Altered neural substrates within cognitive networks of postpartum women during working memory process and resting-state

Abstract

Postpartum working memory decline has been investigated mostly with neuropsychological tests, but neural evidence is almost unknown. Here we investigated task-related neural alterations during working memory task (n-back) and intrinsic alterations during resting-state (rs) in postpartum women using functional MRI (fMRI). Behaviorally, postpartum women showed comparable working memory performances to the controls although there was a tendency of prolonged response time. fMRI analysis results showed hyper-activation in regions belong to the task positive network (TPN) during the task and hypo-rsfMRI values in the default mode network (DMN) regions during rest in postpartum women. Based on these results, we performed network connectivity analysis using nodes of the TPN and DMN. As a result, the DMN showed a tendency of decreased connectivity in postpartum women during the working memory process compared to the controls. Our results suggest that postpartum women might have functional alterations in the DMN, and that hyper-activation in the TPN during a task might be a compensatory mechanism to maintain working memory performance in postpartum women.

Figure 1

n-back task-based fMRI activation analysis results. (A) Main effects revealed by 2 (group: PP vs. CTRL) x 3 (task: 0-back vs. 1-back vs. 2-back) full factorial analysis. There is no significant voxel in the [PP < CTRL] contrast. (B) Interaction effects revealed by 2 (group: PP vs. CTRL) x 3 (task: 0-back vs. 1-back vs. 2-back) full factorial analysis. There is no significant voxel in the [PP < CTRL (2-back > 1-back)] contrast and the [PP < CTRL (2-back > 0-back)] contrast. Abbreviations: CTRL, control group; PP, postpartum group.

Figure 2

Resting-state fMRI analysis results. Regions showing significant group differences in ALFF, fALFF and ReHo values on the two-sample t-test. Abbreviations: CTRL, control group; PP, postpartum group.

Figure 3

Group differences in the within-TPN, within-DMN and DMN-TPN inter-network connectivity strengths during the n-back task. Abbreviations: CTRL, control group; PP, postpartum group.

Figure 4

Correlation analysis between estradiol level and overall RT. Abbreviations: CTRL, control group; PP, postpartum group.

Figure 5

VBM analysis result. (A) Regions showing significant atrophy in the postpartum group compared to the control group. (B) Overlapping regions between cortical atrophy and increased activation during n-back test in the postpartum group. Abbreviations: CTRL, control group; PP, postpartum group.

Figure 6

Six DMN and seven TPN nodes for the network connectivity analysis were derived from the resting-state functional connectivity analysis. Abbreviations: ACC, anterior cingulate cortex; lAG, rAG, bilateral angular gyrus; laIns, raIns, bilateral anterior insula; ldlPFC, rdlPFC, bilateral dorsolateral prefrontal cortex; lMTG, rMTG, bilateral medial temporal gyrus; lSMG, rSMG, bilateral supramarginal gyrus mPFC, medial prefrontal cortex; PCC, posterior cingulate cortex.