Control of bladder sensations: an fMRI study of brain activity and effective connectivity

When the bladder is fairly full, the desire to void can be suppressed, but it can also be called forth deliberately. We studied brain activity during such intentional modulations of bladder sensation in 33 healthy volunteers (17 women, 16 men). The supplementary motor area, midcingulate cortex, insula, frontal operculum, and right prefrontal cortex were consistently more active when the desire to void was enhanced without allowing urine to pass ("attempted micturition") than during a baseline task when bladder sensations were suppressed. The right anterior insula and midbrain periaquaeductal grey (PAG) were more active at higher than at lower bladder volumes. Responses of the right thalamus and several other right-hemispherical regions were stronger in women than in men. Using the psychophysiological interaction (PPI) method, we found that the midcingulate cortex had stronger connectivity (indicated by parallel co-variations of the activation time series) with the PAG and medial motor areas during "attempted micturition" than during the baseline task, possibly reflecting monitoring of urethral sphincter contractions. Conversely, the left and right insula showed decreased connectivity with many other brain regions during "attempted micturition", possibly due to predominant processing of bladder-afferent input. Intentional modulations of the desire to void change the effective connectivity of supraspinal regions involved in bladder control.