Becoming a father may really mess with your head, or at least a monkey’s head.

A new study shows that marmoset monkey fathers display differences in brain structure and hormone receptors compared with nonfathers.

More study is needed to determine if the same changes occur in other mammals, like human males. But the results suggest that fatherhood prompts changes in brain structure that could lead to differences in brain function as well.

The results of the study appear in the journal Nature Neuroscience.

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Researchers say marmosets are unusual among mammals in that fathers care extensively for their young children by carrying, protecting, and feeding them. For example, marmoset dads carry their babies more than half the time during the first three months of their lives.

In the study, Elizabeth Gould of the department of psychology at Princeton University and colleagues compared the brains of first-time and experienced marmoset fathers with the brains of adult male marmosets who weren't fathers.

The results showed that experienced marmoset fathers had a higher density of connections in a region of the brain known as the prefrontal cortex than nonfathers.

Fathers also had more of a particular hormone receptor in this region for vasopressin, which is thought to be involved in parental behavior and social bonding. There were also more of these receptors in fathers whose babies were younger; researchers say this suggests that this change may be caused by contact with infants.

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By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Kozorovitskiy, Y. Nature Neuroscience, Aug. 20, 2006 online edition. News release, Nature Research Journals.