The Role of the Brain in Cognitive Functions

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Scientists have for a long time attempted to explain the mechanism of cognition in the brain. Two schools of thought have existed on this subject. The Phrenology school thought that the various cognitive abilities of the brain and personality traits are controlled by centers located on specific locations of the brain; each relatively independent of the other and controlling its respective function separately; and that damage, either accidental or iatrogenic results in dysfunction of this function only (Sizer, 1888).

This school of thought was largely discredited in the early decades of the twentieth century for not having a credible empirical base. The other school of thought was actually formed as an opposition to the phrenology thesis. This theorized that higher cognitive functions are localized in the cerebral cortex which functioned as a single unit; and that the severity of negative effects on cognitive functions resulting from damage of the cortex is determined by extent rather than the location of the damage. This view almost completely annihilated the former postulate of localization.

However, consequent studies went to show that indeed some of the cognitive functions were localized on specific parts of the brain. For example, aphasias, that is language distinctions, were reported to develop in subjects who had damage to certain locations of the brain known as the Broca and Wernicke areas which are located in the cerebral cortex.

These areas can be demonstrated anatomically; and are found only in the left hemisphere of the brain in over 80% of humans; the former is found below the motor cortex while the latter is located above the temporal auditory cortex.

The Broca’s area controls motor functions of the face; and thus facial expressions during conversations, damage to this area results in incoherent speech. The person can however understand even complicated conversation; but when s/he attempts to respond, they can only speak in gibberish.

On the other hand damage to the Wernicke’s area results in negative effects on the ability to understand language. While the subjects can understand simple requests directed at him/her (by including his/her name in the phrase), they usually cannot conduct a simple conversation. The condition is expressed in the responses which are incongruent; that is, although the phrases may be correctly formed, it is spoken completely out of context.

In this view, the general consensus about the function of the brain in regards to cognitive functions is that it involves a blend of both localized and diffuse organization. Studies carried out, especially on the function of vision and the role of the brain in processing sensory input arriving from the eye showed that some of the processing involved depended on a localized area on the cortex known as higher-order sensory cortices.

In addition to this, other areas, known as association cortices, were shown to respond only to sensory inputs from two sources. This does not mean that the phrenology postulation of localization of cognitive brain functions has been adopted on a wholesale basis; indeed, the major difference between this theory and the modern view of brain function is that the latter views localization as being of systems rather than functions; and that specific cognitive functions are supported by interconnection and interaction among these systems. The end result, therefore, has been a blend of the theories (Lycan, 1999).

Brain damage and Cognitive functions: The case of Phineas Gage

While working on a roadbed for the preparation of laying of a railroad in Vermont, Phineas Gage was involved in a horrendous accident that immortalized him on the pages of academic books and papers. On September 13, 1848, Gage had been assigned the duty of adding gunpowder to holes drilled on the rock in preparation for blasting; around 4.30 pm, the powder exploded accidentally driving the cylindrical tool he was used to compacting the powder through the side of his face; the rod traversed behind his left eye and exited at the top of his head and landed about 25 meters away.

The route of the rod through his head was thought to have severely damaged one or both of his frontal lobes. Gage went ahead to make an amazing physical recovery that was not expected in regards to the extent of his injuries; for example, the attending physician, John Harlow, reported that he touched his two index fingers through the hole marking the trajectory of the rod through the brain (Tranel, 2001).

Of greater interest, however, is the effect of this accident on Gage’s personality; allegedly, after complete physical recovery, his personality changed so much that people concluded that he was ‘no longer Gage’. The formerly industrious, reliable, and likable young man changed into an irresponsible and useless person who could no longer hold down a job. The authenticity of these claims has been disputed; since there was little information about the character of Gage before the accident and that some of the accounts of his behavior were written many years after his death; and were not based on direct observations; and were prone to gross exaggeration (Tranel, 2001).

However, the case of Phineas Gage opened the door to the in-depth study on the role of the brain in cognitive functions; and is the subject of reference of many neurological and psychological studies.

References

Lycan, W. G (ed.1999): Mind and Cognition: An Anthology, 2nd Edition. Malden, Mass: Blackwell Publishers, Inc.

Sizer, Nelson (1888): Forty years in phrenology; embracing recollections of history, anecdote, and experience: Fowler & Wells p. 194.

Tranel, Daniel (2001): Book Review: An Odd Kind of Fame: Stories of Phineas Gage: New England Journal of Medicine 344: 312.

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The Role of the Brain in Cognitive Functions

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