Processing in The Cochlear Nucleus

Transcription

1 Processing in The Cochlear Nucleus Alan R. Palmer Medical Research Council Institute of Hearing Research University Park Nottingham NG7 RD, UK The Auditory Nervous System Cortex Cortex MGB Medial Geniculate Body Excitatory GABAergic Glycinergic IC Inferior Colliculus DNLL Nuclei of the Lateral Lemniscus Cochlear Nucleus DCN PVCN MSO Lateral Lemniscus Lateral Superior Olive Cochlea AVCN MNTB Superior Olive Medial Superior Olive Medial Nucleus of the Trapezoid Body The cochlear nucleus is the site of termination of fibres of the auditory nerve Cochlear Nucleus Auditory Nerve Cochlea 1

2 Frequency Tonotopicity Basilar membrane Inner hair cell Auditory nerve Fibre To the brain Each auditory-nerve fibre responds only to a narrow range of frequencies Tuning curve Action potential Evans 1975

3 Palmer and Evans 1975 There are many overlapping single-fibre tuning curves in the auditory nerve Audiogram Palmer and Evans 1975 Tonotopic Organisation Lorente

4 Tonotopic Organisation Cochlea Basilar Membrane Hair Cells Base Characteristic Frequency Anterior Apex Spiral Ganglion Auditory Nerve Posterior Cochlear Nucleus Tonotopic projection of auditory-nerve fibers into the cochlear nucleus Ryugo and Parks, 3 The cochlear nucleus: the first auditory nucleus in the CNS Best frequency Position along electrode track (mm) Evans 1975

5 stellate (DCN) Inhibitory Synapse Excitatory Synapse cartwheel DAS to inferior colliculus fusiform SUPERIOR OLIVARY COMPLEX OCB INFERIOR COLLICULUS granule vertical AN golgi DORSAL? COLUMN NUCLEUS VESTIBULAR NERVE to VNLL to MSO to DMPO, PPO MNTB, LNTB via TB giant vertical to CN & IC via TB? to PPO IAS to IC? to VNLL from DLPO PRI PRI-N CHOP-S ON-C spherical bushy globular bushy multipolar multipolar octopus COCHLEAR NUCLEUS ARP (after Meddis, Shackleton and Hewitt) II I Auditory Nerve root neurone via TB to reticular pontine formation and deep SC (perhaps via collaterals to contralateral VNLL) Physiological Classification of Cochlear Nucleus Neurones 5

6 LATERAL INHIBITION IN THE DORSAL COCHLEAR NUCLEUS Tone Le evel (~db SPL) Inhibitory side band Palmer 1977 Excitation Excitation Inhibition Inhibition Excitation Excitation Excitation Inhibition Stabler 1991 Inhibition Inhibition Inhibition Stabler

7 Sound Level Auditory Nerve minimum thresholds Kiang 196 7

8 Saturated rate Threshold Dynamic range Spontaneous rate Galambos and Davis 193 Low threshold Guinea pig Low SR High SR High threshold At each frequency, auditory nerve fibres differ in their spontaneous rate, input/output function and dynamic range - these covary. Winter and Palmer Cat Sachs and Abbas 197 8

9 Cochlear nucleus responses Stabler 1991 Young Timing Peri Stimulus Time Histograms 9

10 When a novel stimulus occurs within a frequency channel the discharge rate is immediately increased and then falls (adapts) over a few tens of milliseconds Kiang et al Winter and Palmer 1

11 Dorsal Lesion AVCN DCN Lesion Spikes p er bin 15 1 Pri Anterior Stellate AN Ventral Globular bushy PVCN Posterior Fusiform 8 Pauser Octopus Spherical bushy Stellate 1 Chop-S Chop-T Pri-N On On C L On I Auditory 1 18 Nerve Time in ms Temporal Responses of the Principal Neurones of the Cochlear Nucleus to pure tones Types of neurones in the cochlear nucleus 11

12 Osen 1969 PARALLEL PROCESSING OF INFORMATION IN THE COCHLEAR NUCLEUS To medial superior olive: information about sound localisation using timing (and possibly time coding of speech) To inferior colliculus: information about pinna sound transformations To lateral superior olive: information about sound localisation using interaural intensity To medial nucleus of the trapezoid body: information about sound localisation using interaural intensity Either commisural or to inferior colliculus information about sound level and voice pitch To inferior colliculus: information about complex sounds (possibly place coding of speech) Input from cochlear nerve Bushy Cells Lorente de Nó 1

13 The discharges of cochlear nerve fibres to low- frequency sounds are not random; they occur at particular times (phase locking). Evans (1975) Alt Tab Enhancement of synchronization in Globular Bushy Cells Joris et al

14 Enhancement of synchronization in Spherical Bushy Cells Joris and Smith 8 PARALLEL PROCESSING OF INFORMATION IN THE COCHLEAR NUCLEUS To medial superior olive: information about sound localisation using timing (and possibly time coding of speech) To inferior colliculus: information about pinna sound transformations To lateral superior olive: information about sound localisation using interaural intensity To medial nucleus of the trapezoid body: information about sound localisation using interaural intensity Either commisural or to inferior colliculus information about sound level and voice pitch To inferior colliculus: information about complex sounds (possibly place coding of speech) Input from cochlear nerve Type T Multipolar Cells Lorente de Nó 1

15 16 BF Tones db Spikes/bin Post Stimulus Onset Time (ms) db Sp pikes/bin khz Chop-T BF Tones 7 7 Noise Post Stimulus Onset Time (ms) Level (db) Level (db) 681 Transient Chopper Unit BF khz 681 > Spikes/bin BF Tones db Post Stimulus Onset Time (ms) 1 BF Tones Noise Level (db) Level (db) Spikes/bin + db Post Stimulus Onset Time (ms) Chop-S 19.6 khz 11 15

16 Generation of vowel sounds At low sound levels steady-state vowels are well represented in the mean discharge rate of the population of auditory nerve fibres. Sachs and Young, 1979 At higher sound levels the representation of the formant frequencies becomes less distinct. Sachs, Young and Colleagues 16

17 * * * Theoretical computations, based on optimally weighting the different spontaneous rate populations, reveal eal that mean rate alone may contain sufficient information even at high sound levels. Delgutte, 1996 Selective listening Lai, Winslow and Sachs, 199 Two populations of cochlear nucleus stellate cells retain vowel formant information in their discharge rate at high sound levels Blackburn and Sachs,

18 S S PARALLEL PROCESSING OF INFORMATION IN THE COCHLEAR NUCLEUS To medial superior olive: information about sound localisation using timing (and possibly time coding of speech) To inferior colliculus: information about pinna sound transformations To lateral superior olive: information about sound localisation using interaural intensity To medial nucleus of the trapezoid body: information about sound localisation using interaural intensity Either commisural or to inferior colliculus information about sound level and voice pitch To inferior colliculus: information about complex sounds (possibly place coding of speech) Input from cochlear nerve Type D Multipolar Cells (commisurals) D-stellate cells in the VCN Cant and Gaston Oertel s Group Physiological Responses before injection Spikes/bin Spikes/bin Post Stimulus Onset Time (ms) BF Tones +5 db + db Post Stimulus Onset Time (ms) Spikes/bin Spikes/bin Post Stimulus Onset Time (ms) Noise db db Post Stimulus Onset Time (ms).5 BF Tones.5 5 Noise Level (db) Level (db) Onset-C Unit BF 6.9 khz 8 18

19 S S Physiological Responses after injection Spikes/bin BF Tones +5 db Spikes/bin Noise db Spikes/bin Post Stimulus Onset Time (ms) Post Stimulus Onset Time (ms) db db Spikes/bin Post Stimulus Onset Time (ms) Post Stimulus Onset Time (ms) BF Tones 5 Noise Level (db) Level (db) Onset-C Unit BF 6.9 khz 8 18 Onset-C Unit BF 6.9 khz 8 19

20 Onset-C Unit BF 6.9 khz 8 Onset unit Chopper unit Primarylike unit Cochlear nerve fibre Kim and Leonard, 1988 Kim and Leonard, 1988

21 Octopus Cells Octopus Cells Oertel et al Octopus Cells Oertel et al 1

22 PARALLEL PROCESSING OF INFORMATION IN THE COCHLEAR NUCLEUS To medial superior olive: information about sound localisation using timing (and possibly time coding of speech) To inferior colliculus: information about pinna sound transformations To lateral superior olive: information about sound localisation using interaural intensity To medial nucleus of the trapezoid body: information about sound localisation using interaural intensity Either commisural or to inferior colliculus information about sound level and voice pitch To inferior colliculus: information about complex sounds (possibly place coding of speech) Input from cochlear nerve Pinna Cue Pathway Dorsal Cochlear Nucleus Bipolar Large Multipolar Giant Fusiform Dorsal Cochlear Nucleus Oertel and Young,

23 Temporal Responses (PSTHS) in Dorsal Cochlear Nucleus Monaural spectral localization cues Moore and King 1999 Responses of a Type IV DCN units to sharp spectral edges Reiss and Young 5 3

24 Input from somatosensory system possibly involved in compensation for pinna and head position Cells sensitive to sharp spectral notches Young (Baltimore)

25 Projections of the Major Cell Types of the Cochelar Nucleus Malmierca and Smith 6 Summary of Cochlear Nucleus Responses The cochlear nucleus consists of three parts each of which is tonotopically organized. The cochlear nucleus contains several major cell types that project to other brain areas. As a result of their interconnections, biophysics and input from the auditory nerve these cell groups reprocess the auditory nerve activity for different features of the incoming sounds. PARALLEL PROCESSING OF INFORMATION IN THE COCHLEAR NUCLEUS To medial superior olive: information about sound localisation using timing (and possibly time coding of speech) To inferior colliculus: information about pinna sound transformations To lateral superior olive: information about sound localisation using interaural intensity To medial nucleus of the trapezoid body: information about sound localisation using interaural intensity Either commisural or to inferior colliculus information about sound level and voice pitch To inferior colliculus: information about complex sounds (possibly place coding of speech) Input from cochlear nerve 5