A team of U.S. and Canadian scientists claims to have used an MRI machine and a few monkeys to show that the reality that our consciousness perceives is just a little bit in the future, always having to predict what comes next. The research, among other things, may explain mental paradoxes we all experience, déjà vu being the best example.
Work by Andersen, the James G. Boswell Professor of Neuroscience at Caltech, and his colleagues Grant Mulliken of MIT and Sam Musallam of McGill University, offers the first neural evidence that voluntary limb movements are guided by our brain’s prediction of what will happen an instant into the future. "The brain is generating its own version of the world, a ‘forward model,’ which allows you to know where you actually are in real time. It takes the delays out of the system," Andersen says.
The research in Andersen’s laboratory is focused on understanding the neurobiological underpinnings of brain processes, including the senses of sight, hearing, balance, and touch, and the neural mechanisms of action. The lab is working toward the development of implanted neural prosthetic devices that would serve as an interface between severely paralyzed individuals’ brain signals and their artificial limbs–allowing thoughts to control movement.
In their experiments, Andersen and his colleagues trained two monkeys to use a joystick to move a cursor on a computer screen from a small red circle into a green circle, while keeping their gaze fixed on the red circle. The monkeys typically generated curved trajectories, but to increase the curvature one monkey was trained to move the cursor around an obstacle. The obstacle (a large blue circle) was placed between the initial location of the cursor and the target circle, and the monkey had to guide the cursor around the obstacle, without touching it, and over to the green circle. As the monkeys conducted the tasks, electrodes measured the activity of neurons in the PPC. This allowed Andersen and his colleagues to monitor signals–commands for movement–in real time.
The studies showed that neurons in the PPC produce signals that represent the brain’s estimation of the current and upcoming movement of the cursor. "An internal estimate of the current state of the cursor can be used immediately by the brain to rapidly correct a movement, avoiding having to rely entirely on late-arriving sensory information, which can result in slow and unstable control," Mulliken says.
"The idea is that you feed back the command you make for movement into those areas of the brain that plan the movement (i.e., the PPC)," Andersen says. "The signal about the movement taking place is adjusted to be perfectly aligned in time with the actual movement–what you’re moving in your head matches with what you’re moving in the real world." The effect is akin to an athlete visualizing his performance in his mind. Studies have previously shown that these simulations of movement trajectories run through the posterior parietal cortex, and run at actual speed, taking the same amount of time as the activity would in real life.
Press release: Caltech Scientists Decipher the Neurological Basis of Timely Movement …
Image credit: Wellcome images: Position of the brain inside the head: Futuristic image showing the brain and cervical vertebrae visible through a transparent head….