NEUROLOGY JUST GOT MORE INTERESTING ..
As a medical student in the 1970s I learned that there were two pathways from the body to the brain; one entered the spinal cord and ascended to the brain on the ipsilateral side, carrying discriminatory and pressure touch, and proprioception; the other immediately crossed and ascended on the contralateral side, carrying pain, temperature and something that was (very) vaguely described as ‘fine’ touch. Both these pathways ascended to the midbrain (thalamus) then projected to the somatosensory cortex. End of story.
Enter Bud Craig, a mathematician who strayed into a neuroscience class where they were doing single cell analysis of thalamic neurons, got hooked and changed to neurology. Struck by a number of anomalies in the explanation of these two sensory pathways from the body to the brain, he determined to work out their neuroanatomy. Fast forward 25 years and his extensive catalogue of new discoveries have revolutionised our understanding of emotion and sensation. We learn that pain, and all the sensations ascending in the contralateral pathway, target the emotional brain, not the sensory cortex, so representing emotions rather than sensations; indeed inflammation (interleukines, cytokines), and hypoxia, itch metabolites, plus many others, similarly feed into the emotional brain. We learn that these bodily emotions, positive (that is, affiliative touch — see below) and negative (that is, pain) feed into 2 opposite emotional cortical areas, the left and right insulae respectively, one in each hemisphere, which perform a power calculation by opposing (inhibiting) each other; the negative inhibits the positive and vice versa; ultimately this summated (positive minus negative) power decides if we approach or withdraw from our environment.
This opposition explains how happiness and touch can reduce inflammation and pain, and how pain and inflammation can cause depression. We learn that the ‘fine’ touch fibres ascending in the contralateral pathway actually represent a newly-isolated affiliative social bonding system centred on the hairy parts of the body, upper arms, shoulder and back, it has as many nerve endings as the classical somatosensory cortical system of touch, but again this system heads for the emotional areas. This boosts the positive emotional power in the touched and inhibits pain. When we see another person in distress our natural emotional response will be to touch these areas; for a baby with colic we will stroke the back, in a distressed patient recalling trauma, we touch the upper arm.
This is just a flavour of the many new biological concepts Craig has researched and elucidated that, in my opinion, all doctors should understand, as they provide powerful new insights into mood disorders. Craig is the man who discovered how it all fits together, this is the new face of neurobiology. The book provides a fascinating and compelling account and will change your perception of the relationship between mind and body, and of yourself as a human being.