11-24 – A Healthy Brain Needs 'Vitamin-T'

Chronic stress is the cause of many adverse changes in the brain: increased release of glucocorticoids, widespread inflammation, changes in neuronal morphology such as myelination in prefrontal cortex (PFC) and hippocampus (HC), reduced levels of neurotrophic factors such as Fibroblast Growth Factor2, alterations in brain connectivity especially within PFC-amygdalo-HPC networks and an antecedent of cognitive impairment and dementia. Affiliative tactile interactions are known to buffer social mammals against neurobiological and behavioural effects of stress, but what’s the mechanism? Here a case is made for the role of a relatively recently discovered (in humans) population of low threshold thermo-mechanosensitive nerves called c-low threshold mechanoreceptors (C-LTMR) as a neurobiological substrate responsible for regulating resilience to stress. These 1st order neurones are velocity tuned, preferentially encoding dynamic touch delivered at ~3 cm/sec, projecting centrally to dorsal posterior insular cortex. Due to the delayed nature of their input they could not serve any useful discriminative role and are implicated in the affective and emotional aspects of touch. C-fibres, as a class of unmyelinated afferents, provide a basic vital function in animals – one of protection. For example, children born with a congenital absence of c-nociceptors will put their hands in boiling water and not know it. Children deprived of nurturing touch suffer life-long adverse neurodevelopmental consequences. The CLTM is now being understood to also provide a singular vital protective function, from the nurturing touch of the mother to its absence is loneliness. And now we have evidence of their putative role in dementia and schizophrenia, from recent animal studies. A case will be made here for what we are describing, by analogy with the vital role vitamins play in our physical health, for affective touch and their neuronal substrate the CLTM as