Vigilance and its disorders.

Vigilance has been defined as steady-state alertness-wakefulness. The right cerebral hemisphere, predominantly the right inferior parietal lobule and posterior parietal cortices, seems specialized for vigilance. Studies of the primary disorder of vigilance, a genetically determined condition, should provide a better understanding of the neurobiology of vigilance. Common causes of secondary hypovigilance (depression, learning disability, narcolepsy, and acquired focal right cerebral hemisphere brain lesions) explain the symptom complex of ADHD. If these specific entities producing hypovigilance are correctly identified, treatment is successful and with favorable outcome. The neuroanatomic substrate of lowered vigilance seems to be loss of modulating influence of the right cerebral hemisphere on the diencephalon and select brain stem nuclei. We propose that the right (more than the left) cerebral hemisphere is responsible for alertness and wakefulness (vigilance) with the reticular formation being accountable for sleep.