Neurons Track Body Sense in the Brain

Princeton neuroscientists are studying the brain's complex mechanism for keeping track of the body -- sensing the location of arms, legs, head and torso. "Your body sense is one of the most important senses you have," says Michael Graziano, a research scientist in the psychology department. "Even though you are not always consciously aware of your body sense, if you lost it you wouldn’t know the configuration of your limbs, what parts are your own and what are external objects. You wouldn’t be able to coordinate a movement.”

In a paper published in Science (December 1, 2000), Graziano and colleagues found that the brain achieves this sense of what psychologists call "body schema" by drawing together many types of information. In particular, they found that certain neurons receive and reconcile a variety of sensory signals including visual data and felt data from muscles and joints.

The researchers studied the activity of individual neurons in a specific region of a monkey's brain known to be involved in processing body schema. As expected, these neurons monitored the position of the arm even when a large shoulder-level visor blocked the arm from the monkey's view. However, when the researchers placed a life-like fake arm on top of the visor, within the monkey’s view, the neurons began to monitor the location of the fake arm as if it were the real one. Perhaps more surprising were tests in which the neurons ignored less life-like false arms.

The body schema not only monitors the felt and seen position of the arm – it may also be a critical part of tool use. For example, a fork becomes a natural extension of the arm; the outlines of a car become a natural extension of the driver’s body. "If we could understand the body schema sufficiently, we could perhaps understand more about the neural basis for tool use," Graziano notes.
Click here for full story

< Back