Douglas Oliver University of Connecticut Health Center SUPERIOR OLIVE & LATERAL LEMNISCUS Auditory Pathways
Auditory CORTEX GLUT Cortex GABA GLY Medial Geniculate MGB Body
Inferior IC Colliculus
DLL DLL COCHLEA VLL VLL
DCN
VCN
SOC Auditory Pathways
IC Organization of Superior Olivary Complex
. Subdivisions and Cytoarchitecture . Neuron types . Inputs . Outputs . Synapses . Basic Circuit Cytoarchitecture of Superior Olivary Complex
LSO LSO
MSO MSO MNTB D MNTB M
(somata & dendrites) (axons & endings)
Tsuchitani, 1978, Fig. 10
Comparative anatomy of SOC
Tetsufumi Ito & Shig Kuwada MSO: medialsuperior olive; LSO: lateral superior olive NTB: nucleus of trapezoid body; IC:inferior colliculus Binaural BasicCircuits
Brodal Fig 9-8 Medial Superior Olive (MSO) MSO Principle glutamate Cells
. Fusiform . Bipolar . Disc-shaped . Each dendrite innervated by a different side MSO-In situ hybridization
RPO
MSO
MNTB
SPO LSO
VGLUT1 VGLUT2 VIAAT NISSL
MSO Inputs and Synapses
H=high frequency EI - ILD L=low frequency EE - ITD LSO MSO
L L
B H B B
H G
LNTB TO LSO MNTB
E=Excitation (glutamate) --- I=Inhibition (glycine) ITD CODING Unlike retinal targets, the cochlear nuclei contain maps of frequency, not location. So how does the auditory system know ‘where’ a sound is coming from?
T + ITD
T
By comparing the interaural time differences (ITD) between the ears How is this accomplished?...
LSO MSO Right Input A Right Input B C Time Code Time Code E E A A B B C C D D E E
Output Output abcde Place Code abcde Place Code Excitation MSO creates a response to Left Input Left Input Inhibition interaural time differences I Time Code E Time Code
DEMSO "peak" unit LSO "trough" unit
ITD ITD Figure 14.2 Binaural Responses in MSO MSO Summary . Cytoarchitecture – Laminar stack . Neuron types - glutamate . Inputs – Spherical bushy AVCN . Outputs – Inferior colliculus . Synapses – Excitatory glutamate . Basic Circuit – Coincidence detector for ITD Lateral Superior Olive(LSO) MSO: medialsuperior olive; LSO: lateral superior olive NTB: nucleus of trapezoid body; IC:inferior colliculus Binaural BasicCircuits
Brodal Fig 9-8 LSO-In situ hybridization
RPO
MSO
MNTB
SPO LSO
VGLUT1 VGLUT2 VIAAT NISSL Calyx of Held Calyx VGLUT1 LSO Inputs and Synapses
H=high frequency EI - ILD EE - ITD L=low frequency LSO MSO
L L
B H B B
H G
MNTB
E=Excitation (glutamate) --- I=Inhibition (glycine) MSO LSO Right Input A Right Input B C Time Code Time Code E E A A B B C C D D E E
Output Output abcde Place Code abcde Place Code Excitation Left Input Left Input Inhibition I Time Code E Time Code
DEMSO "peak" unit LSO "trough" unit
ITD ITD Figure 14.2 Binaural Responses in Superior Olive
LSO Summary . Cytoarchitecture – S-shaped laminae . Neuron types – glutamate or glycine . Inputs – Spherical bushy AVCN ipsilateral MNTB principle cells driven by globular bushy cells contralateral . Outputs – Bilateral inferior colliculus . Synapses – Excitatory glutamate from ipsilateral Inhibitory glycine from MNTB . Basic Circuit – Coincidence detector for ILD and ITD MSO: medialsuperior olive; LSO: lateral superior olive NTB: nucleus of trapezoid body; IC:inferior colliculus Output ofSOCtoIC glutamate glycine
Brodal Fig 9-8 Controversy in the mechanisms of ITD coding
• Mechanisms to code ITD are unclear • Delay lines • Inhibition • Other mechanisms
Beckius et al 1999 Too many best delays outside of physiological range Peaks vs slopes
Summary of ITD coding
. Jeffress model of delay lines consistent with avian MSO . Mammalian mechanisms in dispute . Do peaks of activity indicate place in space or is it the relative amount of activity on two sides (slopes) . Animals with larger heads might have peaks . Inhibition plays a role and can shift peaks . Role of plasticity? Ear movements? Interaural Level Difference (ILD) Coding ILD CODING ITDs work only for the low frequency components of sound
What about higher frequencies?
Louder Softer
The sound shadow cast by the head produces interaural level differences
How is this comparison made?... LSO Inputs and Synapses
H=high frequency EI - ILD EE - ITD L=low frequency LSO MSO
L L
B H B B
H G
MNTB
E=Excitation (glutamate) --- I=Inhibition (glycine) LSO Creates ILD Responses
. Excitatory and inhibitory inputs to LSO . When sound is louder in ipsilateral ear, LSO neurons fire action potentials . When sound is louder in the contralateral ear, LSO neurons are inhibited . ILD may overshadow ITD in the LSO
MSO: medialsuperior olive; LSO: lateral superior olive NTB: nucleus of trapezoid body; IC:inferior colliculus Output ofSOCtoIC glutamate glycine
Brodal Fig 9-8 Periolivary nuclei
. Sources of inhibitory inputs . Ascending . Descending Periolivary-In situ hybridization
RPO
MSO
MNTB
SPO LSO
VGLUT1 VGLUT2 VIAAT NISSL Periolivary Nuclei IPSILATERAL DPO VCN
SPO
VLPO
VMPO
CONTRLATERAL VCN Basic Circuit of SPON Other Inputs: Descending System Periolivary Nuclei Summary
. Neurons use GABA, glycine, or acetylcholine . Inputs from cochlear nucleus, one side only . Monaural . Output to IC: SPON Cochlear nucleus: VNTB & VLPO Cochlea -medial OCB: VMPO & other Cochlea -lateral OCB: VLPO & other Lateral Lemniscus
. Sources of inhibitory inputs to inferior colliculus (IC) . Dorsal nucleus of the Lateral Lemniscus GABA inputs to IC . Ventral nucleus of the Lateral Lemniscus Mixed GABA and glycine inputs to IC . Intermediate nucleus of the lateral lemniscus Glutamatergic neurons Cytoarchitecture and subdivisions
Neuron Types-DNLL Cochleotopical organization
DNLL
Neuron Types-VCLL VCLL Batra and Fitzpatrick Hearing Res. 168 - 2002 Neurotransmitters
Percentage of GABA-ir neurons that innervate the inferior colliculus in the rat NLL is the mainsource ofinhibitory inputs to the IC DCN (c) PVCN (c) AVCN (c) OPO (i) SPON (i) MSO (i) LSO (i) CLSO (c) VNLL INLL DNLL (i) DNLL (c) IC (c) (i) INLL + IVNLL = 57.8 %/56.6% IVNLL = INLL + (i) NC CNICd CNICv 0 0.5 0.8 3.4 2.9 0.3 0.6 0.6 48 9.8 9.5 20.3 2.9 0 1.0 1.0 4.0 4.4 0.2 0.4 0.6 47.5 9.1 4.0 4.4 23 J. Comp.Neurol.309–326. 372: the rat. input to the inferior colliculus o (1996) Sources ofGABAergic González-Hernández et al. f