title: Seeing fearful body language rapidly freezes the observer's motor cortex.
abstract: Fearful body language is a salient signal alerting the observer to the presence of a potential threat in the surrounding environment. Although detecting potential threats may trigger an immediate reduction of motor output in animals (i.e., freezing behavior), it is unclear at what point in time similar reductions occur in the human motor cortex and whether they originate from excitatory or inhibitory processes. Using single-pulse and paired-pulse transcranial magnetic stimulation (TMS), here we tested the hypothesis that the observer's motor cortex implements extremely fast suppression of motor readiness when seeing emotional bodies - and fearful body expressions in particular. Participants observed pictures of body postures and categorized them as happy, fearful or neutral while receiving TMS over the right or left motor cortex at 100-125 msec after picture onset. In three different sessions, we assessed corticospinal excitability, short intracortical inhibition (SICI) and intracortical facilitation (ICF). Independently of the stimulated hemisphere and the time of the stimulation, watching fearful bodies suppressed ICF relative to happy and neutral body expressions. Moreover, happy expressions reduced ICF relative to neutral actions. No changes in corticospinal excitability or SICI were found during the task. These findings show extremely rapid bilateral modulation of the motor cortices when seeing emotional bodies, with stronger suppression of motor readiness when seeing fearful bodies. Our results provide neurophysiological support for the evolutionary notions that emotion perception is inherently linked to action systems and that fear-related cues induce an urgent mobilization of motor reactions.
authors.affiliation: Dipartimento di Psicologia and Centro studi e ricerche in Neuroscienze Cognitive, Università di Bologna, Campus di Cesena, Cesena, Italy; IRCCS Fondazione Santa Lucia, Rome, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Borgomaneri
authors.affiliation: Dipartimento di Psicologia and Centro studi e ricerche in Neuroscienze Cognitive, Università di Bologna, Campus di Cesena, Cesena, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Vitale
authors.affiliation: The Netherlands Institute for Neuroscience, Institute of the Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, The Netherlands.
authors.forename: Valeria
authors.initials: V
authors.lastname: Gazzola
authors.affiliation: Dipartimento di Psicologia and Centro studi e ricerche in Neuroscienze Cognitive, Università di Bologna, Campus di Cesena, Cesena, Italy; IRCCS Fondazione Santa Lucia, Rome, Italy. Electronic address: alessio.avenanti@unibo.it.
authors.forename: Alessio
authors.initials: A
authors.lastname: Avenanti
mesh_terms: D000293:Adolescent; D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology; D005239:Fear / Q000523:psychology*; D005260:Female; D006801:Humans; D007697:Kinesics; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult
keywords: Emotional body; Fear processing; Freezing; Intracortical facilitation; Motor cortex; Transcranial magnetic stimulation