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Curr Biol. 2015 Mar 16;25(6):780-785. doi: 10.1016/j.cub.2015.01.055. Epub 2015 Feb 26.

Spatiotemporal neural pattern similarity supports episodic memory.

Author information

1
State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing 100875, China; Center for Collaboration and Innovation in Brain and Learning Sciences, Beijing Normal University, Beijing 100875, China.
2
Department of Psychology and Social Behavior, University of California, Irvine, CA 92697, USA.
3
State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing 100875, China; Center for Collaboration and Innovation in Brain and Learning Sciences, Beijing Normal University, Beijing 100875, China. Electronic address: guixue@gmail.com.

Abstract

Formal computational models of human memory posit a central role of feature representations in episodic memory encoding and retrieval [1-4]. Correspondingly, fMRI studies have found that, in addition to activity level [5, 6], the neural activation pattern similarity across repetitions (i.e., self-similarity) was greater for subsequently remembered than forgotten items [7-9]. This self-similarity has been suggested to reflect pattern reinstatement due to study-phase retrieval [7, 10, 11]. However, the low temporal resolution of fMRI measures could determine neither the temporal precision of study-phase reinstatement nor the processing stage at which the reinstatement supported subsequent memory [12]. Meanwhile, although self-similarity has been shown to correlate with the activity level in the left lateral prefrontal cortex (LPFC) [10, 13], a causal link between left LPFC function and pattern similarity remains to be established. Combining transcranial direct current stimulation (tDCS) and EEG, we found that greater spatiotemporal pattern similarity (STPS) across repetitions of the same item (i.e., self-STPS) during encoding predicted better subsequent memory. The self-STPS located in the right frontal electrodes occurred approximately 500 ms after stimulus onset, reflected item-specific encoding, and contributed to memory above and beyond the effects of ERP amplitude and global pattern similarity (i.e., similarity to all other items in memory space). Anodal stimulation over the left LPFC specifically enhanced memory performance and item-specific STPS in the right frontal electrodes. These results support a causal role of LPFC in enhancing STPS and memory and contribute to a mechanistic understanding of memory formation.

PMID:
25728695
DOI:
10.1016/j.cub.2015.01.055
[Indexed for MEDLINE]
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