Effects of prior knowledge on brain activation and functional connectivity during memory retrieval

Abstract

Previous studies have shown that the ventral medial prefrontal cortex (vmPFC) plays an important role in schema-related memory. However, there is an intensive debate to what extent the activation of subregions of the hippocampus is involved in retrieving schema-related memory. In addition, it is unclear how the functional connectivity (FC) between the vmPFC and the hippocampus, as well as the connectivity of the vmPFC with other regions, are modulated by prior knowledge (PK) during memory retrieval over time. To address these issues, participants learned paragraphs that described features of each unfamiliar word from familiar and unfamiliar categories (i.e., high and low PK conditions) 20 min, 1 day, and 1 week before the test. They then performed a recognition task to judge whether the sentences were old in the scanner. The results showed that the activation of the anterior-medial hippocampus (amHPC) cluster was stronger when the old sentences with high (vs. low) PK were correctly retrieved. The activation of the posterior hippocampus (pHPC) cluster, as well as the vmPFC, was stronger when the new sentences with high (vs. low) PK were correctly rejected (i.e., CR trials), whereas the cluster of anterior-lateral hippocampus (alHPC) showed the opposite. The FC of the vmPFC with the amHPC and perirhinal cortex/inferior temporal gyrus was stronger in the high (vs. low) PK condition, whereas the FC of the vmPFC with the alHPC, thalamus and frontal regions showed the opposite for the CR trials. This study highlighted that different brain networks, which were associated with the vmPFC, subregions of the hippocampus and cognitive control regions, were responsible for retrieving the information with high and low PK.

Figure 1

Procedure of the study and test phases. During the study phase, the participants were presented with paragraphs that described each unfamiliar exemplar from familiar and unfamiliar categories. During the test phase, the participants were asked to judge whether the sentence was correct followed by the confidence rating. The Chinese paragraphs are translated into English for illustration purpose.

Figure 2

Behavioral results. (a) Corrected recognition. (b) RT. (c) Hit rate. (d) CR rate. The effect of PK was manifested in the corrected recognition and CR rate. There were no significant interactions between PK and interval for these parameters. Error bars represent the standard error of the mean (SEM).

Figure 3

Voxel-wise results for Hit and CR trials in the hippocampus. (a) the cluster of the left amHPC showed significant effect of PK for the Hit trials. (b) The cluster of the right alHPC showed significant interaction between PK and interval for the Hit trials. (c) the clusters of the alHPC and pHPC showed different effect of PK for the CR trials. (d) plots showing signal changes of the hippocampal clusters in different PK condition for the Hit and CR trials. The data were collapsed across the retention interval. (e) plot showing signal change of the right alHPC cluster in each condition for the Hit trials. Color bars represent p-values, with the warm colors representing increased activation and the cold colors decreased activation for the contrast of high vs. low PK in A and C. The warm color represented interaction between PK and interval in D. The left is on the left side for each coronal brain slice. Error bars represent the SEM.

Figure 4

Voxel-wise results in the vmPFC for CR trials. (a) the vmPFC showed significant effect of PK for the CR trials. (b) plot showing signal change of the vmPFC in different PK condition for the CR trials. The data were collapsed across the retention interval in B. Color bars represent p-values, with the warm colors representing increased activation and the cold colors decreased activation for the contrast of high vs. low PK. Error bars represent the SEM.

Figure 5

PPI results with the vmPFC as a seed. (a) The clusters in the amHPC and alHPC showed different effect of PK in the CR trials (right). The hippocampal activation is SVC-corrected. (b) The PRC/ITG showed stronger connectivity with the vmPFC for high vs. low PK condition, whereas the bilateral thalamus and cognitive control regions showed stronger connectivity with the vmPFC for low vs. high PK condition at the whole-brain level. (c) Plots showing the connectivity of the vmPFC with the hippocampal cluster in high and low PK conditions. (d) Plots showing the connectivity of the vmPFC with other regions in high and low PK conditions. The data were collapsed across the retention interval in C and D. Color bars represent p-values, with the warm colors representing increased activation and the cold colors decreased activation for the contrast of high vs. low PK. The left is on the left side for each coronal brain slice. Error bars represent the SEM.