Our current neurophysiological experiments in behaving monkeys implant electrodes to record electromyogram (EMG) from the arm and hand. Wires from these electrodes pass sub-cutaneously to a connector on the head. The electrodes yield stable, high quality recordings. However, the permanently open wound around the connector often becomes infected, impairing the welfare of the animal and reducing data quality. In work carried out under a previous award from NC3Rs, we developed a novel implantable electronic device. This amplifies and digitises 16 channels of EMG recording (5 kSamples/s/channel), and transmits the data through the skin by radio. Power is supplied by inductive coupling to an implanted coil antenna, obviating the need for an implanted battery. The system is wholly internal - the skin is closed over the device after implant, which avoids breaching the skin's natural barrier to infection. We tested this system in a macaque monkey. The device integrated well with the tissue, and after 3 months there was no sign of infection or tissue rejection. It powered up, and successfully transmitted data. However, a problem with the function of the front-end amplifier prevented the signals from being of practical use. Thus although we had solved major engineering challenges of high bandwidth radio transmission, inductive powering, and biocompatible and stable encapsulation and insulation of a complex circuit, the device had to be explanted. In this award, we seek to capitalise on the achievements of the previous award to produce a fully functional telemeter. The circuit will be redesigned using a newly developed amplifier, better suited to EMG. We will implant the device into a macaque monkey as part of our ongoing experiments in movement control, providing in vivo performance data. We consider that repeated infections associated with the transcutaneous connector currently represent the major welfare cost to monkeys both in our experiments and those of similar groups around the world. Eliminating these infections would be a considerable refinement of technique. In addition, such infections can reduce the quality of behavioural data which is obtained, due to the clinical malaise suffered by the animal. This limits the science which can be achieved (i.e. new knowledge discovered) per animal used. Finally, severe infections may cause an experiment to be terminated prematurely, before sufficient data has been gathered. This would require the use of a further animal to complete the project. The proposed solution can therefore also achieve a reduction in animal numbers.
- Further Funding: Project Grant: Transcutaneous signal transmission without breaching the skin's natural barrier to infection, January 2007, £149,164
Principal investigatorProfessor Stuart Nicolas Baker
Co-InvestigatorDr Eric Graeme Chester
Professor Nicholas Donaldson