The psychobiology of minor head injury.

Twenty-six consecutive admissions to an accident and emergency unit with minor head injury were examined. This was defined as a head injury warranting brief in-patient overnight stay but with a post-traumatic amnesia of less than 12 hours. Each patient had a neurological examination, a post-traumatic symptom check list completed, EEG power spectra analysis and auditory brain stem-evoked potential recordings, and a four-choice reaction-time measurement. These assessments were repeated six weeks later. Six months after the head injury a symptom check list was completed and four-choice reaction time measured again. Post-traumatic symptoms are persistent in half of all patients at six weeks and six months follow-up. The EEG power spectra showed a significant change in theta power between the first recording and the second one at six weeks, with relative reduction being noted. Approximately half of all patients had significant delays in brain stem conduction time at day 0. There was a trend towards a decrease in brain stem conduction time at six weeks, though in almost half the brain stem conduction time still remained abnormal at six weeks. Head-injured patients had prolonged choice reaction times at day 0 with serial improvement between then and six months, though the values at six weeks were still significantly longer than healthy controls. It is suggested that these findings reflect both cortical and brain stem damage following minor head injury, the brain stem damage being more persistent. There appear to be three patterns of recovery, half recovering within six weeks, a minority persisting over six months with persisting brain stem dysfunction and less than a third showing an exacerbation of symptoms with no evidence of brain stem dysfunction, the exacerbation being possibly a consequence of psychological and social factors.