Descending pain modulation

Descending pain modulation is the brain’s control of pain transmission in the spinal cord and brainstem. Its pathways can suppress or amplify incoming nociceptive signals.

Periaqueductal gray: A midbrain region surrounding the cerebral aqueduct that coordinates pain control, defensive behavior, and autonomic responses. It recruits brainstem pathways that alter nociceptive transmission in the spinal cord.
Nociception: The neural encoding of actual or potential tissue damage. Descending modulation changes nociceptive processing, which is distinct from the experience of pain.
Placebo analgesia: A reduction in pain produced by the expectation or context of treatment rather than its specific active ingredient. Expectations can recruit endogenous opioid and descending pain-control systems.
Descending pain facilitation: Brain-to-spinal-cord signaling that increases nociceptive transmission and pain sensitivity. It is the opposing influence that prevents descending control from meaning only analgesia.
Rostral ventromedial medulla: A medullary region containing neurons that regulate nociceptive processing in the spinal cord. Its output includes both pain-inhibiting and pain-facilitating signals.
Aδ fibers: Thinly myelinated sensory nerve fibers that conduct relatively fast signals, including sharp pain. Their spinal input is among the signals that descending pathways can regulate.
Conditioned pain modulation: A reduction in pain from one stimulus caused by a separate, usually painful, conditioning stimulus. It provides a human experimental measure related to descending inhibitory control.
Spinal sensitization: Increased responsiveness of spinal neurons to sensory input after heightened or repeated activity. It can amplify pain locally, unlike the brain-originating control described here.
Locus coeruleus: A pontine nucleus and major source of noradrenaline in the brain. Noradrenergic projections from this nucleus can suppress spinal nociceptive transmission.
C fibers: Unmyelinated sensory nerve fibers that conduct slowly and carry many burning or aching pain signals. Their nociceptive input is subject to spinal inhibition and facilitation.

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