Age differences in brain activation associated with verbal learning and fatigue

Learning abilities have already started to decline in middle age3. However, middle-aged adults are commonly required to continue to maintain performance in fulltime employment. We investigated whether the ability of middle-aged adults to maintain performance despite the effects of cognitive aging comes at the cost of increased cognitive fatigue. Functional MRI studies in patients with disorders characterised by fatigue, such as Multiple Sclerosis3 and Chronic Fatigue Syndrome4, have shown that, although patients could maintain task performance comparable to healthy participants, their performance was associated with increased and more dispersed brain activation. This finding has been attributed to the exertion of greater cognitive effort by patients which, consequentially, has been suggested to underlie their experience of increased cognitive fatigue. Behavioural studies have shown that cognitive fatigue symptoms can be induced in healthy participants by the prolonged performance of cognitively demanding tasks5. In the present study we used fMRI to examine verbal learning related brain activation in young and middle- aged adults following a control intervention and following a fatigue inducing intervention. Conclusions: 1. Middle-aged maintained comparable verbal learning performance to young, and did not indicate greater feelings of subjective fatigue. 2. Middle-aged showed greater activation than young in areas associated with cognitive control and attentional effort following the fatigue intervention during encoding, but not during recognition. 3. Greater subjective fatigue was associated with decreased activation in the left DLPFC in both age groups during encoding, but in young participants only during recognition. 4. It is suggested that middle-aged responded to the increased demands of verbal recognition by switching to more automatic processing.