Everything you need to know about Understanding Your TMS Treatment Dose: What Motor Threshold Means — how it works, what it costs, and how to find a provider who actually knows what they're doing.
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If you’ve started TMS treatment, you’ve probably noticed that your provider sometimes mentions a number — your “motor threshold.” You may have heard it referenced in passing, or noticed your technician adjusting settings between sessions. What exactly is motor threshold, and why does it matter?
Understanding your treatment dose — and why it was calibrated specifically for you — can demystify the process and help you feel more informed about the treatment you’re receiving.
What You’ll Learn
- What motor threshold is and how it is measured during your first session
- Why motor threshold calibration is essential for personalized treatment dosing
- How your dose is calculated as a percentage of your motor threshold
- What high or low motor threshold values mean for your treatment
- Practical factors that can affect your motor threshold over time
What Is Motor Threshold?
Motor threshold (MT) is the minimum intensity of magnetic stimulation needed to produce a measurable motor response — specifically, a visible twitch of the thumb or hand. During your first TMS session, your technician maps this by delivering brief pulses to your motor cortex (the brain area controlling movement, located near the top of your head) and gradually adjusting the intensity until your thumb reliably twitches.
The motor threshold is measured as a percentage of the machine’s maximum output — which varies widely from patient to patient. This range exists because everyone’s brain anatomy, skull thickness, and distance from coil to cortex differ.
Why Is Motor Threshold Important?
Motor threshold is your personal biological measurement. It matters because:
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It calibrates your dose: Your treatment dose is calculated as a percentage of YOUR motor threshold, not an absolute number. Two patients receiving “100% MT dose” are receiving doses personalized to their individual brain responses.
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It accounts for individual variation: Someone with a thicker skull or more cerebrospinal fluid requires higher machine settings to achieve the same brain activation as someone with a thinner skull. MT measurement accounts for this.
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It’s a proxy for DLPFC dose: While your treatment targets the DLPFC (prefrontal cortex, behind your forehead), we use motor cortex response as a proxy because the two regions are anatomically related. MT gives us a reliable estimate of how much stimulation reaches your treatment target.
How Is Treatment Dose Calculated?
Your treatment dose is typically set at 120% of motor threshold for standard high-frequency TMS. This is the intensity used in the pivotal trials and labeled protocols for standard high-frequency TMS.
Doses can sometimes be adjusted:
- Lower intensities are sometimes used if side effects limit tolerability, at the clinician’s discretion
Theta burst stimulation (TBS) uses its own protocols. In depression trials and device labeling, iTBS has typically been delivered at 120% of resting motor threshold, but protocols differ, so follow your clinic’s labeled parameters.
Does Your Motor Threshold Change Over Time?
Motor threshold is relatively stable within an individual, but it can change over time, and some clinics re-check it periodically. Possible influences include:
- Hormonal and physiological changes: some research suggests hormones can affect cortical excitability
- Medication changes: Certain medications (particularly those affecting neuronal excitability) can alter MT
Practice varies on re-checking motor threshold during a course. A re-check is commonly considered if there is a long treatment pause or if medications change significantly; ask your clinic about its policy.
Can You Influence Your Motor Threshold?
There’s no proven way to voluntarily change your motor threshold — it’s determined by anatomy. However, a few practical notes:
Avoid head positioning changes: The magnetic field path is sensitive to coil angle and position. Consistent head positioning helps ensure you’re always receiving the dose your MT calculation assumes.
Tell your clinician about caffeine, alcohol, sleep, and medications: these can affect cortical excitability and seizure risk, and your clinician may give specific guidance.
Don’t change medications during treatment without telling your provider. Some medications affect seizure risk or cortical excitability.
What If Your MT Is Very High or Very Low?
A high or low motor threshold is not by itself good or bad. A higher threshold generally means higher machine settings are needed, which can mean more scalp discomfort; a lower threshold means lower settings. Your clinician adjusts the dose relative to your own threshold and screens for seizure risk either way.
The Bottom Line
Motor threshold measurement is a core personalization step in your TMS treatment. It’s not an arbitrary number — it’s a measurement of your motor cortex’s responsiveness, used to calibrate your dose. If you’re curious about your motor threshold number, ask your technician. Understanding the numbers behind your treatment is part of being an informed patient.
Frequently Asked Questions
What does it mean if my motor threshold is high?
A higher motor threshold generally means higher machine settings are needed, which can mean more scalp discomfort. A lower threshold means lower settings. Your clinician adjusts the dose relative to your own threshold and screens for seizure risk either way.
Can I do anything to change my motor threshold?
There is no proven way to voluntarily change your motor threshold. Keep your head position consistent during sessions, and tell your provider about medication, caffeine, or sleep changes, since some factors can affect cortical excitability and seizure risk.
How is my treatment dose related to my motor threshold?
Your treatment dose is typically set at 120% of motor threshold for standard high-frequency TMS. Theta burst stimulation has its own protocols; in depression trials iTBS has typically been delivered at 120% of resting motor threshold, so follow your clinic's labeled parameters.
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