Aging Effects on Basic Memory Mechanisms

November 26, 2011

Episodic memory shows substantial decline as a function of aging, shop and fMRI studies have linked age effects on episodic memory to changes in prefrontal cortex (PFC) and medial temporal lobe (MTL) activity (for a review, find see Daselaar & Cabeza, in press). Some age-related PFC and MTL changes could be compensatory (see Compensatory Brain Activity in Older Adults project).

An important distinction regarding age effects on episodic memory is the distinction between vivid memories accompanied by contextual details, or recollection, and a feeling of oldness in the absence of contextual details, or familiarity. Recollection has been linked to the hippocampus and familiarity, to rhinal cortex. Older adults (OAs) tend to be impaired in recollection but not in familiarity. In one fMRI study (Daselaar et al., 2006), we found that, during retrieval, recollection-related hippocampal activity was reduced in OAs, whereas familiarity-related rhinal activity was increased in OAs. Moreover, rhinal activity was a stronger predictor of recognition judgments and was more tightly coupled with PFC activity in OAs than young adults (YAs). These results suggest that OAs compensate for deficits in hippocampal-mediated recollection by relying more on rhinal-mediated familiarity.

Age effects on recollection mechanisms occur also during encoding. In one fMRI study (Dennis et al.., 2008), participants encoded faces, scenes, and face-scene pairs. Encoding success activity (ESA) was identified by comparing subsequently remembered vs. forgotten items. Aging reduced ESA in the hippocampus and dorsolateral PFC for face-scene pairs (relational memory) but not for individual faces and scenes (item memory), consistent with a deficit in recollection. ESA in the fusiform face area (FFA) and the parahippocampal place area was reduced for all items, suggesting a more global deficit in visual memory. Interestingly, even though aging reduced ESA in the hippocampus and PFC, functional connectivity between these regions was stronger in OAs, suggesting a compensatory mechanism.

Another important distinction regarding age effects on episodic memory is the distinction between true and false memories because aging reduces true memories but increases false memories. This increase in false memories has been attributed to a deficit in memory for item-specific information coupled with a reliance on memory for semantic gist. In one study fMRI study (Dennis et al., 2007), OAs showed reduced encoding activity predicting subsequent true memory in regions associated with successful encoding of item-specific information, such as the hippocampus and left ventrolateral PFC, but increased encoding activity predicting subsequent false memory in a region associated with semantic processing: left lateral temporal cortex. We found similar age-related reductions in true-memory hippocampal activity and age-related increases in false-memory left temporal activity during retrieval (Dennis et al., 2008).

  • Daselaar, S.M., Cabeza, R., (in press). Age-related decline in working memory and episodic memory: contributions of the prefrontal cortex and medial temporal lobes. In S. Kosslyn & K. Ochsner (Eds) Oxford Handbook of Cognitive Neuroscience. Oxford University Press.
  • Daselaar, S. M., Fleck, M. S., Dobbins, I. G., Madden, D. J., & Cabeza, R. (2006). Effects of healthy aging on hippocampal and rhinal memory functions: An event-related fMRI study. Cerebral Cortex, 16, 1771-1782.
  • Dennis, N.A., Hayes, S.M., Prince, S.E., Madden, D.J., Huettel, S.A., and Cabeza, R. (2008). Effects of aging on the neural correlates of successful item and source memory encoding. Journal of Experimental Psychology: Learning, Memory, & Cognition, 34, 791-808. 
  • Dennis, N. A., Kim, H. K., & Cabeza, R. (2007). Effects of aging on true and false memory formation: An fMRI study. Neuropsychologia, 45, 3157-3166. 
  • Dennis, N. A., Kim, H., & Cabeza, R. (2008). Age-related differences in brain activity during true and false memory retrieval. Journal of Cognitive Neuroscience, 20, 1390-1402. 

 

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