Article Figures & Data
Figures
- Figure 1.
Experiment paradigm. A, Slow event-related design (16 s for each trial) was used to better estimate brain responses associated with single items. Self-spaced orientation judgment task applied during 8 s intertrial interval to prevent further encoding of the word cue-picture association. B, The arrangement of scanning runs. There were four encoding-retrieval sessions in total. C, Strategies to examine item-specific encoding (left), retrieval (middle), and ERS (right). The item specificity was obtained by comparing similarities between different cues-same picture (C−P+) pairs with different cues-different picture pairs (C−P−; matched with C−P+ pair in memory performance, category, and lag). The words used as cues were actually presented in Chinese.
- Figure 2.
ROI results for item-specific encoding, retrieval, and ERS. A, The location of the pre-defined anatomic ROIs. B, ROI results for item-specific encoding. C, ROI results for item-specific retrieval. D, ROI results for item-specific ERS. Error bars indicate within-subject error. After Bonferroni correction for 14 ROIs (p < 0.0036), effect of item-specific encoding survived in bilateral VVC, item-specific retrieval survived in bilateral AG, MFG, LSMG, and LIFG. ***p < 0.001/14. **p < 0.01/14. *p < 0.05/14.
- Figure 3.
Time-resolved ERS between encoding and retrieval. The BOLD responses for each of the 3 TRs after stimulus onset during encoding and retrieval (with 4 s delay to account for the slow BOLD response) were extracted, and the ERS was calculated between representation at each of the TRs during encoding and that during retrieval. Values in the heat maps are the mean item-specific ERS [ERS(C−P+) − ERS(C−P−)] across subjects.
- Figure 4.
Whole-brain searchlight results. Item-specific representation for encoding and retrieval, their direct comparisons, and ERS were rendered onto a population-averaged surface atlas (Xia et al., 2013). All activations were thresholded using cluster detection statistics, with a height threshold of z > 3.1 and a cluster probability of p < 0.05, corrected for whole-brain multiple comparisons using Gaussian Random Field Theory.
- Figure 5.
Item-specific representation in the MTL subregions. A, The segmentation of the MTL from one sample subject. There are five subregions of hippocampus: CA1, CA2, DG, CA3, and subiculum. CA2 and CA3 were not included in further analysis considering their relatively limited voxels. The anterior portion of parahippocampus was divided into two parts: PRc (which further divided into BA35 and BA36) and ERc. B, Item-specific representation in these regions for encoding (left), retrieval (middle), and ERS (right). Error bars indicate within-subject error. *p < 0.05, uncorrected.
- Figure 6.
Feature selection results. Left, Feature selection results in the VVC. Right, Feature selection results in the FPC. Error bars indicate within-subject error. EE, Item-specific encoding in voxels selected based on encoding data; ER, item-specific retrieval in voxels selected based on encoding data; RE, item-specific encoding in voxels selected based on retrieval data; RR, item-specific retrieval in voxels selected based on retrieval data.
- Figure 7.
Cross-region pattern reinstatement. Representational similarity matrix for encoding (A) and retrieval phase (B). Data are from one ROI (i.e., LVVC) of one participant (Subject 3). For each of the 48 pictures, the representational similarity matrix was obtained by calculating the pairwise Pearson correlation of activation pattern between each of the 48 pictures and the other 23 pictures from different run (the same picture pairs were removed), separately for encoding and retrieval phase. C, Heat-map for group-averaged encoding-retrieval representational connectivity within and across brain regions. D, Bar graphs of within-region encoding-retrieval representational connectivity (i.e., within-region reinstatement). E, F, Bar graphs of across-region encoding-retrieval representational connectivity (i.e., cross-region reinstatement) for the left and right VVC, respectively. Error bars indicate within-subject error.
Tables
Encoding Retrieval ERS F(1,19) p F(1,19) p F(1,19) p LVVC 40.069 0.0000* 4.982 0.0379 1.712 0.2064 RVVC 53.018 0.0000* 8.898 0.0076 0.527 0.4767 LAG 1.296 0.2691 26.779 0.0001* 9.048 0.0072 RAG 2.150 0.1589 12.587 0.0021* 1.434 0.2458 LSMG 1.104 0.3066 24.018 0.0001* 8.433 0.0091 RSMG 0.290 0.5964 6.419 0.0203 1.847 0.1901 LIFG 4.639 0.0443 19.377 0.0003* 4.162 0.0555 RIFG 1.766 0.1996 4.927 0.0388 0.576 0.4571 LMFG 2.367 0.1404 20.915 0.0002* 8.562 0.0087 RMFG 1.683 0.2100 14.300 0.0013* 1.059 0.3164 LSFG 0.013 0.9108 10.357 0.0045 2.132 0.1606 RSFG 0.045 0.8347 6.488 0.0197 0.687 0.4176 mPFC 0.001 0.9799 4.628 0.0445 1.075 0.3129 PCC 1.484 0.2380 12.665 0.0021* 8.738 0.0081 ↵aThe numbers in the table indicate the comparison results between pattern similarities of different cues-same picture (C−P+) pairs and that of different cues-different pictures pairs (C−P−; matched with the C−P+ pairs in memory performance, stimulus category, and lag).
↵*Significant results after Bonferroni correction across 14 ROIs (p < 0.05/14).
Region x y z Maximum z Encoding LLOC −24 −80 36 4.65 RLOC 18 −84 −8 6.43 Retrieval LLOC −26 −66 −50 4.33 LIFG/LMFG −56 10 22 5.35 RIFG/RMFG 50 12 44 5.07 LIPL −50 −48 46 5.15 LTOF −20 −52 −16 5.10 Encoding > retrieval LvLOC/LOFUS −14 −96 −6 4.32 RvLOC/ROFUS 20 −88 −10 5.24 ERS (C−P+) LOC −24 −68 52 4.9 RdLOC 32 −68 56 4.07 ↵aWhole brain corrected (z = 3.1, p < 0.05).
- Table 3.
Correlations between hippocampal subregion activity and cortical item-specific representationsa
Region ERS encoding ERS retrieval Encoding Retrieval CA1 DG CA1 DG CA1 DG CA1 DG LVVC 0.597 0.881 0.130 0.169 0.000* 0.001* 0.003 0.006 RVVC 0.453 0.999 0.417 1.000 0.007 0.003 0.014 0.016 LIFG 0.229 0.369 0.522 0.341 0.149 0.111 0.015 0.003 RIFG 0.340 0.314 0.764 0.857 1.000 0.493 0.054 0.049 LMFG 0.199 0.278 0.860 0.577 0.126 0.388 0.021 0.029 RMFG 0.434 0.154 0.455 0.341 0.204 0.574 0.191 0.050 LAG 0.322 0.466 0.651 0.326 0.314 0.582 0.258 0.379 RAG 0.543 0.236 0.064 0.069 0.550 0.614 0.207 0.174 LSMG 0.189 0.466 0.414 0.151 0.934 0.798 0.154 1.000 RSMG 0.452 0.427 0.192 0.241 0.747 0.345 0.323 0.383 ↵aThe numbers in the table indicate the p value of the mixed-effects model. ERS encoding, Hippocampal encoding activities correlated with ERS; ERS retrieval, hippocampal retrieval activities correlated with ERS; Encoding, hippocampal encoding activities correlated with item-specific representation during encoding; Retrieval, hippocampal retrieval activities correlated with item-specific representation during retrieval.
↵*Significant after Bonferroni correction across 20 models (p < 0.05/20).
- Table 5.
Cross-regions reinstatement (from VVC to frontoparietal cortex) of representational structure
Encoding retrieval LVVC RVVC t p t p LAG 1.583 0.0649 1.459 0.0804 LSMG 2.926 0.0043 1.158 0.1306 LIFG 4.427 0.0001* 2.710 0.0069 LMFG 4.420 0.0001* 4.469 0.0001* RAG 2.667 0.0076 4.279 0.0002* RSMG 3.337 0.0017* 4.431 0.0001* RIFG 3.745 0.0007* 3.473 0.0013* RMFG 4.315 0.0002* 5.995 0.0000* ↵*Significant results after Bonferroni correction for 16 comparisons (p < 0.05/16).
