THEORY:

Sources of abnormal

sensory re-weighting in

fall-prone older adults

Gloria Ammons

Leslie K. Allison, PhD, PT

September 11, 2008

Postural Control

Peripheral sensory inputs: Vision

Somatosensation

Vestibular

Central processing sensory interpretation

central integration

map appropriate response

activate muscular system

Deficient Sensory Processing

Attributed to falls in the elderly

Sources:

1. Peripheral sensory

E.g. Bilateral vestibular loss

2. Central sensory integration

E.g. “Pusher syndrome”

(Karnath 2003)

Sensory Re-weighting

Allison et al. 2006; Oie et al. 2002; Maurer et al. 2006

Central sensory process

Sensitivity to change

Up-weight Reliable sense

Down-weight Unstable sense

Theory 1

Allison et al. 2006

Older adults vs. young adults

Both able to “re-weight” senses accurately

to changing stimuli as long as older adults

are given enough time to adapt

“weight” is measured by gain

Gain = peak response amplitude

peak stimulus amplitude

Allison et al. 2006: Fig 1

Normal re-weighting:

INTER-modality dependence visual display amplitude, gain to vision stimulus motion

INTRA-modality dependence visual display amplitude, gain to somatosensory motion

Allison et al. 2006: Fig 4

Theory 2 Peterka 2002

Persons with known bilateral vestibular loss “weight” vision & proprioceptive cues more highly than individuals with intact vestibular function

Peterka 2002: Fig 3

Despite screening for peripheral sensory loss, older adults “weighted” vision & somatosensory information more highly than young adults

Increased body sway higher gains

Problem: inadequate screening for vestibular sensory loss?

Theory 3

Allison et al. 2006; Borger 1999; Simoneau 1999

Allison et al. 2006: Fig 2

Purpose

To determine if the source of abnormal sensory

re-weighting in fall-prone older adults is due to

peripheral vestibular loss or due to a central

processing deficit.

Hypothesis

Fall-prone older adults with and without known peripheral

vestibular loss will both demonstrate sensory re-

weighting as measured by altered gain responses to

amplitude changes in visual and somatosensory motion

stimuli.

Fall-prone older adults with intact vestibular function will

also demonstrate heightened sensitivity to vision and

somatosensory motion, indicating a central sensory

processing deficiency.

Importance

Fall-risk increases with age

15.9% of people 65 yrs reported falling at least once in 3 mo period

(CDC 2007)

Falls & “fear of falling” are associated with activity avoidance, which

threaten independence among elderly (Stevens 2008; Bertera 2008)

Exercise reduces risk for falls

Current study will help:

Promote EBP & future research

Understand source of sensory processing deficits

Develop effective fall prevention programs (Allison 2006)

References1. Allison LK (2006) The dynamics of multi-sensory re-weighting in healthy and

fall-prone older adults. (Doctoral dissertation, University of Maryland, 2006). Dissertation Abstracts International, 67 (6). (UMI No. 3222601)

2. Allison LK, Kiemel T, Jeka JJ (2006) Multisensory re-weighting of vision and touch is intact in healthy and fall-prone older adults. Exp Brain Res 175:342-352

3. Bertera EM, Bertera RL (2008) Fear of falling and activity avoidance in a national sample of older adults in the United States. Health Soc Work 33:54-62

4. Borger LL, Whitney SL, Redfern MS, Furman JM (1999) The influence of dynamic visual environments on postural sway in the elderly. J Vestibl Res 9:197-205

5. Centers for Disease Control and Prevention [CDC] 2007 Web-based injury statistics query and reporting system. National Center for Injury Prevention and Control, Centers for Disease Control and Prevention. Accessed September 10, 2008 from: www.cdc.gov/ncipc/wisqars

6. Jeka JJ, Allison LK, Saffer M, Zhang Y, Carver S, Kiemel T (2006) Sensory re-weighting with translational visual stimuli in young and elderly adults: the role of state-dependent noise. Exp Brain Res 174:517-527

7. Karnath H, Broetz D (2003) Understanding and treating “pusher syndrome.” Phys Ther 83:1119-1125

References

8. Maurer C, Mergner T, Peterka, RJ (2006) Multisensory control of human upright stance. Exp Brain Res 171:231-250

9. Oie KS, Kiemel T, Jeka JJ (2002) Multisensory fusion: simultaneous re-weighting of vision and touch for the control of human posture. Cogn Brain Res 14:164-176

10. Peterka RJ (2002). Sensorimotor integration in human postural control. J Neurophysiol 88:1097-1118

11. Simoneau M, Teasdale N, Bourdin C, Bard C, Fleury M, Nougier V (1999) Aging and postural control: postural perturbations caused by changing the visual anchor. J Am Geriatr Soc 47:235-239

12. Speers RA, Kuo AD, Horak FB (2002) Contributions of altered sensation and feedback responses to changes in coordination of postural control due to aging. Gait Posture 16:20-30

13. Stevens JA, Mack KA, Paulozzi LJ, Ballesteros MF (2008) Self-reported falls and fall-related injuries among persons aged 65 years – United States, 2006. Journal of Safety Research 39:345-349

METHODS:

Sources of abnormal

sensory re-weighting in

fall-prone older adults

Gloria Ammons

Leslie K. Allison, PhD, PT

October 7, 2008

THEORY

Postural control is influenced by peripheral sensory inputs & central

sensory processing

Both peripheral & central sensory deficits are associated with falls in

the elderly

Normal sensory reweighting (SRW) is characterized by a pattern of

absolute gain responses to changes in environmental stimuli

Increases in vision gain as visual input becomes more reliable;

Decrease in somatosensory gain as vision becomes more reliable

THEORY

No differences in pattern of gain response in young (HY), healthy

older (HO), & fall-prone older adults (FP) if given enough time to

adapt to changing stimulus

People with known bilateral vestibular function loss (VFL) have

heightened sensitivity to changes in vision & proprioceptive cues

compared to people with intact vestibular function (VFI)

FP also have heightened sensitivity to changes in vision &

somatosensation stimuli compared to HO & HY

PURPOSE

To determine if the source of SRW in FP is due to:

Peripheral vestibular loss or

Central processing deficiency

HYPOTHESES

Both HO & FP will demonstrate SRW as measured by altered gain responses to amplitude changes in visual and somatosensory (SS) stimuli

All older adults with VFL will demonstrate heightened sensitivity to vision & SS motion as measured by greater absolute gain responses to the same stimulus.

HO with VFI will not show heightened sensitivity to vision & SS motion

peripheral loss

central impairment

FP with VFI will show heightened sensitivity to vision & SS

peripheral loss

central impairment

METHODS

Subjects Sample

3 groups of 30 each (total 90 expected) Healthy young (HY)

age 18-30

Healthy older (HO) age 70

Fall-prone older (FP) age 70

Selection Flyer

Advertisements

Personal contact Community

ECU students

Informed consent of experimental procedures

Approved by University Institutional Review Board

Volunteers Needed

For Balance Study

If you are 70 years of age or older & have had

falls,

near falls,

or become much less steady than you were a year ago,

Please join the East Carolina University

Balance Study this summer/fall.

You will receive

FREE specialized balance testing

Up to $45.00 compensation for your participation

For more information, please call

Gloria Ammons at 252-327-9631

Leslie Allison at 252-744-6236

This study is funded by East Carolina University.

Subjects

Exclusion Criteria

Hx of psychological,

neurological, or

orthopedic disability;

Consuming

medications that

impair balance

Inclusion Criteria

HY: Normal strength & ROM;

vision corrected to 20/20

HO: No hx of falls; no reported

symptoms of imbalance; No AD;

have high physical activity level

FP: Hx of falls or have high risk of

falls; reported incidence of

multiple near falls; reduced

functional activity level 2

imbalance; with/without AD

Experimental Apparatus

Visual Display

Rear-projected random star

field pattern

Translucent 4m x 3m screen

Software: Microsoft Visual

Studio 2005

Central ellipse w/o stars (Dijkstra et al. 1994)

Refresh rate: 60 Hz

Experimental Apparatus

Surface Motion

NeuroCom v1.2.0

Dynamic Dual Force Plate

Raised platform

A-P translation

Measure GRF, estimated

COM

Collected at 200 Hz

Experimental Apparatus

Kinematics EVaRT v5.0.4 motion analysis

6 cameras

Infrared emitting diode markers

3 head

Bilateral acromioclavicular,

greater trochanters, lat.

femoral-tibial, lat. malleoli,

distal 5th metatarsals

Calculate estimated COM

Signals collected at 120 Hz

Experimental Protocol

3 separate testing sessions for older adults

Clinical screening session (2 hrs)

Performed by PT & GA’s

1st session to establish eligibility

Tests:

Visual Acuity - Snellen eye chart

Mini-mental Exam

Dynamic Handicap Inventory

Berg Balance Scale

1 Minute STS

TUG

LE strength screening

LE somatosensation

Touch - Semmes-Winstein

monofilaments

Vibration - 128 Hz tuning fork

Proprioception - PROM 1st ray & ankle

Experimental Protocol

Vestibular Diagnostic Testing (3 hrs)

Performed by audiologist & GA’s

Tests:

Hearing

Videonystagmography

Dynamic Visual Acuity Test

Vestibular Evoked Myogenic Potentials (VEMP)

Rotary Chair:

Visual-Vestibular interaction

Subjective visual vertical

Multisensory Reweighting Experiment (3 hrs)

SRW Experimental Procedures

Stand on force platform

Face visual display

(distance of ~30”)

Wear goggles

Marker set

Standardized foot

position (McIlroy & Maki 1997)

Safety harness

Limited auditory cues

during trials

Experimental Procedures

Baseline data:

Room lit

Subject instruction

Silent sync trigger

Activates Neurocom & EVaRT

Collect:

Standing calibration

Static postural sway

30 sec

Dynamic LOS

60 sec

SRW data:

Room darkened

Subject instruction

Silent sync trigger

Activates Neurom, EVaRT, & Visual

Two stimuli - vision, & somatosensation

Stimuli have constant frequency, varying amplitude

Ten – 3 min trials

Randomized conditions

2’ seated rests between trials

Randomized

Conditions

Visual

stimulus

(ƒ = .28 Hz)

Somatosensory

stimulus

(ƒ = .20 Hz)

1 High amplitude

(8 mm)

Low amplitude

(2 mm)

2 Low amplitude

(2 mm)

High amplitude

(8 mm)

Data Analysis

Dependent Variables:

Gain

(amplitude)

Phase

(timing)

Independent

Variables:

Fall status HO

FP

Vestibular

function

Intact

(VFI)

Loss

(VFL)

Amplitude = peak COM displacement

Gain = peak response amplitude

peak stimulus amplitude

Gain

Allison et al 2006

INTER-modality dependence

INTRA-modality dependence

Phase

Allison et al 2006

Data Analysis

P 0.05

MANOVA

Repeated measures

2 x 2 Factorial design

References

Dijkstra TMH, Schoner G, Giese MA, Gielen CCAM (1994) Temporal stability of the action-perception cycle for postural control in a moving visual observed with human stationary stance. Exp Brain Res 97:477-486

Hair JF, Anderson RE, Tatham RL, Black WC (1998) Multivariate Data Analysis (5th ed). Prentice Hall

McIlroy WE, Maki BE (1997) Preferred placement of the feet during quiet stance: development of a standardized foot placement for balance testing. Clin Biomech 12:66-70

Allison LK, Kiemel T, Jeka JJ (2006) Multisensory re-weighting of vision and touch is intact in healthy and fall-prone older adults. Exp Brain Res 175:342-352

RESULTS:

Sources of abnormal

sensory re-weighting in

fall-prone older adults

Gloria Ammons

Leslie K. Allison, PhD, PT

December 2, 2008

Purpose / Hypotheses

Purpose: to determine if the source of SRW in fall prone older adults is due

to peripheral vestibular loss or central processing deficiency

Hypotheses:

1. Both young & older adults will demonstrate SRW as measured by

altered gain responses to amplitude changes in visual &

somatosensory (SS) stimuli

2. All older adults with vestibular function loss will demonstrate

heightened sensitivity to vision & SS motion as measured by greater

absolute gain responses to the same stimulus.

3. Fall prone older adults with intact vestibular function will also

demonstrate heightened sensitivity to vision & SS motion.

Experimental Methods

3 groups of 30 each

Healthy young (HY)

age 18-30

Healthy older (HO)

age 70

Fall-prone older (FP)

age 70

Experimental Apparatus

Visual Display

NeuroCom Surface Motion

EVaRT Motion Analysis

Protocol

Clinical Screening Test

Vestibular Testing

MSWR Study

MSWR Procedures

Room lit for baseline data

Static: postural sway

Dynamic: limits of stability

Room darkened for 10 trials (3 minutes each)

Surface motion 0.28 Hz

Visual motion 0.20 Hz

5 conditions Hi to Lo amplitude (.8, .2)

5 conditions Lo to Hi amplitude (.2, .8)

Divided data into 4 segments: Hi pre, Lo post, Lo pre, Hi post

Experimental Design

Independent variables

Age

Fall status

Vestibular function

Dependent variables

Gain

Phase

P 0.05

One way ANOVA

Age (HY, HO, FP)

vs. Gain

vs. Phase

Two way ANOVA

Fall status, vestibular function

vs. Gain

vs. Phase

Actual Methods

Pilot subjects: HY (2)

MSRW

NeuroCom – collect data points @ 200 Hz

Calculate COM, gain, phase

Amplitude

Gain = COM response amplitude @ 0.2 Hz

stimulus amplitude @ 0.2 Hz

Phase = time difference between cycles

(position in degrees)

Use a frequency response function to convert time data into

frequency data to understand the relationship between the input

stimulus (surface motion) and the output (postural sway)

Data Analysis N = 8

Independent t test

Condition (Hi, Lo)

Vs. Gain

Not significant

Identified 2 outliers

Ran Independent t test

Significant p = 0.008 (df = 6)

Pilot 5: Hi pre (0.24), Lo post (2.36)

Pilot 3: Lo pre (10), Hi post (0.43)

Pilot Data Summary

There was a significant difference between conditions Hi & Lo

amplitude and gain without outliers.

Both subjects demonstrated SRW: Lower gain values in Hi condition

versus Lo condition.

Questions?