Sudden stress shifts human brain into survival mode
(Medical Xpress) -- In threatening situations, the brain adapts within seconds to prepare for an appropriate response. Some regions are temporarily suppressed. Others become more active and form temporarily alliances for fight or flight. Noradrenaline is driving force behind this reorganization. (Science, November 25).
Almost instantly after encountering something terrifying, the brain gears up for an adequate response. This can happen within seconds. The resulting integrated state of body and mind is optimized to survive threatening situations. The changes underlying this response have not been mapped previously in this level of detail.
'We feel the fear, our senses are sharpened, and we create lasting memories. But our capacity for careful deliberation is impaired so that we can respond rapidly above all', says Erno Hermans, the first author of the paper that appears in Science on November 25. Hermans works at the Donders Institute for Brain, Cognition and Behaviour of the Radboud University/Radboud Medical Centre.
Hermans showed his participants horror movies in the scanner while recording fluctuations in activity across the entire brain. That is an important new trend in neuroscience. 'Subsequently, you can use statistical methods to determine which regions became active, and which regions formed a network of activity. We think these methods provide more insight into how the brain functions than looking at isolated responses to specific stimuli'.
'Our setup moreover allows us to investigate specifically the response to acute stress. We see activity in other regions than those observed previously by other researchers. We think that this discrepancy can be explained by the fact that in those studies, participants continuously received negative feedback on their performance in a task. This creates pressure to achieve, which urges people to make a stronger effort. That also leads to stress, but not the acute fight-or-flight response in which we were interested.'
Two hormones are involved in the brain's response to stress: Cortisol and noradrenaline. By administering their participants drugs that suppress either cortisol or noradrenaline, Hermans and colleagues were able to determine that noradrenaline triggers the acute stress response. Hermans: 'In response to acute stress, availability of cortisol in the brain increases, but this change is not very fast. Noradrenaline is released directly from the locus coeruleus in the brain. The field has a strong focus on the cortisol response, but we show that noradrenaline is more important in the early phase of the stress response.'
Acute stress shifts the brain into a state that fosters rapid defense mechanisms. Stress-related neuromodulators are thought to trigger this change by altering properties of large-scale neural populations throughout the brain. We investigated this brain-state shift in humans. During exposure to a fear-related acute stressor, responsiveness and interconnectivity within a network including cortical (frontoinsular, dorsal anterior cingulate, inferotemporal, and temporoparietal) and subcortical (amygdala, thalamus, hypothalamus, and midbrain) regions increased as a function of stress response magnitudes. β-adrenergic receptor blockade, but not cortisol synthesis inhibition, diminished this increase. Thus, our findings reveal that noradrenergic activation during acute stress results in prolonged coupling within a distributed network that integrates information exchange between regions involved in autonomic-neuroendocrine control and vigilant attentional reorienting.