Objective: To study LTP-like effect induced by QPS on primary motor cortex of PD patients in “on” or “off” medication state and reveal the relationship between motor symptoms and LTP-like effects of PD patients.

Background: Previous studies using non-invasive brain stimulation (NIBS) techniques demonstrated the loss of motor cortical LTP-like plasticity in PD patients “off” medication state and Levodopa restored motor cortical plasticity. Quadripulse magnetic stimulation (QPS) is a newly reported NIBS technique and effects of QPS on PD patients have not been studied.

Method: Nine PD patients (4 male; mean age 65.5±10.2 years old) participated in this study. The participants visited our hospital twice, once under levodopa “Off” and the other levodopa “On” condition. As an “On” state, the participant took levodopa tablet 1hour prior to the experiment. Before QPS, MDS-Unified Parkinson’s Disease Rating Scale (MDS-UPDRS), motor thresholds (RMT/AMT) and baseline MEP size were measured. Then, QPS was given over the primary motor cortex. The procedures of QPS were the same as previous reports. We employed inter-stimulus intervals of 5 ms (QPS-5) to induce LTP-like effects. After QPS-5, we measured the amplitude of 20 MEPs every 5 min up to 30 min. We calculated grand average of MEP ratio (0min to 30min) and compared between “on” and “off” state. We also analyzed the relationship between MDS-UPDRS PartⅢ score and grand average of MEP ratio.

Results: Seven of 9 patients were evaluated in both “off” and “on” states, 1 was only in “on“ state and 1was only in “off“ state. The RMT and AMT are not different between “off“ and “on“ state (RMT: “off“ 51.3±12.8% vs “on“ 42.1±10.9%, p=0.15, AMT: “off“ 34.1±8.5%, “on“ 31±6.5%, p=0.43,). LTP-like effects induced by QPS-5 tended to be larger in “on” state (+45.8% of baseline MEP) than in “off” state (+8.4% of baseline MEP). MDS-UPDRS Part III score and mean MEP ratio after QPS-5, the degree of QPS-induced LTP-like effects, showed a moderately negative correlation (R^2= -0.58).

Conclusion: Our results were consist with previous studies that showed motor cortical plasticity deficit in “off” state PD patients and was restored by levodopa intake. In addition, our result suggested that the disturbance of LTP in the motor cortex could relate with motor symptoms of PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effects-of-levodopa-on-ltp-like-plasticity-induced-by-quadripulse-magnetic-stimulation-in-parkinsons-disease/