Young and Middle-Aged Schoolteachers Differ in the Neural Correlates of Memory Encoding and Cognitive Fatigue: A Functional MRI Study

Abstract

This investigation was inspired by growing evidence that middle-aged persons in a cognitively demanding profession might be characterized by subtle cognitive fatigue. We studied young and middle-aged male schoolteachers. They were compared in a study with functional magnetic resonance imaging to evaluate differences during successful memory encoding. The schoolteachers were additionally subjected to an induced fatigue condition involving the sustained performance of cognitively demanding tasks and to a control condition. Results showed age-related brain activation differences underlying behavioral performance including: (1) greater activation in middle-aged vs. young teachers in bilateral prefrontal cortex (PFC) areas; and (2) differential fatigue effects in the left anterior cingulate cortex (ACC) depending on age group. Middle-aged schoolteachers showed decreased ACC activation in the fatigue compared to the control condition, whereas no change in activation was found in young teachers. Findings demonstrate age effects in these middle-aged subjects that are typically found in older adults, specifically in PFC over-activation. Findings also indicate that already in middle age cognitive aging may be associated with greater resource depletion following sustained task performance. The findings underscore the notion that persons in a cognitively demanding profession can experience subtle age effects, which are evident on fMRI and which impact daily functioning. Possible practical implications for middle-aged schoolteachers are discussed.

Keywords: aging; episodic memory; fMRI; mental fatigue; middle age; schoolteachers.

Figure 1

Mean subjective ratings (± SE) before the manipulation (time 0), between the manipulation and the fMRI tasks (time 1), and after the fMRI tasks (time 2).

Figure 2

A multislice view of activation effects in the prefrontal cortex (PFC) significant at p_{(Family-wise error corrected)} < 0.05, small volume corrected. Locations of the slides are signified by the y coordinates, presented in blue at the top of the images. Green blobs illustrate the main effect of age group on successful memory encoding activation: greater dorsomedial, dorsolateral and orbital frontal PFC activation in middle-aged compared to young teachers. Red blobs illustrate the main effect of fatigue condition on successful encoding activation: decreased anterior cingulate cortex (ACC) activation in the fatigue compared to control condition (y = 16) as well as the interaction between group and fatigue condition: only the middle-aged teachers showed a significant reduction in activity in the fatigue condition compared to the control condition, and activation of this area in the control condition was higher in middle-aged compared to young teachers (y = 32).

Figure 3

The interaction between the effect of age group and fatigue condition on successful encoding activation in the left ACC (error bars show 90% confidence intervals).