Altered cortical activation from the hand after facial botulinum toxin treatment

Abstract

Plastic interactions between face and hand cortical tactile circuits occur after severe injuries that affect the hand such as in amputation or spinal cord injury. However, whether loss of facial movements alters the cortical circuits involved in processing tactile inputs from the hand remains unknown. In this prospective observational study we used electroencephalography (EEG) to measure cortical activity evoked by tactile stimulation of the hands before and after botulinum toxin-A-induced facial paralysis. We found a reduction in the tactile event-related potentials (ERPs) 6 weeks after the treatment. This suggests that the limited paralysis of facial muscles induced during cosmetic interventions designed to smooth lines and wrinkles on the face is sufficient to alter the cortical processing of tactile inputs from the hand.

Figure 1

Botulinum toxin-A (BT-A) injections in the forehead decreased cortical tactile event-related potentials (ERPs) evoked from the hands. Tactile stimuli were applied to the left (A–D) or the right (E–H) thumbs. (A) Three-dimensional (3D) topographic maps of brain activity in the control group were calculated by using the average of linearly modeled ERPs. The times below each plot indicate the time point after stimulation. (B) 3D topographic maps of brain activity in the experimental group show a reduction in cortical activity after the BT-A injection. (C) Averaged traces recorded from the electrode with the highest mean activity. The gray inset shows the electrode location on a 3D scalp representation. Solid lines indicate the mean brain activity values at each time point, and the shaded lines represent standard errors. The time points shaded with gray showed significant effects of BT-A. (D) 3D topographic maps of the statistical measure (F-statistic) demonstrate the spatial distribution of the effects of BT-A injections on left hand-evoked cortical responses. (E) 3D topographic maps of brain activity in the control group calculated using the average of linearly modeled ERPs. (F) 3D topographic maps of brain activity in the BT-A injected group show a reduction in cortical activity. (G) Averaged traces recorded from the electrode with the highest mean activity. (H) 3D topographic maps of the statistical measure (F-statistic) demonstrate the spatial distribution of the effects of BT-A injections on right hand-evoked cortical responses. The effects of BT-A on right hand-evoked responses were observed in both hemispheres, but were more prominent in the left hemisphere.