How do we remember how to ride a bike?

Do you recall who taught you in the second year of school? Some memories last a lifetime, while others are just a fleeting moment.

About 50 years back, a considerable leap was made in cognitive science. Scientists discovered that a particular region of our brain, the medial temporal lobe (MTL), stood guard over our long-term declarative memories – those of explicit details like names, dates, and events.

When MTL is damaged, these long-term memories get lost, leaving victims living a life of moments, unable to recall information just a minute or two beyond the arena of the present conversation.

Memories of motor skills

Interestingly, those very people with a damaged MTL were observed to possess the capability of learning new motor skills, not only learning them but retaining these skills for days, months, or even more. This gave a clear indicator that MTL damage did minimal to no harm to the memories of motor skills.

This discovery prompts an intriguing question: Where in the human brain are these long-term motor skill memories, like riding a bike or tying a shoelace, stored?

Is it so that our brain compartmentalizes short and long-term sensorimotor memories in distinct, specialized regions?

These questions have baffled researchers for years, provoking curiosity and investigations.

Mysteries of motor skills and memory

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), have found that similar to declarative memories, the memories of short-term and long-term motor skills are also stored in separate regions of our brain.

The experts determined that the cerebellum is the central hub for the storage of long-term skill memories.

The research, offering new perspectives on the role of the cerebellum in sensorimotor learning, was published in the Proceedings of the National Academy of Sciences (PNAS).

Maurice Smith is the Gordon McKay Professor of Bioengineering at SEAS and the principal investigator of the study.

“This work advances our understanding of the role of the cerebellum in sensorimotor learning and points towards the role of the cerebellum as a gateway to the formation of stable memories for sensorimotor skills, largely independent of the short-term memory systems,” said Smith.

Motor memories and the cerebellum

Past studies have shown the crucial role the cerebellum plays in motor learning, but how it contributes to the formation of short-term and long-term skill memory was blurry.

To look deeper into the relationship, Smith and Alkis Hadjiosif, a postdoctoral fellow at SEAS and Massachusetts General Hospital, reviewed previous studies on motor learning in patients with cerebellar damage.

There were disparities in the severity of motor learning impairments among patients with cerebellar damage across different studies. Smith and Hadjiosif theorized that these discrepancies were due to the subtle differences in the time between trials, the “memory window.”

Cerebellar damage and motor memories

The hypothesis was based on the idea that cerebellar damage specifically impairs long-term sensorimotor memory. Therefore, longer memory windows would increase dependency on the impaired long-term memory.

To test their theory, Smith and Hadjiosif explored unreported data from previous studies, specifically the intertrial intervals. They discovered that studies with shorter intertrial intervals reported only minor impairments in learning for patients with severe cerebellar diseases.

Upon further analysis, they found that patients displaying near-normal performance on short interval trials were significantly impaired on long interval trials. This observation held true across the data from different studies.

The finding shed light on the importance of time in understanding the degradation of memory in patients with cerebellar degeneration. This solves the puzzle of varying results across different studies involving cerebellar damage’s effects on sensorimotor learning ability.

Implications for rehabilitation

This nuanced understanding of the cerebellum’s role in sensorimotor memory formation could have profound implications for rehabilitation strategies in patients suffering from cerebellar damage.

The research suggests that traditional approaches that do not differentiate between short and long-term memory strategies may need to be reconsidered.

Therapeutic practices could be adapted to prioritize shorter training intervals, leveraging preserved short-term memory capabilities to compensate for long-term memory impairments.

These adaptive strategies could enhance rehabilitation outcomes, offering a tailored approach designed to exploit the intact facilities of sensorimotor learning.

By focusing on modifying the temporal dynamics of rehabilitation exercises, clinicians might significantly improve motor recovery and skill retention in affected individuals.

Future research directions

The discovery opens numerous avenues for future research on motor skill memories, looking beyond traditional paradigms of memory storage and retrieval. One significant pathway involves exploring how neural plasticity can be harnessed to aid long-term skill formation despite cerebellar deficits.

Additionally, researchers are interested in unraveling how other brain regions might compensate for cerebellar impairments, possibly through the recruitment of alternative neural pathways.

Moreover, understanding the molecular mechanisms underlying these processes could unlock new therapeutic targets to enhance cognitive and motor recovery.

Finally, interdisciplinary collaborations encompassing neuroscience, bioengineering, and clinical therapy are likely to propel advancements in this field, providing new insights into the brain’s remarkable ability to adapt and reorganize itself.

Broader implications of the study

“These findings highlight how important time is to understanding memory degradation in patients with cerebellar degeneration and solve the mystery of the trial-to-trial and study-to-study variability in the effects of cerebellar damage on sensorimotor learning ability,” said Smith.

“Our research usually involves designing new experimental manipulations to acquire novel data sets that can provide insight into the mechanisms for learning and memory, but sometimes simply looking at old data through the right lens can be even more illuminating.”

As we progress in our journey to understand the human brain’s intricate mechanisms, every piece of data counts. Sometimes, a new perspective on old data can lead to breakthroughs in our grasp of learning, motor skills and memory.

Such is the nature of research – a relentless cycle of question and discovery, an eternal quest for understanding.

The study is published in the journal Proceedings of the National Academy of Sciences.

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