On the origins of the sensory output from the bladder: the concept of afferent noise

For many people a recurrent strong desire to void, sometimes with incontinence, diminishes their quality of life. At present there are few insights into what underlies these problems. The condition is described as the 'overactive bladder symptom complex' but this definition is proving to be unhelpful. It focuses on overt bladder contractions rather than the main problem, which is altered and heightened sensation. Also, current approaches that describe bladder sensations as episodic and leading to voiding as 'first and second sensation to void' might also be misleading if they are taken too literally and used to suggest mechanisms. Current research is beginning to focus on the mechanisms that generate afferent information from the bladder and how it can become altered. As these views develop it is crucial that we appreciate the diversity of the bladder afferent system and distinguish between afferent and sensory information; in this review we explore this underlying complexity. The central nervous system (CNS) receives vast amounts of information from the bladder, which arises from different locations, uses different fibre types and involves different methods. The CNS is continually being bombarded with 'afferent noise'. The challenge now is to understand the nature and components of this 'afferent noise' and which components are essential to sensation. The emerging picture is complex, but this complexity must not be negated or oversimplified. It must be embraced and incorporated it into thinking when designing experiments, analysing data, diagnosing patients and evaluating treatment.