Researchers identify areas of the brain that control the ability to perform complex, sequential movements

In a new set of experiments with mice that have been trained to perform a series of movements and “path-change” in real time, Johns Hopkins scientists report that they have identified areas of the animals’ brains that interact to control the ability to perform complex, sequential movements, as well as to help mice recover when they Her movements stop without warning.

They say the research could one day help scientists find ways to target those areas in people and restore motor function caused by injury or disease.

The results of the experiments led by Johns Hopkins were published on March 9 temper nature.

Based on brain activity measurements of specially trained rodents, the researchers found that three major regions of the cortex have distinct roles in how mice navigate through a series of movements: primary motor and primary motor areas and primary somatosensory areas. They are all found in the upper layers of the mammalian brain and are arranged in a fundamentally similar way to humans.

The team concluded that the primary motor and primary somatosensory regions are involved in controlling the mice’s immediate movements in real time, while the frontal motor region appears to control the entire planned sequence of movements, as well as how the mice react and tune when the sequence is unexpectedly disrupted.

Because the animals perform sequential movements, the researchers say, it is possible that the frontal motor area sends electrical signals via special neurons to two other areas of the sensorimotor cortex, and further studies are planned to map the pathways of those signals between and between cortical layers. .

Whether an Olympian is downhill skiing or doing a daily chore like driving, many tasks involve a learned sequence of movements performed over and over again.”

Daniel O’Connor, Ph.D., assistant professor of neuroscience, Johns Hopkins University School of Medicine

O’Connor led the research team. He says that such sequential movements may seem common and simple, but they involve complex regulation and control in the brain, and the brain must not only direct each movement correctly, but also organize it into a whole series of interconnected movements.

O’Connor says that when unexpected things happen to interrupt a continuous sequence, the brain must adapt and direct the body to recreate the sequence in real time. Failure in this process can lead to disaster – a fall or a car accident, for example.

Neuroscientists have long studied how mammals compensate when a single movement is disrupted — such as reaching for a cup of coffee — but the new study is designed to meet the challenges of tracking what happens when complex sequences of multiple movements must be reorganized in real time in order to compensate for unexpected events.

In the case of an Olympic skater, for example, the skater is expected to perform a planned series of movements to approach and pass through gates along a slope, but there are likely to be moments when an obstacle disrupts the skater’s path and forces a lane change.

“How the mammalian brain can take a sensory cue, and use it almost instantly to completely switch from one continuous sequence of movements to another, remains largely a mystery.” O’Connor worked with Duo Xu, PhD, a former graduate student in O’Connor’s lab, to design a set of experiments in mice to track the areas of the brain that process the pathway of change.

For the study, the researchers first created a “cycle” for mice that were trained to stretch out their tongues and touch a “port” – a metal tube. When the investigators moved the port, the mice learned to touch the port again. Over the course of the course, when the port was moved to its final location, the mice that touched it with their tongues got a reward. The goal of all this training was to simulate a repetitive and predictable sequence of learned movements, such as a skater’s path downhill.

To study how an unexpected cue can trigger the brain to change course, the researchers asked mice to perform what scientists call a “regression experiment.” Instead of moving the port to the next location in the sequence, the researchers moved the port to an earlier location, so that when the mice extended their tongues, they failed to find the port, prompting them to reverse course, find the port, and advance through the cycle to get the treatment.

“Each port licking sequence includes a series of complex movements that the mouse brain needs to organize into a movement plan and then perform it correctly, but also to quickly reorganize when they find that the expected port is missing,” says O’Connor. .

During the experiments, the researchers used electrodes in the brain to track and record electrical signals between neurons in the sensorimotor cortex, which controls overall movement. An increase in electrical activity corresponds to an increase in brain activity. Because many areas of the cerebral cortex can be activated when mice move through the course in the experiment, the researchers used mice that had been raised with genetically modified brain cells that in certain parts of the cortex could be selectively “silenced” or disabled. Thus, scientists can narrow down the areas of the brain directly involved in movements.

“The results provide a new picture of how the hierarchy between neural networks in the sensorimotor cortex manages sequential movements,” O’Connor says. “The more we know about these interacting neural networks, the better positioned we will be to understand sensory dysfunction in humans and how to correct it.” “>


Journal reference:

Shaw, Dr.; et al. (2022) Cortical processing of flexible and context-dependent sensory sequences. temper nature.


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