Douglas Oliver University of Connecticut Health Center ... · & LATERAL LEMNISCUS Douglas Oliver University of Connecticut Health Center. CORTEX MGB IC DCN VCN SOC COCHLEA Auditory

SUPERIOR OLIVE & LATERAL LEMNISCUS

Douglas OliverUniversity of Connecticut Health Center

CORTEX

MGB

IC

DCN

VCN

SOC

COCHLEA

Auditory Cortex

Auditory Pathways

DLL

VLL

DLL

VLL

GLUTGABAGLY

InferiorColliculus

Medial Geniculate Body

IC

Auditory Pathways

Organization of Superior Olivary Complex

Subdivisions and Cytoarchitecture Neuron types Inputs Outputs Synapses Basic Circuit

Tsuchitani, 1978, Fig. 10

MSO

LSO

MNTB

MSO

LSO

MNTB

(somata & dendrites) (axons & endings)

D

M

Cytoarchitecture of Superior Olivary Complex

Comparative anatomy of SOC

Tetsufumi Ito &Shig Kuwada

Brod

alFi

g 9-

8

MSO: medial superior olive; LSO: lateral superior oliveNTB: nucleus of trapezoid body; IC: inferior colliculus

Binaural Basic Circuits

Medial Superior Olive (MSO)

MSO Principle Cells

glutamate

Fusiform Bipolar Disc-shaped Each dendrite

innervated by a different side

MSO-In situ hybridization

VGLUT1 VGLUT2 VIAAT NISSL

MSO

MNTB

LSOSPO

RPO

LSO MSO

MNTB

G

BB

B

L

L

H

H

EI - ILD EE - ITD

MSO Inputs and Synapses

E=Excitation (glutamate) --- I=Inhibition (glycine)

H=high frequencyL=low frequency

LNTBTO LSO

Unlike retinal targets, the cochlear nuclei contain maps of frequency, not location.

T

T + ITD

So how does the auditory system know ‘where’ a sound is coming from?

By comparing the interaural time differences (ITD) between the ears

How is this accomplished?...

ITD CODING

A

B

C

D

E

abcd eOutputPlace Code

Left InputTime Code

Right InputTime Code

A

B

C

D

E


Left InputTime Code


MSO "peak" unit LSO "trough" unit

ExcitationInhibition

A C

D E

B

ITD ITD

LSO

E

E E

I

Figure 14.2

MSO

MSO creates a response to interaural time differences

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)

Brod

alFi

g 9-

8


Binaural Basic Circuits

LSO-In situ hybridization


MSO

MNTB

LSOSPO

RPO

Calyx of Held

CalyxVGLUT1

LSO MSO

MNTB

G

BB

B

L

L

H

H

EI - ILD EE - ITD

LSO Inputs and Synapses



A

B

C

D

E


Left InputTime Code


A

B

C

D

E


Left InputTime Code


MSO "peak" unit LSO "trough" unit

ExcitationInhibition

A C

D E

B

ITD ITD

MSO

E

E E

I

Figure 14.2

LSO

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

Brod

alFi

g 9-

8


Output of SOC to IC

glutamate

glycine

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

ITDs work only for the low frequency components of sound

What about higher frequencies?

The sound shadow cast by the head produces interaural level differences

How is this comparison made?...

Louder Softer

ILD CODING

LSO MSO

MNTB

G

BB

B

L

L

H

H

EI - ILD EE - ITD

LSO Inputs and Synapses



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

Brod

alFi

g 9-

8


Output of SOC to IC

glutamate

glycine

Periolivary nuclei

Sources of inhibitory inputs Ascending Descending

Periolivary-In situ hybridization


MSO

MNTB

LSOSPO

RPO

Periolivary Nuclei

CONTRLATERALVCN

IPSILATERALVCN

VMPO

VLPO

SPO

DPO

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

Perc

enta

ge o

f GAB

A-ir

neur

ons t

hat

inne

rvat

e th

e in

ferio

r col

licul

us in

the

rat

González-Hernández et al. (1996) Sources of GABAergic input to the inferior colliculus ofthe rat.J. Comp. Neurol. 372 : 309–326.

IC (c)DNLL (c)DNLL (i)INLL (i)VNLL (i)CLSO (c)LSO (i)MSO (i)SPON (i)OPO (i)AVCN (c)PVCN (c)DCN (c)

2.920.39.59.8480.60.60.32.93.40.80.50

234.44.09.147.50.60.40.24.44.01.01.00

CNICv CNICd

INLL + IVNLL = 57.8 % / 56.6%

NLL is the main source of inhibitory inputs to the IC

Neurotransmitters

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Douglas Oliver University of Connecticut Health Center ... · & LATERAL LEMNISCUS Douglas Oliver University of Connecticut Health Center. CORTEX MGB IC DCN VCN SOC COCHLEA Auditory