NEW DELHI: Brain regions responsible for motor movements work together “like an hourglass” to flexibly control timing while one is moving, according to a study in mice, findings from which could be helpful for restoring movement in disorders such as Parkinson’s.
The ageing-related neurological disorder mainly affects movements and is marked by tremors in limbs and stiffness that can impact limbs, neck or torso.
The study, published in the journal Nature, shows how the brain’s internal timer works through an interaction between two brain regions — the motor cortex, which controls voluntary movements; and striatum, which links motivation to motor movements.
Through experiments in mice, researchers from the US’ Max Planck Florida Institute for Neuroscience found that temporarily silencing the activity in the motor cortex paused the brain’s timer, whereas silencing the striatum rewound the timer.
“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,” said lead researcher Zidan Yang, a PhD student.
The researchers explained that tasks such as speaking or swinging a bat requires one to keep time, the accuracy of which depends on a timer in the brain.
However, how the brain implements the internal timer was previously unknown, they said.
Mice were trained to receive a treat by licking a spout with specific timing, for example, after one second. Activity in neurons in both the motor cortex and striatum was monitored for measuring timing-related patterns.
Optogenetics was also used, which is a technique that employs light to temporarily silence activity in one part of the brain, allowing one to measure timing-related changes produced as a result in another brain region.
The motor cortex is like the top of the hourglass, sending streams of neural signals to the striatum, where the signals accumulate with time — similar to how sand gathers at the bottom of an hourglass, the team said.
Movement is triggered when the signals reach a certain level, they added.
Silencing activity in the motor cortex paused the flow of signals “as if pinching the neck of the hourglass to stop the flow of sand” and stagnating the build-up of activity in the striatum — this delayed the timing of the mice’s lick for the treat, the authors said.
Further, silencing activity in the striatum was found to reset the timing-related signals similar to how an hourglass is “flipped” to restart timer — this delayed the mice’s licking even more, as if time was rewound, the team said.
“Inhibiting the frontal cortex (where the motor cortex is located) and striatum effectively paused and rewound the timer, respectively,” the authors wrote.
“These findings are consistent with a model in which the striatum is part of a network that temporally integrates input from the frontal cortex and generates ramping activity that regulates motor timing,” they said. (PTI)
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