Introduction to Neurobiology Neuroscience of Auditory Processing

							Introduction to Neurobiology & Neuroscience                                (Central) Auditory Processing Disorder
           of Auditory Processing                                     A Disorder of the Central Auditory Nervous System

                                                                   Difficulties in the perceptual processing of auditory stimuli
Central Auditory Nervous System Physiology & Processes              in the central nervous system, & in the neurobiologic
                                                                    activity underlying those processes that gives rise to the
                          Gail D Chermak PhD
                               D. Chermak,                          electrophysiologic auditory potentials
                         Washington State University
                                                                                            ASHA (C)APD Work Group 2005
                                  U.S.A.
                            chermak@wsu.edu
                                                                   Deficits in the perceptual processing of auditory stimuli, &
                                  Cairo, Egypt                      the neurobiological activity underlying that processing that
                                  March 2009                        manifests itself primarily (if not solely) in the auditory
                                                                    modality




                                                                                Neurobiologic Origins of (C)APD
    (C)APD Affects Perceptual & Neural Processes Underlying         Abnormal Neurophysiologic Representation of Auditory Stimuli

                                                                   Abnormal neurophysiologic representation of speech & nonspeech signals
       Sound Localization & Lateralization
                                                                   Interhemispheric transfer deficits (in children likely due to developmental
       Auditory Discrimination                                     delay in myelination)

                                                                   Lack f        i t hemispheric l t li ti
                                                                    L k of appropriate h i h i lateralization
       Auditory Pattern Recognition
                                                                   Atypical hemispheric asymmetries
       Temporal Processing                                        Atypical timing in CANS/imprecise synchrony of neural firing

       Auditory Performance With Competing/Degraded Acoustic      Decreased central inhibition
        Signals
                                                                    Jerger et al.,2002; Kraus et al.,1996; Moncrieff et al., 2004; Musiek et al.,1994




Abnormal Neurophysiologic Representation of Auditory Stimuli        Abnormal Neurophysiologic Representation of Auditory Stimuli

                                                                    Acquired
   Developmental (e.g., cerebromorphological                            Neurological lesions or compromise of the CANS, including
    abnormalities, neuromaturational delays)                              neoplasms, neurodegenerative processes (e.g., MS), trauma,
                                                                          impaired cerebral circulation, metabolic disorders (e.g.,
                                                                          Adrenoleukodystrophy [ALD] a demyelinating disease)
   Acquired
                                                                         Aging

                                                                         Secondary to peripheral hearing loss (i.e., sensory deprivation)

                                                                         Noise Exposure
           Mapping the Auditory System                                         Neural Substrate of Audition
                                                                       Cortical
   Auditory System is EXTENSIVE (& complex                             Temporal, Frontal, Parietal, Limbic & Insular Cortices
    connectivity pattern of subcortical auditory system
                                                                       Corpus Callosum (interhemispheric commisural fibers)
    subserves precise temporal processing)
                                                                       Subcortical
                                                                        Medial Geniculate Body (Thalamus)
   Auditory System Overlaps Other Systems
     Sensory                                                           Striatum & Amygdala (Basal Ganglia)

     Cognitive/Executive                                              Reticular Activating System (neurons project to CN; part of circuit
                                                                        controlling startle reflex)
     Motor   Control                      Poremba et al., 2003




          Listening in Noise/Competition                                           Word Recognition in Noise
                                                                       fMRI activation seen in:
       Activates Auditory, Linguistic, Attention,
        Executive Control, Working Memory, Motor                       Superior temporal gyrus
        Planning Areas of Brain
                                                                       Inferior frontal & prefrontal regions (perhaps reflecting increased
                                                                        subvocal rehearsal to overcome noise and accurately perceive
       Temporal Gyri, Thalamus, Cerebellum,                            words)
        Frontal Gyri
                                                                       Thalamus (reflection of engagement of corticofugal pathway in
                                                                        separating signal from noise)
                                               Salvi et al., 2002                                                   Wong et al., 2008




               What is the Neurophysiologic Basis of
                        Auditory Processing?


    Firing Patterns of Brainstem Nuclei Reflected in

    Post-Stimulus Time Histograms (PSTH)

    Reveal the Nature of Auditory Processing



                                        Musiek
                                                                                                         Neurobiology Underlies Clinical Profile of
                                                                                                                         (C)APD
                                   Tonotopicity
                                                                                                                                 &
                                                                                                                    Guides Diagnosis & Intervention




          Functional Deficits Associated with (C)APD                                                             Functional Deficits Associated with (C)APD
     Difficulty understanding spoken language in competing message or                                          Difficulty following complex auditory directions/commands
      noise backgrounds, in reverberant environments, or when rapidly
      presented
                                                                                                                Difficulty learning songs, nursery rhymes; poor musical &
                                                                                                                 singing skills
     Difficulty localizing sound
                                                                                                                Taking longer to respond in oral communication situations
     Misunderstanding messages
                                                                                                                Inattentive/difficulty paying attention
     Responding inconsistently or inappropriately
                                                                                                                Easily distracted
     Frequently requesting repetitions
                                                                                                                Associated reading, spelling, & learning problems
     Saying “what” and “huh” a lot




          The Non-Modular, Interactive Brain                                                                                              In fact,
 Auditory system is extensive & overlaps other sensory, cognitive, executive, & motor control
     systems.
                                                                                                            Increasing evidence that auditory cortex is under
 Considerable evidence of multimodal convergence or interaction of sensory neurons
     responsive to stimulation of different sensory modalities & the modulation of activity evoked by
     one modality on that evoked by another (Kayser & Logothetis, 2007)
                                                                                                             multisensory influence, AND
         Many nuclei across the brainstem (e.g., DCN, IC, MGB) are sites of integration of acoustic &
          M       l i        th b i t      (      DCN IC             it    fi t     ti    f      ti
          multimodal sensory inputs.

         Polysensory processing areas exist within the cortex.
                                                                                                            Suggestion that ALL sensory processing in
 Most domain-specific functions (including language) typically activate multiple areas across
                                                                                                             neocortex might be multisensory
     widespread regions of the brain.

 Most neural regions support multiple functions (i.e., multiple cognitive domains can activate a
     single neural region).
                                                                    Musiek, Bellis, & Chermak, 2005      See Ghazanfar & Shroeder, 2006 for review
                                                                    ASHA, 2005
                                                                                                    Attention Modulates Auditory Processing:
         The Non-Modular, Interactive Brain                                                                     Cortical Level
   Sensory input is not only modulated by concurrent stimulation from                            Top-down priming of sensory cortex: top-down inputs from other
    other sensory modalities, but also modulated by top-down influences                            cortical areas form majority of input connections to both primary &
    (e.g., attention, memory, or language)                                                         secondary auditory cortex (Scheich et al., 2007)
   Auditory processing is influenced by higher-order, nonmodality-
    specific factors such as attention memory motivation, emotion &
                             attention, memory, motivation emotion,                               Selective attention improves p
                                                                                                                         p      perception of high-priority stimuli in the
                                                                                                                                     p          g p       y
    decision processes, & the underlying multimodal, crossmodal, &                                 environment at expense of other less relevant stimuli (e.g., Cocktail
    supramodal neural interfaces supporting performance of these                                   –Party phenomenon)
    behavioral tasks.

        Emotion (evocative pictures) affects auditory processing to an
                                                                                                  Attentional effort is generally associated with greater task difficulty.
         unchanging auditory (speech) stimulus early (20-130 ms.) in the sensory                   When speech degraded by noise, cortical areas related to attentonal
         processing stream as reflected in ERPs.        (Wang et al., 2008)                        processing show increased activation (Binder et al., 2004; Scott et
                                                                                                   al., 2004) reflecting an increase in relative importance of top-down
                                                                                                   influences in speech perception (Davis & Johnsrude, 2003; Zekveld
   Interactive brain is comprised of interfacing sensory, cognitive, & linguistic networks.       et al. 2006)
                    Musiek, Bellis, & Chermak, 2005; ASHA, 2005




     Attention Modulates Auditory Processing:                                                       Attention Modulates Auditory Processing:
                 Cortical Level                                                                                 Cortical Level
   Focusing attention to a given acoustic feature not only                                       When subjects expect tones of a certain frequency, they tend
    increases neural activity level, it also enhances neuronal                                     to detect the expected frequency tones better than ones with
    selectivity to that feature in the particular part of the auditory                             an unexpected frequency in a continuous noise masker (Dai et
    cortex specialized in processing it. (Kauramaki et al., 2007)                                  al., 1991; Wright & Dai, 1994)

   Attention activates regions of the auditory cortex that respond                               Auditory frequency discrimination learning induced by training
    weakly or not at all to unattended tones. (Woods et al., 1980)                                 with identical stimuli (Amitay et al., 2006; Roth et al., 2008)

                                                                                                  Focused auditory attention selectively modulates sensory
   Attention does not just increase stimulus-dependent activation                                 processing in cortex as early as 20 msec post-stimulus as
    in auditory cortex– it leads to addition of activity in auditory                               evidenced in ERPs & neuromagentic fields (Polley et al., 2006;
    cortex not activated by non-attended sounds. Attention                                         Woldorff et al., 1993)
    activates neural populations separate from those processing
    the stimuli (Petkov et al., 2004)




      Remarkably Strong Effects of Top-Down                                                         Attention Modulates Auditory Processing
         Attention on Auditory Processing                                                               At Subcortical & Cochlear Levels

   Human auditory cortex is activated in silence, in absence of acoustic                         Localization: Attention influences which cue in time/intensity
    stimulation, when there is simply the expectation of sound.                                    trading relationships more weighted (Lang & Buchner, 2008)

   During short quiet interlude between musical transitions (Sridharen                           Auditory attention modulates OAE: Increased OAE amplitude
       al 2007)
    et al., 2007), when subjects are imagining auditory stimuli (Halpern &                         suppression seen at frequencies to which subject’s attention
    Zatorre, 1999), when subjects are prompted by silent visual stimuli                            is focused (counting probes in noise) in contralateral ear,
    that are usually accompanied by sound (Calvert et al., 1997), or                               demonstrating that OCB activity can be selectively enhanced
    when subjects are presented familiar musical passages with gaps                                (Maison et al., 2001) & decreased when attention directed to
    inserted (Kraemer et al., 2005)                                                                ipsilateral ear (de Boer & Thornton, 2007).

         But does attention affect lower level auditory processing?                               Efferent olivocochlear activity predicts improvement in an
                                                                                                   auditory discrimination learning task (de Boer & Thornton,
                                                                                                   2008)
        Auditory (Information) Processing
                        bottom-                              top-
    Neither exclusively bottom-up (i.e., stimulus driven) nor top-down (i.e.,
    strategy related including attentional)
                                                                                             Bottom-up & top-down processing
   Auditory cortex represents characteristics of both incoming auditory
    stimulus & of subjective sensory decisions.                                                  should not be regarded as
   Evidence counters traditional view of hierarchy of processing from more
    stimulus-driven (bottom-up) at early processing levels to more complex &
                                                                                                 i d     d t b t th
                                                                                                 independent, but rather as
    cognitive processing (top-down) at higher levels.
                                                                                                   interacting processes.
   Auditory processing consists of interactive networks, patterns of
    convergence & divergence, as well as parallel processing

                           top-       bottom-
    Relative influence of top-down or bottom-up processing is influenced by
                                                          listening–
    changing listening demands (e.g., focused dichotic listening– attending to
             first–       top-
    one ear first– elicit top-down executive & attentional processes) (Bamiou et
    al. 2007)




                     Comorbid Diagnoses                                                                      Why CoMorbidity?
       (C)APD                                Autism/Asperger’s                        1.Brain Organization & Information Processing

       ADHD
                                              Fragile X                                  Shared Neurophysiologic Substrate &
       Learning Disability (LD)                                                            Vasculature
                                              Nonverbal LD
       Language Impairment
                                                                                          Nonmodular, Temporally Coupled, Interfacing,
                                              Social-Emotional LD                          Polymodal, Overlapping, Interconnected,
       Auditory Neuropathy/AD
                                                                                            Synchronized Networks
                                              Fetal Alcohol Syndrome
                                                                                                                                       Buschman & Miller, 2007




                Why Comorbidity?
        Brain Connectivity & Synchronization                                                                 Why Comorbidity?
                                                                                   3.    Nature of Insults
 Temporally Coupled Across Cortex, Modalities, &
                                                                                            Less than circumscribed; extend across artificial boundaries
    Hemispheres
                                                                                   4.    Shared Risk Factors- e.g., hyperbilirubinemia & prematurity are significant risk
                                                                                         factors for AN/AD & (C)APD; abnormal brainstem function possible risk factor
                                                                                         contributing to learning problems (Banai, Abrams, & Kraus, 2007).
 Deficient Timing (i.e., Prolonged Temporal
                                                                                   5.    Shared Histories– e.g., Recurrent Otitis Media
    Integration & Segmentation) Imposes Limitations
    That Spread or Cascade Across Modalities/Region                                6.    Shared Genetics (e.g., ODD, CD, ADHD, & Reading Disorder; Pax 6 Mutation &
                                                                                         working memory & interhemispheric transfer deficits; 73% of variation in
                                                                                         dichotic listening due to genetic differences)

                                                Merzenich et al. 1993              7.    Shared Functional Deficits-- Working Memory Deficits??
         Brain Non-modularity & Interactivity                          Neurobiology Underlies Functional Presentation of
                    Implications                                         (C)APD & Guides Diagnosis & Intervention

   Little, if any, scientific or clinical data to support existence          Diagnosis
    of unimodal sensory (auditory) exclusive deficits

 C)APD can not be defined as an exclusively modality-
              t b d fi d            l i l      d lit                            Guides Test Development
    specific perceptual dysfunction because the brain is non-
    modular.
                                                                                Guides Interpretation of Auditory Performance
 (C)APD is a primarily modality-specific perceptual
    dysfunction that cannot be attributed to higher-order,                    Intervention
    global cognitive, attention, or related disorders.




                                                                                  Interpreting Dichotic Test Results
    Implications for Diagnosis & Intervention                                     Lesion Studies: Hemisphere & CC

       Complex Clinical Profiles                                         Contralateral effect: Deficit in ear opposite involved hemisphere

                                                                          Paradoxical left ear ipsilateral effect: Deficit in ear ipsilateral to
                                                                           lesion (occurs when corpus callosal fibers compromised in left
       Differential Diagnosis Challenge                                         p     ,       y p         g               g
                                                                           hemisphere, thereby impeding the neural signal before it reaches
                                                                           the auditory cortex of the left hemisphere.)

       Diagnosis of (C)APD Can Be Applied Even                           Bilateral deficits: Dysfunction in both hemispheres; or compromise
        When a Perceptual Deficit is Demonstrated in                       of only one hemisphere (i.e., the left auditory cortex), when
                                                                           accompanied by involvement of callosal fibers. (Left ear deficit
        Other Modalities (Multimodal or Supramodal).                       occurs because of callosal involvement and right ear deficit results
                                                                           from classic contralateral ear effect.
                                                                                                                          Musiek & Pinheiro, 1985




                                                                                                     Myelination
        Neurobiology Underlies Advances in Diagnostic Battery                          Implications for Age-Appropriate Norms


       Behavioral Tests: Dichotics, Pattern Tests,                       ABR adult –like by age two years
                             Gap Detection
                                                                          Event –related potentials-- mature by early adolescence/
       Auditory Evoked Potentials &                                                                                  teenage years
        Event-Related Potentials
                                                                          Many behavioral measures (dichotics, patterns) not
                                                                             mature until 10 -13 years
       Brain Electrical Activity Mapping (&
        Neuroimaging)                                                       But MLDs mature by preschool –early primary
                           Testing
                 Neurobiologic Considerations                                                        Brain Organization & System Interactions

        Age/Gender Appropriate Norms                                                          Underscore the need for comprehensive diagnostic
                                                                                                & multidisciplinary assessment procedures to fully
        Age Appropriate Task and Response Mode                                                 explore the nature of the presenting difficulties of
                                                                                                   h individual         t d f (C)APD.
                                                                                                each i di id l suspected of (C)APD
        Consider Demands on Other Modalities (e.g.,
         Vision), Attention, Memory, Intellect, Decision
         Making, etc.                                                                          The outcomes of these evaluations are used to
                                                                                                develop a comprehensive & multidisciplinary
        Consider Medications (i.e., neurochemistry) &                                          intervention program.
         Patient’s Physical State




                                                                                                  Neuroscience-Based Training Principles
          Implications for Rehabilitation                                                                   Learning Theory

Neuroscience-
Neuroscience-Based Training Principles & Learning Theory                                    2. Extensive (Multidisciplinary) Central Resources Training

                                                                                                Exploits large, shared & overlapping auditory, cognitive, metacognitive, &
1. Intensive Training exploits plasticity & cortical reorganization                             language systems

                                                                                                May extend area of cortical reorganization

  Considerable practice & significant challenge by working near                                 Complements & supplements auditory training & reduces functional deficits
  the patient’s skill threshold
                                                                                                Emphasizes interactions between bottom-up & top-down processing, &
                                                                                                supramodal, crossmodal & multimodal interfaces

                                                                                                Maximizes generalization & effectiveness




         Neuroscience-Based Training Principles                                                            Good News for Rehabilitation!
                   Learning Theory                                                                               Neuroplasticity

 3. Active participation, coupled with salient                                                 Activation of Previously Inactive Neuronal Tissue May Occur
                                                                                                Secondary to Stimulation and/or Improved Neural Synchrony,
    reinforcement & feedback, motivate, augment                                                 As Well As the Development of More Efficient Synaptic
    attention (both task-specific and g
              (           p                          )
                                      general arousal) &                                        Connections Within the Brain.
    maximize learning
                                                                                               Stimulation & Training Induce Plasticity

 Ahissar et al., 1992; Holroyd et al., 2004; Merzenich & Jenkins,1995;Moore et al., 2008;      Modification of Cortex Reflected in Behavioral Change (i.e.,
    Swanson & Cooney,1991                                                                       Learning)
                Physiology of Plasticity                                                   Plasticity
       Dentritic branching or pruning
                                                                  Cortex remains plastic through adulthood (see Feldman &
                                                                   Brecht, 2005 & Ohl & Scheich, 2005 for reviews)
       Increase in synaptic density

       Increase in availability of neurotransmitter              Reorganization/Remapping of C t b E
                                                                   R      i ti /R       i    f Cortex by Experience &
                                                                                                              i

       Increased myelination                                     Plasticity of Brainstem– See See de Boer &Thornton,
                                                                   2008; Johnson et al., 2008; Knudsen, 1998; Nicol &
       Recruitment of “reserve” neurons                           Kraus, 2005; Russo et al. 2005; Snyder et al., 2008; Song
                                                                   et al., 2008)
       Release of “suppressed” neurons




                Neurobiology Mandates
            Early & Aggressive Intervention                                    Shared Neural Substrate
   Appropriate, repeated sensory stimulation can result in
    positive neurochemical, physiologic & morphologic                 Comorbidity
    changes in the brain.

   Y
    Younger brains more malleable; th f
              b i         ll bl therefore, early
                                              l                       Complex Clinical Profiles
    intervention

   Training should be challenging, varied & progressive for          OPPORTUNITIES FOR INTERVENTION
    best results                                                            MULTIDISCIPLINARY TEAM
                           Musiek, Chermak & Weihing, 2007




                        Neurobiology
                Implications for Rehabilitation                        Current Models of Perceptual Learning

    Auditory Training (Treatment) Approaches That Exercise        Depend strongly on top-down influences such as
           Central Auditory Processes Derive From Our
                  Understanding of Neurobiology.
                                                                   attention, reward, & task relevance

 Dichotic Interaural Intensity Difference Training               Underscoring importance of central resources
                               (DIID)                              training

 Interhemispheric Transfer Training                                   (e.g., Gilbert & Sigman, 2007; Keuroghlian & Knudsen, 2007)
  Neurobiology Directs Us To                 www.neuroaudiology.com

                                  Hosted by: University of Connecticut, Neuroaudiology Lab,
                                           Department of Communication Sciences
   Harness Central Resources
To Complement Auditory Training   Site provides access to most recent articles relevant to
                                    (C)APD & electrophysiology from over 20 of the most
   for Rehabilitation of (C)APD     important hearing related journals. Updated weekly.