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Processing in the Superior Olivary Complex.Pdf Processing in The Superior Olivary Complex Alan R. Palmer Medical Research Council Institute of Hearing Research University Park Nottingham NG7 2RD, UK Binaural cues for Localising Sounds in Space time Interaural Time Differences (ITDs) Interaural Level Differences (ILDs) Binaural Mechanisms of Sound Localization • 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 at high frequency are initially analysed in the LSO by input that is inhibitory from one ear and excitatory from the other. 1 The Auditory Nervous System Cortex Cortex MGB Medial Geniculate Body Excitatory GABAergic IC Inferior Colliculus GlycinergicInteraural Level Differences DNLL Nuclei of the Lateral Lemniscus LateralInteraural Lemniscus Time Differences Cochlear Nucleus DCN PVCN MSO Lateral Superior Olive AVCN Medial Superior Olive Cochlea MNTB Medial Nucleus of the Trapezoid Body Superior Olive Binaural Hearing The ability to extract specific forms of auditory information using two ears, that would not be possible using one ear only. 2 Advantages of Two Ears • Improved detection / increased loudness • Removing interference from echoes • Improved detection of sounds in interfering backgrounds • Spatial localization • Detection of auditory motion 20 dB 700 μs Nordlund Interaural level differences ((ghigh freq uency) 3 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 Excitatory Inhibitory _ + + + + 4 Ipsilateral Contralateral 100 100 el (dB SPL) el (dB v Sound le 20 20 0.12532 0.125 32 Frequency (kHz) Caird and Klinke 1983 5 Caspary and Finlayson (1991) Irvine (1986) Interaural time differences ((qy)low frequency) The discharges of cochlear nerve fibres to lowlow-- frequency sounds are not random; they occur at particular times (phase locking). Evans (1975) 6 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 Time Difference Pathway The coincidence detection model of Jeffress (1948) is the widely accepted model for lowlow--frequencyfrequency sound localisation Response 0 Interaural Time Difference 7 Response 0 Interaural Time Difference Department of Neurophysiology,University of Wisconsin ALT TAB Ipsilateral Contralateral Barn Owl: Konishi et al 1988 8 Pena et al 2001 Matches between the inputs from the two ears in the Barn Owl Nucleus Laminaris Fischer and Pena 2009 Pathways for analysing interaural time differences To inferior colliculus Excitatory Cochlear Cochlear Left Ear + Nucleus Nucleus Right Ear Semicircular Canals + + + Window MSO Large calyx synaptic ending 9 0 μs Time Delay 0 μs Cochlear Cochlear Left Ear Nucleus Nucleus Right Ear Semicircular Can als Window MSO Auditory Nerve Activity Large calyx synaptic ending 0 μs Time Delay Arrives at left ear 300 μs later than at the right 300 μs Cochlear Cochlear Left Ear Nucleus Nucleus Right Ear Se micir cul ar Canals Window MSO Auditory Nerve Activity Large calyx synaptic ending 300 μs Time Delay Coincident spikes Arrives at left ear 300 μs 0 μs Time Delay later than at the right 300 μs 0 μs Cochlear Cochlear Left Ear Nucleus Nucleus Right Ear Se micir cul ar Canals Window MSO Auditory Nerve Activity Large calyx synaptic ending 300 μs Time Delay 0 μs Time Delay Coincident spikes 10 -600 -300 0 300 600 ITD (μs) Interaural Phase Sensitivity in the MSO Best Delay 1 ms 1 ms Yin and Chan (1988) Smith et al 1993 11 Bekius et al 1999 Noise BF tones Guinea Pig Palmer et al., 1990 Cat Yin et al., 1986 Palmer et al 1990 Distribution of peaks of ITD functions in response to interaurally-delayed noise Physiological range 80 ones r 60 40 Number of Neu of Number 20 0 -500 0 500 1000 Interaural Delays (μs) McAlpine Jiang and Palmer 2001 12 McAlpine, Jiang and Palmer 1996 1/8 1/4 1/2 cycle 1/16 McAlpine Jiang and Palmer 2001 Brand et al 2002 13 Grothe 2003 Brand et al., 2002 325 Hz 500 Hz 700 Hz ed Response ed -1000 -500 0 500 1000 Normalis ITD (μs) 1.0 kHz 1.4 kHz -1000 -500 0 500 1000 -1000 -500 0 500 1000 McAlpine Jiang and Palmer 2001 ITD (μs) ITD (μs) 14 Distribution of steepest slopes of ITD functions in response to interaurally-delayed noise Physiological range 80 60 urones 40 Number of Ne 20 0 -500 0 500 1000 Interaural Delays (μs) McAlpine Jiang and Palmer 2001 600 0.5 Interaural Phase Difference 1.0 s) μ 500 0.4 0.8 400 0.6 0.3 300 0.4 0.2 200 ural Time Difference Difference ( ural Time ormalised Response 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 ITD processing is BF-BF-dependent.dependent. ITD functions are steepest around midline. The consequence of this is that: As ITD increases across the physiological range the activity at any frequency increases 15 Descending pathways Spangler and Warr 1991 Warr 1978, Warr and Guinan 1979 16 Spoendlin 1971 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 17.
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