Introduction to Neurobiology Neuroscience of Auditory Processing
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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. firstname.lastname@example.org 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. 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