Statistical study of the frequency and reactivity patterns of the electro-encephalograms of aged subjects

Abstract

Previous studies have brought us to consider the variations in frequency of the basic alpha rhythm of the electroencephalograms, as an important and significant factor. Regarding the problem of the aging processus, we have looked for an eventual relationship between this fact and the variations in question. For this, we isolated a group of tracings showing no pathological pattern, or belonging to a group of control with no consumption of neuroleptics and able to be part of a “normal” existence. These 879 selected tracings have shown the alpha rhythm in all cases, and in 262 subjects its association with theta rhythm. They may be divided into 5 groups by decades: 1 test-group from 30 to 39 years (349 tracings). 1 group of comparison from 50 to 59 years (270 tracings). 1 group of comparison from 60 to 69 years (166 tracings). 1 group of comparison from 70 to 79 years (72 tracings). 1 group of comparison from 80 to 89 years (22 tracings). Even if these groups diminish in number with advancing age, as in all populations studied under this aspect, they remain sufficient in number to be compared under histographic form, grouping the different frequencies of alpha rhythm or according to their average frequencies. The first observation issued from this comparison is the decrease of alpha frequency with age. Among the four groups, the first group only can be compared to the test-group from 30 to 39 years of age. From 60 …. years of age, we see a profile clearly diverted to the left, whereas the averages diminish. The presence of theta rhythm in a tracing favors the reduction in the frequency of alpha rhythm as it is seen if we select in each group, the tracings composed of alpha rhythm (pure alpha rhythm) and those composed of both (alpha + theta). In what concerns reactivity, we have observed that during the aging processus: — the blocking is less and less adequate; — hyperventilation is more and more active; — theta rhythm increases; — the photic stimulation follows less the cerebral rhythm but its action increases the “irritative pattern” or in the appearance of theta rhythm. Moreover, the morphology of the tracing changes and the “choppy” rhythms become more and more abundant. In conclusion: The E.E.G. evolves in one way towards a decrease of the alpha frequency, which is considered as a minor but constant indication of “cerebral distress” and in another way, towards a pattern of reactivity showing, either a decrease of physiological responses, or an increase in pathological elements (vascular types, in particular).