All a question of timing

Ever wondered how your brain recalls that you brushed your teeth before you took a shower, and not the other way around?

Keeping track of time is one of the brain's most important tasks - for decades, neuroscientists have theorised that the brain "time stamps" events as they happen, allowing us to keep track of where we are in time and when past events occurred. However, they couldn't find any evidence that such time stamps really existed - until now.

An MIT team led by Professor Ann Graybiel has found groups of neurons in the primate brain that code time with extreme precision. “All you do is time stamp everything, and then recalling events is easy: you go back and look through your time stamps until you see which ones are correlated with the event,” she said.

That kind of precise timing control is critical for everyday tasks such as driving a car or playing the piano, as well as keeping track of past events. The discovery, reported in of the Proceedings of the National Academy of Sciences, could lead to new treatments for diseases such as Parkinson’s disease, where the ability to control the timing of movements is impaired.

The research team trained two macaque monkeys to perform a simple eye-movement task. After receiving the "go" signal, the monkeys were free to perform the task at their own speed. The researchers found neurons that consistently fired at specific times - 100 milliseconds, 110 milliseconds, 150 milliseconds and so on - after the "go" signal.

“Soon enough we realized we had cells keeping time, which everyone has wanted to find, but nobody has found them before,” said Graybiel, who is also an investigator in MIT's McGovern Institute for Brain Research. The neurons are located in the prefrontal cortex and the striatum, both of which play important roles in learning, movement and thought control.

Future studies in this area could shed light on how the brain produces these time stamps and how this function can control behavior and learning. The work also raises questions regarding how the brain interprets the passage of time differently under different circumstances.

“Sometimes time moves quickly, and in some situations time seems to slow down. All of this ultimately has a neural representation,” said Graybiel.