Post by Elisa Guma
What's the science?
Anxiety, often described as an enduring state of apprehension, is thought to be an emotional state independent of fear that influences our behaviour in response to threat. It is thought that the neural response to less imminent or ‘cognitive’ threats involves the ventral hippocampus and the ventromedial prefrontal cortex, whereas the response to more immediate or ‘reactive’ threats involves mid-brain regions such as the periaqueductal gray. This week in Nature, Fung and colleagues set out to investigate whether trait anxiety selectively affects cognitive and reactive fear circuits in response to a threatening stimulus.
How did they do it?
To investigate this question, healthy adults for whom trait anxiety was measured, were tested on a behavioural task in which the goal was to successfully escape different predators, while maximizing money earned by fleeing as late as possible from an attack. In each trial, participants passively earned money while they encountered virtual predators of three colours, representing different attack distances: fast, medium, or slow. Fast attack predators quickly switched from a slow approach to a fast attack, requiring subjects to make quick escape decisions. Slow attack predators slowly approached for longer time periods, allowing participants more time to contemplate an escape. Subjects were given electrical stimulation when they were caught by the virtual predators. In order to measure contributions of the ‘reactive fear’ and cognitive fear’ networks to escape decisions, subjects performed this task while undergoing functional magnetic resonance imaging (fMRI), which measures blood oxygen level dependent (BOLD) changes (or changes in blood flow) throughout the brain, as a reflection of underlying neural activity.
With these data, the authors investigated how trait anxiety affected escape decisions based on predator attack speed. Next, they investigated the effects of trait anxiety on escape success as well as total earnings for the different predator types. For the fMRI data, they investigated the 2 seconds before the escape to examine neural circuitry involved in the anticipation of an escape response. Finally, they also investigated the interaction between brain regions involved in escape decisions by performing a seed-based connectivity analysis. This measures the correlation between patterns of activity in a ‘seed’ region (or region of interest), with activity in the rest of the brain. They chose the ventral hippocampus as a seed region given its critical role in cognitive fear and anxiety.
What did they find?
First, the authors found a significant interaction between the slow predator type and trait anxiety score, suggesting that trait anxiety affected the escape time only for slow predators, potentially via the ‘cognitive’ fear circuitry. More specifically, with every unit of increase in state anxiety there was a 5% increase in the chance of fleeing from a slow predator. Therefore, higher trait anxiety was associated with a greater likelihood of the participant escaping earlier when given enough time to prepare an escape.
Participants with higher trait anxiety were more likely to successfully escape in the slow predator conditions, but not in the medium or fast. However, this negatively impacted how much money they earned in the task because they were more likely to escape before individuals with lower trait anxiety. The authors found a significant BOLD response in regions often associated with fear and anxiety including the amygdala, hippocampus, ventromedial prefrontal cortex, and midcingulate cortex for higher trait anxiety and slow predators. Their seed-based analysis revealed that trait anxiety significantly influenced the coupling between the ventral hippocampus seed, and the bilateral medial prefrontal cortex, right inferior frontal gyrus, and left insula suggesting that anxiety affects these circuits during escape decisions involving slow predators. These areas have previously been shown to be involved in behavioural flexibility and information processing in fear response, so their role in cognitive fear appraisal is fitting. In addition, research from both human and non-human animal work has shown that activity of the ventral hippocampus and medial prefrontal cortex becomes more synchronous in environments that increase anxiety.
What's the impact?
The authors provide compelling evidence in support of the idea that trait anxiety affects behaviour only when there is sufficient time to perceive and recognize a threat, but not when threats require an immediate reactive response. It is possible that the influence of trait anxiety on escape decisions could influence survival outcomes such that individuals with higher trait anxiety escape predators earlier. Future work may apply this task to individuals with anxiety disorders, such as post-traumatic stress disorder, to try to understand in what ways their cognitive and reactive fear responses are affected, which may in turn allow for tailored treatments and interventions.
Fung et al. Slow escape decisions are swayed by trait anxiety. Nature (2019). Access the original scientific publication here.