Why do we forget things?
of thiamine in alcohol amnestic disorder. They report that thiamine is found in all cells of the body but those of the nervous system are particularly sensitive to its absence. According to them, thiamine is vital since ‘the thiamine– dependent enzyme transketolase is an important enzyme in the breakdown of glucose through a biochemical pathway called the pentose phosphate pathway.’ and this is crucial for the production of ‘nucleic acids, complex sugar molecules, and other compounds’, that are vital for normal cell functioning and in particular the functioning of neurons. This decrease in carbohydrate metabolism, caused by thiamine deficiency causes cell death and cebrebral atrophy leading to lesions in the following areas, mamillary bodies, thalamus, hypothalamus, brain stem, and cerebellum. Korsakoff’s syndrome may leave a patient with both retrograde and anterograde amnesia, so he is reduced to living entirely in the present with little context and perhaps mentally stuck in a particular time from the past. There is a wonderful description of the affliction by Sacks (1985) 7 , which depicts the plight of an endearing sufferer stuck in post war 1945 America. While his episodic and factual memory fail him, he remains personable and his life destroying disease may not be apparent during brief conversation. Korsakoff’s therefore highlights, once more, the delicate balance that is found within the human brain and the role that memory plays in maintaining it. Furthermore, The precise descriptions of Sacks reveal how damage to the areas already mentioned translates in real life. 143 Amnesia provides a very obvious example of memory loss due to the fact that it affects the episodic and semantic memory areas, which are commonly thought of as memory in its entirety. According to The Human Memory (2010), 144 there is however another division in long-term memory, which may also be affected by neurological damage. It is known 143 Sacks, O.W., 1985. The Man Who Mistook His Wife For A Hat. London: Gerald Duckworth & Co. ltd 144 The Human Memory, 2010. Types of Human memory. [online] Available at: http://www.human- memory.net/types.html [Accessed 7 July 2012].
as implicit procedural memory, and is summed up nicely by Roediger (1990) as, ‘retention without remembering’ and although it may be overlooked in habitual activities as a form of memory, it is probably more important than conscious recall. For example the mechanism by which you drive a car is stored in procedural memory and requires little thought when at the wheel, however if you suddenly lost this ability, the consequences could be dire. Other examples of an implicit procedural ability could be talking, reading and writing and it could be considered that these are some of the most fundamental of human activities; it is therefore of much interest to study the disease described by Sacks (1985 named aphasia. 145 The scope of the disease may vary from ‘global aphasia’, which presents with a total inability to use written or spoken language as described by Sacks (1985) or perhaps a more subtle form like ‘alexia sine agraphia’, which is chronicled by Sacks (2010) and translates into an ability to write but not read. This disease has a number of presentations which all result from the damage of slightly different brain areas. Work by Medicine Net (2012) 146 indicates that most commonly lesions occur in the temporal lobes and frontal lobes. One of the more interesting causes of aphasia is the herpes simplex virus, which was featured in a recent BMJ article by Sabah, Mulcahy, Zeman (2012). 147 The BMJ reports that herpes simplex encephalitis (HSE) is ‘a severe viral infection…that is usually localized to the temporal and frontal lobes in adults.’ It is important to note however, that it is not a unique ability of HSE to cause aphasia but instead it is a by-product of the indiscriminate damage caused by the infection. This is adduced by the suffering patient’s description from the BMJ article as he was able to speak French but not English as the learning of a foreign language is often stored in the right hemisphere of the brain and the infection had not progressed to that area. The American Speech-Language-Hearing 145 Sacks, O.W., 2010. The Minds Eye. New York: Random House inc. 146 MedicineNet.com, (2012), Aphasia . [online] Availableat: http://www.medicinenet.com/aphasia/a rticle.htm [Accessed 12 July 2012]
147 Sabah, M., Mulcahy, J. and Zeman, A. (2012) ‘Herpes simplex encephalitis’, BMJ 344.
77
Made with FlippingBook - Online Brochure Maker