Unmyelinated tactile afferents signal touch and project to insular cortex

Abstract

There is dual tactile innervation of the human hairy skin: in addition to fast-conducting myelinated afferent fibers, there is a system of slow-conducting unmyelinated (C) afferents that respond to light touch. In a unique patient lacking large myelinated afferents, we found that activation of C tactile (CT) afferents produced a faint sensation of pleasant touch. Functional magnetic resonance imaging (fMRI) analysis during CT stimulation showed activation of the insular region, but not of somatosensory areas S1 and S2. These findings identify CT as a system for limbic touch that may underlie emotional, hormonal and affiliative responses to caress-like, skin-to-skin contact between individuals.

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Figure 1: Psychophysical testing.
Figure 2: Cortical activations evoked by brush stroking on the right forearm of the patient G.L. and two normal subjects.
Figure 3: Activations in the insular region evoked by brush stroking on the right forearm of the patient G.L.
Figure 4: Cortical activations evoked by brush stroking on the right forearm and the palm of the right hand.

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Acknowledgements

This study was supported by the Canadian and Swedish Medical Research Councils (grants 3546, 12170 and 3548), and the Ingabritt and Arne Lundberg Research Foundation.

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Correspondence to H. Olausson.

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The authors declare no competing financial interests.

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