Effects of changing skin mechanics on the differential sensitivity to surface compliance by tactile afferents in the human finger pad.
It is not known how changes in skin mechanics affect the responses of cutaneous mechanoreceptors in the finger pads to compression forces. We used venous occlusion to change the stiffness of the fingers and investigated whether this influenced the firing of low-threshold mechanoreceptors to surfaces of differing stiffness. Unitary recordings were made from 10 slowly adapting type I (SAI), 10 fast adapting type I (FAI) and 9 slowly adapting type II (SAII) units via tungsten microelectrodes inserted into the median nerve at the wrist. A servo-controlled stimulator applied ramp-and-hold forces (1, 2, and 4 N) at a constant loading and unloading rate (2 N/s) via a flat 2.5-cm-diameter silicone disk over the center of the finger pad. Nine silicone disks (objects), varying in compliance, were used. Venous occlusion, produced by inflating a sphygmomanometer cuff around the upper arm to 40 ± 5 mmHg, was used to induce swelling of the fingers and increase the compliance of the finger pulp. Venous occlusion had no effect on the firing rates of the SAI afferents, nor on the slopes of the relationship between mean firing rate and object compliance at each amplitude, but did significantly reduce the slopes for the FAI afferents. Although the SAII afferents possess a poor capacity to encode changes in object compliance, mean firing rates were significantly lower during venous occlusion. The finding that venous occlusion had no effect on the firing properties of SAI afferents indicates that these afferents preserve their capacity to encode changes in object compliance, despite changes in skin mechanics.
School of Medicine, Western Sydney University, Sydney, New South Wales, Australia; School of Science & Health, Western Sydney University, Sydney, New South Wales, Australia;
Kathryn M
KM
Hudson
School of Medicine, Western Sydney University, Sydney, New South Wales, Australia; School of Science & Health, Western Sydney University, Sydney, New South Wales, Australia;
Melia
M
Condon
Department of Clinical Neurophysiology, Göteborg University, Gothenburg, Sweden;
Rochelle
R
Ackerley
John Moores Liverpool University, Liverpool, United Kingdom;
Francis
F
McGlone
Department of Clinical Neurophysiology, Göteborg University, Gothenburg, Sweden;
Håkan
H
Olausson
School of Medicine, Western Sydney University, Sydney, New South Wales, Australia; Neuroscience Research Australia, Sydney, New South Wales, Australia; and MARCS Institute, Western Sydney University, Sydney, New South Wales, Australia v.macefield@westernsydney.edu.au.
Vaughan G
VG
Macefield
School of Science & Health, Western Sydney University, Sydney, New South Wales, Australia; Neuroscience Research Australia, Sydney, New South Wales, Australia; and MARCS Institute, Western Sydney University, Sydney, New South Wales, Australia.
Ingvars
I
Birznieks
D000200:Action Potentials; D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology*; D004548:Elasticity; D005260:Female; D005385:Fingers / Q000294:innervation / Q000502:physiology*; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology*; D008839:Microelectrodes; D009475:Neurons, Afferent / Q000502:physiology*; D010812:Physical Stimulation; D012867:Skin / Q000294:innervation; D012879:Skin Physiological Phenomena; D014110:Touch / Q000502:physiology*; D014690:Venous Pressure / Q000502:physiology; D014953:Wrist / Q000502:physiology; D055815:Young Adult
human; microneurography; sensory coding; skin mechanics; tactile afferents