Functional imaging of structures involved in neural control of the lower urinary tract.

Recent functional brain imaging studies, building on earlier observations, suggest a working model of brain control of the lower urinary tract. It comprises a few cerebral neural circuits that, during the storage phase, act on the midbrain periaqueductal gray to inhibit the long-loop, spinobulbospinal voiding reflex, thus promoting continence. Circuit 1, centered on the medial prefrontal cortex, appears to be concerned with conscious control of both continence and voiding. Circuit 2, centered on the dorsal anterior cingulate (midcingulate) and supplementary motor area, is concerned with emotional aspects of bladder control: desire to void or urgency with concomitant urethral sphincter activation to delay leakage. A subcortical circuit 3 has been less well studied. Circuit 1 is bilateral with a right-sided preference. Scattered studies of the connectivity of the control network suggest that white-matter damage may contribute to urinary incontinence. A few studies confirm that isolated cerebral lesions, if in the medial prefrontal cortex or its connecting pathways, may lead to incontinence. Lower urinary tract dysfunction in other neurologic diseases (normal-pressure hydrocephalus, Parkinson's disease, and multiple systems atrophy) appears consistent with the working model, and even spinal or peripheral lesions have central effects. However, this model omits the contributions of brain regions already observed in some imaging studies and therefore is certainly oversimplified.