The assessment of corticospinal excitability by means of transcranial magnetic stimulation-induced motor evoked potentials is an established diagnostic tool in neurophysiology and a widely used procedure in fundamental brain research. However, concern about low reliability of these measures has grown recently. One possible cause of high variability of MEPs under identical acquisition conditions could be the influence of oscillatory neuronal activity on corticospinal excitability. Based on research showing that transcranial alternating current stimulation can entrain neuronal oscillations we here test whether alpha or beta frequency tACS can influence corticospinal excitability in a phase-dependent manner. We applied tACS at individually calibrated alpha- and beta-band oscillation frequencies, or we applied sham tACS. Simultaneous single TMS pulses time locked to eight equidistant phases of the ongoing tACS signal evoked MEPs. To evaluate offline effects of stimulation frequency, MEP amplitudes were measured before and after tACS. To evaluate whether tACS influences MEP amplitude, we fitted one-cycle sinusoids to the average MEPs elicited at the different phase conditions of each tACS frequency. We found no frequency-specific offline effects of tACS. However, beta-frequency tACS modulation of MEPs was phase-dependent. Post hoc analyses suggested that this effect was specific to participants with low (<19 Hz) intrinsic beta frequency. In conclusion, by showing that beta tACS influences MEP amplitude in a phase-dependent manner, our results support a potential role attributed to neuronal oscillations in regulating corticospinal excitability. Moreover, our findings may be useful for the development of TMS protocols that improve the reliability of MEPs as a meaningful tool for research applications or for clinical monitoring and diagnosis.

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In the natural world, faces are not isolated objects but are rather encountered in the context of the whole body. Previous work has studied the perception of combined faces and bodies using behavioural and electrophysiological measurements, but the neural correlates of emotional face–body perception still remain unexplored. Here, we combined happy and fearful faces and bodies to investigate the influence of body expressions on the neural processing of the face, the effect of emotional ambiguity between the two and the role of the amygdala in this process. Our functional magnetic resonance imaging analyses showed that the activity in motor, prefrontal and visual areas increases when facial expressions are presented together with bodies rather than in isolation, consistent with the notion that seeing body expressions triggers both emotional and action-related processes. In contrast, psychophysiological interaction analyses revealed that amygdala modulatory activity increases after the presentation of isolated faces when compared to combined faces and bodies. Furthermore, a facial expression combined with a congruent body enhanced both cortical activity and amygdala functional connectivity when compared to an incongruent face–body compound. Finally, the results showed that emotional body postures influence the processing of facial expressions, especially when the emotion conveyed by the body implies danger.

Emotional signals, like threatening sounds, automatically ready the perceiver to prepare an appropriate defense behavior. Conjecturing that this would manifest itself in extending the safety zone around the body we used the rubber hand illusion (RHI) to test this prediction. The RHI is a perceptual illusion in which body ownership is manipulated by synchronously stroking a rubber hand and real hand occluded from view. Many factors, both internal and external, have been shown to influence the strength of the illusion, yet the effect of emotion perception on body ownership remains unexplored. We predicted that listening to affective vocalizations would influence how strongly participants experience the RHI. In the first experiment four groups were tested that listened either to affective sounds (angry or happy vocalizations), non-vocal sounds or no sound while undergoing synchronous or asynchronous stroking of the real and rubber hand. In a second experiment three groups were tested comparing angry or neutral vocalizations and no sound condition. There was a significantly larger drift towards the rubber hand in the emotion versus the no emotion conditions. We interpret these results in the framework that the spatial increase in the RHI indicates that under threat the body has the capacity to extend its safety zone.

Expressions of emotion are powerful triggers for situation-appropriate responses by the observer. Of particular interest regarding the preparation of such adaptive actions are parietal and premotor cortices, given their potential for interaction with the amygdala (AMG), which is known to play a crucial role in the processing of affective information and in motor response. We set out to disentangle the respective roles of the inferior parietal lobule (IPL) and ventral premotor cortex (PMv) in humans in the processing of emotional body expressions by assessing remote effects of continuous theta burst stimulation (cTBS) in the action network and in AMG. Participants were presented with blocks of short videos showing either angry or neutral whole-body actions. The experiment consisted of three fMRI sessions: two sessions were preceded by stimulation of either right IPL (rIPL) or right PMv (rPMv); and a third session assessed baseline activity. Interestingly, whereas at baseline the left AMG did not differentiate between neutral and angry body postures, a significant difference between these conditions emerged after stimulation of either rIPL or rPMv, with much larger responses to angry than to neutral stimuli. In addition, the effects of cTBS stimulation and emotion were also observed in two other action-relevant areas, the supplementary motor area and the superior parietal cortex. Together, these results show how areas involved in action and emotion perception and in action preparation interact dynamically.