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Concept of lateralisation of function in the brain

Paper Type: Free Essay Subject: Psychology
Wordcount: 1251 words Published: 8th May 2017

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The concept of brain lateralisation is part of the main cerebral asymmetry in the brain. Laterality of function can be affected by environmental factors as much as genetical factors, such as gender, handedness and emotion. Lateralisation is relative however not absolute because both hemispheres play a role in everyday behaviour. The left hemisphere is well known for the construction of language and the right hemisphere is known to have affect on non verbal factors such as imagery. However many researchers have argued this case, especially about language skills and state of emotion.

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The two cerebral hemispheres are connected by the corpus callosum, this is a large band of axons (Hoptman and Davidson 1994). The corpus callosum connects corresponding parts of the left and right hemispheres: the left and right temporal lobes are connected and so are many similar left-right hemispheric functions. Due to the corpus callosum, each region of the association cortex knows what is happening in the corresponding region of the opposite side of the brain. Some people have the corpus callossum surgically cut in order to alleviate the symptoms of epilepsy.

Lateralisation of function is also illustrated and investigated in linguistics. Davidson and Hugdahl (1995) argued that many researchers over simplify the functions of the left and right hemispheres when it came to language. David and Hugdahl supported the fact that the left hemisphere did play a major role on linguistics particularly for speech production and comprehension. However they both found that the right hemisphere is better than the left when it came to comprehending metaphors and may undertake the linguistics of the left hemisphere when taking such tasks. The right hemisphere also appears to be superior to the left at recognising faces, perceiving emotion and mentally rotating three dimensional images in space (Hugdahl 1996).

Lateralisation takes a look at some of the major functional differences between the left and right cerebral hemispheres. Many researchers would suggest that verbal and motor abilities are very apparent in the left hemisphere (Beeman & Chiarello 1998). Reuter-Lorenz & Miller (1998) believed that past research on lateralisation was focused on the left hemispheric abilities and was over simplified. Reuter-Lorenz & Miller and other researchers evaluated that recent research on lateralisation have mainly been focused on uncovering the abilities of the right hemisphere. However some researchers like Brown & Kosslyn (1993) feel that there aren’t many differences between the two. They claimed that many functions use both hemispheres and that when functional differences do exist, they(researchers) tend to be slightly biased in favour of one hemisphere.

The left hemisphere is dominant for controlling ipsilateral movements, Haaland & Harrington (1996) confirmed this type of lateralisation with functional brain-imaging studies. They found that when complex driven movements are made by one hand, most of the activity is observed in the contra lateral hemisphere, as expected by many researchers. Kim et al (1993) found that when observing activations that happens in the ipsilateral hemisphere, the ipsilateral effects tend to be substantially greater in the left hemisphere than the right. Consistent with previous observations is the fact that left-hemisphere lesions are more likely than right hemisphere lesions to be associated with ipsilateral motor problems.

The right hemisphere tends to have superiority in spatial ability. In a classic study done by Levy (1969), she placed a three dimensional block of a particular shape in either the left or right hand of her split brain subjects. After the subjects tactually investigated it, Levy asked them to point to the two dimensional test stimulus that best represented what the three-dimensional block would look like if it were made of cardboard and unfolded. Levy then found that the right hemisphere was dominantly used in the task and that the two hemispheres seemed to go about the task in very different ways. The performance of the left hand and right hemisphere was rapid and silent, whereas the right hand and left hemisphere was resistant and often accompanied by a running verbal commentary and still found the task difficult.

When it came to males and females the brain lateralisation tend to differ from each other McGlone (1977, 1980). McGlone did a study of lateral stroke victims and found that male victims of unilateral strokes were three times more likely to suffer from aphasia than female victims. She also found that male victims of left hemisphere strokes had deficits on the Wechsler Adult Intelligence Scale also known as WAIS verbal subtests, whereas male victims of right-hemisphere strokes had deficits on the WAIS performance subtests. When it came to female victims who suffered the same disorder they had the same deficits on the WAIS regardless of the side of the hemisphere. On the bases of these findings , McGlone evaluated that the brains of male are more lateralised than the ones of females.

McGlone’s hypothesis of sex differences in the brain lateralisation have been embraced widely. It has also been used for behavioural differences between the two. However some researchers have doubted her study. Inglis & Lawson (1982) don’t support it, whereas some functional brain-imaging studies supported by Jaeger et al (1998), Kansaku, Yamaura & Kitazawa (2000) found that there was still a significant difference. They also found that when it came to language related tasks females used both hemispheres more than males.

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The concept of lateralisation was also investigated in emotions. This is also known as inherent mood valence asymmetry. The first aspects of such research emphasises first on differential roles for the two hemispheres regulating positive and negative emotional orientations. Goldstein (1952) and Gainotti (1969, 1972) found that lesions in the dominant hemisphere were associated with a catastrophic (such as anger) reaction while damage to the minor hemisphere was accompanied by an indifference reaction (unawareness). Gainotti proposed that mood changes were secondary to expressive difficulties in left hemisphere aphasic patients, and to unawareness and neglect in the right hemisphere patients.

Such study was also supported by Terzian (1964), Rossi and Rosadini (1967) in which they also evaluated that the left and right hemispheres were seen to exert opposite influences on emotional tone, with the left hemisphere tending towards a positive affect and the right hemisphere biased towards negative affect. This study was also supported by Sackheim et al (1982), the researchers also replicated the study and found in the results that there was more association of pathologic laughing with the right hemisphere lesions and pathologic crying with left hemisphere lesions.

Overall the brain lateralisation have been investigated in many ways and stages, factors such as linguistics, emotion or even speech can differentiate between the hemispheric abilities. John Hughlings Jackson (1874) would argue that there are many differences in the strengths of the cerebral hemispheres. Although such claim is no longer controversial, many researchers have proved that both hemispheres plays an important role in lateralisation.

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