Estimation of the Motor Threshold for Near-Rectangular Stimuli Using the Hodgkin–Huxley Model

Figure 2

cTMS device pulses as monophasic, unidirectional, and bidirectional waveforms, normalized to unity amplitude which have been tested in different human experiments. (a) Monophasic pulses with positive pulse widths of 30, 60, and 120 μs in [5, 27] with initial PA direction. (b) Unidirectional pulses for negative pulse widths of 40, 80, and 120 μs in [8] with initial AP direction. (c) Three different unidirectional and bidirectional waveforms in [28]; RB : Rectangular bidirectional (m = 1). RU-N : Rectangular unidirectional with initial AP direction (m = 0.2). RU-R : Rectangular unidirectional with initial PA direction. (d) Unidirectional pulses for positive pulse widths of 60 μs and the minimum threshold pulse width (ThPW) in [29] with initial AP direction (m = 0.2). The ratio of the peak of the negative phase to the positive phase is called the m ratio. Generally, the stimulus intensity is proportional to the E-field, (a derivative of the B-field), i.e., the current density in the brain and input to the HH model.

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