Neurotransmitters in the Ageing Brain and Dementia

Abstract

Cognitive processes especially short-term memory are primarily impaired in normal ageing and more dramatically so in dementing diseases. Other psychological effects are also evident. There is with age a general decay in sensorimotor processing including visual, auditory, somatosensory, gustatory and olfactory systems (Flicker et al, 1985) but in dementia these modalities are not enhanced. The control of behaviour is largely mediated within the brain by the limbic system (amygdala, hippocampus, septum, mamillary bodies of the hypothalamus and their connecting fibres). The frontal and parietal lobes of the neocortex (association areas) are more concerned with higher functions of thought and perception. The temporal lobe contains large areas of association cortex and is involved with memory of visual tasks and learning of auditory patterns. More subtle higher functions connected with movement and speech are also controlled by the cortex. There is generally loss of weight in the ageing brain and in non-vascular dementia atrophy may be pronounced. Selective loss or shrinkage also occurs. Biochemical methods have been used to identify the neurotransmitter systems and metabolic pathways affected.