Cognitive Neuroscientist Rich Ivry Is Studying Bimanual Coordination "Firsthand"

By Genevieve Shiffrar

December 18, 2002

Imagine the frustration you would feel dressing in the morning if the right and left sides of your brain had different senses of fashion. One hand might reach for a red rugby shirt, the other hand might grab a blue pin-striped oxford button-down.

This conflict can happen for people who have had brain surgery in which the fibers of the corpus callosum are cut. These fibers connect the right and left sides of our brains, and the surgery is sometimes required to treat severe forms of epilepsy. While this procedure can reduce or even eliminate seizures, it also provides an opportunity for observing how the two cerebral hemispheres function in relative isolation. In the example above, the two hemispheres share the general goal of getting dressed for the day and each sets about to accomplish that goal—even though the action plans may not be in agreement.

Psychology Professor Rich Ivry

Psychology Professor Rich Ivry works with "split-brain" patients, observing their behavior in an effort to understand brain function and structure. He is well known for his studies exploring the different parts of the brain that are involved in the control of skilled movement. Much of his recent work, including that with split-brain patients focuses on bimanual coordination.

We use our two hands for a wide variety of tasks: tying our shoes, cutting vegetables, using a computer keyboard. Activities such as these seem nearly effortless to us. Yet, coordinating the actions of the two hands is quite complex, especially when each hemisphere exerts primary control over the movements of the opposite hand. Try to tie your shoes using a novel form of bimanual coordination: let a friend use her right hand and you use just your left hand. You will see "firsthand" that bimanual coordination is not achieved easily!

The difficulty in trying to complete a bimanual coordination task with a friend arises from the lack of communication that normally takes place between the two sides of your brain. In general, this communication is helpful. But, if you are asked to complete different tasks with each of your hands simultaneously, such as tapping your head with one hand and rubbing your belly with another hand, interhemispheric communication actually disrupts your ability to perform the tasks. This is bimanual interference.

Professor Ivry, director of the Institute of Cognitive and Brain Sciences and a professor with the Helen Wills Neuroscience Institute, and his colleagues have examined bimanual communication and interference in a number of novel experiments. One of their favorites is what they call their personal UC admissions test. Hold two pens, one in each hand. As quickly as you can, draw a U shape with the left hand and a C shape with the right hand. You will find this task nearly impossible, especially if you try to do it as fast as possible. However, if you are a split-brain patient or one of those rare individuals born without a corpus callosum, you won't have difficulty. Without these connecting fibers, the two hands can draw conflicting movement patterns without showing any sign of bimanual interference.

Quickly draw this U shape with the left hand and this C shape with the right hand. Bimanual interference accounts for the challenge.

Phenomena such as these counter previous theories of bimanual interference in which the interference reflected a preference to activate symmetric muscles due to connectivity in the spinal cord. These spinal connections are presumably intact in the patients, yet they do not exhibit any conflict. Rather than revealing something about a low-level interaction between the signals to the muscles, bimanual interference likely reflects the generation of high-level action plans in which a spatial goal for the movement is defined and then each hemisphere sets about to determine how the goal can be achieved. In normal individuals, these plans are in conflict given the requirements for drawing Us and Cs. In the split-brain individual, the conflict doesn't occur.

Using deceptively simple experiments as well as advanced neuroimaging tools such as functional Magnetic Resonance Imaging (fMRI), Rich Ivry is helping to shed light on the beauty and complexity through which our neural system allows some of us to perform exquisite movements, while others feel as if they all thumbs. By studying how coordination is achieved between the two hemispheres, the research addresses fundamental questions concerning our behavior: How do we make a decision? To what extent are we aware of what we do? Do decisions require consciousness?

To Rich Ivry, the study of the relationship between the mind and brain go hand in hand.