The impact of increased relational encoding demands on frontal and hippocampal function in older adults

In the present study, we manipulated the cognitive effort in an associative encoding task using functional magnetic resonance imaging (fMRI). Older and younger adults were presented with two objects that were either semantically related or unrelated, and were required to form a relationship between the items. Both groups self-reported greater difficulty in completing the unrelated associative encoding task providing independent evidence of the associative difficulty manipulation. On both the low and high difficulty tasks, older adults showed a typical pattern of increased right inferior frontal recruitment relative to younger adults. Of particular interest was the finding that both groups showed increased activation as task difficulty increased in the left inferior frontal gyrus and left hippocampus. Overall, the results suggest that the aging brain is characterized by greater prefrontal processing, but that as cognitive demand increases, the networks used by older and younger adults are the largely the same.