Description:

In a TMS pulse waveform, the amplitude can be defined as the maximum intensity or strength of the magnetic field generated by the TMS coil. TMS pulse amplitude is expressed in units of Tesla (T) or as a percentage of the maximum output of the device (MSO, maximum stimulator output).

The amplitude of the TMS pulse is a critical parameter as it determines the intensity of the magnetic field that is applied to the brain. The strength of the magnetic field is directly related to the level of neural activation that is produced, with higher amplitudes leading to greater levels of neural activation [1].

However, the relationship between the amplitude of the TMS pulse and neural activation is complex and depends on various factors, such as the position and orientation of the TMS coil, the frequency of the pulse, and the individual characteristics of the person being stimulated [2].

In clinical and research settings, the amplitude of the TMS pulse is typically adjusted to achieve a desired level of cortical activation, while also ensuring that the stimulation remains within safe limits [3].

References:

[1] Hallett M. Transcranial magnetic stimulation: a primer. Neuron. 2007;55(2):187-199. doi:10.1016/j.neuron.2007.06.026

[2] Lu M, Ueno S, Thorlin T, Persson M. Calculating the activating function in the human brain by transcranial magnetic stimulation. IEEE Transactions on Magnetics. 2008;44(6):1438-1441. doi:10.1109/tmag.2007.916022

[3] Rossini PM, Burke D, Chen R, et al. Non-invasive electrical and magnetic stimulation of the brain, spinal cord, roots and peripheral nerves: Basic principles and procedures for routine clinical and research application. An updated report from an I.F.C.N. Committee. Clin Neurophysiol. 2015;126(6):1071-1107. doi:10.1016/j.clinph.2015.02.001

Description:

In a TMS pulse waveform, the pulse width can be defined as the duration of the pulse, or the amount of time that the magnetic field is applied to the brain for neural activation [4].

The pulse width is typically expressed in units of microseconds (μs) or milliseconds (ms).

It's also important to note that pulse width can be different from the inter-pulse interval, which is the time between successive TMS pulses in a train of pulses and can also be an important parameter in determining the effects of TMS on neural activity [5].

References:

[4] Casula EP, Rocchi L, Hannah R, Rothwell JC. Effects of pulse width, waveform and current direction in the cortex: A combined cTMS-EEG study. Brain Stimul. 2018;11(5):1063-1070. doi:10.1016/j.brs.2018.04.015

[5] Peterchev AV, Luber B, Westin GG, Lisanby SH. Pulse Width Affects Scalp Sensation of Transcranial Magnetic Stimulation. Brain Stimul. 2017;10(1):99-105. doi:10.1016/j.brs.2016.09.007