ReGrasp, a Robotic Tool to Investigate Fine Motor Control and Track Therapy-Induced Neuroplasticity Julio Duenas, Student Member, IEEE, Olivier Lambercy, Member, IEEE, Dominique Chapuis, Member, IEEE, and Roger Gassert, Member, IEEE Abstract— The neural mechanisms of fine motor control and recovery, e.g. after a stroke, are not fully understood, nor how these are influenced by different types of motor therapies, leaving potential for optimization of current rehabilitation strategies. This paper presents the development and evaluation of a novel robotic tool for fMRI-based neuroscience studies allowing to investigate the neural mechanisms of dynamic precision grip and track therapy-induced neuroplasticity. In this proof of principle study we investigate the feasibility of high-fidelity haptic interaction with human motion using remote sensing and actuation. A cable-spring mechanism transmits force to the thumb and index finger in an unconstrained man- ner, actuated over a stiff cable transmission. Characterization of the prototype with a transmission length of two meters revealed good dynamic performance including a 16 Hz open loop force bandwidth and a maximal output force of 28 N. Combined with a remote and shielded conventional electromagnetic actuator, this device could be used to investigate the neural correlates of precision grasping as well as the effect of different hand function therapies on the neural correlates of motor recovery after stroke. I. I NTRODUCTION Stroke is one of the leading causes of disability, affecting more than 15 million people every year worldwide. About 60 to 70% of stroke survivors suffer from upper limb paresis, severely limiting their independence and ability to perform activities of daily living (ADL), such as grasping and manipulating objects. Stroke patients can expect sponta- neous recovery during the first few months following stroke as a result of increased neuroplasticity, i.e. structural and functional reorganization to compensate for the neuronal networks damaged by the stroke. Nudo et al. demonstrated cortical reorganization in monkeys while they retrained hand function after a focal infarct in the motor cortex. Rehabili- tation prevented the reduction of the hand area adjacent to the infarct, a phenomenon that normally occurs following the injury. Furthermore, an expansion of the hand area into the area generally occupied by the shoulder and elbow was observed in some cases [1]. Structural neuroplasticity has also been observed in humans. Studies using transcranial magnetic stimulation (TMS) demonstrated an increased ex- citability of the hand area in the motor cortex after intensive Manuscript received September 15 , 2009. This work is supported by the NCCR Neural Plasticity and Repair, Swiss National Science Foundation. J. Duenas, O. Lambercy, D. Chapuis and R. Gassert are with the Rehabilitation Engineering Lab, ETH Zurich, Switzerland. J. Duenas is with the Universidad Iberoamericana, Mexico City, Mexico. This work was performed at ETH Zurich. {juliod, olambercy, dchapuis, gassertr}@ethz.ch Fig. 1. ReGrasp, a robotic tool for precision grasp studies involving opposition of the index finger against the thumb in conjunction with functional brain imaging. rehabilitation, e.g. Constraint-Induced Movement Therapy (CIMT) [2], [3]. Nevertheless, the neural mechanisms underlying fine mo- tor control and cortical reorganization, e.g. after stroke, are not yet fully understood, nor how these are influenced by different types of motor therapies, leaving potential for optimization of current rehabilitation strategies. By providing high spatial resolution and whole-brain coverage, functional Magnetic Resonance Imaging (fMRI) can provide insights into the neural underpinnings of the functionally highly rel- evant precision grip and the effect of different rehabilitation therapies on cortical reorganization. By combining fMRI with robotics, it becomes possible to render repeatable and well-controlled sensorimotor tasks, and to make a direct comparison with the evolution in behavioral parameters that can be objectively recorded by the robot [4]. Tracking cortical reorganization after brain injury and potentially influencing it through customized training with a robotic device could redefine current neurorehabilitation strategies by reshaping the brain to maximize recovery after injury, or even enhancing sensorimotor skills in healthy subjects [5]. This paper presents a proof of principle study that inves- tigates the feasibility of highly dynamic haptic interaction over a cable transmission with remote sensing and actuation, adapted to future use in an MR environment. A cable-spring mechanism located at the output allows unconstrained move- ment during precision grip, i.e. opposition between thumb and index finger, a basic function required in most prehensile tasks in ADL, and among those stroke survivors desire to 2010 IEEE International Conference on Robotics and Automation Anchorage Convention District May 3-8, 2010, Anchorage, Alaska, USA 978-1-4244-5040-4/10/$26.00 ©2010 IEEE 5084