title: Early changes in corticospinal excitability when seeing fearful body expressions.
abstract: Quick inhibition of approach tendencies in response to signals of potential threats is thought to promote survival. However, little is known about the effect of viewing fearful expressions on the early dynamics of the human motor system. We used the high temporal resolution of single-pulse and paired-pulse transcranial magnetic stimulation (TMS) over the motor cortex to assess corticospinal excitability (CSE) and intracortical facilitation (ICF) during observation of happy, fearful and neutral body postures. To test motor circuits involved in approach tendencies, CSE and ICF were recorded from the first dorsal interosseous (FDI), a muscle involved in grasping, and the abductor pollicis brevis (APB), which served as a control. To test early motor dynamics, CSE and ICF were measured 70-90 ms after stimulus onset. We found a selective reduction in CSE in the FDI when participants observed fearful body expressions. No changes in ICF or in the excitability of APB were detected. Our study establishes an extremely rapid motor system reaction to observed fearful body expressions. This motor modulation involves corticospinal downstream projections but not cortical excitatory mechanisms, and appears to reflect an inhibition of hand grasping. Our results suggest a fast visuo-motor route that may rapidly inhibit inappropriate approaching actions.
authors.affiliation: Dipartimento di Psicologia, Università di Bologna and Centro studi e ricerche in Neuroscienze Cognitive, Campus di Cesena, Università di Bologna; 47521 Cesena, Italy.|IRCCS Fondazione Santa Lucia, 00179 Rome, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Borgomaneri
authors.affiliation: Dipartimento di Psicologia, Università di Bologna and Centro studi e ricerche in Neuroscienze Cognitive, Campus di Cesena, Università di Bologna; 47521 Cesena, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Vitale
authors.affiliation: Dipartimento di Psicologia, Università di Bologna and Centro studi e ricerche in Neuroscienze Cognitive, Campus di Cesena, Università di Bologna; 47521 Cesena, Italy.|IRCCS Fondazione Santa Lucia, 00179 Rome, Italy.
authors.forename: Alessio
authors.initials: A
authors.lastname: Avenanti
mesh_terms: D000328:Adult; D058256:Brain Waves / Q000502:physiology; D003463:Cues; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005239:Fear / Q000523:psychology*; D006240:Happiness; D006801:Humans; D007697:Kinesics; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D019370:Observation; D011712:Pyramidal Tracts / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult