Experiments on Pain Referred From Deep Somatic Tissues

The patterns of deep somatic pain referral were studied with paravertebral injections of 6 per cent. saline solution from the occiput to the sacrum, five subjects being used for each intervertebral level. The distributions were found to approximate a segmental plan, although they overlapped considerably and differed in location from the conventional dermatomes. Pain could not be induced in the radial aspect of the upper limbs and in the feet. Injections into individual peripheral limb muscles showed less regularity in suggesting segmental patterns. As opposed to the hyperalgesia of "Head's zones", areas of hypo-algesia, usually in a concentric manner, were found to overlie the locations of induced deep pain. Sympathetic and somatic (plexus) blocks did not interfere with the segmental referred pain produced by this method, thus suggesting a primarily spinal integrative mechanism. The character of the pain and its autonomic concomitants are described, and the theoretical implications are discussed.