Neuronal tuning

Last updated

In neuroscience, neuronal tuning refers to the hypothesized property of brain cells by which they selectively represent a particular type of sensory, association, motor, or cognitive information. Some neuronal responses have been hypothesized to be optimally tuned to specific patterns through experience. [1] Neuronal tuning can be strong and sharp, as observed in primary visual cortex (area V1) (but see Carandini et al 2005 [2] ), or weak and broad, as observed in neural ensembles. Single neurons are hypothesized to be simultaneously tuned to several modalities, such as visual, auditory, and olfactory. Neurons hypothesized to be tuned to different signals are often hypothesized to integrate information from the different sources. In computational models called neural networks, such integration is the major principle of operation. The best examples of neuronal tuning can be seen in the visual, auditory, olfactory, somatosensory, and memory systems, although due to the small number of stimuli tested the generality of neuronal tuning claims is still an open question.

Contents

Visually Tuned System

Accepted neuronal tuning models suggest that neurons respond to different degrees based on the similarity between the optimal stimulus of the neuron and the given stimulus. [3] (Teller (1984), however, has challenged the "detector" view of neurons on logical grounds) [4] The first major evidence of neuronal tuning in the visual system was provided by Hubel and Wiesel in 1959. [5] They discovered that oriented slits of light were the most effective (of a very small set tested) stimuli for striate cortex “simple cell” neurons. [6] Other neurons, “complex cells," responded best to lines of a certain orientation moving in a specific direction. [5] Overall, the V1 neurons were found to be selectively tuned to certain orientations, sizes, positions, and forms. [5] Hubel and Wiesel won the Nobel Prize in Physiology or Medicine in 1981 for their discoveries concerning information processing in the visual system. [7] (More recently, Carandini et al (2005) have pointed out that the distinction between "simple" and "complex" cells may not be a valid one, observing that "simple and complex cells may not form a dichotomy at all." [2] )

While these simple cells in V1 respond to oriented bars through small receptive fields, the optimal visual stimulus becomes increasing complex as one moves toward the anterior of the brain. [8] Neurons in area V4 are selectively tuned to different wavelengths, hues, and saturations of color. [9] The middle temporal or area V5 is specifically tuned to the speed and direction of moving stimuli. [9] At the apex of the ventral stream called the inferotemporal cortex, neurons became tuned to complex stimuli, such as faces. [8] The specific tuning of intermediate neurons in the ventral stream is less clear, because the range of form variety that can be utilized for probing is nearly infinite. [10]

In the anterior part of the ventral stream, various regions appear to be tuned selectively to identify body parts (extrastriate body area), faces (fusiform face area) (according to a recent paper by Adamson and Troiani (2018) regions of the fusiform face area respond equally to "food"), [11] moving bodies (posterior superior temporal sulcus), or even scenes (parahippocampal place area). [9] Neuronal tuning in these areas requires fine discrimination among complex patterns in each relevant category for object recognition. [10] Recent findings suggest that this fine discrimination is a function of expertise and the individual level of categorization with stimuli. Specifically, work has been done by Gauthier et al (2001) to show fusiform face area (FFA) activation for birds in bird experts and cars in car experts when compared to the opposing stimuli. [12] Gauthier et al (2002) also utilized a new class of objects called Greebles and trained people to recognize them at individual levels. [13] After training, the FFA was tuned to distinguish between this class of objects as well as faces. [13] Curran et al (2002) similarly trained people in a less structured class of objects called "blobs" and showed FFA selective activation for them. [14] Overall, neurons can be tuned selectively discriminate between certain sets of stimuli that are experienced regularly in the world.

Tuning in Other Systems

Neurons in other systems also become selectively tuned to stimuli. In the auditory system, different neurons may respond selectively to the frequency (pitch), amplitude (loudness), and/or complexity (uniqueness) of sounds. [9] In the olfactory system, neurons may be tuned to certain kinds of smells. [9] In the gustatory system, different neurons may respond selectively to different components of food: sweet, sour, salty, and bitter. [9] In the somatosensory system, neurons may be selectively tuned to different types of pressure, temperature, bodily position, and pain. [9] This tuning in the somatosensory system also provides feedback to the motor system so that it may selectively tune neurons to respond in specific ways to given stimuli. [9] Finally, the encoding and storage of information in both short-term and long-term memory requires the tuning of neurons in complex ways such that information may be later retrieved. [9]

Related Research Articles

<span class="mw-page-title-main">Visual cortex</span> Region of the brain that processes visual information

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 then reaches the visual cortex. The area of the visual cortex that receives the sensory input from the lateral geniculate nucleus is the primary visual cortex, also known as visual area 1 (V1), Brodmann area 17, or the striate cortex. The extrastriate areas consist of visual areas 2, 3, 4, and 5.

<span class="mw-page-title-main">Sensory nervous system</span> Part of the nervous system

The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons, neural pathways, and parts of the brain involved in sensory perception and interoception. Commonly recognized sensory systems are those for vision, hearing, touch, taste, smell, balance and visceral sensation. Sense organs are transducers that convert data from the outer physical world to the realm of the mind where people interpret the information, creating their perception of the world around them.

Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation. All sensory modalities work together to heighten stimuli sensation when necessary.

<span class="mw-page-title-main">David H. Hubel</span> Canadian neurophysiologist

David Hunter Hubel was an American Canadian neurophysiologist noted for his studies of the structure and function of the visual cortex. 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. For much of his career, Hubel worked as the Professor of Neurobiology at Johns Hopkins University and Harvard Medical School. In 1978, Hubel and Wiesel were awarded the Louisa Gross Horwitz Prize from Columbia University. In 1983, Hubel received the Golden Plate Award of the American Academy of Achievement.

The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms.

Visual processing is a term that is used to refer to the brain's ability to use and interpret visual information from the world around us. The process of converting light energy into a meaningful image is a complex process that is facilitated by numerous brain structures and higher level cognitive processes. On an anatomical level, light energy first enters the eye through the cornea, where the light is bent. After passing through the cornea, light passes through the pupil and then lens of the eye, where it is bent to a greater degree and focused upon the retina. The retina is where a group of light-sensing cells, called photoreceptors are located. There are two types of photoreceptors: rods and cones. Rods are sensitive to dim light and cones are better able to transduce bright light. Photoreceptors connect to bipolar cells, which induce action potentials in retinal ganglion cells. These retinal ganglion cells form a bundle at the optic disc, which is a part of the optic nerve. The two optic nerves from each eye meet at the optic chiasm, where nerve fibers from each nasal retina cross which results in the right half of each eye's visual field being represented in the left hemisphere and the left half of each eye's visual fields being represented in the right hemisphere. The optic tract then diverges into two visual pathways, the geniculostriate pathway and the tectopulvinar pathway, which send visual information to the visual cortex of the occipital lobe for higher level processing.

<span class="mw-page-title-main">Medial geniculate nucleus</span>

The medial geniculate nucleus (MGN) or medial geniculate body (MGB) is part of the auditory thalamus and represents the thalamic relay between the inferior colliculus (IC) and the auditory cortex (AC). It is made up of a number of sub-nuclei that are distinguished by their neuronal morphology and density, by their afferent and efferent connections, and by the coding properties of their neurons. It is thought that the MGN influences the direction and maintenance of attention.

<span class="mw-page-title-main">Inferior temporal gyrus</span> One of three gyri of the temporal lobe of the brain

The inferior temporal gyrus is one of three gyri of the temporal lobe and is located below the middle temporal gyrus, connected behind with the inferior occipital gyrus; it also extends around the infero-lateral border on to the inferior surface of the temporal lobe, where it is limited by the inferior sulcus. This region is one of the higher levels of the ventral stream of visual processing, associated with the representation of objects, places, faces, and colors. It may also be involved in face perception, and in the recognition of numbers and words.

Neural coding is a neuroscience field concerned with characterising the hypothetical relationship between the stimulus and the neuronal responses, and the relationship among the electrical activities of the neurons in the ensemble. Based on the theory that sensory and other information is represented in the brain by networks of neurons, it is believed that neurons can encode both digital and analog information.

<span class="mw-page-title-main">Simple cell</span> Beaker with Dilute Sulphuric Acid, Zinc and Copper Sheet is known as A Simple Cell

A simple cell in the primary visual cortex is a cell that responds primarily to oriented edges and gratings. These cells were discovered by Torsten Wiesel and David Hubel in the late 1950s.

A topographic map is the ordered projection of a sensory surface, like the retina or the skin, or an effector system, like the musculature, to one or more structures of the central nervous system. Topographic maps can be found in all sensory systems and in many motor systems.

Complex cells can be found in the primary visual cortex (V1), the secondary visual cortex (V2), and Brodmann area 19 (V3).

<span class="mw-page-title-main">Colour centre</span> Brain region responsible for colour processing

The colour centre is a region in the brain primarily responsible for visual perception and cortical processing of colour signals received by the eye, which ultimately results in colour vision. The colour centre in humans is thought to be located in the ventral occipital lobe as part of the visual system, in addition to other areas responsible for recognizing and processing specific visual stimuli, such as faces, words, and objects. Many functional magnetic resonance imaging (fMRI) studies in both humans and macaque monkeys have shown colour stimuli to activate multiple areas in the brain, including the fusiform gyrus and the lingual gyrus. These areas, as well as others identified as having a role in colour vision processing, are collectively labelled visual area 4 (V4). The exact mechanisms, location, and function of V4 are still being investigated.

<span class="mw-page-title-main">Fusiform face area</span> Part of the human visual system that is specialized for facial recognition

The fusiform face area is a part of the human visual system that is specialized for facial recognition. It is located in the inferior temporal cortex (IT), in the fusiform gyrus.

<span class="mw-page-title-main">Hypercomplex cell</span>

A hypercomplex cell is a type of visual processing neuron in the mammalian cerebral cortex. Initially discovered by David Hubel and Torsten Wiesel in 1965, hypercomplex cells are defined by the property of end-stopping, which is a decrease in firing strength with increasingly larger stimuli. The sensitivity to stimulus length is accompanied by selectivity for the specific orientation, motion, and direction of stimuli. For example, a hypercomplex cell may only respond to a line at 45˚ that travels upward. Elongating the line would result in a proportionately weaker response. Ultimately, hypercomplex cells can provide a means for the brain to visually perceive corners and curves in the environment by identifying the ends of a given stimulus.

Sensory maps are areas of the brain which respond to sensory stimulation, and are spatially organized according to some feature of the sensory stimulation. In some cases the sensory map is simply a topographic representation of a sensory surface such as the skin, cochlea, or retina. In other cases it represents other stimulus properties resulting from neuronal computation and is generally ordered in a manner that reflects the periphery. An example is the somatosensory map which is a projection of the skin's surface in the brain that arranges the processing of tactile sensation. This type of somatotopic map is the most common, possibly because it allows for physically neighboring areas of the brain to react to physically similar stimuli in the periphery or because it allows for greater motor control.

An organism is said to be sexually dimorphic when male and female conspecifics have anatomical differences in features such as body size, coloration, or ornamentation, but disregarding differences of reproductive organs. Sexual dimorphism is usually a product of sexual selection, with female choice leading to elaborate male ornamentation and male-male competition leading to the development of competitive weaponry. However, evolutionary selection also acts on the sensory systems that receivers use to perceive external stimuli. If the benefits of perception to one sex or the other are different, sex differences in sensory systems can arise. For example, female production of signals used to attract mates can put selective pressure on males to improve their ability to detect those signals. As a result, only males of this species will evolve specialized mechanisms to aid in detection of the female signal. This article uses examples of sex differences in the olfactory, visual, and auditory systems of various organisms to show how sex differences in sensory systems arise when it benefits one sex and not the other to have enhanced perception of certain external stimuli. In each case, the form of the sex difference reflects the function it serves in terms of enhanced reproductive success.

Feature detection is a process by which the nervous system sorts or filters complex natural stimuli in order to extract behaviorally relevant cues that have a high probability of being associated with important objects or organisms in their environment, as opposed to irrelevant background or noise.

<span class="mw-page-title-main">Orientation column</span>

Orientation columns are organized regions of neurons that are excited by visual line stimuli of varying angles. These columns are located in the primary visual cortex (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.

Binocular neurons are neurons in the visual system that assist in the creation of stereopsis from binocular disparity. They have been found in the primary visual cortex where the initial stage of binocular convergence begins. Binocular neurons receive inputs from both the right and left eyes and integrate the signals together to create a perception of depth.

References

  1. ↑ Sakai, Kuniyoshi; Miyashita, Yasushi. Neuronal tuning to learned complex forms in vision. NeuroReport 1994, 5:829-832.
  2. 1 2 Matteo Carandini, Jonathan B. Demb, Valerio Mante, David J. Tolhurst, Yang Dan, Bruno A. Olshausen, Jack L. Gallant and Nicole C. Rust. Do we know what the early visual system does? Journal of Neuroscience 25:10577-10597.
  3. ↑ Grill-Spector, Kalanit; Witthoft, Nathan. Deos the Bairn Not Raed Ervey Lteter by Istlef, but the Wrod as a Wlohe? Neuron 2009, 62:161-162.
  4. ↑ Teller. Linking propositions. Vision Research 1984,24:1233-2346.
  5. 1 2 3 Hubel, D. H.; Wiesel, T. N. Receptive Fields of Single Neurones in the Cat's Striate Cortex. J. Physiol. 1959, 148:574-591.
  6. ↑ Wurtz, Robert H. Recounting the impact of Hubel and Wiesel. J. Physiol. 2009, 587:2817-2823.
  7. ↑ www.nobelprize.org
  8. 1 2 Riesenhuber, Maximilian; Poggio, Tomaso. Neural mechanisms of object recognition. Current Opinion in Neurobiology 2002, 12:162-168.
  9. 1 2 3 4 5 6 7 8 9 Kolb, B.; Whishaw, I. Q. Fundamentals of Human Neuropsychology (2003). New York, NY: Worth Publishers.
  10. 1 2 Sakai, K.; Naya, Y.; Miyashita, Y. Neuronal tuning and associative mechanisms in form representation. Learning and Memory 1994, 1:83-105.
  11. ↑ Adamson & Troiani. Distinct and overlapping fusiform activation to faces and food. Neuroimage 2018, 174: 393-406
  12. ↑ Gauthier, I.; Skudlarski, P.; Gore, J. C.; Anderson, A. W. Expertise for cars and birds recruits brain areas involved in face recognition. Nat. Neurosci. 2001, 3:191-197.
  13. 1 2 Gauthier, I.; Tarr, M. J. Unraveling mechanisms for expert object recognition: Bridging brain activity and behavior. Journal of Experimental Psychology: Human Perception and Performance 2002, 28(2):431-446.
  14. ↑ Curran, I.; Tanaka, J.; Weiskopf, D. An electrophysiological comparison of visual categorization and recognition memory. Cognitive, Affective, & Behavioral Neuroscience 2002, 18(2):1-18.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.