Mobbs, D. | Search bioRxiv

bioRxiv2018

Attentional set to safety recruits the medial prefrontal cortex

During threat assessment, the early detection of danger is highly adaptive, yet the fast orientation towards safety is also key to survival. The present study aimed to explore how the human brain searches for safety by manipulating subjects attentional set to cues associated with shock probability. Subjects were asked to judge random dots motion (RDM) direction and could be shocked for incorrect responses (RDM task) while keeping alert in detecting the shock probability cues (cue detection task). In contrast to the safe condition, where subjects searched for cues associated with no shock probability, incorrect responses to dangerous+ (D+) cues would increase the shock probability and correct responses to dangerous- (D-) cues would decrease shock probability. In the RDM task, results showed that relative to the D+, the safe attentional set resulted in stronger activation in the ventral medial prefrontal cortex (vmPFC), a core region involved in flexible threat assessment and safety signalling. The vmPFC was also recruited by the D-compared to the D + attentional set. In the cue detection task, shorter response times and greater accuracy were observed for D+ compared to D- and safe cues. Correspondingly, at the neural level D+ cues induced increased activity in the frontoparietal attention network including the inferior parietal lobule and intraparietal sulcus. Overall, our findings demonstrate that attentional set for searching safety recruits the vmPFC, while detection of threat elicits activity in the frontoparietal attention network, suggesting a new role for these regions in human defensive survival circuitry.\n\nSignificance StatementWhile early detection of threat is highly adaptive, the fast orientation towards safety is also key to survival. However, little is known about neural mechanisms underlying attentional set to safety. Using a novel dots motion paradigm combined with fMRI, we explored how human brain prepares for safety searching by manipulating subjects attentional set to cues associated with shock probability. Relative to the dangerous attentional set associated with increasing shock probability, the safe attentional set resulted in stronger activity in the ventral medial prefrontal cortex, a core region involved in flexible threat assessment and safety signalling, suggesting a new role for this region in human defensive survival system in encoding stimuli with survival significance.

neuroscience↗

bioRxiv2017

How Cognitive and Reactive Fear Circuits Optimize Escape Decisions in Humans

Flight initiation distance (FID), the distance at which an organism flees from an approaching threat, is an ecological metric of cost-benefit functions of escape decisions. We adapted the FID paradigm to investigate how fast or slow attacking virtual predators constrain escape decisions. We show that rapid escape decisions rely on reactive fear circuits in the periaqueductal gray and midcingulate cortex (MCC), while protracted escape decisions, defined by larger buffer zones, were associated with cognitive fear circuits which include posterior cingulate cortex, hippocampus and the ventromedial prefrontal cortex, circuits implicated in strategic avoidance and behavioral flexibility. Using a Bayesian Decision Model, we further show that optimization of escape decisions under rapid flight were localized to the MCC, a region involved in adaptive motor control, while the hippocampus is implicated in optimizing decisions that update and control slower escape initiation. These results demonstrate an unexplored link between defensive survival circuits and their role in adaptive escape decisions.\n\nSignificanceHumans, like other animals, have evolved a set of circuits whose primary function is survival. In the case of predation, these circuits include reactive fear circuits involved in fast and immediate escape decisions and cognitive fear circuits that are involved in the conscious feeling of threat as well as slow strategic escape. Using neuroimaging combined with computational modeling, we support this differentiation of fear circuits by showing that fast escape decisions are elicited by the periaqueductal gray and MCC, regions involved in reactive flight. Conversely, slower escape decisions rely on the hippocampus, posterior cingulate cortex and prefrontal cortex, a circuit implicated in behavioral flexibility. These results support the role of the defensive survival circuitry in escape decisions and a separation of fear into reactive and cognitive circuits.

neuroscience↗