Electrophysiological ageing of the brain: Ageing-related impairments in neural and cognitive functions

Abstract

Electrical activity is the functional basis of the nervous system. Even the most complicated forms of information processing such as sensory detection, higher mental function, consciousness, has its basis in electrical signals produced by changes in voltage across the plasma membrane of particular collections of neurons. Ageing of the brain/nervous system involves changes in its electrophysiological activity and age-related disorganization of electrophysiological activity may cause derangement of neural and cognitive functions. Ageing effects on electrical signals will therefore determine the physiological, cognitive and behavioral outcomes of normal ageing as computational processing of information is adversely affected. There is thus a potential link between the electrophysiological and behavioral consequences of ageing. Ageing seems to impact electrophysiological parameters rather selectively. While the resting membrane potential is unaffected, the synaptosomal resting membrane potential is reduced during ageing. The amplitude of action potential is not affected by ageing, the duration and after-hyperpolarization may increase. Normal ageing involves decreased synaptic excitation and increased synaptic inhibitory processes leading to cognitive impairments. The information encoded in hippocampal place field firing may be altered with impaired spatial learning in the aged. The intensity and frequency of stimulation necessary to produce long-term potentiation is increased with advanced age and long-term potentiation decays more rapidly in the aged indicating forgetting or deficiency of memory formation. The electroencephalogram undergoes significant frequency specific and topographically variable age-related changes. Ageing-related alterations in basal electrical neuronal firing may occur in brain regions. Ageing-related disorganization of neuroelectric activity related to age-associated cognitive neuronal outcomes can be restored by appropriately designed pharmacological treatments.