Association between cognitive performance and functional outcome following traumatic brain injury: a longitudinal multilevel examination.

OBJECTIVE: Individuals' cognitive abilities predict functional outcomes following traumatic brain injury (TBI). However, it is not known to what extent concurrent cognitive abilities affect the magnitude or the rate of functional recovery. The current study modeled the progression of functional outcome as it related to background, injury severity, and cognitive variables over the first year postinjury.

METHOD: This study comprised 111 individuals with moderate-to-severe TBI assessed on average at 3, 6, and 13 months postinjury. In addition, 79 healthy controls were assessed at a single time point. Each assessment consisted of an administration of a neuropsychological battery--comprising measures of memory, information processing speed, and executive functions--as well as an administration of the Mayo-Portland Adaptability Inventory to examine functional outcomes.

RESULTS: Older age, lower levels of education, and greater days of posttraumatic amnesia were associated with poorer functional outcomes. The addition of cognitive variables resulted in better models than simply considering background and injury severity variables. However, the results showed that the model comprising executive functions best characterized the progression of functional outcomes.

CONCLUSIONS: The findings indicate that consideration of cognitive ability, rather than reliance on demographic and injury severity variables, provide a more accurate representation of functional outcome over the first year postinjury. In addition, the results suggest that specific cognitive domains, particularly executive functions, are likely to have the strongest effect on functional outcomes.