Brain Stimulation Study Shows Cannabis Users Have Heightened Cortical Excitability

Cannabis users (n = 16) showed significantly higher motor evoked potential amplitude at 130% of resting motor threshold (p = 0.012), delayed cortical silent period onset at multiple intensities, and reduced short-latency intracortical inhibition at 4 ms interstimulus interval (p = 0.028). Resting motor threshold correlated negatively with addiction severity (p = 0.026).

Case-control study comparing 16 cannabis users and 20 controls using transcranial magnetic stimulation (TMS) measures of cortical excitability and inhibition, alongside clinical assessments including SCL-90-R, MoCA, and Hamilton anxiety/depression scales.

This is direct neurophysiological evidence that cannabis use alters the balance between excitation and inhibition in the brain. The correlation between motor threshold and addiction severity suggests these changes track with heavier use.

Altered cortical excitability could help explain cognitive and motor effects reported by cannabis users. If cannabis shifts the brain toward greater excitability with less inhibition, this may have implications for seizure threshold, impulsivity, and other neurological outcomes.

Very small sample (16 vs. 20). Cross-sectional design cannot determine whether cannabis caused the changes or whether people with different baseline excitability are more drawn to cannabis. No information on duration or amount of use.