Analysis of Key Factors on ERD production for BCI Neuro-robotic rehabilitation Yohei Takata, Midori Saeki, Jun Izawa, Kotaro Takeda, Yohei Otaka, Koji Ito and Toshiyuki Kondo Abstract— According to recent neuro-rehabilitation research, an appropriate reafferent sensory feedback synchronized with a voluntary motor intention would be effective for promoting neural plasticity during stroke rehabilitation. Therefore, a BCI- based neuro-rehabilitation is considered to be a promising approach. To detect the motor intention, an event-related desynchronization (ERD), which can be evoked by intrinsic motor imagery, is usually used. However there exists various factors that affect ERD production, and its neural mechanism is still an open question. As a preliminary stage for developing an effective neuro-rehabilitation system, in this study, we evaluate the mutual effects of extrinsic (visual and somatosensory stimuli) and intrinsic (spontaneous motor imagery) factors on ERD production. Experimental results indicate that these three factors interact with each other in a complex relationship and probably affect a person’s sense of agency. I. I NTRODUCTION Because of the rapid aging of the society or a dietary change, there has been an increase in the number of stroke patients. To help them recover from paralysis, it is important for them to receive motor rehabilitation therapy with appro- priate assessments from medical doctors and/or therapists. According to these professionals, to promote neural plasticity during the neuro-rehabilitation, these patients should not only perform a passive range of motion exercises, but also should experience reafferent sensory feedback synchronized with a voluntary motor intention. Although severely impaired stroke patients cannot express their voluntary motor intention, recently, brain–computer interface (BCI) technology has enabled the interpretation of motor intention directly from their brain activities (e.g., an electroencephalogram (EEG)). Especially in BCI neuro- rehabilitation research, degradation of specific sensorimotor rhythms, i.e., event-related desynchronization (ERD), had been widely used for decoding a patient’s motor intention[1], [2], [3], [4], [5], [6], [7], [10], [11], [12]. ERD is known as an EEG feature observed in the human sensorimotor cortex area when actual movement or motor imagery has occurred. Therefore, it can be used as an asynchronous BCI without any external stimuli, unlike a cue-based BCI (SSVEP or P300) [5], [6]. In addition, it is known that the topographical Y.Takata, M.Saeki and T.Kondo are with Computer and Informa- tion Sciences, Tokyo University of Agriculture and Technology, 2- 24-16 Naka-cho, Koganei, Tokyo, Japan. t kondo@cc.tuat.ac.jp, http://www.livingsys.lab.tuat.ac.jp J.Izawa is with ATR Computational Neuroscience Laboratories. K.Takeda is with National Hospital Organization Murayama Medical Center. Y.Otaka is with Tokyo Bay Rehabilitation Hospital, and Department of Rehabilitation Medicine, Keio University. K.Ito is with Ritsumeikan University. region of ERD production corresponds to a homuncular organization in the human primary motor area. For example, motor imagery for the foot can cause ERD around the center of the motor area (i.e., Cz in the international 10-20 system). Furthermore, ERD can be observed in a narrow frequency band that is specific to each body part, e.g., 9-13 Hz for the hand and 18-23 Hz for the foot. It is also known that spontaneous ERD production is innately difficult and this ability can be improved with neuro-feedback training. Also, some research reported that observing a video that includes human movement (e.g., a moving hand) induces ERD in healthy subjects without any training[8], [9]. Moreover, other research has found that somatosensory stimulus by a functional electric stim- ulation (FES) can modulate the motor imagery-based ERD production[1], [3], [7], [10], [11]. Consequently, various factors affect ERD production; however, its neural mechanism is still an open question. As a preliminary stage for developing an effective neuro- rehabilitation system, in this study, we would systemati- cally investigate the mutual effects of extrinsic (visual and somatosensory stimuli) and intrinsic (spontaneous motor imagery) factors on ERD production. II. METHODS A. Subjects Six healthy young volunteers (five males and one female with a mean age of 22.0±1.0 years) participated in the following experiments with written informed consent. All were right-handed and had no neurological disorders. The protocols of the study were approved by the ethical commit- tee at the Tokyo University of Agriculture and Technology. B. Experimental system All subjects were seated in a comfortable high-back chair with a foot rest (Fig.1). As shown in the figure, a 23-inch LCD monitor was placed on an angled table located over their thighs, and they were asked to adjust the tilt angle to be able to see the video on the monitor (Fig.2). We used five Ag/AgCl electrodes to take electroencephalogram measure- ments (g.ACTIVEelectrode, g.tec medical engineering, Aus- tria), and these were placed in the Laplacian derivation layout pattern to cover the sensorimotor area that is considered to be involved in foot motor control, which correspond to Cz in the international 10-20 system. Reference and ground electrodes were located at the left ear lobule and Fz, respectively. The EEG signals were amplified using a multi-telemeter system (WEB5500, NIHON KOHDEN Co., Japan) and recorded The Fourth IEEE RAS/EMBS International Conference on Biomedical Robotics and Biomechatronics Roma, Italy. June 24-27, 2012 978-1-4577-1198-5/12/$26.00 ©2012 IEEE 240