Detection of movement related cortical potentials in freehand drawing on digital tablet*

Background: Cortical activity connected to movements has been investigated long since, and is related, among other factors, to saliency of the gesture. However, experiments performed on movements in actual situations are rare, as most of them have been performed in laboratory simulations. Besides, no research seems to have been carried out on subjects during freehand drawing. New method: We propose a method based upon a commercial drawing tablet and wireless pen, that has been synchronized with EEG recording by means of a piezoelectric sensor attached to the pen tip. Complete freedom of movement is allowed, and any kind of drawing style can be performed using currently available graphics software. Results: EEG recordings during meaningful drawing were compared with recordings where the pen was tapped and shifted on tablet without specific purpose. With reference to T0 event (pen touching tablet), several components could be observed in pre- and post-T0 epochs. The most important appeared to be a triphasic wave (N150, P-40 and N + 30), where P-40 showed a striking difference between drawing and tap session, being much larger in the former. Comparison with existing methods: Onset of muscle EMG is usually employed for synchronization. In complex and free gestures too many muscles are active to allow reliable identification of such reference. Our method provides a precise trigger event easily detected without movement constraints. Conclusions: With this method it will be possible to record EEG activity related to creative aspects of drawing and explore other skilled movements.