Research Article Do Aging and Tactile Noise Stimulation ...downloads.hindawi.com/journals/cggr/2016/2941964.pdf · Research Article Do Aging and Tactile Noise Stimulation Affect Responses

Research ArticleDo Aging and Tactile Noise Stimulation Affect Responses toSupport Surface Translations in Healthy Adults

Marius Dettmer12 Amir Pourmoghaddam12 Beom-Chan Lee2 and Charles S Layne2

1Memorial Bone amp Joint Research Foundation 1140 Business Center Drive Suite 101 Houston TX 77043 USA2Health and Human Performance Department University of Houston 3855 Holman Street Houston TX 77204-6015 USA

Correspondence should be addressed to Marius Dettmer mariusdettmeruthtmcedu

Received 10 October 2015 Revised 23 February 2016 Accepted 4 April 2016

Academic Editor Mariano Malaguarnera

Copyright copy 2016 Marius Dettmer et alThis is an open access article distributed under theCreative CommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Appropriate neuromuscular responses to support surface perturbations are crucial to prevent falls but aging-related anatomical andphysiological changes affect the appropriateness and efficiency of such responses Low-level noise application to sensory receptorshas shown to be effective for postural improvement in a variety of different balance tasks but it is unknownwhether this interventionmay have value for improvement of corrective postural responses Ten healthy younger and ten healthy older adults were exposedto sudden backward translations of the support surface Low-level noise (mechanical vibration) to the foot soles was added duringrandom trials and temporal (response latency) and spatial characteristics (maximum center-of-pressure excursion and anterior-posterior path length) of postural responses were assessed Mixed-model ANOVA was applied for analysis of postural responsedifferences based on age and vibration condition Age affected postural response characteristics but older adults were well ableto maintain balance when exposed to a postural perturbation Low-level noise application did not affect any postural outcomesHealthy aging affects some specific measures of postural stability and in high-functioning older individuals a low-level noiseintervention may not be valuable More research is needed to investigate if recurring fallers and neuropathy patients could benefitfrom the intervention in postural perturbation tasks

1 Introduction

Maintenance of upright stance is a demanding task that re-quires complex neuromuscular control However in healthyadults postural control mostly occurs without consciouscontribution More impressively the central nervous system(CNS) is able to maintain or reestablish balance after expe-riencing postural threats by applying a number of differentcompensatory strategiesThis remarkable capacity of theCNSto respond to a vast amount of different balance perturbationshas been the topic of numerous motor control experimentsTo investigate the postural control mechanisms responsi-ble for maintenance of postural stability researchers oftenemploy experimental methods that involve tasks resemblingreal-life situations such as postural perturbance in the formof rotational or translational movements of the supportsurface [1 2] Assessing temporal and spatial characteristicsof the associated balance processes then allows investigatorsto make conclusions about the effects of task characteristics

or effects of pathology and aging on such postural featuresAdditionally individual postural response characteristics tosudden platform perturbations have shown to be a significantpredictor of future falls [3]

It is well known that sensorimotor control and staticbalance performance decline due to both aging [4] andpathologies [5] and such deterioration is reflected by resultsfrom postural perturbation experiments [6] Aging and taskconstraints significantly affect responses to postural pertur-bations and associated orchestration of correctivemovements[7ndash14] It is believed that about 50 of all falls are causedby sudden movements of the base of support trips and slipsor because of other external perturbations affecting center ofmass displacement over the base of support [15] Whereasa healthy sensorimotor system is able to overcome pertur-bance with rapid accurate muscular responses in manyolder adults this efficiency is reduced whereas responses toperturbation may become delayed or inappropriate [16 17]

Hindawi Publishing CorporationCurrent Gerontology and Geriatrics ResearchVolume 2016 Article ID 2941964 9 pageshttpdxdoiorg10115520162941964

2 Current Gerontology and Geriatrics Research

Table 1 Anthropometric characteristics and foot sole vibration threshold of younger and older participants

119873 Gender Height Weight Age Foot length of vib

Younger 10 f 5 1656 plusmn 92 1483 plusmn 272 251 plusmn 23 254 plusmn 23 21 plusmn 06m 5

Older 10 f 8 1656 plusmn 106 1511 plusmn 352 786 plusmn 54 254 plusmn 16 232 plusmn 218m 2

To improve older adultsrsquo postural performance and toimprove corrective responses during postural perturbationsseveral different interventions have been developed Traininginterventions have been shown to be useful to improveneuromuscular performance and to improve balance [18]Alternatively it is possible to target and augment sensoryfeedback from peripheral sensory sources to improve senso-rimotor control and postural performance

An improvement of postural recovery has been shownwhen using polyethylene tubes around the plantar surfacein experiments requiring participants to generate a rapidstepping response due to support surface perturbations [1920] This indicates that enhancement of tactile informationstemming from the mechanoreceptors of the feet could bebeneficial in balance-threatening situations Some interven-tions aiming at the improvement of sensory information fromrelevant sources for postural control apply the principles ofstochastic resonance (SR)

SR is a phenomenon associated with addition of noiseinto a nonlinear system that is applicable to natural and someman-made systems [21ndash23] SR describes the enhancementof information transmission and weak stimuli detectionwhen noise is added to a system In biological systemsthe application of ldquothreshold SRrdquo is based on the lowerlimits of sensory signals humans can consciously perceiveA ldquothresholdrdquo is defined as the stimulus magnitude requiredto be perceived by the central nervous system A beneficialeffect in a system can be observed when combination andinteraction of (a) a specific threshold (b) a below-thresholdstimulus (subthreshold stimulus) and (c) nonzero-level noise[24] cause a positive effect on system function in contrastto higher level noise which has negative effects on systemfunction [25]

The value of SR for postural control purposes has beenshown in a number of studies [20 26ndash33] Specifically recep-tors that provide pressure information on the plantar surfacehave been a major target for augmentation of sensory feed-back [32ndash34] with the goal of stabilization of upright stanceMore recently mechanical stimulation has been shown tobe valuable in more demanding postural tasks such as tasksincluding visual conflicts like a sway-referenced surrounding[35] or a rotating visual scene [36] Despite promising resultsregarding the utilization of SR in specific tasks it is yetunknown how noise induction affects postural control pro-cessing during balance-threatening tasks that require rapidreactive responses Results from such experiments could shedlight on potential benefits or limitations of vibration tools formodifying postural control and improving upright stability insituations where improved control is crucial for prevention offalls

Here we designed an experiment to determine thespecific differences in healthy younger and older adultswhen facing a translational support surface perturbation Wehypothesized that spatial and temporal features of perturba-tion response are different in regard to age group

We also employed a SR based intervention to investi-gate potential benefits from low-level noise induction Wehypothesized that subthreshold noise would affect spatial andtemporal features of motor control (generation of correctivepostural responses) but potentially only in older adults

2 Materials and Methods

21 Participants This study was conducted according toUniversity of Houston policies concerning the protection ofparticipants in human research The protocol was approvedby theUniversity of HoustonCommittee for the Protection ofHuman Subjects (CPHS) All participants in the study signedan informed consent form before participation We recruited20 healthy older (119899 = 10) and younger (119899 = 10) participantsTo be included in the study prospective participants had tobe free of any significant medical conditions which includedboth physical and cognitive impairments Age range forinclusion in the study was 20ndash35 years for the younger agegroup and 70ndash85 years for the older age groupThe age rangefor the older adults group was based on existing knowledgeabout the onset of sensory decline and associated higherrisk for falls It has been shown that there is an age-relatedacceleration of sensory decline around the age of 70 [37]therefore this age was chosen as the lower limit for inclusion(see Table 1 for demographic information)

Physical health and inclusion in the study were deter-mined based on a modified version of the Physical ActivityReadiness Questionnaire (PAR-Q) Answers to the PAR-Qwere analyzed to determine whether participants could beincluded in the study which was only if they answered ldquonordquoto all question items (or reported health concerns that did notput them at any risk during the experimental trials andorcould have affected postural performance) and reported tobe in overall good health If they reported current use ofmedication we further evaluated whether the medicationwould or would not interfere with postural performance Dueto the nature of the experiments only individuals withoutcognitive impairments as represented by a score of 27 orhigher on the Minimental State Examination (MMSE) [38]were included in the study An initial sensory detection testwas administered to ensure that older adults displayed anelevated sensory threshold (touchpressure threshold) Onlythose individuals displaying an elevated threshold (comparedto the younger group) were included in the study

Current Gerontology and Geriatrics Research 3

Figure 1 Position of tactors under the sole of the foot (1st and 5thmetatarsal-phalangeal joint region and heel)

Participants were excluded if they reported significantphysiological problems based on question items on themodified PAR-QThis included but was not limited to generalhealth problems or severe sensorimotor impairments (egneuropathies chest pain upon exertion dyspnea infectionand functionally significant musculoskeletal dysfunction)Due to the potential effects of obesity on postural stabilityindividuals with a body mass index (BMI) gt 30 kgm2 wereexcluded

22 Mechanical Vibration of the Foot Sole Vibrotactile stim-ulation of the foot sole was administered via vibrating chipsembedded into a custom-made foam sole three vibrationstimulators (C-2 Engineering Acoustics FL) were integratedinto a custom-made silicone rubber sole [27] with a hardnessof Shore 50A [20] There were three specific locations for thetactors under the feet to expose cutaneous afferents to tactilestimuli (Figure 1)

TheC-2 tactors that were embedded in the rubber sole aremoving magnet motor devices with a diameter of 305mma height (in actuation direction) of 79mm and maximumdisplacement amplitude of about 0635mm The use of C-2 tactors as actuators has been established via foot solestimulation experiments that exposed participants to low-level vibration noise [39 40] Other authors suggested theuse of C-2 tactors based on their dimensions the possiblefrequency range that is available and the range of ampli-tudes [20] All six tactors were connected to a control boxincluding amplifiers a memory bank for storing sequences ofstimuli and the power supply (battery) The control box wasconnected to a PC via a USB connector Custom-designedsoftware was used to generate pseudorandom white-noisevibration For the current experiments a white-noise signalwas added to a generated sinusoidal signal band limited to1Hz to about 500Hz thereby including vibration frequenciesthat encompass the response bandwidth ofmechanoreceptorsof the foot sole

The amplifiers for the specific tactors are based on audioamplifiers Magnitude of vibration stimuli (gain) is expressed

Figure 2 NeuroCom EquiTest system Participants stood on cus-tomized soles with embedded vibrating units during all trials

in terms of voltage The drive current is approximately300mA (rms) at the highest gain (which is 4) The currentcan then be modifiedreduced by manipulating gainvoltageIn addition to the gain integer an attenuation parameter (1ndash63) can be set which scales the gain between global levels(1ndash4) Therefore the generated amplitude is based on twoparameters the global integer (1ndash4) and then a number (1ndash63) for the attenuation between global integers Customizedsoftware was created to allow the investigators to manipulatestimulus magnitude as required using a guided user interfacedisplayingmagnitude of stimulus as ofmaximumvibrationoutput

23 Force Data Collection Center-of-pressure data was com-puted based on force data acquired using a force platesystem (NeuroCom EquiTest NeuroCom Intl ClackamasOR) The device consists of a dynamic 1810158401015840 times 1810158401015840 dual forceplate and provides both rotation (plusmn10∘ from center eithertoes-up or toes-down maximum velocity of 50∘s) andtranslation capabilities (plusmn635 cm from center maximum of127 cm in the forward-backward direction and maximumvelocity of 20 cms) A visual scene can be programmed tomove independently of the force plates via servomotors (plusmn10∘from center maximum velocity of 15∘s) This allows for atype of postural investigation called computerized dynamicposturography (CDP) The NeuroCom system (Figure 2)measures forces exerted by participantsrsquo feet while providinga safety harness to prevent falls in participants (see Figure 2)The NeuroCommeasurement device has been used in a widevariety of clinical and scientific studies related to posturalcontrol [41ndash43] Force plate data was collected at 100Hzand processed via Windows-based software on a connectedcomputer (Research module NeuroCom software version80 NeuroCom Intl Clackamas OR)

3 Procedures

31 Foot Sensitivity Testing It is known that older adultsexhibit higher sensory thresholds [37 44] An initial test


determined whether participants in this study (older group)actually had elevated tactile thresholds At the beginning ofthe experimental session individuals were asked to removeshoes and socks and to sit in a chair We applied a tactilesensation via a Semmes-Weinstein Monofilament (50710 g)A forced-choice method was applied whereas participantswere asked to report whether they could feel a stimulus ornot All testing was done over the first metatarsal joint andfour trials were performed on each foot Older adults wereincluded if they did not feel the stimulus in more than threeout of four trials on each foot [45]

32 Stimulator Fitting and Familiarization All participantsof the study were accustomed to the rubber soles whichwere custom-fitted to ensure positioning of the tactors at thefoot positions described earlier (Figure 1) Participants wereasked about their shoe size prior to data collection Basedon this information the tactor sole was modified to fit theparticipantrsquos foot (using silicone blocks that could be insertedin themidfoot section of the sole to increase or decrease size)Participants were seated comfortably with their feet plantedon the tactor surface The necessity for potential adjustmentswas then determined via visual inspection by the principalinvestigator to ensure an optimal fit

33 Sensory Threshold Evaluation The evaluation of indi-vidual threshold was crucial in this experiment since itallowed the determination of the respective experimentalstimulus magnitudeamplitude (approximately 90 of sen-sory threshold intensity) Stimuli set at a level of around 90have been shown to be effective to elicit the desired effectsof subthreshold vibration and have been used in previousstudies that have included subthreshold vibration noise to thefeet [27 34 39]

To determine the 90 threshold level participants wereasked to stand on the rubber sole containing the tactorsVibration stimuli of about 5 s duration were presented atintervals of several seconds The individual threshold wasdetermined using a method applying stimuli at specificlevels and based on feedback from each participant [46]Participants were asked to indicate when they could feelthe vibration under the sole of the foot (ldquoforced-choicerdquo) Alarge stimulus was provided (one that is detectable) followedby an undetectable one The next stimulus magnitude wascalculated based on the midpoint of the first two If a partic-ipant was able to detect this new stimulus the next stimuluswas based on the midpoint between the former undetectedstimulus and this detected level The final threshold wasthen evaluated based on a predetermined range betweenundetected and detected stimulus [37]

During the experimental trials participants stood bare-foot on the rubber sole containing the vibrating tactorelements They wore a harness that was attached to a metalframe around the NeuroCom to prevent injury if a falloccurred Participants were blinded regarding the currentvibration condition

The support surface moved (translation of support sur-face) in posterior direction for three consecutive times witha small displacement (familiarization trials) During these

initial trials participants were familiarized with the sensationof the translating platform The next 10 trials were the exper-imental trials in blocks of five trials with stimulation eitherturned on or turned off (order of blocks randomized) Thetrials consisted of customized translations (400ms duration)with amplitude matched to the participantsrsquo height to elicita sway equivalent of about 32 degrees The amplitude ofdisplacement (in inches) was calculated and generated by theNeuroCom system using the following equation

225 lowast (height72) (1)

which is the standard for the clinically established MotorControl Test [47] Participants were instructed to try tostand as quiet as possible and to take a step if necessaryParticipants were given a ldquoGordquo signal afterwhich the platformtranslated (after a pseudorandom period between one andthree seconds) After five trials participants were given a two-minute break to prevent fatigue

34 Data Reduction Force plate data was collected at 100Hzand for durations of 3 seconds (for 5 seconds beforeonset of perturbation and for 25 seconds after onset ofperturbation) Outcome measures were generated either viaintegrated software (Research module NeuroCom softwareversion 80 NeuroCom Intl) or with a customMatLab script(Mathworks USA R2013b) Anterior-posterior path lengthwas calculated by summarizing the total anterior-posteriordisplacement of COP (as calculated from force plate data) foreach trial Data was then averaged over five trials

Temporal (latency) analysis of evoked active neuromotorresponses was calculated based on the initiation of eachindividualrsquos active response (force response) after onset ofperturbation The onset of force activation is based on asudden change of the position of the center of force due toforce generation at the feet This ldquotake-offrdquo instant is directedforward for backward translations [48] The measurement oflatency based on force plate data has to be adjusted since theresponses measured by the force plate are lagging comparedto a measurable EMG response around the ankles by about30ndash50ms [6 49] To determine the actual onset of an activecorrective response we used amethod applied toCOPdata inan earlier study [50] This included an analysis of the deriva-tives of the COP time-series and subsequent visual inspectionof the dataThismethod is based on the observation of severalzero crossings in the second derivative (acceleration) of COPposition data which is considered the ldquopassive recoveryrdquophase that does not include active generation of torque forcompensation of the perturbation (but is based on passivestructures) The onset of active recovery is defined as thefirst zero crossing of the first derivative (velocity) after thisfirst phase [50] A MatLab script was used to determine thisinstant with a visual inspection follow-up whereas in caseswhere a lack of zero-crossings was present visual inspectionwas used to determine initiation of active response Resultsfrom five trials were then averaged

Additionally we assessed maximal COP excursion inanterior-posterior direction COP excursion was based onthemaximumvalue for anterior-posterior COPdisplacement


Table 2 Summary of results from experiment 3 YA younger adults OA older adults (119899 = 20)

Maximum COP excursion (in cm) APPlength (in cm) Latency (in ms)YA OA YA OA YA OA

No vibration 595 plusmn 06 595 plusmn 14 1577 plusmn 25 2187 plusmn 78 126 plusmn 7 138 plusmn 11Vibration 58 plusmn 09 616 plusmn 14 150 plusmn 42 2088 plusmn 55 126 plusmn 5 134 plusmn 13

during each trial Initial COP position was defined as averageCOP position in the 5 seconds before onset of supportsurface translation A customMatLab script was used to findthe point of maximum excursion throughout each trial (inrelation to baseline position) Maximum anterior-posteriorCOP displacement was then averaged over five trials (oneblock) per subject a method applied before elsewhere [51]

35 Data Analysis Mixed-model ANOVA was utilized forstatistical comparisons There were two independent vari-ables (age and vibration) with one between-groups factor(age) and one within-group factor (vibration) The mixed-model approach allowed the analysis of main effects (vibra-tion and age) and potential interactions (age and vibration) totest the main hypotheses Significance of statistical compar-isons was tested at 120572 lt 05 level and effect size was evaluatedby generating partial eta-squared (1205782

119901)

4 Results

41 Vibration Threshold Prior to the experimental datacollection a vibration threshold test was conductedwith eachparticipant to determine the vibration levels correspondingto lowest perceivable (threshold) vibration amplitude Theresults are expressed as a fraction of the maximal vibrationamplitude as determined by the vibration controller unitThe younger age group showed high sensitivity of the footreceptors requiring only very low vibration amplitude andthe older age group required significantly higher vibrationamplitudes Results from this initial test have been publishedbefore [35]

42 Response to Postural Perturbation Results are summa-rized in Table 2 APPlength was significantly greater in olderadults than in younger adults (Figure 3) 119865(1 18) = 7482119901 = 0012 and 1205782

119901= 303 Over the course of each trial

(25 s) older adultsrsquo total COP displacement was on averagelarger than that in younger adults Vibration did not affectAPPlength in older or younger adults

Maximum COP excursion did not differ between olderand younger adults and there was no effect of vibration onCOP excursion

Latency of corrective responses (Figure 4) was differentbetween groups 119865(1 18) = 032 and 1205782

119901= 232 There was no

significant interaction effect vibration did not affect latencyin older or younger adults

5 DiscussionThe current experiment was designed to investigate thedifferences between older and younger adults when facing

Vibration off Vibration on

YAOA

0

5

10

15

20

25

30

35

APP

leng

th (c

m)

Figure 3 Comparison of APPlength in postural perturbation taskbetween older adults (OA) and younger adults (YA)


YAOA

100

110

120

130

140

150

160

Cor

rect

ive r

espo

nse l

aten

cy (m

s)

Figure 4 Latency of corrective responses in postural perturbationtask between older adults (OA) and younger adults (YA)

postural perturbations Further we aimed to evaluatewhether a vibration intervention could affect temporal andspatial measures of postural performance and postural con-trol with the ultimate goal to improve performance whenfacing balance threats Participants were instructed to quietlystand on the force plate which then moved repeatedly in


the posterior direction (posterior translation) Repeated trialswere performed and spatial and temporal postural measureswere analyzed

51 Age-Related Associations Our hypothesis was that olderand younger adultsrsquo postural performance would differwhich was confirmed for two of the three outcome measures(APPlength and Latency) The effectiveness of neuromuscu-lar responses during support surface perturbations dependson the generation of muscular contractions of the lowerbody (and trunk) and on the accuracy and adequacy of suchresponses

The main goal of the combination of passive and activemechanisms in place for such situations is the avoidance of afall and the prevention of excessive displacement of the bodyrsquosCOM Alternatively humans can react quickly by applyinga stepping strategy to maintain balance (increasing the areaof the base of support) In our study participants did notactually generate a stepping response in any of the trials andtherefore balancemaintenancewas based on a quick responsestrategy involving generation of torque exerted on the forceplate via the feet

Our results from analysis of maximum COP excursionsuggest that age is not necessarily associated with the max-imum displacement of COP when facing postural perturba-tions The observed similarities between older and youngeradults may be due to a number of compensatory mechanismsand strategies Although it is known that reaction timesmuscular strength and muscular coordination are affectedby aging excursion of COP during perturbations might becontrolled in older humans by increasing the magnitude ofmuscular responses compared to younger adults to counter-act the surface translation This is possible since the overalljoint torques required to maintain balance in quiet stanceor when facing perturbations are still generated well byolder healthy adults [17] Alternatively potentialmodificationof balance strategies supports the compensation of somesensorimotor effects of aging as indicated by often observedincreased agonist-antagonist cocontraction associated withincreased lower leg stiffness [51 52] Additionally a reversalof the regular muscle activation order when facing perturba-tions (from distal-to-proximal strategy to proximal-to-distalstrategy) has been reported as another strategy in older adults[53]

Results from perturbation studies in older adults arecontroversial since some research has shown that aging doesnot affect COM measures [54] whereas another evidencesuggests that aging increases COM and COP displacementsin backward or forward platform perturbation [17 55 56]Results from the current study support findings by de Freitaset al [54] who found changes in onset of postural muscu-lature EMG activity in older adults when facing posturalperturbations and due to aging (starting in the fifth lifedecade) However changes in EMG activity due to aging werenot reflected in changes of kinematic measures (joint angleexcursion for ankle knee and hip maximum displacementof COM and COM time-to-reversal after onset of pertur-bation) Those earlier results could indicate that changesin onset of neuromuscular activity are an adaptive strategy

that enables older adults to maintain overall postural controlstrategies similar to those used by younger adults Resultsfrom the current study provide evidence for the ability ofhealthy older adults to effectively maintain postural balancesimilar to younger adults

The onset of corrective responses was observed primarilywithin the range of 120ndash140ms whereas group averages in anearlier study were between 155 and 165ms [50] This discrep-ancy could be due to methodological differences between thetwo experiments In the former experiment the amount oftranslationwas fixedwhereas in the current study translationamplitude was calculated based on each participantrsquos heightAdditionally in the current study participants knew prior toeach trial the perturbationrsquos direction (posterior translation)whereas in Mueller amp Redfernrsquos study 50 consecutive trialsof randomized (25 anterior versus 25 posterior translations)order were conducted Not having accurate knowledge ofthe direction of the impending perturbation would logicallyeliminate the ability to implement anticipatory activity thatmay have influenced response latency Conversely the cur-rent participants knew what direction the perturbation wasto occur and could prepare accordingly This would in turnhave an effect of response onsets It is also possible that overthe duration of 50 perturbation trials onset of fatigue couldhave negatively affected latency over time and may have ledto results that were different from the ones in the currentstudy

In the current experiment groups differed in APPlengthwith the older adults displayingmoreCOP total displacementover the course of each trial (25 seconds) This result is notin agreement with results from maximum COP excursionanalysis This may indicate a loss of postural stability withaging when facing perturbations of the support platformAlternatively it is possible that APPlength in our case isnot an indicator of decreased postural performance but anindicator ofmore exploratory behavior in the older group andas a means of increasing sensory feedback Sway stimulatesmuscle spindles and cutaneous receptors of the foot which incase of the current experiment are important contributors ofsensory cues This sensory information is then used to deter-mine postural orientation and to generate effective responsesPotentially the younger group required less sway since theirsensory feedback operates at near-optimal levels whereasolder adults required this strategy for better performance

52 Effects of Subthreshold Vibration The vibration inter-vention applied in the current experiment did not havesignificant effects on any of the analyzed outcome measuresSensory feedback is considered crucial for the generationof corrective responses (with adequate force production)and the generation of postural adjustments even before theonset of the perturbation Relatively strong perturbations asadministered in this experiment may not be affected by afairly subtle improvement of sensory feedback It is possiblethat SR effects are more likely to appear (per definition) whenotherwise undetectable small magnitude stimuli occur

However it is still possible that over time (eg moretrials) participants could benefit from enhancements of footsole feedback to better prepare (eg a leaning strategy) for


the perturbation and to learn to exploit the enhancement offoot sole feedback

Alternatively a reason for lack of observed effects is thatthe older adults recruited for this studywere highly active andexhibited no functional impairments for gait mechanical SRstimulation has been shown to be especially effective in moreunstable individuals (those exhibiting higher gait variability)when applied to the soles of the feet [57] Similar results werefound for SR based interventions regarding postural sway Ina comparison between stroke patients diabetic neuropathypatients and healthy older adults it was shown that theimpact of SR on postural performance improvement dependson initial baseline performance [27] The authors concludedthat it is possible to predict the magnitude of the SR effect byevaluating baseline performance

Since the effects of SR seem to be dependent on baselinelevels of performance the group recruited for this studycould have consisted of ldquotoo-high-functioningrdquo individualsConsidering the earlier results it would be valuable totest the intervention in more frail individuals and thosesuffering from severe neuropathy Such investigations ofthe relationship between severity of postural sensorimotorimpairments and effects of the intervention in challengingreactive postural perturbation tasks would provide importantinformation about the value for individuals at the highest riskfor falls

6 Conclusion

Healthy aging is associated with some changes regardingspecific aspects of control and performance in posturalperturbation tasks whereas healthy older adults are able tocompensate for potential functional loss to maintain stability

The observed discrepancy between different posturaloutcomes highlights the importance of including a varietyof different measures in postural control research Althougha number of different outcome variables may be predictorsof falls they detect and evaluate different components ofpostural performance and should be in agreement withexperimental hypotheses Analysis of a variety of differentmeasures including spatial and temporal components isvaluable to gain further insight into posture and potentialeffects of aging or interventions

A low-level vibration intervention seems to not be effec-tive in modifying postural response patterns when facinga support surface perturbation More research is neededto investigate whether there are benefits for more frailindividuals or those suffering from neuropathies

Competing Interests

The authors report no competing interests

References

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[2] R G Norrie B E Maki R W Staines andW E McIlroy ldquoThetime course of attention shifts following perturbation of uprightstancerdquo Experimental Brain Research vol 146 no 3 pp 315ndash3212002

[3] B E Maki P J Holliday and A K Topper ldquoA prospective studyof postural balance and risk of falling in an ambulatory andindependent elderly populationrdquo Journals of Gerontology vol49 no 2 pp M72ndashM84 1994

[4] S R Lord R D Clark and I W Webster ldquoPostural stabilityand associated physiological factors in a population of agedpersonsrdquo Journals of Gerontology vol 46 no 3 pp M69ndashM761991

[5] A Pourmoghaddam M Dettmer D P OrsquoConnor W HPaloski and C S Layne ldquoIdentification of changing lowerlimb neuromuscular activation in PARKINSonrsquos disease duringtreadmill gait with and without levodopa using a nonlinearanalysis indexrdquo Parkinsonrsquos Disease vol 2015 Article ID 4978258 pages 2015

[6] L M Nashner ldquoFixed patterns of rapid postural responsesamong legmuscles during stancerdquoExperimental Brain Researchvol 30 no 1 pp 13ndash24 1977

[7] A Mansfield and B E Maki ldquoAre age-related impairments inchange-in-support balance reactions dependent on the methodof balance perturbationrdquo Journal of Biomechanics vol 42 no8 pp 1023ndash1031 2009

[8] B Bloem J H J Allum M Carpenter J Verschuuren andF Honegger ldquoTriggering of balance corrections and compen-satory strategies in a patient with total leg proprioceptive lossrdquoExperimental Brain Research vol 142 no 1 pp 91ndash107 2002

[9] D J Beckley B R Bloem M P Remler R A C Roos and JG Van Dijk ldquoLong latency postural responses are functionallymodified by cognitive setrdquo Electroencephalography and ClinicalNeurophysiologyEvoked Potentials Section vol 81 no 5 pp353ndash358 1991

[10] S G Brauer M Woollacott and A Shumway-Cook ldquoTheinteracting effects of cognitive demand and recovery of posturalstability in balance-impaired elderly personsrdquo The Journals ofGerontology Series A vol 56 no 8 pp M489ndashM496 2001

[11] H C Diener J Dichgans F Bootz and M Bacher ldquoEarlystabilization of human posture after a sudden disturbanceinfluence of rate and amplitude of displacementrdquo ExperimentalBrain Research vol 56 no 1 pp 126ndash134 1984

[12] F B Horak C L Shupert and A Mirka ldquoComponents ofpostural dyscontrol in the elderly a reviewrdquo Neurobiology ofAging vol 10 no 6 pp 727ndash738 1989

[13] J T Inglis F B Horak C L Shupert and C Jones-RycewiczldquoThe importance of somatosensory information in triggeringand scaling automatic postural responses in humansrdquo Experi-mental Brain Research vol 101 no 1 pp 159ndash164 1994

[14] E T Hsiao-Wecksler and S N Robinovitch ldquoThe effect of steplength on young and elderly womenrsquos ability to recover balancerdquoClinical Biomechanics vol 22 no 5 pp 574ndash580 2007

[15] F B Horak S M Henry and A Shumway-Cook ldquoPosturalperturbations new insights for treatment of balance disordersrdquoPhysical Therapy vol 77 no 5 pp 517ndash533 1997

[16] S-I Lin andMWoollacott ldquoAssociation between sensorimotorfunction and functional and reactive balance control in theelderlyrdquo Age and Ageing vol 34 no 4 pp 358ndash363 2005

[17] M-J Gu A B Schultz N T Shepard and N B AlexanderldquoPostural control in young and elderly adults when stance isperturbed dynamicsrdquo Journal of Biomechanics vol 29 no 3 pp319ndash329 1996


[18] M Lesinski T Hortobagyi T Muehlbauer A Gollhofer and UGranacher ldquoEffects of balance training on balance performancein healthy older adults a systematic review and meta-analysisrdquoSports Medicine vol 45 pp 1721ndash1738 2015

[19] I Pyykko P Jantti and H Aalto ldquoPostural control in elderlysubjectsrdquo Age and Ageing vol 19 no 3 pp 215ndash221 1990

[20] J M Hijmans J H B Geertzen B Schokker and K PostemaldquoDevelopment of vibrating insolesrdquo International Journal ofRehabilitation Research vol 30 no 4 pp 343ndash345 2007

[21] A Collins J T Blackburn C Olcott B Yu and P WeinholdldquoThe impact of stochastic resonance electrical stimulation andknee sleeve on impulsive loading and muscle co-contractionduring gait in knee osteoarthritisrdquo Clinical Biomechanics vol26 no 8 pp 853ndash858 2011

[22] J Collins A Priplata D Gravelle J Niemi J Harry and LLipsitz ldquoNoise-enhanced human sensorimotor functionrdquo IEEEEngineering inMedicine and BiologyMagazine vol 22 no 2 pp76ndash83 2003

[23] A T Collins J T Blackburn C W Olcott D R Dirschl andP S Weinhold ldquoThe effects of stochastic resonance electricalstimulation and neoprene sleeve on knee proprioceptionrdquoJournal of Orthopaedic Surgery and Research vol 4 article 32009

[24] Z Gingl L B Kiss and F Moss ldquoNon-dynamical stochasticresonance theory and experiments with white and arbitrarilycoloured noiserdquo Europhysics Letters vol 29 no 3 pp 191ndash1961995

[25] M Dettmer A Pourmoghaddam D P OrsquoConnor and C SLayne ldquoInteraction of support surface stability and Achillestendon vibration during a postural adaptation taskrdquo HumanMovement Science vol 32 no 1 pp 214ndash227 2013

[26] FHMagalhaes andA F Kohn ldquoVibratory noise to the fingertipenhances balance improvement associated with light touchrdquoExperimental Brain Research vol 209 no 1 pp 139ndash151 2011

[27] A A Priplata B L Patritti J B Niemi et al ldquoNoise-enhancedbalance control in patients with diabetes and patients withstrokerdquo Annals of Neurology vol 59 no 1 pp 4ndash12 2006

[28] M Costa A A Priplata L A Lipsitz et al ldquoNoise and poiseenhancement of postural complexity in the elderly with astochastic-resonance-based therapyrdquo Europhysics Letters vol77 no 6 Article ID 68008 2007

[29] A P Mulavara M J Fiedler I S Kofman et al ldquoImproving bal-ance function using vestibular stochastic resonance optimizingstimulus characteristicsrdquo Experimental Brain Research vol 210no 2 pp 303ndash312 2011

[30] R Goel I Kofman J Jeevarajan et al ldquoUsing low levels ofstochastic vestibular stimulation to improve balance functionrdquoPLoS ONE vol 10 no 8 Article ID e0136335 2015

[31] G Samoudi M Jivegard A P Mulavara and F BergquistldquoEffects of stochastic vestibular galvanic stimulation andLDOPA on balance and motor symptoms in patients withParkinsonrsquos diseaserdquo Brain Stimulation vol 8 no 3 pp 474ndash480 2015

[32] A M Galica H G Kang A A Priplata et al ldquoSubsensoryvibrations to the feet reduce gait variability in elderly fallersrdquoGait and Posture vol 30 no 3 pp 383ndash387 2009

[33] L A Lipsitz M Lough J Niemi T Travison H Howlett andB Manor ldquoA shoe insole delivering subsensory vibratory noiseimproves balance and gait in healthy elderly peoplerdquoArchives ofPhysical Medicine and Rehabilitation vol 96 no 3 pp 432ndash4392015

[34] J M Hijmans J H B Geertzen W Zijlstra A L Hof andK Postema ldquoEffects of vibrating insoles on standing balancein diabetic neuropathyrdquo Journal of Rehabilitation Research andDevelopment vol 45 no 9 pp 1441ndash1450 2008

[35] M Dettmer A Pourmoghaddam B-C Lee and C S LayneldquoEffects of aging and tactile stochastic resonance on posturalperformance and postural control in a sensory conflict taskrdquoSomatosensory and Motor Research vol 32 no 2 pp 128ndash1352015

[36] E A Keshner J C Slaboda L L Day and K Darvish ldquoVisualconflict and cognitive load modify postural responses to vibro-tactile noiserdquo Journal of NeuroEngineering and Rehabilitationvol 11 article 6 2014

[37] S D Perry ldquoEvaluation of age-related plantar-surface insensi-tivity and onset age of advanced insensitivity in older adultsusing vibratory and touch sensation testsrdquoNeuroscience Lettersvol 392 no 1-2 pp 62ndash67 2006

[38] M F Folstein S E Folstein and P R McHugh ldquolsquoMini-mentalstatersquo A practical method for grading the cognitive state ofpatients for the clinicianrdquo Journal of Psychiatric Research vol12 no 3 pp 189ndash198 1975

[39] A Priplata J Niemi M Salen J Harry L A Lipsitz and JJ Collins ldquoNoise-enhanced human balance controlrdquo PhysicalReview Letters vol 89 no 23 Article ID 238101 4 pages 2002

[40] A A Priplata J B Niemi J D Harry L A Lipsitz and JJ Collins ldquoVibrating insoles and balance control in elderlypeoplerdquoThe Lancet vol 362 no 9390 pp 1123ndash1124 2003

[41] DMWrisley M J Stephens S Mosley AWojnowski J Duffyand R Burkard ldquoLearning effects of repetitive administrationsof the sensory organization test in healthy young adultsrdquoArchives of Physical Medicine and Rehabilitation vol 88 no 8pp 1049ndash1054 2007

[42] M J E Turnock and C S Layne ldquoVariations in linear andnonlinear postural measurements under achilles tendon vibra-tion and unstable support-surface conditionsrdquo Journal of MotorBehavior vol 42 no 1 pp 61ndash69 2009

[43] J T Cavanaugh V S Mercer and N Stergiou ldquoApproximateentropy detects the effect of a secondary cognitive task onpostural control in healthy young adults a methodologicalreportrdquo Journal of NeuroEngineering and Rehabilitation vol 4article 42 2007

[44] D R Kenshalo Sr ldquoSomesthetic sensitivity in young and elderlyhumansrdquo Journals of Gerontology vol 41 no 6 pp 732ndash7421986

[45] B Manor M D Costa H Kun et al ldquoPhysiological com-plexity and system adaptability evidence from postural controldynamics of older adultsrdquo Journal of Applied Physiology vol 109no 6 pp 1786ndash1791 2010

[46] M E Shy E M Frohman Y T So et al ldquoQuantitative sensorytesting report of the therapeutics and technology assessmentsubcommittee of the American academy of neurologyrdquoNeurol-ogy vol 60 no 6 pp 898ndash904 2003

[47] Neurocom ldquoClinical Interpretation Guide-ComputerizedDynamic Posturographyrdquo 2009

[48] N T Shepard A Schultz N B Alexander Mian Ju Gu and TBoismier ldquoPostural control in young and elderly adults whenstance is challenged clinical versus laboratory measurementsrdquoAnnals of Otology Rhinology and Laryngology vol 102 no 7 pp508ndash517 1993

[49] F B Horak and L M Nashner ldquoCentral programming ofpostural movements adaptation to altered support-surface


configurationsrdquo Journal of Neurophysiology vol 55 no 6 pp1369ndash1381 1986

[50] M L T M Muller and M S Redfern ldquoCorrelation betweenEMG and COP onset latency in response to a horizontalplatform translationrdquo Journal of Biomechanics vol 37 no 10 pp1573ndash1581 2004

[51] Z Halicka J Lobotkova D Bzduskova and F Hlavacka ldquoAge-related changes in postural responses to backward platformtranslationrdquo Physiological Research vol 61 no 3 pp 331ndash3352012

[52] M G Carpenter J H J Allum F Honegger A L Adkin andB R Bloem ldquoPostural abnormalities to multidirectional stanceperturbations in Parkinsonrsquos diseaserdquo Journal of NeurologyNeurosurgery and Psychiatry vol 75 no 9 pp 1245ndash1254 2004

[53] M H Woollacott A Shumway-Cook and L M NashnerldquoAging and posture control changes in sensory organizationand muscular coordinationrdquo International Journal of Aging andHuman Development vol 23 no 2 pp 97ndash114 1986

[54] P B de Freitas C A Knight and J A Barela ldquoPostural reactionsfollowing forward platform perturbation in young middle-ageand old adultsrdquo Journal of Electromyography and Kinesiologyvol 20 no 4 pp 693ndash700 2010

[55] H Nakamura T Tsuchida and Y Mano ldquoThe assessment ofposture control in the elderly using the displacement of thecenter of pressure after forward platform translationrdquo Journalof Electromyography and Kinesiology vol 11 no 6 pp 395ndash4032001

[56] S Okada K Hirakawa Y Takada and H Kinoshita ldquoAge-related differences in postural control in humans in responseto a sudden deceleration generated by postural disturbancerdquoEuropean Journal of Applied Physiology vol 85 no 1-2 pp 10ndash18 2001

[57] D G Stephen B J Wilcox J B Niemi J Franz D CaseyKerrigan and S E DrsquoAndrea ldquoBaseline-dependent effect ofnoise-enhanced insoles on gait variability in healthy elderlywalkersrdquo Gait and Posture vol 36 no 3 pp 537ndash540 2012

Submit your manuscripts athttpwwwhindawicom

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


MEDIATORSINFLAMMATION

of


Behavioural Neurology

EndocrinologyInternational Journal of



Disease Markers


BioMed Research International

OncologyJournal of



Oxidative Medicine and Cellular Longevity


PPAR Research

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Immunology ResearchHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

ObesityJournal of



Computational and Mathematical Methods in Medicine

OphthalmologyJournal of


Diabetes ResearchJournal of



Research and TreatmentAIDS


Gastroenterology Research and Practice


Parkinsonrsquos Disease

Evidence-Based Complementary and Alternative Medicine

Volume 2014Hindawi Publishing Corporationhttpwwwhindawicom


Table 1 Anthropometric characteristics and foot sole vibration threshold of younger and older participants

119873 Gender Height Weight Age Foot length of vib

Younger 10 f 5 1656 plusmn 92 1483 plusmn 272 251 plusmn 23 254 plusmn 23 21 plusmn 06m 5

Older 10 f 8 1656 plusmn 106 1511 plusmn 352 786 plusmn 54 254 plusmn 16 232 plusmn 218m 2

To improve older adultsrsquo postural performance and toimprove corrective responses during postural perturbationsseveral different interventions have been developed Traininginterventions have been shown to be useful to improveneuromuscular performance and to improve balance [18]Alternatively it is possible to target and augment sensoryfeedback from peripheral sensory sources to improve senso-rimotor control and postural performance

An improvement of postural recovery has been shownwhen using polyethylene tubes around the plantar surfacein experiments requiring participants to generate a rapidstepping response due to support surface perturbations [1920] This indicates that enhancement of tactile informationstemming from the mechanoreceptors of the feet could bebeneficial in balance-threatening situations Some interven-tions aiming at the improvement of sensory information fromrelevant sources for postural control apply the principles ofstochastic resonance (SR)

SR is a phenomenon associated with addition of noiseinto a nonlinear system that is applicable to natural and someman-made systems [21ndash23] SR describes the enhancementof information transmission and weak stimuli detectionwhen noise is added to a system In biological systemsthe application of ldquothreshold SRrdquo is based on the lowerlimits of sensory signals humans can consciously perceiveA ldquothresholdrdquo is defined as the stimulus magnitude requiredto be perceived by the central nervous system A beneficialeffect in a system can be observed when combination andinteraction of (a) a specific threshold (b) a below-thresholdstimulus (subthreshold stimulus) and (c) nonzero-level noise[24] cause a positive effect on system function in contrastto higher level noise which has negative effects on systemfunction [25]

The value of SR for postural control purposes has beenshown in a number of studies [20 26ndash33] Specifically recep-tors that provide pressure information on the plantar surfacehave been a major target for augmentation of sensory feed-back [32ndash34] with the goal of stabilization of upright stanceMore recently mechanical stimulation has been shown tobe valuable in more demanding postural tasks such as tasksincluding visual conflicts like a sway-referenced surrounding[35] or a rotating visual scene [36] Despite promising resultsregarding the utilization of SR in specific tasks it is yetunknown how noise induction affects postural control pro-cessing during balance-threatening tasks that require rapidreactive responses Results from such experiments could shedlight on potential benefits or limitations of vibration tools formodifying postural control and improving upright stability insituations where improved control is crucial for prevention offalls

Here we designed an experiment to determine thespecific differences in healthy younger and older adultswhen facing a translational support surface perturbation Wehypothesized that spatial and temporal features of perturba-tion response are different in regard to age group

We also employed a SR based intervention to investi-gate potential benefits from low-level noise induction Wehypothesized that subthreshold noise would affect spatial andtemporal features of motor control (generation of correctivepostural responses) but potentially only in older adults

2 Materials and Methods

21 Participants This study was conducted according toUniversity of Houston policies concerning the protection ofparticipants in human research The protocol was approvedby theUniversity of HoustonCommittee for the Protection ofHuman Subjects (CPHS) All participants in the study signedan informed consent form before participation We recruited20 healthy older (119899 = 10) and younger (119899 = 10) participantsTo be included in the study prospective participants had tobe free of any significant medical conditions which includedboth physical and cognitive impairments Age range forinclusion in the study was 20ndash35 years for the younger agegroup and 70ndash85 years for the older age groupThe age rangefor the older adults group was based on existing knowledgeabout the onset of sensory decline and associated higherrisk for falls It has been shown that there is an age-relatedacceleration of sensory decline around the age of 70 [37]therefore this age was chosen as the lower limit for inclusion(see Table 1 for demographic information)

Physical health and inclusion in the study were deter-mined based on a modified version of the Physical ActivityReadiness Questionnaire (PAR-Q) Answers to the PAR-Qwere analyzed to determine whether participants could beincluded in the study which was only if they answered ldquonordquoto all question items (or reported health concerns that did notput them at any risk during the experimental trials andorcould have affected postural performance) and reported tobe in overall good health If they reported current use ofmedication we further evaluated whether the medicationwould or would not interfere with postural performance Dueto the nature of the experiments only individuals withoutcognitive impairments as represented by a score of 27 orhigher on the Minimental State Examination (MMSE) [38]were included in the study An initial sensory detection testwas administered to ensure that older adults displayed anelevated sensory threshold (touchpressure threshold) Onlythose individuals displaying an elevated threshold (comparedto the younger group) were included in the study










3 Procedures





















119901)

4 Results











YAOA

0

5

10

15

20

25

30

35

APP

leng

th (c

m)



YAOA

100

110

120

130

140

150

160

Cor

rect

ive r

espo

nse l

aten

cy (m

s)


















6 Conclusion




Competing Interests


References


































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

























3 Procedures





















119901)

4 Results











YAOA

0

5

10

15

20

25

30

35

APP

leng

th (c

m)



YAOA

100

110

120

130

140

150

160

Cor

rect

ive r

espo

nse l

aten

cy (m

s)


















6 Conclusion




Competing Interests


References


































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of



































119901)

4 Results











YAOA

0

5

10

15

20

25

30

35

APP

leng

th (c

m)



YAOA

100

110

120

130

140

150

160

Cor

rect

ive r

espo

nse l

aten

cy (m

s)


















6 Conclusion




Competing Interests


References


































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of






















119901)

4 Results











YAOA

0

5

10

15

20

25

30

35

APP

leng

th (c

m)



YAOA

100

110

120

130

140

150

160

Cor

rect

ive r

espo

nse l

aten

cy (m

s)


















6 Conclusion




Competing Interests


References


































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of































6 Conclusion




Competing Interests


References


































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of




















6 Conclusion




Competing Interests


References


































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of
































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of





















of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of
















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Research Article Do Aging and Tactile Noise Stimulation ...downloads.hindawi.com/journals/cggr/2016/2941964.pdf · Research Article Do Aging and Tactile Noise Stimulation Affect Responses