Insights from A-beta or C-fibre denervated subjects

Abstract

CT afferents have been known for years, since 1939 when Zotterman suggested they might contribute to itch. But their study has been hampered because any low threshold tactile stimulus will also activate large numbers of Aβ afferents. To investigate the psychophysics of CT afferents has recently become possible through microneurography, allowing selective recording from groups of these nerves, (Löken et al., Nat Neurosci 12(5):547-548, 2009 and this volume), and through the study of two rare cohorts of people who have lost either large fibre afferents due to disease or have selective loss of C afferents themselves due to hereditary neuropathy. This chapter details this latter work, and though comparisons between those with neurological conditions and control subjects must always be done with caution, such work can allow some insights into the normal functioning of the CT system. Slow stroking on the hairy skin of deafferented subjects is poorly localised, but described, during forced choice experiments, as pleasant, and leads to activations in insula cortex but not sensory cortex. Since Ct activation is perceived poorly, if at all in deafferented subjects this suggests that a role for CT afferents may be to-in some way-set, or prime, information through Aβ pathways with affective valence.