Event-related potentials as an index of cognitive function during recovery from severe closed head injury

To evaluate the utility and neuropsychological correlates of serially performed recordings of event-related potentials (ERPs) in patients recovering from a severe closed head injury (CHI).

Prospective longitudinal study.

Brain injury rehabilitation unit based in a national rehabilitation hospital.

Sixteen patients with severe CHI (significant degree of impaired consciousness greater than 24 hours) subclassified into two severity groups according to initial Glasgow Coma Scale (GCS) score: those with initial GCS score < 9, consistent with a more severe injury; and those with initial GCS score > 8, indicating a less severe injury.

ERPs were elicited using the standard auditory P300 "oddball" detection paradigm. ERP recordings were carried out three times: 2 months after injury, 1 month later, and 2.5 months or more after the initial study. Parameters analyzed included latencies and amplitudes of the P3, N2, P2, and N1 components of the ERPs. Correlations between changes in these ERP parameters and specific neuropsychological test results were evaluated.

Initial P3 latencies in the more severely injured group were significantly longer (P < .05) than those recorded in the less severely injured patients. In subsequent recordings, P3 latency was found to be significantly shorter compared with the initial P3 latency, and the difference in P3 latency between the two patient groups was no longer statistically significant by the time of the third recording. For the group as a whole, P3 latency decreased significantly on each repeated recording. N2 latency was found to be significantly shorter (P < .05) between the first and third recordings. Cognitive performance significantly improved between the first and third recordings. P3 latency shortening was correlated with improvement in neuropsychological test scores for short-term and long-term story recall and for word recall. N2 latency shortening was correlated with improvement in the neuropsychological test scores for word recall only.

ERP recordings performed in the subacute stage after CHI may assist in evaluating injury severity. Moreover, serially performed recordings of P3 latency may be used as a physiologic index of brain activity that correlates with recovery from CHI.