Effect of paired-pulse stimulus parameters on the two phases of short interval intracortical inhibition in the quadriceps muscle group.
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ABSTRACT: BACKGROUND:Short interval intracortical inhibition (SICI) is commonly used to assess inhibition in the motor cortex and is known to be affected by the paired-pulse stimulus parameters (i.e., interstimulus interval [ISI], conditioning stimulus intensity [CSI] and test stimulus intensity [TSI]) used during testing. While the effects of stimulus parameters are well-studied in the upper-extremity, evidence in the lower-extremity is lacking. OBJECTIVE:To comprehensively examine the effects of alterations in paired-pulse stimulus parameters on the two phases of SICI in the quadriceps muscle group. METHODS:Seventeen adults (8 males, 9 females) volunteered to participate in this study. SICI was examined over a range of CSIs (70-90% active motor threshold [AMT]), TSIs (100-140% AMT), and ISIs (1.0-3.0?ms) using both EMG and torque responses elicited by transcranial magnetic stimulation (TMS). RESULTS:The results indicated that SICI at 1.0?ms ISI was best revealed with a CSI of 70% and TSI ?110% AMT, whereas SICI at 2.5?ms ISI was best revealed with a CSI of 80-90% and a TSI of ?130% AMT. Unlike upper-extremity muscles, evaluating SICI with a CSI of 70% AMT and an ISI of 1.0?ms produced the greatest inhibition for all TSIs. In general, inhibitory effects were contaminated by facilitatory effects when using a TSI of 100% AMT. CONCLUSIONS:The amount of inhibition was dependent on the stimulation parameters used during testing. A CSI of 70% AMT, ISI of 1.0?ms, and TSI of ?110% AMT appear to be optimal for measuring SICI in the quadriceps muscle; however, other parameters can be used if careful consideration is given to the described interaction between the parameters.
SUBMITTER: Krishnan C
PROVIDER: S-EPMC6995364 | biostudies-literature | 2019
REPOSITORIES: biostudies-literature
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