Water-Induced Finger Wrinkles Do Not Affect Touch Acuity or Dexterity in Handling Wet Objects Julia Haseleu 1. , Damir Omerbas ˇic ´ 1. , Henning Frenzel 1 , Manfred Gross 2 , Gary R. Lewin 1 * 1 Department of Neuroscience, Max Delbru ¨ ck Center for Molecular Medicine, Berlin-Buch, Germany, 2 Department of Audiology and Phoniatrics, Charite ´ Universita ¨tsmedizin, Berlin, Germany Abstract Human non-hairy (glabrous) skin of the fingers, palms and soles wrinkles after prolonged exposure to water. Wrinkling is a sympathetic nervous system-dependent process but little is known about the physiology and potential functions of water- induced skin wrinkling. Here we investigated the idea that wrinkling might improve handling of wet objects by measuring the performance of a large cohort of human subjects (n = 40) in a manual dexterity task. We also tested the idea that skin wrinkling has an impact on tactile acuity or vibrotactile sensation using two independent sensory tasks. We found that skin wrinkling did not improve dexterity in handling wet objects nor did it affect any aspect of touch sensitivity measured. Thus water-induced wrinkling appears to have no significant impact on tactile driven performance or dexterity in handling wet or dry objects. Citation: Haseleu J, Omerbas ˇic ´ D, Frenzel H, Gross M, Lewin GR (2014) Water-Induced Finger Wrinkles Do Not Affect Touch Acuity or Dexterity in Handling Wet Objects. PLoS ONE 9(1): e84949. doi:10.1371/journal.pone.0084949 Editor: Daniel Goldreich, McMaster University, Canada Received May 24, 2013; Accepted November 19, 2013; Published January 8, 2014 Copyright: ß 2014 Haseleu et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The work was supported by grants from the European Research Council (ERC) and the Deutsche Forschungsgemeinschaft via collaborative research center 665. None of the the funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: glewin@mdc-berlin.de . These authors contributed equally to this work. Introduction Water-induced wrinkling of human non-hairy (glabrous) skin of the fingers, palms and soles is an as yet not fully understood phenomenon influenced by water temperature, pH, and tonicity [1,2]. Interestingly, glabrous skin that lacks sweat glands, like the clitoris and glans penis, does not wrinkle after water immersion [3]. In the 1930s, Lewis and Pickering first described the absence of wrinkling in patients with median nerve palsy which suggested that the nervous system plays a central role in wrinkling [4]. Since then, other studies have described the dependence of wrinkling on the sympathetic nervous system. These discoveries led to the implementation of the wrinkling test as a bedside test of sympathetic nerve function [5–13]. Like water-induced wrinkling, heat-induced vasoconstriction is controlled by the sympathetic nervous system and was shown to occur upon warm water immersion of the glabrous skin which is rich in arterio-venous shunts or anastomoses and sweat glands [14–16]. By measuring changes in blood flow in the digital arteries upon water immersion of the hands, Wilder-Smith and Chow [17] showed that water-induced skin wrinkling is directly linked to vasoconstriction. Considering the unique features of the glabrous skin at the extremities, i.e. finger and toe digits, they suggested that dyselectrolytemia caused by water entry through sweat ducts induces sympathetic nervous system-dependent vasoconstriction. The resulting negative pressure in the finger pulp exerts forces on the overlying epidermal layers, which eventually leads to skin wrinkling [18]. Hsieh et al. [11] provided supportive evidence for a causal relationship between water-induced wrinkling and vaso- constriction by measuring blood flow velocity before and after water-immersion of the hands in patients who underwent digital replantation. They observed that upon water immersion the skin of replanted fingers failed to wrinkle and the blood flow was increased (vasodilatatory effect). Given that water-induced skin wrinkling is controlled by the sympathetic nervous system, Changizi et al. [19] hypothesized that wrinkles may serve an adaptive function in wet conditions. By analyzing the wrinkle pattern of 28 fingers of 13 hands, found in the public online domain, and comparing them to convex mountain promontories they suggested that wrinkles serve as drainage networks for channeling water away during grip in wet conditions (‘rain tread’ hypothesis). A recently published study by Kareklas et al. [20] provided support for the ‘‘rain tread’’ hypothesis with evidence that water-induced wrinkles selectively improve handling of wet objects. In a behavioral study with 20 participants, they showed that subjects transferred submerged objects faster with wrinkled fingers than with non-wrinkled fingers. Furthermore, the authors postulated that, despite not having a detrimental effect on handling dry objects, wrinkles might be disadvantageous in other ways under dry conditions, e.g. by impairing touch sensitivity. We decided to test the above speculation directly by repeating the wrinkling paradigm intro- duced by Kareklas and colleagues [20] and measuring the effect of wrinkling on measures of touch acuity. In order to perform such a study we chose to reinvestigate the effect of water-induced wrinkling on the handling of wet objects in our human test subjects. We found that touch sensitivity, assessed by measuring tactile spatial acuity with a grid test or vibration detection thresholds at 10 Hz and 125 Hz, was unaffected by wrinkling the finger pad skin. Furthermore, the finding that fingertip wrinkles PLOS ONE | www.plosone.org 1 January 2014 | Volume 9 | Issue 1 | e84949