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Double Dissociations

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One reason why neuropsychologists study brain lesion patients is that it enables us to identify double dissociations within complex cognitive functions, for example: memory. Memory involves several multifarious components and modalities which makes it a very difficult process to investigate. In addition, memory has more than one distinct process. In order to gain a detailed understanding of specific memory processes, brain lesion patients have to be studied. Healthy participants also play an important role in discovering double dissociations in memory as they can act as the control group for comparisons but they do not allow researchers to establish specific localisations. Double dissociations provide neurological evidence that a patient has…show more content…
Broca (1861) was treating a patient who had suffered a stroke and found that the patient could understand language but was unable to produce language - despite his vocal tract and other production components being intact. The individual was able to mumble some small words such as “tan” but it he no longer had the ability to create sentences. Broca identified that the left inferior frontal lobe was damaged in his patient’s brain and he labelled this the ‘Broca's area’. Similarly, Wernicke (1876) who reported a stroke victim aged 26 who had the ability to speak freely but made little sense (could produce language but was unable to comprehend language). This patient had a brain lesion in the posterior region of the superior temporal gyrus in the left hemisphere - which is now known as ‘Wernicke's area’ (as cited in Gazzaniga et al, 2014). Therefore, there is sufficient evidence to suggest a double dissociation between language production and language comprehension as they are controlled by independent parts of the…show more content…
In one case, four adults aged 26-42 who had injected heroin were essentially immobile, unable to speak, had frozen facial expressions and were extremely rigidity in their arms. According to Langston (1984) these symptoms are highly similar to those experienced by an advanced Parkinson’s disease (PD) patient. PD results from substantia nigra cell death which is a region within the basal ganglia. These cells are the main source of dopamine but Langston (1984) was unable to visualise any structural brain damage on CT or MRI scans, however, PET scans confirmed hypo metabolism of dopamine. After a chemical analysis, the drug injected by these four patients actually had little resemblance to heroin but had a similar structure to meperidine (a synthetic opioid) which is now known as MPTP. Lab experiments indicate that MPTP is selectively destructive for dopamine cells. Since this drug discovery, various surgical procedures have been developed to reduce the inhibition in those with PD either by lesioning the output structure of the basal ganglia - which has many limitations or by deep-brain stimulation. Therefore, as a result of studying these four patients suffering from Parkinsonian symptoms, drug discoveries have been made which can thus be used to make advancements in our understanding and effective treatments of Parkinson’s disease which to this date,
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