Stretch-induced muscle responses under threat vs safety

In a demanding circumstance, the ability to make swift and precise choices is paramount. Prior research has indicated that sensorimotor decisions can enhance under stress. Nonetheless, it remains uncertain whether these enhancements stem from improved perceptual or motor abilities. This study explores two hypotheses regarding how threat might impact motor preparation, employing muscular stretch reflexes to examine both.

The task-unspecific hypothesis posits that threat facilitates motor preparation, regardless of the target, via tonic upregulation of the short latency stretch reflex. Conversely, the task-specific hypothesis suggests that threat augments sensory processing for a specific target, resulting in direction-selective up- and down-regulation of the long latency stretch reflex.

Participants were required to reach towards one of two targets that emerged shortly before a perturbation triggering a stretch reflex, with the task executed under either threat of an electric shock or in safe conditions. The findings from skin conductance and heart rate indicate that the threat manipulation significantly heightened sympathetic activation, without affecting parasympathetic activation.

The electromyography (EMG) results corroborate the task-specific hypothesis, revealing a direction-selective modulation of the long-latency response of stretch reflexes, commencing approximately 100 milliseconds post perturbation onset. Taken together, these results imply that stress influences action preparation through the upregulation of cortical visuomotor circuits.