Neural adaptation
Encyclopedia
Neural adaptation or sensory adaptation is a change over time in the responsiveness of the sensory system
to a constant stimulus
. It is usually experienced
as a change in the stimulus. For example, if one rests one's hand on a table, one immediately feels the table's surface on one's skin. Within a few seconds, however, one ceases to feel the table's surface. The sensory neurons stimulated by the table's surface respond immediately, but then respond less and less until they may not respond at all; this is neural adaptation.
Neural adaptations can be contributed to changes in V-waves and the Hoffmann’s reflex. H-reflex can be used to assess the excitability of spinal α-motoneurons, whereas V-wave measure the magnitude of efferent motor output from α-motoneurons. Studies showed that after a 14 week resistance training regime that subjects expressed V-wave amplitude increases of ~50% and H-reflex amplitude increases of ~20%. This showed that neural adaptation accounts for changes to functional properties of the spinal cord circuitry in humans without affecting organization of the motor cortex.
.). When an observers’ visual stream adapts to a single direction of real motion, imagined motion can be perceived at various speeds. If the imagined motion is in the same direction as that experienced during adaptation, imagined speed is slowed; when imagined motion is in the opposite direction, its speed is increased; when adaptation and imagined motions are orthogonal, imagined speed is unaffected. Studies using magnetoencephalography (MEG) have proven that subjects exposed to a repeated visual stimulus at brief intervals become attenuated to the stimulus in comparison to the initial stimulus. The results revealed that visual responses to the repeated compared with novel stimulus showed a significant reduction in both activation strength and peak latency but not in the duration of neural processing.
. For example, walking uphill requires different muscles than walking on flat pavement. When the brain recognizes that the body is walking uphill, it makes neural adaptations that send more activity to muscles required for uphill walking.
The rate of neural adaptation is affected by the area of the brain and by the similarity between sizes and shapes of previous stimuli. Adaptations in the inferior temporal gyrus
are very dependent on previous stimuli being of similar size, and somewhat dependent on previous stimuli being of a similar shape. Adaptations in the Prefrontal Cortex
are less dependent on previous stimuli being of similar size and shape.
(TMS) is an important technique in modern cognitive neuropsychology
that is used to investigate the perceptual and behavioral effects of temporary interference of neural processing. Studies have shown that when a subject’s visual cortex is disrupted by TMS, the subject views colorless flashes of light, or phosphenes. When a subjects’ vision was subjected to the constant stimulus of a single color, neural adaptations occurred that made the subjects used to the color. Once this adaptation had occurred, TMS was used to disrupt the subjects’ visual cortex again, and the flashes of light viewed by the subject were the same color as the constant stimulus before the disruption.
, spatial cognition and affective development areas of the brain showed deficits in those areas as compared to those without injury. Due to neural adaptations, however, by early school-age, considerable development to those areas was observed.
Sensory system
A sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for vision, hearing, somatic...
to a constant stimulus
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
. It is usually experienced
Perception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
as a change in the stimulus. For example, if one rests one's hand on a table, one immediately feels the table's surface on one's skin. Within a few seconds, however, one ceases to feel the table's surface. The sensory neurons stimulated by the table's surface respond immediately, but then respond less and less until they may not respond at all; this is neural adaptation.
Weight training
Studies have shown that there is neural adaptation after as little as one weight training session. Strength gains are experienced by subjects without any increased muscle size. Muscle surface recordings using electromyographic (SEMG) techniques have found that early strength gains throughout training are associated with increased amplitude in SEMG activity. These findings along with various other theories explain increases in strength without increases in muscle mass. Other theories for increases in strength relating to neural adaptation include: agonist-antagonist muscle decreased co-activation, motor unit synchronization, and motor unit increased firing rates.Neural adaptations can be contributed to changes in V-waves and the Hoffmann’s reflex. H-reflex can be used to assess the excitability of spinal α-motoneurons, whereas V-wave measure the magnitude of efferent motor output from α-motoneurons. Studies showed that after a 14 week resistance training regime that subjects expressed V-wave amplitude increases of ~50% and H-reflex amplitude increases of ~20%. This showed that neural adaptation accounts for changes to functional properties of the spinal cord circuitry in humans without affecting organization of the motor cortex.
Visual
Adaptation is considered to be the cause of perceptual phenomena like afterimages and the motion aftereffect. In the absence of fixational eye movements, visual perception may fade out or disappear due to neural adaptation. (See Adaptation (eye)Adaptation (eye)
In ocular physiology, adaptation is the ability of the eye to adjust to various levels of darkness and light.-Efficacy:The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude. This means that the brightest and the...
.). When an observers’ visual stream adapts to a single direction of real motion, imagined motion can be perceived at various speeds. If the imagined motion is in the same direction as that experienced during adaptation, imagined speed is slowed; when imagined motion is in the opposite direction, its speed is increased; when adaptation and imagined motions are orthogonal, imagined speed is unaffected. Studies using magnetoencephalography (MEG) have proven that subjects exposed to a repeated visual stimulus at brief intervals become attenuated to the stimulus in comparison to the initial stimulus. The results revealed that visual responses to the repeated compared with novel stimulus showed a significant reduction in both activation strength and peak latency but not in the duration of neural processing.
Pain
While large mechanosensory neurons such as type I/group Aß display adaptation, smaller type IV/group C nociceptive neurons do not. As a result, pain does not usually subside rapidly but persists for long periods of time; in contrast, one quickly stops receiving touch or sensory information if surroundings remain constant.Short-term adaptations
Short term neural adaptations occur in the body during rhythmic activities. One of the most common activities when these neural adaptations are constantly happening is walking. As a person walks, the body constantly gathers information about the environment and the surroundings of the feet, and slightly adjusts the muscles in use according to the terrainTerrain
Terrain, or land relief, is the vertical and horizontal dimension of land surface. When relief is described underwater, the term bathymetry is used...
. For example, walking uphill requires different muscles than walking on flat pavement. When the brain recognizes that the body is walking uphill, it makes neural adaptations that send more activity to muscles required for uphill walking.
The rate of neural adaptation is affected by the area of the brain and by the similarity between sizes and shapes of previous stimuli. Adaptations in the inferior temporal gyrus
Inferior temporal gyrus
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 border on to the inferior surface of the temporal lobe, where it is limited by the inferior sulcus...
are very dependent on previous stimuli being of similar size, and somewhat dependent on previous stimuli being of a similar shape. Adaptations in the Prefrontal Cortex
Prefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
are less dependent on previous stimuli being of similar size and shape.
Long-term adaptations
Some rhythmic movements, such as respiratory movements, are essential for survival. Because these movements must be used over the course of the entire lifetime, it is important for them to function optimally. Neural adaptation has been observed in these movements in response to training or altered external conditions. Animals have been shown to have reduced breathing rates in response to better fitness levels. Since breathing rates were not conscious changes made by the animal, it is presumed that neural adaptations occur for the body to maintain a slower breathing rate.Transcranial magnetic stimulation
Transcranial magnetic stimulationTranscranial magnetic stimulation
Transcranial magnetic stimulation is a noninvasive method to cause depolarization or hyperpolarization in the neurons of the brain...
(TMS) is an important technique in modern cognitive neuropsychology
Cognitive neuropsychology
Cognitive neuropsychology is a branch of cognitive psychology that aims to understand how the structure and function of the brain relates to specific psychological processes. It places a particular emphasis on studying the cognitive effects of brain injury or neurological illness with a view to...
that is used to investigate the perceptual and behavioral effects of temporary interference of neural processing. Studies have shown that when a subject’s visual cortex is disrupted by TMS, the subject views colorless flashes of light, or phosphenes. When a subjects’ vision was subjected to the constant stimulus of a single color, neural adaptations occurred that made the subjects used to the color. Once this adaptation had occurred, TMS was used to disrupt the subjects’ visual cortex again, and the flashes of light viewed by the subject were the same color as the constant stimulus before the disruption.
Drug induced neural adaptation
Neural adaptation can occur for other than natural means. Antidepressant drugs, such as those that cause down regulation of β- adrenergic receptors, can cause rapid neural adaptations in the brain. By creating a quick adaptation in the regulation of these receptors, it is possible for drugs to reduce the effects of stress on those taking the medication.Post-injury neural adaptation
Studies in children with early childhood brain injuries have shown that neural adaptations slowly occur after the injury. Children with early injuries to the linguisticsLinguistics
Linguistics is the scientific study of human language. Linguistics can be broadly broken into three categories or subfields of study: language form, language meaning, and language in context....
, spatial cognition and affective development areas of the brain showed deficits in those areas as compared to those without injury. Due to neural adaptations, however, by early school-age, considerable development to those areas was observed.