Lead author Benedetta Leuner of Ohio State University in Columbus said the study showed an increase of dendritic spines in new mothers' brains was associated with improved cognitive function on a task that requires behavioral flexibility -- in essence, enabling more effective multitasking. Dendritic spines are hair-like growths on brain cells that are used to exchange information with other neurons.
The dendritic spines increased by about 20 percent in the brain regions associated with learning, memory and mood, Leuner said.
However, the study found chronic stress negated the brain benefits of motherhood, causing the stressed rats' brains to match brain characteristics of animals that had no reproductive or maternal experience.
"Animal mothers in our research that are unstressed show an increase in the number of connections between neurons. Stressed mothers don't," Leuner said in a statement. "We think that makes the stressed mothers more vulnerable. They don't have the capacity for brain plasticity that the unstressed mothers do, and somehow that's contributing to their susceptibility to depression."
Leuner presented the findings at Neuroscience, the annual meeting of the Society for Neuroscience in New Orleans.