Neural Noise

Spatial activation of MEPs and paired-pulse TMS orientation and intensity

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  • Spatial activation of motor evoked potentials (MEPs) depends on paired-pulse transcranial magnetic stimulation (TMS) orientation and intensity.1
  • TMS and MEP mapping methods inform motor cortex excitability and targeting.1 1

Gardner updates

  • The accuracy of motor evoked potential (MEP) determination is influenced by surface electrode montage; revisiting montage choice is relevant to clinical neurophysiology and motor mapping. 2

Weekly enrichment (2026-07-20)

  • Using multi-coil TMS (mTMS) to steer stimulation electronically without moving the coil, the study probed how conditioning-stimulus orientation, intensity, and interstimulus interval (ISI) shape the spatial activation of motor evoked potentials (MEPs) in forearm flexor muscles, recorded with a high-density surface EMG (HDsEMG) grid.34
  • Conditioning stimuli (CS) were delivered at anterior-to-medial (0°) and posterior-to-medial (90°) orientations at 70-90% of resting motor threshold (rMT), followed by test stimuli at 0° and 110% rMT, with ISIs of 0.5 ms and 8 ms probing neuronal refractoriness and intracortical facilitation.34
  • MEPs were facilitated at the 8 ms ISI and suppressed at the 0.5 ms ISI; at 0.5 ms, changing CS orientation from 0° to 90° reduced the suppression.34
  • Increasing CS intensity shifted MEP activation centroids medially in most cases, and centroids were more medial at 8 ms versus more lateral at 0.5 ms, indicating orientation, intensity, and ISI jointly control both MEP magnitude and spatial recruitment.34
  • The authors highlight mTMS-HDsEMG as a tool for probing corticomotor control mechanisms with diagnostic and therapeutic clinical implications; the article appears in Clinical Neurophysiology (2026).4
  • The mTMS approach derives from a 5-coil transducer that electronically shifts the induced electric-field maximum within an approximately 30 mm-diameter cortical region, delivering stimuli to multiple locations and orientations within milliseconds and with millimeter precision — faster and more precise than physically repositioning a coil.5
  • A clinical-use mTMS system built on the same overlapping-coil principle has been designed, constructed, and deployed, enabling interstimulus intervals as short as about 1 ms while targeting separate locations at different intensities for automated motor mapping.6
  • On the companion montage question, a pilot study using a 64-channel array over brachioradialis and biceps brachii found surface electrode montage strongly affects MEP peak-to-peak amplitude — a modest difference for brachioradialis (~175 µV bipolar vs ~200 µV pseudomonopolar) but a roughly five-fold difference for biceps brachii (~40 µV vs ~200 µV) — underscoring the need to standardize sEMG protocols since MEP amplitude sets motor threshold and rTMS dosing.7

Footnotes

  1. https://www.sciencedirect.com/science/article/pii/S138824572501329X?dgcid=rss_sd_all ↩ ↩2 ↩3

  2. https://www.sciencedirect.com/science/article/pii/S1388245725013355?dgcid=rss_sd_all ↩

  3. https://pubmed.ncbi.nlm.nih.gov/41421051/ ↩ ↩2 ↩3 ↩4

  4. https://doi.org/10.1016/j.clinph.2025.2111477 ↩ ↩2 ↩3 ↩4 ↩5

  5. https://pmc.ncbi.nlm.nih.gov/articles/PMC8807400/ ↩

  6. https://biomedical-engineering-online.biomedcentral.com/articles/10.1186/s12938-025-01393-6 ↩

  7. https://europepmc.org/article/MED/40928607 ↩

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