Brain activation in response to bladder filling and simultaneous stimulation of the dorsal clitoral nerve—An fMRI study in healthy women

Using functional magnetic resonance imaging (fMRI) we investigated the cortical and subcortical representations during bladder filling and the effect of simultaneous stimulation of the dorsal clitoral nerve on these cortical and subcortical structures. After approval of the local ethics committee, 8 healthy females were included. Prior to scanning, subjects were catheterized and the bladder was filled until first desire to void occurred. In a block design protocol we performed repetitive manual bladder filling (FILLING) and emptying of additional 80 ml saline, alternating with rest conditions (REST) of constant bladder volume. The protocol was repeated with simultaneous stimulation of the dorsal clitoral nerve during the filling periods (COMBINED). Activation maps were calculated by means for 3 different contrasts: 1) FILLING > REST, 2) COMBINED > REST and 3) FILLING > COMBINED. A group analysis of contrast 1) showed activation of the right prefrontal and orbitofrontal cortices, the insula bilaterally, the left precuneus, the parietal operculum bilaterally, the cerebellum bilaterally ( q(FDR) ≤ 0.001), the right anterior cingulate gyrus ( q(FDR) ≤ 0.005) and the right anterior mid pons ( q(FDR) ≤ 0.05). Contrast 2) showed activation in the right frontal area, the left insula, the parietal operculum bilaterally and the left cerebellum ( q(FDR) ≤ 0.001). Deactivations were found in the middle frontal gyrus bilaterally and the post- and paracentral gyri bilaterally. Contrast 3) revealed stronger activation during FILLING in the bilateral frontal and prefrontal areas, the right anterior cingulated gyrus, and the right putamen ( q(FDR) ≤ 0.05). Only the right insula showed stronger activation during the COMBINED condition. Simultaneous dorsal clitoral nerve stimulation during bladder filling reduced the activation of certain cortical areas suggesting a neuromodulatory effect of this stimulation on supraspinal centres involved in lower urinary tract control.