Age-related differences in brain activity during verbal recency memory

In the current event-related fMRI study young and older adults underwent fMRI scanning while performing recognition, recency and reverse alphabetizing tasks. The reverse alphabetizing task served as a control for executive processes, such as working memory manipulation and monitoring (Henson, R.N., Shallice, T., et al., 1999. Right prefrontal cortex and episodic memory retrieval: a functional MRI test of the monitoring hypothesis. Brain 122 (Pt 7), 1367-1381; Dobbins, I.G., Schnyer, D.M., et al., 2004a. Cortical activity reductions during repetition priming can result from rapid response learning. Nature 428 (6980), 316-319; Rajah, M.N., McIntosh, A.R., 2006. Dissociating prefrontal contributions during a recency memory task. Neuropsychologia 44 (3), 350-364). Multivariate spatio-temporal partial least squares (ST-PLS) analysis was used to identify task-related similarities and differences in regional activity in young versus older adults. The behavioural results indicated that older adults performed disproportionately worse on recency, but not recognition memory, compared to young adults. The fMRI results show the older adults activated right parahippocampal, right parietal, left precuneus and right prefrontal regions to a greater degree during both recognition and recency retrieval, compared to young adults. Brain-behaviour correlation analysis showed that increased activity in right parahippocampal and parietal cortex was related to poorer retrieval performance in older adults, but was related to improved recency accuracy and reverse alphabetizing accuracy in young adults, respectively. In contrast, the age-related increase in right prefrontal. and left precuneus activity was related to improved recognition, but not recency, performance in older adults. In young adults, activity in these regions was not strongly related to retrieval performance. These results suggest that older adults exhibited deficits in medial temporal and parietal function during retrieval, which was functionally compensated for by increased recruitment of prefrontal and precuneus regions. This functional compensation was sufficient for maintaining recognition but not recency retrieval in older adults.