Simulating sensory-motor incongruence in healthy volunteers: implications for a cortical model of pain.

OBJECTIVES: Conflict between motor-sensory central nervous processing has been suggested as one cause of pain in those conditions where a demonstrable or local nociceptive aetiology cannot be convincingly established (e.g. complex regional pain syndrome type 1, repetitive strain injury, phantom limb pain and focal hand dystonia). The purpose of this study was to discover whether pain could be induced in pain-free healthy volunteers when this conflict was generated transiently in a laboratory setting.
METHODS: Forty-one consecutively recruited healthy adult volunteers without a history of motor or proprioceptive disorders performed a series of bilateral upper and lower limb movements whilst viewing a mirror/whiteboard, which created varied degrees of sensory-motor conflict during congruent/incongruent limb movements. A qualitative method recorded any changes in sensory experience.
RESULTS: Twenty-seven subjects (66%) reported at least one anomalous sensory symptom at some stage in the protocol despite no peripheral nociceptive input. The most frequent symptoms occurred when incongruent movement was performed whilst viewing the reflected limb in the mirror condition, the time of maximum sensory-motor conflict. Symptoms of pain were described as numbness, pins and needles, moderate aching and/or a definite pain. Other sensations included perceived changes in temperature, limb weight, altered body image and disorientation. There were indications that some individuals were more susceptible to symptom generation than others.
CONCLUSIONS: Our findings support the hypothesis that motor-sensory conflict can induce pain and sensory disturbances in some normal individuals. We propose that prolonged sensory-motor conflict may induce long-term symptoms in some vulnerable subjects.