Abstract
Observing others’ actions enhances muscle-specific cortico-spinal excitability, reflecting putative mirror neurons activity. The exposure to emotional stimuli also modulates cortico-spinal excitability. We investigated how those two phenomena might interact when they are combined, i.e., while observing a gesture performed with an emotion, and whether they change during the transition between adolescence and adulthood, a period of social and brain maturation. We delivered single-pulse transcranial magnetic stimulation (TMS) over the hand area of the left primary motor cortex of 27 healthy adults and adolescents and recorded their right first dorsal interossus (FDI) muscle activity (i.e., motor evoked potential – MEP), while they viewed either videos of neutral or angry hand actions and facial expressions, or neutral objects as a control condition. We reproduced the motor resonance and the emotion effects – hand-actions and emotional stimuli induced greater cortico-spinal excitability than the faces/control condition and neutral videos, respectively. Moreover, the influence of emotion was present for faces but not for hand actions, indicating that the motor resonance and the emotion effects might be non-additive. While motor resonance was observed in both groups, the emotion effect was present only in adults and not in adolescents. We discuss the possible neural bases of these findings.
Highlights
Previous studies have shown that visual information received during actions’ observation is processed as motor information, i.e., in terms of a motor resonance
We observed that angry face stimuli (FA) were rated as showing significantly greater anger intensity than angry hand stimuli [FA/HA: t(31) = 6.58, p < 0.0001]
The ANOVA of the normalized motor evoked potentials (MEPs) amplitudes revealed a main effect of video type [F(4,3211) = 8.86, p = 4. 10−7], a main effect of group [F(1,3211) = 7.79, p = 0.0053] and an interaction between group and video condition [F(4,3211) = 2.743, FIGURE 2 | Motor evoked potential (MEP) amplitudes for each kind of videos (i.e., Hand Anger, Hand Neutral, Face Anger, Face Neutral, Control) for adults and adolescents
Summary
Previous studies have shown that visual information received during actions’ observation is processed as motor information, i.e., in terms of a motor resonance. At the neural level this is implemented by the engagement of mirror neurons, mainly found in the premotor and parietal cortices, which are active both during action observation and during action execution. This mirror neurons system (MNS) might provide the foundation for social understanding. Mirroring external events would allow us to “resonate” with others while viewing them acting and might be crucial for understanding their intentions, beliefs and goals (Rizzolatti et al, 2001; Rizzolatti and Craighero, 2004; Fadiga et al, 2005; Agnew et al, 2007; Catmur et al, 2007). Understanding others’ intentions requires emotional and empathic processing (Agnew et al, 2007). MNS activity has been shown to be higher in individuals showing higher accuracy in emotion discrimination
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