Time-related changes in the distribution of sleep stages in brain injured patients.

The correlation between sleep pattern and cognition was studied in a follow-up of 9 patients with traumatic brain injury. The follow-up extended for a mean of 38 weeks after regaining consciousness, with 4-7 study periods for each patient. In addition to sleep pattern, 3 other variables were evaluated: independence in activities of daily living, locomotor and cognitive functions. In 7 patients there was a high correlation (r greater than 0.89) between cognition and REM sleep improvement whereas in 2 patients the correlation was lower (r less than 0.6). It is suggested that in the first group the REM mechanism was intact whereas in the latter, where a brain stem lesion was present, the REM mechanism was damaged. It is also suggested that the sleep pattern recovery time constant depends on the insult to the sleep mechanism structure whereas the REM steady-state recovery process depends on both cognitive maximal capacity and REM neural mechanism integrity.