Refining the use of chronic implants in non-human primate neuroscience

We are working to refine the design and use of chronic implants in long term neuroscience experiments with macaques.

Recordings are made of the electrical signals in single neurons, or groups of neurons, whilst the monkey performs a trained task. For reliable recordings to be made, the monkey’s head is restrained in a stable position, and the particular brain area of interest is accessed via craniotomy. Conventionally these are achieved by surgical implantation of two devices onto the animal’s skull under deep general anaesthesia – a headpost for restraint, and an air-tight recording chamber to protect the brain area exposed by the craniotomy.

The implants are made of either biocompatible material (e.g. stainless steel) or a tissue-friendly material (e.g. titanium coated with hydroxyl apatite), sometimes in combination with dental cement, and secured to the skull using screws, bolts or other devices. Although these methods reliably restrain the monkeys head, many types of implant are not tissue-friendly, and eventually pressure on the implant leads to inflammation and infection, bone necrosis and instability or breakage of the implant.

Information sharing

To share information on the pros and cons of different implant designs and approaches, how they should be evaluated, and how the complications that can occur can best be prevented or addressed, we organised a workshop with the University of Oxford in 2012. A range of opportunities were identified for refining implant design, surgery and maintenance to improve animal welfare. To disseminate these approaches more widely within the neuroscience community, we established an expert working group. The group has developed a wiki on chronic implants (www.ciwiki.net) and also explored development of a clincial score sheet for monitoring the response to implanted devices.

Research funding

With NC3Rs funding, Professor Roger Lemon, Institute of Neurology, University College London, developed a novel implanted head restraint device which minimises tissue damage and infection and has scientific advantages over conventional devices. The TEKAPEEK© headpost has been adopted by a number of UK laboratories.

Dr Chris Petkov, Newcastle University, evaluated alternative non-invasive means of head immobilisation: an individually-customised helmet and a face mask, which allow the monkeys to voluntarily engage with temporary head restraint for brief periods.

To encourage further research in this area, we issued a call for proposals under our strategic awards scheme in 2015. One award was made to Professor Alex Thiele and colleagues at Newcastle University to apply advances in human prosthetics to chronic implants in macaque neuroscience studies, concentrating on skin adherence with the implant surface.

Prize winning research 

Dr Daniel Adams, University of California San Francisco, won an NC3Rs prize for his pioneering work to develop a titanium recording chamber and headpost with reduced incidence of infection and tissue damage.

Working group