REFERENCE · DIAGNOSTIC TECHNIQUE

Midline and Vibration Splitting: Interpretation and Limits

Clinician-focused educational reference; assessment requires suitable training and consent.

Purpose and Suitability
Anatomy and Physiology
Preparation and Safety
Performing the Assessment
Interpreting Findings
Explaining the Result
Evidence and Limitations
Media and Accessibility
Research and Sources

Purpose and Suitability

This page explains two traditional sensory observations and why neither should independently establish FND. It is not a recommendation to add them routinely or repeat them until a particular answer appears.

Midline splitting: A reported abrupt change in feeling at the centre line of the body. Vibration splitting: A reported difference when vibration is compared across a continuous bony surface.

Anatomy and Physiology

The historical vibration comparison assumes that a connected bony surface transmits vibration across it. This assumption does not make a person’s perceived asymmetry diagnostic. Midline sensory loss can also occur with a thalamic lesion. [1][3]

Thalamus: A deep brain structure involved in relaying and processing sensory information.

An anatomical argument must be tested against actual comparison groups rather than treated as proof.

Preparation and Safety

Obtain consent and explain the clinical question. Consider painful skin, injury, fatigue and sensory intolerance. Use only gentle, clinically appropriate stimuli. Stop for discomfort or at the person’s request. Do not ask supporters to repeat the comparison at home.

Performing the Assessment

If clinically indicated, a trained examiner can document light-touch perception on comparable sites on either side of the midline, using neutral instructions. A vibration comparison records perception at paired sites over a continuous bony surface, traditionally the forehead or sternum. Document the sites, stimulus and response rather than merely writing “positive splitting.” [1]

This is a description of the observations, not a standardized validated protocol. A difference in intensity and complete absence on one side are different findings. There is no justified diagnostic cutoff supplied here.

Interpreting Findings

Finding present: Consider it a description requiring context; it is not sufficient to rule in FND.

Finding absent: FND remains possible.

Comparison unreliable: Record the technical or clinical limitation and avoid a diagnostic conclusion.

The inherited literature cautions that traditional criteria lack specificity. A seemingly clear dividing line must not delay assessment of an acute neurological change. [2][3]

These observations do not quantify symptom severity, injury risk or assistance needs. Continue assessment of what the altered sensation means for daily activities.

Explaining the Result

An authored example:

“You felt a difference between the two sides. That finding occurs in more than one condition, so it cannot tell us the cause on its own. We will put it together with your history and the rest of the assessment.”

Evidence and Limitations

The 2026 comparison found poor specificity for classic splitting signs. Participants already had motor-FND or recent stroke; this does not establish accuracy in an unselected sensory clinic. See the study summary. [1]

Specificity: How often a finding is absent in the comparison group without the target diagnosis.

The older Chabrol source is retained from the inventory; its full methods have not been rechecked in this expansion. No numerical accuracy estimate is inferred from its title. [2]

Media and Accessibility

A diagram should label this as an observation with limited diagnostic value. Avoid a “functional versus stroke” body-map illustration that suggests the shape alone distinguishes them. Any demonstration needs consent, captions and a clear statement of the limits. No media has been added.

Research and Sources

Citation	Full citation
[1]	Nielsen G, Higgins R, Stone J, Coebergh J, Edwards MJ. Functional sensory symptoms and signs: a case-control study of 102 patients. Brain Communications. 2026;8(1):fcag031. FND-CIT-0023. https://doi.org/10.1093/braincomms/fcag031
[2]	Chabrol H, Peresson G, Clanet M. Lack of specificity of the traditional criteria for conversion disorders. European psychiatry : the journal of the Association of European Psychiatrists. 1995;10(6):317-319. DOI. PMID: 19698360. FND-CIT-0126.
[3]	Koh PX, Ti J, Saffari SE, Lim ZYIC, Tu T. Hemisensory syndrome: Hyperacute symptom onset and age differentiates ischemic stroke from other aetiologies. BMC Neurology. 2021;21:179. DOI. FND-CIT-0243.