Dependence of cortical neuronal strength-duration properties on TMS pulse shape
•The TMS pulse shape and selection of pulse widths influences the properties of the cortical strength-duration curve.•Larger hyperpolarizing TMS pulse trailing phase increases motor thresholds resulting in longer cortical strength-duration time constant and smaller rheobase.•Modulation of transient...
Saved in:
Published in | Clinical neurophysiology Vol. 150; pp. 106 - 118 |
---|---|
Main Authors | , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Netherlands
Elsevier B.V
01.06.2023
|
Subjects | |
Online Access | Get full text |
Cover
Loading…
Summary: | •The TMS pulse shape and selection of pulse widths influences the properties of the cortical strength-duration curve.•Larger hyperpolarizing TMS pulse trailing phase increases motor thresholds resulting in longer cortical strength-duration time constant and smaller rheobase.•Modulation of transient sodium channels by the trailing hyperpolarising phase is likely to mediate the effects of TMS pulse shape on cortical strength-duration curve properties.
The aim of present study was to explore the effects of different combinations of transcranial magnetic stimulation (TMS) pulse width and pulse shape on cortical strength-duration time constant (SDTC) and rheobase measurements.
Resting motor thresholds (RMT) at pulse widths (PW) of 30, 45, 60, 90 and 120 µs and M−ratios of 0.2, 0.1 and 0.025 were determined using figure-of-eight coil with initial posterior-to-anterior induced current. The M−ratio indicates the relative phases of the induced current with lower values signifying a more unidirectional stimulus. Strength-duration time constant (SDTC) and rheobase were estimated for each M−ratio and various PW combinations. Simulations of biophysically realistic cortical neuron models assessed underlying neuronal populations and physiological mechanisms mediating pulse shape effects on strength-duration properties.
The M−ratio exerted significant effect on SDTC (F(2,44) = 4.386, P = 0.021), which was longer for M−ratio of 0.2 (243.4 ± 61.2 µs) compared to 0.025 (186.7 ± 52.5 µs, P = 0.034). Rheobase was significantly smaller when assessed with M−ratio 0.2 compared to 0.025 (P = 0.026). SDTC and rheobase values were most consistent with pulse width sets of 30/45/60/90/120 µs, 30/60/90/120 µs, and 30/60/120 µs. Simulation studies indicated that isolated pyramidal neurons in layers 2/3, 5, and large basket-cells in layer 4 exhibited SDTCs comparable to experimental results. Further, simulation studies indicated that reducing transient Na+ channel conductance increased SDTC with larger increases for higher M−ratios.
Cortical strength-duration curve properties vary with pulse shape, and the modulating effect of the hyperpolarising pulse phase on cortical axonal transient Na+ conductances could account for these changes, although a shift in the recruited neuronal populations may contribute as well.
The dependence of the cortical strength-duration curve properties on the TMS pulse shape and pulse width selection underscores the need for consistent measurement methods across studies and the potential to extract information about pathophysiological processes. |
---|---|
Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1388-2457 1872-8952 |
DOI: | 10.1016/j.clinph.2023.03.012 |