Ocular dominance columns are stripes 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 in the

visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalam ...

of certain

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

(including

humans Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

) that respond preferentially to input from one eye or the other. The

columns A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member ...

span multiple cortical layers, and are laid out in a striped pattern across the surface of the striate cortex (V1). The stripes lie perpendicular to the orientation columns. Ocular dominance columns were important in early studies of cortical plasticity, as it was found that monocular deprivation causes the columns to degrade, with the non-deprived eye assuming control of more of the cortical cells. It is believed that ocular dominance columns must be important in

binocular vision Binocular vision is seeing with two eyes. The Field_of_view, field of view that can be surveyed with two eyes is greater than with one eye. To the extent that the visual fields of the two eyes overlap, #Depth, binocular depth can be perceived. Th ...

. Surprisingly, however, many

squirrel monkeys Squirrel monkeys are New World monkeys of the genus ''Saimiri''. ''Saimiri'' is the only genus in the subfamily Saimiriinae. The name of the genus is of Tupi origin (''sai-mirím'' or ''çai-mbirín'', with ''sai'' meaning 'monkey' and ''mirím' ...

either lack or partially lack ocular dominance columns, which would not be expected if they are useful. This has led some to question whether they serve a purpose, or are just a byproduct of development.

History

Discovery

Ocular dominance columns were discovered in the 1960s by Hubel and Wiesel as part of their

Nobel Prize The Nobel Prizes ( ; ; ) are awards administered by the Nobel Foundation and granted in accordance with the principle of "for the greatest benefit to humankind". The prizes were first awarded in 1901, marking the fifth anniversary of Alfred N ...

winning work on the structure of the visual cortex in

cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

s. Ocular dominance columns have since been found in many animals, such as

ferret The ferret (''Mustela furo'') is a small, domesticated species belonging to the family Mustelidae. The ferret is most likely a domesticated form of the wild European polecat (''Mustela putorius''), as evidenced by the ferret's ability to inter ...

macaque The macaques () constitute a genus (''Macaca'') of gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit ranges throughout Asia, North Africa, and Europe (in Gibraltar). Macaques are principally f ...

s, and

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s. Notably, they are also absent in many animals with

, such as

rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include '' Neotoma'' (pack rats), '' Bandicota'' (bandicoo ...

Structure

Ocular dominance

are stripe shaped regions of the

primary visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus ...

that lie perpendicular to the orientation columns, as can be seen in the accompanying figure. Different species have somewhat different morphologies and levels of organization. For example,

cats The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

, ferrets, and

macaques The macaques () constitute a genus (''Macaca'') of gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit ranges throughout Asia, North Africa, and Europe (in Gibraltar). Macaques are principally fru ...

all have fairly well defined columns, while

have quite variable columns. There is even variation in expression in individuals of the same

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

and in different parts of the cortex of the same individual. The columns are innervated by input from the

lateral geniculate nucleus 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, Anatomical ter ...

(LGN) into cortical layer 4 and have mostly reciprocal projections to many other parts of the visual cortex.

Relation to other features of V1

The ocular dominance

cover the primary (striate) visual cortex, with the exception of monocular regions of the cortical map corresponding to

peripheral vision Peripheral vision, or ''indirect vision'', is vision as it occurs outside the point of fixation, i.e. away from the center of gaze or, when viewed at large angles, in (or out of) the "corner of one's eye". The vast majority of the area in the ...

and the blind spot. If the columns corresponding to one eye were colored, a pattern similar to that shown in the accompanying figure would be visible when looking at the surface of the cortex. However, the same region of cortex could also be colored by the direction of edge that it responds to, resulting in the orientation columns, which are laid out in a characteristic pinwheel shape. Similarly, there are columns in the cortex that have high levels of the protein cytochrome oxidase. These are called cytochrome oxidase " blobs" because of their scattered blob-like appearance. All three types of

column A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member ...

are present in the

of humans and macaques, among other animals. In macaques, it was found that both blobs and pinwheel centers tend to lie in the center of ocular dominance columns, but no particular relation has been found between pinwheel centers and blobs. In humans, the

layout In general terms, a layout is a structured arrangement of items within certain limits, or a plan for such arrangement. Specifically, layout may refer to: * Page layout, the arrangement of visual elements on a page ** Comprehensive layout (comp), ...

of the columns is similar; however, humans have somewhat variable column expression with at least one subject having disordered columns similar to those commonly found in squirrel monkeys. Most early

models A model is an informative representation of an object, person, or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin , . Models can be divided int ...

of the columns supposed that there were

discrete Discrete may refer to: *Discrete particle or quantum in physics, for example in quantum theory * Discrete device, an electronic component with just one circuit element, either passive or active, other than an integrated circuit * Discrete group, ...

"modules" or " hypercolumns" tiling the cortex, consisting of a repeating unit containing a full set of orientation and ocular dominance columns. While such units can be constructed, the map of columns is so distorted that there is no repeating structure and no clear boundaries between modules. Additionally, practically every combination of having or not having orientation, dominance, and cytochrome oxidase columns has been observed in one

or another. Further confusing the issue,

don't always express columns, and even when they do the cytochrome oxidase blobs are not in

register Register or registration may refer to: Arts, entertainment, and media Music * Register (music), the relative "height" or range of a note, melody, part, instrument, etc. * ''Register'', a 2017 album by Travis Miller * Registration (organ), ...

with the ocular dominance columns.

Development

Formation

There is no consensus yet as to how ocular dominance

are initially developed. One possibility is that they develop through

Hebbian learning Hebbian theory is a neuropsychological theory claiming that an increase in synaptic efficacy arises from a presynaptic cell's repeated and persistent stimulation of a postsynaptic cell. It is an attempt to explain synaptic plasticity, the adaptat ...

triggered by spontaneous activity coming from retinal waves in the

eyes An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

of the developing

fetus A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic development, embryonic stage, the fetal stage of development takes place. Pren ...

, or from the LGN. Another possibility is that axonal guidance cues may guide the formation, or a combination of mechanisms may be at work. It is known that ocular dominance columns develop before birth, which indicates that if an activity dependent mechanism is involved it must work based on intrinsic activity rather than being sensory experience dependent. It is known that spontaneous

waves United States Naval Reserve (Women's Reserve), better known as the WAVES (for Women Accepted for Volunteer Emergency Service), was the women's branch of the United States Naval Reserve during World War II. It was established on July 21, 1942, ...

of activity in the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

occur before birth and that these waves are crucial for eye specific segregation of inputs to the LGN by correlating the activity of nearby neurons. Similarly, the

correlated In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistic ...

activation for the retinal waves may direct development of the ocular dominance columns, which receive input from the LGN. Similar spontaneous activity in the cortex may also play a role. In any case, it has been shown that disrupting the retinal waves at least alters the pattern of ocular dominance columns.

Plasticity

Sensitive periods

Although the ocular dominance

are formed before birth, there is a period after birth—formerly called a "

critical period In developmental psychology and developmental biology, a critical period is a maturational stage in the lifespan of an organism during which the nervous system is especially sensitive to certain environmental stimuli. If, for some reason, the org ...

" and now called a " sensitive period"—when the ocular dominance columns may be modified by activity dependent plasticity. This plasticity is so strong that if the signals from both eyes are blocked the ocular dominance columns will completely desegregate. Similarly, if one eye is closed (" monocular deprivation"), removed(" enucleation"), or silenced during the sensitive period, the size of the columns corresponding to the removed eye shrink dramatically.

Models

Many models have been proposed to explain the development and plasticity of the ocular dominance columns. In general these models can be split into two categories, those that posit formation via

chemotaxis Chemotaxis (from ''chemical substance, chemo-'' + ''taxis'') is the movement of an organism or entity in response to a chemical stimulus. Somatic cells, bacteria, and other single-cell organism, single-cell or multicellular organisms direct thei ...

and those that posit a

Hebbian Hebbian theory is a neuropsychological theory claiming that an increase in synaptic efficacy arises from a presynaptic cell's repeated and persistent stimulation of a postsynaptic cell. It is an attempt to explain synaptic plasticity, the adaptat ...

activity dependent mechanism. Generally, chemotaxis models assume activity independent formation via the action of axon guidance molecules, with the structures only later being refined by activity, but there are now known to be activity dependent and activity modifying guidance molecules.

Modified Hebbian learning

One major model of the formation of the stripes seen in ocular dominance

is that they form by

competition Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indi ...

between axon terminals. The ocular dominance columns look like Turing patterns, which can be formed by modified Hebbian mechanisms. In a normal Hebbian model, if two neurons are connected to a neuron and fire together, they increase the strength of the synapses, "moving" the

axon terminals An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

closer together. The model must be modified to incorporate incoming activity that is locally excitatory and long range inhibitory, because if this is not done then the column width will only be dependent on the width of the axonal arbor, and also segregation will often fail in the presence of inter eye correlation. This basic model has since been extended to be more physiologically plausible with the addition of long term potentiation and depression, synaptic normalization, neurotrophin release, reuptake, and spike-timing-dependent plasticity.

Chemotaxis

Chemotactic models posit the existence of axon guidance molecules that direct the initial formation of the ocular dominance columns. These molecules would guide the axons as they develop based on markers specific to the

axons An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see spelling differences) is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action pot ...

from each eye. All chemotactic models must take into account the activity dependent effects demonstrated in later development, but they have been called for because several pieces of evidence make entirely activity dependent formation unlikely. First, it has been shown that the ocular dominance columns in squirrel monkeys have mirror symmetry across the cortex. This is very unlikely to occur by activity dependent means because it implies a correlation between the nasalToward or near the nose

of one eye and the temporalToward or near the

temple A temple (from the Latin ) is a place of worship, a building used for spiritual rituals and activities such as prayer and sacrifice. By convention, the specially built places of worship of some religions are commonly called "temples" in Engli ...

retina of the other, which has not been observed. Furthermore, work in achiasmaticHaving no optic chiasm Belgian sheepdogs has shown that columns can form between the projections from the temporal and nasal retina of the same eye, clearly suggesting a nasal-temporal labeling, rather than

contralateral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

vs. ipsilateral, which would be much easier to explain with activity dependent mechanisms. Despite this, a molecular label that directs the formation of the ocular dominance columns has never been found.

Function

It has long been believed that ocular dominance columns play some role in

. Another candidate function for ocular dominance columns (and for columns in general) is the minimization of connection lengths and processing time, which could be evolutionarily important. It has even been suggested that the ocular dominance columns serve no function.