Table 1.
Parameter Test Values.
Fig 1.
Stimulation signal and motor evoked potential responses.
Part (a) depicts the parameters of the constant-current, biphasic square waveform stimulus. Part (b) depicts the MEP onset and offset definition and the scale in part b applies to parts b-i. Parts b-i demonstrate that a variety of signal envelopes were evoked by the stimulus parameter ranges tested. The duration of the response was determined by subtracting the signal onset time from the offset time. The response onset was defined as the first instance where ten sequential sample points of the MEP signal remained above the trial’s baseline level. Similarly, the response offset was the last instance in which the MEP signal returned to the baseline level and remained there until the end of the trial.
Fig 2.
MEP main response duration (mean ± SE) as a function of stimulus amplitude.
The effects of amplitude paired with three frequency levels (a), pulse durations (b), interphase intervals (c) and train durations (d) are depicted. Note the difference in scale for trials involving train duration (part d). Square symbols represent conditions with an insufficient number of responding sites (n<5) and were not included in statistical analyses. Circular symbols represent conditions with reliable responses (n = 5–14). Control values for each parameter were: A = 50 μA, F = 303 Hz, P = 0.2 ms, I = 0 ms, T = 43 ms. A = amplitude, F = frequency, P = pulse duration, I = interphase interval, T = train duration, SE = standard error.
Fig 3.
MEP main response duration (mean ± SE) as a function of stimulus frequency.
The effects of frequency paired with three amplitude levels (a), pulse durations (b), interphase intervals (c) and train durations (d) are depicted. Note the difference in scale for trials involving train duration (part d). Square symbols represent conditions with an insufficient number of responding sites (n<5) and were not included in statistical analyses. Circular symbols represent conditions with reliable responses (n = 5–14). Control values for each parameter were: A = 50 μA, F = 303 Hz, P = 0.2 ms, I = 0 ms, T = 43 ms. A = amplitude, F = frequency, P = pulse duration, I = interphase interval, T = train duration, SE = standard error.
Fig 4.
MEP main response duration (mean ± SE) as a function of stimulus pulse duration.
The effects of pulse duration paired with three amplitude levels (a), frequencies (b), interphase intervals (c) and train durations (d) are depicted. Note the difference in scale for trials involving train duration (part d). Square symbols represent conditions with an insufficient number of responding sites (n<5) and were not included in statistical analyses. Circular symbols represent conditions with reliable responses (n = 5–14). Control values for each parameter were: A = 50 μA, F = 303 Hz, P = 0.2 ms, I = 0 ms, T = 43 ms. A = amplitude, F = frequency, P = pulse duration, I = interphase interval, T = train duration, SE = standard error.
Fig 5.
MEP main response duration (mean ± SE) as a function of stimulus train duration.
The effects of train duration paired with three current amplitudes (a), frequencies (b), pulse durations (c) and interphase intervals (d) are depicted. Square symbols represent conditions with an insufficient number of responding sites (n<5) and were not included in statistical analyses. Circular symbols represent conditions with reliable responses (n = 5–14). Control values for each parameter were: A = 50 μA, F = 303 Hz, P = 0.2 ms, I = 0 ms, T = 43 ms. A = amplitude, F = frequency, P = pulse duration, I = interphase interval, T = train duration, SE = standard error.
Fig 6.
MEP main response duration (mean ± SE) as a function of stimulus interphase interval.
The effects of interphase interval paired with three amplitude levels (a), frequencies (b), pulse durations (c) and train durations (d) are depicted. Note the difference in scale for trials involving train duration (part d). Square symbols represent conditions with an insufficient number of responding sites (n<5) and were not included in statistical analyses. Circular symbols represent conditions with reliable responses (n = 5–14). Control values for each parameter were: A = 50 μA, F = 303 Hz, P = 0.2 ms, I = 0 ms, T = 43 ms. A = amplitude, F = frequency, P = pulse duration, I = interphase interval, T = train duration, SE = standard error.
Table 2.
Summary of Parameter Influence on Response Duration.