The involuntary nature of conversion disorder

Area of Science:

• Neuroscience
• Psychiatry
• Neurology

Background:

• Motor conversion disorders present movement symptoms without a neurological cause.
• Conversion movements feel involuntary despite using voluntary motor pathways.
• Self-agency, the sense of causing one's actions, is linked to comparing predicted and actual sensory feedback, involving the right inferior parietal cortex.

Purpose of the Study:

• To investigate the neural correlates of self-agency in conversion tremor.
• To compare brain activity during conversion tremor versus voluntary mimicked tremor.

Main Methods:

• Utilized a within-subject functional magnetic resonance imaging (fMRI) block design.
• Examined brain activity in 8 patients diagnosed with conversion tremor.
• Compared brain activity during conversion tremor and voluntary mimicked tremor.

Main Results:

• Conversion tremor showed hypoactivity in the right temporoparietal junction (TPJ) compared to voluntary tremor (p < 0.05).
• Reduced functional connectivity was observed between the right TPJ and sensorimotor/limbic regions during conversion tremor.
• Affected regions included sensorimotor cortices, cerebellar vermis, ventral anterior cingulate, and right ventral striatum.

Conclusions:

• Right TPJ hypoactivity and reduced connectivity may indicate a deficient sensory prediction signal.
• A mismatch in proprioceptive feedback perception could lead to the feeling of movements not being self-generated.
• This suggests impaired internal prediction-feedback comparison underlies the lack of self-agency in conversion disorder.