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The Auditory Nervous System

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The Auditory Nervous System The Auditory Nervous System Cortex Processing in The Superior Olivary Complex Cortex Advantages of Two Ears MGB Medial Geniculate Body • Improved detection / increased loudness Excitatory Alan R. Palmer GABAergic IC Inferior Colliculus • Removing interference from echoes GlycinergicInteraural Level Differences • Improved detection of sounds in Medical Research Council Institute of Hearing Research DNLL Nuclei of the Lateral Lemniscus interfering backgrounds University Park LateralInteraural Lemniscus Time Differences Nottingham NG7 2RD, UK Cochlear Nucleus • Spatial localization DCN • Detection of auditory motion PVCN MSO Lateral Superior Olive AVCN Medial Superior Olive Cochlea MNTB Medial Nucleus of the Trapezoid Body Superior Olive Binaural cues for Localising Sounds in Space 20 dB time 700 μs Interaural Time Differences (ITDs) Interaural Level Differences (ILDs) Nordlund Binaural Mechanisms of Sound Localization Binaural Hearing • Interaural time (or phase) difference at low frequency are initially analysed in the MSO by coincidence detectors connected by a delay line system. Interaural level differences • Interaural level differences at high frequency are initially The ability to extract specific forms of auditory analysed in the LSO by input that is inhibitory from one information using two ears , that would not be ((ghigh freq uency) ear and excitatory from the other. possible using one ear only. 1 PARALLEL PROCESSING OF INFORMATION IN THE COCHLEAR NUCLEUS To medial superior olive: information about sound To inferior colliculus: information about pinna localisation using timing (and possibly time coding of speech) sound transformations To lateral superior olive: information about sound localisation using interaural intensity To medial nucleus of the trapezoid body: information Either commisural or to inferior colliculus about sound localisation using interaural intensity information about sound level and voice pitch To inferior colliculus: information about complex sounds (possibly place coding of speech) Input from cochlear nerve Interaural Level Difference Pathway Caspary and Finlayson (1991) Irvine (1986) Excitatory Inhibitory Interaural time differences ((qy)low frequency) _ + + + + Ipsilateral Contralateral The discharges of cochlear nerve fibres to lowlow-- 100 100 frequency sounds are not random; they occur at particular times (phase locking). el (dB SPL) el (dB v Sound le 20 20 0.12532 0.125 32 Frequency (kHz) Caird and Klinke 1983 Evans (1975) 2 PARALLEL PROCESSING OF INFORMATION IN THE COCHLEAR NUCLEUS To medial superior olive: information about sound To inferior colliculus: information about pinna localisation using timing (and possibly time coding of speech) sound transformations Response 0 Interaural Time Difference To lateral superior olive: information about sound localisation using interaural intensity To medial nucleus of the trapezoid body: information Either commisural or to inferior colliculus about sound localisation using interaural intensity information about sound level and voice pitch To inferior colliculus: information about complex sounds (possibly place coding of speech) Input from cochlear nerve Interaural Time Difference Pathway Pena et al 2001 The coincidence detection model of Jeffress (1948) is the widely accepted model for lowlow--frequencyfrequency sound Matches between the inputs from the two ears localisation in the Barn Owl Nucleus Laminaris Department of Neurophysiology,University of Wisconsin ALT TAB Fischer and Pena 2009 Pathways for analysing interaural time differences Ipsilateral Response To inferior colliculus Excitatory 0 Interaural Time Difference Cochlear Cochlear Left Ear + Nucleus Nucleus Right Ear Semicircular Canals + + + Window MSO Contralateral Large calyx synaptic ending Barn Owl: Konishi et al 1988 3 0 μs Time Delay 0 μs -600 -300 0 300 600 ITD (μs) Cochlear Cochlear Left Ear Nucleus Nucleus Right Ear Se micir cul ar Canals Window MSO Auditory Nerve Activity Large calyx synaptic ending 0 μs Time Delay Bekius et al 1999 Interaural Phase Sensitivity in the MSO Arrives at left ear 300 μs later than at the right Best Delay Noise BF tones 300 μs Cochlear Cochlear Left Ear Nucleus Nucleus Right Ear Se micircular 1 ms 1 ms Canals Guinea Pig Win dow Palmer et al., 1990 MSO Cat Yin et al., 1986 Auditory Nerve Activity Large calyx synaptic ending 300 μs Time Delay Coincident spikes Yin and Chan (1988) Palmer et al 1990 Arrives at left ear 300 μs Smith et al 1993 0 μs Time Delay later than at the right Distribution of peaks of ITD functions in response to interaurally-delayed noise 300 μs Physiological range 0 μs Cochlear Cochlear 80 Left Ear Nucleus Nucleus Right Ear Semicircular Canals ones r 60 Win dow MSO 40 Number of Neu of Number Auditory Nerve Activity 20 Large calyx synaptic ending 300 μs Time Delay 0 μs Time Delay 0 -500 0 500 1000 Interaural Delays (μs) Coincident spikes McAlpine Jiang and Palmer 2001 4 Distribution of steepest slopes of ITD functions in response to interaurally-delayed noise Physiological range 80 60 urones 40 Number of Ne of Number 20 0 -500 0 500 1000 Interaural Delays (μs) Grothe 2003 McAlpine, Jiang and Palmer 1996 McAlpine Jiang and Palmer 2001 1/8 1/4 1/2 cycle 600 0.5 Difference Phase Interaural 1.0 s) μ 500 0.4 0.8 400 1/16 0.6 0.3 300 0.4 0.2 rmalised Response rmalised 200 ural Time Difference ( Difference Time ural o a (cycles) N 0.2 0.1 Inter 100 0.0 -1000 -500 0 500 1000 0 0.0 Interaural Time Difference (μs) 0.00 0.25 0.50 0.75 1.00 1.25 1.50 Frequency (kHz) McAlpine Jiang and Palmer 2001 Brand et al., 2002 McAlpine Jiang and Palmer 2001 325 Hz ITD processing is BF-BF-dependent.dependent. 500 Hz ITD functions are steepest around midline. 700 Hz ed Response ed -1000 -500 0 500 1000 The consequence of this is that: Normalis ITD (μs) 1.0 kHz As ITD increases across the physiological range the activity at any frequency increases 1.4 kHz -1000 -500 0 500 1000 -1000 -500 0 500 1000 McAlpine Jiang and Palmer 2001 Brand et al 2002 ITD (μs) ITD (μs) 5 Descending pathways Spoendlin 1971 Spangler and Warr 1991 Wiederhold and Kiang 1971 Function of the descending or centrifugal innervation • Protection from acoustic trauma • Control of the mechanical state of the cochlea • Involvement in selective attention • Detection of complex signal in noise Warr 1978, Warr and Guinan 1979 6.
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