Journal of Neuroscience Methods 134 (2004) 81–90 High frequency block of selected axons using an implantable microstimulator Chih-Wei Peng a , Jia-Jin Jason Chen a,∗ , Chou-Ching K. Lin b , Paul Wai-Fung Poon c , Chih-Kuo Liang d , Kang-Ping Lin e a Institute of Biomedical Engineering, National Cheng Kung University, 1 University Road, Tainan 701, Taiwan b Department of Neurology, National Cheng Kung University Hospital, Tainan 701, Taiwan c Institute of Physiology, National Cheng Kung University, Tainan, Taiwan d Department of Electrical Engineering, Southern Taiwan University of Technology, Tainan, Taiwan e Department of Electrical Engineering, Chung Yuan Christine University, Chung-Li, and Biomedical Engineering Center, ITRI, Hsinchu, Taiwan Received 28 May 2003; received in revised form 13 November 2003; accepted 18 November 2003 Abstract Currently, the majority of neural stimulation studies are limited to acute animal experiments due to lack of suitable implantable microstim- ulation devices. As an initial step to observe the long-term effects of neural stimulation, a system consisting of an external wireless controller and an implantable dual-channel microcontroller-based microstimulator for tripolar high frequency blocking was developed. The system is not only small in size, and thus suitable for short-term implantation, but also has sufficient current output parameter ranges to meet the demand for high frequency blocking experiments. Using this implantable microstimulator, a series of experiments were conducted on New Zealand rabbit’s tibial nerve, including frequency and amplitude selection in driving stimulus and blocking effect tests, which were designed to assess the feasibility and efficiency of the device via torque measurements. Our results showed that the implantable microstimulator system gave a satisfactory performance and could be utilized to achieve selective stimulation and blocking on various sizes of nerve fibers. Our implantable microstimulation system is not only a novel tool for neuromuscular control studies but could also provide a basis for developing various types of sophisticated neural prostheses. © 2003 Elsevier B.V. All rights reserved. Keywords: Implantable microstimulator; High frequency blocking; Tibial nerve 1. Introduction Both the sensory and motor nerves in the peripheral ner- vous system (PNS) are controlled by the central nervous system (CNS). Injuries to the CNS, e.g., spinal cord lesion or stroke, can cause permanent loss of voluntary motor and sensation functions. Electrical activation can restore the de- prived motor/sensory functions as long as the peripheral mo- tor and/sensory nerves and muscle below the level of CNS lesion remain intact (Stein et al., 1992). Various types of electrical stimulation techniques have made it possible to re- store some motor and sensory functions (Bhadra et al., 2001; Clements et al., 1999; Davis et al., 2001; Loeb et al., 2001). The development of electrical stimulation systems has moved from surface stimulation (Kralj et al., 1983) and ∗ Corresponding author. Tel.: +886-6-2757575/63423; fax: +886-6-2343270. E-mail address: pcw@jason.bme.ncku.edu.tw (J.-J.J. Chen). percutaneous stimulation (Scheiner et al., 1994) to a totally implanted stimulation (Bourret et al., 1997). Surface elec- trical stimulation is used to stimulate the peripheral nerve or muscle by using larger size electrodes attached to the skin surface at some distance from the nerve innervation zone. Generally, surface stimulation is only useful for mus- cle strengthening but provides less significant functional benefit and lacks selectivity for small muscle groups. In order to obtain a more sophisticated movement or organ function, selective electrical stimulation is applied closely to or directly to the nerve (Fang and Mortimer, 1991; Grill and Mortimer, 1996). Selective stimulation on peripheral nerves is essential for achieving bladder control (Shanker et al., 1998), natural recruitment order for neuroprosthesis control (Solomonow, 1984) and even spasticity suppression (Stefanovska et al., 1988). In addition to spatial selectiv- ity, another important aspect of the electrical stimulation is the fiber diameter selectivity, which refers to the ability to stimulate nerve fibers within a given range of diameters 0165-0270/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jneumeth.2003.11.005