Douglas Oliver University of Connecticut Health Center SUPERIOR OLIVE 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: NTB: Binaural
medial nucleus
superior of trapezoid
olive; Basic body;
LSO:
IC: lateral Circuits inferior
superior colliculus
olive
Brodal Fig 9‐8 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 DE MSO "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 MSO: NTB: Binaural
medial nucleus
superior of trapezoid
olive; Basic body;
LSO:
IC: lateral Circuits inferior
superior colliculus
olive
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 DE MSO "peak" unit LSO "trough" unit
ITD ITD Figure 14.2 Binaural Responses in Superior Olive 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 vs MNTB Response to ILD LSO Creates ILD Responses
. EI 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
EI - ILD EE - ITD LSO MSO L L
B H E B B H G I MNTB MSO: NTB:
medial nucleus Output
superior of trapezoid
olive; of glutamate
body;
LSO: SOC
IC: lateral
inferior to
superior
glycine IC colliculus
olive
Brodal Fig 9‐8 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 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