Cognitive reorganization during pregnancy and the postpartum period: an evolutionary perspective

Cognitive costs of reproduction: life-history trade-offs explain cognitive decline during pregnancy in women

Life-history theory predicts that access to limited resources leads to trade-offs between competing body functions. Women, who face higher costs of reproduction when compared to men, should be especially vulnerable to these trade-offs. We propose the 'cognitive costs of reproduction hypothesis', which states that energy trade-offs imposed by reproduction may lead to a decline in maternal cognitive function during gestation. In particular, we hypothesize that the decline in cognitive function frequently observed during pregnancy is associated with the allocation of resources between the competing energetic requirements of the mother's brain and the developing foetus. Several distinctive anatomical and physiological features including a high metabolic rate of the brain, large infant size, specific anatomical features of the placenta and trophoblast, and the lack of maternal control over glucose flow through the placenta make the occurrence of these trade-offs likely. Herein, we review several lines of evidence for trade-offs between gestation and cognition that are related to: (i) energy metabolism during reproduction; (ii) energy metabolism of the human brain; (iii) links between energy metabolism and cognitive function; and (iv) links between gestation and cognitive function. We also review evidence for the important roles of cortisol, corticotropin-releasing hormone and sex hormones in mediating the effects of gestation on cognition, and we discuss possible neurophysiological mechanisms underlying the observed effects. The evidence supports the view that energy trade-offs between foetal growth and maternal endocrine and brain function lead to changes in maternal cognition, and that this phenomenon is mediated by neuroendocrine mechanisms involving the hypothalamic-pituitary-adrenal axis, brainstem nucleus locus coeruleus and hippocampus.

Potential Brain Age Reversal after Pregnancy: Younger Brains at 4-6 Weeks Postpartum

Pregnancy is accompanied by complex biological adaptations, including extreme hormonal fluctuations. Moreover, changes on the endocrine level are accompanied by changes in cerebral anatomy, such as reductions in brain or gray matter volume. Since declining brain and tissue volumes are characteristic for normal aging, the question arises of whether such pregnancy-induced anatomical effects are permanent or transient. To answer this question, we acquired high-resolution brain image data of 14 healthy women in their mid-twenties to late thirties at two time points: within 1-2 days of childbirth (early postpartum) and at 4-6 weeks after childbirth (late postpartum). At both time points, we estimated the brain ages for each woman using a well-validated machine learning approach based on pattern recognition. Ultimately, this algorithm - designed to identify anatomical correlates of age across the entire brain - reveals a single score for each individual: the BrainAGE index. Comparing the BrainAGE indices between both time points, female brains at late postpartum were estimated to be considerably younger than at early postpartum. On average, that difference was about five years (mean ± SD: 5.4 ± 2.4 years). These findings suggest a substantial restoration/rejuvenation effect after giving birth, which is evident already within the first couple of months.

Disrupted Spontaneous Neural Activity Related to Cognitive Impairment in Postpartum Women

Purpose: Prior research has demonstrated that the postpartum period is associated with an increased risk of cognitive impairment. This study aims to investigate whether disrupted spontaneous neural activity exists in postpartum women without depression using resting-state functional magnetic resonance imaging (rs-fMRI) and to detect the relationship between these abnormalities and cognitive impairment.

Materials and Methods: Postpartum women (n = 22) were compared with age- and education-matched nulliparous women (n = 23) using rs-fMRI. We calculated the amplitude of low-frequency fluctuation (ALFF) and regional homogeneity (ReHo) values to evaluate spontaneous neural activity and detect the relationship between rs-fMRI data and cognitive performance.

Results: Relative to nulliparous women, postpartum women had significantly decreased ALFF and ReHo values primarily in the left posterior cingulate cortex (PCC) and prefrontal cortex and increased ALFF values in left cerebellar posterior lobe. We found a positive correlation between the ALFF and ReHo values in the PCC and the complex figure test (CFT)-delayed scores in postpartum women (r = 0.693, p = 0.001; r = 0.569, p = 0.011, respectively). Moreover, the clock-drawing test (CDT) scores showed positive correlations with the ALFF and ReHo values in the right superior frontal gyrus (SFG; r = 0.492, p = 0.033; r = 0.517, p = 0.023, respectively).

Conclusion: Our combined ALFF and ReHo analyses revealed decreased spontaneous neural activity, mainly in the PCC and prefrontal cortex, which was correlated with specific impaired cognitive functioning in postpartum women. This study may elucidate the neurophysiological mechanisms underlying postpartum cognitive impairment and enhance our understanding of the neurobiological aspects of the postpartum period.

Disturbed retrieval network and prospective memory decline in postpartum women

Prospective memory (PM) refers to the ability to remember to execute an intended action in the future. For successful PM performance, both top-down strategic monitoring and bottom-up spontaneous retrieval processes need to be appropriately recruited. We assessed PM performance and used fMRI to discover relevant neural correlates and possible predictors for PM performance in 25 postpartum and 26 nulliparous age- and education-matched women. Postpartum women showed decreased PM performance, a higher number of nocturnal awakenings, and lower estradiol level. The postpartum women had decreased functional connectivity (FC) in the right hippocampus and ventral frontoparietal networks (FPN) during retrieval-dominant PM trials relative to maintenance-dominant ongoing trials in the PM block. On multivariate analyses, decreased FC between the right hippocampus and ventral FPN and a higher number of nocturnal awakenings were independent predictors for poor PM performance after adjusting for age, education, estradiol level, and depressive symptoms. On mediation analyses, the estradiol level was found to have an indirect effect on PM accuracy via altered FC as a mediator. This suggests that decreased FC within the spontaneous retrieval-related regions including the right hippocampus and ventral FPN, disrupted sleep rhythms, and decreased estradiol level may contribute to poor PM performance in postpartum women.

Duration of motherhood has incremental effects on mothers' neural processing of infant vocal cues: a neuroimaging study of women

The transition to motherhood, and the resultant experience of caregiving, may change the way women respond to affective, infant signals in their environments. Nonhuman animal studies have robustly demonstrated that mothers process both infant and other salient signals differently from nonmothers. Here, we investigated how women with and without young infants respond to vocalisations from infants and adults (both crying and neutral). We examined mothers with infants ranging in age (1-14 months) to examine the effects of duration of maternal experience. Using functional magnetic resonance imaging, we found that mothers showed greater activity than nonmothers to vocalisations from adults or infants in a range of cortical regions implicated in the processing of affective auditory cues. This main effect of maternal status suggests a general difference in vocalisation processing across infant and adult sounds. We found that a longer duration of motherhood, and therefore more experience with an infant, was associated with greater infant-specific activity in key parental brain regions, including the orbitofrontal cortex and amygdala. We suggest that these incremental differences in neural activity in the maternal brain reflect the building of parental capacity over time. This is consistent with conceptualizations of caregiving as a dynamic, learning process in humans.

Working memory in pregnant women: Relation to estrogen and antepartum depression

This article is part of a Special Issue "Estradiol and cognition". Subjective changes in concentration and memory are commonly reported by women during the second or third trimesters of pregnancy, but the nature of the problem is poorly understood. We hypothesized that these self-reports might reflect difficulties in working memory (WM). It was further hypothesized that antepartum depression (depression arising during pregnancy) may play an etiological role, either on its own or due to secondary changes in endocrine function or sleep. Using WM tasks that emphasized executive control processes mediated by the prefrontal cortex (PFC) we compared pregnant women tested at 34-36 weeks of gestation (n = 28) with age- and education-matched non-pregnant controls (n = 26). All pregnant women were screened for depression. Evidence of a WM disturbance was found, and was evident only among pregnant women showing depressive symptoms. In contrast, pregnant women who were not depressed showed WM performance that equalled, or even significantly exceeded, non-pregnant controls. No significant differences were observed on control tests of other cognitive functions. Multiple regression revealed that serum estradiol concentrations, along with severity of depressive affect but not sleep disruption, significantly predicted variation in the WM scores. In agreement with studies of estradiol and WM in other contexts, higher estradiol was associated with better WM, while higher levels of depressive symptoms predicted poorer WM. We conclude that memory disturbance during gestation might not be as widespread as commonly believed, but can be seen among women experiencing antepartum depression. The high level of WM performance found in healthy, non-depressed, pregnant women is discussed from an adaptationist perspective.

Cerebral white matter lesions and perceived cognitive dysfunction: the role of pregnancy

OBJECTIVE

Women who suffered eclampsia or preterm preeclampsia are twice as likely to demonstrate cerebral white matter lesions (WML) on magnetic resonance imaging compared with age-matched women who had normotensive pregnancies, and they report more cognitive dysfunctions in everyday life. We aimed to determine whether pregnancy in and of itself has a relationship with the presence of WML and subjective cognitive dysfunction.

STUDY DESIGN

Eighty-one parous women who had a normotensive pregnancy were matched for age with 65 nulliparous women and all underwent cerebral magnetic resonance imaging. Presence of cerebral WML was rated and blood pressure was measured. Subjective cognitive functioning was assessed using the Cognitive Failures Questionnaire.

RESULTS

There was no difference in the presence (22% vs 19%) of WML between parous and nulliparous women. Age was a predictor for the presence of WML, whereas the presence of current hypertension was not. Average score on the Cognitive Failures Questionnaire was not different between both groups, nor related to WML.

CONCLUSION

A history of pregnancy in and of itself is not related to the presence of cerebral WML and the perception of cognitive dysfunction. Because of the relationship with preterm preeclampsia and eclampsia, future research should focus on the clinical importance and development throughout the years of such cerebral WML in young women and focus on risk factors for cardiovascular disease.