Today, many people are under stress, it is undeniable. But although the subjective feeling of stress is ubiquitous and seemingly an inescapable part of the human condition, there is still much we do not understand about how our feelings occur.
When we experience physiological stress, such as pain, hunger or any other immediate physical stress, the hypothalamus triggers the production of hormones called glucocorticoids from our adrenal glands, helping to regulate our response to stress.
But what about subjective stress, which we might otherwise consider emotional or psychological stress? Where exactly are these negative feelings of pressure, anxiety and foreboding in the brain? Scientists are not sure at the moment, but previous research has indicated that feelings of subjective or emotional stress (hereinafter simply “stress”) are not always linked to physiological stress, suggesting that the neurobiological origins of stress may lie elsewhere.
As to where exactly it might be in the brain, there is a lot of evidence in animals and humans that points to mechanisms involving the hippocampus: a region of the brain that helps regulate memory, emotions, and navigation. Although the links of the hippocampus with stress have been much studied, the nature of these remains unclear.
In a new study, scientists from Yale University took a closer look at what’s going on, giving us a new perspective on how the neurological underpinnings of stress work inside the human brain.
Researchers recruited 60 healthy adults and showed them a series of highly aversive and threatening images designed to produce some form of stress response (such as anger, disgust, fear and sadness), alternated with various scenes neutral, designed to help them relax. During the experiment, the participants saw their brain activity measured by functional magnetic resonance imaging (fMRI), and also evaluated to what extent they felt stressed and awake from each set of images to which they were faced.
When the research team analyzed the results, they found that a higher activity linking the hippocampus to the hypothalamus, the parahippocampal cortex and the inferior temporal gyrus, corresponded to a feeling of increased stress in the participants. This, the researchers say, was an example of a positive experience network, where more activity equals higher stress levels.
In contrast, the connectivity of the hippocampus with the dorsolateral prefrontal cortex, the postcentral gyrus and the cerebellum, formed a negative network, with increased activity between these clusters indicating that the participants were less stressed in the experience.
As a result, the researchers found that the participants’ overall stress level is determined by an adaptive interaction of activity between these two networks, which combine to both create and relieve the stress they feel. ” Despite the distinct roles of these networks, our results suggest that individuals have engaged in positive and negative networks in an adaptive way to alleviate feelings of stress, ” explain the researchers in their study. ” That is, participants had higher connectivity with negative networks (whose strength predicted a less stressed feeling), but, at the same time, had lower connectivity with positive networks .”
Of course, we still have a lot to learn and discover to really understand how the hippocampus regulates stress, not to mention the other neurobiological mechanisms that most certainly contribute to it. However, the researchers remain optimistic and think that these discoveries could one day help develop future treatments for stress: ” These results can help us to adapt the therapeutic intervention to several targets, such as the increase in the strength of the connections of the hippocampus to the frontal cortex or the decrease in signaling to physiological stress centers , ”explains Rajita Sinha, principal researcher and neuroscientist.