Frontier: Scientists Identify Navigation System

by Kelli Whitlock Burton

July, 2007

Sidestepping a hole in the sidewalk may seem simple. What leads up to such motion, however, is a series of complex calculations performed by specialized cells deep in the cerebellum, according to a new study in monkeys.

“Navigating through our world requires our ability to take our own presence and position of our different body parts and dynamically orient them in the surrounding world,” says David Dickman, co-author of the study and a professor of anatomy and neurobiology at Washington University School of Medicine in St. Louis. “One of the main problems of the brain is how to coordinate the information about the body in space to space itself.”

The brain receives information on the body’s movement and orientation from the vestibular system in the inner ear. But vestibular sensors track head position only and cannot distinguish between movement and gravitational force, presenting a computation problem for this type of navigation.

Scientists suspected that inertial motion was calculated by combining rotational signals from the semicircular canal in the inner ear with gravity signals. However, which neurons in the brain were responsible for these computations was unknown.

Dickman and colleagues focused on Purkinje cells, neurons found in a region of the cerebellum that receives information from the vestibular system. During the study, the monkeys’ heads were guided through a precise series of rotations and accelerations while the scientists measured the electrical activity of the Purkinje cells.

In the June 21 issue of Neuron, the researchers report that Purkinje cells do, in fact, perform calculations to determine inertial motion, offering what they call an “elegant solution” to the computational problems involved in inertial navigation.

Researchers now plan to examine how perception of motion occurs and how it combines with other sensory experiences to provide a complete picture of moving relative to objects.