Abstract
The biological significance of pain is to protect the organism from possible injury. However, there exists a situation, where, in the interest of survival, it is more important not to perceive pain.
Spontaneous suppression of pain or weakening of nociception is mediated by an endogenous antinociceptive (analgesic) system. Its anatomical substrate ranges from the periaqueductal gray matter of the midbrain, through the noradrenergic and serotonergic nuclei of the brain stem to the spinal neurons, which receive "pain" information from nociceptors.
Moreover, the activity of this system is under significant control of emotional and cognitive circuits. Pain can be moderated primarily through stimulation of positive emotions, while negative emotions increase pain.
Paradoxically, one pain can also suppress another pain. Analgesia can be induced by stress, physical exercise, orosensory stimulation via a sweet taste, listening to music, and after placebo, i.e. when relief from pain is expected.
Since pain has sensory, affective, and cognitive components, it turns out that activation of these entire systems can, in specific ways, contribute to pain suppression.