A new generation of electronic brain implants could help restore natural motion to people who have suffered nervous system damage by studying and simulating the brain's behaviour during motion.

Researchers at Newcastle University's Institute of Neurosciences are developing autonomous electronic implants, or neurochips, to investigate and modulate neural activity. From this, they aim to develop brain-computer interfaces and prosthetics technology to restore motor function to patients after nervous system injury.

Andrew Jackson, research associate in neurotechnology at Newcastle, said: 'The university has a very strong engineering and neuro-scientific base and we're using those strengths to apply engineering techniques to neuroscience problems.'

The specific field this project will investigate is known as neural prosthetics. 'Any prosthesis is a replacement for a part of the body that is damaged, and in this case it's part of the nervous system that is damaged,' said Jackson. 'In the case of spinal cord injury, for example, the neural pathway from the brain to the periphery, which makes the muscles move, may be damaged. We'd like to create artificial connections using microelectronics with which we can close the connection between the brain and the muscles in order to reanimate the limbs following paralysis.'

Jackson previously worked at the University of Washington in Seattle developing the first generation of the chips using off-the-shelf surface-mounted microelectronics. He used a programmable microprocessor known as PSoC, or programmable system on chip.

That technology allowed the researchers to put in a single artificial connection. The circuit would continuously 'listen' to the neural signal coming from one electrode positioned in the brain over several days. Every time it detected a neural event from a cell close to that electrode, it would deliver a brief pulse of electrical stimulation to a second electrode somewhere else in the nervous system. The chip acted as an artificial connection between these two sites.

'That was great as a proof of principle and we did some important experiments,' said Jackson, 'but it wasn't enough to be able to put in a useful system that could compensate for the full complexity of a real neural connection between two areas. What we'd like to do now is to develop a more sophisticated version of these electronics with multiple channels of recording and multiple channels of stimulation.'

An associated area of research is the neural control of natural behaviour in animals. 'These circuits allow us to continually monitor what is going on in the brain,' said Jackson. 'Using a small, battery-powered implant, we can continually study the behaviour of animals over long periods while they move unconstrained by wires. These let us see for the first time what's going on inside the brain during completely natural, unrestrained behaviour.'

Information gathered in this way will ultimately allow researchers to develop prostheses that can restore natural movement to patients. Jackson's previous work in the US studied the motor area of primates' brains. He discovered strong, consistent relationships between what was happening in the brain and the motion of a limb, which in future could allow those relationships to be replicated using electronics.

The project team is now recruiting a research associate to develop the electronics to identify neural events and control the stimulator. Other team members are working on the new design of electrodes to reliably capture signals from the brain.

'The devices will detect the characteristic events which represent a cell in the brain, firing off what is known as an action potential,' said Jackson. 'The electronics need to be small and low power to be implanted in the body and run for a long time using a battery or a radio frequency power supply. They will detect these neural events and stimulate the circuits, which we already have to deliver stimulation to downstream parts of the motor system.'

Jackson believes they will have an implant ready for human clinical trials within five years. 'There are obviously a lot of safety and efficacy trials to carry out before we can do human testing on this,' he said. 'From the engineering side we could have a device which, in theory, could be put in a human in that timeframe. A number of groups are already quite advanced on several elements of this project and we're hoping to integrate the technology into a complete system.'

Berenice Baker