Spatial ability during pregnancy and motherhood in rats and humans: a comparative study
Maternal physiology and behavior change dramatically over the course of pregnancy to nurture the fetus and prepare for motherhood. Further, the experience of motherhood itself continues to influence brain functioning well after birth, shaping behavior to promote the survival of offspring. To meet these goals, cognitive abilities, such as spatial memory and navigation, may be enhanced to facilitate foraging. Existing studies on pregnant and maternal rats demonstrate enhanced cognitive function in specific spatial domains. However, in humans, anecdotal reports abound regarding impaired cognition during pregnancy, colloquially termed baby brain. Epidemiological studies indicate that 50 to 80 percent of pregnant women report problems with thinking and/or with memory. When tested objectively, the most consistent finding indicates impaired verbal memory. However, no studies to date have focused specifically on the effects of pregnancy and motherhood on human spatial cognition. We used analogous tests of spatial memory and navigation at matched phases of reproduction to study changes in spatial memory across pregnancy and motherhood in both rats and humans. Parallel studies with closely matched paradigms allowed us to better understand evolutionary conservation of the effects of pregnancy and motherhood on spatial abilities, while contributing to our knowledge of each species individually. Results indicated a persistent advantage in object-in-place memory of primiparous female rats that emerged during lactation not during pregnancy, and was not related to non-mnemonic factors of anxiety or neophobia. On a modified water maze task to assess learning strategy, both primiparous and nulliparous females learned the task at similar rates and accuracies, but neither group demonstrated a preference for place strategy or stimulus-response strategy. In humans, pregnant and lactating women were not objectively impaired compared to women who had never been pregnant when tested on several measures of spatial performance to assess object-in-place memory and spatial navigation. Despite objectively equivalent performance, both pregnant and lactating women subjectively rated themselves as more impaired on spatial tasks than never-pregnant women. Disparate results on the effects of pregnancy and motherhood on cognitive function in rats and humans calls into question the fitness of the rat model as applied to human cognition.