Whether a tree branch or a computer mouse is the target, reaching for objects is fundamental primate behaviour. Neurons in the brain prepare for such movements, and this neural activity can now be deciphered, allowing researchers to predict what movements will occur. This discovery could help us develop prosthetic limbs that can be controlled by thought alone.
To find out what goes on in the brain when we reach for things, biomedical engineers Daniel Moran and Thomas Pearce at Washington University in St Louis, Missouri, trained two rhesus macaques to participate in a series of exercises. When the monkeys reached for items, electrodes measured the activity of neurons in their dorsal premotor cortex, a region of the brain that is involved in the perception of movement.
The monkeys were trained to reach for a virtual object on a screen to receive a reward. In some tasks the monkeys had to reach directly for an object, in others they had to reach around an obstacle to get to the target.
Moran and Pearce managed to identify the neural activity corresponding with several aspects of the planned movement, such as angle of reach, hand position and the final target location.
The findings could one day allow the design of prosthetic limbs that can be controlled with thought alone, which is "one of the reasons we did the study", says Moran.
"The two subjects actually used different strategies to perform the task, and we were able to see this in their neural activity," Moran says. One monkey waited to receive all the information before reaching, but the other reached immediately, even though there was a good chance that an obstacle might appear and the reaching action would need to be rethought.
"If the decoding strategy is a robust finding, then this has wider consequences concerning mind-reading – particularly if we can get equivalent results for more complex strategic differences at higher cognitive levels," says Richard Cooper, a cognitive researcher at Birkbeck, University of London. "However, this is all very speculative."
Journal reference: Science, DOI: 10.1126/science.1220642
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