Participants sat in front of a computer screen and achieved reaching movements while holding a handle, the position of which was recorded on a digitization tablet. Credit: Johns Hopkins School of Medicine and Cell Reports
Researchers from the Department of Physical Medicine and Rehabilitation at Johns Hopkins Medicine report that an automated study of 36 healthy adult volunteers who were asked to repeat the same exercise time and time again, is significantly faster when asked to repeat that movement on request – a result that did not happen because they expected the movement, but because of a previously unknown mechanism that their brains prepared to repeat the same action.
The findings add, according to the researchers, a clue to a growing body of research into how the brain generates movement in the first place, and could eventually help scientists understand how brain-controlled motor reactions go wrong after neurological disorders or injuries such as strokes.
Since the early 1950s, researchers know that repeating a movement can improve the response time needed to generate it, says study author Adrian Mark Haith, Ph.D., assistant professor of neurology at Johns Hopkins University School of Medicine. This effect has been attributed for a long time to & # 39; anticipation & # 39 ;: Be prepared to repeat a movement by default in accordance with the expectations about which motion would probably be required.
Other experiments with transcranial magnetic stimulation – a technique that uses magnetic pulses to stimulate the brain and record reactions – show that repetitive movements can influence the movements that occur when stimulating the motor cortex of the brain, thereby typically random movements more closely resemble those that were practiced.
"These studies suggest that something other than anticipation could happen with repetition," says Haith.
In a study designed to clarify how repeated movements can affect the motor response, Haith, along with colleagues Pablo A. Celnik, MD, professor of physical medicine and rehabilitation, neurology and neuroscience at Johns Hopkins University School of Medicine; Firas Mawase, Ph.D., a former postdoc in Celnik's laboratory; and Daniel Lopez, BS, a research assistant at the Johns Hopkins University School of Medicine, devised a series of experiments to bully whether the practice could influence the movement through anticipation or any other mechanism.
The researchers recruited 36 right-handed adult volunteers, of whom 22 were women, ranging in age from 19 to 30 years. All volunteers were sitting at a desk in front of a large computer screen. There was a touch-sensitive tablet on the desktop. When a target appeared on the screen, volunteers were asked to move a cursor to hit the target as quickly as possible using a stylus on the tablet.
In the initial tests, the volunteers took about 215 milliseconds (each millisecond is 1 / 1000th of a second) to respond and achieve the changing goal, regardless of the direction in which they moved their hands. However, after practicing moving the cursor hundreds of times in only a single direction, the volunteers were significantly faster in responding and moving the cursor in that direction to the target, even though their response times remained the same when targeting in other directions appeared.
"The benefit you get is 20 to 30 milliseconds," says Celnik. "It sounds small, but if you look at performance that can make a difference in sports and other areas that require fast motor movements, that time increase can mean the gap between a winner and a loser."
The scientists argued that there were two possibilities for the reaction times of the subjects: an idea is that they had learned to anticipate the movement and suspected that the target would appear in the preferential (usual) direction of the habit. Another is that repetitive exercises in one way or another have trained their brains to select the exercise more quickly in the future, while the subjects were given the same amount of flexibility as before they practiced to choose other goals.
To unravel these possibilities, the researchers tried a different experiment like the one in which the subjects were asked to move their hand to a target that appeared on the screen, but with a twist: they were asked to hand each fourth of a metronome, regardless of whether the target appeared or not. When the target appeared, it appeared in different time intervals just before the fourth beat, effectively setting a reaction time on each trial.
If, as previous theories held, the subjects moved forward in the practiced direction, the researchers reasoned that they would prefer to move their hand in that direction if the target did not appear, or if the reaction time was so narrow that they would not have time to hit the target accurately. That was not the case, however, says Firas. "
" The subjects preferred to move their hands when they had to guess, but it was mainly clues that were comfortable for right-handed people, "he says." They chose either up and to the right or down and to the left. , rather than in the direction they had practiced. "
Together, the researchers say that these results, published in Cell Reports, July 24, 2018, suggest that repeatedly repeating a movement stimulates the brain to be more efficient in making that movement in the future.
Celnik says that he and his team are planning to investigate what happens in the brain itself to better understand this effect, gaining insight into the neural mechanisms behind the phenomenon, adds he added, could lead to more effective therapies for stroke and other conditions that affect brain control over physical exercise.
This article has been updated w published from materials supplied by Johns Hopkins School of Medicine. Note: Material may have been edited for length and content. For more information, contact the mentioned source.
Mawase, F., Lopez, D., Celnik, P.A., & Haith, A.M. (2018). Motion repetition Facilitates the response preparation. Cell reports, 24 (4), 801-808.