'Muscle memories' get 'zipped and unzipped' in the brain, like computer files

Tapping into your "muscle memory" to tie your shoes or play an instrument may feel automatic — but to execute these learned motions, the brain erupts into a flurry of activity, rapidly "unzipping" and "zipping" all the key information about the movement being performed, a new study suggests.

The study, published Feb. 1 in the Journal of Neuroscience, used a brain scanning technique called functional magnetic resonance imaging (fMRI) to collect snapshots of people's brains as they played simple melodies on a keyboard. fMRI tracks the flow of oxygenated blood through the brain, and because active brain cells require more oxygen than inactive ones do, the scans provide an indirect measure of brain activity. 

The 24 study participants — none of them trained musicians — learned simple, one-handed keyboard melodies over several days and were then asked to play these sequences from memory while in the fMRI scanner. In each trial in the scanner, the participant would receive a visual cue to prepare to perform one of the melodies and then a second cue to execute it. 

In some of the trials, the participants weren't given the second cue, so the researchers got snapshots of the brain both planning and executing movements. 

Related: How does the brain store memories? 

These scans revealed that movement-related regions of the brain's wrinkled outer surface, the cerebral cortex, lit up during the planning stage, and this activity reflected the order and timing of the notes to come. In other words, specific patterns of brain activity reliably translated to particular sequences of notes, and separately, other activity patterns reflected the durations of those notes. 

"This happens very rapidly and automatically each time in the hundreds of milliseconds before the action starts," Katja Kornysheva, the study's senior author and co-director of the Centre for Human Brain Health at the University of Birmingham in the U.K., told Live Science in an email. 

Then, when it comes time to actually play the notes, these separate patterns representing note order and timing become integrated, or "zipped," resulting in a new, unique pattern of brain activity. 

"The integrated patterns were those that were unique for a particular combination of key-press order and timing, not something that transferred across these combinations," Kornysheva said. So the brain went from handling each element of the movement separately, like paint and a canvas, to considering them a single, integrated unit, like a completed painting. 

An established theory suggests that the parts of the cortex that control movement are in a kind of hierarchy, but this study runs counter to that idea, said Tanuj Gulati, an assistant professor of biomedical sciences at Cedars-Sinai Medical Center in Los Angeles who was not involved in the new research. 

Two regions, known as the premotor and parietal areas, are thought to store "high-level" information about movements — in this case, the order and timing of keystrokes. The primary motor cortex, which communicates with muscles via the spinal cord, handles only "low-level" information — what muscles in the fingers and forearms actually need to activate to make the keystrokes happen.

"This notion is challenged in this study," Gulati told Live Science in an email. "The areas thought to be 'low-level' that can only communicate fixed commands to downstream muscles were instead found to be constantly updating based on order and timing challenges of a movement," and so they were dynamically involved in movement planning and execution.

Kornysheva and her team are currently studying muscle memory in the context of disorders such as dyspraxia, a neurological disorder that affects the ability to plan and coordinate movements. Their work could also be useful for helping people regain motor skills after they've had a stroke, Kornysheva added. 

The team is also starting to study motor learning in trained musicians, in addition to novices, she said. 

"Musicians with seasoned finger proficiency and their sequence/timing control are akin to elite athletes, say a gymnast with excellent postural control," Gulati said. It may be that, in highly trained individuals, certain movement sequences become "hardwired" in the motor cortex and the rapid adjustments to high-level features of those movements may unfold differently than they do in the brains of novices, he said.