18. Which one of the following statement is correct?
(A) Changes in excitability occur in second-order neurons when repetitive or prolongedhigh-intensity input is received from primary afferent C-fibers.
(B) A characteristic of spinal nociceptive systems is that they are under tonic descending inhibitionsuch that a common effect of injury to spinal pathways is a release from this inhibition.
(C) The midbrain periaqueductal grey (PAG) and the rostral ventral medulla (RVM), in particularthe medullary nucleus raphe magnus (NRM) figured prominently in the original analyses ofdescending modulation of pain.
(D) Stimulation of both somatosensory cortex (SSC) and motor cortex (MC) have been used in theclinical treatment of neuropathic pain, central poststroke pain, and phantom limb pain.
(E) All of the above are correct.