Professor Stuart Baker, from Newcastle University, has used funding from the NC3Rs to develop a wireless recording device which minimises the risk of infection associated with traditional methods used in movement control studies in non-human primates.
Principal Investigator: Stuart Baker, Professor of Movement Neuroscience
Organisation: Newcastle University
Awards: £149,176, in 2006, over 24 months; £71,994, in 2011, over 18 months
Titles: Transcutaneous signal transmission without breaching the skin's natural barrier to infection; Wireless high-bandwidth trans-cutaneous signal transmission
Read more about Professor Baker's research
Monkeys are used to study muscle and brain activity
Macaque monkeys are used for the study of movement control and coordination. Experiments typically involve evaluating the electrical activity of skeletal muscles using electromyography. Current methods for electromyogram (EMG) recording from the arm and hand involve wires fed subcutaneously from electrodes in the muscles of interest to a connector surgically implanted on the animal’s back or head. A recording device is plugged into this connector to make measurements, which are transferred to a computer for analysis. The electrodes can yield high quality recordings for over one year.
Methods for recording muscle activity can lead to infections
The presence of the connector prevents the skin from healing fully, which means that the animal can be prone to infections that can track down the electrodes and can be difficult to treat. As well as affecting animal welfare, the infections can also compromise the quality of behavioural data obtained, due to the clinical malaise suffered by the monkey. Very severe infections can require the animal to be euthanised, prematurely ending an otherwise productive experiment and requiring another animal to be used to complete the research.
A telemetry device for EMG recording
Professor Stuart Baker, Newcastle University, was awarded NC3Rs funding in 2006 to develop a radiotransmitter for implantation under the skin, which would be capable of communicating information wirelessly to a receiver outside of the body. An internal device would avoid a permanently open wound, enabling the skin to heal and restore its natural barrier to infection. Similar telemetry devices are already widely used in other types of animal research, but the commercially available systems cannot transmit the large amount of data that is required to enable the effective study of muscle and brain activity.
Pushing telemetry technology to new limits
Working with electronics and bioengineering experts from Newcastle University and University College London, Professor Baker initially developed a prototype device capable of amplifying and digitising up to 16 channels of EMG recording (5kHz sampling rate per channel) and faithfully transmitting rapidly changing signals through the skin by radio. Power is supplied by inductive coupling to an implanted coil antenna, avoiding the need for frequent battery changes and allowing a long implant life without further surgery.
The prototype device has undergone extensive bench testing and trialling in one monkey. It integrated well with tissue, ‘powered up’ on demand, transmitted data and remained infection free. Although the major engineering challenges of high bandwidth radio transmission, inductive powering, and biocompatible and stable encapsulation and insulation of a complex circuit have been addressed, the signal amplifier integrated circuit did not adequately high-pass filter the recordings, leading to signal drift and saturation. In 2011, Professor Baker was awarded further NC3Rs funding to produce a fully functional telemeter in which the circuit was redesigned using a newly developed amplifier integrated circuit, with high-pass filtering better suited to EMG recording.
The improved device has been tested so far in two animals at collaborating laboratories in London and Fribourg (Switzerland), where it has delivered high quality telemetry data without infection. It has the potential to benefit around 20 monkeys per year globally.
Scale up to maximise use
Many experiments require signals from inside the body to be transmitted transcutaneously. These are affected by the same problems with infection caused by wired interconnects and the technology therefore has considerable potential to refine experiments, not just in monkeys but also in other species such as rabbits, pigs and cats.
A key aspect of the design is that the radio communication is controlled by a field programmable gate array (FPGA). This allows straightforward reassignment of the available transmission bandwidth according to the requirements of individual experiments. Professor Baker uses the device to transmit 16 channels at 5k samples per second per channel with 12-bit resolution – parameters suitable for EMG recording. By simple changes to the FPGA program, it is possible to transmit four channels at 20k samples per second per channel with 12-bit resolution, which would be suitable for single unit neural recording from the brain. This flexibility greatly increases the possible applications and the aim now is to develop the system commercially.
This case study was published in a review of our research portfolio in November 2013.