The Neurocomputational link between Defensive Cardiac States and Approach-Avoidance Arbitration under Threat

Research Background

Threat avoidance often comes at a cost, especially in situations involving threat-reward conflict, where avoiding threats might reduce the opportunity to gain potential rewards. In threat-reward conflicts, individuals need to balance the potential rewards and threat outcomes of their decisions to generate adaptive behavior. However, this process can be problematic in various psychopathologies (e.g., anxiety disorders), which are often characterized by excessive avoidance behavior. Despite recent significant progress in decision science and computational psychiatry modeling value decisions in healthy and patient populations, research on threat-induced physiological states (such as bradycardia associated with freezing) remains relatively sparse. The freezing response is a defensive reaction to threats, characterized by immobility and a slowed heart rate. Freezing has been shown to facilitate sensory regulation and risk assessment while minimizing the likelihood of detection under threat. For example, bradycardia during freezing is thought to be associated with enhanced sensory sensitivity and readiness for action.

Source Introduction

This paper, written by Felix H. Klaassen and others, was published in the journal Communications Biology. The authors are from Radboud University Donders Institute for Brain, Cognition, and Behaviour, Radboud University Behavioural Science Institute, and Leiden University Institute of Psychology and Leiden Institute for Brain and Cognition. It was published in 2024.

Research Process

This paper aims to explore how the freezing state affects approach-avoidance mediation under threat. To fill this knowledge gap, the authors propose three potential mechanisms by which the freezing state might influence approach-avoidance mediation in the context of threat:

1. The freezing state may be related to enhancing the aversive value processing of potential threats via the amygdala-periaqueductal gray (PAG) circuit.
2. The freezing state might alter the comparative process between reward and threat.
3. The freezing state might increase the body’s response speed to threatening situations through action motivation.

To test these hypotheses, the research team developed a Passive-Active Approach-Avoidance Task (PAT). In this task, 58 participants were required to make approach or avoidance decisions when facing varying levels of reward and threat. Simultaneously, brain responses were measured using fMRI, and the freezing state was assessed through heart rate measurements.

Research Results

Freezing State is Associated with Shock-Induced Avoidance

In the PAT task, participants were able to balance the rewards of money against the punishment of electric shocks effectively. Specifically, higher levels of money prompted more approach decisions, while higher levels of electric shocks prompted more avoidance. Additionally, bradycardia during the freezing state, indicated by a slowed heart rate, was associated with increased threat-related avoidance. This suggests that freezing under threat enhances sensitivity to threats, leading to more avoidance behavior.

Neural Networks in Task Outcomes

Task outcomes revealed that different neural networks are involved in the predictive processing of rewards and threats, as well as approach-avoidance decisions. Specifically, higher levels of money were positively correlated with increased BOLD activity in the ventral striatum (VS), whereas shock levels were positively correlated with BOLD activity in regions such as the supplementary motor area (SMA/DCACC) and anterior insula (AI). Approach and avoidance choices activated brain regions associated with reward and threat, respectively, such as the ventral striatum, amygdala, and ventromedial prefrontal cortex (VMPFC).

Bradycardia State and Neural Computational Mechanisms

fMRI-based analysis of the model showed that the relationship between bradycardia and aversive values mainly involved the amygdala, whereas the relationship with value comparison involved the dorsal anterior cingulate cortex (DACC) and supplementary motor area (SMA). Specifically, in trials with stronger bradycardia, higher shock levels led to more avoidance behavior, which was negatively correlated with amygdala activity. This might indicate that under bradycardia, amygdala deactivation could be related to enhanced attention processing under threat.

Meanwhile, when the anticipated reward was greater than the threat, bradycardia was associated with more approach behavior, regulated by the activity of the DACC and SMA. This suggests that the participants’ conflict processing might be reduced when earning rewards, leading to a higher probability of approach behavior.

Summary

This study reveals the role of the freezing state in approach-avoidance mediation under threat, establishing a neural computational link between bradycardia and approach-avoidance decisions. These findings are significant for understanding optimal coping strategies under threat and offer new perspectives for optimizing decision-making interventions. Future research should explore the clinical application value of these findings in individuals with anxiety and depression disorders.