Spine-brain dynamics during human defensive threat-reactions

Synchrony between central and autonomic nervous system responses during threat rely on spine-brain interactions. Activation of the parasympathetic autonomic nervous system during acute threat has been linked to optimized action preparation and longer-term stress-resilience. However, it is unclear how this is orchestrated by spine-brain interactions during our widely used models of threat conditioning. Here we used a well-established threat conditioning procedure to test whether freezing-related bradycardia modulates the strength of motor- and sensory-relevant spinal-brain connectivity patterns. Conditioning elicited the expected autonomic and psychophysiological responses, with significant bradycardia and heightened differentiation between conditioned stimuli. Heart rate bradycardia modulated activity in the cingulate cortex and spinal cord, emphasizing their role in freezing. Notably, bradycardia-modulated spinal cord activity during threat was functionally coupled with motor cortex activity, suggesting a preparatory response for defensive actions. Establishing these effects for the first time in humans helps discovery of biomarkers for threat coping-relevant body-brain interactions, essential for clinical evaluations.