Asymmetry of rapid eye movements in chronic unilateral neglect does not change with behavioral improvement induced by rehabilitation treatment

A strong reduction of leftward rapid eye movements (REMs) during REM sleep was recently documented in patients with severe and chronic left unilateral neglect. The aim of the present research was to study the stability of the unilateral suppression of REMs before and after a rehabilitative treatment for neglect disorders. Six right-brain-damaged patients were tested for neglect at the beginning and at the end of a 2 month cognitive rehabilitation treatment. REMs were recorded during I night of undisturbed sleep before and after the training: Five out of 6 patients improved considerably their ability to attend the previously neglected left hemispace; in all patients REM asymmetry remained unchanged. The lack of relationship between the improvement of the neglect disorder and the persistence of REM asymmetry suggests that the sensorimotor mechanisms activated by rehabilitation are different from those involved in the production of REMs. It is proposed that: (a) the directional vectors of REMs are computed on the basis of the exclusive or predominant endogenous activation of the central attentional mechanisms related to vestibular input; (b) the presence of rightward and leftward saccades and the positive effects of the rehabilitation treatment are functionally linked to attentional oculomotor mechanisms that are not active in REM sleep.