P161. Manipulating motor performance in simple motor tasks by online-TMS: The role of ipsilateral M1

Abstract

Introduction Coordinated hand movements derive from fine-tuned interactions of various motor regions. Transcranial magnetic stimulation (TMS) allows to test the role of cortical motor areas. Disturbing the activity of the primary motor cortex (M1) ipsilateral to the moving hand via ‘online’ TMS, i.e., applied during task execution, has been shown to alter the recruitment of hand muscles in grip-lift-tasks ( Davare et al., 2007 ). Then again, similar stimulation had no effect on the performance of simple reaction-time tasks ( Nardone et al., 2013 ). Conflicting data might result from differences in stimulation parameters (e.g., stimulation intensity) or from motor task specific effect of online-TMS interference. We, here, applied online TMS to M1 while subjects performed motor-tasks of different complexities with the ipsilateral hand to further our insights into the exact role of the ipsilateral M1 in hand movement. Material and methods 16 healthy, right-handed subjects performed three different motor tasks with the right index finger (simple reaction-time and maximum finger-tapping task) or the right hand (maximum grip strength over one second). TMS Pulses were applied as 10 Hz-trains time-locked to motor task execution. Performance was measured for four different conditions. Real-stimulation was applied at three different intensities: (i) 70%, (ii) 80%, or (iii) 90% of the resting motor threshold (RMT) to the right M1. Sham-stimulation was applied at 90% RMT over parieto-occipital vertex. The order of stimulation blocks was pseudo-randomized across subjects. Results Online TMS applied to the right M1 differentially affected motor task performance with the right (ipsilateral) hand. Maximum finger-tapping frequency and the integrated grip strength time course were significantly reduced by real compared to sham stimulation. Of note, we found a stimulation intensity dependent effect with higher stimulation intensities leading to stronger reduction in motor performance. In contrast, performance in the simple reaction-time task was not affected by online TMS. Discussion We found online TMS applied to M1 to impact on the motor function of the ipsilateral hand. Importantly, the ‘virtual lesion’ effect induced by online TMS strongly depended on the intensity at which pulses were applied and the given motor task. Our results suggest M1 to functionally contribute to the repetitive and timely precise recruitment of ipsilateral hand muscles. Finally, our experimental approach also offers the opportunity to study the altered role of the ipsilateral M1 in disease, e.g., during motor network reorganization following stroke.