The Effects of Age, Memory Performance, and Callosal Integrity on the Neural Correlates of Successful Associative Encoding

Abstract

This functional magnetic resonance imaging study investigated the relationship between the neural correlates of associative memory encoding, callosal integrity, and memory performance in older adults. Thirty-six older and 18 young subjects were scanned while making relational judgments on word pairs. Neural correlates of successful encoding (subsequent memory effects) were identified by contrasting the activity elicited by study pairs that were correctly identified as having been studied together with the activity elicited by pairs wrongly judged to have come from different study trials. Subsequent memory effects common to the 2 age groups were identified in several regions, including left inferior frontal gyrus and bilateral hippocampus. Negative effects (greater activity for forgotten than for remembered items) in default network regions in young subjects were reversed in the older group, and the amount of reversal correlated negatively with memory performance. Additionally, older subjects' subsequent memory effects in right frontal cortex correlated positively with anterior callosal integrity and negatively with memory performance. It is suggested that recruitment of right frontal cortex during verbal memory encoding may reflect the engagement of processes that compensate only partially for age-related neural degradation.

The cognitive neuroscience of ageing

“…In addition, more activation in old adults can sometimes be associated with poorer, not better, performance 54 . Recent studies have reported greater activity in the PFC during memory encoding 55 or retrieval 56 in older adults, both of which were correlated with poorer memory. Similarly, higher activity in a distributed set of regions, including PFC and parietal cortex, in old adults compared to young adults 57,58 was found to be correlated with slower and more variable reaction times on a set of visual tasks.…”

“…In some cases, over-recruitment of brain areas may reflect a greater demand on neural resources or less efficient use of them, and may or may not be related specifically to individual differences in behavior. One explanation for this is the 'partial compensation hypothesis' 55 , whereby over-recruitment of the right PFC during memory encoding may aid old adults in carrying out the encoding task because of less effective use of the left PFC, which would normally carry out this task 21,59,60 . However, this additional right PFC activity during encoding cannot compensate for a reduction in encoding effectiveness of the left PFC, and so does not provide a benefit for subsequent memory of the encoded items.…”

“…A longitudinal study 135 showed that both hippocampal volume and integrity of white matter in the corpus callosum were reduced in older adults and correlated with declining memory performance. Some studies 49,55 have found that age differences in activation within PFC were mediated by white matter integrity, such that more intact white matter was related to more activation, but others have failed to find this effect 94,136 . Despite this inconsistency in results, the use of DTI to assess white matter integrity holds considerable promise for the study of cognitive aging, particularly as the integrity of specific tracts has been shown to be related to speed of performance in older adults 137 or to accuracy of performance [138][139][140] .…”

Age differences in brain activity related to unsuccessful declarative memory retrieval

“…For example, a number of experiments have focused on brain activity during encoding of items that are remembered successfully, the so-called subsequent memory effect, and shown differences between younger and older adults indicating that successful encoding is supported by somewhat different brain areas (Cansino et al, 2010;de Chastelaine et al, 2011;Dennis et al, 2007;Duverne et al, 2009;Gutchess et al, 2005;Morcom et al, 2003). Similarly, a number of studies examining brain activity for successful recognition have reported differences between young and older adults in both frontal and parietal cortex (e.g., Daselaar et al, 2006;Duarte et al, 2008;Giovanello and Schacter, 2012;Kalpouzos et al, 2012;Morcom et al, 2007;Rajah et al, 2010;Spaniol and Grady, 2012).…”

Images of the Cognitive Brain Across Age and Culture

“…A dominant observation of age-related over-recruitment is the bilateral activation of homologous prefrontal regions in older adults on tasks where their younger counterparts show unilateral activation pattern. Specifically, whereas young adults typically engage left lateralized frontal activity for tasks that involve verbal working memory, semantic processing, and recognition memory, older adults tend to show preserved left frontal activity with additional contralateral recruitment in the homologous site of the right hemisphere that is not observed in young adults ( Figure 4; Cabeza et al, 1997;de Chastelaine et al, 2011;Daselaar et al, 2003;Duverne et al, 2009;Leshikar et al, 2010;Madden et al, 1999;Reuter-Lorenz et al, 2000;Schneider-Garces et al, 2010). Similarly, older adults engage both right and left prefrontal activity during tasks in which younger adults engage only right lateralized prefrontal activity, such as in tasks associated with face processing, spatial working memory, non-verbal spatial judgment, and episodic recall (Cabeza et al, 1997;Grady et al, 1995;Reuter-Lorenz et al, 2000).…”