The Galvanic Skin Response
The simple psycho-galvanometer was one of the earliest tools of psychological research. A psycho-galvanometer measures the resistance of the skin to the passage of a very small electric current. It has been known for decades that the magnitude of this electrical resistance is affected, not only by the subject's general mood, but also by immediate emotional reactions. Although these facts have been known for over a hundred years and the first paper to be presented on the subject of the psycho-galvanometer was written by Tarchanoff in 1890, it has only been within the last 25 years that the underlying causes of this change in skin resistance have been discovered.
The Tarchanoff Response is a change in DC potential across neurones of the autonomic nervous system connected to the sensori-motor strip of the cortex. This change was found to be related to the level of cortical arousal. The emotional charge on a word, heard by a subject, would have an immediate effect on the subject's level of arousal, and cause this physiological response. Because the hands have a particularly large representation of nerve endings on the sensori-motor strip of the cortex, hand-held electrodes are ideal. As arousal increases, the "fight or flight" stress response of the autonomic nervous system comes into action, and adrenaline causes increased sweating amongst many other phenomena, but the speed of sweating response is nowhere near as instantaneous or accurate as the Tarchanoff response.
The most advanced layers of the cortex, unique to Man, link to the thumb and forefinger especially, and there is a further complex physiological response which occurs when the forebrain is aroused. Changes in Alpha rhythms cause blood capillaries to enlarge, and this too affects resistance.
By virtue of the Galvanic Skin Response, autonomic nervous system activity causes a change in the skin's conductivity. The overall degree of arousal of the hemispheres, and indeed the whole brain, is shown by the readings of the GSR psychometer, which does not differentiate between the hemispheres, or between cortical and primitive brain responses. Higher arousal (such as occurs with increased involvement) will almost instantaneously (0.2 - 0.5 sec) cause a fall in skin resistance; reduced arousal (such as occurs with withdrawal) will cause a rise in skin resistance.
Thus a rise or fall relates directly to reactive arousal, due to re-stimulation of repressed mental conflict. Initially this may cause a rise in resistance as this emerging, previously repressed, material is fought against.
In 1997 Vilayanur Ramachandran and his colleagues from the University of California at San Diego headed a research study. The team studied patients of temporal lobe epilepsy measuring galvanic skin response on the left hands of the patients (11). This measurement allowed the research team to monitor arousal (specific autonomic nervous system response) and indirectly surmise the communication between the inferior temporal lobe and the amygdala, both important in response related to fear and arousal (9). In addition to two control groups a religious control group and a non-religious control group, each group was shown forty words, including violent words, sexual words, and simple words (like "wheel"), and finally, religious-related words. The results of the study showed a greater arousal in the temporal lobe epilepsy sufferers to religious words in comparison to the non-religious, whom were aroused by sexual words, and religious control groups, whom were aroused by religious and sexual words (10).
When a receptor is activated and the stimulus is taken to the hypothalamus and then relayed out to the “limbic system and neocortical areas…impulses stimulate the neuroendocrine and autonomic nervous system,” which can cause an array of issues if not careful and if the stress signal is prolonged. (3)
Sympathetic pathways change nerve activity during times of stress, exercise, low blood glucose levels, excitement or fear, due to the flight or fight response. These changes can have an effect on homeostasis by increasing heart rate, increasing blood flow, dilating pupils, sweating, releasing glycogen, increasing oxygen intake and diverting blood flow away from the gastrointestinal tract.
In this lab we apply the technique known as a two point discrimination test. This test will allow us to determine which regions of the skin are best able to discriminate between two simultaneous sensory impulses. According to (Haggard et al. 2007), tactile discrimination depends on the size of the receptive fields located on the somatosensory neurons. However receptive fields for other types of sensations are located elsewhere. For vision we find that the receptive fields are located inside the visual cortex, and for hearing we find receptive fields in the auditory cortex. The ability for the body to discriminate two points depends on how well that area of the body is innervated with neurons; and thus conferring to the size of the receptive fields (Haggard et al. 2007). It is important to note that the size of the receptive field generally decreases in correlation to higher innervations. As was seen in the retinal receptive fields, the peripheries of tissue had contained larger receptive fields (Hartline, 1940). In our test we hypothesized that the finger region will be able to discriminate better than the forearm. This means that they will be much more innervated with neurons than the forearm, and likewise contain smaller receptive fields. This also means that convergence is closer to a 1:1 ratio, and is less the case the farther from the fingers we go. We also think that the amount of convergence is varied with each individual. We will test to see if two people will have different interpretations of these results.
Somatosensory system is a complex sensory system that is made up of different types of sensory receptors. These sensory receptors include thermo-receptors (specialised heat receptors), mechanoreceptors (specialised cells that senses pressure and distortion), chemo- receptors (specialised receptors cells that converts chemical signals in action potential), and photo- rectors (specialised cells that converts light signals in to chemical signals) and so on. In this complex system there are lots of neural mechanisms or physiological mechanisms that regulate behaviour voluntary and involuntary system. In this essay one specific neural mechanism that focuses on neural activity in the central nervous system will be discussed. That is the surround inhibition (centre-surround inhibition). Its functions or rolls, its benefits and its involvements in different parts of the body will be discussed. In addition surround inhibition plays a major role in many disorders and two of them will be discussed in here. That its involvement in focal hand dystonia (FHD) and Schizophrenia disorders.
The mechanoreceptors contain the most types of touch receptors. Free nerve endings inform the brain about pain, and they are located over the entire body. Located in the deep layers of dermis in both hairy and glabrous skin, the pacinian corpuscles detect pressure, telling the brain when a limb has moved. After the brain has told a limb, such as an arm, to move, the pacinian corpuscles tells the brain that that limb has actually moved into the correct position.
Emotion is the “feeling” aspect of consciousness that includes physical, behavioral, and subjective (cognitive) elements. Emotion also contains three elements which are physical arousal, a certain behavior that can reveal outer feelings and inner feelings. One key part in the brain, the amygdala which is located within the limbic system on each side of the brain, plays a key role in emotional processing which causes emotions such as fear and pleasure to be involved with the human facial expressions.The common-sense theory of emotion states that an emotion is experienced first, leading to a physical reaction and then to a behavioral reaction.The James-Lange theory states that a stimulus creates a physiological response that then leads to the labeling of the emotion. The Cannon-Bard theory states that the physiological reaction and the emotion both use the thalamus to send sensory information to both the cortex of the brain and the organs of the sympathetic nervous system. The facial feedback hypothesis states that facial expressions provide feedback to the brain about the emotion being expressed on the face, increasing all the emotions. In Schachter and Singer’s cognitive arousal theory, also known as the two-factor theory, states both the physiological arousal and the actual arousal must occur before the emotion itself is experienced, based on cues from the environment. Lastly, in the cognitive-mediational theory
Interestingly, the same type of brain arousal takes place whether people actually do finger tapping or only imagine it. What surprised Sutton most, however, was the detection of remarkably similar activity in much larger networks spanning areas of the cortex dealing with both input from the senses and output signals to the muscles. "Patterns of activity in small, more primitive areas of the brain are recapitulated in larger, more advanced parts," Sutton says. "This means that nature did not have to develop new rules of operation for different levels of the brain from small clusters of cells to large systems."
Examining the interplay between cognition and peripheral nervous activity is crucial for understanding the individual experience of human emotion. Schachter and Singer (1962) demonstrated that the cognitive attribution made by an individual to explain his or her heightened state of arousal following mimicked excitation of the sympathetic nervous system (SNS) influences the resultant emotional state he or she experiences. Furthermore, previous research has demonstrated that residual excitation from a prior stimulus is open to misattribution to a different source (Cantor, Zillmann, & Bryant, 1975; Rickwood & Price, 1988; White, Fishbein, & Rutstein, 1981; Zillmann, 1971). Informed by these observations, excitation-transfer theory (Zillmann, 1971;
Some past studies have shown that emotion’s influence on cognitive control ability. The relationship between emotion and action has become the major concern to many exercise physiologists. J.Zhu and P.Thagard have argue that emotions contribute significantly to the processes of the action generation as well as action execution and control. Emotion is an underlying factors to interfere before an intention or plan has done that can be realised by muscle-skeleton system. These actions of control are affected unintentionally. For example, your lips tremble while speaking when you are in the state of fear and anxiety or they may shiver with fear before a presentation or interview. Furthermore, pain is also another major factors always associated with these negative emotions.
Simon, J. R. (1969). Reactions towards the source of stimulation. Journal of experimental Psychology, 81, 174-176 .
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