The pain gate mechanism involves a delicate balance between the activity of small-diameter and large-diameter fibers. When the balance is disrupted, pain can occur. For example, if the small-diameter fibers are overactive or the large-diameter fibers are underactive, the gate may open, allowing pain signals to flood the brain. On the other hand, if the large-diameter fibers are overactive or the small-diameter fibers are underactive, the gate may close, reducing or eliminating pain.
The pain gate explains why TENS (Transcutaneous Electrical Nerve Stimulation) units work: electrical pulses preferentially activate A-Beta fibers to "close the gate." It also explains phantom limb pain and central sensitization. pain gate ddsc 018 link