Operant Up-Conditioning of the Tibialis Anterior Motor-Evoked Potential in Multiple Sclerosis: Feasibility Case Studies

Figure 2

Changes in tibialis anterior (TA) motor-evoked potential (MEP), maximum voluntary contraction (MVC), and silent period (SP) over the course of study, and bilateral locomotor EMG activity in subject A. (a) Rectified EMG signals from the fourth baseline session (dashed black) and the last (i.e., 24th) conditioning session (solid red). Two hundred twenty-five responses were averaged together for each sweep. A pair of dashed vertical lines (green) indicates the time window for this subject’s MEP size calculation. The horizontal line at 30 μV indicates the background EMG level. (b) Mean MEP size (i.e., the mean of 225 control (in baseline sessions) or 225 conditioned (in conditioning sessions) MEP trials) (filled triangle) and MVC (cross) in 6 baseline (shaded part of the panel) and 24 conditioning sessions. (c) Mean SP duration (i.e., as marked in panel (a)). (d) Rectified locomotor EMG activity in soleus, TA, vastus lateralis (VL), and biceps femoris (BF) muscles of both legs before (dashed black) and after (solid red) conditioning. The step cycle is divided into 12 equal bins, starting from foot contact. Generally, bins 1–7 (i.e., up to 60% of the step cycle) are for the stance phase and bins 8–12 (i.e., 60–100% of the step cycle) are for the swing phase. After successful MEP up-conditioning, EMG modulation over the step cycle becomes greater in the muscles of both legs.

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