Although the stress of motherhood may make them feel insane at times, new moms aren't losing their minds. In fact, it's just the opposite: Their brains grow larger in certain regions within months of delivering the newborn, a new study suggests.

And those moms who are particularly awestruck and gushy over their babies show more growth in the brain areas associated with motivation, reward and the regulation of emotion, the researchers said.

The team, led by Pilyoung Kim, a developmental psychologist who is now with the National Institute of Mental Health, used magnetic resonance imaging (MRI) to scan the brains of 19 moms two to four weeks after the birth of a child, then again up to four months afterward. Images showed small but significant increases in the gray matter in certain parts of the brain, including those responsible for sensory perception, reasoning and judgment.

A change in gray matter over such a short period is unusual among adults, according to the researchers.

Research in animal mothers has linked changes in the brain with the stimuli of touching, smelling, seeing and suckling babies. The hormones that accompany motherhood, including estrogen, oxytocin and prolactin, influence animal moms' behavior and also change their brain anatomy.

In humans, however, it's impossible to say what causes the changes in brain structure in new mothers, according to Kim.

"Whether this is affecting mothers' behaviors or are mothers' behaviors affecting the brain? It's not clear," Kim told LiveScience.

However, the areas where the changes were observed are clearly implicated in maternal behavior and motivation, as well as higher cognitive functions – all of which are involved in parenting, she said.

These areas include the prefrontal cortex (associated with reasoning and judgment), the parietal lobe (associated with sensory perception) and a number of areas within the midbrain. In particular, women who most enthusiastically rated their babies as beautiful, perfect, special and so on saw more growth in their midbrains, including the hypothalamus, amygdala and substantia nigra, parts of the brain involved in motivation, reward and emotion processing.

Roughly half of the 19 participants gave birth to boys, eight had given birth previously and none suffered from severe postpartum depression. Brain scans of depressed moms would likely have shown no changes or different ones, Kim said.

Given the small size of the study, its results need to be replicated with a larger group of mothers, according to the authors. Their work is published in the October issue of the journal Behavioral Neuroscience.

Article was reprinted with permission from LiveScience.

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