The effects of aging and mild traumatic brain injury on neuropsychological performance

Clinically, elderly individuals show poorer outcome compared to young individuals following an equivalent traumatic brain injury (TBI). This could be due to either additive (aggregate) or synergistic (interactive) effects of age and TBI. This study examined the separate and combined effects of age and mild TBI (MTBI) on neuropsychological performance in four groups of 20 participants each: healthy young (M age = 26.8), young MTBI (M age = 27.5), healthy elderly (M age = 69.1) and elderly MTBI (M age = 66.7). Standard clinical measures of attention, memory, language and executive function were examined. Age-related declines were observed on measures of focused attention, verbal learning, and executive function. Error rates were low, indicating that older individuals were less efficient but generally accurate. MTBI participants performed more poorly than healthy controls on attention, verbal learning and executive function tasks. The effects of age and MTBI had a combined impact on performance in the elderly MTBI group leading to overall poorer performance as compared to other groups. This relative performance deficit was due to additive rather than interactive effects of MTBI and aging factors, indicating that age and MTBI produce independent decrements. The findings may be best explained in terms of brain reserve capacity theory, which posits a protective factor of reserve capacity that is vulnerable to depletion via organismic and extrinsic events, and a threshold level of functioning neurons below which normal function can no longer be maintained.