The brain is one of the central nervous system and is divided into different parts including the cerebellum and cerebrum. It is divided into right and left cerebral hemispheres which have a layer of grey matter on the outer side known as the cerebral cortex. The cerebral cortex of the brain is involved with rational functions and is partitioned by the corpus callout (a thick band of nerve fibers) into two hemispheres. The nerve fibers are responsible for message transfer between the two hemispheres. (McManus, 2006) Meanwhile the left hemisphere is involved with language and sequential and logical processes while the right hemisphere is involved with visual and holistic, random and intuitive processes. According to the 1960s research on the corpus callosum it was established that the hemispheres worked together but specialized in various thinking modes.
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The right hemisphere controls the left side of the body while the left hemisphere controls the right side of the body. These hemispheres have other behaviors that are dominant. The right hemisphere is dominant in face recognition, visual imagery, spatial abilities and music. The left hemisphere is dominant in math, logical abilities and calculations. The organization form across the lateral plane differentiates the right and left hemispheres in the primary cognitive functions localization perspective. The behavioral processing by each respective hemisphere also results to their differences. (Lezak, 1998)The right hemisphere is believed to be more organized than the left hemisphere since the constructional and visuopatial disabilities in people with damage on the right hemisphere doesn’t vary not considering the damage degree.
The brain activity
The brain is involved with many different activities including balance maintenance. The brain activity is determined by various processes including the event related brain potential (ERP).ERP refers to a variety of responses by the brain which inicate time relationships that are stable to anticipated or actual stimuli. It is generated due to specific stimulus response and is a sample average. They are time locked to stimuli which is specific. It has been proven that ERP is dependent on both psychological and physical stimuli characters though they are independent of stimuli that are specific. Endogenous ERPS occur when they are stimulated by internal events. Event related potentials of the brain is classified into motor potential, long latency potentials, sensory ERPs and steady potential shifts(SPS).
The sensory event related potentials include events produced by auditory, visual, olfactory and somato sensory stimuli. Motor potentials are those that head and go together with voluntary movements. According to Vaughan motor potential varies with the speed and strength of the contracting muscles. Long latency potentials are those negative and positive components of event related potentials which happen between 250 and 750 milliseconds after a given event. They indicate subjective responses to unexpected or expected stimuli. A positive component occurring about 300ms after onset is known as P3 while the negative component includes the N400 (N4) and occurs due to unexpected sentences endings and has a relation with semantic deviations. Contingent negative variation (CNV) is an example of the steady potential shift (SPS) that is observed when a warning sign is given before an event. Others include the readiness potential (RP),Bereitshafts potential (BP).
The sources of components and the different kind of ERPs in the brain is under investigation which would aid in the understanding of the different brain parts participation in mental processes and ERP results application in practical clinical situations. The determination of the sources is achieved by activity recording from the cortical and sub cortical regions of the brain which generate the ERPs in human beings and animals.
Asymmetries of hemisphere in ERPs
Stimuli presentation in the right and left visual fields aids in studying the processing differences of the brain by the left and right hemispheres. The right and the left hemisphere produce different event related potential depending on the stimuli. (Andreassi, 2006) After observation it has been shown that the occipital region receiving from the retinal area the primary projections gave out ERPs of large amplitude than the other lobe. The left hemisphere in the right visual field serves as the primary for stimuli while the right hemisphere in the left visual field acts as the primary for stimuli. This occurs since the nasal retina of the left eye and the temporal retina of the right eye are primarily stimulated by objects in left visual field. (ANDREASSI, 1984) The visual impulses from these retinal areas are projected to the right hemisphere while the visual impulses in the right visual field project to the left hemisphere.
However the study of the hemispheric asymmetry by stimulation in different visual fields requires screening of the strabismism because displacement of stimuli from the central visual field doesn’t lead to contra lateral hemisphere. Strabismus refers to imbalance of the two eyes muscles hence the individuals have a problem when focusing on an object. (M, 2007). Auditory stimulation also has an effect on the hemisphere activity. There have been some evidence that indicate that ERP asymmetries have a relation with cognitive and intelligence functioning. Slow potential shifts (SPS) of higher amplitude have been shown to occur to the right hemisphere during spatial task performance. This however was observed in females while in males there were no differences in hemispheric amplitudes. The ability of the right hemisphere to process emotional materials is shown by the engagement of the right hemisphere P3 system by the positive and negative attributes.
Is there a difference between left and right hemisphere with respect to the words and shapes
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