If stress tends to completely paralyse you, mentally speaking, it's probably due to the unique way your brain works, a new study suggests. By mapping stress-related brain activity in mice, researchers have pinpointed specific areas and patterns of brain activity that changed depending on if the animals felt helpless or not in a tense situation.

The mice that showed helpless behaviour had "vastly different brain activity" from those that showed signs of resilient behaviour, the researchers found. By identifying areas of the brain that could be linked to stress-induced depression in humans, it's hoped that we could develop new ways to treat and diagnose depression in the future.

The helpless mice in the experiment tended to show a lower level of neuronal activation in the brain when placed in a stressful situation (a series of escapable electric shocks), suggesting that elements of thought-processing might have been interrupted.

The activity in the minds of helpless mice was also more consistent between individual animals, which indicates that the helpless mice had more brain activity in common than the resilient mice.

One area of the brain showing lower levels of activity in the helpless mice was the prefrontal cortex, which is linked to our ability to organise thoughts and actions, and is thought to relate to mood and anxiety disorders as well. Other areas of the brain with subdued activity in the helpless group included those associated with processing emotion and motivation, initiating defensive behaviour, coping with stress, and learning and memory.

But one part of the brain showed more, not less, activity in helpless mice - the locus coeruleus, an area that's previously been linked to physiological responses to stress and panic. The research suggests that this part of our brain has a major role to play in stress-induced depression, and that gives scientists some useful clues for further studies.

The team, which spans several insitutions across the US and the UK, says more research is required to determine whether the neural changes that they observed are causally related to the expression of helplessness or resilience - in other words, whether or not the brain activity is actually causing the response of the mice. 

And we still have to confirm that similar things are going on in human brains that have been observed in these mouse brains. Right now, there's still a whole lot we don't know about the neurobiological mechanisms behind some of our physical responses.

"Our study demonstrates the utility of inspecting brain-wide activity patterns for revealing circuits participating in specific behaviours, and supports the view that defining neuronal circuits underlying stress-induced depression-like behaviour in animal models can help identify new targets for the treatment of depression," concludes the report, which has been published in Frontiers in Neural Circuits.