Slowing of the Alpha-Rhythm of the Electroencephalogram and its Association with Mental Deterioration and Epilepsy

Abstract

There are few studies relating electroencephalographic characters with mental deterioration. Romano and Engel (1) (2) made an EEG and clinical study of “delirium” which they defined as the “toxic-infective state or psychosis associated with somatic disease” which was accompanied by “fluctuation in the level of awareness” and “intellectual, emotional and motor regressive behaviour”; the group included cases of chronic and acute cardiac decompensation, chronic alcoholism, hypertensive states, and severe Addison's disease. These authors considered that the EEG changes could be graded into three main groups, in order of severity: firstly,” decrease in frequency,” with increase of slow 4–7 frequencies and normal blocking responses to visual attention; next, “disorganization,” with irregular slow 2–7 frequencies and poor blocking responses; and finally,” reorganization at a lower energy level,” with moderately high voltage slow 3–7 c./sec. activity, few or no normal frequencies, and absent blocking response to visual attention. This latter stage was, in some cases, found to be irreversible. Previously, Engel and Margolin (3) had published the results of an investigation into the effect of both oxygen and glucose-deprivation on the human electro-encephalogram. Both these conditions produced bursts of diffuse generalized 3–6 c./sec. activity which, in those cases with an acute onset, reverted to normal rhythms as clinical improvement occurred. However, 4 patients with chronic cerebral anoxaemia were examined (end-stages of chronic bronchitis with right-sided heart-failure) in whom the EEG abnormalities persisted; at an early stage, activity with a frequency of 5–6 c./sec. appeared, and still later the records became completely disorganized. There was one patient who ultimately recovered whose EEG showed a regular dominant alpha rhythm with a frequency of 7.5 to 8 c./sec. It had already been noticed that, in a few cases where the EEG had apparently returned to normal in prolonged anoxic and hypoglycaemic cases, there yet remained some degree of intellectual deficit on psychological testing. Hill (4) had observed that a type of EEG with a slower dominant alpha-rhythm than the normal 8–13 c./sec. (i.e. a rhythm at 6–8c./sec.) was frequently associated with mental deterioration. An investigation was accordingly instituted to determine to what degree mental deterioration and slowing of the dominant rhythm in the post-central areas (alpha-rhythm) were associated.