Reduced Specificity of Hippocampal and Posterior Ventrolateral Prefrontal Activity during Relational Retrieval in Normal Aging

Neuroimaging studies of episodic memory in young adults demonstrate greater functional neural activity in ventrolateral pFC and hippocampus during retrieval of relational information as compared with item information. We tested the hypothesis that healthy older adults—individuals who exhibit behavioral declines in relational memory—would show reduced specificity of ventrolateral prefrontal and hippocampal regions during relational retrieval. At study, participants viewed two nouns and were instructed to covertly generate a sentence that related the words. At retrieval, fMRIs were acquired during item and relational memory tasks. In the relational task, participants indicated whether the two words were previously seen together. In the item task, participants indicated whether both items of a pair were previously seen. In young adults, left posterior ventrolateral pFC and bilateral hippocampal activity was modulated by the extent to which the retrieval task elicited relational processing. In older adults, activity in these regions was equivalent for item and relational memory conditions, suggesting a reduction in ventrolateral pFC and hippocampal specificity with normal aging.Psycholog

The Role of Medial Temporal Lobe Regions in Incidental and Intentional Retrieval of Item and Relational Information in Aging: Medial Temporal Lobes in Aging and Memory

Considerable neuropsychological and neuroimaging work indicates that the medial temporal lobes are critical for both item and relational memory retrieval. However, there remain outstanding issues in the literature, namely the extent to which medial temporal lobe regions are differentially recruited during incidental and intentional retrieval of item and relational information, and the extent to which aging may affect these neural substrates. The current fMRI study sought to address these questions; participants incidentally encoded word pairs embedded in sentences and incidental item and relational retrieval were assessed through speeded reading of intact, rearranged, and new word-pair sentences, while intentional item and relational retrieval were assessed through old/new associative recognition of a separate set of intact, rearranged, and new word pairs. Results indicated that, in both younger and older adults, anterior hippocampus and perirhinal cortex indexed incidental and intentional item retrieval in the same manner. In contrast, posterior hippocampus supported incidental and intentional relational retrieval in both age groups and an adjacent cluster in posterior hippocampus was recruited during both forms of relational retrieval for older, but not younger, adults. Our findings suggest that while medial temporal lobe regions do not differentiate between incidental and intentional forms of retrieval, there are distinct roles for anterior and posterior medial temporal lobe regions during retrieval of item and relational information, respectively, and further indicate that posterior regions may, under certain conditions, be over-recruited in healthy aging

Reduced Specificity of Hippocampal and Posterior Ventrolateral Prefrontal Activity during Relational Retrieval in Normal Aging

Neuroimaging studies of episodic memory in young adults demonstrate greater functional neural activity in ventrolateral prefrontal cortex and hippocampus during retrieval of relational, as compared to item, information. We tested the hypothesis that healthy older adults – individuals who exhibit behavioral declines in relational memory – would show reduced specificity of ventrolateral prefrontal and hippocampal regions during relational retrieval. At study, participants viewed two nouns and were instructed to covertly generate a sentence that related the words. At retrieval, functional magnetic resonance images were acquired during item and relational memory tasks. In the relational task, participants indicated whether the two words were previously seen together. In the item task, participants indicated whether both items of a pair were previously seen. In young adults, left posterior ventrolateral PFC and bilateral hippocampal activity was modulated by the extent to which the retrieval task depended on relational processing. In older adults, activity in these regions was equivalent for item and relational memory conditions, suggesting a reduction in ventrolateral PFC and hippocampal specificity with normal aging

The effects of attention on age-related relational memory deficits: Evidence from a novel attentional manipulation.

Healthy aging is often accompanied by episodic memory decline. Prior studies have consistently demonstrated that older adults show disproportionate deficits in relational memory (RM) relative to item memory (IM). Despite rich evidence of an age-related RM deficit, the source of this deficit remains unspecified. One of the most widely investigated factors of age-related RM impairment is a reduction in attentional resources. However, no prior studies have demonstrated that reduced attentional resources are the critical source of age-related RM deficits. Here, we utilized qualitatively different attention tasks, and tested whether reduced attention for relational processing underlies the RM deficit observed in aging. In Experiment 1, we imposed either item-detection or relation-detection attention tasks on young adults during episodic memory encoding, and found that only the concurrent attention task involving relational processing disproportionately impaired RM performance in young adults. Moreover, by ruling out the possible confound of task-difficulty on the disproportionate RM impairment, we further demonstrated that reduced relational attention is a key factor for the age-related RM deficit. In Experiment 2, we replicated the results from Experiment 1 using different materials of stimuli and found that the effect of relational attention on RM is material-general. The results of Experiment 2 also showed that reducing attentional resources for relational processing in young adults strikingly equated their RM performance to that of older adults. Thus, the current study documents the first evidence that reduced attentional resources for relational processing are a critical factor for the relational memory impairment observed in aging

The Effects of Attention on Age-related Relational Memory Deficits: fMRI Evidence from a Novel Attentional Manipulation

Numerous studies have documented that older adults (OAs) do not perform as well as young adults (YAs) when task demands require the establishment or retrieval of a novel link between previously unrelated information (relational memory: RM). Nonetheless, the source of this age-related RM deficit remains unspecified. One of the most widely investigated factors is an age-related reduction in attentional resources. To investigate this factor, previous researchers have tested whether dividing YAs' attention during encoding equated their RM performance to that of OAs. However, results from these studies failed to replicate the age-related RM impairment observed in aging. The current study investigated whether a reduction in attentional resources for processing of relational information (i.e., relational attention) underlies age-related RM deficits. Using fMRI, we examined whether the effect of reduced attentional resources for processing of relational information is similar to that observed in aging at both behavioral and neural levels. The behavioral results showed that reduced attentional resources for relational information during encoding equated YAs RM performance to that of OAs. Furthermore, the fMRI results demonstrated that both aging, as well as reductions in relational attention in YAs, significantly reduced activity in brain areas associated with successful RM formation, namely, the ventrolateral and dorsolateral PFC, superior and inferior parietal regions, and left hippocampus. Such converging evidence from behavioral and neuroimaging studies suggests that a reduction in attentional resources for relational information is a critical factor for the RM deficit observed in aging

Aged-Related Neural Changes During Memory Conjunction Errors

Human behavioral studies demonstrate that healthy aging is often accompanied by increases in memory distortions or errors. Here we used event-related functional MRI to examine the neural basis of age-related memory distortions. We used the memory conjunction error paradigm, a laboratory procedure known to elicit high levels of memory errors. For older adults, right parahippocampal gyrus showed significantly greater activity during false than during accurate retrieval. We observed no regions in which activity was greater during false than during accurate retrieval for young adults. Young adults, however, showed significantly greater activity than old adults during accurate retrieval in right hippocampus. By contrast, older adults demonstrated greater activity than young adults during accurate retrieval in right inferior and middle prefrontal cortex. These data are consistent with the notion that age-related memory conjunction errors arise from dysfunction of hippocampal system mechanisms, rather than impairments in frontally-mediated monitoring processes.Psycholog

The status of rapid response learning in aging.

Strong evidence exists for an age-related impairment in associative processing under intentional encoding and retrieval conditions, but the status of incidental associative processing has been less clear. Two experiments examined the effects of age on rapid response learning – the incidentally learned stimulus-response association that results in a reduction in priming when a learned response becomes inappropriate for a new task. Specifically, we tested whether priming was equivalently sensitive in both age groups to reversing the task-specific decision cue. Experiment 1 showed that cue inversion reduced priming in both age groups using a speeded inside/outside classification task, and in Experiment 2 cue inversion eliminated priming on an associative version of this task. Thus, the ability to encode an association between a stimulus and its initial task-specific response appears to be preserved in aging. These findings provide an important example of a form of associative processing that is unimpaired in older adults

The effect of age on relational encoding as revealed by hippocampal functional connectivity

The neural processes mediating cognition occur in networks distributed throughout the brain. The encoding and retrieval of relational memories, memories for multiple items or multifeatural events, is supported by a network of brain regions, particularly the hippocampus. The hippocampal coupling hypothesis suggests that the hippocampus is functionally connected with the default mode network (DMN) during retrieval, but during encoding, decouples from the DMN. Based on prior research suggesting that older adults are less able to modulate between brain network states, we tested the hypothesis that older adults’ hippocampus would show functional connectivity with the DMN during relational encoding. The results suggest that, while the hippocampus is functionally connected to some regions of the DMN during relational encoding in both younger and older adults, older adults show additional DMN connectivity. Such age-related changes in network modulation appear not to be mediated by compensatory processes, but rather to reflect a form of neural inefficiency, most likely due to reduced inhibition

Neural correlates of familiarity-based associative retrieval

The current study compared the neural correlates of associative retrieval of compound (unitized) stimuli and unrelated (non-unitized) stimuli. Although associative recognition was nearly identical for compounds and unrelated pairs, accurate recognition of these different pair types was associated with activation in distinct regions within the medial temporal lobe (MTL). Recognition of previously presented compound words was associated with left perirhinal activity, whereas recognition of unrelated word pairs was associated with activity in left hippocampus. These results provide evidence that perirhinal cortex mediates familiarity-based associative memory of stimuli unitized at encoding, while the hippocampus is required for recollection-based associative memory

Episodic Memory in Former Professional Football Players with a History of Concussion: An Event-Related Functional Neuroimaging Study

Previous research has demonstrated that sport-related concussions can have short-term effects on cognitive processes, but the long-term consequences are less understood and warrant more research. This study was the first to use event-related functional magnetic resonance imaging (fMRI) to examine long-term differences in neural activity during memory tasks in former athletes who have sustained multiple sport-related concussions. In an event-related fMRI study, former football players reporting multiple sport-related concussions (i.e., three or more) were compared with players who reported fewer than three concussions during a memory paradigm examining item memory (i.e., memory for the particular elements of an event) and relational memory (i.e., memory for the relationships between elements). Behaviorally, we observed that concussion history did not significantly affect behavioral performance, because persons in the low and high concussion groups had equivalent performance on both memory tasks, and in addition, that concussion history was not associated with any behavioral memory measures. Despite demonstrating equivalent behavioral performance, the two groups of former players demonstrated different neural recruitment patterns during relational memory retrieval, suggesting that multiple concussions may be associated with functional inefficiencies in the relational memory network. In addition, the number of previous concussions significantly correlated with functional activity in a number of brain regions, including the medial temporal lobe and inferior parietal lobe. Our results provide important insights in understanding the long-term functional consequences of sustaining multiple sports-related concussions