FINE-TUNING THE AUDITORY SUBCORTEX Measuring processing dynamics along the auditory hierarchy. Christopher Slugocki (Widex ORCA) WAS 5.3.2017
AUDITORY DISCRIMINATION
AUDITORY DISCRIMINATION /pi//k/ /pi//t/ /pi//k/ /bi//k/
AUDITORY DISCRIMINATION /ti/ /bi/? /pi/? /ti/?
AUDITORY DISCRIMINATION /ti/ /bi/ /pi/ /bi/? /pi/ /ti/?
AUDITORY DISCRIMINATION?
AUDITORY DISCRIMINATION?
THE ASCENDING AUDITORY PATHWAY Auditory Percept Neural Representation Physical Sound
THE ASCENDING AUDITORY PATHWAY Auditory Percept Neural Representation Physical Sound
THE DESCENDING AUDITORY PATHWAY Ascending Auditory System Descending Auditory System Chandrasekaran et al., (2009)
DYNAMIC CONTROL LOOPS Sensory information Brainstem Encoding (bottom-up/exogenous) AC Encoding/Prediction/ Expectancy Corticofugal fine-tuning (top-down/endogenous) Bajo & King, 2013; Chandrasekaran et al., 2014
DYNAMIC CONTROL LOOPS An Example Sensory information Brainstem Encoding (bottom-up) Target Voice: F 0 = 110 Hz F 1 = 220 Hz AC Encoding/Prediction/ Expectancy Corticofugal fine-tuning (top-down/endogenous) Boost response to 110 and 220 Hz
CANDIDATE NEURAL CIRCUITRY
THE INFERIOR COLLICULUS (IC) Major convergence hub in rostral brainstem Central nucleus (ICc): Target of bottom-up tonotopic projections from lower nuclei in auditory brainstem (Baumann et al., 2011). Wide variety of neural cell types (Peruzzi et al., 2000). Dorsal nucleus (ICd): Target of top-down projections thalamus and primary auditory cortex (Winer, 2005).
EVIDENCE OF SUBCORTICAL TUNING IN ANIMAL MODELS Suga et al., (2008) Best Frequency frequency at which neuron s response threshold is lowest Stimulating region of bat auditory cortex with certain BF leads to:
EVIDENCE OF SUBCORTICAL TUNING IN ANIMAL MODELS Suga et al., (2008) Best Frequency frequency at which neuron s response threshold is lowest Stimulating region of bat auditory cortex with certain BF leads to: Centripetal shift of closely matched (in BF) neurons in IC towards BF of stimulated cortical region.
EVIDENCE OF SUBCORTICAL TUNING IN ANIMAL MODELS Suga et al., (2008) Best Frequency frequency at which neuron s response threshold is lowest Stimulating region of bat auditory cortex with certain BF leads to: Centripetal shift of closely matched (in BF) neurons in IC towards BF of stimulated cortical region. Centrifugal shift of unmatched (in BF) neurons in IC away from BF of stimulated cortical region.
AUDITORY-EVOKED POTENTIALS
AUDITORY-EVOKED POTENTIALS Reflect summed post-synaptic potentials across populations of neurons.
COMPLEX AUDITORY BRAINSTEM RESPONSE (cabr) Reflects phase-locked activity in rostral brainstem Complex ABR: (1) Transient component (2) Steady-state component Frequencyfollowing Response (FFR) Stimulus Response (cabr)
COMPLEX AUDITORY BRAINSTEM RESPONSE (cabr) Reflects phase-locked activity in rostral brainstem Complex ABR The FFR: Represents signal periodicity up to about 1500 Hz (Skoe & Kraus, 2012). Major generators in IC Subcortical cooling of IC dramatically reduces amplitude of FFR signal in cats (Smith et al., 1978; 1975). Stimulus Response (cabr)
COMPLEX AUDITORY BRAINSTEM RESPONSE (cabr) Slugocki et al., 2017 Envelope Sound Inner Hair Cell Transduction cabr Temporal Fine Structure
DYNAMIC CONTROL LOOPS Sensory information Brainstem Encoding (exogenous) Target Voice: F 0 = 110 F 1 = 220 AC Encoding/Prediction/ Expectancy Corticofugal modulation (top-down/endogenous) Sharpen tuning around 110 and 220 Hz
cabr EXPECTANCY AND PREDICTION Chandrasekaran et al., 2009
cabr EXPECTANCY AND PREDICTION Chandrasekaran et al., 2009
cabr EXPECTANCY AND PREDICTION Chandrasekaran et al., 2009
INTERIM SUMMARY Listening can no longer be accurately modeled as a purely passive sensory process Ascending (bottom-up) and descending (top-down) projections work in dynamic loops to modulate input of auditory information. cabr/ffr represents subcortical activity (at IC) that is sensitive to topdown modulation. Ability to modulate subcortical signal appears related to speech-in-noise performance (HINT).
CONCURRENT MEASUREMENT OF SUBCORTICAL AND CORTICAL AEPs
DYNAMIC CONTROL LOOPS Sensory information Brainstem Encoding (exogenous) Target Voice: F 0 = 110 F 1 = 220 AC Encoding/Prediction/ Expectancy Corticofugal modulation (top-down/endogenous) Sharpen tuning around 110 and 220 Hz
DYNAMIC CONTROL LOOPS Sensory information Brainstem Encoding (exogenous) Target Voice: F 0 = 110 F 1 = 220 AC Encoding/Prediction/ Expectancy Corticofugal modulation (top-down/endogenous) Sharpen tuning around 110 and 220 Hz
DYNAMIC CONTROL LOOPS Sensory information Brainstem Encoding (exogenous) Target Voice: F 0 = 110 F 1 = 220 AC Encoding/Prediction/ Expectancy Corticofugal modulation (top-down/endogenous) Sharpen tuning around 110 and 220 Hz
DYNAMIC CONTROL LOOPS Sensory information Brainstem Encoding (exogenous) Target Voice: F 0 = 110 F 1 = 220 AC Encoding/Prediction/ Expectancy Corticofugal modulation (top-down/endogenous) Sharpen tuning around 110 and 220 Hz
CORTICAL AEPs N1-P2 Complex Indexing integration of exogenous stimulus features. N1 possible correlate of listening effort.
CORTICAL PREDICTIONS The Mismatch Negativity (MMN) Sensitive to degree of deviance (similar to SSA) Sensitive to violations in auditory tends (unlike SSA) Suggests involvement of memory processes S S S O S S
CORTICAL AEPs The P3a component Reflects attention-orienting mechanisms triggered by acoustic novelty. Might also reflect listening effort.
SEAP EXPECTANCY AND PREDICTION Slugocki et al. (In prep.) Forward S S S O S S Reverse S S S O S S
SEAP EXPECTANCY AND PREDICTION Slugocki et al. (In prep.) Stimuli:
SEAP EXPECTANCY AND PREDICTION Slugocki et al. (In prep.) Transients:
SEAP EXPECTANCY AND PREDICTION Slugocki et al. (In prep.) FFRs:
SEAP EXPECTANCY AND PREDICTION Slugocki et al. (In prep.) FFRs:
SEAP EXPECTANCY AND PREDICTION Slugocki et al. (In prep.) FFRs:
SEAP EXPECTANCY AND PREDICTION
DYNAMIC CONTROL LOOPS Sensory information Brainstem Encoding (bottom-up/exogenous) AC Encoding/Prediction/ Expectancy Corticofugal modulation (top-down/endogenous)
POSSIBLE IMPLICATIONS FOR HEARING LOSS
ENHANCED TEMPORAL ENVELOPE Anderson et al., 2013
ENHANCED TEMPORAL ENVELOPE Anderson et al., 2013
ENHANCED TEMPORAL ENVELOPE Anderson et al., 2013
ENHANCED TEMPORAL ENVELOPE Anderson et al., 2013
ENVELOPE VS. TEMPORAL FINE STRUCTURE Anderson et al., 2013
ENVELOPE VS. TEMPORAL FINE STRUCTURE Anderson et al., 2013
ENHANCED TEMPORAL ENVELOPE Anderson et al., 2013
N1 LATENCY AND FFR Bidelman et al., 2014
WHAT CAN BE DONE?
TRAINING AND SUBCORTICAL TUNING Bidelman & Alain, 2015
TRAINING AND CORTICAL PROCESSING Bidelman & Alain, 2015
FINAL SUMMARY Peripheral hearing loss might lead to changes in top-down modulation that increase representation of temporal envelope especially in noise and might require greater listening effort (i.e. augmented N1). Concurrent measurement of subcortical and cortical AEPs can elucidate how brain regions interact during different listening situations. Such approaches might help us to better characterize how hearing loss affects different individuals and to develop interventions and corrective amplification appropriately tailored to the needs of the patient. Auditory training might be particularly useful in re-establishing efficient processing at subcortical and cortical structures.
THANKS FOR LISTENING! Questions? Comments? Concerns?