Cortical column
Encyclopedia
A cortical column, also called hypercolumn or sometimes cortical module, is a group of neurons in the brain
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,...

 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...

 which can be successively penetrated by a probe inserted perpendicularly to the cortical surface, and which have nearly identical receptive field
Receptive field
The receptive field of a sensory neuron is a region of space in which the presence of a stimulus will alter the firing of that neuron. Receptive fields have been identified for neurons of the auditory system, the somatosensory system, and the visual system....

s. Neurons within a minicolumn
Cortical minicolumn
A cortical minicolumn is a vertical column through the cortical layers of the brain, comprising perhaps 80–120 neurons, except in the primate primary visual cortex , where there are typically more than twice the number. There are about 2×108 minicolumns in humans...

 encode similar features, whereas a hypercolumn "denotes a unit containing a full set of values for any given set of receptive field parameters". A cortical module is defined as either synonymous with a hypercolumn (Mountcastle) or as a tissue block of multiple overlapping hypercolumns (Hubel&Wiesel).

Human cerebral cortex

The human 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...

 is composed of 6 somewhat distinct layers; each layer identified by the nerve cell type and the destination of these nerve cell's axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

s (within the brain). The human cortex is a roughly 2.4 mm thick sheet of neuronal cell bodies that forms the external surface of the telencephalon
Telencephalon
The cerebrum or telencephalon, together with the diencephalon, constitutes the forebrain. The cerebrum is the most anterior region of the vertebrate central nervous system. Telencephalon refers to the embryonic structure, from which the mature cerebrum develops...

. The dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...

 cortical column is composed of 5 layers, the reptilian
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

 cortex is composed of three.

Columnar functional organization

The columnar functional organization, as originally framed by Vernon Mountcastle
Vernon Mountcastle
Vernon Benjamin Mountcastle is Professor Emeritus of Neuroscience at Johns Hopkins University.He discovered and characterized the columnar organization of the cerebral cortex in the 1950s...

, suggests that neurons that are horizontally more than 0.5 mm (500 µm) from each other do not have overlapping sensory receptive fields, and other experiments give similar results: 200–800 µm (Buxhoeveden 2002, Hubel 1977, Leise 1990, etc.). Various estimates suggest there are 50 to 100 cortical minicolumn
Cortical minicolumn
A cortical minicolumn is a vertical column through the cortical layers of the brain, comprising perhaps 80–120 neurons, except in the primate primary visual cortex , where there are typically more than twice the number. There are about 2×108 minicolumns in humans...

s in a hypercolumn, each comprising around 80 neurons.

An important distinction is that the columnar organization is functional by definition, and reflects the local connectivity of the cerebral cortex. Connections "up" and "down" within the thickness of the cortex are much denser than connections that spread from side to side.

Hubel and Wiesel studies

David Hubel
David H. Hubel
David Hunter Hubel is the John Franklin Enders Professor of Neurobiology, Emeritus, at Harvard Medical School. He was co-recipient with Torsten Wiesel of the 1981 Nobel Prize in Physiology or Medicine, for their discoveries concerning information processing in the visual system; the prize was...

 and Torsten Wiesel
Torsten Wiesel
Torsten Nils Wiesel was a Swedish co-recipient with David H. Hubel of the 1981 Nobel Prize in Physiology or Medicine, for their discoveries concerning information processing in the visual system; the prize was shared with Roger W...

 followed up on Mountcastle's discoveries in the somatic sensory cortex with their own studies in vision. A part of the discoveries that resulted in them winning the 1981 Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...

 was that there were cortical columns in vision as well, and that the neighboring columns were also related in function in terms of the orientation of lines that evoked the maximal discharge. Hubel and Wiesel followed up on their own studies with work demonstrating the impact of environmental changes on cortical organization, and the sum total of these works resulted in their Nobel Prize.

Size of cortex

From the size of the cortex and the typical size of a column, it can be estimated that there are about two million function columns in humans. There may be more if the columns can overlap, as suggested by Tsunoda et al..

External links

  • Mission to build a simulated brain begins "the initial phase of Blue Brain will model the electrical structure of neocortical columns - neural circuits that are repeated throughout the brain. These are the network units of the brain, says Markram. Measuring just 0.5 millimetres by 2 mm, these units contain between 10 and 70,000 neurons, depending upon the species. Once this is complete, the behaviour of columns can be mapped and modelled"
  • The Blue Brain Project aims to simulate a cortical column
  • On Intelligence
    On Intelligence
    On Intelligence: How a New Understanding of the Brain will Lead to the Creation of Truly Intelligent Machines is a book by Palm Pilot-inventor Jeff Hawkins with New York Times science writer Sandra Blakeslee. The book explains Hawkins' memory-prediction framework theory of the brain and describes...

     -- a popsci book about column function by Jeff Hawkins
    Jeff Hawkins
    Jeffrey Hawkins is the founder of Palm Computing and Handspring...

  • Confusing cortical columns by Pasko Rakic in the Proceedings of the National Academy of Sciences of the United States of America summarizes what is known and corrects some misconceptions.
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