A team led by Stanford electrical engineering professor Krishna Shenoy has revealed a previously unknown process that helps two brain regions cooperate when joint action is required to perform a task.
“This is among the first mechanisms reported in the literature for letting brain areas process information continuously but only communicate what they need to,” said Matthew T. Kaufman, who was a postdoctoral scholar in the Shenoy’s lab when he co-authored the paper.
The Neural Prosthetic Systems Lab (NPSL) at Stanford, famously called as Shenoy lab, has been a pioneer in analysing how large numbers of neurons function as a unit. Kaufman initially designed his experiments to study how preparation helps the brain make fast and accurate movements – something that is central to the Shenoy lab’s efforts to build prosthetic devices controlled by the brain.
The researchers used a new approach to examine arm movements. “Our neurons are always firing, and they’re always connected. So it’s important to control what signals are communicated from one area to the next,” explained Kaufman.
The scientists derived their findings by studying monkeys that had been trained to make precise arm movements. The monkeys were taught to pause briefly before making the reach, thus letting their brain prepare for a moment before moving.
To understand how this worked with the monkey’s arm, the scientists took electrical readings at three places during the experiments: from the arm muscles, and from each of two motor cortical regions in the brain known to control arm movements.
The muscle readings enabled the scientists to ascertain what sorts of signals the arm receives during the preparatory state compared with the action step. The key findings emerged from understanding how individual neurons worked together as a population to drive the muscles.
As the monkey prepared for movement but held its arm still, many neurons in both of the motion-control regions registered big changes in activity. The scientists realised that, during the preparatory stage, the brain carefully balanced the activity changes of all those individual neurons inside each region.
While some neurons fired faster, others slowed down so that the entire population broadcast a constant message to the muscles. “The serendipitous interplay between basic science and engineering never ceases to amaze me,” said Shenoy.
“Some of the best ideas for the design of prosthetic systems to help people with paralysis come from basic neuroscience research, as is the case here, and some of the deepest scientific insights come from engineering measurement and medical systems,” he explained in a paper published in the journal Nature Neuroscience.