Our bodies are colonized by a teeming, ever-changing mass of microbes that help power countless biological processes. Now, a new study has identified how these microorganisms get to work shaping the brain before birth.

Researchers at Georgia State University studied newborn mice specifically bred in a germ-free environment to prevent any microbe colonization. Some of these mice were immediately placed with mothers with normal microbiota, which leads to microbes being transferred rapidly.

That gave the study authors a way to pinpoint just how early microbes begin influencing the developing brain. Their focus was on the paraventricular nucleus (PVN), a region of the hypothalamus tied to stress and social behavior, already known to be partly influenced by microbe activity in mice later in life.

Immune cells released from bone marrow in the skull in response to chronic stress and adversity could play a key role in symptoms of depression and anxiety, say researchers.

The discovery—found in a study in mice—sheds light on the role that inflammation can play in mood disorders and could help in the search for new treatments, in particular for those individuals for whom current treatments are ineffective.

Around 1 billion people will be diagnosed with a mood disorder such as depression or anxiety at some point in their life. While there may be many underlying causes, chronic inflammation —when the body’s immune system stays active for a long time, even when there is no infection or injury to fight—has been linked to depression. This suggests that the immune system may play an important role in the development of mood disorders.

A suspected perpetrator who can barely remember his name, several traffic violations committed by a woman in her mid-fifties who is completely unreasonable and doesn’t understand her behavior—should such cases be brought before a court? And how does the state deal with people who commit acts of violence without meaning to?

Those questions come to mind if one hears those examples from everyday clinical praxis with persons suffering from dementia. Neurodegenerative diseases might affect several functions of the brain, ranging from memory in Alzheimer’s disease to behavior, such as in behavioral variant frontotemporal dementia, and to sensorimotor function in Parkinson’s disease.

One of the most interesting consequences of these alterations is the fact that persons affected by these diseases might develop criminal risk behavior like harassment, traffic violation, theft or even behavior causing harm to other people or animals, even as the first disease sign.