Monkey see, monkey do? Not so fast. Scientists understand a great deal about how a primate receives visual signals and even how the monkey orchestrates an action in response. But what happens in between? After a monkey sees, he must decide what to do.

Dr. Michael Shadlen, UW assistant professor of physiology and biophysics, conducts studies on how primates make decisions. Shadlen's work in sensory-motor integration reveals a connection between a monkey's decision to act and how the monkey's brain organizes sensory information.

"It's the way an engineer might approach the problem of cognition," says Shadlen. "We are asking how the brain operates on sensory information to turn it into something useful for behavior."

Shadlen works with rhesus macaque monkeys at the UW Regional Primate Research Center. For a minimum six months, Shadlen and his research team train the macaques to perform a visual discrimination task and to answer questions about what they are seeing by making eye movements.

"Basically the monkeys are responding to rapidly flickering dots of light," says Shadlen. Monkeys watch a screen of flickering light resembling a low-density version of TV snow. Some of the dots appear at nearby positions to give the appearance of motion, as in the frames of a movie. "The dots come and go very quickly," explains Shadlen. "Even you and I would find it difficult to follow."

Researchers then measure the monkey's judgment of direction by recording his eye movements. If the monkey correctly judges the direction of the flickering light, he receives a reward. Shadlen can predict the monkey's judgment by measuring the activity from neurons in the brain.

"These neurons often give away what the monkey is thinking several seconds before the monkey actually answers our questions about the direction of motion," says Shadlen. "When we do these experiments, we feel like we're reading the monkey's mind. The challenge is to figure out how these neurons achieve this kind of activity. We think that answering this question will give us insight into how the brain makes interpretations and cogitates, so to speak, about the environment."

Over 30 areas of the primate brain are known to be involved in vision. When a monkey sees something, neuronal signals from the eye's retina travel to one or more of these areas in the brain. Shadlen's research indicates that there is an actual accumulation of information distributed across many sections of the brain.

"When a monkey makes a decision as to which way our random dots are moving, its brain transforms the information in a series of neural computations," says Shadlen. These computations are performed by nerve cells (neurons) and ensembles of cells termed neural circuits.

"The way the brain makes decisions and the way it forms interpretations and judgments looks very much like the kind of processes that link sensation to action--so-called sensory-motor integration--as in catching a ball," explains Shadlen. "We think that understanding the steps of sensory-motor integration will help us understand what can go wrong when we do really complicated things, like making decisions."

In fact the data from sensory-motor integration studies will have implications for the study of many neurological disorders that affect higher brain function.

"We are trying to understand how the brain interprets sensory information for some purpose," Shadlen adds. "That framework would encompass many types of mental and neurological illness: dementia, many types of stroke, psychomotor retardation, mental retardation and psychiatric disorders, especially schizophrenia."

Shadlen received a Ph.D. in neurobiology in 1985 from the University of California, Berkeley and an M.D. from Brown University in 1988. He was a resident in neurology, and chief resident in 1991-92, at Stanford University Medical Center. Shadlen joined the UW Department of Physiology and Biophysics UW in 1995. He is a core staff scientist at the UW Regional Primate Research Center, an adjunct assistant professor of neurology and a Howard Hughes Medical Institute Investigator.