Disorders of Memory and Behaviour

Some neurological disorders are associated with impairment of memory. It is now known that discrete areas of the brain are involved in memory, and that different areas influence different modalities of memory. The observations given below should be regarded as tentative and may well need modification.

1. The best known ‘system’ damage of which leads to defects of memory consists of the hippocampus(including the subiculum), the fimbria and fornix, the mamillary bodies, the mamillothalamic tract, the anterior nuclei of the thalamus, and the gyrus cinguli (and the fibres of the cingulum). It has been shown that damage anywhere along this pathway results in loss of memory of events, leaving general knowledge of the person intact.

2. In contrast, ablation (in monkeys) of the perirhinal cortex (a strip of cortex lying lateral to therhinal sulcus) leads to loss of knowledge about objects (as distinct to knowledge of events).

3. Other regions of the brain important in memory probably include the amygdala and the prefrontalcortex. The amygdala are probably responsible for evaluating the significance of environtal events, for example in recognising what objects are edible, or in recognising attributes of the opposite sex. Damage to the amygdala leads to the Kluver Bucy syndromein which such ability is disorganised. This results in marked changes in ingestive behaviour, the animal ingesting material (like foeces) not normally eaten. Abnormalities in sexual behaviour are also seen probably because of the failure to distinguish between male and female animals

The nucleus accumbens, located in the ventral striatum is a part of the mesolimbic dopamine system. It has acquired importance following the recognition that this nucleus is concerned with the stimulating and pleasure giving effects of addictive drugs (including nicotine and alcohol).