Brain-computer interface study sheds light on neural activity during observation, or “mirror neurons”

PROVIDENCE, R.I. [Brown University] - Scientists have known for years that neural activity in the brain's motor cortex doesn't just happen when people are performing actions. Neurons associated with actions -reaching with a hand to grasp an object, for example - also fire when a person watches an action performed by someone else. This observational activity, which underlies a concept known as "mirror neurons," may play a role in how humans and other primates learn to perform physical tasks.

Now, neuroscientists have uncovered new insights into how this observational motor activity works. In a study that recorded the activity of individual neurons as people watched hand-like agents perform actions, the research team found that observational activity is tied to how human-like the hand performing the action appears to be. Actions performed by realistic-looking hands elicited the strongest observational response, while robotic hands or more abstract representations were associated with proportionally weaker responses.

The findings, published in Proceedings of the National Academy of Sciences, suggest that observational neural activity is not the work of specialized mirror neuron cells that light up when watching human actions, but rather an ensemble of neural networks that respond in a graded fashion to different stimuli. The results could be helpful in designing new brain-controlled assistive devices aimed at restoring function in people affected by paralysis.

The work, part of the BrainGate clinical trial, was led by neuroscientists at Brown University, the Mass General Brigham Center for Neurotechnology and Neurorecovery and the VA Center for Neurorestoration and Neurotechnology. The BrainGate trial aims to design intracortical brain-computer interface (BCI) systems that restore function in people who have lost the ability to move or communicate from illness or injury.

"The main motivation for this work was to look at how visual feedback may influence people's ability to use BCIs to control different types of external devices like computer cursors or assistive robotics," said Jacob Gusman, the study's lead author who performed the work as a graduate student at Brown. "We also gained some fundamental insights into basic neuroscience questions surrounding this idea of mirror neurons."

No specialized cells

For the study, the researchers worked with two people with tetraplegia - the loss of mobility in all four limbs. As part of the BrainGate clinical trial, both participants had tiny electrode arrays placed surgically in the motor cortex of their brains. The arrays record the activity of individual neurons as people think about performing movements with their limbs. Those brain signals can be used to control external assistive devices, enabling people to operate robotic arms, computers and other technologies just by thinking about the movement of their own limbs or speaking.