Does regular Cannabis use affect motor skills?
Current estimates indicate that nearly 20% of the United States population has used cannabis.
In 2011, approximately 6% of young adults said that they used cannabis every day, which rose sharply to 10.8% by 2021.
Despite the increasing and enduring popularity of cannabis as a recreational drug, there are many unanswered questions about how cannabis affects the brain. Research has shown that cannabis impairs memory and attention, while the evidence regarding inhibitory control, psychomotor control, learning, processing speed, and decision-making remains inconclusive.
Long-term and persistent effects of cannabis use are beginning to emerge. However, 'regular cannabis use' is not consistently defined across these studies.
Motor control, which is key to balance, coordination, stability, and motion, involves coordination of the brain, muscles, and limbs. In neurophysiological studies on motor control in healthy children and adults, scientists established that beta oscillations arise when individuals process cues regarding where to move and while moving. The associated event-related desynchronization (ERD) of the beta frequency band (β-ERD), which is between 16 and 25 Hz, increases in amplitude as the task's difficulty increases.
About the study
In the present study, researchers utilized magnetoencephalographic (MEG) imaging and time series analysis to assess how regular cannabis use affects β-ERD dynamics involved in the planning and execution of motor sequences.
A total of 18 individuals between the ages of 25 and 57 who regularly used cannabis were recruited for the study. The study participants did not have any other substance use disorders.
Each cannabis user was matched to a non-user control based on age, race, sex, and alcohol use. The study defined 'regular cannabis use' as using the drug for at least three years and at a minimum of three times each week.
To be eligible for the control group, participants should never have used illicit substances, including cannabis, except for experimental use and not in the past three months. Participants in the study were not pregnant and did not have diagnosed psychiatric or neurological disorders, central nervous system (CNS) dysfunction, head traumas, or metallic implants.
Participants were assigned a sequencing task, in which they were shown three numbers, each corresponding to a digit of their hand. Once they were given a movement cue, the participants tapped out the sequence indicated by the numbers. MEG images were collected from the participants while they performed the tasks.
Time series were generated from the virtual sensor data and subsequently analyzed using a mixed-model Analysis of Variance (ANOVA) to compare before and after the execution of movement. Whole-brain models from the oscillatory maps using a mixed-model ANOVA were generated by comparing planning to executive motor functions between cannabis users and non-users.
Study findings
Cannabis users did not differ significantly from non-users in terms of accuracy and were slightly more accurate at 86.67% compared to 84.51% among non-users. The two groups had no significant differences in reaction time or movement duration.
The next stage of analysis was to compare the β-ERD response of the two groups. To this end, a window of 1,000 milliseconds (ms) starting 500 ms before movement began was used. Participants, independent of the group, showed a stronger response during execution as compared to planning; however, there was no significant difference between the groups.
Beta oscillations were stronger in the left superior parietal cortices, right posterior insula, and right inferior frontal gyrus among participants who used cannabis during the execution phase but not during planning.
Conclusions
As compared to non-users, cannabis users exhibited stronger β-ERD responses in several motor regions and primary motor cortices. Notably, these differences were observed during execution but not in planning.
Previous research has shown that β-ERD response amplitude is associated with performance. Since performance was similar between the two groups, increased β-ERD response may serve a compensatory function, allowing users to perform at the same accuracy and reaction time level as control subjects.
These neurological differences may be a precursor to behavioral deficits that cannabis users could develop in the future. Since β-ERD response increases with the difficulty of tasks, cannabis users may be unable to solve more challenging problems.
Thus, future studies could formulate more demanding tasks to assess how these compensatory mechanisms function and when they stop functioning.
