Neural plastic changes have been studies in neurological disorders using many kinds of non-invasive brain stimulations (NIBS). Those results were sometimes inconsistent. Our group developed a new NIBS technique named as Quadripulse stimulation (QPS) which consists of bursts of four monophasic transcranial magnetic stimulation (TMS) pulses repeated every five minutes for 30 minutes. Bidirectional plasticity, namely long-term potentiation (LTP) and depression (LTD), can be induced by QPS depending on the interstimulus intervals of the four pulses. Here, I will present several issues about QPS.
Interindividual variability: The interindividual variability is one challenge to all NBS techniques for plasticity induction. We will show a direct comparison between QPS and the most popular NBS [theta burst stimulation (TBS)] in the same individuals. QPS was more robust than QPS.
Age dependency: Comparisons of the degree of plasticity induction and responder rate among the different aged subjects showed that elder subjects had lower degree of plasticity induction than younger ones, as expected.
Anti-parkinsonian drugs on effects of QPS: L-dopa enhanced both LTP/LTD by QPS in normal volunteers, which is consistent with animal experimental knowledge that L-dopa contributes to the bidirectional plasticity. Dopa agonists did not enhance any plasticity in normal volunteers. It may be explained that D1/5 function is requisite for both LTP/LTD, but dopamine agonist has mainly D2/3 function and almost no D1/5 function.
Parkinson’s disease (PD), progressive supranuclear palsy (PSP) and others: We applied QPS to several movement disorders. The LTP/LTD were involved in PD, but they were restored by L-dopa. The degree of LTP had a negative correlation with parkinsonian symptoms, especially rigidity and akinesia. The plasticity was also involved and the degree of LTP had a correlation with rigidity and akinesia in PSP. The QPS plasticity may be one of physiological biomarkers of parkinsonian motor symptoms.
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