Mushroom bodies
Encyclopedia
The mushroom bodies or corpora pedunculata are a pair of structures in the brain
of insect
s and other arthropod
s.
s, i.e. as dense networks of neuron
al processes (dendrite
and axon terminals) and glia. They get their name from their roughly hemispherical calyx, a protuberance that is joining to the rest of the brain by a central nerve tract or peduncle. They were first identified in 1850 by the French biologist Félix Dujardin
.
Most of our current knowledge of the mushroom bodies comes from studies of a few species of insect, especially the cockroach
Periplaneta americana, the honey bee
Apis mellifera, the locust
and the fruit fly Drosophila melanogaster
. Studies of fruit fly mushroom bodies have been particularly important for understanding the genetic basis of their functioning, since the genetics of this species are known in exceptional detail.
In the insect brain, the peduncles of the mushroom bodies extend through the midbrain. They are mainly composed of the long, densely packed nerve fibres of the Kenyon cell
s, the intrinsic neurons of the mushroom bodies. These cells have been found in the mushroom bodies of all species that have been investigated, though their number varies; for example fruit flies have around 2,500 whereas cockroaches have about 200,000.
and memory
, particularly for smell. They are largest in the Hymenoptera
, which are known to have particularly elaborate olfactory control over behaviour. In larger insects, studies suggest that mushroom bodies have other learning and memory functions, like associative memory, sensory filtering, motor control, and place memory.
Comparisons between genes early in mushroom body development show a homology
with similar developing genes in the forebrain of mammals.
The mushroom bodies are currently the subject of intense research. They have been compared to the cerebral cortex
of mammal
s. Because they are small compared to the brain structures of vertebrate
s, and yet many arthropods are capable of quite complex learning, it is hoped that investigations of the mushroom bodies will allow a clear view of the neurophysiology
of animal cognition
. The most recent research is also beginning to reveal the genetic
control of processes within the mushroom bodies.
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s and other arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s.
Structure
Mushroom bodies are usually described as neuropilNeuropil
In neuroanatomy, a neuropil, which is sometimes referred to as a neuropile, is a region between neuronal cell bodies in the gray matter of the brain and blood-brain barrier . It consists of a dense tangle of axon terminals, dendrites and glial cell processes...
s, i.e. as dense networks of neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
al processes (dendrite
Dendrite
Dendrites are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project...
and axon terminals) and glia. They get their name from their roughly hemispherical calyx, a protuberance that is joining to the rest of the brain by a central nerve tract or peduncle. They were first identified in 1850 by the French biologist Félix Dujardin
Félix Dujardin
-External sources:* @ Encyclopædia Britannica Online...
.
Most of our current knowledge of the mushroom bodies comes from studies of a few species of insect, especially the cockroach
Cockroach
Cockroaches are insects of the order Blattaria or Blattodea, of which about 30 species out of 4,500 total are associated with human habitations...
Periplaneta americana, the honey bee
Honey bee
Honey bees are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis...
Apis mellifera, the locust
Locust
Locusts are the swarming phase of short-horned grasshoppers of the family Acrididae. These are species that can breed rapidly under suitable conditions and subsequently become gregarious and migratory...
and the fruit fly Drosophila melanogaster
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
. Studies of fruit fly mushroom bodies have been particularly important for understanding the genetic basis of their functioning, since the genetics of this species are known in exceptional detail.
In the insect brain, the peduncles of the mushroom bodies extend through the midbrain. They are mainly composed of the long, densely packed nerve fibres of the Kenyon cell
Kenyon cell
In arthropods' nervous system, Kenyon cells are mushroom body neurons derived from globuli cells. Some species possess hundreds of thousands of Kenyon cells. The cells are subdivided into subtypes; for example, those that have their cell bodies outside of the calyx cup are called clawed Kenyon...
s, the intrinsic neurons of the mushroom bodies. These cells have been found in the mushroom bodies of all species that have been investigated, though their number varies; for example fruit flies have around 2,500 whereas cockroaches have about 200,000.
Function
Mushroom bodies are known to be involved in learningLearning
Learning is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information. The ability to learn is possessed by humans, animals and some machines. Progress over time tends to follow learning curves.Human learning...
and memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
, particularly for smell. They are largest in the Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
, which are known to have particularly elaborate olfactory control over behaviour. In larger insects, studies suggest that mushroom bodies have other learning and memory functions, like associative memory, sensory filtering, motor control, and place memory.
Comparisons between genes early in mushroom body development show a homology
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
with similar developing genes in the forebrain of mammals.
The mushroom bodies are currently the subject of intense research. They have been compared to the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
of mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s. Because they are small compared to the brain structures of vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, and yet many arthropods are capable of quite complex learning, it is hoped that investigations of the mushroom bodies will allow a clear view of the neurophysiology
Neurophysiology
Neurophysiology is a part of physiology. Neurophysiology is the study of nervous system function...
of animal cognition
Animal cognition
Animal cognition is the title given to the study of the mental capacities of non-human animals. It has developed out of comparative psychology, but has also been strongly influenced by the approach of ethology, behavioral ecology, and evolutionary psychology...
. The most recent research is also beginning to reveal the genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
control of processes within the mushroom bodies.