REFERENCE · DIAGNOSTIC TECHNIQUE

Entrainment in Functional Tremor

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Purpose and Suitability

Entrainment means that an involuntary tremor takes on the rhythm of a deliberate movement made by another limb. The clinician compares the tremor with the rhythm the person actually produces, not simply with the metronome’s setting. A pause, irregularity or smaller movement is recorded separately. [1]

Metronome: A device or cue that marks a regular beat. Frequency: How many movement cycles occur in one second; measured in hertz (Hz).

The method described here concerns limb tremor, especially the hands. It is a diagnostic comparison for a trained clinician. Rehabilitation may use rhythm for a different purpose; that is covered in the recovery technique.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Anatomy and Physiology

The hand’s movement reflects muscle contractions around its joints. Tapping the other hand introduces a second rhythm that can be compared with the ongoing tremor. In laboratory assessment, skin electrodes record muscle activity and movement sensors record motion in both limbs. [2]

Contralateral: On the opposite side. Coherence: A signal-analysis measure of how consistently two recordings share a rhythm.

The important question is whether the original tremor changes into the tapping rhythm. A movement transmitted through a shared surface, or an extra mirrored movement, may create a misleading appearance of matching rhythms. A case report demonstrates why the original tremor signal still matters. [4]

Mirror movement: An unintended movement on one side that accompanies a deliberate movement on the other.

The comparison shows how the involuntary shaking responds to another movement rhythm. [1]

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Preparation and Examination

Explain the comparison, obtain consent and agree a stop signal. Check whether the less affected limb can carry out the task. Use a comfortable seated position with appropriate support; record any adaptation needed for pain, fatigue, weakness or sensory access.

Observe the original tremor. Record its position, size and approximate rhythm before adding a tapping task.
Explain and practise the tapping instruction. Ask the less affected hand to make small movements to a tolerable pacing cue. Small taps reduce mechanical transmission between limbs. [1]
Compare at different rhythms. Observe both limbs while the tapping rate changes. The 2011 laboratory protocol used 1, 3 and 5 Hz with recordings under defined conditions. A comfortable bedside demonstration is not equivalent to completing that protocol. [2]
Check the rhythm actually produced. If the person cannot follow the requested beat, record that. Do not call the tremor entrained to a rhythm the tapping limb never maintained.
Separate the possible responses. Describe matching of the tremor to tapping, a frequency shift without matching, suppression, irregularity or no clear change. Return to baseline and repeat only enough for interpretation.
Resolve uncertainty rather than forcing a result. When matching is uncertain or another tremor may coexist, a specialist may use surface EMG and movement recordings. Stop if the task becomes painful, exhausting or otherwise intolerable.

Keep the camera or recording position stable. Never steady a limb by force to produce a preferred response.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Interpretation and Explanation

Matching at one rate close to the original tremor is difficult to interpret. Following more than one distinctly different tapping rhythm provides a clearer comparison. Suppression during tapping can be relevant to distractibility; it should not be relabelled as entrainment. [1][2]

Record uncertainty if the original tremor persists beneath an added rhythm. In the 2018 case report, recordings revealed a continuing tremor component alongside the apparent rhythm coupling. The authors considered mirror movement and functional overlap. That single case illustrates a pitfall rather than its frequency. [4]

A small later series described “mixed entrainment,” with both original and tapping-frequency peaks. It does not settle the differential or make every extra peak evidence of FND. [5]

An authored example explanation is: “When your other hand changed its tapping rhythm, the shaking followed it. That pattern helps explain why we think this tremor is functional. We still need to understand what it prevents you doing and whether another condition is present.”

A positive comparison does not establish reliable writing, eating or sustained hand use. Record assistance and everyday impact separately; see assessment and everyday function.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Evidence and Limitations

The 2026 meta-analysis found variable results across methods, with comparatively good performance for combined electrophysiological tests. Its pooled results cover different tests and cannot be assigned to entrainment alone. [6]

The 2016 prospective validation supports a complete battery assessed by raters blinded to diagnosis. The distractibility evidence section reports its cohort and accuracy figures. Most validation concerns limb tremor; mixed tremors and other body sites require their own assessment. [1][3]

In the earlier 2011 development study, entrainment occurred in five of 13 functional tremors and none of 25 comparison tremors. Many functional tremors did not entrain, so its absence cannot exclude the diagnosis. [2]

Murgai and Iskhakova’s later ten-patient series found pure, mixed or both entrainment patterns in seven patients. Without a comparison group, it cannot establish how specifically those patterns identify functional tremor. [5]

Specificity: How often a test is negative in people without the condition being assessed.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Media and Accessibility

Use one continuous medium-width shot that includes the tremulous limb, the tapping limb and the clinician’s instructions. Add a small on-screen rhythm label—such as “slow,” “medium” and “fast”—and preserve the original audio so viewers can match the tapping to any tremor change.

Show baseline, clearly explained tapping at different rates, and return to baseline before any replay. Keep the actual tapping visible so the requested beat is not confused with the performed movement. Obtain separate consent for recording and public use.

Do not use rapid cuts, speed changes or music over the examination. Those edits would make frequency comparison unreliable. Captions should describe the task rather than declare that the sign “proves FND.”

Provide a transcript describing each condition and what changed. Keep pacing sound comfortable and optional for viewers; a video should not need flashing cues.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Research and Sources

Begin with the IFCN clinical review and 2026 evidence synthesis. Functional tremor is involuntary, and diagnosis rests on the movement pattern within a clinical assessment. The older development study contributes laboratory observations; the later small series explores a question about mixed rhythms. [1]

Citation	Figure	Full citation
[1]	—	Edwards MJ, Koens LH, Liepert J, Nonnekes J, Schwingenschuh P, van de Stouwe AMM, Morgante F. Clinical neurophysiology of functional motor disorders: IFCN Handbook Chapter. Clinical Neurophysiology Practice. 2024;9:69–77. https://doi.org/10.1016/j.cnp.2023.12.006 FND-CIT-0022.
[2]	—	Schwingenschuh P, Katschnig P, Seiler S, et al. Moving toward “laboratory-supported” criteria for psychogenic tremor. Movement disorders : official journal of the Movement Disorder Society. 2011;26(14):2509-2515. FND-CIT-0177.
[3]	—	Schwingenschuh P, Saifee TA, Katschnig-Winter P, et al. Validation of “laboratory-supported” criteria for functional (psychogenic) tremor. Movement disorders : official journal of the Movement Disorder Society. 2016;31(4):555-562. DOI. PMID: 26879346. FND-CIT-0178.
[4]	—	Merchant SH, Haubenberger D, Hallett M. Mirror movements or functional tremor masking organic tremor. Clinical neurophysiology practice. 2018;3:107-113. DOI. PMID: 30215019. FND-CIT-0154.
[5]	—	Murgai A, Iskhakova S. Entrainment characteristics of functional tremor. Movement Disorders Clinical Practice. 2025;12(2):253–254. Published online November 4, 2024. DOI. Full text. FND-CIT-0222.
[6]	—	Rujirussawarawong S, Ounmuang C, Aungsumart S, Kasemsuk C, Limotai N. Electrophysiology in distinguishing functional tremor from organic tremor: a systematic review and meta-analysis of diagnostic accuracy. Movement Disorders Clinical Practice. Published online June 11, 2026. DOI. PubMed. FND-CIT-0224.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources