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KMID : 0311120070480050795
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Yonsei Medical Journal
2007 Volume.48 No. 5 p.795 ~ p.801
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Different Modulation of the Cortical Silent Period by Two Phases of Short Interval Intracortical Inhibition
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Kang Suk-Yun
Shin Hae-Won
Sohn Young-Ho
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Abstract
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Purpose: To investigate the influence of 2 phases of short interval intracortical inhibition (SICI) on the cortical silent period (SP).
Materials and Methods: Single- and paired-pulse transcranial magnetic stimulations (TMSs) at 1 and 2.5ms interstimulus intervals (ISIs) were applied to the left motor cortex in 12 healthy subjects while their right hand muscles were moderately activated. Conditioning stimulation intensity was 90% of the active motor threshold (AMT). Test stimulation intensities were 120, 140, 160, 180, 200, 220, 240, 260% of the AMT and at 100% of the maximal stimulator output, the order of which was arranged randomly. The rectified electromyography area of motor evoked potential (MEP) and duration of the SP were measured off-line using a computerized program.
Results: At high-test stimulation intensities, MEP areas were saturated in both single- and paired-pulse stimulations, except that saturated MEPs were smaller for the paired-pulse TMS at 1ms ISI than for the other conditions. As the test stimulation intensity increased, SP was progressively prolonged in both single- and paired-pulse stimulations but was shorter in paired-pulse than single-pulse TMS. Overall, the ratio of SP duration/MEP area was comparable between single- and paired-pulse TMS except for the paired-pulse TMS at 1 ms ISI with a test stimulation intensity at 140-180% of the AMT, in which the ratio was significantly higher than in the single pulse TMS.
Conclusion: These results suggest that 2 phases of SICI modulate MEP saturation and SP duration differently and provide additional evidence supporting the view that 2 phases of SICI are mediated by different inhibitory mechanisms
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KEYWORD
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Transcranial magnetic stimulation, motor cortex, neurophysiology, motor evoked potential
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