Neural Mechanisms underlying the Switch from Freeze to Action

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Defensive freezing is characterized by postural immobility and heart rate deceleration (bradycardia), and has been linked to action preparation. Although subregions of the medial cingulate cortex (MCC) and anterior cingulate cortex (ACC) are activated during freeze and the switch to action, respectively, it remains unclear whether and how they communicate with the sensorimotor cortex (SMC). To examine the neural mechanisms underlying freeze and the subsequent switch to action, we applied magnetoencephalography (MEG) during an active shooting task, in which participants prepared and performed actions under the threat of shock. Threat anticipatory freezing was indicated by more severe heart rate deceleration under the threat of shock versus safety. Importantly, decreased alpha- and beta-band rhythmic activity was shown during action preparation under threat of shock. Finally, the ACC is suggested to be related to the switch from freeze to action, which is associated with a release from MCC to SMC inhibition. Taken together, the results confirm that freezing can be seen as an active state that relates to action preparation. However, we could only include the first half (N = 24) of the target number of participants in the analysis. Therefore, future investigations including a powerful sample size are needed to obtain a more reliable overview of the electrophysiological mechanisms underlying the switch from freeze to action. Keywords: Freezing, Action Preparation, Switch to Action, MEG, Anterior/Medial Cingulate Cortex, Sensorimotor Cortex
Faculteit der Sociale Wetenschappen