Introduction

Women will undergo numerous changes including behaviours, emotions, physical, hormone, and among others during the pregnant and postpartum periods. We previously demonstrated that in the late postpartum women, brain structural plasticity exists compared to the early postpartum women using a longitudinal voxel-based morphometric study. In the current study, we look at possible changes in spontaneous neuronal activity including the amplitude of low-frequency fluctuation (ALFF), regional homogeneity (ReHo) and functional connectivity occurring longitudinally over a period of two years. Second, we aim to determine the relationships of spontaneous neuronal activity and empathetic abilities in postpartum women.

Materials and Methods

Twenty-three postpartum women (mean age: 30.2 ± 2.0 years) were selected for this longitudinal functional magnetic resonance imaging (fMRI) study. All subjects were scanned twice: the first scan (scan 1) was collected one year after delivery, and the second scan (scan 2) was performed two years after delivery. The average time interval between scans was 704 days (SD = 2.0 days). MRI scanning sessions were performed on a Siemens 3.0 T Trio Tim MR system using a 12-channel head coil with the following acquisitions: a high-resolution three-dimensional T1-weighted sequence images were acquired for anatomical reference (TR = 2530 ms, TE = 2.34 ms, 192 slices) and resting-state T₂∗-weighted images with the following parameters TR = 2000ms, TE = 30 ms, 33 slices, 210 volumes were acquired. Subjects were instructed to relax and rest, with their eyes closed during the resting-state fMRI scan. ALFF (0.01 - 0.08 Hz) and ReHo were analyzed to measure spontaneous brain activity and functional connectivity was analyzed to investigate empathy-related brain network using Data Processing Analysis for Brain Imaging and Statistical Parametric Mapping software. We further investigated relationships between empathetic abilities and the differential brain regions showing altered ALFF in postpartum women.

Results

The results showed that ALFF increased in the superior medial prefrontal cortex and decreased in the precuneus, angular gyrus, supramarginal gyrus, hippocampus, posterior cingulate gyrus, thalamus, postcentral gyrus and inferior parietal lobule from scan 1 to scan 2. Decreased ReHo was found in the insula, inferior frontal gyrus, precentral gyrus, precuneus and posterior cingulate gyrus while increased ReHo was discovered in the left cerebellum posterior lobe (Figure 1). When significantly altered with ALFF of brain regions (e.g. precuneus, posterior cingulate gyrus) as the region of interest, postpartum women showed longitudinal altered connectivity regions in the frontal lobe and parietal lobe (e.g. superior middle frontal gyri, parahippocampal gyrus) (Figure 2). Correlation analysis showed significant correlations between the alterations of spontaneous neuronal activity and empathetic abilities in postpartum women.

Discussion

Results demonstrated that spontaneous neuronal activity and functional connectivity altered in postpartum women from 1 to 2 years during nurturing infants. We reported altered ALFF and ReHo values in these regions such as supramarginal gyrus, angular gyrus and among others, all of which are related to higher-level cognitive functions and emotional processing^{1, 2}. Functional connectivity analysis showed regions that were observed in ALFF analysis work in concert with other regions as a network that correlates with empathy. Our study first provides evidence for alterations spontaneous neuronal activity and brain network in postpartum women, which can implicate the neurophysiological mechanism in women after delivery. The detected changes suggested that postpartum women can exhibit functional reorganization, which is the dynamic development for adaptive changes including cognitive function and empathic processing over nurturing infants.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (grants 81571658 and U1632274) and the Social Science Foundation of China (grant 15ZDB016).