There are some instances in which I like to make use of the “gate-control theory” (Melzack and Wall, 1965) – especially in cases where clients are looking for immediate pain relief. A device like the TENS unit has a practical application in moments like this.
The infamous gate theory proposes that pain is caused by activity in small-diameter nerve fibers. By stimulating the larger-diameter sensory nerve fibers, we can reduce the client’s perception of pain. Melzack and Wall hypothesized that within the dorsal horn of the spinal cord, a “gating mechanism” exists, which can be manipulated (i.e. opened or closed) to allow or inhibit the transmission of painful information through it, essentially preventing the brain from processing these painful signals. TENS works, in theory, by selectively exciting A-beta nerve fibres in the skin, which reduces the amount of painful stimulation being transmitted by A-delta and C-fibers (which are smaller). Optimal frequency for this to occur is ~90-130Hz. There is also potential for TENS to affect extra-segmental, descending pain pathways by decreasing the release of excitatory neurotransmitters (aspartate + glutamate), and increasing the release of inhibitory neurotransmitters (GABA + serotonin). Also, potential for modulation of endogenous opiods i.e. endorphins.