Functional Interplay Between Posterior Parietal Cortex and Hippocampus During Detection of Memory Targets and Non-targets

Abstract

Posterior parietal cortex is frequently activated during episodic memory retrieval but its role during retrieval and its interactions with the hippocampus are not yet clear. In this fMRI study, we investigated the neural bases of recognition memory when study repetitions and retrieval goals were manipulated. During encoding participants studied words either once or three times, and during retrieval they were rewarded more to detect either studied words or new words. We found that (1) dorsal parietal cortex (DPC) was more engaged during detection of items studied once compared to three times, whereas regions in the ventral parietal cortex (VPC) responded more to items studied multiple times; (2) DPC, within a network of brain regions functionally connected to the anterior hippocampus, responded more to items consistent with retrieval goals (associated with high reward); (3) VPC, within a network of brain regions functionally connected to the posterior hippocampus, responded more to items not aligned with retrieval goals (i.e., unexpected). These findings support the hypothesis that DPC and VPC regions contribute differentially to top-down vs. bottom-up attention to memory. Moreover, they reveal a dissociation in the functional profile of the anterior and posterior hippocampi.

Keywords: episodic memory; functional magnetic brain imaging (fMRI); hippocampus; posterior parietal cortex; recognition memory decision.

FIGURE 1

(A) Hit rates and response times for items studied once (1x) and for items studied three times (3x). (B) Frequency of correct responses for 1x, 3x, and new items in the Incentive-old (INC-old) and in the Incentive-new (INC-new) conditions. Error bars represent standard errors of the mean. Asterisks denote a significant difference (p < 0.05).

FIGURE 2

Brain regions related to study repetitions. (A) Regions more active during correct recognition of 3x items (H3) than 1x (H1). Panel (B): regions more active during H1 than H3. DPC, dorsal parietal cortex; VPC, ventral parietal cortex; pHIPP, posterior hippocampus; BSR, salience/standard error ratio from the bootstrap analysis.

FIGURE 3

Brain regions related to memory targetness. (A) regions more active during detection of memory targets (hits in the Incentive-old condition and CRs in the Incentive-new condition) than non-targets (CRs in the Incentive-old and hits in the Incentive-new condition). (B) regions more active during detection of non-targets than memory targets. DPC, dorsal parietal cortex; VPC, ventral parietal cortex; aHIPP, anterior hippocampus; BSR, salience/standard error ratio from the bootstrap analysis.