Neuronal Mechanisms of Working Memory Performance in Younger and Older Employees

As working memory (WM) is compromised with advancing age, older people may have performance deficits in WM tasks. This is probably due to a great number of WM operations which should be performed for extended periods of time. The reduction of a number of these operations was expected to reduce WM load and age-related deficits in WM performance. Fifty younger (29±3 years) and 49 older (55±3 years) healthy employees had to perform a visual 0-back (oddball) task and a 2-back task. Within the 2-back task, the short (3 or 4 items, low WM load) and long (5 or 6 items, high WM load) target-totarget sub-sequences were analysed separately. Older workers performed worse than younger ones at higher WM loads, except for the oddball condition and low WM load condition. The N2 latency of the event-related potentials (ERPs) increased with WM load and was generally longer in older than younger adults. In addition, the N2 latency decreased with WM load in younger adults but did not change in older ones. Older workers also showed a delayed P3a as well as a delayed and reduced P3b. By contrast, age-related enhancements of the occipital N1 and frontal P2 components under WM load were observed. The parietal slow positive wave (SPW) increased under high WM load but did not vary with age. The results indicate that older adults are able to compensate for age-related WM impairments when the amount of WM operations required does not exceed the limits of their WM capacity. The allocation of cognitive resources to stimulus encoding (N1) and memory retrieval (P2) are putative neuronal mechanisms for these WM improvements. However, older adults have maintenance problems at higher WM loads. This is associated with deficits in neuronal processes relating to response selection (N2), detection of changes in WM representations (P3a) and WM updating (P3b). These results provide a basis for the development of work load criteria and training opportunities for older workers who have to do complex work requiring working memory.