Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists discover how brain draws and re-draws picture of world

26.11.2003


Children usually spill if trying to drink from a full cup, but adults rarely do. How we learn to almost automatically complete complex movements -- like how to lift a cup and tip it so the liquid is right at the edge when we’re ready to drink -- is one of our brain’s mysterious abilities.



Now, by conducting experiments with robots and humans, scientists at Johns Hopkins have solved part of this mystery and created a new computer model that accurately reflects how the brain uses experience to improve motor control.

"Now we have a much better idea of how the brain uses information from a variety of sources to create a model of the world around us, and how errors modify that model and change subsequent movements," says Reza Shadmehr, Ph.D., associate professor of biomedical engineering at The Johns Hopkins University School of Medicine. "We don’t just know how to control objects around us, we have to learn how."


The researchers’ work is described in the November issue of PLoS Biology, a new peer-reviewed journal launched by the Public Library of Science.

In the researchers’ experiments, volunteers grasped the end of a robot arm that precisely tracked their attempts to overcome resistance to reach a target, a stopping point 10 centimeters (about four inches) away. While real-life resistance might be a paperweight or a full mug, in these experiments the researchers programmed forces that would hinder movement of the robot arm in predictable ways. To reach the target in the allotted time (half a second), volunteers had to learn to balance those forces.

To provide the spatial information necessary for the brain to create a model, or map, of forces expected in the "world" of the experiment, subjects started from one of three positions -- left, center or right. For different groups of subjects, starting positions were separated by as little as half a centimeter (less than a quarter inch) up to 12 centimeters (about four and three-quarter inches).

In initial trials without resistance, subjects moved the robot arm in a straight line toward the target from each of the starting positions. In the next set of trials, subjects had to overcome resistance when beginning from the left and right starting positions, but not from the center.

At first, the resistance pushed subjects’ movements aside. With practice, most groups of subjects were able to reach the target in a more-or-less straight line again, indicating they had learned to account for the forces applied to the robot arm.

However, if the starting positions were too close together, the brain failed to draw appropriate conclusions about where to expect forces, even though visual cues reinforced whether the subject was starting from the left, middle or right, the researchers report.

"When the starting positions were just half a centimeter apart, the brain couldn’t create an accurate picture of the forces -- even with practice -- and improve movement," says Shadmehr. "When the starting positions were farther apart, however, subjects more easily adjusted to the resistance and generalized their experiences to anticipate forces likely outside of the tested space."

With information from these experiments, the scientists developed a new computer model of how the brain uses experience to create an impression of the world to apply to similar but new situations. The new computer model matches observations from this and all previous experiments, and Shadmehr says it’s the first to show that the brain multiplies, rather than adds, electrical signals from nerve cells that convey the arm’s position and velocity.

"We know the brain transforms sensory cues -- the arm’s position and velocity, among other things -- into motor commands," says Shadmehr. "Our model suggests that it does so by multiplying signals of position and velocity to create what we call a gain field -- a system that allows the brain to predict appropriate movement for a wide range of new but similar movements."

In subsequent experiments with volunteers, the researchers proved correct two predictions based on the computer model: how people generalize experience in the tests to other starting positions and under what circumstances people most effectively learn to balance the resistance.

Authors on the paper are Shadmehr, graduate student Eun Jung Hwang and postdoctoral fellows Opher Donchin and Maurice Smith, all of Johns Hopkins. Funding for the study was provided by the National Institute of Neurological Diseases and Stroke, and by postdoctoral fellowships from the National Institutes of Health and the Johns Hopkins Department of Biomedical Engineering.

Joanna Downer | EurekAlert!
Further information:
http://www.plosbiology.org/
http://www.hopkinsmedicine.org

More articles from Life Sciences:

nachricht Newly designed molecule binds nitrogen
23.02.2018 | Julius-Maximilians-Universität Würzburg

nachricht Atomic Design by Water
23.02.2018 | Max-Planck-Institut für Eisenforschung GmbH

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Attoseconds break into atomic interior

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...

Im Focus: Good vibrations feel the force

A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.

By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Basque researchers turn light upside down

23.02.2018 | Physics and Astronomy

Finnish research group discovers a new immune system regulator

23.02.2018 | Health and Medicine

Attoseconds break into atomic interior

23.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>