Cognitive Reserve in Individuals Aging With Traumatic Brain Injury: Independent and Interactive Effects on Cognitive Functioning.

OBJECTIVE: To examine the influence of 2 temporal factors-age and injury chronicity-on the relationship between cognitive reserve (CR) and cognitive functioning in older adults with chronic traumatic brain injury (TBI). SETTING: Outpatient research laboratory. PARTICIPANTS: Adults, 50 years or older, with a 1- to 45-year history of moderate or severe TBI (N = 108). DESIGN: Cross-sectional observational study. MAIN MEASURES: CR was estimated using demographically corrected performance on a word-reading test (an approximation of premorbid IQ). Injury chronicity was operationalized as number of years since the date of injury. Composite cognitive scores were computed from performances on neuropsychological tests of processing speed, executive functioning, and memory. RESULTS: CR was positively and significantly related to all cognitive performances independent of age, injury chronicity, and injury severity. Greater injury chronicity significantly attenuated the effect of CR on processing speed such that individuals more distal from their injury date evidenced a weaker positive relationship between CR and performance. CONCLUSION: Temporal factors may modify associations between CR and cognition. Findings suggest that the protective effects of CR are temporally delimited, potentially contending with declines in brain reserve. The prognostic value of traditional outcome determinants should be considered in the context of injury chronicity.