Brain is free for the thinking prosthesis

4. December 2012

The use of prostheses is limited generally to the replacement of the function of limbs. A new development by U.S. researchers is the neuroprosthesis. They should be able to restore lost cognitive abilities.

The neuronal activity of nerve cells can be influenced electrically. This is therapeutically already usable with various diseases such as Parkinson’s disease or epilepsy. In this, the so-called brain pacemaker stimulates specific brain regions in order to prevent the failures of nerve cells or to suppress them. Researchers at the Wake Forest Baptist Medical Center in North Carolina have now developed a neural prosthesis which can influence cognition. Using the prosthesis, not only can existing circuits be recorded, but can also be changed at the cellular level.

MIMO model

Initially Robert Hampson et al. identified using positron emission tomography (PET) on five rhesus monkeys an area of the prefrontal cortex which is important in decision making. There followed the implantation of two electrodes in two different layers of the six laminae of the cerebral cortex. The two selected laminae were: an outer layer for the processing of sensory stimuli (input of stimuli) and an inner layer with a connection to other brain layers (output). The placement of the electrodes and the recording of the pattern of neural impulses took place according to the “multi-input multi-output nonlinear (MIMO) model”, a mathematical model researchers at the University of South Carolina developed. Roughly speaking it enables recording of signals from the outer layer and emitting of signals to the inner layer.

Signal amplification of correct decisions

The monkeys took part in a training where they were to notice different icons on the computer screen and then after a time delay of two minutes they were to recognise them again from among several different symbols. Correct decisions were rewarded. After two years of training, the researchers recorded the neuronal activity that was associated with the right decision making in choosing the pictures. The researchers made use of this particular pattern of brain signals in making the right decisions and reinforced the brain signals for making proper selection while the monkeys were still considering their decision. Correct decision making was able to be increased in this way.

Cocaine simulates cognitive damage

The scientists then simulated a more serious type of brain injury which impairs cognition. This was made possible using intravenous administering of cocaine. As expected, cognitive ability suffered and was reduced by 13 percent. The activation of the prosthesis in this situation was able to increase the output again, even to a point beyond the performance of the monkeys without simulated brain damage, because the results were better by ten percent than those in the experiment without cocaine. The limited cognition under influence of cocaine could therefore at least in the experimental animals be effectively counteracted with targeted electrical stimulation. Well, the human brain does not differ so deeply from monkeys, so the researchers harbour the hope one day to be able to help people with brain damage and cognitive impairment.

Research needs

Nevertheless, the use of the neuroprosthesis is limited to a single task. With a brain injury several areas usually break down and more than one faculty is impaired. As is known from the treatment of Parkinson’s, electrical stimulation is also associated with problems and not all patients benefit from the therapy. Side effects of treatment can turn up as speech and balance problems, and what’s more effectiveness of the treatment also wears off over time.

In Parkinson’s research therefore the focus of a research project started in May 2012 called DBS SMART, sponsored by the Federal Ministry of Education and Research, is on the development of new brain pacemakers which influence damaged nerve assocations in a targeted manner.

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