HST.722 Brain Mechanisms of Speech and Hearing Fall 2005 Dorsal Cochlear Nucleus September 14, 2005 Ken HancockDorsal Cochlear Nucleus (DCN)Slide 3The cochlear nucleusAN fibers terminate in a “tonotopic” or “cochleotopic” patternMajor subdivisions of the cochlear nucleusSummary of pathways originating in the cochlear nucleusProjections suggest DCN is a different animal than VCNDorsal Cochlear NucleusSlide 10PowerPoint PresentationSlide 12Slide 13Slide 14Response Map classification schemeDCN: Vertical cells are type II and type III unitsAntidromic stimulationDCN: “Principal” cells are type III and type IV unitsNeural circuitry underlying DCN physiology: type II units inhibit type IV unitsClassic experiment: type II units inhibit type IV unitsDCN physiology so far…Inhibition from type II units doesn’t account for everythingDCN notch noise sensitivity due to wideband inhibitionPVCN: is the D-stellate cell the wideband inhibitor?Summary: Circuitry of DCN deep layerSummary of DCN anatomy and physiologySlide 27Slide 28Filtering by the pinna provides cues to sound source locationType IV units are sensitive to HRTF first notchSlide 31DCN is a “cerebellum-like structure”Synaptic plasticity: Long-Term Potentiation (LTP)Electric fish provide clues to cerebellum-like functionElectric fields provide information about nearby objectsWhat do cerebellum-like structures do???Slide 37DCN may play a role in tinnitusSlide 39HST.722 Brain Mechanisms of Speech and HearingFall 2005Dorsal Cochlear NucleusSeptember 14, 2005Ken HancockDorsal Cochlear Nucleus (DCN)•Overview of the cochlear nucleus and its subdivisions•Anatomy of the DCN•Physiology of the DCN•Functional considerationsDorsal Cochlear Nucleus (DCN)•Overview of the cochlear nucleus and its subdivisions•Anatomy of the DCN•Physiology of the DCN•Functional considerationsDCNVCNANThe cochlear nucleusAN fibers terminate in a “tonotopic” or “cochleotopic” patternAVCNPVCNDCN36.0 kHz10.2 kHz2.7 kHz0.17 kHzMajor subdivisions of the cochlear nucleusSpherical bushyGlobular bushyMultipolarOctopusSummary of pathways originating in the cochlear nucleusSBCGBCMAOAInferior colliculusLateral lemniscusSuperior oliveProjections suggest DCN is a different animal than VCN•(All roads lead to the inferior colliculus)•VCN projects directly to structures dealing with binaural hearing and olivocochlear feedback•DCN ???Dorsal Cochlear Nucleus•Overview of the cochlear nucleus and its subdivisions–DCN projections do not reveal its function•Anatomy of the DCN•Physiology of the DCN•Functional considerationsDorsal Cochlear Nucleus•Overview of the cochlear nucleus and its subdivisions–DCN projections do not reveal its function•Anatomy of the DCN•Physiology of the DCN•Functional considerationsDCNPVCNI.C.SomatosensoryAuditoryVestibularTD??granulegiantfusiformauditory nervestellategolgicartwheelverticalKanold Young2001Tzounopoulos 2004Dorsal Cochlear Nucleus•Overview of the cochlear nucleus and its subdivisions–DCN projections do not reveal its function•Anatomy of the DCN–more complex than other CN subdivisions–nonauditory inputs–similar organization to cerebellar cortex•Physiology of the DCN•Functional considerationsDorsal Cochlear Nucleus•Overview of the cochlear nucleus and its subdivisions–DCN projections do not reveal its function•Anatomy of the DCN–more complex than other CN subdivisions–nonauditory inputs–similar organization to cerebellar cortex•Physiology of the DCN•Functional considerationsEric YoungResponse Map classification schemeYoung 1984~ Auditory Nerve increasing inhibitionDCN: Vertical cells are type II and type III unitstype IIBFBF tonenoisetype III•Narrow V-shaped region of excitation•No spontaneous activity•Tone response >> noise response•V-shaped region of excitation•Inhibitory sidebandsEvidence: Antidromic stimulation (Young 1980)Antidromic stimulationDASVCNDCNfusiformgiantverticalrecordingelectrodestimulatingelectroderecordingelectrodestimulating electrode•record from neuron•shock its axonDCN: “Principal” cells are type III and type IV unitssponttype III•“Island of excitation” & “Sea of inhibition”•BF rate-level curve inhibited at high levels•Noise rate-level curve ~ monotonicEvidence:•Antidromic stimulation (Young 1980)•Intracellular recording and labeling(Rhode et al. 1983, Ding et al. 1996)type IVNeural circuitry underlying DCN physiology:type II units inhibit type IV unitstype IIBFBF tonenoisetype IVspontgiantfusiformverticalYoung & Brownell 1976“reciprocal” responsestype IV firing rate given type II fires at t=0inhibitory troughCross-correlogramClassic experiment: type II units inhibit type IV unitstype II unittype IV unit• multiunit recording Voigt & Young (1980, 1990)Voigt & Young 1980,1990DCN physiology so far…IV• type II units inhibit type IV units• BUT this analysis based on pure-tone responses what happens with more general stimuli???IIauditory nerve~ vertical cells~ principal cells++Inhibition from type II units doesn’t account for everything Type IV unit response mapspectrum levelNotch noise stimuli•(DCN responses to broadband stimuli cannot be predicted from responses to tones: nonlinear)•Type II units do not respond to notch noise—whither the inhibition?•Response map has two inhibitory regions?Upper Inhibitory SidebandNotch noisefrequencyDCN notch noise sensitivity due to wideband inhibition• strong AN input dominates• type IV response is excitatoryBroadband noiseAN input to type IV unitfrequencylevel levelAN input to WBI• type IV loses greater portion of its excitatory input• WBI input dominates• type IV response is inhibitoryWBINelken & Young 1994PVCN: is the D-stellate cell the wideband inhibitor?• such responses arise from radiate or stellate neurons (Smith & Rhode 1989)• stellate cells send axons dorsally into the DCN, thus called “D-stellate cells” (Oertel et al. 1990) • D-stellate cells are inhibitory (Doucet & Ryugo 1997)DCNPVCN• broadly-tuned, onset-chopper units are found in the PVCN (Winter & Palmer 1995)• typically respond better to broadband noise than to tonesSummary: Circuitry of DCN deep layerSpirou and Young 1991type IItype IIW.B.I.W.B.I.“reciprocal” response propertiesSummary of DCN anatomy and physiologyNonauditorySomatosensoryAuditoryVestibulargranulefusiform•vertical cell•type II unit•narrowband