The effects of normal ageing on neuropsychological functioning following traumatic brain injury.

Increasing age is associated with greater absolute neuropsychological impairment (e.g. slower processing speed, diminished memory), although it is unclear if older individuals with traumatic brain injury (TBI) show greater relative impairment than younger individuals with TBI. The current study evaluated the effects of normal ageing on TBI by using age-based normative data to calculate indices of relative decline from pre-morbid levels (expressed as z-deficit scores) for different age groups (20-39 years, 40-59 years, 60+ years). The sample included 279 individuals with TBI between the ages of 20 and 65 who were assessed in a department of rehabilitation neuropsychology laboratory over a 4-year period. Spearman correlations and ANOVAs did not show age-related differences in relative memory, attention or speed of processing abilities, although results did indicate that increasing age is associated with relatively less impairment in intelligence. The results suggest that the greater neuropsychological impairment noted in older individuals with TBI is most likely related to normal ageing. The importance of considering both absolute and relative degrees of impairment is discussed.