Resumo

Introduction: Daily in life we grasp emotional-laden objects. Is the object valence incorporated into the motor planning? Aim: The aim of this study was to investigate the corticospinal excitability during the motor preparation enrolled in grasping emotional-laden objects. Methods: Nine volunteers (males; 18-35 years old) were instructed either to reach and grasp real emotional-laden objects (pleasant, unpleasant and neutral) or simply to watch those same objects while transcranial magnetic stimulation (TMS) was applied into the primary motor cortex. Four blocks (2 grasp and 2 watch) containing 14 stimuli of each valence were randomly presented. Trials began with a 3 seconds stimulus presentation, followed by a go signal indicating that the subject should start to move. TMS single pulses were randomly delivered at 500 or 250 ms before the go signal. Motor evoked potentials (MEP) were measured by recording the EMG signal from the first dorsalis interosseous (FDI) and the abductor digiti minimi (ADM). Results A main effect of valence (F(2,16)=7,88, p<0.01) was found for the FDI, involved in the grasping movement. Post hoc analysis showed that MEP amplitudes in the grasping blocks were smaller for pleasant compared to unpleasant and neutral conditions (p<0.01). No valence effect was found in the watch block. Likewise, no MEP difference across conditions and blocks was verified for the control muscle ADM. Conclusion: In conclusion, preparing to grasp pleasant stimuli associates to lower corticospinal excitability in a muscle directly enrolled in the required action. Taken together these results suggest that positive stimuli lead to action preparation facilitation. Key-words:corticospinal excitability, emotion, grasping