Language as a means of human communication is an interesting but really wide topic as it can be seen by the many approaches and subcategories of linguistics like Psycho-, Social- or Neurolinguistics. In the following essay I will try to answer the question whether language is localised to a specific part of the brain so I take a neurolinguistical approach. In order to answer the question above, I will make use of well documented linguistic experiments, the findings from examinations of various aphasia patients and of brain imaging scans. After analysing and discussing the different outcomes I will try to come up with a conclusion which should include a satisfying answer to the question.
Broca's and Wernicke's area
The question I try to answer has been around for nearly two hundred years. In the mid of the 19th century the question has been addressed by Marc Dax who found out that “paralysis of the right side of the body was often accompanied by loss of speech”. (Atchison 2012: 44) He concluded that the left side of the brain controlled the right side of the body as well as it controlled speech. Even if some cases where a patient's left side was paralysed resulted in the inability to speak indicated that it was not as simple as it seemed, he should essentially be proven right by Paul Broca and Paul Wernicke around thirty years later. Paul Broca discovered the anterior speech cortex which he claimed responsible for the articulation of speech. He was able to make this claim because of a patient, often referred to as Tan-Tan who could only utter this specific combination of sound namely “tan tan”, whom he performed an autopsy on after his death. Broca found the frontal convolution of the left hemisphere of the brain to be severely damaged and thus concluded that this must be where thoughts are articulated into speech. (cf. Atchison 2012: 45) The anterior speech cortex is often simply referred to as Broca's area while conditions, similar to the one Tan-Tan suffered from was henceforth called Broca's aphasia.
Briefly after Broca's discovery of the anterior speech cortex's role in speech production another kind of aphasia had been examined by Karl Wernicke in 1847. In contrast to Tan-Tan's language issues Wernicke's patients did not show problems in producing fluent utterances, but in understanding questions and in formulating meaningful sentences. He found that “damage to the left temporal lobe […] was associated with a profound problem with language comprehension and speech that is meaningless or devoid of intelligible meaning.” (“Lateralisation and Localisation of Brain Function: C 2”) A person suffering from this kind of aphasia will use words that make no sense in the given context of conversation. Moreover the individuals who suffer from this so called Wernicke's aphasia may even be unaware of their speech and comprehension difficulties.
Although one might conclude from Broca's and Wernicke's findings that speech is exclusively located in the left hemisphere of the brain, one must not forget that in a complex system such as the human brain a function can be “narrowly localised in an individual in a particular area, […] localized equally narrowly in another area in another individual, and carried out in a much larger area in a third.” (Caplan qtd. in Atchison 2012: 45) In the following analysis of split brain experiments I will show why this statement by David Caplan is remarkably true.
Split Brain Experiments
Until recent brain imaging techniques were used to find out where in the head language is located, major results came from split-brain experiments. The operation in which the two hemispheres are separated was mostly performed on patients who suffered from severe epilepsy in order to prevent the seizures from affecting the body as a whole. The surgery was an attempt to contain the seizures in that part of the brain of which they emerged from. Even if this seemed to be drastic surgery it appeared to have little effect on the patients wellbeing or cognitive abilities. (cf. “Lateralisation and Localisation of Brain Function: D”) Roger Sperry and his graduate student Ronald Myers engaged in some experiments with split-brain cats and asserted, that "it was as though each hemisphere were a separate mental domain operating with complete disregard […] of what went on in the other. The split-brain animal behaved in the test situation as if it had two entirely separate brains" (Sperry qtd. in Todmann 2008: 3) In the following examinations on humans, split-brain patients were blindfolded and given an object in one hand. When the given object was felt by the right hand the patients were able to identify and name the object. In contrast to this, when the given object was felt with the left which connects to the right hemisphere it could be identified as familiar, but not be named. These experiments revealed that the left hemisphere of the brain is superior to the right one in analytical and linguistic processing backing the findings of Broca and Wernicke. Moreover, they found the same symptoms as in the previously examined cats, namely the fact that the disconnected hemispheres could not communicate and acted as two independent brains with their own memories, emotions and streams of consciousness. (cf. “Lateralisation and Localisation of Brain Function: D 1”)
The results of the examination of hemispherectomy patients presented by Ewa Dąbrowska in “Language, Mind and Brain: Some Psychological and Neurological Constraints on Theories of Grammar” however very much oppose the view on the localisation issue shown above. She argues that in “a recent survey [by Curtiss and de Bode from 1998] of 49 post-hemispherectomy patients […] no significant relationship between side of lesion and language outcome” could be found. Moreover 23 per cent of the left-hemispherectomised patients' speech was unaffected by the surgery, while “nearly a third of the right hemisperectomised patients had no productive language at all, compared to 16.7 per cent of the left hemispherectomies [...]”. (Dąbrowska 2004: 42)
So even if Broca's and Wernicke's area are crucial to language production and comprehension there must be something about the right one that is as important for the ability to speak as the former. If something can be inferred from what we have investigated so far I claim that it is the fact that there is not that one area in which language is produced and processed and that even this vaguely curtailed area might be different for every individual. This claim is also supported by the fact that “language impairment sometimes occurs after brain damage outside the classical language areas” or damaged 'language-areas' which do not result in impaired speech at all. (Donkers et al. qtd. in Dąbrowska 2004: 41)
Speech Development in Children
By taking a closer look at how language develops in early childhood and how children recover from brain damage one should be able to make more specific claims about where language locates to in the brain. As Dąbrowska points out that aphasic symptoms in children differ vastly from those observed in adults. More precisely, Wernicke's aphasia is quite rare even if the corresponding area is damaged and children suffering from Broca's aphasia rarely make errors but they make use of simpler structures. However, children are most likely to suffer from some form of aphasia “after just about any kind of brain damage, including damage to the right hemisphere and the non-linguistic parts” of the brain. (Dąbrowska 2004: 42) This suggests that the speech production and comprehension areas in a child's brain are even harder to pin down than those of an adult and are spread through most of the brain. This means that while growing up the brain slowly specialises certain parts in linguistic disciplines but had used other regions to process language before. Once fully developed, the brain can partly relocate these abilities when damaged, but only with great effort and training while it seems to do so easily at a younger age. These interpretations go well with the 'critical period' during which children pick up language quite easy and fast. Since the human brain is not fully developed from the beginning and the child's capability of speech quite limited “it is generally thought the lateralisation process begins in early childhood” which coincides with the period during which language acquisition takes place”. (Yule 2010: 167) If language is not acquired during this period it will nearly be impossible to do so later on.
- Quote paper
- M. A., M. Ed. Felix Krenke (Author), 2014, Is language localised to a specific area of the brain?, Munich, GRIN Verlag, https://www.grin.com/document/1007989