scholarly journals Reward Modulation of Hippocampal Subfield Activation during Successful Associative Encoding and Retrieval

2012 ◽  
Vol 24 (7) ◽  
pp. 1532-1547 ◽  
Author(s):  
Sasha M. Wolosin ◽  
Dagmar Zeithamova ◽  
Alison R. Preston
Keyword(s):  
Dentate Gyrus ◽  
Medial Temporal Lobe ◽  
Recall Performance ◽  
Memory Formation ◽  
Cued Recall ◽  
Retrieval Task ◽  
Parahippocampal Cortex ◽  
Retrieval Processes ◽  
Shed Light ◽  
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/CA2,3 during encoding and enhanced functional connectivity between dentate gyrus/CA2,3 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/CA2,3 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.

scholarly journals Neural Mechanisms of Context Effects on Face Recognition: Automatic Binding and Context Shift Decrements

2010 ◽  
Vol 22 (11) ◽  
pp. 2541-2554 ◽  
Author(s):  
Scott M. Hayes ◽  
Elsa Baena ◽  
Trong-Kha Truong ◽  
Roberto Cabeza
Keyword(s):  
Face Recognition ◽  
Medial Temporal Lobe ◽  
Context Effects ◽  
Recognition Performance ◽  
Neural Mechanisms ◽  
Context Change ◽  
Parahippocampal Cortex ◽  
The Face ◽  
Context Shift ◽  
Encoding And Retrieval

Although people do not normally try to remember associations between faces and physical contexts, these associations are established automatically, as indicated by the difficulty of recognizing familiar faces in different contexts (“butcher-on-the-bus” phenomenon). The present fMRI study investigated the automatic binding of faces and scenes. In the face–face (F–F) condition, faces were presented alone during both encoding and retrieval, whereas in the face/scene–face (FS–F) condition, they were presented overlaid on scenes during encoding but alone during retrieval (context change). Although participants were instructed to focus only on the faces during both encoding and retrieval, recognition performance was worse in the FS–F than in the F–F condition (“context shift decrement” [CSD]), confirming automatic face–scene binding during encoding. This binding was mediated by the hippocampus as indicated by greater subsequent memory effects (remembered > forgotten) in this region for the FS–F than the F–F condition. Scene memory was mediated by right parahippocampal cortex, which was reactivated during successful retrieval when the faces were associated with a scene during encoding (FS–F condition). Analyses using the CSD as a regressor yielded a clear hemispheric asymmetry in medial temporal lobe activity during encoding: Left hippocampal and parahippocampal activity was associated with a smaller CSD, indicating more flexible memory representations immune to context changes, whereas right hippocampal/rhinal activity was associated with a larger CSD, indicating less flexible representations sensitive to context change. Taken together, the results clarify the neural mechanisms of context effects on face recognition.

scholarly journals Neural Activity in the Hippocampus and Perirhinal Cortex during Encoding Is Associated with the Durability of Episodic Memory

2010 ◽  
Vol 22 (11) ◽  
pp. 2652-2662 ◽  
Author(s):  
Valerie A. Carr ◽  
Indre V. Viskontas ◽  
Stephen A. Engel ◽  
Barbara J. Knowlton
Keyword(s):  
Neural Activity ◽  
Medial Temporal Lobe ◽  
Memory Performance ◽  
Perirhinal Cortex ◽  
Memory Formation ◽  
Short Delay ◽  
Parahippocampal Cortex ◽  
The Relationship ◽  
Over Time ◽  
Subsequent Memory Effect

Studies examining medial temporal lobe (MTL) involvement in memory formation typically assess memory performance after a single, short delay. Thus, the relationship between MTL encoding activity and memory durability over time remains poorly characterized. To explore this relationship, we scanned participants using high-resolution functional imaging of the MTL as they encoded object pairs; using the remember/know paradigm, we then assessed memory performance for studied items both 10 min and 1 week later. Encoding trials were classified as either subsequently recollected across both delays, transiently recollected (i.e., recollected at 10 min but not after 1 week), consistently familiar, or consistently forgotten. Activity in perirhinal cortex (PRC) and a hippocampal subfield comprising the dentate gyrus and CA fields 2 and 3 reflected successful encoding only when items were recollected consistently across both delays. Furthermore, in PRC, encoding activity for items that later were consistently recollected was significantly greater than that for transiently recollected and consistently familiar items. Parahippocampal cortex, in contrast, showed a subsequent memory effect during encoding of items that were recollected after 10 min, regardless of whether they also were recollected after 1 week. These data suggest that MTL subfields contribute uniquely to the formation of memories that endure over time, and highlight a role for PRC in supporting subsequent durable episodic recollection.

scholarly journals High-resolution fMRI of Content-sensitive Subsequent Memory Responses in Human Medial Temporal Lobe

2010 ◽  
Vol 22 (1) ◽  
pp. 156-173 ◽  
Author(s):  
Alison R. Preston ◽  
Aaron M. Bornstein ◽  
J. Benjamin Hutchinson ◽  
Meghan E. Gaare ◽  
Gary H. Glover ◽  
...  
Keyword(s):  
High Resolution ◽  
Dentate Gyrus ◽  
Temporal Lobe ◽  
Medial Temporal Lobe ◽  
Functional Neuroimaging ◽  
Perirhinal Cortex ◽  
Memory Effects ◽  
Long Term Memory ◽  
Memory Strength ◽  
Parahippocampal Cortex

The essential role of the medial temporal lobe (MTL) in long-term memory for individual events is well established, yet important questions remain regarding the mnemonic functions of the component structures that constitute the region. Within the hippocampus, recent functional neuroimaging findings suggest that formation of new memories depends on the dentate gyrus and the CA3 field, whereas the contribution of the subiculum may be limited to retrieval. During encoding, it has been further hypothesized that structures within MTL cortex contribute to encoding in a content-sensitive manner, whereas hippocampal structures may contribute to encoding in a more domain-general manner. In the current experiment, high-resolution fMRI techniques were utilized to assess novelty and subsequent memory effects in MTL subregions for two classes of stimuli—faces and scenes. During scanning, participants performed an incidental encoding (target detection) task with novel and repeated faces and scenes. Subsequent recognition memory was indexed for the novel stimuli encountered during scanning. Analyses revealed voxels sensitive to both novel faces and novel scenes in all MTL regions. However, similar percentages of voxels were sensitive to novel faces and scenes in perirhinal cortex, entorhinal cortex, and a combined region comprising the dentate gyrus, CA2, and CA3, whereas parahippocampal cortex, CA1, and subiculum demonstrated greater sensitivity to novel scene stimuli. Paralleling these findings, subsequent memory effects in perirhinal cortex were observed for both faces and scenes, with the magnitude of encoding activation being related to later memory strength, as indexed by a graded response tracking recognition confidence, whereas subsequent memory effects were scene-selective in parahippocampal cortex. Within the hippocampus, encoding activation in the subiculum correlated with subsequent memory for both stimulus classes, with the magnitude of encoding activation varying in a graded manner with later memory strength. Collectively, these findings suggest a gradient of content sensitivity from posterior (parahippocampal) to anterior (perirhinal) MTL cortex, with MTL cortical regions differentially contributing to successful encoding based on event content. In contrast to recent suggestions, the present data further indicate that the subiculum may contribute to successful encoding irrespective of event content.

scholarly journals Dissociation of Frontal and Medial Temporal Lobe Activity in Maintenance and Binding of Sequentially Presented Paired Associates

2009 ◽  
Vol 21 (7) ◽  
pp. 1244-1254 ◽  
Author(s):  
Jena B. Hales ◽  
Sarah L. Israel ◽  
Nicole C. Swann ◽  
James B. Brewer
Keyword(s):  
Prefrontal Cortex ◽  
Temporal Lobe ◽  
Medial Temporal Lobe ◽  
Memory Formation ◽  
Sequential Presentation ◽  
Paired Associates ◽  
Parahippocampal Cortex ◽  
New Evidence ◽  
Response Specificity ◽  
Over Time

Substructures of the prefrontal cortex (PFC) and the medial-temporal lobe are critical for associating objects presented over time. Previous studies showing frontal and medial-temporal involvement in associative encoding have not addressed the response specificity of these regions to different aspects of the task, which include instructions to associate and binding of stimuli. This study used a novel paradigm to temporally separate these two components of the task by sequential presentation of individual images with or without associative instruction; fMRI was used to investigate the temporal involvement of the PFC and the parahippocampal cortex in encoding each component. Although both regions showed an enhanced response to the second stimulus of a pair, only the PFC had increased activation during the delay preceding a stimulus when associative instruction was given. These findings present new evidence that prefrontal and medial-temporal regions provide distinct temporal contributions during associative memory formation.

Episodic Memory Impairment in Parkinson’s Disease: Disentangling the Role of Encoding and Retrieval

2020 ◽  
pp. 1-9
Author(s):  
Antònia Siquier ◽  
Pilar Andrés
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Episodic Memory ◽  
Recall Performance ◽  
Retrieval Processes ◽  
Initial Learning ◽  
List Learning ◽  
Mixed Pattern ◽  
Selective Reminding Test ◽  
Encoding And Retrieval

Abstract Objective: The source of episodic memory (EM) impairment in Parkinson’s disease (PD) is still unclear. In the present study, we sought to quantify specifically encoding, consolidation, and retrieval process deficits in a list-learning paradigm by a novel method, the item-specific deficit approach (ISDA). Methods: We applied the ISDA method to the Free and Cued Selective Reminding Test (FCSRT) in a sample of 15 PD patients and 15 healthy participants. Results: The results revealed differences in free recall performance between PD patients and controls. These patients, however, benefited from cues as much as controls did, and total recall did not differ between groups. When analyzing the ISDA indices for encoding, consolidation, and retrieval deficits, the results showed a general memory deficit, but with a clear focus on encoding and retrieval, as revealed by the sensitivity values. Moreover, controlling for initial learning did not eliminate group effects in retrieval. Conclusions: Our findings reveal a mixed pattern in PD patients, with deficits in both encoding and retrieval processes in memory. Also, despite the fact that an encoding dysfunction may explain some of the deficits observed at retrieval, it cannot fully account for the differences, highlighting that both encoding and retrieval factors are necessary to understand memory deficits in PD.

Children show adult-like hippocampal pattern separation for familiar but not novel events

2020 ◽  
Author(s):  
Susan L. Benear ◽  
Elizabeth A. Horwath ◽  
Emily Cowan ◽  
M. Catalina Camacho ◽  
Chi Ngo ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Temporal Lobe ◽  
Medial Temporal Lobe ◽  
Developmental Change ◽  
Pattern Separation ◽  
Developmental Changes ◽  
Similarity Analysis ◽  
Separation Processes ◽  
Parahippocampal Cortex ◽  
Pattern Similarity

The medial temporal lobe (MTL) undergoes critical developmental change throughout childhood, which aligns with developmental changes in episodic memory. We used representational similarity analysis to compare neural pattern similarity for children and adults in hippocampus and parahippocampal cortex during naturalistic viewing of clips from the same movie or different movies. Some movies were more familiar to participants than others. Neural pattern similarity was generally lower for clips from the same movie, indicating that related content taxes pattern separation-like processes. However, children showed this effect only for movies with which they were familiar, whereas adults showed the effect consistently. These data suggest that children need more exposures to stimuli in order to show mature pattern separation processes.

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