Effect of lithium on reaction time--a study of diurnal variations.

Continuous reaction time performance was measured in groups of normal controls, psychiatric controls and patients treated with lithium. The reaction times were slower for the patients treated with lithium compared to both groups of controls, but the performance was not impaired to the same degree as in patients with various forms of cerebral dysfunction. For all groups reaction times were slower in the morning than in the evening or at night. Slow reaction times at the first investigation in the groups of normal and psychiatric controls were positively correlated with larger variations in the 24 h course. However, this correlation could not be demonstrated for patients on lithium treatment, probably because these patients do not approach their limit of speed as often as other patients or controls.