The Origin of the Interoceptive Pathway

This chapter describes the functional and anatomical characteristics of interoceptive processing at the levels of the primary sensory fiber and the spinal cord. The association of the spinothalamic pathway with pain and temperature had already been described in textbooks for years. The clinical evidence indicated that a knife cut that severed the spinal cord on one side produced a loss of pain and temperature sensations only on the opposite (contralateral) side of the body, as tested with pinprick and a cold brass rod, combined with the loss of discriminative touch sensation and skeletal motor function on the same (ipsilateral) side as the injury to the spinal cord. The anatomical basis for this dissociated pattern of sensory loss is the distinctness of the two ascending somatosensory pathways to the brain-discriminative touch sensation in the uncrossed (ipsilateral) dorsal column pathway, and pain and temperature sensations in the crossed (contralateral) spinothalamic pathway.