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      Remote vibrotactile noise improves light touch sensation in stroke survivors’ fingertips via stochastic resonance


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          Background and purpose

          Stroke rehabilitation does not often integrate both sensory and motor recovery. While subthreshold noise was shown to enhance sensory signal detection at the site of noise application, having a noise-generating device at the fingertip to enhance fingertip sensation and potentially enhance dexterity for stroke survivors is impractical, since the device would interfere with object manipulation. This study determined if remote application of subthreshold vibrotactile noise (away from the fingertips) improves fingertip tactile sensation with potential to enhance dexterity for stroke survivors.


          Index finger and thumb pad sensation was measured for ten stroke survivors with fingertip sensory deficit using the Semmes-Weinstein Monofilament and Two-Point Discrimination Tests. Sensation scores were measured with noise applied at one of three intensities (40%, 60%, 80% of the sensory threshold) to one of four locations of the paretic upper extremity (dorsal hand proximal to the index finger knuckle, dorsal hand proximal to the thumb knuckle, dorsal wrist, volar wrist) in a random order, as well as without noise at beginning (Pre) and end (Post) of the testing session.


          Vibrotactile noise of all intensities and locations instantaneously and significantly improved Monofilament scores of the index fingertip and thumb tip ( p < .01). No significant effect of the noise was seen for the Two-Point Discrimination Test scores.


          Remote application of subthreshold (imperceptible) vibrotactile noise at the wrist and dorsal hand instantaneously improved stroke survivors’ light touch sensation, independent of noise location and intensity. Vibrotactile noise at the wrist and dorsal hand may have enhanced the fingertips’ light touch sensation via stochastic resonance and interneuronal connections. While long-term benefits of noise in stroke patients warrants further investigation, this result demonstrates potential that a wearable device applying vibrotactile noise at the wrist could enhance sensation and grip ability without interfering with object manipulation in everyday tasks.

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          Most cited references25

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          Stochastic resonance and sensory information processing: a tutorial and review of application.

          To review the stochastic resonance phenomena observed in sensory systems and to describe how a random process ('noise') added to a subthreshold stimulus can enhance sensory information processing and perception. Nonlinear systems need a threshold, subthreshold information bearing stimulus and 'noise' for stochastic resonance phenomena to occur. These three ingredients are ubiquitous in nature and man-made systems, which accounts for the observation of stochastic resonance in fields and conditions ranging from physics and engineering to biology and medicine. The stochastic resonance paradigm is compatible with single-neuron models or synaptic and channels properties and applies to neuronal assemblies activated by sensory inputs and perceptual processes as well. Here we review a few of the landmark experiments (including psychophysics, electrophysiology, fMRI, human vision, hearing and tactile functions, animal behavior, single/multiunit activity recordings). Models and experiments show a peculiar consistency with known neuronal and brain physiology. A number of naturally occurring 'noise' sources in the brain (e.g. synaptic transmission, channel gating, ion concentrations, membrane conductance) possibly accounting for stochastic resonance phenomena are also reviewed. Evidence is given suggesting a possible role of stochastic resonance in brain function, including detection of weak signals, synchronization and coherence among neuronal assemblies, phase resetting, 'carrier' signals, animal avoidance and feeding behaviors. Stochastic resonance is a ubiquitous and conspicuous phenomenon compatible with neural models and theories of brain function. The available evidence suggests cautious interpretation, but justifies research and should encourage neuroscientists and clinical neurophysiologists to explore stochastic resonance in biology and medical science.
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            Recovery of upper extremity function in stroke patients: the Copenhagen Stroke Study.

            Time course and degree of recovery of upper extremity (UE) function after stroke and the influence of initial UE paresis were studied prospectively in a community-based population of 421 consecutive stroke patients admitted acutely during a 1-year period. UE function was assessed weekly, using the Barthel Index subscores for feeding and grooming. UE paresis was assessed by the Scandinavian Stroke Scale subscores for hand and arm. The best possible UE function was achieved by 80% of the patients within 3 weeks after stroke onset and by 95% within 9 weeks; in patients with mild UE paresis, function was achieved within 3 and 6 weeks, respectively, and in patients with severe UE paresis within 6 and 11 weeks, respectively. Full UE function was achieved by 79% of patients with mild UE paresis and only by 18% of patients with severe UE paresis. A valid prognosis of UE function can be made within 3 and 6 weeks in patients with mild and severe UE paresis, respectively. Further recovery of UE function should not be expected after 6 and 11 weeks respectively, in these groups of patients.
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              Roles of glabrous skin receptors and sensorimotor memory in automatic control of precision grip when lifting rougher or more slippery objects.

              To be successful, precision manipulation of small objects requires a refined coordination of forces excerted on the object by the tips of the fingers and thumb. The present paper deals quantitatively with the regulation of the coordination between the grip force and the vertical lifting force, denoted as the load force, while small objects were lifted, positioned in space and replaced by human subjects using the pinch grip. It was shown that the grip force changed in parallel with the load force generated by the subject to overcome various forces counteracting the intended manipulation. The balance between the two forces was adapted to the friction between the skin and the object providing a relatively small safety margin to prevent slips, i.e. the more slippery the object the higher the grip force at any given load force. Experiments with local anaesthesia indicated that this adaptation was dependent on cutaneous afferent input. Afferent information related to the frictional condition could influence the force coordination already about 0.1 s after the object was initially gripped, i.e. approximately at the time the grip and load forces began to increase in parallel. Further, "secondary", adjustments of the force balance could occur later in response to small short-lasting slips, revealed as vibrations in the object. The new force balance following slips was maintained, indicating that the relationship between the two forces was set on the basis of a memory trace. Its updating was most likely accounted for by tactile afferent information entering intermittently at inappropriate force coordination, e.g. as during slips. The latencies between the onset of such slips and the appearance of the adjustments (0.06-0.08 s) clearly indicated that the underlying neural mechanisms operated highly automatically.

                Author and article information

                J Neuroeng Rehabil
                J Neuroeng Rehabil
                Journal of NeuroEngineering and Rehabilitation
                BioMed Central
                11 October 2013
                : 10
                : 105
                [1 ]Department of Industrial and Manufacturing Engineering, University of Wisconsin-Milwaukee, Milwaukee, USA
                [2 ]Department of Physical Medicine and Rehabilitation, Medical College of Wisconsin, Milwaukee, WI, USA
                [3 ]Department of Occupational Science and Technology, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
                Copyright © 2013 Enders et al.; licensee BioMed Central Ltd.

                This is an open access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                : 20 December 2012
                : 3 October 2013

                stroke,sensory deficit,biomechanics,stochastic resonance,noise
                stroke, sensory deficit, biomechanics, stochastic resonance, noise


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