Harvard SEAS researchers discover that the cerebellum is essential for forming long-term motor skill memories, challenging previous beliefs and opening new avenues for understanding sensorimotor learning.
For decades, scientists have known that the medial temporal lobe (MTL) is pivotal to our ability to remember explicit facts, such as names and dates, but it appears to have minimal impact on our capacity to retain motor skills. New research, however, has pinpointed the cerebellum as the key brain region responsible for long-term motor skill memories, like riding a bike.
Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have discovered that short-term and long-term memories for motor skills indeed form in different regions of the brain. Their groundbreaking study, published in the Proceedings of the National Academy of Sciences, underscores the cerebellum’s indispensable role in forming enduring motor skill memories.
“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,” senior author Maurice Smith, the Gordon McKay Professor of Bioengineering at SEAS, said in a news release.
Smith and first author Alkis Hadjiosif, a postdoctoral fellow at SEAS and Massachusetts General Hospital, delved into previous studies on motor learning in patients with cerebellar damage. Despite all studies confirming impaired sensorimotor learning, the extent of this impairment varied significantly.
The team suspected that differences in intertrial intervals, referred to as the memory window, might be at the root of this inconsistency.
“This would be the case if long-term sensorimotor memory was specifically impaired by cerebellar damage because longer memory windows would increase reliance on the impaired long-term memory,” Hadjiosif said in the news release.
By acquiring raw data from previous studies and analyzing these crucial time intervals, Smith and Hadjiosif found that patients with cerebellar degeneration showed minimal impairment in tasks with short intervals between trials. However, when longer intervals were introduced, these patients displayed significant memory impairment.
“When we examined these trial-to-trial differences, we found that the same patients who displayed near-normal performance on their short-interval practice trials were dramatically impaired on long-interval trials within the same session. And this was the case in the data from both studies,” added Hadjiosif.
The findings were further validated by reviewing over a dozen additional studies. Tasks with more movement directions, which prolong memory windows, resulted in dramatically increased memory impairment in individuals with cerebellar degeneration compared to tasks with fewer movement directions.
“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,” added 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.”
The study, co-authored by Tricia Gibo, not only enhances our understanding of the cerebellum’s role in skill memory formation but also opens new paths for exploring cognitive and motor function rehabilitation strategies, potentially benefiting those affected by cerebellar degeneration and other neurological conditions.