Comparative study of eye movements in the alert state and rapid eye movement sleep

Abstract

Eye movements, in particular their speed during rapid eye movement (REM) sleep. were analyzed in five young normal subjects using electrooculography with a direct-coupled amplifier. Analysis was made mainly of horizontal movements. Eye movements were classified into two types by their velocity: those with speeds of more than 60° per second were categorized as rapid eye movements (REMs) and those with speeds of less than 60° slow eye movements. Comparisons between alert saccadic eye movements with a target, voluntary saccadic movements with lid closure, and REMs were made. The REMs were slower at all amplitudes of the eye movements.

Two cases of left medial longitudinal fasciculus (MLF) syndrome were analyzed by the same method. They had the following eye movement characteristics during REM sleep: absence of adduction of the involved eye, disjugate movement, nystagmus-like movement in the eye contralateral to the eye affected by the MLF syndrome, convergence-like movements, and slow vertical movement mixed with small saccadic movements, simulating nystagmus. These findings were almost identical to the abnormal eye movements noted in the alert state in these patients. The results may indicate that the REMs seen in normal subjects are mediated through the MLF.