Of course the gate control theory is not the only one in the pain modulation field; a more up-to-date interpretation foresees a chemical-humoral control mechanism, based on the stimulated production of endogenous substances “similar to morphine” (bodily produced morphine) the so called endorphins and enkephalins.
These both act on the pain control system, decrease the pain, provocating a high analgesic effect, even if they use a different bio-chemical mechanism. For the endorphin stimulated production the same discrimination criteria of the impulse width does not count.
The role of pulse-width (WIDTH) in the analgesic stimulation
As above described we can resume, the analgesic action of the electric stimulation is attributed to
different mechanisms, according to the impulse intensity and length, as follows:
- SHORT pulses of moderate intensity – acting upon large diameter fibers only (more sensitive and with high-speed conductivity). The analgesic action is derived from a pain blockage at the posterior corn spinal marrow. The said analgesic action is immediate and short length.
- WIDER and higher intensity pulses, simultaneously stimulating “sensitive” and “painful” fibers. Their analgesic action is not attributed to gate control but to central system reflexive stimulation, resulting in the production of bodily produced morphine (endorphins/enkephalins) like substance.
The central pain control system produces these analgesic effect substances each time it receives a fringe “pain signal”; the quantity of endorphins normally produced is only just sufficient to limit the pain to a “bearable” level. A “hyper-secretion” stimulated at hypophysis level, of these substances can lower the pain level further, up to stopping the pain altogether. These substances have a slower but certainly longer lasting action.