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 Binaural Basic Circuits 8 ‐ 9 Brodal Fig MSO: medial superior olive; LSO: lateral superior olive NTB: nucleus of trapezoid body; IC: inferior colliculus 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 Binaural Basic Circuits 8 ‐ 9 Brodal Fig MSO: medial superior olive; LSO: lateral superior olive NTB: nucleus of trapezoid body; IC: inferior colliculus 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 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 Output of SOC to IC 8 ‐ 9 glutamate Brodal Fig glycine MSO: medial superior olive; LSO: lateral superior olive NTB: nucleus of trapezoid body; IC: inferior colliculus 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.