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Driven by Distraction: Can the Brain Be Tricked into Responding?

When patients with conversion disorder are distracted, functional MRI shows that inactive areas of the brain can respond.

What is going on in the brain when a patient complains of a symptom for which there is no objective evidence? Conversion disorder is the prototypical disorder involving unexplained sensory or motor symptoms, and clinical tests such as the Hoover sign can reveal inconsistencies in the patient’s symptoms. To explore brain activity in three patients with unexplained unilateral sensory loss, investigators used functional MRIs and unilateral and bilateral vibrotactile stimulation of the affected regions.

The patients did not meet criteria for any other Axis I disorder and had no history of neurologic disease. Stimulation of the anesthetic region did not activate the appropriate brain area (contralateral S1 region). However, bilateral stimulation activated the S1 region bilaterally, just as it did in six healthy comparison subjects.

Comment: Various PET and SPECT studies in conversion disorder have implicated activity in the anterior cingulate, thalamus, basal ganglia, or frontal lobe but have not utilized both bilateral and unilateral stimulation. The authors suggest that bilateral stimulation serves as a distractor and overcomes the inhibition of the appropriate brain region. PET or SPECT performed under this research design might provide additional information as to which brain regions are involved.

These results bring up many interesting issues about conversion disorder and the interpretation of abnormalities on functional imaging. First, regarding the diagnosis of sensory conversion disorder, we do not know whether underlying psychodynamic reasons for the symptoms exist (and I doubt the reliability of such determinations in most cases). Would the results for "malingering" patients be similar? Second, one must be cautious in interpreting functional imaging tests to "diagnose" brain damage. The lack of activation of the contralateral S1 region on fMRI would not indicate brain pathology but reflects the experience of local anesthesia, which reverts to normal with bilateral stimulation.

— Jonathan Silver, MD

Published in Journal Watch Psychiatry January 12, 2007

Citation(s):

Ghaffar O et al. Unexplained neurologic symptoms: An fMRI study of sensory conversion disorder. Neurology 2006 Dec 12; 67:2036-8.

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• Medline abstract (Free)

Hurwitz TA and Prichard JW. Conversion disorder and fMRI. Neurology 2006 Dec 12; 67:1914-5.

• Original article (Subscription may be required)
• Medline abstract (Free)