A koniocellular cell (konio: Greek, dust or poison, also known as K cell) is a neuron with a small cell body that is located in the koniocellular layer of the lateral geniculate nucleus (LGN) in primates, including humans.
Koniocellular layers are located ventral to each parvocellular and magnocellular layer of the LGN. Even if the quantity of neurons is approximately equal to the number of magnocellular cells the koniocellular layers are much thinner due to their size. In comparison to the parvocellular and magnocellular system, fewer studies have been conducted to investigate the koniocellular system. Koniocellular cells are a heterogeneous population differing in many aspects, such as response properties and connectivity.
K cells are neurochemically and anatomically distinct from M and P cells. There are three proteins by which K cells can be clearly distinguished:
K cells differ in their size from M and P cells, they are much smaller. Unlike M and P cells, K cells are structurally similar to other thalamocortical neurons. This suggests that K cells act like other thalamocortical cells.
Since K cells are a heterogeneous group of cells, it is likely that they contain subclasses which fulfill different functions. Some cells respond to colour, some to achromatic gratings and still others are unresponsive to any types of gratings. Experimental results suggest that K cells could contribute to aspects of spatial and temporal vision, but it is unclear exactly how. Some hypotheses are:
Ventral to each of the magnocellular and parvocellular layers lie the koniocellular layers which differ in thickness. In macaques there are two magnocellular and four parvocellular layers and accordingly six konicellular layers. K1, the layer ventral to M1, is the largest. K2, K3 and K4 are thinner but nonetheless substantial bands of neurons. The two most dorsal layers K5 and K6 are mostly monolayers.Similar in physiology and connectivity to W cells in cat LGN, K cells form three pairs of layers in macaques.
K cells are not restricted to the koniocellular layers. They are also found in small groups, in pairs or as single cells within M and P layers. Larger subpopulations form bridges spanning the distance between two adjacent K layers.
Each koniocellular layer is innervated by the same retina part as the M or P layer dorsal to the respective K layer. Thus, the LGN contains six koniocellular layers. K1, K4 and K6 receive contralateral retinal inputs, and K3 and K5 receive ipsilateral retinal input. K2 receives input from both retinae but the input from the two eyes is relayed in separate tiers. The more dorsal tier is innervated by the ipsilateral retina and the more ventral is innervated by the contralateral retina.K cells receive input from a heterogeneous group of wide-field cells, including small bistratified cells, sparse cells and possibly also large bistratified cells and broad thorny cells. Those bistratified cells are ganglion cells that send short-wavelength signals to the LGN. Retinogeniculate axons terminating in the middle K layers display center-only blue-ON/yellow-OFF receptive fields. Sparse cells are presumed to transmit blue-OFF signals. Both, small bistratified cells and sparse cells project to K cells. Therefore, K cells are believed to relay short-wavelength visual information.
Corticogeniculate axons appear to be quantitatively dominant within the LGN. The same holds for K cells but unlike M and P cells they also receive input from the extrastriate cortex. Axons arising from the superficial grey layer of the superior colliculus terminate in every K layer with the most ventral layers receiving the strongest input. Thus, it is assumed that the K layers are functionally related to the superior colliculus, e.g. reflexive control of eye movements.As a conclusion, retinal inputs compete with a quantitatively dominant corticothalamic innervation and a rich innervation from brainstem nuclei.
K cells terminate in the superficial blobs and layer I of V1. The dorsal-most K layers (K5 and K6) have many axons terminating in layer I of V1, whereas K1 – K4 rather send their axons to the blobs. However, this division is not clear-cut. For example, it has been found that axons from neurons in the ventral-most pair (K1 and K2) innervate layer I of V1, too.The innervation of blobs follows the pattern known from the retinogeniculate terminations:
In macaques, about 30 K cells send their axons to one blob. Anatomically distinct subpopulations of K cells innervate different types of blobs, such as blue/yellow blobs or red/green blobs. Neurons in these blobs display blue/yellow antagonism or red/green antagonism.
Moreover, K cells innervate extrastriate areas. These K cells are rather large, sending their axons to V2 and inferotemporal cortex (IT). Immunostaining revealed only a few, sparse and broadly distributed large K cells, apart from the K cells innervating the foveal representation of V2 which are more densely packed and found along the caudal and medial margin of the LGN.Throughout each K layer there are neurons that innervate the extrastriate cortex and that are likely to sustain some visual behaviors in the absence of V1. The fact that K cells directly project to hMT supports this hypothesis (see below "theory of blindsight").
It is assumed that K cells generate and migrate contemporaneously with neighboring M and P cells (Hendry, p. 134). Neurons in the most ventral part of the LGN develop before neurons in more dorsal layers. Neurons of layer K1 develop close to the time of final mitosis for neurons in layer M1 and neurons of K6 develop slightly before neurons of layer P6. While M and P layers in LGN and their axonal terminations in V1 degenerate after a loss of patterned visual input, K cells are not affected.
Blindsight is the phenomenon where patients with injury in the primary visual cortex (V1) show persistence in motion detection without visual awareness. The brain area responsive to motion in the human brain is called V5 or hMT. Many approaches have been examined to reveal the underlying mechanisms of blindsight. In the past it has been shown that superior colliculus ablation has an effect on V1-independent vision, which in turn advocates the role of the superior colliculus for blindsight. In case of V1 lesions, additional LGN inactivation leads to a strong reduction of neural activity in the extrastriate areas, such as MT.Research has shown that there exists a direct pathway from the LGN to MT consisting mostly of koniocellular cells. In fact, 63% of the neurons directly projecting to MT are koniocellular cells. The input MT receives directly from the LGN makes up about 10% of the V1 neuron population projecting to MT. These results suggest that the koniocellular layers play a key role in V1-independent vision. Since the koniocellular layers receive input from the superior colliculus, the previously obtained results can be complemented by the role of the koniocellular layers.
This direct connection from the LGN, more precisely the koniocellular layers, to MT could account for the phenomenon of blindsight as well as for rapid detection of moving objects in healthy subjects.
The visual cortex of the brain is that part of the cerebral cortex which processes visual information. It is located in the occipital lobe. Visual nerves run straight from the eye to the primary visual cortex to the visual association cortex.
Blindsight is the ability of people who are cortically blind due to lesions in their striate cortex, also known as the primary visual cortex or V1, to respond to visual stimuli that they do not consciously see. The majority of studies on blindsight are conducted on patients who have the conscious blindness on only one side of their visual field. Following the destruction of the striate cortex, patients are asked to detect, localize, and discriminate amongst visual stimuli that are presented to their blind side, often in a forced-response or guessing situation, even though they do not consciously recognize the visual stimulus. Research shows that blind patients achieve a higher accuracy than would be expected from chance alone. Type 1 blindsight is the term given to this ability to guess—at levels significantly above chance—aspects of a visual stimulus without any conscious awareness of any stimuli. Type 2 blindsight occurs when patients claim to have a feeling that there has been a change within their blind area—e.g. movement—but that it was not a visual percept. Blindsight challenges the common belief that perceptions must enter consciousness to affect our behavior; showing that our behavior can be guided by sensory information of which we have no conscious awareness. It may be thought of as a converse of the form of anosognosia known as Anton–Babinski syndrome, in which there is full cortical blindness along with the confabulation of visual experience.
Color vision is an ability of animals to perceive differences between light composed of different wavelengths independently of light intensity. Color perception is a part of the larger visual system and is mediated by a complex process between neurons that begins with differential stimulation of different types of photoreceptors by light entering the eye. Those photoreceptors then emit outputs that are then propagated through many layers of neurons and then ultimately to the brain. Color vision is found in many animals and is mediated by similar underlying mechanisms with common types of biological molecules and a complex history of evolution in different animal taxa. In primates, color vision may have evolved under selective pressure for a variety of visual tasks including the foraging for nutritious young leaves, ripe fruit, and flowers, as well as detecting predator camouflage and emotional states in other primates.
The visual system comprises the sensory organ and the part of the central nervous system which gives organisms the ability to process visual detail as sight, as well as enabling the formation of several non-image photo response functions. It detects and interprets information from visible light to "build a representation" of the surrounding environment. The visual system carries out a number of complex tasks, including the reception of light and the formation of monocular representations, the neural mechanisms underlying stereo vision, the identification and categorization of visual objects, assessing distances to and between objects, motion perception, guiding body movements in relation to the objects seen, colour vision, and more. The psychological side of visual information procesing is known as visual perception, a lack of which is called blindness. Non-image forming visual functions, independent of visual perception, include the pupillary light reflex (PLR) and circadian photoentrainment.
The lateral geniculate nucleus is a relay center in the thalamus for the visual pathway. It receives a major sensory input from the retina. The LGN is the main central connection for the optic nerve to the occipital lobe, particularly the primary visual cortex. In humans, each LGN has six layers of neurons alternating with optic fibers.
Brodmann area 19, or BA 19, is part of the occipital lobe cortex in the human brain. Along with area 18, it comprises the extrastriate cortex. In humans with normal sight, extrastriate cortex is a visual association area, with feature-extracting, shape recognition, attentional, and multimodal integrating functions.
The paraventricular nucleus is a nucleus in the hypothalamus. It is a group of neurons that can be activated by physiological changes including stress. Many PVN neurons project directly to the posterior pituitary where they release oxytocin into the general circulation. The supraoptic nucleus releases vasopressin. Both the PVN and the supraoptic nucleus do produce small amounts of the other hormone, ADH and Oxytocin respectively. Other PVN neurons control various anterior pituitary functions, while still others directly regulate appetite and autonomic functions in the brainstem and spinal cord.
Magnocellular neurosecretory cells are large neuroendocrine cells within the supraoptic nucleus and paraventricular nucleus of the hypothalamus. They are also found in smaller numbers in accessory cell groups between these two nuclei, the largest one being the nucleus circularis. There are two types of magnocellular neurosecretory cells, oxytocin-producing cells and vasopressin-producing cells, but a small number can produce both hormones. These cells are neuroendocrine neurons, are electrically excitable, and generate action potentials in response to afferent stimulation.
A retinal ganglion cell (RGC) is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina amacrine cells. Retina amacrine cells, particularly narrow field cells, are important for creating functional subunits within the ganglion cell layer and making it so that ganglion cells can observe a small dot moving a small distance. Retinal ganglion cells collectively transmit image-forming and non-image forming visual information from the retina in the form of action potential to several regions in the thalamus, hypothalamus, and mesencephalon, or midbrain.
Parvocellular cells, also called P-cells, are neurons located within the parvocellular layers of the lateral geniculate nucleus (LGN) of the thalamus. "Parvus" is Latin for "small", and the name "parvocellular" refers to the small size of the cell compared to the larger magnocellular cells. Phylogenetically, parvocellular neurons are more modern than magnocellular ones.
Magnocellular cells, also called M-cells, are neurons located within the Adina magnocellular layer of the lateral geniculate nucleus of the thalamus. The cells are part of the visual system. They are termed "magnocellular" since they are characterized by their relatively large size compared to parvocellular cells.
The superior colliculus is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates the homologous structure, is known as the optic tectum or optic lobe. The adjective form tectal is commonly used for both structures.
Thalamocortical radiations are the fibers between the thalamus and the cerebral cortex.
The cochlear nuclear (CN) complex comprises two cranial nerve nuclei in the human brainstem, the ventral cochlear nucleus (VCN) and the dorsal cochlear nucleus (DCN). The ventral cochlear nucleus is unlayered whereas the dorsal cochlear nucleus is layered. Auditory nerve fibers, fibers that travel through the auditory nerve carry information from the inner ear, the cochlea, on the same side of the head, to the nerve root in the ventral cochlear nucleus. At the nerve root the fibers branch to innervate the ventral cochlear nucleus and the deep layer of the dorsal cochlear nucleus. All acoustic information thus enters the brain through the cochlear nuclei, where the processing of acoustic information begins. The outputs from the cochlear nuclei are received in higher regions of the auditory brainstem.
The superior olivary complex (SOC) or superior olive is a collection of brainstem nuclei that functions in multiple aspects of hearing and is an important component of the ascending and descending auditory pathways of the auditory system. The SOC is intimately related to the trapezoid body: most of the cell groups of the SOC are dorsal to this axon bundle while a number of cell groups are embedded in the trapezoid body. Overall, the SOC displays a significant interspecies variation, being largest in bats and rodents and smaller in primates.
Blobs are sections of the visual cortex where groups of neurons that are sensitive to color assemble in cylindrical shapes. They were first identified in 1979 by Margaret Wong-Riley when she used a cytochrome oxidase stain, from which they get their name. These areas receive input from parvocellular cells in layer 4Cβ of the primary visual cortex and output to the thin stripes of area V2. Interblobs are areas between blobs which receive the same input, but are sensitive to orientation instead of color. They output to the pale stripes of area V2.
A midget cell is one type of retinal ganglion cell (RGC). Midget cells originate in the ganglion cell layer of the retina, and project to the parvocellular layers of the lateral geniculate nucleus (LGN). The axons of midget cells travel through the optic nerve and optic tract, ultimately synapsing with parvocellular cells in the LGN. These cells are known as midget retinal ganglion cells due to the small sizes of their dendritic trees and cell bodies. About 80% of RGCs are midget cells. They receive inputs from relatively few rods and cones. In many cases, they are connected to midget bipolar cells, which are linked to one cone each.
A parasol cell, sometimes called an M cell or M ganglion cell, is one type of retinal ganglion cell (RGC) located in the ganglion cell layer of the retina. These cells project to magnocellular cells in the lateral geniculate nucleus (LGN) as part of the magnocellular pathway in the visual system. They have large cell bodies as well as extensive branching dendrite networks and as such have large receptive fields. Relative to other RGCs, they have fast conduction velocities. While they do show clear center-surround antagonism, they receive no information about color. Parasol ganglion cells contribute information about the motion and depth of objects to the visual system.
Peter H. Schiller is a professor emeritus of Neuroscience in the Department of Brain and Cognitive Sciences at the Massachusetts Institute of Technology (MIT). He is well known for his work on the behavioral, neurophysiological and pharmacological studies of the primate visual and oculomotor systems.
The tectopulvinar pathway and the geniculostriate pathway are the two visual pathways that travel from the retina to the early visual cortical areas. From the optic tract, the tectopulvinar pathway sends neuronal radiations to the superior colliculus in the tectum, then to the lateral posterior-pulvinar thalamic complex.. Approximately 10% of retinal ganglion cells project onto the tectopulvinar pathway.