EEG sleep patterns in mental retardation

Abstract

EEG and eye movement were recorded continously during sleep in thirty-two adult subjects with mental retardation. Included were patients with mongolism, phenylketonuria (PKU), brain damage and undifferentiated retardation. The intellectual level of these patients was independently evaluated with the Wechsler Pre-School and Primary Scale of Intelligence (WPPSI). Sleep measures in the retardates were compared with data available for normal adults and for elderly patients with chronic brain syndrome. WPPSI scores were positively correlated with emergent stage 1 EEG and with rapid eye movement (REM) activity, findings consistent with the sleep-cognition hypothesis. Compared with normal adults, mongoloid subjects showed low amounts of REM sleep, with an extreme reduction in the amount of eye movement, and quite prominent beta activity. PKU subjects showed a trend toward low values for REM and their sleep tracings manifested much epiletiform activity. Brain-damaged subjects had normal amounts of REM sleep but little stage 4 EEG compared to normal controls or to other retardates. Undifferentiated patients showed widely varying amounts of REM activity, ranging from extremely low to quite high values. Total sleep time was not reduced below normal levels in any of the retardate groups. All four groups showed atypical K complexes and a paucity of sleep spindles. The effects of age on the sleep patterns of the retardates were similar to those previously found in normals. The results suggest that investigation of the sleep EEG pattern in conditions of altered brain function may prove of diagnostic value and may lead to new insights into such fundamental questions as the neurobiology of intelligence, the effects of aging on the central nervous system, and the nature and function of sleep itself.