HEIDELBERG, 30 September 2015 – Male mice dramatically change their social behaviour towards newborn pups after mating and cohabitation with pregnant females. Japanese neurobiologists now report in The EMBO Journal that activation of defined small regions of the mouse brain determine whether a male mouse will show infanticidal or paternal behaviour. Mice that were only motivated for, but did not actually carry out infanticide, display the same activity patterns, indicating that it may be possible to detect motivation for complex behaviours by studying activation of a small selection of brain nuclei.
Why parents are innately caring towards their children remains a complex scientific question, with implications also for prevalent societal problems such as child-directed aggression and its causes. Simpler forms of such behaviours in animals allow to study them under defined conditions, and to elucidate their sensory and neuronal basis. In various mammalian species, including monkeys and lions, infanticide of other males' offspring represents a strategy by which males increase their mating opportunities and reproductive success. Also in mice, virgin males that have not yet mated and fathered offspring tend to attack and kill unrelated pups, but they gradually switch towards paternal behaviour after mating and living with a pregnant female. Intriguingly, once having fathered children a male mouse will be caring even towards unrelated pups.
A team led by Kumi Kuroda of the RIKEN Brain Science Institute in Japan monitored the trace of neuronal activation of nine histologically defined areas in the mouse forebrain. Two of these areas showed strikingly distinct activation patterns depending on whether the male mouse had displayed parental care or aggression towards pups a few hours earlier. Selective inactivation of these brain areas confirmed that they were indeed responsible for controlling paternal versus infanticidal behaviour. Moreover, using optogenetics, a novel method allowing to artificially activate certain brain neurons through light, the scientists could trigger development of sustained infanticide suppression even in previously aggressive virgin males. "The most striking finding in our studies was that the observed activation patterns did not depend on whether the male mouse had actually performed infanticide or parenting, or had only intended to do so upon being indirectly presented with a protected pup", remarked Kuroda. "This is therefore the first time that we can detect an individual's motivation towards a certain social behaviour simply through activation patterns of a small defined brain area".
The area at the bottom of the forebrain, where the two identified brain regions are situated, contains controlling centers for instinctive behaviours and autonomic functions and is generally conserved in mammalian species. This suggests that similar mechanisms may govern primate parental interactions, even though the situation in humans is likely to be more complex due to higher cognitive abilities. Possible future application of this knowledge to predict aggressive behaviour in advance would require establishment of appropriate non-invasive live imaging or scanning technologies, and–like other insight predictive of social behaviour–require careful ethical considerations.