Variability in Response to Quadripulse Stimulation of the Motor Cortex.
Responses to plasticity-inducing brain stimulation protocols are highly variable. However, no data are available concerning the variability of responses to quadripulse stimulation (QPS).



We assessed the QPS parameters of motor cortical plasticity induction in a systematic manner, and later investigated the variability of QPS using optimal parameters.



First, two different interburst intervals (IBI) with the same total number of pulses were compared. Next we investigated three different IBIs with a different total number of pulses but with same duration of intervention. We also compared the after-effects of monophasic and biphasic QPS. Finally, variability of QPS was tested in 35 healthy subjects. Twenty motor evoked potentials (MEPs) were measured every 5-10 min for up to one hour after intervention.



QPS at an IBI of 5 s produced MEPs changes that are dependent on the interstimulus interval of the four magnetic pulses, consistent with previous reports. Unexpectedly, QPS at an IBI of 2.5 s did not induce any plasticity, even with the same total number of pulses, that is, 1440. QPS at an IBI of 7.5 s produced a variable response but was likely to be comparable to conventional QPS. Biphasic QPS had shorter lasting after-effects compared with monophasic QPS. Finally, the after-effects of QPS were relatively consistent across subjects: more than 80% of subjects responded as expected in the excitatory QPS at an IBI of 5 s.



The IBI, total duration of the procedure and pulse waveform strongly affected the magnitude or duration of the plasticity induced by QPS. In this cohort, 80% of subjects responded to excitatory QPS as expected.
Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan.
Koichiro
K
Nakamura
Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan; Department of Neurology, Center for Movement Disorders and Neuromodulation, Institute of Clinical Neuroscience, Medical Psychology Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany.
Stefan Jun
SJ
Groiss
Department of Neurology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
Masashi
M
Hamada
Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan.
Hiroyuki
H
Enomoto
Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan.
Suguru
S
Kadowaki
Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan.
Mitsunari
M
Abe
Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan.
Takenobu
T
Murakami
Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan.
Winnugroho
W
Wiratman
Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan.
Fangyu
F
Chang
Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan.
Shunsuke
S
Kobayashi
Department of Neurology, School of Medicine, Kitasato University, Sagamihara, Japan.
Ritsuko
R
Hanajima
Department of Neurology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
Yasuo
Y
Terao
Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan; Fukushima Global Medical Science Center, Advanced Clinical Research Center, Fukushima Medical University. Electronic address: ugawa-tky@umin.net.
Yoshikazu
Y
Ugawa
D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
Motor cortex; Plasticity; Quadripulse stimulation (QPS); Variability