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

Tracking the intrusion of unwanted memories into awareness with event-related potentials

Involuntary retrieval of unwanted memories is a common symptom in several clinical disorders, including post-traumatic stress disorder. With an aim to track the temporal dynamics of such memory intrusions, we recorded electrophysiological measures of brain activity while participants engaged in a Think/No-Think task. We presented the left hand word (the cue) of previously encoded word pairs in green or red font. We asked participants to think of the associated right hand word (the associate) when the cue appeared in green (Think condition) and to avoid thinking of the associate when the cue appeared in red (No-Think condition). To isolate cases when participants experienced an intrusive memory, at the end of each trial, participants judged whether the response had come to mind; we classified memories that came to mind during No-Think trials, despite efforts to stop retrieval, as intrusions. In an event-related potential (ERP) analysis, we observed a negative going slow wave (NSW) effect that indexed the duration of a trace in mnemonic awareness; whereas voluntary retrieval and maintenance of the associate was related to a sustained NSW that lasted throughout the 3-s recording epoch, memory intrusions generated short-lived NSWs that were rapidly truncated. Based on these findings, we hypothesize that the intrusion-NSW reflects the associate briefly penetrating working memory. More broadly, these findings exploit the high temporal resolution of ERPs to track the online dynamics of memory intrusions

Alpha suppression as a neural marker of task demands in voluntary vs involuntary retrieval in older and younger adults

Voluntary episodic memory relies on intentionally controlled retrieval, while involuntary episodic memory comes to mind automatically. Consistent with findings of reduced cognitive control with age, recent work suggests that voluntary memory declines with age while involuntary memory is relatively preserved. However, the neurophysiology underlying these age differences has yet to be established. The current study used EEG to test 31 young and 35 older adults during voluntary vs. involuntary retrieval (manipulated between-subjects). Participants first encoded sounds, half of which were paired with pictures, the other half unpaired. EEG was then recorded as they listened to the sounds, with participants in the involuntary group performing a sound localization task, and those in the voluntary group additionally attempting to recall the associated pictures. Participants later retrospectively reported which sounds brought the paired picture to mind during the sound task. Older adults said they remembered as many pictures as young adults, but their objective memory was lower on a final cued recall test. For the EEG analysis, older adults showed greater alpha event-related desynchronization (ERD; a neural marker of memory reactivation) for paired than unpaired sounds at occipital sites, possibly reflecting visual reactivation of the associated pictures. Young adults did not show memory-related alpha ERD effects. However, young adults did show greater alpha ERD during voluntary than involuntary retrieval at frontal and occipital sites, while older adults showed pronounced alpha ERD (indicative of effortful retrieval) regardless of condition. These data suggest that alpha ERD can be used as a neural marker of memory in older adults; however, a more naturalistic paradigm may be required to study true involuntary memory with age

Functional Interplay Between Posterior Parietal Cortex and Hippocampus During Detection of Memory Targets and Non-targets

© Copyright © 2020 Ciaramelli, Burianová, Vallesi, Cabeza and Moscovitch. Posterior parietal cortex is frequently activated during episodic memory retrieval but its role during retrieval and its interactions with the hippocampus are not yet clear. In this fMRI study, we investigated the neural bases of recognition memory when study repetitions and retrieval goals were manipulated. During encoding participants studied words either once or three times, and during retrieval they were rewarded more to detect either studied words or new words. We found that (1) dorsal parietal cortex (DPC) was more engaged during detection of items studied once compared to three times, whereas regions in the ventral parietal cortex (VPC) responded more to items studied multiple times; (2) DPC, within a network of brain regions functionally connected to the anterior hippocampus, responded more to items consistent with retrieval goals (associated with high reward); (3) VPC, within a network of brain regions functionally connected to the posterior hippocampus, responded more to items not aligned with retrieval goals (i.e., unexpected). These findings support the hypothesis that DPC and VPC regions contribute differentially to top-down vs. bottom-up attention to memory. Moreover, they reveal a dissociation in the functional profile of the anterior and posterior hippocampi

From Cue to Recall : The Temporal Dynamics of Long-Term Memory Retrieval

A fundamental function of long-term memory is the ability to retrieve a specific memory when encountering a retrieval cue. The purpose of this dissertation was to further our understanding of such cued recall by investigating the temporal dynamics from the presentation of the retrieval cue until the target memory is recalled. Retrieval cues are often related with several memories. When such a retrieval cue is presented, the associated memories will compete for retrieval and this retrieval competition needs to be handled in order to retrieve the sought after target memory. Study 1 and Study 2 investigated the temporal dynamics of such competitive semantic cued recall. Interestingly, previous research has shown that the ability to retrieve the currently relevant target memory comes with a cost, namely retrieval-induced forgetting of the competing memories. These studies also investigated the role of competitor activation and target retrieval in this forgetting phenomenon. Study 1 investigated the electrophysiological correlates of reactivation of competing currently irrelevant memories and the role of such competitor activation in retrieval-induced forgetting. Competitor activation was related to an FN400 event-related potential (ERP) effect and this effect predicted increased levels of retrieval-induced forgetting, indicating that this forgetting effect is dependent on competitor activation. Study 2 examined processes involved in target retrieval in a similar competitive semantic cued recall task. The main finding in this study was that attempts to retrieve the target memory were related to a late posterior negativity ERP effect. Another important finding was that behavioural and ERP measures of target retrieval were unrelated to retrieval-induced forgetting. Retrieval cues can sometimes elicit involuntary retrieval of unwanted memories. Such memory intrusions are a core symptom of post-traumatic stress disorder. Study 3 investigated the temporal dynamics of such memory intrusions. One of the key findings was that memory intrusions were related to a negative slow wave ERP effect possibly reflecting the activation of the intruding memory in working memory. Taken together the findings in the dissertation indicate that cued recall involves several cognitive processes ranging from early automatic memory reactivation to conscious processes such as working memory activation and recollection. The findings have implications for cognitive theories of memory and have relevance for several clinical conditions including depression and post-traumatic stress disorder

The Role of Working Memory in Spontaneous Recognition: Neural Correlates and Behavioural Influences in the Memory Stroop Paradigm

Research suggests that unintentional recognition of distracting non-target stimuli can bias goal-related, intentional recognition judgements to target stimuli encountered in the same environment. Spontaneous recognition (SR) effect can be defined as the unintentional recognition of stimuli and is measured by the effect of familiarity to distractors on a recognition task. This thesis investigated how previously seen or not-seen distractors affect recognition of targets when working memory (WM) resources are manipulated by a secondary WM load task (chapter 2), using both behavioural and ERP measures (Chapter 3). The findings suggest that when working memory resources are low, SR is then easier to observe. Additionally, neural and memory processes are dissociable for unintentional and intentional recognition and retrieval monitoring is found to be enhanced when the new targets were paired with old distractors. Furthermore, the findings on the early ERPs may suggest that the proactive control might be activated. Finally, a set of experiments revealed that, SR effect may not be related to conscious awareness since having a low or high confidence did not modulate the SR effect indicating a lack of conscious awareness of the SR effect (Chapter 4). Together these findings may help to understand the mechanisms underlying the SR effect