The usefulness of the technique of transcutaneous electrical nerve stimulation is explained by which of the following?

Transcutaneous electrical nerve stimulation is a method used to lessen severe, chronic pain by overly stimulating the involved neurons. This is thought to trigger inhibitory interneurons in lamina II of the spinal cord, thereby paially blocking the transmission of pain impulses. These interneurons are considered to be "gatekeepers", that can, to some degree, isolate the peripherally generated signals from the brain. Allodynia is the term used for the perception of pain following a normally innocuous stimulation of a mechanoreceptor. Central pain, such as that caused by thalamic lesions, is pain that originates at the level of the brain rather than in the periphery. Referred pain is the perception of pain initiated in one body site (typically an internal organ) as being localized to another body site (frequently on the more superficial pas of the body). An example is that of diaphragmatic pain, which may be referred to the top of the shoulder. The phenomenon occurs because both internal organs and more superficial structures may arise from, and consequently be innervated by, the same dermatome.