Differential Left Hippocampal Activation during Retrieval with Different Types of Reminders: An fMRI Study of the Reconsolidation Process

Abstract

Consolidated memories return to a labile state after the presentation of cues (reminders) associated with acquisition, followed by a period of stabilization (reconsolidation). However not all cues are equally effective in initiating the process, unpredictable cues triggered it, predictable cues do not. We hypothesize that the different effects observed by the different reminder types on memory labilization-reconsolidation depend on a differential neural involvement during reminder presentation. To test it, we developed a declarative task and compared the efficacy of three reminder types in triggering the process in humans (Experiment 1). Finally, we compared the brain activation patterns between the different conditions using functional magnetic resonance imaging (fMRI) (Experiment 2). We confirmed that the unpredictable reminder is the most effective in initiating the labilization-reconsolidation process. Furthermore, only under this condition there was differential left hippocampal activation during its presentation. We suggest that the left hippocampus is detecting the incongruence between actual and past events and allows the memory to be updated.

Western High-Fat Diet Consumption during Adolescence Increases Susceptibility to Traumatic Stress while Selectively Disrupting Hippocampal and Ventricular Volumes

“…A trial-limited optogenetics study in mice supports our finding by showing that only the left HPC is required for associative spatial long-term memory (Shipton et al, 2014), an important outcome evaluated in our habituation-test behavioral paradigm and implicated in the pathophysiology of PTSD. The left HPC has been also implicated in memory reconsolidation by detecting mismatches between actual and learned events (Forcato et al, 2016). We report reduced ventral HPC volumes in the rats that consumed the WD.…”

Surprise and destabilize: prediction error influences episodic memory reconsolidation

“…Hippocampal responses during memory reactivation are strongest when there is a similar-but-different stimulus paired with a learned cue, predicting memory updating (Long et al 2016). Similarly, incomplete reminders of learned paired-associates make memories susceptible to subsequent interference (Forcato et al 2009(Forcato et al , 2010(Forcato et al , 2016. Moreover, subtle contextual cues, rather than comprehensive reminders, can destabilize memory for a list of objects (Hupbach et al 2007(Hupbach et al , 2009(Hupbach et al , 2013.…”

“…Despite this accumulating evidence that reactivating a memory while violating expectations can destabilize it, to our knowledge, no existing human studies have directly bridged prediction error to the reconsolidation of richly detailed episodic memories. The bulk of prior studies that contrasted complete and incomplete reminders relied on associative learning or list memorization (Hupbach et al 2007;Forcato et al 2009Forcato et al , 2016Debiec et al 2011;Sevenster et al 2014). Faced with the challenge of generating prediction errors with naturalistic stimuli, we had the insight to use videos that violated expected action-outcome contingencies.…”

Topography of Hippocampal Connectivity with Sensorimotor Cortex Revealed by Optimizing Smoothing Kernel and Voxel Size

“…Optimal voxel size should generally be commensurate with activation volume, although due to susceptibility field gradients, smaller voxel sizes may sometimes increase sensitivity despite less total signal intensity [12,13]. Larger voxel sizes improve signal strength but provide lower spatial resolution, whereas hippocampal studies generally prefer better resolution due its small size; during analysis, voxel dimensions within any plane typically range from 1mm to 3mm [14][15][16][17][18][19][20][21].…”

“…Nonetheless, several hippocampal studies have used larger smoothing kernels of 8mm [14,15,18,20,30].…”