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After reading this article you will learn about the relationship between brain function and language behaviour.
Language is perhaps the most evolved among the different forms of human behaviour. At the human level language is very complex and diverse and enters into almost every transaction. The role of language in human life is very crucial. One cannot live without language of some kind or other.
Here, we may just say that it is the complexity of linguistic activities that makes for one of the criteria which clearly differentiates between the human being and the most evolved sub-human organisms. Similarly, from the side of the body, the one feature which differentiates the human being and sub-human being is the fact that the human brain is much more developed and complex and complicated compared to that of man’s closest animal ancestors. The average weight of the human brain is about 1.37 kilograms.
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More crucial is the fact that the ratio of the weight of the human brain to the total body weight is much higher about 1/47 compared to that of the chimpanzee where the ratio is 1/104. It is therefore no wonder that those who are interested in studying language behaviour have been concerned with the relationship between the brain and language behaviour.
In fact, this interest in studying the relationship between the brain and the language behaviour dates back as far as the ancient Egyptian civilization. The ancient Egyptians had recorded the presence of brain injuries in the cases of persons who suffered from speech difficulty or what we now call aphasia.
Study of the relationship between brain function and language behaviour can come from two sources:
The first is recording of brain activities of people who are involved in different forms of language related activities like speaking, listening, thinking, etc. This can be done with the help of the Electro-Encephalograph or the EEG.
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The other source is clinical study of the brains of people known to suffer from a brain injury. Considerable amount of evidence of the latter type is available to enable us to arrive at a few generalizations on the relationships between the brain and language behaviour.
Some of these generalizations are as follows:
a. It is the left hemisphere of the cerebrum that plays a dominant role in human language behaviour. Damage to the left hemisphere has been found to be associated with different degrees and kinds of aphasia or speech problems.
b. It has been noticed that in the first few years, both the hemispheres of the brain are equally capable of controlling language behaviour. But, after the age of four, the left hemisphere assumes dominance and the right hemisphere gradually loses its capacity to stimulate language activity.
c. Another crucial role of the brain in language functions relates to the fact that it is the brain or the cerebral cortex that provides the timing process. Temporal organisation is of pivotal importance in speech and language behaviour. It is very obvious that words have to be organised in a particular order of occurring first, second, etc.
d. Further the process of perception and comprehension involved in speech and language behaviour definitely are based on the activities of cerebral cortex.
What is it about the brain that is so crucial for the development of language behaviour and its effective operation? Earlier it was believed that the weight of the brain or its ratio to the total body weight may be crucial, the absolute or relative mass of the brain. But today, it is realized that this is not the case and that the complex role of the human brain does not depend on its weight by itself or in relation to the body.
Evidence for this comes from an observation of the people suffering from a condition known as manocephalic dwarfism. Such individuals usually are about 2½ feet tall even as adults, and the average brain weight of these people has been found to be about 0.4 kg. Their brain weight – body weight ratio is about 1/34. Such subjects show a level of language mastery which is substantial and comparable to that of a five-year-old.
Other organisms with a similar brain weight or brain-body weight ratio do not acquire language. According to scientists like Lenneberg such a thing is possible because the brain of the manocephalic dwarf, while it may be small, it is nevertheless different in that it happens to be a human brain.
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Thus, what appears to be important is not just the size of the brain but its structure and the way in which the human brain functions. More particularly, it is the cerebral cortex that plays a crucial role in the development of language behaviour and its effectiveness.
Cortical Localization:
A major point of interest in studying the role of the brain in general and the cerebral cortex, in particular, in relation to language behaviour has focused around identifying different areas or parts of the cerebral cortex which may be related to different kinds of language related activities.
The pioneering discovery in this connection was that of Paul Broca who identified a certain area of the cerebral cortex as the one basically involved in speech. This area is known as Broca area. Broca’s discovery that was made in 1861 is still held valid by many authorities though this has also been contested. Another area, known as Wernicke area, named after another pioneer Wernicke has been identified as the receptive area for language process.
Broca’s area, has been found to be essentially connected with expressive functions. Yet another area closely associated with language behaviour is the supplementary motor area. It is generally accepted that the Broca area, the Wernicke area, and the supplementary motor area are involved in language behaviour, but how they are involved in different kinds of language activities is not very clear. In addition to the cerebral cortex, there is no doubt that certain sub-cortical parts of the brain are also involved in language behaviour.
Lateralization of Language Abilities:
There is a large mass of evidence to show that the left hemisphere of the cerebrum is more connected with the language behaviour. In fact, this has been substantiated ever since Broca arrived at his findings. Evidence for this comes from a number of sources.
The first source, of course, has been the clinical observations of brain injured patients where it has been found that the injury to certain parts of the left hemisphere has been associated with speech difficulties. Another source of evidence has been the findings of experiments carried out when Sodium Amytal was injected into the carotid artery which supplies blood to the two hemispheres.
It has been reported by leading authorities like Penfield and Rasmussen that if the left hemisphere was paralyzed, then it was found to result in loss of speech which has not been found if the right hemisphere is paralyzed. An interesting piece of evidence was produced by Kinenes through the technique of dichotic learning or stimulating the two ears separately and simultaneously. Kinenes’ findings showed that in most of his subjects the right ear is found to be more effective than the left ear.
Since it is generally established that the right side of the body is connected to the left side of the brain (contra lateral connection), these findings also go to prove the dominance of the left hemisphere in language behaviour. More recently, research findings have suggested that the initial stage of speech production or process occurs in both the hemispheres. However, gradually it comes about that complex and higher levels of language process get to be processed by left hemisphere.
An interesting piece of evidence comes from the study of split-brain patients in whom the two hemispheres have been separated by a surgical operation on the corpus callosum, the bridge like tissue which connects the two hemispheres. In such cases, it has been shown that the patients cannot name pictures or pronounce words shown only to the right hemisphere.
These are experienced as flashes of light. But, the same stimuli when presented to the left hemisphere are named and repeated. However, there are some findings which point to the dominance of the right hemisphere in certain types of language activities like recognition of geometric forms, recognition of phrases, etc.
In line with the findings is the observation that when it comes to non-speech sounds like music, the left ear appears to be more effective than the right ear. As in the case of speech perhaps it is better to leave this question here with the indication that the role of the brain and the nature of the brain itself is much too complex to be clearly concluded about.