Age-related memory impairment associated with loss of parietal deactivation but preserved hippocampal activation

Abstract

The neural underpinnings of age-related memory impairment remain to be fully elucidated. Using a subsequent memory face-name functional MRI (fMRI) paradigm, young and old adults showed a similar magnitude and extent of hippocampal activation during successful associative encoding. Young adults demonstrated greater deactivation (task-induced decrease in BOLD signal) in medial parietal regions during successful compared with failed encoding, whereas old adults as a group did not demonstrate a differential pattern of deactivation between trial types. The failure of deactivation was particularly evident in old adults who performed poorly on the memory task. These low-performing old adults demonstrated greater hippocampal and prefrontal activation to achieve successful encoding trials, possibly as a compensatory response. Findings suggest that successful encoding requires the coordination of neural activity in hippocampal, prefrontal, and parietal regions, and that age-related memory impairment may be primarily related to a loss of deactivation in medial parietal regions.

Fig. 1.

Hippocampal activation and medial parietal deactivation during successful encoding in young and old adults. (A and B) SPM2 random effects analysis demonstrates that young (A) and old (B) adults activate the hippocampus bilaterally (P < 0.005 minimum threshold). (C) The medial parietal region (peak MNI coordinates x, y, z: −6, −75, 45) shows significantly greater deactivation during successful encoding for young adults than old adults. (D) Estimated hemodynamic responses for HC-hits (solid lines) and misses (dashed lines) demonstrate that old adults (blue) show similar MR responses to that of young adults (red) during HC-hits (solid lines) and misses trials (dashed lines) in the bilateral hippocampus but not in medial parietal region.

Fig. 2.

Medial parietal deactivation by age and performance. (A) HC-hits percent signal change estimates extracted from the medial parietal cluster show significant differences in deactivation between young and old adults. (B) Additional analysis reveals significant correlations between memory performance and HC-hit percent signal change estimates extracted from the precuneus among old adults (r = −0.59, P < 0.05) but not among young adults.

Fig. 3.

Activation and deactivation among old adults by performance. (A and B) Low-performing old adults (blue) show significantly increased MR responses to that of high-performing old adults (red) during HC-hits (solid lines), but not misses (dashed lines), in the right hippocampus (A) and right superior frontal region (B). (C) Low-performing old adults also demonstrate reduced deactivation (below baseline HC-hits percent signal change) in the precuneus.