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March 22, 2026 · 6 min read
Why motor threshold drifts mid-course — and what to do about it
Motor threshold isn't a one-time number. A short protocol for re-checking it and documenting the change without slowing the day.
By Faisal Rafiq, MD
Most programs measure motor threshold on day one and treat it as fixed. In practice, MT drifts — sometimes within the first two weeks of a course.
When to recheck
Recheck MT if the patient reports a sudden change in scalp sensation, if you change coil position, or at the midpoint of any course longer than 20 sessions.
The 90-second protocol
- Reseat the patient with the same headrest position used on day one.
- Find the hotspot using the same landmarks, not from memory.
- Document the new value in the chart alongside the original, with the reason for the recheck.
Why it matters for outcomes
A 5% drift in MT can change the effective dose at the cortex more than you'd expect. Retitrating early prevents an entire course from underdosing in silence.