Unlabelled

The neural processes giving rise to human memory strength signals remain poorly understood. Inspired by formal computational models that posit a central role of global matching in memory strength, we tested a novel hypothesis that the strengths of both true and false memories arise from the global similarity of an item's neural activation pattern during retrieval to that of all the studied items during encoding (i.e., the encoding-retrieval neural global pattern similarity [ER-nGPS]). We revealed multiple ER-nGPS signals that carried distinct information and contributed differentially to true and false memories: Whereas the ER-nGPS in the parietal regions reflected semantic similarity and was scaled with the recognition strengths of both true and false memories, ER-nGPS in the visual cortex contributed solely to true memory. Moreover, ER-nGPS differences between the parietal and visual cortices were correlated with frontal monitoring processes. By combining computational and neuroimaging approaches, our results advance a mechanistic understanding of memory strength in recognition.

Significance statement

What neural processes give rise to memory strength signals, and lead to our conscious feelings of familiarity? Using fMRI, we found that the memory strength of a given item depends not only on how it was encoded during learning, but also on the similarity of its neural representation with other studied items. The global neural matching signal, mainly in the parietal lobule, could account for the memory strengths of both studied and unstudied items. Interestingly, a different global matching signal, originated from the visual cortex, could distinguish true from false memories. The findings reveal multiple neural mechanisms underlying the memory strengths of events registered in the brain.

Previous research reported that serotonin receptor 2A gene (HTR2A) polymorphisms were associated with memory. However, it is unknown whether these genetic variants were associated with both true and false memories. The current study of 336 Han Chinese subjects tested 30 single nucleotide polymorphisms (SNPs) within the HTR2A gene for potential associations with true and false memories. False memories were assessed using the Deese-Roediger-McDermott (DRM) paradigm, in which people falsely remember semantically related (but unpresented) words. We found that 11 SNPs within the HTR2A gene were associated with true memory (p=0.000076-0.043). The associations between true memory and seven adjacent SNPs (i.e., rs1923888, rs1745837, rs9567739, rs3742279, rs655888, rs655854, and rs2296972) were still significant after multiple testing corrections. Haplotype-based association analysis revealed that, true memory was positively associated with haplotype A-C-C-G-C-T-A for these seven adjacent SNPs (p=0.000075), which was still significant after multiple testing correction. Only one SNP rs655854 was associated with false memory (p=0.023), and it was not significant after multiple testing correction. This study replicates, in an Asian population, that genetic variation in HTR2A is associated with episodic memory, and also suggests that this association is restricted to true memory.

This paper reports a new experimental manipulation that increased false memories 1 month after the manipulation. Mirroring the standard three-stage misinformation paradigm (original event, misinformation, and test), subjects in the experimental group were first given a colour-slide presentation of two stories (events), then given an accurate account (instead of misinformation) of the events in narrations, and finally tested for their memory of the original events. One month later, they underwent the standard misinformation paradigm with two new events. The comparison group was given the standard misinformation tasks at both time points. Results showed that the experimental group produced more false memories in the subsequent misinformation paradigm than did the comparison group. We focus on trust and credibility as possible mechanisms underlying this effect. © 2010 John Wiley & Sons, Ltd.

This research investigated the relationship between false memories induced by two different paradigms (misinformation and Deese-Roediger-McDermott [DRM]). The misinformation effect refers to the phenomenon that a person's recollection of a witnessed event can be altered after exposure to misleading information about the event. DRM false memory represents the intrusion of words that are semantically related but not actually presented in the study session. Subjects (N = 432) completed both misinformation and DRM false memory tests. Results showed a small but significant correlation (r = .12, p = .02) between the misinformation and DRM false memories. Furthermore, using signal detection theory, we found that the discrimination ability index (d') was related to both the misinformation and DRM false memories (r = -.12 and -.13, p = .01), while the response bias was related only to DRM false memory (r = -.46, p < .001). These results suggest that misinformation and DRM false memories generally involve different mechanisms and that their shared mechanism may involve the global discrimination ability.

There is a keen interest in identifying specific brain regions that are related to individual differences in true and false memories. Previous functional neuroimaging studies showed that activities in the hippocampus, right fusiform gyrus, and parahippocampal gyrus were associated with true and false memories, but no study thus far has examined whether the structures of these brain regions are associated with short-term and long-term true and false memories. To address that question, the current study analyzed data from 205 healthy young adults, who had valid data from both structural brain imaging and a misinformation task. In the misinformation task, subjects saw the crime scenarios, received misinformation, and took memory tests about the crimes an hour later and again after 1.5 years. Results showed that bilateral hippocampal volume was associated with short-term true and false memories, whereas right fusiform gyrus volume and surface area were associated with long-term true and false memories. This study provides the first evidence for the structural neural bases of individual differences in short-term and long-term true and false memories.

The current study explored the intellectual factors in false memories of 139 patients with schizophrenia, using a recognition task and an IQ test. The full-scale IQ score of the participants ranged from 57 to 144 (M = 100, SD = 14). The full IQ score had a negative correlation with false recognition in patients with schizophrenia, and positive correlations with high-confidence true recognition and discrimination rates. Further analyses with the subtests' scores revealed that false recognition was negatively correlated with scores of performance IQ (and one of its subtests: picture arrangement), whereas true recognition was positively correlated with scores of verbal IQ (and two of its subtests: information and digit span). High-IQ patients had less false recognition (overall or high-confidence false recognition), more high-confidence true recognition, and higher discrimination abilities than those with low IQ. These findings contribute to a better understanding of the cognitive mechanism in false memory of patients with schizophrenia, and are of practical relevance to the evaluation of memory reliability in patients with different intellectual levels.

The misinformation effect occurs when people's memory of an event is altered by subsequent inaccurate information. No study has systematically tested theories about the dynamics of human hippocampal representations during the three stages of misinformation-induced false memory. This study replicates behavioral results of the misinformation effect, and investigates the cross-stage pattern similarity in the hippocampus and cortex using functional magnetic resonance imaging. Results show item-specific hippocampal pattern similarity between original-event and post-event stages. During the memory-test stage, hippocampal representations of original information are weakened for true memory, whereas hippocampal representations of misinformation compete with original information to create false memory. When false memory occurs, this conflict is resolved by the lateral prefrontal cortex. Individuals' memory traces of post-event information in the hippocampus predict false memory, whereas original information in the lateral parietal cortex predicts true memory. These findings support the multiple-trace model, and emphasize the reconstructive nature of human memory.

Previous research reported that a rare serotonin receptor 2B gene (HTR2B) stop codon mutation predisposes subjects to severe impulsivity and novelty seeking. In this study, we expanded this previous work by testing six single nucleotide polymorphisms (SNPs) within the HTR2B gene for potential associations with the behavioral inhibition system (BIS) and the three components of the behavioral approach systems (BAS: fun seeking, drive, and reward responsiveness) in a Han Chinese sample (N= 478). Association analysis for individual SNPs indicated that four of the six SNPs (i.e., rs6437000, rs10194776, rs16827801, and rs1549339) were significantly associated with BAS fun seeking (p= 0003-0022). Haplotype-based association analysis revealed that fun seeking was positively associated with haplotype A-A-G-A for SNPs rs6437000- rs10194776- rs16827801- rs1549339 (p= 0002), which survived Bonferroni correction. Except for the association between BAS reward responsiveness and rs16827801 (p= 005), no other association was found for BAS drive, BAS reward responsiveness, or BIS. This study provides the first evidence for the involvement of the HTR2B gene in BAS fun seeking. A better understanding of the genetic basis of the BIS and BAS would allow us to develop more effective diagnosis, treatment, and prevention of impulsive behavioral problems. © 2012 Elsevier Ltd.

Theoretical and computational models such as transfer-appropriate processing (TAP) and global matching models have emphasized the encoding-retrieval interaction of memory representations in generating false memories, but relevant neural mechanisms are still poorly understood. By manipulating the sensory modalities (visual and auditory) at different processing stages (learning and test) in the Deese-Roediger-McDermott task, we found that the auditory-learning visual-test (AV) group produced more false memories (59%) than the other three groups (42∼44%) [i.e., visual learning visual test (VV), auditory learning auditory test (AA), and visual learning auditory test (VA)]. Functional imaging results showed that the AV group's proneness to false memories was associated with (i) reduced representational match between the tested item and all studied items in the visual cortex, (ii) weakened prefrontal monitoring process due to the reliance on frontal memory signal for both targets and lures, and (iii) enhanced neural similarity for semantically related words in the temporal pole as a result of auditory learning. These results are consistent with the predictions based on the TAP and global matching models and highlight the complex interactions of representations during encoding and retrieval in distributed brain regions that contribute to false memories.