The link between brain and behaviour has been a crucial area of study in psychology, enabling psychologists to gain a greater understanding of the human mind and more specifically, what happens if something goes wrong. The work of Paul Broca during 1861, led to a significant
breakthrough in the understanding of the brain and it’s role in speech development. Similarly, in 1961 and 1982, Roger Sperry led groundbreaking research into the interaction between the two hemispheres of the brain and what would happen if the corpus callosum (the link between the hemispheres) was severed. Throughout this essay, I will be comparing the work of Broca and Sperry, looking at the similarities of their findings as well as the weaknesses they may present.
Broca had a imperative insight that damage to a specific part of the brain would impair a specific mental function. Broca observed this whilst working with two patients, Leborgne and Lelong. Whilst studying Leborgne, Broca recognised that due to damage in small part of the left side of his brain, Leborgne was unable to speak other than the single syllable ‘tan’ although he understood everything said to him and could communicate through gestures*. Broca singled out the specific area (Broca’s area), located in the left frontal cortex that is involved in the production of the sequential patterns in the vocal and sign languages. Similarly, when studying his second patient Lelong, Broca observed that Lelong was only able to produce the same five words, but was able to understand everything said to him*. Broca predicted that Lelong also suffered from an injury in this area of the brain and this was confirmed upon autopsy of both patients. Broca discovered that both patients had large lesions in a similar area of their brains which had led to their speech difficulties. Broca’s area becomes increasingly specialised as the brain matures, meaning when damage occurs later in life, it results in Broca’s aphasia; a condition resulting in difficulty producing or comprehending speech. This causes the patient to struggle with grammatical structure and often they speak in staccato phrases that consist mostly of content morphemes (e.g. cat) as seen with Leborgne and Lelong. From these studies, Broca gathered fundamental information to support his theory. In normal language development, Broca’s area becomes specialised for processing and producing language. However this must take place during a critical period during a child’s development. If the brain does not receive enough language input, then the process is permanently disrupted. This can be seen in the case of Genie Wiley. After being held captive with no interaction for the majority of her childhood, Genie was unable to speak. After speech therapy, Genie was able to learn words but could not speak grammatically. This was caused by the disruption to her brain’s development and resulted in her not having the capacity for language. Broca’s discovery revolutionised how psychologists viewed the link between brain and behaviour, as it showed how damage Broca’s area was linked to speech production and how if this was disrupted, it could result in Broca’s aphasia. However, it could be argued that damage to Broca’s area disrupts the process from the thought of speech to actually saying it, rather than difficulty in producing or comprehending speech, since both of Broca’s patients understood what was being said to them, this would require some level of comprehension and processing. Therefore, this could suggest that it is also linked to the nerves in the brain and being unable to link thought and physical speech. In a similar way, Roger Sperry conducted split brain experiments which showed how the two hemispheres interacted in order to produce speech and movement.
Sperry’s research into brain and behaviour consisted of finding a new approach to prevent epileptic seizures. Sperry noticed that the seizure would often start in one hemisphere and then would travel across the corpus callosum. This would result in a feedback loop, ultimately causing a firestorm in the brain*. Therefore, Sperry created the ‘split brain procedure’ – an operation resulting in the severing of the corpus callosum. This prevents the two hemispheres communicating, and therefore limiting the seizure to the one hemisphere. Although this was beneficial to prevent seizures, it affected the neurological function of the brain. This is due to information being isolated to one hemisphere and therefore it is unable to transfer into the other hemisphere and link functions, for example in Sperry’s experiment a patient was asked to describe something that she saw and the left hemisphere would describe it, as this is the location of broca’s area. However, she would be unable to use the right hemisphere to perform tasks in relation to that object e.g. correctly identifying it from a group of objects with her left hand*. This is known as contralateral control. This also applies in reverse, for example of someone was presented with a key, they may be able to demonstrate how to use the key but would be unable to describe it. This is due to the specialisation of specific parts of the brain. This can be seen with Broca’s area, being localised for speech and the right hemisphere being specialised for movement and control of the body.
Although the experiments presented by Broca and Sperry are not completely similar, there are a few consistencies between them. This can be seen in Broca and Sperry’s predictions on where the speech processing area of the brain is. Both experiments clearly suggest that the area of the brain responsible for speech processing and production is located in the left hemisphere. This shows a level of accuracy in their experiments as they both prove this in their own ways. As well as having similarities to strengthen their research, there is also a number of weaknesses between both of these experiments. For Broca, it can be argued that his findings may not apply to everyone. This is due to the fact that the two cases presented were individual people and they are only a small representation of the population. Therefore, to have two cases represent such a large amount of people may not be accurate. In Sperry’s experiment, it can be noted that the brain damage that the patient has is man made and is not naturally occurring brain damage. It could be argued that Sperry’s experiment is not ethical behaviour, since the side affects are much greater than the positive outcome – limiting the affect of the seizures. For some, the idea of giving a patient permanent issues with linking mental functions together is an extreme length to go to prevent seizures when there may be an alternative option.
In conclusion, the research conducted by both Broca and Sperry was a breakthrough in psychology and understanding the brain, which led to crucial insight into brain and behaviour. When comparing both pieces of research, it was clear that the predictions of speech production being in the left hemisphere were accurate as there was consistencies between both pieces of work, helping to focus on which parts of the brain are responsible for certain specialised functions. However, the research conducted by Broca leaves the question of how accurate it is to claim that two individual cases are enough to support the idea for an entire population. Similarly, Sperry’s research raises ethical issues, leaving some to question wether it is ethical to give someone brain damage in order to prevent seizures, since the affects of severing the corpus callosum will affect their day to day life.