In a first, researchers led by an Indian-origin scientist have recorded the moment-by-moment fluctuations in brain signals that occur when a monkey making free choices has a change of mind.
The study was led by electrical engineering Professor Krishna Shenoy at Stanford University, whose lab focuses on movement control and neural prostheses - such as artificial arms - controlled by the user's brain.
"This basic neuroscience discovery will help create neural prostheses that can withhold moving a prosthetic arm until the user is certain of their decision, thereby averting premature or inopportune movements," Shenoy said.
Neuroscientist Matthew Kaufman, who was a graduate student in Shenoy's lab, taught laboratory monkeys to perform a decision-making task.
He then developed a technique to track the brain signals that occur during a single decision with split-second accuracy.
This improvement on what's called the "single trial decoder" algorithm revealed the neural signals that occurred during a momentary hesitation or when the monkey changed his mind.
"We are seeing many cognitive phenomena in the brain for the first time," said Kaufman, who is now a postdoctoral scholar at Cold Spring Harbor Laboratory.
"The most critical result of our work here is that we can track a single decision and see how the monkey arrived there: whether he decided quickly, slowly, or changed his mind halfway through," he said.
The experiments involved a monkey that was trained to reach for either of two targets on a computer screen. It was often possible to reach either target, inviting a free choice. Sometimes, one target was blocked, resulting in a forced choice.
Other times, the researchers would switch between these configurations while the monkey was deciding, encouraging a change of mind.
The research focused on the time the monkey spent deliberating, before the actual movement began. The monkey was trained to sit motionless while two jittering targets were positioned on either side of a computer screen.
Coloured barriers on the screen created a simple maze. When the targets stopped jittering the monkey was trained to move to one or the other target by sweeping his fingertip through the maze until he touched one of the targets.
During the experiments, 192 electrodes in the monkey's motor and premotor cortex began measuring brain activity the moment that the targets appeared on screen.
The measurements continued until the targets stopped jittering and the monkey began to move. The interval between the targets' appearance and the beginning of movement marked the time of decision or, in some cases, hesitation.
This deeper understanding of decision-making will help researchers to fine-tune the control algorithms of neural prostheses to enable people with paralysis to drive a brain-controlled prosthetic arm or guide a neurally-activated cursor on a computer screen, researchers said.
