Effects of age on working memory: an event-related potential study

The effects of age on behavioural performance and event-related potentials recorded during a working memory task using digits presented either acoustically or visually, were studied in 37 healthy subjects with an age range from 19 to 71 years. With increasing age, psychological tests showed a progressive decline in visuo-spatial performance and both auditory and visual reaction times (RT) increased. There were multiple and varying effects of age on both early and late ERP components. For both auditory and visual responses, increasing age was associated with an increased amplitude of early positive waves (auditory P100 and visual P145) and, in the oldest subjects, significant delays of the major late positive waves. Other changes were modality-specific with a progressive shift of amplitude maxima in the early negative waves of the visual ERPs (from an N190 peak maximal at Pz in the young, to an N270 peak maximal at Cz in the older subjects) and an altered amplitude distribution of late potentials (after the P250 wave) in the auditory responses. The age at which ERP changes occurred varied-significant latency prolongations and increases in the amplitude of the major frontal positive waves occurred only in the oldest subjects, whereas a redistribution of late auditory ERPs also occurred in the intermediate age group. There was no interaction between age and increasing memory load, suggesting that there is no specific effect of age on memory scanning in this age range for these levels of task difficulty. Thus, although performance in working memory was apparently unaffected by age, as judged by behavioural parameters (apart from slowing of the reaction times), ERPs revealed significant changes in both early and late electrical brain processes associated with working memory as age increases. These changes which were not symptomatically manifest and only revealed by sensitive tests, may represent subtle dysfunction of working memory (or associated processes) which does not prevent the successful completion of our task, compensatory mechanisms (which are essential to successfully complete the task), or a combination of both age-induced dysfunction and compensatory mechanisms.