auditory processing disorders related to traumatic brain...

Auditory Processing DysfunctionAuditory Processing DysfunctionRelated to Traumatic Brain InjuryRelated to Traumatic Brain Injury

in the Veteran Populationin the Veteran Population

Frederick J. Gallun, PhDFrederick J. Gallun, PhDStephen A. Fausti, PhDStephen A. Fausti, PhDMarjorie R. Leek, PhDMarjorie R. Leek, PhD

National Center for Rehabilitative National Center for Rehabilitative Auditory Research (NCRAR)Auditory Research (NCRAR)

VA Medical Center, Portland, Oregon

ObjectivesObjectives

Describe the auditory brain structures that could be Describe the auditory brain structures that could be damaged in Traumatic Brain Injury.damaged in Traumatic Brain Injury.

Describe the relationship between damage to auditory Describe the relationship between damage to auditory brain structures and various types of auditory brain structures and various types of auditory processing dysfunction.processing dysfunction.

Discuss the types of behavioral and electrophysiological Discuss the types of behavioral and electrophysiological testing that might be useful in determining the testing that might be useful in determining the rehabilitation needs of a patient with known or rehabilitation needs of a patient with known or suspected injury to auditory brain areas.suspected injury to auditory brain areas.

Discuss the challenges associated with using tests of Discuss the challenges associated with using tests of auditory processing with the veteran population.auditory processing with the veteran population.

More Than Noise Exposure: More Than Noise Exposure: Blast InjuryBlast Injury

11% 11% -- 28% of 1.4 million troops who have 28% of 1.4 million troops who have served in OEF/OIF may have mild TBI from served in OEF/OIF may have mild TBI from blast exposure.blast exposure.

30% of casualties treated at Walter Reed Army 30% of casualties treated at Walter Reed Army Medical Center have mild, moderate or severe Medical Center have mild, moderate or severe TBI.TBI.

USA Today (3/8/07) USA Today (3/8/07)

More Than Noise Exposure: More Than Noise Exposure: Blast InjuryBlast Injury

Improvements in armor and military medicine Improvements in armor and military medicine have increased the chances of survival, but the have increased the chances of survival, but the result is a higher number of survivors with result is a higher number of survivors with devastating injuries.devastating injuries.

One of the structures most commonly injured in One of the structures most commonly injured in an explosion is the peripheral auditory system. an explosion is the peripheral auditory system. Is the central auditory system similarly at risk?Is the central auditory system similarly at risk?

1. Mechanisms of Blast Injury1. Mechanisms of Blast Injury

Mechanisms of Blast InjuryMechanisms of Blast Injury

Primary: Primary:

impact of blast waveimpact of blast waveSecondary: Secondary:

shrapnel, debrisshrapnel, debrisTertiary: Tertiary:

projection of individualprojection of individualQuarternaryQuarternary: :

burns, inhalation injuriesburns, inhalation injuries


Primary Blast InjuryPrimary Blast Injury

Due to Due to ““blast overpressureblast overpressure”” or or ““blast waveblast wave””

Rapid increase in air pressure due to an explosion.

Causes damage to air-filled cavities in the body.

Injuries to lungs, gastrointestinal tract, and ears


Secondary Blast InjurySecondary Blast Injury

Results from flying objects or debrisResults from flying objects or debris

May cause blunt head trauma or penetration


Tertiary Blast InjuryTertiary Blast Injury

Results when a body is thrown by blast Results when a body is thrown by blast ““windwind””, , striking an objectstriking an object

Blunt head trauma, fractures, amputationsBlunt head trauma, fractures, amputations


Quaternary Blast InjuryQuaternary Blast Injury

Any other injuries such as burns, crushingAny other injuries such as burns, crushingInhalation of toxic materialsInhalation of toxic materialsExacerbation of existing disease statesExacerbation of existing disease states

These various mechanisms of These various mechanisms of blast injury can result in damage blast injury can result in damage

to the to the entire auditory systementire auditory system

2. Potential Damage to the Auditory 2. Potential Damage to the Auditory System from Blast Exposure System from Blast Exposure

Potential Damage to the Auditory System Potential Damage to the Auditory System from Blast Exposurefrom Blast Exposure

PeripheralPeripheralTympanic MembraneTympanic MembraneOssicularOssicular ChainChainCochlear DamageCochlear Damage

CentralCentralBrainstemBrainstemCorpus Corpus CallosumCallosumTemporal LobeTemporal LobeFrontal LobeFrontal Lobe

• Damage to auditory brain areas

Peripheral DamagePeripheral Damage::Noise Exposure from Explosions/WeaponsNoise Exposure from Explosions/Weapons

Intense and/or long duration sounds Intense and/or long duration sounds can permanently damage the can permanently damage the cochleacochlea..

A few milliseconds of exposure to A few milliseconds of exposure to impulsive blast noise can cause damage impulsive blast noise can cause damage equivalent to 10 years worth of noise equivalent to 10 years worth of noise exposure.exposure.

Peripheral DamagePeripheral Damage::Blast Pressure Wave and Flying DebrisBlast Pressure Wave and Flying Debris

PinnaPinna damage: damage: Burns and shrapnel damageBurns and shrapnel damage

Tympanic Membrane perforationTympanic Membrane perforation: : Common Common otologicotologic

finding and recommended as a marker of blast exposure.finding and recommended as a marker of blast exposure.((DePalmaDePalma, 2005), 2005)

OssicularOssicular disruptiondisruptionCochlear damageCochlear damage: : 3535--54% of blast injuries result in 54% of blast injuries result in permanent permanent sensorineuralsensorineural hearing loss.hearing loss.

Traumatic Brain Injury Traumatic Brain Injury from Blast Exposurefrom Blast Exposure

The central auditory system is one of the many The central auditory system is one of the many brain systems at risk for blast injury.brain systems at risk for blast injury.

What is known about the locations and types of What is known about the locations and types of traumatic brain injury that can accompany blast traumatic brain injury that can accompany blast exposure suggest that the auditory brain areas exposure suggest that the auditory brain areas may be particularly vulnerable.may be particularly vulnerable.

The Auditory BrainstemThe Auditory Brainstem

Viewed from in front Viewed from the midline

The Cortical SystemThe Cortical System

Viewed from the side Viewed from the midline

Damage to Auditory Brain AreasDamage to Auditory Brain Areas::I. Primary Mechanism:I. Primary Mechanism:

Blast Pressure Wave from ExplosionBlast Pressure Wave from Explosion

Stretching or shearing of Stretching or shearing of thalamusthalamus and and corpus corpus callosumcallosum connections, resulting in disconnection of connections, resulting in disconnection of inputs or cell death.inputs or cell death.

Taber et al., 2006

Contusions: blueDiffuse axonal injury: pink

Damage to Auditory Brain AreasDamage to Auditory Brain Areas::II. Secondary and Tertiary Mechanisms:II. Secondary and Tertiary Mechanisms:

Blunt Head Trauma, PenetrationsBlunt Head Trauma, Penetrations

Contusions to Contusions to temporaltemporal and and frontal lobesfrontal lobes..

Hemorrhage damage to Hemorrhage damage to frontalfrontal and and parietal lobesparietal lobes..

Taber et al., 2006Contusions: blueHemorrhage: purple

3. Organization and Functions of the 3. Organization and Functions of the Auditory Brain AreasAuditory Brain Areas

andandPotential Impacts of Damage Potential Impacts of Damage

Organization of Auditory Brain AreasOrganization of Auditory Brain Areas

Connections are both Connections are both ““bottombottom--upup”” (ascending)(ascending)

andand

““toptop--downdown”” (descending)(descending)

Winer and Lee, 2007

Functions of the Auditory Brain Areas: Functions of the Auditory Brain Areas: BrainstemBrainstem

Cochlear nucleus regions extract Cochlear nucleus regions extract timing and spectral information.timing and spectral information.

Superior Superior olivaryolivary complex codes complex codes binaural differences in time and binaural differences in time and level.level.

Inferior colliculus codes Inferior colliculus codes information about modulation, information about modulation, binaural differences, and complex binaural differences, and complex spectra.spectra.

Potential Impact of Thalamic and Brainstem Potential Impact of Thalamic and Brainstem Damage on Auditory ProcessingDamage on Auditory Processing

Reduced transmission of information, Reduced transmission of information, resulting in a lower neural resulting in a lower neural ““signalsignal--toto--noisenoise”” ratio.ratio.

Binaural processing impaired through Binaural processing impaired through degraded timing of inputs to binaural degraded timing of inputs to binaural comparison sites within the superior comparison sites within the superior olivaryolivary complex.complex.

Modulation sensitivity reduced through Modulation sensitivity reduced through damage to inferior colliculus and damage to inferior colliculus and thalamus, resulting in reduced speech thalamus, resulting in reduced speech envelope processing.envelope processing.

Which Auditory Processing Tests Could be Used for Which Auditory Processing Tests Could be Used for Thalamic and Brainstem Damage?Thalamic and Brainstem Damage?

Speech in NoiseSpeech in Noise and and Competing SpeechCompeting Speech Tests Tests QuickSINQuickSINHINTHINTDichotic DigitsDichotic Digits

LocalizationLocalization and and Spatial ProcessingSpatial Processing TestsTestsBinaural Masking Level DifferencesBinaural Masking Level Differencestests of localization accuracytests of localization accuracy

Temporal ModulationTemporal Modulation, , Temporal PatterningTemporal Patterning and and Spectral ContrastSpectral Contrast TestsTests

Gaps In Noise TestGaps In Noise TestTemporal or Spectral Modulation FunctionsTemporal or Spectral Modulation FunctionsProfile Analysis TestsProfile Analysis TestsFrequency Pattern Sequences TestFrequency Pattern Sequences Test

The The ““corecore”” areas are areas are tonotopicallytonotopically organizedorganizedThe The ““beltbelt”” areas are nonareas are non--tonotopictonotopic and/or multimodaland/or multimodalThe other sensory systems and The other sensory systems and the limbic system connect the limbic system connect directly to the auditory cortical directly to the auditory cortical regionsregions

These cortical areas contain regions precisely These cortical areas contain regions precisely tuned to specific attributes of sounds sources tuned to specific attributes of sounds sources and auditory objects.and auditory objects.

Winer and Lee, 2007

Organization and FunctionOrganization and Functionof the Auditory Brain Areas: Temporal Lobeof the Auditory Brain Areas: Temporal Lobe

All areas of the earAll areas of the ear--brain brain system are massively system are massively interconnected, but this is interconnected, but this is especially true of the especially true of the auditory cortex and the auditory cortex and the thalamus.thalamus.

Relationship Between Cortex and ThalamusRelationship Between Cortex and Thalamus

auditory cortex thalamusauditory cortex thalamus

NarainNarain et al. (2003) using et al. (2003) using functional Magnetic functional Magnetic Resonance Imaging (Resonance Imaging (fMRIfMRI) ) found specialization for found specialization for intelligible speech as compared intelligible speech as compared to spectrally and temporallyto spectrally and temporally--matched nonmatched non--speech stimuli.speech stimuli.

The speechThe speech--specific areas were specific areas were very well localized, suggesting very well localized, suggesting that damage to such areas that damage to such areas could produce profound could produce profound effects due to a lack of effects due to a lack of redundancy in coding across redundancy in coding across the cortex.the cortex.

Function of Central Auditory Brain AreasFunction of Central Auditory Brain Areas

NarainNarain et al. (2003)et al. (2003)

Some areas are Some areas are more active in more active in auditory auditory localization tasks localization tasks than in auditory than in auditory recognition tasks.recognition tasks.


MaederMaeder et al. (2001)et al. (2001)

Other areas are Other areas are more active in more active in auditory auditory recognition tasks recognition tasks than in auditory than in auditory localization tasks.localization tasks.


MaederMaeder et al. (2001)et al. (2001)

Potential Impact of Temporal Lobe Damage Potential Impact of Temporal Lobe Damage on Auditory Processingon Auditory Processing

Reduced speech intelligibility.Reduced speech intelligibility.Impaired spatial perception.Impaired spatial perception.Decreased accuracy on specific tasks Decreased accuracy on specific tasks performed by precisely tuned performed by precisely tuned components of the earcomponents of the ear--brain system.brain system.

Which Auditory Processing Tests Could be Used for Which Auditory Processing Tests Could be Used for Temporal Lobe Damage?Temporal Lobe Damage?

Staggered Spondaic Words testsStaggered Spondaic Words testsLocalization accuracy testsLocalization accuracy testsGaps in Noise TestGaps in Noise TestDichotic Digits TestDichotic Digits TestFrequency Pattern Sequences TestFrequency Pattern Sequences Test

Function of Frontal Lobe inFunction of Frontal Lobe inAuditory ProcessingAuditory Processing

Frontal lobe is Frontal lobe is connected to multiple connected to multiple regions of the regions of the temporal lobe and temporal lobe and seems to be involved seems to be involved in cognitive processing in cognitive processing and and ““toptop--downdown””attentionalattentional modulation modulation of activity.of activity.

Hugdahl et al. (2003) found that activity in the temporal lobe can be modulated more strongly by the task the listener is performing than by the stimuli presented. Presumably, the frontal lobe mediates these effects.

Function of Frontal Lobe inFunction of Frontal Lobe inAuditory ProcessingAuditory Processing

In all of these cases, the stimuli presented were the same.

Hugdahl et al. (2003)

Potential Impact of Frontal Lobe Damage Potential Impact of Frontal Lobe Damage on Auditory Processingon Auditory Processing

Decreased Decreased attentionalattentional focus.focus.Decreased performance on tasks Decreased performance on tasks involving taskinvolving task--dependent selection and dependent selection and segregation of competing information.segregation of competing information.

Which Auditory Processing Tests Could be Used for Which Auditory Processing Tests Could be Used for

Frontal Lobe Damage?Frontal Lobe Damage?

Speech in competition (speech or noise) Speech in competition (speech or noise) QuickSINQuickSINDichotic DigitsDichotic Digits

Attention to competing sounds?Attention to competing sounds?Informational masking?Informational masking?

Auditory Brain Area SummaryAuditory Brain Area Summary

Auditory brainstem: Auditory brainstem: binaural, binaural, spectral, modulation, and other timing spectral, modulation, and other timing information.information.

Thalamus: Thalamus: transmit and organize transmit and organize

information.information.

Auditory cortex: Auditory cortex: specialized specialized processing of specific attributes of sound processing of specific attributes of sound sources and auditory objectssources and auditory objects

Damage to any of these areas can Damage to any of these areas can lead to substantial impairments even lead to substantial impairments even if peripheral function is unimpaired.if peripheral function is unimpaired.

4. Clinical Diagnosis and Treatment of 4. Clinical Diagnosis and Treatment of Auditory Brain Injuries Auditory Brain Injuries

The Rate of Central Dysfunction in The Rate of Central Dysfunction in Returning Veterans is UnknownReturning Veterans is Unknown

Currently mandated TBI screening for returning Currently mandated TBI screening for returning veterans takes the form of a questionnaire rather veterans takes the form of a questionnaire rather than electrophysiological or behavioral tests.than electrophysiological or behavioral tests.

There is no electrophysiological or behavioral There is no electrophysiological or behavioral screening test for TBI or for central auditory screening test for TBI or for central auditory dysfunction.dysfunction.

There are no electrophysiological or behavioral tests There are no electrophysiological or behavioral tests for recovery of function for those diagnosed with for recovery of function for those diagnosed with central auditory dysfunction.central auditory dysfunction.

Challenges Associated With Testing for Auditory Challenges Associated With Testing for Auditory Processing Dysfunction in Veterans with Potential TBIProcessing Dysfunction in Veterans with Potential TBI

Tests of auditory processing have been developed for Tests of auditory processing have been developed for and and normednormed primarily on children.primarily on children.

For blast exposed listeners, we donFor blast exposed listeners, we don’’t know either thet know either the

““SensitivitySensitivity”” (chance of detecting existing dysfunction)(chance of detecting existing dysfunction)

oror

““SpecificitySpecificity”” (chance of distinguishing among dysfunctions)(chance of distinguishing among dysfunctions)

Behavioral Auditory Processing TestsBehavioral Auditory Processing Tests

Most tests of central auditory processing can be characterized aMost tests of central auditory processing can be characterized as s testing one of the following areas testing one of the following areas (ASHA, 2005) (ASHA, 2005) ::

1) auditory performance in the presence of 1) auditory performance in the presence of competing acoustic signals competing acoustic signals

2) temporal aspects of audition 2) temporal aspects of audition

3) auditory pattern recognition3) auditory pattern recognition

4) auditory discrimination4) auditory discrimination

5) auditory performance with degraded acoustic 5) auditory performance with degraded acoustic signalssignals

6) sound localization and lateralization6) sound localization and lateralization

Behavioral Auditory Processing TestsBehavioral Auditory Processing TestsSchow and Seikel (2007) report that few data exist showing the utility of screening in all of these areas. Further work is needed to determine whether or not such tests are useful for those exposed to blasts.


2) temporal aspects of audition 2) temporal aspects of audition

3) auditory pattern recognition3) auditory pattern recognition

4) auditory discrimination4) auditory discrimination

5) auditory performance with degraded acoustic 5) auditory performance with degraded acoustic signalssignals

6) sound localization and lateralization6) sound localization and lateralization

Examples of Auditory Processing TestsExamples of Auditory Processing Tests1) 1) Dichotic DigitsDichotic Digits ((MusiekMusiek, 1983), 1983)

Assesses auditory processing in the presence of competing stimulAssesses auditory processing in the presence of competing stimulii

4 numbers presented to both ears at comfortable listening levels4 numbers presented to both ears at comfortable listening levels. .

2 numbers are presented to one ear and 2 numbers are presented t2 numbers are presented to one ear and 2 numbers are presented to o the other ear. the other ear.

The subject repeats all numbers that were heard. The subject repeats all numbers that were heard.

Probable Site ofLesion

Sensitivity Specificity Influenced by mild-moderate hearing loss?

CortexCorpus callosum

80%[1] 80% Resistant[2]

[1]Musiek (1983); [2] Musiek et al. (1991) Sensitivity and specificity for diagnosing various brain lesions, not specifically for diagnosing TBI.

Examples of Auditory Processing TestsExamples of Auditory Processing Tests2) 2) Frequency Pattern Sequences TestFrequency Pattern Sequences Test

((MusiekMusiek and and PinheiroPinheiro, 1987), 1987)

Assesses temporal patterning ability. Assesses temporal patterning ability. Test items are sequences of three tone bursts that are presentedTest items are sequences of three tone bursts that are presentedto each ear independently. to each ear independently. In each of the sequences, two tone bursts have the same In each of the sequences, two tone bursts have the same frequency, while the third tone is a different frequency. frequency, while the third tone is a different frequency. Listener reports the order of the pitches (frequencies) on each Listener reports the order of the pitches (frequencies) on each presentation.presentation.




Brainstem

85%(cerebral)[3]45%(brainstem)[4]

88% (cochlear vs. central)

Resistant[5]

[3] Bamiou et al. (2006); [4] Musiek and Pinhero (1987); [5] Humes et al. (1996)

Examples of Auditory Processing TestsExamples of Auditory Processing Tests3) 3) Gaps in Noise TestGaps in Noise Test ((MusiekMusiek et al., 2005) et al., 2005)

Assesses temporal resolution Assesses temporal resolution

A series of sixA series of six--second broadband noise segments are presented. second broadband noise segments are presented.

Each noise segment contains 0 to 3 silent intervals (gaps). Each noise segment contains 0 to 3 silent intervals (gaps).

Gap durations are 2, 3, 4, 5, 6, 8, 10, 12, 15, and 20 millisecoGap durations are 2, 3, 4, 5, 6, 8, 10, 12, 15, and 20 milliseconds and nds and are are pseudorandomizedpseudorandomized with regard to their occurrence and location with regard to their occurrence and location in the noise segment. in the noise segment.




67%[6] 85% Resistant[6]

[6] Musiek et al. (2005)

Examples of Auditory Processing TestsExamples of Auditory Processing Tests4) 4) BinauralBinaural MaskingMasking--Level Difference (BMLD) Level Difference (BMLD)

(McFadden, 1975)(McFadden, 1975)

Tests the integrity of the binaural processing system. Tests the integrity of the binaural processing system.

Sensitive to lesions of the superior Sensitive to lesions of the superior olivaryolivary complex in the brainstem. complex in the brainstem.

Thresholds for pureThresholds for pure--tones determined in the presence of a masking noise. tones determined in the presence of a masking noise.

The noise is either inThe noise is either in--phase or outphase or out--ofof--phase between the two ears. phase between the two ears.

Thresholds for the pure tones should be improved when the maskerThresholds for the pure tones should be improved when the masker is outis out--ofof--phase at the two ears. phase at the two ears.



Brainstem 89%[7] 92%May be

compensated[8]

[7] Olsen et al. (1976); [8] Jerger et al. (1984).

Sensitivity and Specificity of Behavioral Tests for Sensitivity and Specificity of Behavioral Tests for Central Auditory LesionsCentral Auditory Lesions

Test Probable Site ofLesion


Dichotic Digits Test


80%[1] 80% Resistant[2]

Frequency Pattern

Sequences Test


Brainstem

85%(cerebral)[3]45%(brainstem)[4]

88% (cochlear vs. central)

Resistant[5]

Gaps-in-Noise Test


67%[6] 85% Resistant[6]

Binaural Masking

Level Difference

Brainstem 89%[7] 92%May be

compensated[8]

[1]Musiek (1983); [2] Musiek et al. (1991); [3] Bamiou et al. (2006); [4] Musiek and Pinhero (1987); [5] Humes et al. (1996); [6] Musiek et al. (2005); [7] Olsen et al. (1976); [8] Jerger et al. (1984).

Sensitivity and specificity for diagnosing various brain lesions, not specifically for diagnosing TBI.

Electrophysiological Measures of Electrophysiological Measures of Auditory ProcessingAuditory Processing

In addition to behavioral measures, it is possible to assess audIn addition to behavioral measures, it is possible to assess auditory itory processing with electrophysiological measures:processing with electrophysiological measures:

Auditory Brainstem Evoked Response (Wave V latency)Auditory Brainstem Evoked Response (Wave V latency)Long (or Late) Latency Responses (P300 latency and amplitude)Long (or Late) Latency Responses (P300 latency and amplitude)

Test Probable Site of

Lesion


ABR (Wave V latency)

Brainstem 80%[9] 75%Resistant/

Compensable[10]

LLR (P300) Cortex 80%[11] 70%May be

compensated[11]

[9] Musiek and Lee, 1995; [10] Musiek and Chermak, 1994; [11] Musiek et al., 1992

Sensitivity and specificity for diagnosing various brain lesions, not specifically for diagnosing TBI.

Currently, there are no tests of auditory processing Currently, there are no tests of auditory processing that make use of that make use of fMRIfMRI..

The fact that The fact that fMRIfMRI is an established tool for assessing is an established tool for assessing temporal lobe function suggests that it would be ideal temporal lobe function suggests that it would be ideal for tracking changes in auditory processing over time for tracking changes in auditory processing over time and could perhaps even be used for detecting and could perhaps even be used for detecting deviations from normal function.deviations from normal function.

fMRIfMRI Measures of Auditory ProcessingMeasures of Auditory Processing

Challenges Associated with Using Auditory Challenges Associated with Using Auditory Processing Tests for Veterans Exposed to BlastsProcessing Tests for Veterans Exposed to Blasts

Unless tests of central auditory processing are used, Unless tests of central auditory processing are used, deficits could be mistaken for PTSD, mentaldeficits could be mistaken for PTSD, mental--health health issues, and/or nonissues, and/or non--auditory cognitive deficits. auditory cognitive deficits.

The already complex task of auditory processing The already complex task of auditory processing assessment is even more difficult in a TBI population assessment is even more difficult in a TBI population because of confounding variables such as:because of confounding variables such as:

motivationmotivationcooperationcooperationemotional emotional labilitylability

noise toxicitynoise toxicitymetabolic and metabolic and circulatory changescirculatory changes

Despite these difficulties, anecdotal evidence from VA Despite these difficulties, anecdotal evidence from VA audiologists suggests that a significant number of those audiologists suggests that a significant number of those who have been exposed to blasts during combat have who have been exposed to blasts during combat have normal hearing sensitivity, yet still reported difficulties normal hearing sensitivity, yet still reported difficulties hearing speech, especially in background noise. hearing speech, especially in background noise.

As this is exactly the sort of deficit we would expect to As this is exactly the sort of deficit we would expect to see if the auditory brain were damaged, it is crucial that see if the auditory brain were damaged, it is crucial that appropriate tests of central function are applied to this appropriate tests of central function are applied to this population.population.

Challenges Associated with Using Auditory Challenges Associated with Using Auditory Processing Tests for Veterans Exposed to BlastsProcessing Tests for Veterans Exposed to Blasts

How Do We Know How Do We Know Which Tests to Use?Which Tests to Use?

Very little research has been done on establishing the Very little research has been done on establishing the relationship between blast exposure and the incidence relationship between blast exposure and the incidence of central auditory processing disorders.of central auditory processing disorders.

In order to begin to address this problem, a new In order to begin to address this problem, a new research program has been initiated by the NCRAR and research program has been initiated by the NCRAR and Walter Reed Army Medical CenterWalter Reed Army Medical Center……

GoalsGoalsObtain behavioral and Obtain behavioral and neurophysiologicalneurophysiological measures measures of central auditory processing in soldiers returning of central auditory processing in soldiers returning from OIF/OEF following blast exposurefrom OIF/OEF following blast exposure

Retest one year later to evaluate spontaneous Retest one year later to evaluate spontaneous recovery, ongoing problems, and delayed onset recovery, ongoing problems, and delayed onset disabilitiesdisabilities

Measures of Central Auditory Processing Deficits Measures of Central Auditory Processing Deficits Associated with Blast ExposureAssociated with Blast ExposurePrinciple Investigators: Leek and FaustiPrinciple Investigators: Leek and Fausti

CoCo--Investigators: Walden and LewisInvestigators: Walden and Lewis

Two groups (matched for hearing loss, age and gender)Blast exposed and Non-blast-exposed

Immediate and One-Year Follow-up Testing

Comprehensive Audiometric Evaluation

Binaural Masking-Level DifferenceGaps in Noise testFrequency Pattern Sequences TestDichotic Digits testStaggered-Spondaic-Word test

Auditory Brainstem Evoked ResponseLong Latency Responses

Measures of Central Auditory Processing Deficits Measures of Central Auditory Processing Deficits Associated with Blast ExposureAssociated with Blast Exposure

Questions to be AddressedQuestions to be AddressedIs there a Is there a significant difference in central significant difference in central auditory processingauditory processing between patients with between patients with and without blast exposure? and without blast exposure? Which testsWhich tests are most likely to provide are most likely to provide indication of central disorders among the indication of central disorders among the blastblast--exposed population, and exposed population, and what areas of what areas of the brainthe brain are most susceptible to auditory are most susceptible to auditory processing dysfunction, as reflected by processing dysfunction, as reflected by performance on individual tests? performance on individual tests? Will patients who show some deficit on Will patients who show some deficit on auditory testing experience a auditory testing experience a change of change of functionfunction after nine to twelve months ?after nine to twelve months ?

The results of studies such as this one The results of studies such as this one will help to guide clinical practice in will help to guide clinical practice in the the diagnosisdiagnosis and and rehabilitationrehabilitation of of auditory processing dysfunction in auditory processing dysfunction in

blast exposed veterans. blast exposed veterans.

Treatment of Auditory Processing Treatment of Auditory Processing DysfunctionDysfunction

BottomBottom--Up ApproachesUp ApproachesAmplificationAmplificationAuditory TrainingAuditory Training

TopTop--Down ApproachesDown ApproachesCompensatory StrategiesCompensatory Strategies

Environmental ModificationsEnvironmental ModificationsFM Systems, Sound Field Enhancements, FM Systems, Sound Field Enhancements, ComputerComputer--based Toolsbased Tools

Treatment of Auditory Processing Treatment of Auditory Processing DysfunctionDysfunction

Each of these approaches (bottomEach of these approaches (bottom--up, topup, top--down, down, and environmental) is theoretically motivated, but and environmental) is theoretically motivated, but currently unverifiedcurrently unverified for TBI sufferers.for TBI sufferers.

Research is needed to determine Research is needed to determine which approaches which approaches work bestwork best and and for which typesfor which types of auditory of auditory processing dysfunction.processing dysfunction.

Research is also needed on Research is also needed on ways to evaluateways to evaluate the the success of these interventions.success of these interventions.

SummarySummaryThe auditory brainstem, The auditory brainstem, midbrain, thalamus and midbrain, thalamus and auditory cortex (including the auditory cortex (including the frontal lobe) frontal lobe) can all be can all be damageddamaged by exposure to blasts.by exposure to blasts.

Perhaps as important as Perhaps as important as damage to these processing damage to these processing areas, exposure to blasts can areas, exposure to blasts can result in result in damage to connectionsdamage to connectionsamong and within auditory among and within auditory brain areas.brain areas.

Damage to brainstem Damage to brainstem regions could impair regions could impair processing of processing of temporal, temporal, spectral and binauralspectral and binauralinformation.information.

Damage to midbrain and Damage to midbrain and thalamic regions could thalamic regions could impair impair transmission of transmission of informationinformation and the and the formation of formation of precisely precisely tunedtuned cortical receptive cortical receptive fields.fields.

SummarySummary

Behavioral tests:Behavioral tests:


2) temporal aspects of audition 2) temporal aspects of audition 3) auditory pattern recognition3) auditory pattern recognition4) auditory discrimination4) auditory discrimination5) auditory performance with degraded acoustic 5) auditory performance with degraded acoustic

signalssignals6) sound localization and lateralization6) sound localization and lateralization

SummarySummary

ElecrophysiologicalElecrophysiological tests:tests:

ABR: Wave V LatencyABR: Wave V Latency

LLR: P300 Amplitude and LatencyLLR: P300 Amplitude and Latency

Functional Magnetic Resonance Imaging Functional Magnetic Resonance Imaging ((fMRIfMRI))

SummarySummary

Research Challenges for the FutureResearch Challenges for the FutureWhat are the What are the sensitivity and specificitysensitivity and specificity of of various tests of auditory processing?various tests of auditory processing?

What are the best What are the best interventionsinterventions for for confirmed auditory processing confirmed auditory processing dysfunction?dysfunction?

Which are the most reliable tests of the Which are the most reliable tests of the ways in which auditory processing ability ways in which auditory processing ability changeschanges over time?over time?

Research Challenges for the FutureResearch Challenges for the FutureHow can auditory processing be How can auditory processing be assessed as assessed as rapidlyrapidly as possible?as possible?

What are the What are the longlong--termterm effects of injury effects of injury to the earto the ear--brain system?brain system?

How do central and peripheral damage How do central and peripheral damage interactinteract? ?

Does this interaction change Does this interaction change over timeover timeand with and with ageage??

Thank You for Thank You for ListeningListening

auditory processing disorders related to traumatic brain...

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