Discriminative and affective touch in human experimental tactile allodynia.
Recently, several studies have suggested a role for unmyelinated (C-tactile, CT) low-threshold mechanoreceptive afferents in the allodynic condition. In this psychophysical study we explored the integrity of both Aβ and CT afferent processing following application of the heat capsaicin model of tactile allodynia on the left forearm in healthy subjects (n=40). We measured tactile direction discrimination (TDD) to target the integrity of Aβ processing (n=20). The TDD accuracy was significantly lower in the allodynic compared to a control zone. In addition, we measured the perceived pleasantness and pain of brush stroking at CT targeted (slow) and CT sub-optimal (fast) stroking velocities to investigate the integrity of CT processing (n=20). When comparing touch pleasantness in the allodynic and control zone, there was a significantly larger difference in ratings for CT targeted compared to CT suboptimal stimulation. The results suggest a disturbance in both Aβ-mediated discriminative and CT-mediated affective touch processing in human experimental tactile allodynia. Our findings support the canonical view that tactile allodynia is signaled by Aβ afferents but that CTs seem to contribute by the loss of a pain inhibiting role.
Institute of Neuroscience and Physiology, University of Gothenburg, Box 430, 405 30 Gothenburg, Sweden; Department of Clinical Neurophysiology, Sahlgrenska University Hospital, Blå Stråket 5 vån 3, 413 45 Gothenburg, Sweden. Electronic address: jaquette.liljencrantz@neuro.gu.se.
Jaquette
J
Liljencrantz
Department of Clinical Neurophysiology, Sahlgrenska University Hospital, Blå Stråket 5 vån 3, 413 45 Gothenburg, Sweden; Department of Neurophysiology, Salford Royal Hospital NHS Trust, Stott Lane Salford Greater Manchester M6 8HD, UK; Faculty of Human and Medical Science, University of Manchester, Oxford Road M13 9PL, UK. Electronic address: Andrew.Marshall@manchester.ac.uk.
Andrew
A
Marshall
Institute of Neuroscience and Physiology, University of Gothenburg, Box 430, 405 30 Gothenburg, Sweden; Department of Clinical Neurophysiology, Sahlgrenska University Hospital, Blå Stråket 5 vån 3, 413 45 Gothenburg, Sweden. Electronic address: rochelle.ackerley@physiol.gu.se.
Rochelle
R
Ackerley
Institute of Neuroscience and Physiology, University of Gothenburg, Box 430, 405 30 Gothenburg, Sweden; Department of Clinical Neurophysiology, Sahlgrenska University Hospital, Blå Stråket 5 vån 3, 413 45 Gothenburg, Sweden. Electronic address: Hakan.Olausson@neuro.gu.se.
Håkan
H
Olausson
D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D004192:Discrimination, Psychological; D006801:Humans; D006930:Hyperalgesia / Q000503:physiopathology / Q000523:psychology*; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology; D014110:Touch; D055698:Touch Perception; D055815:Young Adult
Aβ afferents; C-tactile afferents; Heat/capsaicin; Psychophysics