Aside from a growing belly, a pregnant woman's brain also grows, a study has revealed.

Pregnancy is associated with a number of physiological changes from surge in hormones to anemia. As to why a woman becomes forgetful during pregnancy is often overlooked. It turns out, the gray matter of the brain increases during pregnancy.

Pregnancy-induced mental fog or mommy brain is often attributed to exhaustion and lack of sleep. In a video by Discovery News, Lissette Padilla explained that at the onset of pregnancy, women experience neurological changes, such as an increase in gray matter volume, which persists until after child birth.

A study published in Behavioral Neuroscience found, using magnetic resonance imaging (MRI), that pregnancy causes an increase in gray matter in specific regions of the brain, including the prefrontal cortex and the parietal lobe. Notable growths were also seen in the hypothalamic region and amygdala, both of which regulate hormones and emotions.

Researchers said that the increase in gray matter is associated with the positive connection that the mother has with the child. This is why mothers can attend to their child up to six times a night without feelings of frustration, which eventually causes exhaustion and forgetfulness.

To identify whether an amygdala would have any significant changes when mothers look at their own child versus other babies, researchers from the University of Toronto in Mississauga examined the brain activity of 22 mothers. While the amygdala does not appear to become more sensitive during pregnancy, the result showed reduced amygdala response is evident in mothers who are experiencing a stressful motherhood.

Postpartum depression often results when mothers experience severe maternal exhaustion and this is strongly associated with brain receptors that regulate the amygdala and other brain structures relevant to the reward system.

Researchers postulated that comparison of brain regions of non-depressed mothers with those with postpartum depression can shed light on the condition.

"The abnormal changes may be associated with difficulties in learning the rewarding value of infant stimuli and in regulating emotions during the postpartum period," said the researchers.

Production of oxytocin is particularly heightened during pregnancy and because the amygdala is packed with oxytocin receptors, mothers tend to bond more and feel positive towards caring for their children.

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