Orientation columns are organized regions of

neuron A neuron, neurone, or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous ...

s that are excited by visual line stimuli of varying angles. These columns are located in 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 and ...

(V1) and span multiple cortical layers. The geometry of the orientation columns are arranged in slabs that are perpendicular to the surface of the primary visual cortex.Hubel, D. H., & Wiesel, T. N. (1974). SEQUENCE REGULARITY AND GEOMETRY OF ORIENTATION COLUMNS IN MONKEY STRIATE CORTEX. rticle Journal of Comparative Neurology, 158(3), 267-294.Hubel, D. H., & Wiesel, T. N. (1968). RECEPTIVE FIELDS AND FUNCTIONAL ARCHITECTURE OF MONKEY STRIATE CORTEX. Journal of Physiology-London, 195(1), 215-&.

History

In 1958, David Hubel and

Torsten Wiesel Torsten Nils Wiesel (born 3 June 1924) is a Swedish neurophysiologist. With David H. Hubel, he received the 1981 Nobel Prize in Physiology or Medicine, for their discoveries concerning information processing in the visual system; the prize was ...

discovered cells in the visual cortex that had orientation selectivity. This was found through an experiment by giving a cat specific visual stimuli and measuring the corresponding excitation of the neurons in striate cortex (V1). The experimental set up was of a slide projector, a cat, electrodes, and an electrode monitor. They discovered this orientation selectivity when changing slides on the projector. The act of changing the slides produced a faint shadow line across the projector, and excited the neuron they were measuring. At the time of this experiment it was not conclusive that these orientation selective cells were in a "columnar" structure but the possibility of this structure was considered by research conducted by Vernon Mountcastle in 1956 about the topographic properties of the

somatosensory system In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch ( haptic perception), as well as temperature ( thermoception), body position ( proprioception), and pain. I ...

. Hubel, D. H., & Wiesel, T. N. (1959). Receptive Fields of Single Neurones in the Cat's Striate Cortex. rticle Journal of Physiology, 148, 574-591. Hubel, D. H., & Wiesel, T. N. (2005). Brain and Visual Perception. New York: Oxford Press. Mountcastle, V. B. (1956). Modality and Topographic Properties of Single Neurons of Cat's Somatic Sensory Cortex. rticle Journal of Neurophysiology, 20(4), 408-435. In 1974 Hubel and Wiesel wrote a paper about the geometry of orientation columns. They recorded 1410 cells in 45 penetrations into the striate cortex. Through this 1-dimensional technique they conceptualized that the orientation columns are not columns but slabs. In 1985, Gary Blasdel discovered a technique to visualize these orientation columns in 2D. His technique used photodiodes to detect optical changes in the visual cortex with the metabolic marker,

2-deoxyglucose 2-Deoxy--glucose is a glucose molecule which has the 2- hydroxyl group replaced by hydrogen, so that it cannot undergo further glycolysis. As such; it acts to competitively inhibit the production of glucose-6-phosphate from glucose at the phos ...

, which labels active neurons. This confirmed Hubel and Wiesel's studies and also brought to light the swirls and pinwheel formations in the striate cortex. Blasdel G. G., & Salama G. (1986). Voltage-sensitive dyes reveal a modular organization in monkey striate cortex. rticle Nature, 321, 579-585. Hubel and Wiesel received the

Nobel Prize in Physiology and Medicine The Nobel Prize in Physiology or Medicine ( sv, Nobelpriset i fysiologi eller medicin) is awarded yearly by the Nobel Assembly at the Karolinska Institute for outstanding discoveries in physiology or medicine. The Nobel Prize is not a single ...

in 1981 for their contributions to our knowledge of the development of the visual system.

Physiology

Orientation columns are located in the

also known as the striate cortex. These orientation columns are not cylindrical in shape as the word column implies but are flat slabs that are parallel to each other. The slabs are perpendicular to the surface of the visual cortex and are lined up similar to slices of bread. These neurons are highly discriminatory for visual orientations and their motion. Hubel, D. H., & Wiesel, T. N. (1977). Ferrier Lecture: Function architecture of macaque monkey visual cortex. ypescript Proc. R. Soc. Lond., 198, 1-59. Most of the cells in orientation columns are complex cells.

Complex cells Complex cells can be found in the primary visual cortex (V1), the secondary visual cortex (V2), and Brodmann area 19 ( V3). Like a simple cell, a complex cell will respond primarily to oriented edges and gratings, however it has a degree of spa ...

will respond to a properly orientated line in any location of the

receptive field The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms. Complexity of the receptive field ranges from the unidimensional chemical structure of odo ...

, whereas simple cells have a narrower receptive field where a properly oriented line will excite it.

Simple cells A simple cell in the primary visual cortex is a cell that responds primarily to oriented edges and gratings (bars of particular orientations). These cells were discovered by Torsten Wiesel and David Hubel in the late 1950s. Such cells are tuned ...

have distinct subdivisions of excitatory and inhibitory regions. It is proposed that complex cells receive input from many simple cells, which explains why the complex cells have a slightly wider receptive field. Hubel, D. H., & Wiesel, T. N. (1962). Receptive fields, binocular interaction and functional architecture in the cat's visual cortex. rticle Journal of Physiology, 160, 106-154. Hubel, D. H. (1995). Eye, Brain and Vision. Scientific American Library. There are possible biological advantages to the highly ordered structures of orientation columns. The first possible advantage is that orientation selectivity may be intensified with

lateral inhibition In neurobiology, lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral directio ...

from neighboring cells of a slightly different preferred orientation. This would provide an efficient system for wiring between the striate cortex and 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, ventral proj ...

(LGN).Blakemore, C., & Tobin, E. A. (1972).

Lateral inhibition In neurobiology, lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral directio ...

between orientation detectors in the cat's visual cortex. rticle Exp. Brain Res., 15, 439-440. The second possible advantage is the ordered structure aids in development, by guaranteeing all orientations are represented throughout the visual field with minimal redundancy and no deficiencies. The third possible advantage is that if columns with similar orientation selectivity are close together, fewer afferents from the LGN are needed. This allows for efficient wiring. So by removing a few LGN inputs and adding a few, the orientation selectivity can be changed marginally.

Ocular dominance columns Ocular dominance columns are stripes of neurons in the visual cortex of certain mammals (including humans) that respond preferentially to input from one eye or the other. The columns span multiple cortical layers, and are laid out in a striped pa ...

are also found in the striate cortex. These columns were found to prefer crossing iso-orientation lines perpendicularly. During microelectrode experiments, it is normal to see penetrations where eye dominance changes between the

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

eye and

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

eye but this does not interrupt the orientation sequence.

Preferred orientation

Recently, studies involving human models were conducted with high-field

fMRI Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...

. These studies demonstrated the existence of orientation preference in humans and showed similarities to the studies conducted with monkey models. It was found in these models that there was an over-representation of the 90° orientation preference. This corresponds to a bias towards processing vertical visual stimuli with horizontal movement. This bears resemblance to the

oblique effect Oblique effect is the name given to the relative deficiency in perceptual performance for oblique contours as compared to the performance for horizontal or vertical contours. Background The earliest known observation of this effect came about in 18 ...

where there is a deficiency in perception to oblique contours (45° and 90°). Yacoub, E., & Harel, N., & Ugurbil, K. (2008). High-Field fMRI unveils orientation columns in humans. rticle Proc Natl Acad Sci, 105, 10607-10612.

Pinwheels

Using 2D optical techniques, pinwheel formations (also known as whorls) of orientation columns were discovered. Pinwheels are the location where multiple orientation columns converge. Orientation columns are organized radially around a point known as a singularity. The arrangement, around the singularity, can be observed to be in both a counter-clockwise or clockwise fashion. It is suggested that an artifact of the optical recordings may cause these singularities. Limitations in the resolution of the optical technique may be to explain for these singularities.

Fractures

Fractures are breaks in the sequence of orientation selectivity from microelectrode studies. In these studies the fractures occur randomly during trials. Optical methods in trying to explain why these fractures occur, have had limited success.

Development

Orientation maps in monkeys are innately determined at birth. Like other parts of the brain, the visual cortex goes through a critical period where the visual environment can change the orientation maps due to its

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

nature during this period. Visual deprivation during this period will cause a deterioration of these innate connections.Hubel, D. H., & Wiesel, T. N. (1974). Ordered Arrangement of Orientation Columns in Monkeys Lacking Visual Experience. rticle Journal of Comparative Neurology, 158, 307-318. Also if the visual environment is confined to only vertical or horizontal lines during this critical period the distribution of the preferred orientation of cells in the striate cortex become abnormal. This is probably due to cells maturing their preferred orientation to that of the most common type of visual stimulus.Blakemore, C., Cooper, G. F. (1970). Development of the brain depends on the visual environment. Nature, 228, 477-478.

Modeling

Hebbian development of a multilayer neural network

A multilayer neural network model by Linsker, having local connections from each cell layer to the next, whose connection strengths develop according to a Hebbian rule, generates orientation-selective cells and orientation columns.Linsker R. (1986). From basic network principles to neural architecture (series of three papers). PNAS 83, 7508-7512, 8390-8394, 8779-8783. doi:10.1073/pnas.83.19.7508; doi:10.1073/pnas.83.21.8390; doi:10.1073/pnas.83.22.8779 . The resulting columnar arrangement contains fractures and "pinwheel" singularities of the same types as those found experimentally.

Moire interference

A highly debatedSchottdorf M., Eglen S. J., Wolf F. & Keil W. (2014). Can Retinal Ganglion Cell Dipoles Seed Iso-Orientation Domains in the Visual Cortex? PLoS ONE 9(1), e86139. doi:10.1371/journal.pone.0086139.Hore, V. R. A., Troy, J. B., & Eglen, S. J. (2012). Parasol cell mosaics are unlikely to drive the formation of structured orientation maps in primary visual cortex. Visual Neuroscience, 29(6), 283–299. doi:10.1017/S0952523812000338. model for the origin of orientation maps is Moiré interference from

retinal ganglion cells A retinal ganglion cell (RGC) is a type of neuron located near the inner surface (the ganglion cell layer) of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina ...

(RGCs).Paik, S., & Ringach, D. L. (2011). Retinal origin of orientation maps in the visual cortex. Nature Neuroscience, 14(7), 919-925. The ideal case takes two layers of perfect hexagonal lattices of the on-center and off-center

receptive fields The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms. Complexity of the receptive field ranges from the unidimensional chemical structure of od ...

of the RGCs. These two layers are superimposed on each other with an angled offset that produces a periodic interference pattern. This pattern produces dipoles of these RGCs that have a preferred orientation scattered throughout the visual field. This mosaic produces periodic map of preferred orientation that fulfills all orientations with regularity. Cortical inputs from this mosaic of RGCs through the LGN can explain the origin of the orientation maps in the visual cortex.

Further research

Orientation scotomas

The theory of Moire interference patterns governing the orientation map predicts the existence of orientation

scotomas A scotoma is an area of partial alteration in the field of vision consisting of a partially diminished or entirely degenerated visual acuity that is surrounded by a field of normal – or relatively well-preserved – vision. Every normal m ...

. This is because the lattice of the RGCs are not perfectly hexagonal and therefore, at some locations, representation of specific orientations will be missing. Currently there is research that is testing this hypothesis by "mapping human orientation discrimination thresholds of very small stimuli in the far periphery."

References

{{Reflist Visual system Cerebral cortex