Age-related brain activation during forward and backward verbal memory tasks

The present study used fMRI to investigate the neural basis of memory for verbal information using a forward repeat (FRT) and backward repeat task (BRT) administered in participants ranging between 20 and 65 years who were divided into four non-overlapping age groups. Results of behavioral performance on the FRT revealed no significant difference across age groups. In contrast, behavioral performance on the BRT decreased with increasing age. fMRI results demonstrate that both FRT and BRT activated frontal areas, temporal areas and the cerebellum. However, parietal areas were only activated in BRT, suggesting increased task demands during the task. Furthermore, almost all activated areas demonstrated a larger number of activated voxels and greater percent signal change during BRT compared to FRT. Interestingly, there was an apparent laterality shift with aging in that those areas that normally show a leftward asymmetry in young participants change to more rightward asymmetry in the older participants. In the FRT, areas involved in the laterality shift were the superior temporal gyrus, Heschl's gyrus and cerebellum, whereas in BRT the laterality shift involved the middle frontal gyrus, superior parietal lobe and Heschl's gyrus. In all, the behavioral results were consistent with the fMRI results, with a decline in performance on the BRT with age, in contrast to rather unchanging performance on the FRT, possibly reflecting effective neurocompensatory processes in the latter. These results suggest that different neural mechanisms may be involved in FRT and BRT, issues which are elaborated with respect to memory processes during aging.