Normal and pathological changes in alpha rhythms.

Normal alpha rhythm begins to appear at three months. It was possible to observe successively, the rhythmicity, visual reactivity, occipital topography, and at the end of the first year, the first bursts of 7-8 Hz waves. Evolution of alpha was not linear with the age. Alpha frequency acceleration was important before the age of 11 years. In adults it decreased from 20 to 55, then there was a tendency to increase with aging. Amplitude was highest at 11-12 years, then its tendency was to decrease until 40, and to increase later. In pathology, for instance, alpha could be observed too early in newborn and infants with malformations, in children, in some psychiatric diseases, in adults and old people, alpha was replaced by theta waves in dementia: it seemed to be a very reliable sign, at the beginning of the disease.