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Abstract

Several studies have shown that a brain-computer interface (Thought Translation Device, TTD), controlled by self-regulation of slow cortical potentials (SCP), can contribute to communication of completely paralysed patients (Birbaumer et al., 1999; Kübler et al., 2001). However, some patients as well as healthy subjects have not been able to control their SCP even after extended neurofeedback training. Is there a possibility to support those non-learners in learning to control their SCP?
The main goal of our study is to explore whether it is possible to shift the SCP by means of transcranial magnetic stimulation (TMS) and hence to develop further methods in order to support the learning process.
Since our fMRI data show that negative SCP are accompanied by a significant activation
of the supplementary motor area (SMA) and positive SCP by a significant deactivation
of the SMA, we study the changes in SCP after low- and high-frequency repetitive
transcranial magnetic stimulation (rTMS) over the SMA, known respectively for their
inhibitory and excitatory effect on the cortex (Boroojerdi et al. 2000; Mottaghy et al.
1999). Ten healthy volunteers were trained for four days with the TTD to self regulate their SCP.
The electroencephalogram (EEG) was recorded from the following positions against
both mastoids: Cz, FC3, CP3, FC4, CP4. Training included 11 blocks on each of the
four sessions, each block comprised 34 feedback trials. A trial consisted of a 2 seconds passive phase, in which no feedback was provided, and a baseline was recorded. An active phase followed lasting 3.5 s, in which visual feedback of SCP was provided as a cursor movement on a feedback screen. The cursor moved up and down proportionally to the current SCP amplitude compared to the previously recorded baseline (the algorithm is described in Kübler et al. 2001). In each trial participants had to move the cursor towards the top (by producing a negative shift of their SCP) or towards the bottom of the feedback screen (by producing a positive SCP shift). The experimental design contained the following conditions: 1) feedback without rTMS, 2) feedback after highfrequency rTMS( 15 Hz, 2 s.), 3) feedback after low-frequency rTMS (1 Hz, 30 s.), 4-5) feedback after high- and low-frequency sham (= placebo) stimulation. TMSw as delivered over the SMA with a focal figure-of-eight magnetic coil (DANTEC MagPro). During sham stimulation the coil was placed at a 90° angle to the SMA.
RTMSh ad a differential effect on self-regulation of SCP: 15 Hz rTMS enhanced negative SCP and reduced positive SCP, whereas 1 HZ rTMS enhanced positive SCP but reduced negative SCP. These findings are in line with the notion that rTMS can be used to support locked-in patients in self-regulating their SCP.