2,3) Clinical studies of TENS have used a variety of outcome measures to assess the effectiveness of TENS; these include serf-report pain rating scales, joint function, analgesic intake, primary hyperalgesia (increased responsiveness to nociceptive stimuli at the site of injury), secondary hyperalgesia (increased responsiveness to nociceptive stimuli outside the site of injury), and various outcome measure questionnaires (for a review, see Sluka and Walsh (4)).

In the skin, VR1 is essential to selective modalities of pain sensation and to tissue injury-induced thermal hyperalgesia (Caterina et al.

Hyperacusis resembles the hyperalgesia of chronic pain except that it is manifested in the auditory cortex.