Lecture5

Audition

Cogs17*UCSD

SoundWaves

Frequency =#Cycles/Second=Hz

6cycles/sec=6Hz

1second

Perspeed atwhichmoleculesofmedium(air)ossicillate

Frequency =#Cycles/Second=Hz

6000cycles/sec=6000Hz=6kHz

.001second

Perspeed atwhichmoleculesofmedium(air)ossicillate

Phase =placeincycleofcondensation&rarefaction

Peakofphase

Peakofphase

Troughofphase

Troughofphase

Amplitude =Distance agivenmoleculeofmedium(air)travelsduringitsosscillation

Ifdistance<xmeters=LowAmplitude(softsound)

Ifdistance>xmeters=HighAmplitude(loudsound)

AuditoryReception

AlsocalledTympanicMembrane

n

(HammerAnvil

Stirrup)

Ossicles

OVALWINDOWofCochlea

ofStirrup

ConvertlargevibrationsofbigTympanicMembraneintosmaller,butmorepowerfulvibrationsofOvalWindow

OvercomesIMPEDANCEMISMATCHAirmoleculesareeasytovibrate,butviscousCOCLEARFLUIDmolecules

inCochleamuchhardertovibrate

TheCochlea

TheCochlea

OrganofCorti

Cross-SectionofCochlea

BasilarMembraneFloorofmiddlechamber

&ofOrganofCorti,onwhichtheHairCells

(Receptors)sit

TectorialMembraneWithinmiddlechamber,TopofOrganofCorti

OrganofCorti

HairCellsAuditoryReceptors

StandbetweenTectorialMembrane

above,andBasilarMembrane

below.

AsmembranesvibrateCILLIA(hairs)are

bent>>releaseNT.

HairCells

Cillia

K+Gate

K+

TransductioninHairCellsisPotassium(K+)based(NoNa+)

K+

WhenCillia arebent,K+gatesarepulledopened

K+

CochlearFluidisrichinPotassium

K+GateK+Gate

K+

K+K+

K+K+

K+

HairCells

K+

K+

K+ K+

K+

K+

K+

K+

K+

K+K+

K+

K+

K+K+

K+

K+K+

K+K+

K+

HigherConcentrationofK+OUTSIDEcell>>soK+enters

ThischangeinpolarityopensCa++gates

Ca++in,Neurotransmitterout

...aGraded response

Frequency(Pitch)

Humanshearfrom20Hzto20,000Hz(or20kHz)

But,wemakeourmostdetaileddiscriminationbetweenfrequenciesupto~5kHz

Thepianokeyboardrangesfrom27.5Hzatlowend

to4,186Hz(~4.2kHz)athighend

CodingforFrequency

• PlaceCoding

• Temporal(Rate)Coding

PlaceCoding

PlaceCoding

APEX

BasilarMembrane

Narrow&Stiff Wide&Floppy

PlaceCoding

Narrow&Stiffresonates

toHIGH Frequencies

Wide&Floppyresonates

toLOW Frequencies

BasilarMembrane(Timelapseimageofoscillation)

PlaceCoding

ThemoretheBasilarMembrane

resonates,thefartheritmoves... ...themorethe

Cillia oftheHairCellsare

BENTagainstthe

TectorialMembrane...

...themoreNeurotransmittertheHairCellsrelease.

PlaceCoding

HIGH Frequenciesresonate

BASEofcochlea

LOW Frequenciesresonate

APEXofcochlea

So,itisDISTRIBUTIONofNTreleasealongBasilarMembrane

thatcodesforFrequency

PlaceCoding

High frequencysound=moreresponsefromBasethanApex

BasilarMembraneHighFrequencyLowFrequency

Base Apex

Low frequencysound=moreresponsefromApexthanBase

BasilarMembraneHighFrequencyLowFrequency

Base Apex

Mid frequencysound=moreresponsefromMid-Membrane

HighFrequencyLowFrequencyBase ApexBasilarMembrane

HairCells accomodate thiswithagraded response,respondingtorelativeamountsofvibrationalongBasilarMembrane

BUTHairCellscommunicatetoSpiralGanglions(whoseaxonsmakeuptheAuditoryNerve)

whichfireActionPotentials

RefractoryPeriodforActionPotentialslimithowfrequentlySpiralGanglionscanfire!

Maximum~1000/second

Inadditiontodifferent"places"resonatingmorethanothers,WHOLE BasilarMembranevibratesatrateofinput

(e.g.3000Hz>>3000oscillations/sec)

Sohowcantheycodefora3000Hztone?!!

TemporalCoding(RateCoding)

TemporalCoding(RateCoding)

ANSWER:NosingleGanglioncellcan!ButagroupofthemworkingtogetherCAN!!

3000Hztone

SpiralGanglions(ANFs)

SGa

SGb

SGc

SGd

SGe

AllrespondingtoSAMEHairCell

OverallresponsefromAuditoryNerve

ProducesVOLLEYSofactivityatrateofinput(3000/sec)

TemporalCoding(RateCoding)

VolleyPrinciple– DependsonGanglionsbeingPhaseLocked

SpiralGanglionsdonotjustfirewhen

theyareready,butarelockedtothe

PHASEofinput(onlyfire~PEAK)

Inthisway,AuditoryNerve

producesVOLLEYSofactivityatcorrectintervals

Localization - viaAmplitude differences

"HeadShadow"Headabsorbssomeof

soundenergy,sosoundislouderatearclosertosource.

WorksbestwithHigherFrequencies(shorterwavelengths)sincelowerfrequencies

passaroundhead,lesslikelytobeabsorbed.

High frequencysoundshaveshort wavelengths

Low frequencysoundshavelong wavelengths

Localization - viaPhase differences

Localization - viaPhase differences

NotePHASEdifferenceattwoearsSmall-headedanimalsdonotusephase,

sinceoftenambiguous

WorksbestwithLowerFrequencies(longerwavelengths)

Localization - viaTiming DifferencesAxonfrom

COCHLEARNUCLEUS

LeftEar

Axonfrom

COCHLEARNUCLEUS

RightEar

SuperiorOlive(Medulla)

EachCochlearNucleusaxonbranchestosynapseononeofmanySuperiorOlivecells

Localization - viaTiming DifferencesAxonfrom

COCHLEARNUCLEUS

LeftEar

Axonfrom

COCHLEARNUCLEUS

RightEar

SoundcametotheLEFT earfirst

SuperiorOlive(Medulla)

Localization - viaTiming DifferencesAxonfrom

COCHLEARNUCLEUS

LeftEar

Axonfrom

COCHLEARNUCLEUS

RightEar

SuperiorOlive(Medulla)

IfRIGHT sideofSuperiorOlivefires,soundcametotheLEFT earfirst

OnlywheninputfromBOTHearsconvergeswillSuperiorOlivefire

SoundcametotheLEFT earfirst

Localization – viaTiming DifferencesAxonfrom

COCHLEARNUCLEUS

LeftEar

Axonfrom

COCHLEARNUCLEUS

RightEar

SuperiorOlive(Medulla)

IfLEFT sideofSuperiorOlivefires,soundcametotheRIGHT earfirst

SoundcametotheRIGHT earfirst

Localization – viaTiming DifferencesAxonfrom

COCHLEARNUCLEUS

LeftEar

Axonfrom

COCHLEARNUCLEUS

RightEar

SuperiorOlive(Medulla)

IfMIDDLE ofSuperiorOlivefires,soundcametoBOTH earsatsametime

Soundreachesbothearsatsametime

AuditoryPathways

BeginwithHairCells(Receptors)inCochlea

HairCells– AuditoryReceptorsCochlea

OrganofCorti

HairCells– AuditoryReceptors

Inner HairCells Outer HairCells

SpiralGanglions

AxonsmakeupAuditoryNerve

CochlearNucleus(inMedulla)

“Divergent”Connection

1:8

“Convergent”Connection

20:1

SpiralGanglion

CochlearNucleus(inMedulla)

ForDetails

(e.g.DiffFreqs)

NOT forDetails

(e.g.Amp)

AuditoryPathways

AuditoryNerveto

CochlearNucleusin

Medulla

Monaurali.e.eachAuditoryNerve

connects onlytoIPSI-lateralside

CochlearNucleusCells

SpiralGanglion(ANF)

Primary-Like

Build-Up

Onset

Phaser

CellRe

spon

se

CellRe

spon

seCe

llRe

spon

seCe

llRe

spon

se

Time

Time

Time

Time

Time

CellRe

spon

se

EachSpiralGanglionsynapsesonmultipleCochlearNucleusCells

AuditoryPathways

FibersfromCochlearNucleusgotoIPSI-lateraland CONTRA-lateralSuperiorOlivesinCerebellum

Thus,these,andallsubsequentconnections,

areBinaural

Combininginfofromboth earsallowsforlocalization.

AuditoryPathways

...isinputtoSuperiorOlivelocalizationcircuit

Onset signalfromCochlearNucleus...

AuditoryPathways

FromSuperiorOlives,

connecttoInferiorColliculi

inMidbrain

Thesecommunicatew/SuperiorColliculi(visualmotionmaps)

andTegmentum,todirecteyestosourceofsound

AuditoryPathwaysFromInferiorColliculi to

MedialGeniculateNucleus(MGN)

ofThalamus

MGNMedialGeniculateNucleus

MNEMONICS:NucleioftheThalamus

• LGN (LateralGeniculateNucleus)

• MGN (MedialGeniculateNucleus)

• VPN (VentralPosteriorNucleus)

• DMN (DorsalMedialNucleus)

• VLN (Ventro LateralNucleus)

• MDN (MedialDorsalNucleus)

• L isforLight(Visual)

• M isforMusic(Auditory)

• VP isforVeryPersonal(Touch)

• DM isforDogMuzzle(Smell)

• VL isforVictoryLap(Motor)

• MD isforMemoryDoctor(Memory)

Others?!

TopologicalMapsinAuditorySystemHighfrequency

soundBasilarMembrane

HighFrequencyLowFrequency

DistributionofactivityacrosstheBasilarMembrane(“Place-coded”frequency)ispreservedupthepathway

(Cochlea)

CochlearNucleus

HighFrequencyLowFrequency

(Medulla)

SuperiorOlive

HighFrequencyLowFrequency

(Medulla)

InferiorColliculus

HighFrequencyLowFrequency

(Midbrain)

MGN

HighFrequencyLowFrequency

(Thalamus)

A1

HighFrequencyLowFrequency

(Cortex)

SpiralGanglion

HighFrequencyLowFrequency

(Cochlea)

IntheAuditorysystem,suchTopologicalmaps

arecalled"Tonotopic Maps"

AuditoryPathways

FromMGNtoA1(PrimaryProjectionArea)

inMedialTemporalCortex

AuditoryCortex

PrimaryProjectionAreaforAudition

OnMedialfaceofTemporalLobe,inLateralFissure

A1 – PrimaryProjectionAreaforAuditioninCortex

500Hz,HighAmp

500Hz,LowAmp

TopologicalFrequencyMapAlsomappedper

Amplitude

1600Hz,HighAmpAllcellsineachcolumn

(through6layers,beloweachdot)havesamepreferredstimulus

A2 – SecondaryAuditoryCortex

A1

A1 – Respondsbesttosinglefrequency

A2 – Respondsbesttochangingfrequency

A2

Wernicke’sArea

HigherAuditoryCortex

Wernicke’sArea– SpecializedforcomprehendingSPEECH

InteractswithBroca's AreainPrefrontalCortex,forspeechProduction