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How Does Practice Hardwire Long-Term Muscle Memory?

Neuroscientists have pinpointed a new mechanism behind long-term motor memory.

Esther Lim / Wikimedia Commons
Source: Esther Lim / Wikimedia Commons

Why is it that once you've learned how to ride a bicycle or serve a tennis ball that you never forget the muscle memory involved in these actions? A team of neuroscientists recently pinpointed a new mechanism behind the consolidation of long-term motor memory.

The March 2015 study, "Modeling Memory Consolidation During Posttraining Periods in Cerebellovestibular Learning,” was published in the Proceedings of the National Academy of Sciences.

Every athlete, musician, surgeon—or anyone who regularly performs a motor skill that becomes fine-tuned with practice—knows that through repetition and practice motor skills become automatic. Everyday activities like typing on a keyboard, driving a car, or tying your shoelaces become automatic over time for anyone without a neurological disorder. What is happening in the brain that hardwires and consolidates the formation of motor skills into long-term memory?

The Cerebellum Is the Seat of Muscle Memory

When I was growing up, my father, Richard Bergland, M.D., was my tennis coach. My dad was a neurosurgeon and nationally ranked tennis player who believed that his “eye for the ball” was directly linked to his proficiency in the operating room. He would say, "Of this I am absolutely positive, becoming a neurosurgeon was a direct consequence of my eye for the ball."

The ability to lock your eyes onto a target while tying a surgical knot or hitting a tennis ball in the sweet spot of your racquet is called the vestibulo-ocular reflex (VOR) and is a function of the cerebellum. New research has identified a connection between Purkinje cells in the cerebellum and vestibular nuclear neurons working together to form long-term motor memory.

Ramón y Cajal / Public Domain
Purkinje cell illustration by Ramón y Cajal c. 1899
Source: Ramón y Cajal / Public Domain

As a coach in the 1970s, my dad would say to me, “Chris, think about hammering and forging the muscle memory held in the Purkinje cells of your cerebellum with every stroke.”

The traditional view of long-term motor memory that my father was referring to was based on the “Marr-Albus model” which proposed that muscle memory was the result of long-term depression (LTD) of the parallel fiber synapses onto Purkinje cells in the cerebellum. The result of 'long-term depression' reduces activity following a stimulus which allows for fluidity of movement and precision of fine-tuned motor skills.

The March 2015 findings resulted from a collaboration of researchers at the University of Electro-Communications and the RIKEN Brain Science Institute in Japan, and the University of California, San Diego.

The researchers were able to integrate the multiple plasticity mechanisms of the cerebellum to explain the formation of long-term motor memory. Their findings suggest that multiple plasticity mechanisms in the cerebellar cortex and cerebellar/vestibular nuclei participate in long-term motor memory formation.

Life Sciences Database / Wikimedia Commons
Cerebellum in red.
Source: Life Sciences Database / Wikimedia Commons

For this new study, Tadashi Yamazaki and colleagues developed simulations based on a mathematical model for the optokinetic reflex (OKR) in eye movement that incorporated long-term potentiation (LTP). This is a state of increased efficacy following a stimulus in the synapses of vestibular nuclear neurons.

The optokinetic reflex is a combination of a saccade and smooth pursuit movements of the eye. The OKR is seen when an individual follows a moving object like a tennis ball with his or her eyes. When the object moves out of the field of vision, the reflexive response is for the eye to move back to the position it was in when it first saw the object. This reflex typically develops at about 6 months of age.

The model used in the new study incorporated two distinct plasticity sites that work together and function synergistically. It showed that one hour of training resulted in a short-term increase of OKR gain, for which long-term depression of the Purkinje cells was responsible.

Interestingly, repetition of this training once a day gradually increased the level of OKR gain after training—but not during the training. This led to long-term potentiation and strengthening of synaptic connections for which the vestibular nucleus neurons were found to be responsible.

The researchers were able to reproduce OKR gain changes that were consistent with the changes in the vestibulo-ocular reflex (VOR) previously reported in some gene-manipulated mice.

Conclusion: The Cerebellum Is Key to Motor Memory in Sport and Life

The researchers concluded that if a short-term memory forms in the Purkinje cells after one hour of training that it is then transferred to the vestibular nuclear neuron where it is consolidated into long-term motor memory.

These findings have implications beyond the playing field. Recently, Purkinje cells and abnormal cerebellar function have been linked to autism spectrum disorders (ASD). This research could hold new clues for interventions and treatments for ASD.

This is a very exciting time to be researching the cerebellum. Revolutionary findings about the cerebellum are being released at breakneck speed. Please stay tuned to The Athlete's Way for the latest updates on the cerebellum.

If you'd like to read more on the cerebellum, please check out a free sample of The Athlete's Way or my previous Psychology Today blog posts:

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