neuron to qualify as a command neuron, its activity had to be both necessary and sufficient for the initiation of the behavior it was purported to command. The article initiated a torrent of tumultuous debate about which neurons, if any, could fit the new, more rigorous definition proposed by Kupfermann and Weiss.


Modern view

Many believe that the command neuron concept needs to be reworked in light of the subtleties uncovered by Kupfermann and Weiss' careful methodology. Even the
Mauthner cell The Mauthner cells are a pair of big and easily identifiable neurons (one for each half of the body) located in the rhombomere 4 of the hindbrain in fish and amphibians that are responsible for a very fast escape reflex (in the majority of animals ...
, an archetypal command cell, has been criticized as being neither necessary nor sufficient for the initiation of the
C-start The Mauthner cells are a pair of big and easily identifiable neurons (one for each half of the body) located in the rhombomere 4 of the hindbrain in fish and amphibians that are responsible for a very fast escape reflex (in the majority of animals � ...
response it supposedly governs. Command decisions are increasingly seen as being governed by networks of interacting and redundant cells, not simply by single neurons. Critics believe that the less restrictive category of "command-like" neurons would repair the flaws in the overly strict Kupfermann and Weiss definition while more accurately classifying the role of single neurons in command decisions. Despite Kupfermann and Weiss' scathing critique of the loose fashion with which the command neuron concept was being used in the late 1970s and the resultant abandonment of the concept by some, the command neuron concept is still extant in the most current neurobiological literature. Some accept the revisionist "command-like" neuron concept—believing that no neurons exist which can satisfy the strictures outlined in "The Command Neuron Concept". Others cling to the use of the original command neuron concept as useful, rejecting the Kupfermann and Weiss strictures, and using less stringent definitions of the term (most seem to believe that there is a spectrum of pre-motor command organization: from parallel distributed networks on the one end, to command neurons on the other).


See also

*
Neuroethology Neuroethology is the evolutionary and comparative approach to the study of animal behavior and its underlying mechanistic control by the nervous system. It is an interdisciplinary science that combines both neuroscience (study of the nervous syste ...


References


External links


Mauthner NeuronKupfermann and Weiss commentary on their seminal articleAnother definition of the command neuron
{{Neuroethology Neurons