All dermatomes below the level of injury to the spinal cord may lose sensation. So the pain is "referred to" the related dermatomes of the same spinal segment. However, at axial lines, adjacent dermatomes do not overlap. The first drum dermatomes, developed in the 1930s, were manually operated. Rhombencephalitis may also result in hypoesthesia of the V1 through V3 dermatomes. There are several types of dermatomes, usually named after their inventor. Those are manual dermatomes and the term "knife" or "scalpel" is used to describe them. Dermatomes can be operated either manually or electrically. Dermatomes are similar; however, a dermatome only specifies the area served by a spinal nerve.