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. 2014 Jan 24;6:5. doi: 10.3389/fnagi.2014.00005

Figure 2.

Figure 2

(A) Mean and standard error of motor evoked potentials (MEPs) during unilateral force production for young (blue) and middle-aged subjects (red). The left side of the panel shows MEPs obtained during an ipsilateral contraction at increasing force levels. Only MEPs were included that were not preceded by any voluntary activity; all MEPs of 8 out of 40 experiments (seven subjects: five middle-aged, two young adults) were excluded because more than half of the MEPs at high force levels showed small signs of EMG activity. The right side of the panel the MEPs obtained during a contralateral contraction (only for the MEPs of the same subjects as included in the ipsilateral contraction). The MEPs increased with ipsilateral and contralateral force without significant difference between young and middle-aged subjects. (B) Mean and standard error of RMS-EMG (100 ms before MEP) upon which the MEPs were evoked at increasing force levels of the hand ipsilateral to the motor cortex receiving the TMS pulse (left panel) and the contralateral hand (right panel) for young (blue) and middle-aged subjects (red). The background RMS-EMG was close to zero during the ipsilateral contraction and increased proportional with the force during the contralateral contraction. No differences were observed between young and middle-aged subjects.