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. Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information In Physiology, a stimulus is a detectable change in the internal or external environment Receptive fields have been identified for neurons of the auditory system, the somatosensory system, and the visual system. The auditory system is the Sensory system for the sense of hearing. The visual system is the part of the Nervous system which allows organisms to see.
The concept of receptive fields can be extended to further up the neural system; if many sensory receptors all form synapses with a single cell further up, they collectively form the receptive field of that cell. Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called For example, the receptive field of a ganglion cell in the retina of the eye is composed of input from all of the photoreceptors which synapse with it, and a group of ganglion cells in turn forms the receptive field for a cell in the brain. A ganglion cell (more correctly a retinal ganglion cell or RGC) is a type of Neuron typically located near the inner surface of the Retina The vertebrate retina is a light sensitive part inside the inner layer of the Eye. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain Photoreceptor can refer to In anatomy/cell biology Photoreceptor cell: a photosensitive cell most commonly referring to a specialized type of neuron This process is called convergence. In the absence of a more specific context convergence denotes the approach toward a definite value as time goes on or to a definite point a common view or opinion or
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Auditory system
In the auditory system, receptive fields can be volumes in auditory space, or can be regions of auditory frequencies. Frequency is a measure of the number of occurrences of a repeating event per unit Time. Researchers rarely equate auditory receptive fields to particular regions of the sensory epithelium such as, in the case of mammals, hair cells in the cochlea. In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Hair cells are the Sensory receptors of both the Auditory system and the Vestibular system in all Vertebrates. The cochlea is the auditory portion of the Inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along
Somatosensory system
In the somatosensory system, receptive fields are regions of the skin or of internal organs. The skin is the outer covering of living tissue of an animal (or plant In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument Some types of mechanoreceptors have large receptive fields, while others have smaller ones. A mechanoreceptor is a Sensory receptor that responds to mechanical pressure or distortion
Large receptive fields allow the cell to detect changes over a wider area, but lead to a less precise perception. Thus, the fingers, which require the ability to detect fine detail, have many, densely packed mechanoreceptors with small receptive fields, while the back and legs, for example, have fewer receptors with large receptive fields. Receptors with large receptive fields usually have a "hot spot", an area within the receptive field (usually in the center, directly over the receptor) where stimulation produces the most intense response.
Visual system
In the visual system, receptive fields are volumes in visual space. For example, the receptive field of a single photoreceptor is a cone-shaped volume comprising all the visual directions in which light will alter the firing of that cell. Photoreceptor can refer to In anatomy/cell biology Photoreceptor cell: a photosensitive cell most commonly referring to a specialized type of neuron Its apex is located in the center of the lens and its base essentially at infinity in visual space. The lens is a transparent biconvex structure in the Eye that along with the Cornea, helps to Refract Light to be focused Infinity (symbolically represented with ∞) comes from the Latin infinitas or "unboundedness Traditionally, visual receptive fields were portrayed in two dimensions (e. g. , as circles, squares, or rectangles), but these are simply slices, cut along the screen on which the researcher presented the stimulus, of the volume of space to which a particular cell will respond. In the case of binocular neurons in the visual cortex, receptive fields do not extend to optical infinity. The term visual cortex refers to the primary visual cortex (also known as striate cortex or Instead, they are restricted to a certain interval of distance from the animal, or from where the eyes are fixating (see Panum's area).
The receptive field is often identified as the region of the retina where the action of light alters the firing of the neuron. The vertebrate retina is a light sensitive part inside the inner layer of the Eye. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 In retinal ganglion cells (see below), this area of the retina would encompass all the photoreceptors, all the rods and cones from one eye that are connected to this particular ganglion cell via bipolar cells, horizontal cells, and amacrine cells. Photoreceptor can refer to In anatomy/cell biology Photoreceptor cell: a photosensitive cell most commonly referring to a specialized type of neuron Rod cells, or rods, are Photoreceptor cells in the Retina of the Eye that can function in less intense Light than can the other type Cone cells, or cones, are Photoreceptor cells in the Retina of the Eye which function best in relatively bright Light. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain A bipolar cell is a type of Neuron which has two extensions Bipolar cells are specialized sensory neurons for the transmission of special senses Horizontal cells are the laterally interconnecting neurons in the outer plexiform layer of the Retina of mammalian eyes Amacrine cells are Interneurons in the Retina. Amacrine cells are responsible for 70% of input to retinal ganglion cells In binocular neurons in the visual cortex, it is necessary to specify the corresponding area in both retinas (one in each eye). Although these can be mapped separately in each retina by shutting one or the other eye, the full influence on the neuron's firing is revealed only when both eyes are open.
Hubel and Wiesel (e. g. , Hubel, 1963) advanced the theory that receptive fields of cells at one level of the visual system are formed from input by cells at a lower level of the visual system. In this way, small, simple receptive fields could be combined to form large, complex receptive fields. Later theorists elaborated this simple, hierarchical arrangement by allowing cells at one level of the visual system to be influenced by feedback from higher levels.
Receptive fields have been mapped for all levels of the visual system from photoreceptors, to retinal ganglion cells, to lateral geniculate nucleus cells, to visual cortex cells, to extrastriate cortical cells.
Retinal ganglion cells
The organization of ganglion cells' receptive fields, composed of inputs from many rods and cones, provides a way of detecting contrast, and is used for detecting objects' edges. Each receptive field is arranged into a central disk, the "centre", and a concentric ring, the "surround", each region responding oppositely to light. For example, light in the centre might increase the firing of a particular ganglion cell, whereas light in the surround would decrease the firing of that cell.
There are two types of bipolar cells: "on-center" and "off-center". An on-center cell is stimulated when the center of its receptive field is exposed to light, and is inhibited when the surround is exposed to light. Off-center cells have just the opposite reaction. Stimulation of the center of an on-center cell's receptive field produces depolarization and an increase in the firing of the ganglion cell, stimulation of the surround produces a Hyperpolarization and a decrease in the firing of the cell, and stimulation of both the center and surround produces only a mild response (due to mutual inhibition of center and surround). In biology depolarization is a decrease in the Absolute value of a cell's Membrane potential. 51, Multichannel audio, Multichannel music Surround 3D Surround 5 An off-center cell is stimulated by activation of the surround and inhibited by stimulation of the center (see figure).
Photoreceptors that are part of the receptive fields of more than one ganglion cell are able to excite or inhibit postsynaptic neurons because they release the neurotransmitter glutamate at their synapses, which can act to depolarize or to hyperpolarize a cell, depending on the ion channels it opens. Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands See Chemical synapse for an introduction to concepts and terminology used in this article Glutamic acid (abbreviated as Glu or E) is one of the 20 Alpha Amino acids It is not among the human Essential amino acids Its Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands Ion channels are pore-forming Proteins that help establish and control the small Voltage Gradient across the Plasma membrane of all living
The center-surround receptive field organization allows ganglion cells to transmit information not merely about whether photoreceptor cells are firing (Photoreceptors do not actually fire action potentials), but also about the differences in firing rates of cells in the center and surround. This allows them to transmit information about contrast. The size of the receptive field governs the spatial frequency of the information: small receptive fields are stimulated by high spatial frequencies, fine detail; large receptive fields are stimulated by low spatial frequencies, coarse detail. In Mathematics, Physics, and Engineering, spatial frequency is a characteristic of any structure that is periodic across position in space Retinal ganglion cell receptive fields convey information about discontinuities in the distribution of light falling on the retina; these often specify the edges of objects.
Lateral geniculate nucleus
Further along in the visual system, groups of ganglion cells form the receptive fields of cells in the lateral geniculate nucleus. The lateral geniculate nucleus ( LGN) of the Thalamus is a part of the Brain, which is the primary processor of visual information received from the Receptive fields are similar to those of ganglion cells, with an antagonistic center-surround system and cells that are either on- or off center.
Visual cortex
Receptive fields of cells in the visual cortex are larger and have more-complex stimulus requirements than retinal ganglion cells or lateral geniculate nucleus cells. Hubel and Wiesel (e. g. , Hubel, 1963) classified receptive fields of cells in the visual cortex into simple cells, complex cells, and hypercomplex cells. A simple cell in the primary visual cortex is a cell that responds primarily to oriented edges and gratings (bars of particular orientations Complex cells can be found both in the primary visual cortex (V1 and the secondary visual cortex (V2. Hypercomplex cells - Hubel and Wiesel named cells in the Visual cortex that exhibit end stopping properties hypercomplex cells but later research has found them to be subclasses Simple cell receptive fields are elongated, for example with an excitatory central oval, and an inhibitory surrounding region, or approximately rectangular, with one long side being excitatory and the other being inhibitory. Images for these receptive fields need to have a particular orientation in order to excite the cell. For complex-cell receptive fields, a correctly oriented bar of light might need to move in a particular direction in order to excite the cell. For hypercomplex receptive fields, the bar might also need to be of a particular length.
Extrastriate visual areas
In extrastriate visual areas, cells can have very large receptive fields requiring very complex images to excite the cell. For example in the inferotemporal cortex, receptive fields cross the midline of visual space and require images such as radial gratings or hands. The inferior temporal gyrus is placed below the Middle temporal sulcus, and is connected behind with the Inferior occipital gyrus; it also extends around the infero-lateral It is also believed that in the fusiform face area, images of faces excite the cortex more than other images. The Fusiform face area (FFA is a part of the human Visual system which seems to specialize in facial recognition although there is also good evidence that it also processes This property was one of the earliest major results obtained through fMRI (Kanwisher, McDermott and Chun, 1997); the finding was confirmed later at the neuronal level (Tsao, Freiwald, Tootell and Livingstone, 2006). In a similar vein, people have looked for other category-specific areas; some recent research for example suggests the parahippocampal place area might be somewhat specialised for buildings. The parahippocampal gyrus (or hippocampal gyrus) is a Grey matter cortical region of the Brain that surrounds the Hippocampus. However, more recent research has suggested that the fusiform face area is specialised not just for faces, but also for any discrete, within-category discrimination.
References
- Hubel, D. H. (1963). The visual cortex of the brain. Scientific American, 209(5), 54-62.
- Kandel E. R. , Schwartz, J. H. , Jessell, T. M. (2000). Principles of Neural Science, 4th ed. , pp. 515-520. McGraw-Hill, New York.
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