Pseudo-hypersomnia and pre-sleep behaviour with bilateral paramedian thalamic lesions

The sleep/wake status of three patients with bilateral lesions involving the paramedian thalamic regions was investigated. Long-term monitoring with infrared video camera and polygraphy were performed. In spite of presenting a behavioural aspect of sleep with sleep posture, eyes closed and lack of activity for 15-17 h per day, these subjects did not develop the normal non-rapid eye movement (NREM) and rapid eye movement (REM) sleep states during the daytime. The EEG indicated presence of a mixture of low amplitude, irregular, diffuse theta and alpha range frequencies during hours associated with this 'sleep-like' behaviour. Multiple sleep latency tests performed some time after the acute insult gave varying results, but while stage 1 NREM sleep might have been noted for three to four epochs, other states of sleep never appeared. Patients were apathetic and 'drowsy' but could develop sleep only during the normal circadian period for sleep, i.e. during the night. Even several years later, in one of the subjects in whom follow-up recordings were obtained, apathetic behaviour and sleep 'posturing' were present during much of the day, even though the subject, if requested, could perform tasks adequately all day long. Subjects with such lesions do not present a 'hypersomnia' but a 'de-arousal' or 'subwakefulness' with inability to develop sleep outside the normal circadian boundaries for its appearance. However, these subjects, at least initially, also lacked full wakefulness. They have a behavioural impairment with a compulsive sleep posture and are left in the transition between wakefulness and sleep.