Neuroimaging Correlates of HumanAuditory BehaviorHST 722Brain Mechanisms for Hearing and SpeechOctober 27, 2005Jennifer MelcherHarvard-MIT Division of Health Sciences and TechnologyHST.722J: Brain Mechanisms for Hearing and SpeechCourse Instructor: Jennifer R. Melcher"The Problem"Figure by MIT OCW.SoundPerceptionNoninvasivePhysiologicMeasuresNeuralActivityFigure above illustrates how auditory evoked potentials are measured. Potential shown wasevoked by a click stimulus and was recorded in a human subject. Waveform is the averagedresponse to many click presentations. (AEP record from R.A. Levine)(Courtesy of Robert Aaron Levine. Used with permission.)Furst et al. (1985) “Click lateralization is related to the βcomponent of the dichotic brainstem auditory evokedpotentials of human subjects”For binaural clicks with different ITDs and ILDs, quantifiedperceptionbinaural difference potential Attributes of the binaural difference are correlated withthe perception of binaural sound.Binaural difference (BD) is derived from BAEPs evoked bymonaural and binaural stimuli (above). BAEP: brainstem auditoryevoked potential The BD reflects an interaction between converging signalsfrom the two ears at the level of the brainstem.Binaural Difference PotentialFig. 9. Binaural, sum of the monaurals, and binaural difference waveforms for both species.The binaural (solid lines) and sum of the monaural waveforms (dotted lines) aresuperimposed. The difference between these two waveforms, the binaural difference (BD)waveform, is plotted below. The recording electrodes were vertex to nape for both species.Stimuli were 10/sec; rarefaction clicks at 40 dB SL for the cat and 38 dB HL for the human.(from Fullerton et al., 1987)0 4 8 12 0 4 8 12msec msecCAT 24SU 44bdacβα7.0 µV0.2 µVCAT HUMANΣMONBINBDP4P5Figures by MIT OCW.Cellular Generators of the Binaural Difference PotentialCellular generators of the binaural difference potential in cat. Diagonal line shadingsindicate the generators of the first peak (‘b’; white on black) and possible generatorsof the second peak (‘d’; black on white). The schematic of the lower auditory system(at bottom) shows the generators’ relationship to other cells. NLL, nuclei of thelateral lemniscus; IC, inferior colliculus.(From Melcher, 1996)LEFT SOCMidlineTrapezoidbodyAuditorynerveLaterallemniscusNLL/IC?MSOLSOPrincipal cellCOCHLEARNUCLEUSCellular generators of the binaural difference potential in cat. Green color indicate the generatorsof the first peak ('b'; white on black) and possible generators of the second peak ('d'; black on white).The schematic of the lower auditory system (at bottom) shows the generators' relationship to other cells.NLL, nuclei of the lateral lemniscus; IC, inferior colliculus.DCNPVCNpPVCNaAVCNpAVCNaRIGHT SOCSphericalcellBinaural difference waveformbdFigure by MIT OCW.Discussion Questions:If the generator results are combined with the findings ofFurst et al., what can be said about the neural processingunderlying sound lateralization and binaural fusion?We generally think of the MSO as a coincidence detector.Are Furst et al.’s binaural difference data consistent with this idea?Late Responses: dependence on attention and stimulus contextIdealized AEP evoked by transient stimuli( ___ ) including components that are dependent onstimulus context and subject attention ( ….. , ----- ).(from Hillyard and Kutas, 1983; also see Hillyard etal., 1973; Donchin et al., 1978).Figure 1-12. Schematic diagram of oddballstimulus presentation paradigm for P300measurement (from Squires & Hecox, 1983).Selected measurement parameters areindicated. Responses are averaged separatelyfor Stimulus Type 1 (i.e. the frequent stimulus)and Stimulus Type 2 (i.e. the rare or oddballstimulus). Note. From “ElectrophysiologicalEvaluation of Higher Level AuditoryProcessing” by K.C. Squires and K.E. Hecox,1983, Seminars in Hearing, 4 (4), p. 422.Reprinted by permission.(from Hall, 1992)NdN2P3- or “processing negativity”- produced when the subject attends to the stimuli- visualized by taking the difference between responses to attended and unattended stimuli- or “N2000”, “mismatch negativity- occurs in response to “rare” stimuli (S2 below) in oddball paradigm- can occur even when the subject is not attending to the stimuli- dependent on stimulus modality (e.g. auditory vs. visual)- or “P300”- occurs in response to “rare” stimuli (S2 below) in oddball paradigm when the subject is attending to the stimuli- independent of stimulus modalityIIIIIIIVVVIP0N0NaN1NdN2NbPaP1P2P3(P300)-5µv+5µvStimulus Onset10Time (msec)Auditory Event-Related Potential1000100S1 S1 S1 S1 S2 S1 S2Average 1 Average 2Two Stimuli, S1 & S2Train with fixed intervalsProbabilities of S1 & S2 unequalS1 & S2 mixed randomlyODDBALL PROCEDUREFigure by MIT OCW.Figure by MIT OCW.N2 (N200), P3 (P300)Fig. 1. Mean for eight subjects of the non-signal (NS), signal (S) and difference (Δ) waveforms at each electrode site in theauditory condition. Isopotential topographic distributions are expressed as percentages of maximum response amplitude forthe N1 and P2 components of the non-signal response (left) and the negative (N2 Δ) and positive (P3 Δ) components of theΔ waveform (right). Supraorbital (0) and vertex (electrode 3) traces from the 3 runs are superimposed.(From Simson et al., 1977)NS - responses to standard stimuli (2000 Hz tone bursts)S - responses to rare stimuli (1000 Hz tone bursts)Δ - response to rare stimuli minus response to standard stimuliFig. 4. Frontal, vertex, and parietal(across-subjects averaged) differencewaveforms obtained by subtracting theERP to the 1000-Hz standard stimulusfrom that to the 1044-Hz deviant stimulusat different deviant-stimulus probabilities.The continuous line indicates the countingcondition and the broken line the ignorecondition. The amplitude of the fronto-centrally distributed MMN is decreasedwhen the probability is increased from 2%to 10%. When the two stimuli areequiprobable, no MMN is seen.From Sams et al., 1985)MMN - mismatch negativity100 ms+5µv-12345670507090050709001N1NS S ∆P2N2∆P3∆2345678910111213991211108507090705090Figure by MIT OCW.MMN2% 10% 50%P3PzOzFzPzOzFzPzOzFzs200 msec10µVFigure by MIT OCW.Kraus et al. (1996) “Auditory neurophysiologic responsesand discrimination deficits in children with learning problems” Stimuli: Syllables, varied along two continua Subjects: