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.

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 — typically ranging from 35% to 65% of machine power across patients. 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:

1. 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.

2. 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.

3. 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 most evidence-backed dosing level — high enough to reliably activate neurons, low enough to avoid seizure risk.

Some patients receive higher doses:

• 130% MT: Used for patients with high treatment resistance or inadequate response at 120%
• 100% MT (at threshold): Sometimes used for patients with low motor thresholds or those particularly sensitive to side effects

Theta Burst Stimulation (TBS) uses different dosing protocols — typically 80% MT, since the burst pattern is more efficient at activating neurons.

Does Your Motor Threshold Change Over Time?

Motor threshold is relatively stable within an individual — it doesn’t drift significantly over weeks of treatment. However, it can change over longer periods due to:

• Hormonal fluctuations: Some research suggests estrogen levels can affect motor threshold, which is why some women may notice subtle efficacy variations across menstrual cycles
• Medication changes: Certain medications (particularly those affecting neuronal excitability) can alter MT
• Significant weight changes: Very large changes in body composition can marginally affect the magnetic field path

Most providers don’t re-check motor threshold during a standard acute course. However, if treatment pause extends beyond 2–3 weeks, or if medications change significantly, a redetermination is appropriate.

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.

Be consistent about caffeine: High caffeine intake can raise your seizure threshold (not MT, but related), making your effective dose slightly different on high-caffeine days. Most providers don’t require caffeine restriction, but very high intake may reduce TMS efficacy.

Don’t change medications during treatment without telling your provider. Some psychiatric medications interact with TMS mechanisms in ways that might affect your dose-response relationship.

What If Your MT Is Very High or Very Low?

High MT (>55% of machine output): This typically means you have more resistance to magnetic field penetration. Your provider may need to use higher machine settings, which sometimes means more scalp discomfort. Some evidence suggests very high-MT patients may benefit from slightly longer treatment courses to achieve the same neural activation.

Low MT (<40% of machine output): Lower motor thresholds generally mean your brain is more easily stimulated. This can actually be an advantage — lower machine settings may produce fewer side effects while achieving good efficacy. However, it also means your provider will be extra cautious about seizure risk.

The Bottom Line

Motor threshold measurement is one of the most important personalization steps in your TMS treatment. It’s not an arbitrary number — it’s a direct measurement of your brain’s responsiveness, used to calibrate the dose specifically right for you. 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 — and informed patients tend to be more engaged, which itself predicts better outcomes.