If you take a long bath, your skin starts to wrinkle but the moisture doesn’t cause that: someone whose finger has been cut off and re-attached will not get wrinkles on that finger. Your body decides that it has to be wrinkly and relays that message via your nerves.
This knowledge can help us find out whether a person’s nerves are working properly. Three Leiden neurologists describe how to establish a certain kind of nerve damage in Clinical Neurophysiology. At the moment, this is done by alternating heating and cooling a block, but it takes time and requires the patient’s cooperation.
The “wrinkle test” is cheap, but does not work as well in some people as in others. Another option is the “Neuropad plaster” which tests whether your foot can still produce sweat. The Neuropad produces fewer false alarms than the wrinkle test, but misses a patient more often. The researchers advise that it is best to combine these two tests, although it is not clear whether this is better than using the standard method, but at least it is faster and cheaper.