Relief of fecal incontinence by sacral nerve stimulation linked to focal brain activation.

Objective: This study aimed to test the hypothesis that sacral nerve stimulation affects afferent vagal projections to the central nervous system associated with frontal cortex activation in patients with fecal incontinence.

Patients: Nine women and one man received temporary sacral nerve stimulation with permanent electrodes as a treatment for fecal incontinence.

Interventions: We used positron emission tomography to record indices of regional cerebral blood flow before and after 30 minutes of continuous stimulation. We repeated this procedure after 2 weeks of continued stimulation, before and 30 minutes after arrest of the stimulation.

Results: The initial stimulation activated a region of the contralateral frontal cortex that normally is active during focused attention. After 2 weeks of stimulation, this activation had been replaced by activity in parts of the ipsilateral caudate nucleus, a region of the brain thought to be specifically involved in learning and reward processing.

Conclusions: Sacral nerve stimulation induces changes in cerebral activity consistent with an effect on afferent projections of the vagus. The initial activation of the frontal cortex may reflect focused attention, whereas the subsequent activation of the caudate nucleus may reflect recruitment of mechanisms involved in learning and reward processing. These changes may contribute to the improved continence, which is an acquired result of the stimulation.