What's New: MIT researchers have identified populations of neurons that code time with extreme precision in the primate brain. These neurons are found in two interconnected brain regions, the prefrontal cortex and the striatum, both of which are known to play critical roles in learning, movement, and thought control.
Why it matters: The timing of individual actions, whether we are speaking, driving a car, or playing the piano, require very precise control. Although our daily life is extremely dependent on this remarkable capability, surprisingly little has been known about how time is represented in the activity of brain cells. The discovery made by MIT neuroscientists is an important step toward answering this fundamental question.
How they did it: The team of researchers, led by Institute Professor Ann Graybiel, a member of the McGovern Institute for Brain Research and the Department of Brain and Cognitive Sciences, trained two macaque monkeys to perform a simple eye-movement task. After receiving a "go" signal, the monkeys were free to perform the task at their own speed. The researchers found that neurons in the prefrontal cortex and the striatum that consistently fired at specific times -- 100 milliseconds, 110 msec, 150 msec, and so on -- after the "go" signal. Like a stopwatch, these neurons provided a fine-scale coverage over a period of several seconds. The combined activity of these neurons provided "time stamps" that could specify any given time point with a remarkable precision of less than 50 milliseconds, more than sufficient to account for most behaviors.
Next steps: The discovery opens the door to many questions. How does the brain produce this time code, and how is it used to control behavior and learning? In the longer term, the ability to read the brain's natural time-code may facilitate the development of neural prosthetic devices for conditions such as Parkinson's disease, in which neurons in the prefrontal cortex and basal ganglia are disrupted and the ability to control the timing of movements is impaired.
Source: Jin DZ, Fujii N, Graybiel AM. (2009). Neural representation of time in corticobasal ganglia circuits. Proceedings of the National Academy of Sciences, week of Oct. 19 2009.
Funding: National Eye Institute, National Parkinson Foundation, Alfred P. Sloan Foundation, and the Huck Institutes of the Life Sciences at Penn State University.
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