Influence of short-interval intracortical inhibition on short-interval intracortical facilitation in human primary motor cortex.
- PubMed: 20505127
Abstract
Using the paired-pulse paradigm, transcranial magnetic stimulation (TMS) has revealed much about the human primary motor cortex (M1). A preceding subthreshold conditioning stimulus (CS) inhibits the excitability of the motor cortex, which is named short-interval intracortical inhibition (SICI). In contrast, facilitation is observed when the first pulse (S1) is followed by a second one at threshold (S2), named short-interval intracortical facilitation (SICF). SICI and SICF have been considered to be mediated by different neural circuits within M1, but more recent studies reported relations between them. In this study, we performed triple-pulse stimulation consisting of CS-S1-S2 to further explore putative interactions between these two effects. Three intensities of CS (80-120% of active motor threshold: AMT) and two intensities of S2 (120 and 140% AMT) were combined. The SICF in the paired-pulse paradigm exhibited clear facilitatory peaks at ISIs of 1.5 and 3 ms. The second peak at 3 ms was significantly suppressed by triple-pulse stimulation using 120% AMT CS, although the first peak was almost unaffected. Our present results obtained using triple-pulse stimulation suggest that each peak of SICF is differently modulated by different intensities of CS. The suppression of the second peak might be ascribed to the findings in the paired-pulse paradigm that CS mediates SICI by inhibiting later I waves such as I3 waves and that the second peak of SICF is most probably related to I3 waves. We propose that CS might inhibit the second peak of SICF at the interneurons responsible for I3 waves.
Influence of short-interval intracortical inhibition on short-interval intracortical facilitation in human primary motor cortex.
Influence of short-interval intracortical inhibition on short-interval intracortical 1
facilitation in human primary motor cortex 2
3
Authors: 4
Yuichiro Shirota
1
, Masashi Hamada
1
, Yasuo Terao
1
, Hideyuki Matsumoto
1
, Shinya 5
Ohminami
1
, Toshiaki Furubayashi
2
, Setsu Nakatani-Enomoto
2
, Yoshikazu Ugawa
2
, 6
Ritsuko Hanajima
1
7
8
1
Department of Neurology, Division of Neuroscience, Graduate School of Medicine, 9
University of Tokyo, Tokyo, Japan 10
2
Department of Neurology, School of Medicine, Fukushima Medical University, 11
Fukushima, Japan 12
13
Running head: Influence of SICI on SICF 14
15
Word counts: 5485 words 16
17
Contact information: 18
Yuichiro Shirota, MD 19
Department of Neurology, Division of Neuroscience, Graduate School of Medicine, 20
University of Tokyo 21
7-3-1 Hongo, Bunkyo-Ku, Tokyo 113-8655, Japan 22
Phone: +81 3-5800-8672, FAX: +81 3-5800-6548 23
E-mail: yshirota-tky@umin.ac.jp 24
25
26
Articles in PresS. J Neurophysiol (May 26, 2010). doi:10.1152/jn.00164.2010
Copyright ' 2010 by the American Physiological Society.
Abstract 27
Using the paired-pulse paradigm, transcranial magnetic stimulation (TMS) has 28
revealed much about the human primary motor cortex (M1). A preceding 29
subthreshold conditioning stimulus (CS) inhibits the excitability of the motor cortex, 30
which is named short-interval intracortical inhibition (SICI). In contrast, facilitation is 31
observed when the first pulse (S1) is followed by a second one at threshold (S2), 32
named short-interval intracortical facilitation (SICF). SICI and SICF have been 33
considered to be mediated by different neural circuits within M1, but more recent 34
studies reported relations between them. In this study, we performed triple-pulse 35
stimulation consisting of CS-S1-S2 to further explore putative interactions between 36
these two effects. Three intensities of CS (80%–120% of active motor threshold: AMT) 37
and two intensities of S2 (120% and 140% AMT) were combined. The SICF in the 38
paired-pulse paradigm exhibited clear facilitatory peaks at ISIs of 1.5 and 3 ms. The 39
second peak at 3 ms was significantly suppressed by triple-pulse stimulation using 40
120% AMT CS, although the first peak was almost unaffected. Our present results 41
obtained using triple-pulse stimulation suggest that each peak of SICF is differently 42
modulated by different intensities of CS. The suppression of the second peak might be 43
ascribed to the findings in the paired-pulse paradigm that CS mediates SICI by 44
inhibiting later I waves such as I3 waves and that the second peak of SICF is most 45
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