by j.w.gibson, m.s.
Advanced technology in body imaging has greatly increased the ability of researchers and clinicians to investigate cognitive functioning and diagnose brain dysfunctions. Two techniques that are currently enjoying widespread use are Functional Magnetic Resonance Imaging (fMRI) and Positron Emission Tomography (PET). These techniques are in vivo, that is, they do not require invasive intrusion in to the body to study the underlying mechanisms. In vivo techniques are advantageous because they can illuminate cognitive processing while it is happening, giving cognitive scientists a tangible picture of which parts of the brain function to produce certain cognitive activities.
Magnetic Resonance Imaging (MRI) has been used for more than fifteen years to analyze the soft tissue of the human body (Noll, 2001). MRI is an imaging technique that uses the property of Nuclear Magnetic Resonance (NMR) to differentiate between atomic nuclei with different magnetic properties (Ugurbil, 2001). Some types of atoms have nuclei that have an odd number of neutrons, odd number of protons, or perhaps both, which leads to a "net magnetic moment and will therefore be NMR active" (Noll, 2001). Hydrogen1 or simply a proton, is the most common type of nuclei used for NMR because of its high concentration in the human body (Noll, 2001). When these nuclei are subjected to a magnetic field they will align themselves parallel or anti-parallel to the static magnetic field (Ugurbil, 2001). Electromagnetic radiation is used to create discrete resonances in different chemical nuclei (Ugurbil, 2001). Imaging is then performed by assigning specific spatial encoding and contrast mechanisms to the resonance information (Noll, 2001). Colors or gray-scale coding are used to create a visual image of different tissue based on resonation differences.
Functional MRI (fMRI) is the application of MRI technology to investigate the physiologic changes that occur in brain tissue. For instance, fMRI is able to measure changes in "phosphorus metabolism and metabolic byproducts, blood flow, blood volume, and blood oxygenation" (Noll, 2001). Blood oxygen level dependent (BOLD) contrast is the most frequently used technique. Hemoglobin that is oxygenated has different magnetic properties than hemoglobin that has been deoxygenated by the metabolic processes of the cells. Since neural processing requires the use of neural cells, which in turn use oxygen, it is possible to identify which parts of the brain are more active during a specific cognitive task. However, the differences between magnetic resonances are typically so small that it is necessary to perform numerous trials and then subtract out the difference from the control and experimental data (Noll, 2001). Only then is there enough statistical difference to be superimposed onto brain images thus highlighting activated brain structures (Noll, 2001; Ugurbil, 2001).
Researchers have used fMRI to study a wide range of cognitive processing including the fundamental layout and relationship of brain structures during normal processing (Salvador et al., 2005) to dysfunctional processing (Pantano et al., 2005). However, most studies using fMRI do not utilize multivariate methods for analysis and so may not be realizing the full potential of fMRI data (Friman, Cedefamn, Lundberg, Borga, & Knutsson, 2001). New methods for detecting neural activity are constantly being developed, such as the Canonical Correlation Analysis (CCA) suggested by Friman et al. (2001). It is clear that MRI and especially fMRI have enormous potential as an investigative and diagnostic tool.
Positron Emission Tomography (PET) is an imaging technique that utilizes the properties of annihilation radiation that occurs when positrons are absorbed into matter (Riachle, 2001). Subjects are injected with a radioactive substance, called a radiotracer, which then flows through the heart and eventually to the brain. The decay of positrons produces gamma rays that can then be detected by machines. The patterns of gamma rays provides data, which is then processed by algorithm, to create an image (Montandon & Zaidi, 2002). Because PET relies on regional cerebral blood flow (rCBF), it is understood that more active areas of the brain will require more rCBF and thus have greater concentrations of the radiotracer. In the early days of PET it was realized that while both blood flow and metabolism could be accurately measured, blood flow provided a greater practical advantage because of it could be measured in less than a minute, and with a widely available radiopharmaceutical (H215O) (Riachle, 2001).
Researchers typically use a subtractive methodology for the measurement of thought processes. That is, they take a base measurement, for instance, how long it takes to respond to a light, and then subtract the difference in response times for responding to a particular color of light (Riachle, 2001). Using this same technique, researchers have been aided in the studying the relationship between certain types of brain disorders. For example, low serotonergic activity seems to be related to both Borderline Personality Disorder (BPD) and Major Depressive Disorder (MDD) (Oquendo et al., 2005). PET technology has helped researchers to demonstrate that both BPD and MDD are associated with unusual activity in the parietotemporal and anterior cingulate cortical regions (Oquendo et al., 2005).
References
Barlow, H. (2001). Cerebral cortex. In R. A. Wilson & F. C. Keil (Eds.), The MIT encyclopedia of the cognitive sciences (pp. 111-113). Cambridge, MA: The MIT Press.
Bloom, H. (2000). Global brain: The evolution of mass mind from the big band to the 21 century. New York: John Wiley & Sons, Inc.
Carlson, N. R. (2004). Physiology of behavior (8th ed.). Boston; MA: Pearson Education, Inc.
Eliassen, J. C., Baynes, K., & Gazzaniga, M. S. (2000). Anterior and posterior callosal contributions to simultaneous bimanual movements of the hands and fingers. Brain, 123(12), 2501-2511.
Friman, O., Cedefamn, J., Lundberg, P., Borga, M., & Knutsson, H. (2001). Detection of neural activity in functional MRI using canonical correlation analysis. Magnetic Resonance in Medicine, 45, 323-330.
Gandhi, S. P., & Stevens, C. F. (2003). Three modes of synaptic vesicular recycling revealed by single-vesicle imaging. Nature, 423, 607-613.
Gazzaniga, M. S. (1995). Principals of human brain organization derived from split-brain studies. Neuron, 14, 217-228.
Gazzaniga, M. S. (2002). The split-brain revisited. Retrieved September 1, 2006, from http://people.brandeis.edu/~teuber/splitbrain.pdf
Green, R., Clark, A., Hickey, W., Hutsler, J., & Gazzaniga, M. S. (1999). Braincutting for psychiatrists: The time is ripe. The Journal of Neuropsychiatry and Clinical Neuroscience, 11(3), 301-306.
Humphrys, M. (1997). AI is possible . .but AI won't happen: The future of artificial intelligence. Retrieved September 11, 2006, from http://www.computing.dcu.ie/~humphrys/newsci.html
Kalat, J. W. (2001). Biological psychology (7th ed.). Belmont, CA: Wadsworth/Thomson Learning.
Koch, C. (2004). The quest for consciousness: A neurobiological approach. Englewood: CO: Roberts and Company Publishers.
Montandon, M.-L., & Zaidi, H. (2002). Perspectives in quantitative brain positron emission tomography imaging. Business Briefing: Global Healthcare(3), 2-4.
Mycek, M. J., Harvey, R. A., & Champe, P. C. (Eds.). (2000). Pharmacology (2nd ed.). Philadelphia: Lippincott Williams & Wilkins.
Noll, D. C. (2001). A primer on MRI and functional MRI. Retrieved September 13, 2006, from http://www.eecs.umich.edu/~dnoll/primer2.pdf#search=%22a%20primer%20on%20MRI%20and%20functional%20MRI%22
Oquendo, M. A., Krunic, A., Parsey, R., Milak, M., Malone, K. M., Anderson, A., et al. (2005). Positron emission tomography of regional brain metabolic responses to a serotonergic challenge in major depressive disorder with and without borderline personality disorder. Neuropsychopharmacology, 30, 1163-1172.
Pantano, P., Mainero, C., Lenzi, D., Caramia, F., Iannetti, G. D., Piattella, M. C., et al. (2005). A longitudinal fMRI study on motor activity in patients with multiple sclerosis. Brain, 128(2146-2153).
Pinker, S. (1997). How the mind works. New York: W.W. Norton & Company.
Riachle, M. (2001). Positron emission tomography. In R. A. Wilson & F. C. Keil (Eds.), The MIT Encyclopedia of the Cognitive Sciences (pp. 656-659). Cambridge, MA: The MIT Press.
Rosenzweig, M. R., Leiman, A. L., & Breedlove, S. M. (1999). Biological psychology: An introduction to behavioral, cognitive, and clinical neuroscience (2nd ed.). Sunderland, MA: Sinauer Associates.
Salvador, R., Suckling, J., Coleman, M. R., Pickard, J. D., Menon, D., & Bullmore, E. (2005). Neurophysiological architecture of functional magnetic resonance images of human brain. Cerebral Cortex, 15, 1332-1342.
Shepard, G. (2001). Neuron. In R. A. Wilson & F. C. Keil (Eds.), The MIT encyclopedia of the cognitive sciences (pp. 603-604). Cambridge: MA: The MIT Press.
Sperry, R. W. (1964). The great cerebral commissure. Scientific American, 210(1), 42-52.
Sternberg, R. J. (2003). Cognitive psychology (3rd ed.). Belmont, CA: Wadsworth/Thompson Learning.
Ugurbil, K. (2001). Magnetic resonance imaging. In R. A. Wilson & F. C. Keil (Eds.), The MIT Encyclopedia of the Cognitive Sciences (pp. 505-507). Cambridge, MA: The MIT Press.
Wills, T. A., DuHamel, K., & Vaccaro, D. (1995). Activity and mood temperament as predictors of adolescent substance use: Test of a self-regulation mediational model. Journal of Personality and Social Psychology, 68(5), 901-916.
Showing posts with label Biopsychology. Show all posts
Showing posts with label Biopsychology. Show all posts
Tuesday, February 16, 2010
Analysis of a Split-Brain Drawing Task with Both Right and Left Hands
by j.w.gibson, ms
A procedure to help alleviate seizures associated with severe epilepsy is to surgically sever the corpus callosum. The corpus callosum is a large bundle of nerves that connects corresponding parts of the brain to each other (Carlson, 2004). It allows for the brain to send messages back and forth between the right and left hemispheres. Patients suffering from severe epilepsy may suffer from seizures that occur numerous times in a day. Researchers have found that severing the corpus callosum drastically decreases the frequency and intensity of epileptic seizures since the different hemispheres of the brain are no longer able to transfer excessive electrical energy.
Lateralization of brain functioning has been known for quite some time. In 1826, a French doctor named Marc Dax noted that more than 40 of his patients suffering from loss of speech consistently had damage to the left side of the brain (Sternberg, 2003). It is now well supported that the left and right hemispheres are indeed specialized for different types of neural processing, and indeed in some respects can be considered as separate brains (Sternberg, 2003). Both hemispheres of the brain receive sensory information from the opposite side of the body. They share this information via the corpus callosum so that each knows what the other is "perceiving and doing" (Carlson, 2004). Extensive research of Sperry (Sperry, 1964) and Gazzaniga (Gazzaniga, 1995), among others has lead to a strong argument for hemispheric specialization.
The left hemisphere contains language processing while the right hemisphere seems to be dominant for spatial visualization (Green, Clark, Hickey, Hutsler, & Gazzaniga, 1999; Kalat, 2001; Rosenzweig, Leiman, & Breedlove, 1999; Sternberg, 2003; Wills, DuHamel, & Vaccaro, 1995). In addition to language processing, the left hemisphere is also important for smooth skilled movement (Gazzaniga, 1995). Researchers have found that while the right is far superior in terms of spatial processing, it does have some limited ability to comprehend verbal instructions; however, it is wholly incapable of producing speech (Carlson, 2004; Eliassen, Baynes, & Gazzaniga, 2000).
Cutting the corpus callosum leads to some interesting behaviors. Because the two hemispheres are incapable of communicating with each other, split-brain patients have noted that their left-hand seems to act on its own. For instance, "patients may find themselves putting down a book held in the left hand, even if they have been reading it with great interest. This conflict occurs because the right hemisphere, which controls the left hand, cannot read and therefore fids the book boring" (Carlson, 2004). The left-hemisphere receives sensory information from the right side, and vice versa. Because sensory information is processed on the opposite site, split-brain patients are not able to access certain types of information when asked to recall. An exception to this rule of crossed representation is olfaction.
Olfaction occurs on the same side of the brain that the nostril resides. Therefore, a scent detected in the right nostril is processed on the right side of the brain. When split-brain patients are asked to identify the odor of something presented to their left-hemisphere, there are able to name it. However, when the odor is presented to the right side they are unable to find the word, but they are able to physically find an object that represents the odor (Kalat, 2001; Rosenzweig, Leiman, & Breedlove, 1999).
When split-brain patients try to replicate drawings from pairs of words presented to different hemispheres there is no integration of the concepts. For instance, Kingstone and Gazzaniga conducted an experiment where they flashed two words "Bow" and "Arrow" to different hemispheres. They then asked the participant to draw what they had seen and surprisingly the participant drew a bow and arrow, leading the researchers to believe that the concepts had been integrated (Gazzaniga, 2002). However, upon further tasks with different word pairs (sky, scraper) the participants obviously did not integrate the concept into skyscraper, but instead drew a "comb-like scraper" with a sky above (Gazzaniga, 2002). Thus split-brain patients are not capable of integrating both hemispheres knowledge about visual information to make a unified concept or representation. Instead, it is as if the two hemispheres are unaware of each other's processing.
Split-brain patients cannot access the lexiconal information of words that reside in the left-hemisphere when information requiring this type of information is presented to the right-hemisphere. While the right side is capable of some language processing such as matching words to pictures, performing spelling and rhyming tasks, and categorizing objects, it is incapable of syntactical meaning, and indeed most people's right hemispheres "cannot handle even the most rudimentary language" (Gazzaniga, 2002).
If a patient was presented with a three-dimensional object to draw they would be successful with the left hand yet not the right. This is because of the contralateral wiring of the brain. Visual-spatial processing resides in the right-hemisphere, which controls the left hand. Without the corpus callosum intact, there exists virtually no communication or transfer of information from one hemisphere to the other. The right hand, which is controlled by the left-hemisphere, has no knowledge of the 3-dimensional object therefore it cannot replicate it. If instead the object was translated into a word such as "cube" the left side could process this language information and instruct the right hand to represent the three-dimensional object.
References
References
Barlow, H. (2001). Cerebral cortex. In R. A. Wilson & F. C. Keil (Eds.), The MIT encyclopedia of the cognitive sciences (pp. 111-113). Cambridge, MA: The MIT Press.
Bloom, H. (2000). Global brain: The evolution of mass mind from the big band to the 21 century. New York: John Wiley & Sons, Inc.
Carlson, N. R. (2004). Physiology of behavior (8th ed.). Boston; MA: Pearson Education, Inc.
Eliassen, J. C., Baynes, K., & Gazzaniga, M. S. (2000). Anterior and posterior callosal contributions to simultaneous bimanual movements of the hands and fingers. Brain, 123(12), 2501-2511.
Friman, O., Cedefamn, J., Lundberg, P., Borga, M., & Knutsson, H. (2001). Detection of neural activity in functional MRI using canonical correlation analysis. Magnetic Resonance in Medicine, 45, 323-330.
Gandhi, S. P., & Stevens, C. F. (2003). Three modes of synaptic vesicular recycling revealed by single-vesicle imaging. Nature, 423, 607-613.
Gazzaniga, M. S. (1995). Principals of human brain organization derived from split-brain studies. Neuron, 14, 217-228.
Gazzaniga, M. S. (2002). The split-brain revisited. Retrieved September 1, 2006, from http://people.brandeis.edu/~teuber/splitbrain.pdf
Green, R., Clark, A., Hickey, W., Hutsler, J., & Gazzaniga, M. S. (1999). Braincutting for psychiatrists: The time is ripe. The Journal of Neuropsychiatry and Clinical Neuroscience, 11(3), 301-306.
Humphrys, M. (1997). AI is possible . .but AI won't happen: The future of artificial intelligence. Retrieved September 11, 2006, from http://www.computing.dcu.ie/~humphrys/newsci.html
Kalat, J. W. (2001). Biological psychology (7th ed.). Belmont, CA: Wadsworth/Thomson Learning.
Koch, C. (2004). The quest for consciousness: A neurobiological approach. Englewood: CO: Roberts and Company Publishers.
Montandon, M.-L., & Zaidi, H. (2002). Perspectives in quantitative brain positron emission tomography imaging. Business Briefing: Global Healthcare(3), 2-4.
Mycek, M. J., Harvey, R. A., & Champe, P. C. (Eds.). (2000). Pharmacology (2nd ed.). Philadelphia: Lippincott Williams & Wilkins.
Noll, D. C. (2001). A primer on MRI and functional MRI. Retrieved September 13, 2006, from http://www.eecs.umich.edu/~dnoll/primer2.pdf#search=%22a%20primer%20on%20MRI%20and%20functional%20MRI%22
Oquendo, M. A., Krunic, A., Parsey, R., Milak, M., Malone, K. M., Anderson, A., et al. (2005). Positron emission tomography of regional brain metabolic responses to a serotonergic challenge in major depressive disorder with and without borderline personality disorder. Neuropsychopharmacology, 30, 1163-1172.
Pantano, P., Mainero, C., Lenzi, D., Caramia, F., Iannetti, G. D., Piattella, M. C., et al. (2005). A longitudinal fMRI study on motor activity in patients with multiple sclerosis. Brain, 128(2146-2153).
Pinker, S. (1997). How the mind works. New York: W.W. Norton & Company.
Riachle, M. (2001). Positron emission tomography. In R. A. Wilson & F. C. Keil (Eds.), The MIT Encyclopedia of the Cognitive Sciences (pp. 656-659). Cambridge, MA: The MIT Press.
Rosenzweig, M. R., Leiman, A. L., & Breedlove, S. M. (1999). Biological psychology: An introduction to behavioral, cognitive, and clinical neuroscience (2nd ed.). Sunderland, MA: Sinauer Associates.
Salvador, R., Suckling, J., Coleman, M. R., Pickard, J. D., Menon, D., & Bullmore, E. (2005). Neurophysiological architecture of functional magnetic resonance images of human brain. Cerebral Cortex, 15, 1332-1342.
Shepard, G. (2001). Neuron. In R. A. Wilson & F. C. Keil (Eds.), The MIT encyclopedia of the cognitive sciences (pp. 603-604). Cambridge: MA: The MIT Press.
Sperry, R. W. (1964). The great cerebral commissure. Scientific American, 210(1), 42-52.
Sternberg, R. J. (2003). Cognitive psychology (3rd ed.). Belmont, CA: Wadsworth/Thompson Learning.
Ugurbil, K. (2001). Magnetic resonance imaging. In R. A. Wilson & F. C. Keil (Eds.), The MIT Encyclopedia of the Cognitive Sciences (pp. 505-507). Cambridge, MA: The MIT Press.
Wills, T. A., DuHamel, K., & Vaccaro, D. (1995). Activity and mood temperament as predictors of adolescent substance use: Test of a self-regulation mediational model. Journal of Personality and Social Psychology, 68(5), 901-916.
A procedure to help alleviate seizures associated with severe epilepsy is to surgically sever the corpus callosum. The corpus callosum is a large bundle of nerves that connects corresponding parts of the brain to each other (Carlson, 2004). It allows for the brain to send messages back and forth between the right and left hemispheres. Patients suffering from severe epilepsy may suffer from seizures that occur numerous times in a day. Researchers have found that severing the corpus callosum drastically decreases the frequency and intensity of epileptic seizures since the different hemispheres of the brain are no longer able to transfer excessive electrical energy.
Lateralization of brain functioning has been known for quite some time. In 1826, a French doctor named Marc Dax noted that more than 40 of his patients suffering from loss of speech consistently had damage to the left side of the brain (Sternberg, 2003). It is now well supported that the left and right hemispheres are indeed specialized for different types of neural processing, and indeed in some respects can be considered as separate brains (Sternberg, 2003). Both hemispheres of the brain receive sensory information from the opposite side of the body. They share this information via the corpus callosum so that each knows what the other is "perceiving and doing" (Carlson, 2004). Extensive research of Sperry (Sperry, 1964) and Gazzaniga (Gazzaniga, 1995), among others has lead to a strong argument for hemispheric specialization.
The left hemisphere contains language processing while the right hemisphere seems to be dominant for spatial visualization (Green, Clark, Hickey, Hutsler, & Gazzaniga, 1999; Kalat, 2001; Rosenzweig, Leiman, & Breedlove, 1999; Sternberg, 2003; Wills, DuHamel, & Vaccaro, 1995). In addition to language processing, the left hemisphere is also important for smooth skilled movement (Gazzaniga, 1995). Researchers have found that while the right is far superior in terms of spatial processing, it does have some limited ability to comprehend verbal instructions; however, it is wholly incapable of producing speech (Carlson, 2004; Eliassen, Baynes, & Gazzaniga, 2000).
Cutting the corpus callosum leads to some interesting behaviors. Because the two hemispheres are incapable of communicating with each other, split-brain patients have noted that their left-hand seems to act on its own. For instance, "patients may find themselves putting down a book held in the left hand, even if they have been reading it with great interest. This conflict occurs because the right hemisphere, which controls the left hand, cannot read and therefore fids the book boring" (Carlson, 2004). The left-hemisphere receives sensory information from the right side, and vice versa. Because sensory information is processed on the opposite site, split-brain patients are not able to access certain types of information when asked to recall. An exception to this rule of crossed representation is olfaction.
Olfaction occurs on the same side of the brain that the nostril resides. Therefore, a scent detected in the right nostril is processed on the right side of the brain. When split-brain patients are asked to identify the odor of something presented to their left-hemisphere, there are able to name it. However, when the odor is presented to the right side they are unable to find the word, but they are able to physically find an object that represents the odor (Kalat, 2001; Rosenzweig, Leiman, & Breedlove, 1999).
When split-brain patients try to replicate drawings from pairs of words presented to different hemispheres there is no integration of the concepts. For instance, Kingstone and Gazzaniga conducted an experiment where they flashed two words "Bow" and "Arrow" to different hemispheres. They then asked the participant to draw what they had seen and surprisingly the participant drew a bow and arrow, leading the researchers to believe that the concepts had been integrated (Gazzaniga, 2002). However, upon further tasks with different word pairs (sky, scraper) the participants obviously did not integrate the concept into skyscraper, but instead drew a "comb-like scraper" with a sky above (Gazzaniga, 2002). Thus split-brain patients are not capable of integrating both hemispheres knowledge about visual information to make a unified concept or representation. Instead, it is as if the two hemispheres are unaware of each other's processing.
Split-brain patients cannot access the lexiconal information of words that reside in the left-hemisphere when information requiring this type of information is presented to the right-hemisphere. While the right side is capable of some language processing such as matching words to pictures, performing spelling and rhyming tasks, and categorizing objects, it is incapable of syntactical meaning, and indeed most people's right hemispheres "cannot handle even the most rudimentary language" (Gazzaniga, 2002).
If a patient was presented with a three-dimensional object to draw they would be successful with the left hand yet not the right. This is because of the contralateral wiring of the brain. Visual-spatial processing resides in the right-hemisphere, which controls the left hand. Without the corpus callosum intact, there exists virtually no communication or transfer of information from one hemisphere to the other. The right hand, which is controlled by the left-hemisphere, has no knowledge of the 3-dimensional object therefore it cannot replicate it. If instead the object was translated into a word such as "cube" the left side could process this language information and instruct the right hand to represent the three-dimensional object.
References
References
Barlow, H. (2001). Cerebral cortex. In R. A. Wilson & F. C. Keil (Eds.), The MIT encyclopedia of the cognitive sciences (pp. 111-113). Cambridge, MA: The MIT Press.
Bloom, H. (2000). Global brain: The evolution of mass mind from the big band to the 21 century. New York: John Wiley & Sons, Inc.
Carlson, N. R. (2004). Physiology of behavior (8th ed.). Boston; MA: Pearson Education, Inc.
Eliassen, J. C., Baynes, K., & Gazzaniga, M. S. (2000). Anterior and posterior callosal contributions to simultaneous bimanual movements of the hands and fingers. Brain, 123(12), 2501-2511.
Friman, O., Cedefamn, J., Lundberg, P., Borga, M., & Knutsson, H. (2001). Detection of neural activity in functional MRI using canonical correlation analysis. Magnetic Resonance in Medicine, 45, 323-330.
Gandhi, S. P., & Stevens, C. F. (2003). Three modes of synaptic vesicular recycling revealed by single-vesicle imaging. Nature, 423, 607-613.
Gazzaniga, M. S. (1995). Principals of human brain organization derived from split-brain studies. Neuron, 14, 217-228.
Gazzaniga, M. S. (2002). The split-brain revisited. Retrieved September 1, 2006, from http://people.brandeis.edu/~teuber/splitbrain.pdf
Green, R., Clark, A., Hickey, W., Hutsler, J., & Gazzaniga, M. S. (1999). Braincutting for psychiatrists: The time is ripe. The Journal of Neuropsychiatry and Clinical Neuroscience, 11(3), 301-306.
Humphrys, M. (1997). AI is possible . .but AI won't happen: The future of artificial intelligence. Retrieved September 11, 2006, from http://www.computing.dcu.ie/~humphrys/newsci.html
Kalat, J. W. (2001). Biological psychology (7th ed.). Belmont, CA: Wadsworth/Thomson Learning.
Koch, C. (2004). The quest for consciousness: A neurobiological approach. Englewood: CO: Roberts and Company Publishers.
Montandon, M.-L., & Zaidi, H. (2002). Perspectives in quantitative brain positron emission tomography imaging. Business Briefing: Global Healthcare(3), 2-4.
Mycek, M. J., Harvey, R. A., & Champe, P. C. (Eds.). (2000). Pharmacology (2nd ed.). Philadelphia: Lippincott Williams & Wilkins.
Noll, D. C. (2001). A primer on MRI and functional MRI. Retrieved September 13, 2006, from http://www.eecs.umich.edu/~dnoll/primer2.pdf#search=%22a%20primer%20on%20MRI%20and%20functional%20MRI%22
Oquendo, M. A., Krunic, A., Parsey, R., Milak, M., Malone, K. M., Anderson, A., et al. (2005). Positron emission tomography of regional brain metabolic responses to a serotonergic challenge in major depressive disorder with and without borderline personality disorder. Neuropsychopharmacology, 30, 1163-1172.
Pantano, P., Mainero, C., Lenzi, D., Caramia, F., Iannetti, G. D., Piattella, M. C., et al. (2005). A longitudinal fMRI study on motor activity in patients with multiple sclerosis. Brain, 128(2146-2153).
Pinker, S. (1997). How the mind works. New York: W.W. Norton & Company.
Riachle, M. (2001). Positron emission tomography. In R. A. Wilson & F. C. Keil (Eds.), The MIT Encyclopedia of the Cognitive Sciences (pp. 656-659). Cambridge, MA: The MIT Press.
Rosenzweig, M. R., Leiman, A. L., & Breedlove, S. M. (1999). Biological psychology: An introduction to behavioral, cognitive, and clinical neuroscience (2nd ed.). Sunderland, MA: Sinauer Associates.
Salvador, R., Suckling, J., Coleman, M. R., Pickard, J. D., Menon, D., & Bullmore, E. (2005). Neurophysiological architecture of functional magnetic resonance images of human brain. Cerebral Cortex, 15, 1332-1342.
Shepard, G. (2001). Neuron. In R. A. Wilson & F. C. Keil (Eds.), The MIT encyclopedia of the cognitive sciences (pp. 603-604). Cambridge: MA: The MIT Press.
Sperry, R. W. (1964). The great cerebral commissure. Scientific American, 210(1), 42-52.
Sternberg, R. J. (2003). Cognitive psychology (3rd ed.). Belmont, CA: Wadsworth/Thompson Learning.
Ugurbil, K. (2001). Magnetic resonance imaging. In R. A. Wilson & F. C. Keil (Eds.), The MIT Encyclopedia of the Cognitive Sciences (pp. 505-507). Cambridge, MA: The MIT Press.
Wills, T. A., DuHamel, K., & Vaccaro, D. (1995). Activity and mood temperament as predictors of adolescent substance use: Test of a self-regulation mediational model. Journal of Personality and Social Psychology, 68(5), 901-916.
How Neurons Communicate
How Neurons Communicate
Anatomy of the Neuron
The human body can be described on many levels. Macroscopic descriptions would focus on how our organ systems, such as our skin, heart, intestines, lungs, and others, work together to accomplish a specific task. As we descend to the microscopic level, we see how different tissues make up individual organs, and how those tissues themselves are made up of dense assemblages of cells. In the body, the cell is the central unit for biological study. Schwann first proposed the cell theory in 1839, which, stated that, "all body organs and tissues are composed of individual cells" (Shepard, 2001). Psychology owes a huge debt of gratitude to neurology and developmental biology for the amount of information that has been gained concerning the exact processes and structures of the cell.
The neuron is the cell of the nervous system and brain. Neurons are different then the other cells of the body in numerous ways, but it is their information-processing and transmitting ability (Carlson, 2004) that enables consciousness, communication, and indeed life to progress at all. Like other specialized cells of the body, neurons perform numerous tasks. Therefore they come in variegated shapes and sizes depending upon their function (Kalat, 2001). Neurons share the same basic structure; this includes the (1) cell body, otherwise known as the soma; (2) dendrites, (3) axons, and (4) terminal buttons (Carlson, 2004). Neurons might be described to look like tiny spindly sea stars, arms dangling delicately out in any direction that a connection with another neuron might be found.
The soma is the command center of the cell; it contains the nucleus, which houses the life operations of the cell including the cytoplasm, the mitochondria, the nucleus, the endoplasmic reticulum among other structures. The nucleus directs cell functioning via chemical messengers which pass through the nuclear membrane and deliver different chemical triggers to other parts of the cell (Mycek, Harvey, & Champe, 2000).
The word dendron comes from the Greek word for tree, and the dendrites of a neuron very much resemble branch like forms (Carlson, 2004). Dendrites are long, thin spider web-like structures that branch off from one end of the soma. They are the receivers of messages being sent from other neurons, through the synapse, the small gap between neurons. Axons, look like long slender tubes, that more often than not, are covered by a protective coating called myelin (Koch, 2004). Myelin, which is roughly 80 percent lipid and 20 percent protein, is made by oligodendrocytes (Rosenzweig, Leiman, & Breedlove, 1999), specialized cells that provide support to the axon. The myelin sheath surrounding axons serves to speed up transmission down the axon. The sheath of myelin is not continuous but rather segmented into small sections approximately 1-2 micrometers long with a gap in between the next segment of myelin. This gap is known as the node of Ranvier (Kalat, 2001). The axon is responsible for carrying information from the soma to the terminal buttons.
At the end of the axon are a collection of small branches which end in button-like structures called terminal buttons (Sternberg, 2003). Terminal buttons receive the information from the soma via the axon in the form of an action potential. This causes an electro-chemical change in the terminal button, which then releases certain chemicals into the synaptic gap, signaling other nearby dendrites of the message.
Neurons are typically classified according to the way in which the axons and dendrites are branched out from the soma. Multipolar neurons have numerous dendritic trees yet only one axon; bipolar neurons have only one dendritic tree and axon, while unipolar neurons consist of one axon that splits in two directions, both receiving and sending information to the central nervous system (CNS) (Carlson, 2004).
The Action Potential
On the most basic level in neuroscience is the acknowledgement that the action potential is "the primary means of conveying information rapidly form one neuron to the next" (Koch, 2004). Diffusion is the mechanism by which different molecules of a substance tend to spread out evenly, bouncing off of each other, until they are evenly spaced within a mixture (Carlson, 2004). When electrolytes are dissolved in water they break into component parts, separating into ions. For instance, NaCl (sodium chloride) will break into Na+ and Cl-, where sodium is now a positively charged ion, chlorine a negative charged ion. Because like charges repel each other, sodium ions push away from other sodium ions and chlorine ions push away from other chlorine ions. The net effect of diffusion and ionization of electrolytes in a cell is to create an even distribution of charges. Because the intracellular and extracellular fluid contain different ions, this contributes to the membrane potential, or the difference in electrical charge in and out of a cell (Carlson, 2004; Pinker, 1997). The difference in charge (about 70 millivolts) is caused by a higher concentration of Potassium ions (K+) outside the cell and a higher concentration of both Sodium (Na+) and Chlorine (Cl-) inside the neuron. Because like charged ions have a natural inclination to push away from each other, and diffusion serves to push ions to areas of higher concentration to areas of lower concentration, electrostatic pressure builds up on the membrane of the neuron.
The neural membrane is made up of linked molecules of lipids. This membrane has openings which are controlled by "gates" that allow the transport of different ions into and out of the neuron. Ion channels are controlled by a lock and key mechanism, that is, only certain chemical shapes can fit onto the outer structure of the membrane and thus activate the channel to open. When ion channels are opened, the electrostatic pressure forces ions through the channel causing a depolarization in the neuron. This depolarization of the membrane potential triggers an electric pulse down the neuron, this is known as an action potential (Kalat, 2001). Specific gates in the membrane actively pump out Sodium ions, which results in a low concentration of intracellular sodium. Because the membrane is not permeable to sodium ions (unless the gates are open) there exists a much higher level of Na+ outside the cell than inside. When the neuron is stimulated by an outside event, such as by pain receptors, the gates are opened up and the rush of sodium ions into the cell changes the polarization and thus begins the action potential.
Action potentials generally start in the dendrites spines, although they can begin in the axon itself, and travel through the soma, down the length of the axon. Passage of an action potential through a myelinated axon is achieved by a process called salutatory conduction (Kalat, 2001). Myelinated axons have two distinct advantages over non-myelinated axons. First, the myelin decreases the ability of Na ions to enter the cell since they may only enter a myelinated axon at the node of Ranvier. This means that the cell spends less energy pumping ions into and out of the axon (Carlson, 2004). Secondly, myelin speeds up the rate of transmission, reaching speeds of up to 100 meters per second (Sternberg, 2003).
When the signal finally reaches the terminal button, synaptic vesicles bind themselves to calcium channels on the synaptic membrane (Rosenzweig, Leiman, & Breedlove, 1999) causing their contents, neurotransmitters, to be released through the membrane into the synaptic cleft. These neurotransmitters travel small distances to the postsynaptic neuron where they dock with specific receptor sites and then trigger other ion channels to open, leading to yet another action potential. After some molecules of the neurotransmitters have docked to the postsynaptic neuron, a process of reuptake pulls back leftover chemicals into the cytoplasm of the terminal button for reuse (Carlson, 2004).
Released neurotransmitters can produce either excitory or inhibitory responses which lead to depolarizations (EPSPs) or hyperpolarizations (IPSPs) (Carlson, 2004). The specific combinations of EPSPs and IPSPs that occur thus determine the firing rate of neurons. Neurons communicate through a process of chemical and electrical changes. When the action potential (electrical) reaches the terminal button it activates channels that are voltage dependent. These channels open to release Calcium ions, which are able to bind to the synaptic vesicles and thus allow them to break open, spilling their contents into the synaptic cleft. Neurotransmitters then bind to sites on the postsynaptic membrane causing the opening of ion channels, which then cause another depolarization or hyperpolarization depending upon which ion channels are opened. The presynaptic neuron then releases molecules that retrieve left over neurotransmitters and return them to the cytoplasm for recycling (Gandhi & Stevens, 2003), this process normally prevents the re-stimulation of an action potential when the postsynaptic neuron resets. Other chemicals such as peptides, neuromodulators, and hormones can also trigger action potentials by proxy of second messengers (Mycek, Harvey, & Champe, 2000).
By j.w.gibson copyright 2006
References
Anatomy of the Neuron
The human body can be described on many levels. Macroscopic descriptions would focus on how our organ systems, such as our skin, heart, intestines, lungs, and others, work together to accomplish a specific task. As we descend to the microscopic level, we see how different tissues make up individual organs, and how those tissues themselves are made up of dense assemblages of cells. In the body, the cell is the central unit for biological study. Schwann first proposed the cell theory in 1839, which, stated that, "all body organs and tissues are composed of individual cells" (Shepard, 2001). Psychology owes a huge debt of gratitude to neurology and developmental biology for the amount of information that has been gained concerning the exact processes and structures of the cell.
The neuron is the cell of the nervous system and brain. Neurons are different then the other cells of the body in numerous ways, but it is their information-processing and transmitting ability (Carlson, 2004) that enables consciousness, communication, and indeed life to progress at all. Like other specialized cells of the body, neurons perform numerous tasks. Therefore they come in variegated shapes and sizes depending upon their function (Kalat, 2001). Neurons share the same basic structure; this includes the (1) cell body, otherwise known as the soma; (2) dendrites, (3) axons, and (4) terminal buttons (Carlson, 2004). Neurons might be described to look like tiny spindly sea stars, arms dangling delicately out in any direction that a connection with another neuron might be found.
The soma is the command center of the cell; it contains the nucleus, which houses the life operations of the cell including the cytoplasm, the mitochondria, the nucleus, the endoplasmic reticulum among other structures. The nucleus directs cell functioning via chemical messengers which pass through the nuclear membrane and deliver different chemical triggers to other parts of the cell (Mycek, Harvey, & Champe, 2000).
The word dendron comes from the Greek word for tree, and the dendrites of a neuron very much resemble branch like forms (Carlson, 2004). Dendrites are long, thin spider web-like structures that branch off from one end of the soma. They are the receivers of messages being sent from other neurons, through the synapse, the small gap between neurons. Axons, look like long slender tubes, that more often than not, are covered by a protective coating called myelin (Koch, 2004). Myelin, which is roughly 80 percent lipid and 20 percent protein, is made by oligodendrocytes (Rosenzweig, Leiman, & Breedlove, 1999), specialized cells that provide support to the axon. The myelin sheath surrounding axons serves to speed up transmission down the axon. The sheath of myelin is not continuous but rather segmented into small sections approximately 1-2 micrometers long with a gap in between the next segment of myelin. This gap is known as the node of Ranvier (Kalat, 2001). The axon is responsible for carrying information from the soma to the terminal buttons.
At the end of the axon are a collection of small branches which end in button-like structures called terminal buttons (Sternberg, 2003). Terminal buttons receive the information from the soma via the axon in the form of an action potential. This causes an electro-chemical change in the terminal button, which then releases certain chemicals into the synaptic gap, signaling other nearby dendrites of the message.
Neurons are typically classified according to the way in which the axons and dendrites are branched out from the soma. Multipolar neurons have numerous dendritic trees yet only one axon; bipolar neurons have only one dendritic tree and axon, while unipolar neurons consist of one axon that splits in two directions, both receiving and sending information to the central nervous system (CNS) (Carlson, 2004).
The Action Potential
On the most basic level in neuroscience is the acknowledgement that the action potential is "the primary means of conveying information rapidly form one neuron to the next" (Koch, 2004). Diffusion is the mechanism by which different molecules of a substance tend to spread out evenly, bouncing off of each other, until they are evenly spaced within a mixture (Carlson, 2004). When electrolytes are dissolved in water they break into component parts, separating into ions. For instance, NaCl (sodium chloride) will break into Na+ and Cl-, where sodium is now a positively charged ion, chlorine a negative charged ion. Because like charges repel each other, sodium ions push away from other sodium ions and chlorine ions push away from other chlorine ions. The net effect of diffusion and ionization of electrolytes in a cell is to create an even distribution of charges. Because the intracellular and extracellular fluid contain different ions, this contributes to the membrane potential, or the difference in electrical charge in and out of a cell (Carlson, 2004; Pinker, 1997). The difference in charge (about 70 millivolts) is caused by a higher concentration of Potassium ions (K+) outside the cell and a higher concentration of both Sodium (Na+) and Chlorine (Cl-) inside the neuron. Because like charged ions have a natural inclination to push away from each other, and diffusion serves to push ions to areas of higher concentration to areas of lower concentration, electrostatic pressure builds up on the membrane of the neuron.
The neural membrane is made up of linked molecules of lipids. This membrane has openings which are controlled by "gates" that allow the transport of different ions into and out of the neuron. Ion channels are controlled by a lock and key mechanism, that is, only certain chemical shapes can fit onto the outer structure of the membrane and thus activate the channel to open. When ion channels are opened, the electrostatic pressure forces ions through the channel causing a depolarization in the neuron. This depolarization of the membrane potential triggers an electric pulse down the neuron, this is known as an action potential (Kalat, 2001). Specific gates in the membrane actively pump out Sodium ions, which results in a low concentration of intracellular sodium. Because the membrane is not permeable to sodium ions (unless the gates are open) there exists a much higher level of Na+ outside the cell than inside. When the neuron is stimulated by an outside event, such as by pain receptors, the gates are opened up and the rush of sodium ions into the cell changes the polarization and thus begins the action potential.
Action potentials generally start in the dendrites spines, although they can begin in the axon itself, and travel through the soma, down the length of the axon. Passage of an action potential through a myelinated axon is achieved by a process called salutatory conduction (Kalat, 2001). Myelinated axons have two distinct advantages over non-myelinated axons. First, the myelin decreases the ability of Na ions to enter the cell since they may only enter a myelinated axon at the node of Ranvier. This means that the cell spends less energy pumping ions into and out of the axon (Carlson, 2004). Secondly, myelin speeds up the rate of transmission, reaching speeds of up to 100 meters per second (Sternberg, 2003).
When the signal finally reaches the terminal button, synaptic vesicles bind themselves to calcium channels on the synaptic membrane (Rosenzweig, Leiman, & Breedlove, 1999) causing their contents, neurotransmitters, to be released through the membrane into the synaptic cleft. These neurotransmitters travel small distances to the postsynaptic neuron where they dock with specific receptor sites and then trigger other ion channels to open, leading to yet another action potential. After some molecules of the neurotransmitters have docked to the postsynaptic neuron, a process of reuptake pulls back leftover chemicals into the cytoplasm of the terminal button for reuse (Carlson, 2004).
Released neurotransmitters can produce either excitory or inhibitory responses which lead to depolarizations (EPSPs) or hyperpolarizations (IPSPs) (Carlson, 2004). The specific combinations of EPSPs and IPSPs that occur thus determine the firing rate of neurons. Neurons communicate through a process of chemical and electrical changes. When the action potential (electrical) reaches the terminal button it activates channels that are voltage dependent. These channels open to release Calcium ions, which are able to bind to the synaptic vesicles and thus allow them to break open, spilling their contents into the synaptic cleft. Neurotransmitters then bind to sites on the postsynaptic membrane causing the opening of ion channels, which then cause another depolarization or hyperpolarization depending upon which ion channels are opened. The presynaptic neuron then releases molecules that retrieve left over neurotransmitters and return them to the cytoplasm for recycling (Gandhi & Stevens, 2003), this process normally prevents the re-stimulation of an action potential when the postsynaptic neuron resets. Other chemicals such as peptides, neuromodulators, and hormones can also trigger action potentials by proxy of second messengers (Mycek, Harvey, & Champe, 2000).
By j.w.gibson copyright 2006
References
References
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