Elucidating medial temporal and frontal lobe contributions to approach-avoidance conflict decision-making using functional MRI and the hierarchical drift diffusion model.

The prefrontal cortex (PFC) has long been associated with arbitrating between approach and avoidance in the face of conflicting and uncertain motivational information, but recent work has also highlighted medial temporal lobe (MTL) involvement. It remains unclear, however, how the contributions of these regions differ in their resolution of conflict information and uncertainty. We designed an fMRI paradigm in which participants approached or avoided object pairs that differed by motivational conflict and outcome uncertainty (complete certainty vs. complete uncertainty). Behavioral data and decision-making parameters estimated using the hierarchical drift diffusion model revealed that participants' responding was driven by conflict rather than uncertainty. Our neural data suggest that PFC areas contribute to cognitive control during approach-avoidance conflict by potentially adjusting response caution and the strength of evidence generated towards either choice, with differential involvement of anterior cingulate cortex and dorsolateral prefrontal cortex. The MTL, on the other hand, appears to contribute to evidence generation, with the hippocampus linked to evidence accumulation for stimuli. Although findings within perirhinal cortex were comparatively equivocal, some evidence suggests contributions to perceptual representations, particularly under conditions of threat. Our findings provide evidence that MTL and PFC regions may contribute uniquely to arbitrating approach-avoidance conflict.

Perirhinal Cortex is Involved in the Resolution of Learned Approach-Avoidance Conflict Associated with Discrete Objects.

The rodent ventral and primate anterior hippocampus have been implicated in approach-avoidance (AA) conflict processing. It is unclear, however, whether this structure contributes to AA conflict detection and/or resolution, and if its involvement extends to conditions of AA conflict devoid of spatial/contextual information. To investigate this, neurologically healthy human participants first learned to approach or avoid single novel visual objects with the goal of maximizing earned points. Approaching led to point gain and loss for positive and negative objects, respectively, whereas avoidance had no impact on score. Pairs of these objects, each possessing nonconflicting (positive-positive/negative-negative) or conflicting (positive-negative) valences, were then presented during functional magnetic resonance imaging. Participants either made an AA decision to score points (Decision task), indicated whether the objects had identical or differing valences (Memory task), or followed a visual instruction to approach or avoid (Action task). Converging multivariate and univariate results revealed that within the medial temporal lobe, perirhinal cortex, rather than the anterior hippocampus, was predominantly associated with object-based AA conflict resolution. We suggest the anterior hippocampus may not contribute equally to all learned AA conflict scenarios and that stimulus information type may be a critical and overlooked determinant of the neural mechanisms underlying AA conflict behavior.

Exploring the interaction between approach-avoidance conflict and memory processing.

The medial temporal lobe (MTL) has been implicated in approach-avoidance (AA) conflict processing, which arises when a stimulus is imbued with both positive and negative valences. Notably, since the MTL has been traditionally viewed as a mnemonic brain region, a pertinent question is how AA conflict and memory processing interact with each other behaviourally. We conducted two behavioural experiments to examine whether increased AA conflict processing has a significant impact on incidental mnemonic encoding and inferential reasoning. In Experiment 1, participants first completed a reward and punishment AA task and were subsequently administered a surprise recognition memory test for stimuli that were presented during high and no AA conflict trials. In Experiment 2, participants completed a reward and punishment task in which they learned the valences of objects presented in pairs (AB, BC pairs). Next, we assessed their ability to integrate information across these pairs (infer A-C relationships) and examined whether inferential reasoning was more challenging across objects with conflicting compared to non-conflicting incentive values. We observed that increased motivational conflict did not significantly impact encoding or inferential reasoning. Potential explanations for these findings are considered, including the possibility that AA conflict and memory processing are not necessarily intertwined behaviourally.

Post-learning stress reduces the misinformation effect: effects of psychosocial stress on memory updating.

Episodic memories can be modified when exposed to new and related information. This phenomenon, known as memory updating, is generally thought to be adaptive but can also lead to incorporating false information into a memory trace. Given the well-known effects of stress on episodic memory, we used a false information paradigm to investigate if acute stress during memory updating (i.e., post-learning stage) affected false memory formation. In a between-subject design, young healthy participants completed the initial phases of the misinformation experiment - they studied an event via a slideshow and then were exposed a related narrative that contained misleading information about that event. After, half of the participants were exposed to acute psychosocial stress and the other half completed a control task. Once stress levels returned to baseline, all of the participants completed the final phase of the experiment, which was a memory test for slideshow that included items containing true facts and misinformation. Participants in the stress condition showed a reduced misinformation effect and were better able to discriminate true from false information compared to control participants. This pattern of results held even when participants were tested on the same memory test after a multiple day delay, illustrating the long-lasting effects of stress on false memory formation specifically, and memory updating generally. We discuss how our results add to the understanding of the time-dependent factors that moderate stress effects on memory, and speculate how stress effects on memory updating can be positive, by limiting intrusions into encoded events, but also negative, by limiting the ability to integrate information with other concepts, harming memory generalization.

The dynamic interplay between acute psychosocial stress, emotion and autobiographical memory.

Although acute psychosocial stress can impact autobiographical memory retrieval, the nature of this effect is not entirely clear. One reason for this ambiguity is because stress can have opposing effects on the different stages of autobiographical memory retrieval. We addressed this issue by testing how acute stress affects three stages of the autobiographical memory retrieval - accessing, recollecting and reconsolidating a memory. We also investigate the influence of emotion valence on this effect. In a between-subjects design, participants were first exposed to an acute psychosocial stressor or a control task. Next, the participants were shown positive, negative or neutral retrieval cues and asked to access and describe autobiographical memories. After a three to four day delay, participants returned for a second session in which they described these autobiographical memories. During initial retrieval, stressed participants were slower to access memories than were control participants; moreover, cortisol levels were positively associated with response times to access positively-cued memories. There were no effects of stress on the amount of details used to describe memories during initial retrieval, but stress did influence memory detail during session two. During session two, stressed participants recovered significantly more details, particularly emotional ones, from the remembered events than control participants. Our results indicate that the presence of stress impairs the ability to access consolidated autobiographical memories; moreover, although stress has no effect on memory recollection, stress alters how recollected experiences are reconsolidated back into memory traces.

What versus where: Investigating how autobiographical memory retrieval differs when accessed with thematic versus spatial information.

Autobiographical memory research has investigated how cueing distinct aspects of a past event can trigger different recollective experiences. This research has stimulated theories about how autobiographical knowledge is accessed and organized. Here, we test the idea that thematic information organizes multiple autobiographical events whereas spatial information organizes individual past episodes by investigating how retrieval guided by these two forms of information differs. We used a novel autobiographical fluency task in which participants accessed multiple memory exemplars to event theme and spatial (location) cues followed by a narrative description task in which they described the memories generated to these cues. Participants recalled significantly more memory exemplars to event theme than to spatial cues; however, spatial cues prompted faster access to past memories. Results from the narrative description task revealed that memories retrieved via event theme cues compared to spatial cues had a higher number of overall details, but those recalled to the spatial cues were recollected with a greater concentration on episodic details than those retrieved via event theme cues. These results provide evidence that thematic information organizes and integrates multiple memories whereas spatial information prompts the retrieval of specific episodic content from a past event.