Pause and rewind: How the brain keeps time to control action - Neuroscience - Parkinson's & Movement disorders

Flexible control of movement timing is essential for behavior, relying on an adjustable timer in the brain. By measuring and manipulating activity in interacting brain regions, scientists could pause and rewind timing, revealing how the brain implements such a timer. Credit: Helena Pinheiro

Whether speaking or swinging a bat, precise and adaptable timing of movement is essential for everyday behavior. Although we do not have sensory organs like eyes or a nose to sense time, we can keep time and control the timing of our actions. Such timing accuracy depends on a timer in the brain, but how the brain implements this timer was previously unknown.

In research published in Nature, MPFI scientists Zidan Yang, Hidehiko Inagaki, and colleagues reveal how this timer works through the interaction of two brain regions—the motor cortex and the striatum. Together, these areas track the passage of time much like an hourglass.

Discovering the brain's hourglass

Prior studies on how the brain might time movement have highlighted both the motor cortex and the striatum as key brain regions. These regions show neural activity patterns consistent with timing functions and cause movement timing deficits when damaged in diseases such as Parkinson's and Huntington's.

Dr. Zidan Yang, lead scientist of the study, explains, "We understood there was an adjustable timer in the brain, but it was unclear how the brain was implementing this timer and what the specific role of each brain region was. We wanted to understand precisely how the brain keeps time because it is such a critical function for our everyday activities." 

MPFI Scientists explain their latest discovery that the brain uses an hourglass-like mechanism to keep time, enabling us to precisely control our movements. Credit: Kevin Albertini

To achieve this, the scientists trained mice to receive a treat by licking a spout with specific timing, for example, after 1 second. During this task, the researchers recorded the activity of thousands of neurons in both the motor cortex and the striatum to measure their timing-related patterns.

To understand how the brain's timer might work, scientists combined these measurements with a technique called optogenetics, which allowed them to temporarily silence the activity of one brain area with flashes of light and measure the resulting changes in the timing-related patterns in the other area.

"By combining neural recordings with brief changes in the activity of specific brain regions, we were able to identify the role that each region played in the brain's internal timer. We realized that these brain regions work together to track time, but play unique roles—similar to the top and bottom of an hourglass," says Dr. Yang.

Pausing and rewinding the timer

The researchers discovered that the motor cortex is like the top of an hourglass, sending streams of neural signals to the striatum. In the striatum, those signals accumulate as time passes, just like the sand at the bottom of the hourglass. Once the signal reaches a certain level, movement is triggered.

When the researchers temporarily silenced the motor cortex, it paused the flow of these signals as if pinching the neck of the hourglass to stop the flow of sand. This paused the buildup of activity in the striatum and delayed the timing of the mouse's lick for the treat, as if time itself had been paused.

On the other hand, when the researchers silenced the striatum, it reset the timing signals as if the hourglass had been flipped to restart the timer. This delayed the mouse's licking even further, as if time had been rewound.

Broader impacts

The team's findings mark a significant advancement in understanding how neural activity across these two areas interact to coordinate the timing of actions. Dr. Hidehiko Inagaki, MPFI research group leader and senior author of the study, describes his ultimate goal: "The motor cortex and striatum are the two key brain areas that control our movement and are damaged in many motor disorders.

"We are working to understand how the brain's activity patterns across these critical brain areas lead to precise control of behavior, such as fluid movements. We hope that this understanding can be harnessed to restore movement functions to those facing the challenges of living with a motor disorder." 

Provided by Max Planck Florida Institute for Neuroscience  

by Max Planck Florida Institute for Neuroscience

edited by Sadie Harley, reviewed by Robert Egan 

Source: Pause and rewind: How the brain keeps time to control action