GENETICS AND ENVIRONMENT MEET IN THE STUDY OF STRESS.

This next point you already know but I repeat it here. How we respond to stress, in the short-term or over time is determined by a complex combination life experiences and genetics and the interaction of the two in our brains. While you might say ‘but of course’ what is not obvious at all are all the details of how that interaction works in our heads.

We of course keep learning more. For example, in a recent article in the Journal Neuroscience (see article by Li and colleagues, 2 May 2014) we learn that when the prefrontal cortex of mice is activated the mice act totally helpless to stressors that they previously had learned to avoid with ease. Sound familiar. Learned helplessness has long been used as concept to account for some of the core symptoms in depression. Incidentally the role of brain structures like the prefrontal cortex have been studied in detail for decades as a vital system in cognition and emotion.

In an earlier posting I pointed out that not unlike us, when rats are stressed they rely on habits, routines even conditions clearly should induce them to behave differently. Stress related changes in brain anatomy are what is the cause of the rat’s rigidity when stressed. I just noticed the study published by Rui Costa and colleagues two years ago in Science (30 July 2009) and was intrigued by the finding that “rats that had been stressed repeatedly and unpredictably for three weeks were more likely than unstressed animals to continue performing habitual behaviors, even when it no longer made sense to do so”. Sounds like many of us.

We know a god deal about the brain’s response to stress. There is the release of corticosteroids, causing neuronal reorganization, primarily in the hippocampus and medial prefrontal cortex. Rui Costa and colleagues also found that when they measured brains structures in stressed and unstressed rats, they found that the prelimbic cortex and the dorsomedial striatum were smaller in stressed animals and these are brain structures implicated in goal-directed actions and at the same time dorsolateral striatum — necessary for habit formation, routine behavior — was enlarged, suggesting a neurological mechanism for how stress produces non-adaptive repetitive behavior.

What is elegant about the study is how systematic manipulation and measurement of behavior can be integrated with sophisticated neurobiology producing a picture of what may be responsible for complex behavior. Isn’t that what good cognitive science should be about.

And colleagues published a study entitled “Inheritance of stress-induced, ATF-2-dependent epigenetic change, (in the Journal Cell, June 21, 2011) in which the scientists could shows that when flies are stressed, a transcription factor releases its hold on regions of DNA called heterochromatin, allowing them to unravel and be copied. What is interesting is that the effects on heterochromatin can be passed on parents to children. Obviously jumping from fruit fly to people is huge leap but the very notion of stress in parents being heritable is a fascinating an important line of research that will undoubtedly be followed in the coming years.