Memory Task and Experimental Procedure

(A) Trial Structures in the Experimental Task. (i) In the Initial Encoding phase, participants were instructed to remember object-location pairs by creating a story or making a “mental photo” of the scene, memorizing the exact location of each object within the scene. (ii) In the Learning Phase, participants chose one location out of three choices and received feedback for their response. After receiving feedback, the correct object-location association was shown again. (iii) In the Retrieval Phase participants chose the location of the object in the scene out of three options without feedback. The retrieval phase took place in the MR scanner. (B) Experimental Procedure. The testing took place across three days. On Day 0, participants learned 60 object-location associations (remote items). On Day 1, participants learned 30 new object-location associations (recent items). For retrieval (short delay), 30 remote pairs learned on Day 0 and 30 recent pairs learned on Day 1 were retrieved. A similar procedure was followed on Day 14 (long delay), with another 30 new object-location associations. Across all testing days, participants also completed socio-demographic questionnaires and other psychometric tests, which were distributed across sessions. Note: RT – reaction time; s – second, fMRI – functional magnetic resonance imaging.

Overview if Mnemonic Performance

(A) Learning Performance. Final learning accuracy is calculated as the percentage of correct responses during the last learning cycle for both children and young adults. Final learning accuracy was significantly higher in young adults compared to children across all sessions. Children needed between two to four learning-retrieval cycles to reach the criterion of 83% correct responses, while young adults required on average two cycles. Grey dashed line indicates the criteria of 83% correctly learned items. (B) Memory retrieval. Memory accuracy is operationalized as the percentage of correct responses in the retrieval task conducted during the MRI scanning sessions. Memory accuracy for recently consolidated items did not differ between sessions in young adults, while for children, recent memory accuracy on Day 1 was higher than on Day 14. Memory accuracy for remotely consolidated items differed between sessions in both young adults and children, showing higher remote memory accuracy on Day 1 than on Day 14. All tests used Sidak correction for multiple comparisons. Red dashed line indicates the threshold for random performance. *p < .05; **p < .01; ***p < .001(significant difference); non-significant differences were not specifically highlighted. Error bars indicate standard error based on the underlying LME-model.

Sample characteristics by age group

Overview of the main and interaction effects of the linear mixed effects model for remote > recent neural activation

Model-based results for ROIs.

Mean signal difference for remote > recent memories on Day 1 and Day 14 in (A) anterior and posterior hippocampus; anterior and posterior parahippocampal gyrus; (C) medial prefrontal cortex; (D) ventrolateral prefrontal cortex; E) cerebellum; (F) retrosplenial cortex; (G) precuneus; (H) lateral occipital cortex. Note: Error bars indicate standard error based on the underlying LME-model. *p < .05; **p < .01; ***p < .001(significant difference); non-significant differences were not specifically highlighted.

Representational (Dis)similarity Analysis.

(A) Index Computation (Scene). A representational dissimilarity index was computed by assessing the average dissimilarity between fixation and scene time window separately for recent, remote (Day 1), and remote (Day 14) scenes. (B) Scene-specific index computation. A corrected scene-specific reinstatement index was computed by assessing the average dissimilarity in fixation and scene time window within each trial and subtracting it from the average set dissimilarity between the fixation and scene time window across trials. (C) Index Computation (Category). A representational dissimilarity index was computed by assessing the average dissimilarity for fixation time window for within-category and between-category scenes separately for recent, remote (Day 1), and remote (Day 14) scenes. (D) Category-based index computation. A category-based reinstatement index was computed by assessing the average dissimilarity in fixation time window for same-category pairs and subtracting it from the any-other-category pairs. S – scene time window; F – fixation time window; r – Pearson’s correlation index.

Statistical overview of the main and interaction effects of the linear mixed effects model for scene-specific reinstatement.

Corrected scene-specific neural reinstatement.

All FDR-adjusted scene-specific reinstatement indices that were significantly different from zero were marked with green asterisk (Table S6). (A) Hippocampus; (B) Parahippocampal Gyrus; (C) Cerebellum; (D) Lateral Occipital Cortex; (E) Medial Prefrontal Cortex; (F) Ventrolateral Prefrontal Cortex; (G) Retrosplenial Cortex; (H) Precuneus.

Statistical overview of the main and interaction effects of the linear mixed effects model for category-based reinstatement.

Category-based reinstatement.

Category-based reinstatement depicts the difference between pattern dissimilarity for within-category items and between-category items during fixation period before the actual scenes were shown. Higher values mean higher category-based reinstatement. The index was tested for significance against zero and all results were FDR corrected for multiple comparisons. Significant reinstatement of category-based information is depicted by a green asterisk (*) (A) Hippocampus; (B) Parahippocampal Gyrus; (C) Cerebellum; (D) Lateral Occipital Cortex; (E) Medial Prefrontal Cortex; (F) Ventrolateral Prefrontal Cortex; (G) Retrosplenial Cortex; (H) Precuneus; *p < .05; **p < .01; ***p < .001(significant difference); non-significant difference was not specifically highlighted. Error bars indicate standard error.

Neural-behavioural Correlations.

Reinstatement indices were averaged across ROIs with significant reinstatement index. (A) Item-specific reinstatement indices were significantly positively related to long-delay memory retention rates in children (in purple) and young adults (in yellow). (B) Category-based reinstatement indices were significantly negatively related to long-delay memory retention rates in children (in purple), but not in young adults (in yellow). R = correlation coefficient, p = p-value. All p-values were FDR-adjusted for multiple comparisons.