Exploring interhemispheric interaction in complex regional pain syndrome

Complex regional pain syndrome (CRPS) is characterised by sensorimotor disturbances in the painful limb, coupled with neuroimaging evidence of functional changes in the primary somatosensory cortex (S1). However, the interaction between S1 in both hemispheres is unknown; altered interhemispheric interaction may contribute to this disorder. We conducted the first study of sensory interhemispheric interaction in CRPS, specifically S1. This is also the first study to compare S1 interhemispheric inhibition in both directions in healthy controls. Somatosensory evoked potentials were read with electroencephalography following paired median nerve stimulation at interstimulus intervals of 20, 25 and 30 ms. There was an inhibitory effect of the non-dominant on the dominant hemisphere in controls (ß = −0.308, SE 0.089, [CI −0.535, −0.081], t (914.9) = -3.49, p = 0.003), driven by changes in the N20/P25 SEP (i.e. S1). Importantly, this pattern of interhemispheric interaction was not seen in CRPS; in the CRPS group there was no evidence of interhemispheric inhibition – in either direction. Given the difference in interhemispheric inhibition between CRPS and control groups, the role of S1 interhemispheric inhibition in CRPS needs further investigation. This may shed light on the sensorimotor disturbances characteristic of this disorder.