The impact of cannabis use on cortical excitability and inhibitory mechanisms: A case-control study

Cannabis use has been linked to alterations in brain function, yet its effects on cortical excitability and inhibition remain unclear. This study aimed to assess the impact of cannabis use on cortical excitability, intracortical inhibition and sensory inhibition, and to examine whether changes correlate with clinical data. A total of 16 cannabis users and 20 controls were included in this study. Each was assessed with the following: Symptom checklist-90-Revised (SCL-90-R), Montreal cognitive assessment (MoCA), and Hamilton Anxiety and depression scales (HAMA and HAMD). Measures of resting and active motor threshold (RMT and AMT), motor evoked potential amplitude (MEP-A), cortical silent period (CSP), short latency intracortical inhibition (SICI), and short-latency afferent inhibition (SAI) were assessed using transcranial magnetic stimulation (TMS). Significant differences emerged between the cannabis group and the control group across various clinical rating scales. Cannabis users showed a significantly higher MEP-A at 130 % of RMT (p = 0.012) and delayed CSP onset at 130, 140, and 150 % of rMT (p = 0.036, 0.026, 0.018, respectively), indicating enhanced cortical excitability and altered motor inhibition. Reduced SICI was noted in the cannabis group at interstimulus intervals (ISI) 4 ms (P = 0.028), but no significant differences were found for SAI. Significant negative correlations were observed between RMT and somatization (p = 0.048), and RMT and addiction severity index (p = 0.026). Cannabis use appears to enhance cortical excitability and alter motor inhibition, as evidenced by increased MEP-A, reduced SICI and delayed CSP onset with potential clinical implications.