Affiliations: [a] NeuRRo Lab, Department of Physical Medicine and Rehabilitation, Michigan Medicine, Ann Arbor, MI, USA
| [b] Michigan Robotics Institute, University of Michigan, Ann Arbor, MI, USA
| [c] School of Kinesiology, University of Michigan, Ann Arbor, MI, USA
| [d] Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
Correspondence:
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Corresponding author: Chandramouli Krishnan, PT, PhD, Director, Neuromuscular & Rehabilitation Robotics Laboratory (NeuRRo Lab), Department of Physical Medicine and Rehabilitation, Michigan Medicine, University of Michigan, 325 E Eisenhower Parkway (Suite 3013), Ann Arbor, MI – 48108, USA. Tel.: +1 319 321 0117; Fax: +1 734 615 1770; E-mail: [email protected].
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.
Keywords: Cortical excitability, knee, paired-pulse stimulation, two phases, twitch, bayesian
