This cross-sectional TMS study (n=39) reports that reduced GABAergic intracortical corticomotor inhibition correlates with poorer static, dynamic, and functional balance in early-stage Parkinson's, with sitting-state TMS providing relatively stable measures.

Provides a measurable neurophysiological biomarker linked to balance dysfunction and a plausible target for neuromodulation or GABAergic interventions to improve postural stability in PD, though findings are preliminary and require replication and interventional validation.

OBJECTIVE: This study aimed to explore the relationship between corticomotor inhibition, assessed by transcranial magnetic stimulation (TMS), and balance performance in people with Parkinson's disease (PwPD). METHODS: Thirty-nine PwPD, ranging from Hoehn and Yahr stages 1 - 3, underwent TMS to assess corticomotor inhibition-specifically GABAergic intracortical inhibition-under three postural conditions: lying, sitting, and standing. Balance performance was evaluated, including static, dynamic, and functional balance. RESULTS: Participants' ages ranged from 52 to 76, and disease duration ranged from 2 months to 30 years. Most individuals were in the early stages of the disease, with 59% being in stages 1 and 1.5. The results revealed that intracortical inhibition was associated with functional balance performance. Individuals with lower levels of corticomotor inhibition tended to demonstrate poorer balance. TMS measurements in the sitting position were relatively more stable and sensitive in reflecting corticomotor inhibition. CONCLUSION: Corticomotor inhibition is related to balance performance in PwPD. Across the three postural conditions assessed during TMS measurements, results obtained during the resting state were similar. SIGNIFICANCE: These findings highlight the potential of corticomotor inhibition as a neurophysiological marker and target for future interventions addressing balance dysfunction in PwPD.