Anterior hippocampus orchestrates successful encoding and retrieval of non-relational memory: an event-related fMRI study (original) (raw)
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Neuroanatomical correlates of episodic encoding and retrieval in young and elderly subjects
Brain, 2003
Lesion studies have shown convincingly that the medial temporal lobes (MTL) and frontal lobes are critical to episodic memory. Ageing generally has been found to have a generally negative effect on episodic memory performance, which might relate to neurofunctional changes in the frontal and medial temporal brain regions. In the present study, we used functional MRI (fMRI) to investigate separately the contributions of encoding and retrieval to the age-related decline in memory. To this end, we compared brain activity patterns obtained during incidental encoding (pleasant/ unpleasant judgements about nouns) and subsequent retrieval (recognition) in three groups: a group of young subjects, a group of elderly subjects showing reduced memory performance (ELD-RED), and a group of elderly subjects who still performed in the normal range (ELD-NORM). This allowed us to differentiate between age-related changes in brain activity that affect memory function and those that do not have an apparent effect on memory function, because they are found in both elderly groups. Contrary to previous imaging studies on this topic, we used (self-paced) event-related fMRI to control for differences in per-formance level across groups by including correct responses only. Comparing the encoding of successfully remembered items with baseline (press left/press right), the young subjects showed a signi®cant increase in brain activation in the left anterior MTL compared with the ELD-RED but not the ELD-NORM subjects. Comparing correctly rejected items (retrieval attempt) with baseline, the ELD-RED group showed much increased overall activity throughout the brain compared with the other groups. However, when correctly recognized items (retrieval attempt + success) were compared directly with correctly rejected items (retrieval attempt), these differences were greatly reduced, revealing common activity in the left parietal, retrosplenial and left anterior prefrontal regions. Therefore, we conclude that the reduced performance in the ELD-RED group is likely to be due to MTL dysfunction during encoding. The differences observed during retrieval attempts may re¯ect strategic differences. The lack of differences observed in relation to retrieval success suggests that ageing does not affect the processes that support the actual recovery of information.
Neuroreport, 2001
The temporal lobe regions involved in memory retrieval were examined using fMRI. During an associative recognition test, participants made memory judgments about the study color of previously presented drawings of objects, and during item recognition tests they made old/new judgments about previously studied objects or new objects. Associative recognition compared with old item recognition led to activations in bilateral hippocampal and parahippocampal regions, as well as in the left middle occipital gyrus. Old item recognition compared with new item recognition led to activation in the left middle occipital gyrus and the left middle temporal gyrus, and relative deactivations in bilateral hippocampal regions. The results indicate that partially distinct temporal lobe regions are involved during recognition memory for item and associative information.
2020
Age-related episodic memory decline is characterized by striking heterogeneity across individuals. Hippocampal pattern completion is a fundamental process supporting episodic memory. Yet, the degree to which this mechanism is impaired with age, and contributes to variability in episodic memory, remains unclear. We combine univariate and multivariate analyses of fMRI data from a large cohort of cognitively normal older adults (N=100; 60-82 yrs) to measure hippocampal activity and cortical reinstatement during retrieval of trial-unique associations. Trial-wise analyses revealed that hippocampal activity predicted cortical reinstatement strength, and these two metrics of pattern completion independently predicted retrieval success. However, increased age weakened cortical reinstatement and its relationship to memory behaviour. Critically, individual differences in the strength of hippocampal activity and cortical reinstatement explained unique variance in performance across multiple as...
Behavioural Brain Research, 2006
The main goal of the present fMRI-study was to identify the neural correlates underlying the successful encoding of words which can subsequently be freely recalled or recognized but not recalled. We were particularly interested in common as well as distinct neural substrates of both retrieval modes. To assess qualitatively differently activated brain areas, categorical subsequent memory analyses were applied. In addition, we used linear parametric modulation to detect brain regions associated with "memory-strength". Our findings suggest that the successful verbal encoding of words, which were recognized but not recalled relies on a subset of the regions engaged during successful encoding of freely recalled words. Furthermore, it seems to be dependent on the magnitude of relational binding in a prefrontal-hippocampal circuit whether a word can subsequently be recalled freely or only recognized.
Cognitive and neural correlates of memory retrieval in young and older adults
2004
Older adults are impaired in episodic and semantic retrieval but the extent of these deficits and their neural correlates is unknown. In episodic memory, older adults appear particularly impaired in retrieving bound information, such as conjunctions of items or of an item and its context. These retrieval deficits, however, may be merely the downstream effects of poor encoding. Chapter 1 presents a series of studies that test the theory that age-related recollection deficits are due to encoding failures. Results revealed that older adults were impaired in associative recognition when self-initiated processes were required at acquisition. Additional encoding support eliminated age differences, however, even when the retrieval task was made more difficult. The results support the hypothesis that recollection deficits are primarily due to poor encoding. Although older adults with encoding support can retrieve information as well as young adults, it is an open question whether brain activity supporting retrieval is identical in the two groups. In past studies, greater left prefrontal activity has been observed in older adults even when their performance does not differ from young adults. However, the circumstances under which this pattern arises and its functional significance are still unknown. Chapter 2 presents a functional magnetic resonance imaging (fMRI) study of associative recognition by young and older adults who performed equally well but who showed different patterns of recollection-related activity. Young adults exhibited greater activity in left inferior prefrontal cortex (LIPC) and inferior temporal/ fusiform gyri for retrieval based on recollection relative to retrieval based on familiarity. In the same regions, older adults exhibit increased activity whenever recollection was attempted, independent of the level of recollection success. The results are consistent with the hypothesis that increased left-lateralized retrieval activity in older adults supports recollection attempt. Age deficits in semantic memory are more subtle than in episodic memory. However, older adults are impaired when automatic, data-driven processes are not sufficient to support the retrieval of conceptual knowledge. The fMRI study described in Chapter 3 used semantic repetition priming to test two theories of the role LIPC plays in semantic retrieval. Young adults exhibited repetition-related BOLD response reductions in LIPC that were specific to the particular semantic task engaged, consistent with the hypothesis that LIPC supports controlled semantic retrieval. Older adults, in contrast, exhibited repetition-related signal reductions even when the semantic judgment made about a word differed across the two exposures, consistent with the
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1998
The medial temporal lobe (MTL) is essential for episodic memory encoding, as evidenced by memory deficits in patients with MTL damage. However, previous functional neuroimaging studies have either failed to show MTL activation during encoding or they did not differentiate between two MTL related processes: novelty assessment and episodic memory encoding. Furthermore, there is evidence that the MTL can be subdivided into subcomponents serving different memory processes, but the extent of this functional subdivision remains unknown. The aim of the present functional magnetic resonance imaging (fMRI) study was to investigate the role of the MTL in episodic encoding and to determine whether this function might be restricted to anatomical subdivisions of the MTL. Thirteen healthy volunteers performed a word list learning paradigm with free recall after distraction. Functional images acquired during encoding were analyzed separately for each participant by a voxel-wise correlation (Kendal...
Effects of Healthy Aging on Hippocampal and Rhinal Memory Functions: An Event-Related fMRI Study
Bioethics, 2006
Event-related functional magnetic resonance imaging was used to study the effects of healthy aging on hippocampal and rhinal memory functions. Memory for past events can be based on retrieval accompanied by specific contextual details (recollection) or on the feeling that an event is old or new without the recovery of contextual details (familiarity). There is evidence that recollection is more dependent on hippocampus, whereas familiarity is more dependent on the rhinal cortex, and that healthy aging has greater effects on recollection than on familiarity. However, little evidence is available about the neural correlates of these effects. Here, we isolated activity associated with recollection and familiarity by distinguishing between linear and quasi-exponential ''perceived oldness'' functions derived from recognition confidence levels. The main finding was a double dissociation within the medial temporal lobes between recollection-related activity in hippocampus, which was reduced by aging, and familiarity-related activity in rhinal cortex, which was increased by aging. In addition, age dissociations were found within parietal and posterior midline regions. Finally, aging reduced functional connectivity within a hippocampal--retrosplenial/parietotemporal network but increased connectivity within a rhinal--frontal network. These findings indicate that older adults compensate for hippocampal deficits by relying more on rhinal cortex, possibly through a top--down frontal modulation. This finding has important clinical implications because early Alzheimer's disease impairs both hippocampus and rhinal cortex.
Age effects on the neural correlates of successful memory encoding
Brain, 2003
Event-related functional MRI (fMRI) was used to investigate the neural correlates of memory encoding as a function of age. While fMRI data were obtained, 14 younger (mean age 21 years) and 14 older subjects (mean age 68 years) made animacy decisions about words. Recognition memory for these words was tested at two delays such that older subjects' performance at the short delay was comparable to that of the young subjects at the long delay. This allowed age-associated changes in the neural correlates of encoding to be dissociated from the correlates of differential recognition performance. Activity in left inferior prefrontal cortex and the left hippocampal formation was greater for subsequently recognized words in both age groups, consistent with the ®ndings of previous studies in young adults. In the prefrontal cortex, these`subsequent memory effects' were, however, left-lateralized in the younger group but bilateral in the older subjects. In addition, for the younger group only, greater activity for remembered words was observed in anterior inferior temporal cortex, as were reversed effects (`subsequent forgetting' effects) in anterior prefrontal regions. The data indicate that older subjects engage much of the same neural circuitry as younger subjects when encoding new memories. However, the ®ndings also point to age-related differences in both prefrontal and temporal activity during successful episodic encoding.
Hippocampus, 2004
Neuroscientific research has established that the hippocampal formation, a structure within the medial temporal lobe (MTL), plays a critical role in memory for facts and events (declarative memory) (Milner et al., 1998). However, its precise role remains unclear. According to one view, the hippocampus has a special role in relating or binding together previously unrelated pieces of information, while another view proposes that the hippocampus is equally involved in all forms of declarative memory, regardless of their demands on relational processing. Using functional magnetic resonance imaging (fMRI), we show that hippocampal activation is modulated by the extent to which a retrieval task depends on relational processing.