An implantable selective nerve stimulator

An implantable stimulator system, suitable for selective stimulation of nerves, has being developed at University College London. This device should be capable of selectively stimulating nerve either by fibre position, fibre size or to send action potentials in one direction only, using implanted nerve cuff electrodes. The stimulator produces either quasi-trapezoidal current pulses, to allow anodal blocking, or conventional rectangular-shaped current pulses, of amplitude 20mA to 5mA (in 20mA steps) with duration of 16ms to 1ms (in 8ms steps). For safety, both active and passive charge balancing is used. The amplitude of the active charge-balancing phase can be varied between 1/7 and 1/47 of the pulse amplitude. During manufacture, each implant is customised so as to drive either 4 tripolar or 2 pentapolar electrode cuffs. The implant comprises two custom-integrated circuits, a stimulator circuit and a digital control circuit, and other components. At present, stimulator-command signals are generated by a microprocessor, with a PC interface. The system is currently being evaluated in acute animal experiments and the implant should be ready for chronic experiments later this year.