Scientists have been following the brains of first-time and experienced fathers in marmosets, small monkeys that live in trees. These little monkeys belong to a rare specie, in which males take care of their offspring.
The study found that their males experienced changes in their hormones once the parenting and caring had started. The most structural changed occurred in the prefrontal cortex, a region of the brain important for planning and memory. It seems that fathering causes changes in the high-cognitive brain parts. Neurons had more connections and there were also more receptors sites for the hormone vasopressin, stress-related hormone that is partly responsible for aggression (protective role maybe).
Scientists suggest that neuron enhancements represent changes in the reward system, which make the fathers bond and care.