Early ideas of referred pain without hyperalgesia were founded on viscerosomatic convergence theory. This theory is based upon afferent fibers along with multiple peripheral branches supplying the somatic and viscera. However, the amount of converging peripheral fibers is limited which makes it unlikely that this theory alone can explain the result of referred pain. It is known that centrally there is a convergence of somatic and visceral afferent inputs as described by extensive electrophysiologic and anatomic studies for neurons in the spinal cord and higher centers. Using this information, it is possible that referred pain processing can result from processing in the CNS. The convergence-projection theory states that a message from the viscera would be interpreted by higher brain centers as coming from the somatic structure because of the mnemonic traces of previous experiences of somatic pain.
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