Priming for novel object associations: Neural differences from object item priming and equivalent forms of recognition

The neural substrates of associative and item priming and recognition were investigated in a functional magnetic resonance imaging study over two separate sessions. In the priming session, participants decided which object of a pair was bigger during both study and test phases. In the recognition session, participants saw different object pairs and performed the same size‐judgement task followed by an associative recognition memory task. Associative priming was accompanied by reduced activity in the right middle occipital gyrus as well as in bilateral hippocampus. Object item priming was accompanied by reduced activity in extensive priming‐related areas in the bilateral occipitotemporofrontal cortex, as well as in the perirhinal cortex, but not in the hippocampus. Associative recognition was characterized by activity increases in regions linked to recollection, such as the hippocampus, posterior cingulate cortex, anterior medial frontal gyrus and posterior parahippocampal cortex. Item object priming and recognition recruited broadly overlapping regions (e.g., bilateral middle occipital and prefrontal cortices, left fusiform gyrus), even though the BOLD response was in opposite directions. These regions along with the precuneus, where both item priming and recognition were accompanied by activation, have been found to respond to object familiarity. The minimal structural overlap between object associative priming and recollection‐based associative recognition suggests that they depend on largely different stimulus‐related information and that the different directions of the effects indicate distinct retrieval mechanisms. In contrast, item priming and familiarity‐based recognition seemed mainly based on common memory information, although the extent of common processing between priming and familiarity remains unclear. Further implications of these findings are discussed. © 2015 Wiley Periodicals, Inc.     

Selective and shared contributions of the hippocampus and perirhinal cortex to episodic item and associative encoding

Although the general role of the medial-temporal lobe (MTL) in episodic memory is well established, controversy surrounds the precise division of labor between distinct MTL subregions. The perirhinal cortex (PrC) has been hypothesized to support nonassociative item encoding that contributes to later familiarity, whereas the hippocampus supports associative encoding that selectively contributes to later recollection. However, because previous paradigms have predominantly used recollection of the item context as a measure of associative encoding, it remains unclear whether recollection of different kinds of episodic detail depends on the same or different MTL encoding operations. In our current functional magnetic resonance imaging study, we devised a subsequent memory paradigm that assessed successful item encoding in addition to the encoding of two distinct episodic details: an item-color and an item-context detail. Hippocampal encoding activation was selectively enhanced during trials leading to successful recovery of either an item-color or item-context association. Moreover, the magnitude of hippocampal activation correlated with the number, and not the kind, of associated details successfully bound, providing strong evidence for a role of the hippocampus in domain-general associative encoding. By contrast, PrC encoding activation correlated with both nonassociative item encoding as well as associative item-color binding, but not with item-context binding. This pattern suggests that the PrC contributions to memory encoding may be domain-specific and limited to the binding of items with presented item-related features. Critically, together with a separately conducted behavioral study, these data raise the possibility that PrC encoding operations -- in conjunction with hippocampal mechanisms -- contribute to later recollection of presented item details.     

Associative reinstatement: A novel approach to assessing associative memory in patients with unilateral temporal lobe excisions

We investigated whether unilateral medial temporal lobe (MTL) damage disrupts associative reinstatement, which represents the gain in item memory when the studied associative information is reinstated at retrieval. We were interested to see whether associative reinstatement relies on the same relational binding operations that support other types of associative memory (associative identification and recollection) thought to be subserved by the MTL. In addition, we examined whether such damage affects the different types of associative memory to a greater extent than item memory and item familiarity, and whether a different pattern is seen in patients with language dominant relative to non-dominant temporal lobe resection when the studied material consists of verbal information. To do so, we used a word pair recognition paradigm composed of two tasks: (1) a pair recognition task that provides measures of associative reinstatement and item memory, and (2) an associative identification recognition task that provides a measure of associative identification memory. Estimates of item familiarity and recollection were derived from performance on both tasks using a variant of the process-dissociation procedure. Our results showed that associative reinstatement, like other types of associative memory measures, was impaired in patients with unilateral resection, irrespective of the side of damage. Item familiarity, however, was impaired solely following language dominant resection. The lack of a laterality effect in our relational measures was likely due to using an encoding task that promoted formation of both verbal and visual associations, whereas item-based familiarity could rely exclusively on verbal operations. We propose that associative reinstatement provides a sensitive measure of relational memory that is less dependent on strategic processing and therefore more appropriate for evaluating MTL function in patients.     

Associative encoding of pictures activates the medial temporal lobes

It remains unresolved whether the medial temporal lobe activations found in recent neuroimaging studies are mediated by novelty detection alone, by specific kinds of encoding or consolidation operations, or both. This study attempted to see whether associative encoding or consolidation is sufficient to cause such activation by matching for novelty across conditions. Using single-photon emission computer tomography (SPECT) (with Tc^99mHMPAO), we compared the activation patterns produced by the associative encoding and the perceptual matching of novel complex scenes in 10 normal subjects using both statistical parametric mapping (SPM) and a regions-of-interest (ROI) approach. During the encoding condition, significant activations were detected in the left hippocampal/parahippocampal region, the left cingulate cortex, and the right prefrontal cortex, using both statistical techniques. Additionally, activation was found in the right cingulate cortex, and a trend towards activation was found in the right hippocampal/parahippocampal region using the ROI approach. In contrast, no medial temporal activations were found during the matching condition, which produced bilateral occipito-parietal and right posterior inferior parietal (supramarginal gyrus) activations. These results not only confirm that the associative encoding and/or consolidation of complex scenes is partially mediated by medial temporal lobe structures, but also demonstrate, for the first time, that associative encoding/consolidation is sufficient to produce such an activation. The implications of the high degree of consistency revealed by the results of the SPM and ROI comparison are discussed. Hum. Brain Mapping 6:85–104, 1998. © 1998 Wiley-Liss, Inc.     

Repetition suppression in the medial temporal lobe and midbrain is altered by event overlap

Repeated encounters with the same event typically lead to decreased activation in the medial temporal lobe (MTL) and dopaminergic midbrain, a phenomenon known as repetition suppression. In contrast, encountering an event that overlaps with prior experience leads to increased response in the same regions. Such increased responding is thought to reflect an associative novelty signal that promotes memory updating to resolve differences between current events and stored memories. Here, we married these ideas to test whether event overlap significantly modulates MTL and midbrain responses—even when events are repeated and expected—to promote memory updating through integration. While undergoing high‐resolution functional MRI, participants were repeatedly presented with objects pairs, some of which overlapped with other, intervening pairs and some of which contained elements unique from other pairs. MTL and midbrain regions showed widespread repetition suppression for nonoverlapping pairs containing unique elements; however, the degree of repetition suppression was altered for overlapping pairs. Entorhinal cortex, perirhinal cortex (PRc), midbrain, and PRc—midbrain connectivity showed repetition‐related increases across overlapping pairs. Notably, increased PRc activation for overlapping pairs tracked individual differences in the ability to reason about the relationships among pairs—our behavioral measure of memory integration. Within the hippocampus, activation increases across overlapping pairs were unique to CA₁, consistent with its hypothesized comparator function. These findings demonstrate that event overlap engages MTL and midbrain functions traditionally implicated in novelty processing, even when overlapping events themselves are repeated. Our findings further suggest that the MTL—midbrain response to event overlap may promote integration of new content into existing memories, leading to the formation of relational memory networks that span experiences. Moreover, the results inform theories about the division of labor within MTL, demonstrating that the role of PRc in episodic encoding extends beyond familiarity processing and item‐level recognition. © 2016 Wiley Periodicals, Inc.     

Neural correlates of memory for items and for associations: an event-related functional magnetic resonance imaging study

Although results from cognitive psychology, neuropsychology, and behavioral neuroscience clearly suggest that item and associative information in memory rely on partly different brain regions, little is known concerning the differences and similarities that exist between these two types of information as a function of memory stage (i.e., encoding and retrieval). We used event-related functional magnetic resonance imaging to assess neural correlates of item and associative encoding and retrieval of simple images in 18 healthy subjects. During encoding, subjects memorized items and pairs. During retrieval, subjects made item recognition judgments (old vs. new) and associative recognition judgments (intact vs. rearranged). Relative to baseline, item and associative trials activated bilateral medial temporal and prefrontal regions during both encoding and retrieval. Direct contrasts were then performed between item and associative trials for each memory stage. During en- coding, greater prefrontal, hippocampal, and parietal activation was observed for associations, but no significant activation was observed for items at the selected threshold. During recognition, greater activation was observed for associative trials in the left dorsolateral prefrontal cortex and superior parietal lobules bilaterally, whereas item recognition trials showed greater activation of bilateral frontal regions, bilateral anterior medial temporal areas, and the right temporo-parietal junction. Post hoc analyses suggested that the anterior medial temporal activation observed during item recognition was driven mainly by new items, confirming a role for this structure in novelty detection. These results suggest that although some structures such as the medial temporal and prefrontal cortex play a general role in memory, the pattern of activation in these regions can be modulated by the type of information (items or associations) interacting with memory stages.     

Multiple repetitions reveal functionally and anatomically distinct patterns of hippocampal activity during continuous recognition memory

We used a continuous recognition procedure that included multiple presentations of test items, along with high-resolution functional magnetic resonance imaging (fMRI), to investigate the relationship between item novelty and recognition-related activity in the medial temporal lobe (MTL). In several regions of hippocampus and parahippocampal cortex, activity elicited by new items exceeded that for old items, whereas no MTL regions exhibited greater activity for old items. Critically, anatomically distinct regions of MTL were engaged by item novelty in two different ways, as evidenced by statistically dissociable profiles of activity. In bilateral medial hippocampus and left posterior parahippocampal cortex, activity followed a categorical profile in which it was greater for new than old items but did not differ further with additional presentations of old items. By contrast, effects in adjacent regions of right lateral hippocampus and left parahippocampal cortex were graded, whereby activity declined linearly with respect to each successive item presentation. These findings suggest that the relationship between hippocampal (and parahippocampal) activity and continuous psychological dimensions, such as item novelty, cannot be captured by a unitary function.     

Associative memory encoding and recognition in schizophrenia: an event-related fMRI study.

BACKGROUND: We used an event-related functional Magnetic Resonance Imaging (fMRI) approach to examine the neural basis of the selective associative memory deficit in schizophrenia. METHODS: Fifteen people with schizophrenia and 18 controls were scanned during a pair and item memory encoding and recognition task. During encoding, subjects studied items and pairs of visual objects. In a subsequent retrieval task, participants performed an item recognition memory test (old/new decisions) and an associative recognition test (intact/rearranged decisions). The fMRI analysis of the recognition data was restricted to correct items only and a random effects model was used. RESULTS: At the behavioral level, both groups performed equally well on item recognition, whereas people with schizophrenia demonstrated lower performance on associative recognition relative to the control group. At the brain level, the comparison between associative and item encoding revealed greater activity in the control group in the left prefrontal cortex and cingulate gyrus relative to the schizophrenia group. During recognition, greater left dorsolateral prefrontal and right inferior prefrontal activations were observed in the control group relative to the schizophrenia group. CONCLUSION: This fMRI study implicates the prefrontal cortex among other brain regions as the basis for the selective associative memory encoding and recognition deficit seen in schizophrenia.     

Reward modulation of hippocampal subfield activation during successful associative encoding and retrieval

Emerging evidence suggests that motivation enhances episodic memory formation through interactions between medial-temporal lobe (MTL) structures and dopaminergic midbrain. In addition, recent theories propose that motivation specifically facilitates hippocampal associative binding processes, resulting in more detailed memories that are readily reinstated from partial input. Here, we used high-resolution fMRI to determine how motivation influences associative encoding and retrieval processes within human MTL subregions and dopaminergic midbrain. Participants intentionally encoded object associations under varying conditions of reward and performed a retrieval task during which studied associations were cued from partial input. Behaviorally, cued recall performance was superior for high-value relative to low-value associations; however, participants differed in the degree to which rewards influenced memory. The magnitude of behavioral reward modulation was associated with reward-related activation changes in dentate gyrus/CA(2,3) during encoding and enhanced functional connectivity between dentate gyrus/CA(2,3) and dopaminergic midbrain during both the encoding and retrieval phases of the task. These findings suggests that, within the hippocampus, reward-based motivation specifically enhances dentate gyrus/CA(2,3) associative encoding mechanisms through interactions with dopaminergic midbrain. Furthermore, within parahippocampal cortex and dopaminergic midbrain regions, activation associated with successful memory formation was modulated by reward across the group. During the retrieval phase, we also observed enhanced activation in hippocampus and dopaminergic midbrain for high-value associations that occurred in the absence of any explicit cues to reward. Collectively, these findings shed light on fundamental mechanisms through which reward impacts associative memory formation and retrieval through facilitation of MTL and ventral tegmental area/substantia nigra processing.     

Common pathway in the medial temporal lobe for storage and recovery of words as revealed by event-related functional MRI

Lesion studies have provided compelling evidence that episodic memory is dependent on the integrity of the medial temporal lobe (MTL). This role of the MTL in episodic memory has been supported by several neuroimaging studies during both episodic encoding and retrieval. After two meta-analyses of positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies, we investigated a possible dissociation within the MTL memory system in relation to encoding and retrieval processes. Based on previous reports that specifically related the function of the MTL in episodic memory to successful encoding and actual recovery of information, we applied event-related fMRI to compare successful encoding of words (ES) directly with successful recognition of those same words (RS). Our results did not indicate a clear dissociation between encoding and retrieval activations in the MTL. Instead, a region in the left MTL, covering the parahippocampal cortex and hippocampal formation, which was activated during ES almost completely overlapped with the area that was activated during RS. An additional region in the left anterior MTL, including the entorhinal cortex, was found to be activated exclusively during ES. Research has indicated that a large percentage of cells in this region are particularly sensitive to the relative novelty of stimuli. Our results, therefore, suggest that the parahippocampal/hippocampal region is involved in the formation and subsequent reactivation of memory traces, whereas the activity observed in the entorhinal cortex may reflect elementary memory processes related to novelty detection.     

Encoding of novel picture pairs activates the perirhinal cortex: an fMRI study

It is well established in nonhuman primates that the medial temporal lobe (MTL) structures, the hippocampus and the entorhinal and perirhinal cortices, are necessary for declarative memory encoding. In humans, the neuropathological and neuropsychological changes in early Alzheimer's disease (AD) further support a role for the rhinal cortex in the consolidation of new events into long-term memory. Little is known, however, regarding the function of the rhinal cortex in humans in vivo. To examine the participation of the interconnected MTL structures as well as the whole-brain network of activated brain areas in visual associative long-term memory, functional magnetic resonance imaging (fMRI) was used to determine the brain regions that are activated during encoding and retrieval of paired pictures in 12 young control subjects. The most striking finding in the MTL activation pattern was the consistent activation of the perirhinal cortex in the encoding-baseline and encoding-retrieval comparisons with a strict statistical threshold (P < 0.00001). In contrast, no perirhinal cortex activation was detected in the retrieval-baseline or retrieval-encoding comparisons even with a low statistical threshold (P < 0.05). The location of the perirhinal activation area was in the transentorhinal part of the perirhinal cortex, in the medial bank of the collateral sulcus. The hippocampus and the more posterior parahippocampal gyrus were activated in both encoding and retrieval conditions. During the encoding processing, MTL activations were more consistent and the hippocampal activation area located more anteriorly than during retrieval. The frontal, parietal, temporal, and occipital association cortices were also activated in the encoding-baseline and retrieval-baseline comparisons. The data suggest that encoding, but not retrieval, of novel picture pairs activates the perirhinal cortex. To our knowledge, this is the first fMRI study reporting encoding activation in this transentorhinal part of the perirhinal cortex, the site of the very earliest neuropathological changes in AD.     

Involvement of the medial temporal lobe in priming for new associations

This study was addressed to the question of whether the medial temporal lobe (MTL) plays a critical role in implicit memory for new associations. Priming for new associations was examined in two different tasks in 18 patients with focal lesions all involving the MTL. In Experiment 1, following a study phase for pairs of unrelated words, subjects performed a perceptual identification task on old, recombined, and new pairs of words presented at brief exposure durations. In contrast to control subjects, and despite a normal level of item priming, the patients failed to show superior identification of the old pairs relative to the recombined pairs, the measure of associative priming. In Experiment 2, subjects engaged in speeded naming of the print color for previously studied words presented in the original color or in a different old color, and for unstudied words. Again, in contrast to control subjects and despite a normal level of item facilitation on color naming reaction time (RT), the patients failed to show priming for recently experienced new associations between words and colors. Explicit recognition memory by the patients was abnormal in both experiments. This study records an absence of priming for new associations, in two different tasks in which the nature of the stimuli was considerably different, in a large group of patients with lesions in the MTL. Although some previous research has reported significant associative priming in other tasks for patients with MTL lesions, the present results suggest that this region is critical for forming new associations of the types assessed here.     

Relating medial temporal lobe volume to frontal fMRI activation for memory encoding in older adults

Neuroimaging research on the brain basis of memory decline in older adults typically has examined age-related changes either in structure or in function. Structural imaging studies have found that smaller medial temporal lobe (MTL) volumes are associated with lower memory performance. Functional imaging studies have found that older adults often exhibit bilateral frontal-lobe activation under conditions where young adults exhibit unilateral frontal activation. As yet, no one has examined whether these MTL structural and frontal-lobe functional findings are associated. In this study, we tested whether these findings were correlated in a population of healthy older adults in whom we previously demonstrated verbal memory performance was positively associated with left entorhinal cortex volume in the MTL (Rosen et al., 2003) and right frontal lobe activation during memory encoding (Rosen et al., 2002). Thirteen, non-demented, community-dwelling older adults participated both in a functional MRI (fMRI) study of verbal memory encoding and structural imaging. MRI-derived left entorhinal volume was measured on structural images and entered as a regressor against fMRI activation during verbal memory encoding. Right frontal activation (Brodmann's Area 47/insula) was positively correlated with left entorhinal cortex volume. These findings indicate a positive association between MTL volume and right frontal-lobe function that may underlie variability in memory performance among the elderly, and also suggest a two-stage model of memory decline in aging.     

Medial temporal lobe activation during encoding and retrieval of novel face-name pairs

The human medial temporal lobe (MTL) is known to be involved in declarative memory, yet the exact contributions of the various MTL structures are not well understood. In particular, the data as to whether the hippocampal region is preferentially involved in the encoding and/or retrieval of associative memory have not allowed for a consensus concerning its specific role. To investigate the role of the hippocampal region and the nearby MTL cortical areas in encoding and retrieval of associative versus non-associative memories, we used functional magnetic resonance imaging (fMRI) to measure brain activity during learning and later recognition testing of novel face-name pairs. We show that there is greater activity for successful encoding of associative information than for non-associative information in the right hippocampal region, as well as in the left amygdala and right parahippocampal cortex. Activity for retrieval of associative information was greater than for non-associative information in the right hippocampal region also, as well as in the left perirhinal cortex, right entorhinal cortex, and right parahippocampal cortex. The implications of these data for a clear functional distinction between the hippocampal region and the MTL cortical structures are discussed.     

Differential roles for medial prefrontal and medial temporal cortices in schema-dependent encoding: From congruent to incongruent

Information that is congruent with prior knowledge is generally remembered better than incongruent information. This effect of congruency on memory has been attributed to a facilitatory influence of activated schemas on memory encoding and consolidation processes, and hypothesised to reflect a shift between processing in medial temporal lobes (MTL) towards processing in medial prefrontal cortex (mPFC). To investigate this shift, we used functional magnetic resonance imaging (fMRI) to compare brain activity during paired-associate encoding across three levels of subjective congruency of the association with prior knowledge. Participants indicated how congruent they found an object-scene pair during scanning, and were tested on item and associative recognition memory for these associations one day later. Behaviourally, we found a monotonic increase in memory performance with increasing congruency for both item and associative memory. Moreover, as hypothesised, encoding-related activity in mPFC increased linearly with increasing congruency, whereas MTL showed the opposite pattern of increasing encoding-related activity with decreasing congruency. Additionally, mPFC showed increased functional connectivity with a region in the ventral visual stream, presumably related to the binding of visual representations. These results support predictions made by a recent neuroscientific framework concerning the effects of schema on memory. Specifically, our findings show that enhanced memory for more congruent information is mediated by the mPFC, which is hypothesised to guide integration of new information into a pre-existing schema represented in cortical areas, while memory for more incongruent information relies instead on automatic encoding of arbitrary associations by the MTL.     

Entorhinal cortex structure and functional MRI response during an associative verbal memory task

Entorhinal cortex (ERC) volume in adults with mild cognitive impairment has been shown to predict prodromal Alzheimer's disease (AD). Likewise, neuronal loss in ERC has been associated with AD, but not with normal aging. Because ERC is part of a major pathway modulating input to the hippocampus, structural changes there may result in changes to cognitive performance and functional brain activity during memory tasks. In 32 cognitively intact older adults, we examined the relationship between left ERC thickness and functional magnetic resonance imaging (fMRI) activity during an associative verbal memory task. This task has been shown previously to activate regions that are sensitive to aging and AD risk. ERC was manually defined on native space, high resolution, oblique coronal MRI scans. Subjects having thicker left ERC showed greater activation in anterior cingulate and medial frontal regions during memory retrieval, but not encoding. This result was independent of hippocampal volume. Anterior cingulate cortex is directly connected to ERC, and is, along with medial frontal cortex, implicated in error detection, which is impaired in AD. Our results suggest that in healthy older adults, processes that engage frontal regions during memory retrieval are related to ERC structure. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.     

The medial temporal lobes distinguish between within‐item and item‐context relations during autobiographical memory retrieval

During autobiographical memory retrieval, the medial temporal lobes (MTL) relate together multiple event elements, including object (within‐item relations) and context (item‐context relations) information, to create a cohesive memory. There is consistent support for a functional specialization within the MTL according to these relational processes, much of which comes from recognition memory experiments. In this study, we compared brain activation patterns associated with retrieving within‐item relations (i.e., associating conceptual and sensory‐perceptual object features) and item‐context relations (i.e., spatial relations among objects) with respect to naturalistic autobiographical retrieval. We developed a novel paradigm that cued participants to retrieve information about past autobiographical events, non‐episodic within‐item relations, and non‐episodic item‐context relations with the perceptuomotor aspects of retrieval equated across these conditions. We used multivariate analysis techniques to extract common and distinct patterns of activity among these conditions within the MTL and across the whole brain, both in terms of spatial and temporal patterns of activity. The anterior MTL (perirhinal cortex and anterior hippocampus) was preferentially recruited for generating within‐item relations later in retrieval whereas the posterior MTL (posterior parahippocampal cortex and posterior hippocampus) was preferentially recruited for generating item‐context relations across the retrieval phase. These findings provide novel evidence for functional specialization within the MTL with respect to naturalistic memory retrieval. © 2015 Wiley Periodicals, Inc.     

The parahippocampal gyrus links the default‐mode cortical network with the medial temporal lobe memory system

The default‐mode network (DMN) is a distributed functional‐anatomic network implicated in supporting memory. Current resting‐state functional connectivity studies in humans remain divided on the exact involvement of medial temporal lobe (MTL) in this network at rest. Notably, it is unclear to what extent the MTL regions involved in successful memory encoding are connected to the cortical nodes of the DMN during resting state. Our findings using functional connectivity MRI analyses of resting‐state data indicate that the parahippocampal gyrus (PHG) is the primary hub of the DMN in the MTL during resting state. Also, connectivity of the PHG is distinct from connectivity of hippocampal regions identified by an associative memory‐encoding task. We confirmed that several hippocampal encoding regions lack significant functional connectivity with cortical DMN nodes during resting state. Additionally, a mediation analysis showed that resting‐state connectivity between the hippocampus and posterior cingulate cortex—a major hub of the DMN—is indirect and mediated by the PHG. Our findings support the hypothesis that the MTL memory system represents a functional subnetwork that relates to the cortical nodes of the DMN through parahippocampal functional connections. Hum Brain Mapp 35:1061–1073, 2014. © 2013 Wiley Periodicals, Inc.     

Goal-dependent modulation of declarative memory: neural correlates of temporal recency decisions and novelty detection

Declarative memory allows an organism to discriminate between previously encountered and novel items, and to place past encounters in time. Numerous imaging studies have investigated the neural processes supporting item recognition, whereas few have examined retrieval of temporal information. In the present study, functional magnetic resonance imaging (fMRI) was conducted while subjects engaged in temporal recency and item novelty decisions. Subjects encountered three-alternative forced-choice retrieval trials, each consisting of two words from a preceding study phase and one novel word, and were instructed to either identify the novel item (Novelty trials) or the more recently presented study item (Recency trials). Relative to correct Novelty decisions, correct Recency decisions elicited greater activation in a network of left-lateralized regions, including frontopolar and dorsolateral prefrontal cortex and intraparietal sulcus. A conjunction analysis revealed that these left-lateralized regions overlapped with those previously observed to be engaged during source recollection versus novelty detection, suggesting that during Recency trials subjects attempted to recollect event details. Consistent with this interpretation, correct Recency decisions activated posterior hippocampus and parahippocampal cortex, whereas incorrect Recency decisions elicited greater anterior cingulate activation. The magnitude of this latter effect positively correlated with activation in right dorsolateral prefrontal cortex. Finally, correct Novelty decisions activated the anterior medial temporal lobe to a greater extent than did correct Recency decisions, suggesting that medial temporal novelty responses are not obligatory but rather can be modulated by the goal-directed allocation of attention. Collectively, these findings advance understanding of how subjects strategically engage frontal and parietal mechanisms in the service of attempting to remember the temporal order of events, and how retrieval goals impact novelty processing within the medial temporal lobe.     

Priming older adults and people with Alzheimer’s disease analogical problem-solving with true and false memories

We investigated the extent to which activation of specific information in associative networks during a memory task could facilitate subsequent analogical problem solving in healthy older adults as well as those with early onset Alzheimer’s disease. We also examined whether these priming effects were stronger when the activation of the critical solution term during the memory task occurred when the item was actually presented (true memories) or when this item arose due to spreading activation to a related but nonpresented item (false memory). Older adult controls (OACs) and people with Alzheimer’s disease (AD) were asked to solve 9 verbal proportional analogies, 3 of which had been primed by Deese/Roediger-McDermott lists where the critical lure (and problem solution) was presented as a word in the list (true memory), 3 of which were primed by DRM lists whose critical lures were spontaneously activated during list presentation (false memory), and 3 of which were unprimed. As expected, OACs were better (both in terms of speed and accuracy) at solving problems than people with AD and both groups were better when false memories were primes than when true memories were primes or there were no primes. There were no reliable differences between unprimed and true prime problems. These findings demonstrate that (a) priming of problem solutions extends to verbal proportional analogies in OACs and people with AD, (b) false memories are more effective at priming problem solutions than true memories, and (c) there are clear positive consequences to the production of false memories.