Single-Dipole Analyses of the N100m Are Not Suitable for Characterizing the Cortical Representation of Pitch

In several previous studies, the deflection N100m of the auditory evoked field (AEF), occurring about 100 ms after the onset of a sound, has been used to investigate whether complex tones are represented in the auditory cortex by their spectrum or their periodicity pitch. However, the results partially contradict each other. Moreover, the basic assumption that N100m originates from a single cortical source has been questioned. To gain clarity, the AEF elicited by a complex tone with a periodicity of 4 ms (pitch 250 Hz) and a spectrum between 1000 and 2000 Hz was compared with the AEF in response to pure tones of 250 and 1000 Hz, respectively (on 12 subjects). While a previous analysis [Audiol Neurootol 2001;6: 263–278] was exclusively devoted to the N100m latency, this article presents source analyses with two variants of a single-dipole model (moving dipole and fixed dipole). Earlier reports, suggesting that N100m arises from a cortical source representing the pitch rather than the spectrum of the sound, could not be reproduced, independent of the method used. It appears that an investigation of the functional organization of the human auditory cortex based on N100m source modeling requires a much higher degree of sophistication than a single-dipole model can provide.

[1]  R. Hari.  The neuromagnetic method in the study of the human auditory cortex , 1990 .

[2]  M Hoke,et al.  Identification of sources of brain neuronal activity with high spatiotemporal resolution through combination of neuromagnetic source localization (NMSL) and magnetic resonance imaging (MRI). , 1990, Electroencephalography and clinical neurophysiology.

[3]  Bernd Lütkenhöner,et al.  Localization of Primary Auditory Cortex in Humans by Magnetoencephalography , 2003, NeuroImage.

[4]  D. Poeppel,et al.  Latency of auditory evoked M100 as a function of tone frequency , 1996, Neuroreport.

[5]  S. Kuriki,et al.  Neuromagnetic study of the auditory responses in right and left hemispheres of the human brain evoked by pure tones and speech sounds , 2004, Experimental Brain Research.

[6]  G. Barkley,et al.  Evidence for multiple generators in evoked responses using finite difference field mapping: Auditory evoked fields , 2005, Brain Topography.

[7]  L. Kaufman,et al.  Tonotopic organization of the human auditory cortex. , 1982, Science.

[8]  Christo Pantev,et al.  Reproducibility and Validity of Neuromagnetic Source Localization Using A Large Array Biomagnetometer , 1991 .

[9]  J M Badier,et al.  Evoked potentials recorded from the auditory cortex in man: evaluation and topography of the middle latency components. , 1994, Electroencephalography and clinical neurophysiology.

[10]  K. Lehnertz,et al.  Tonotopic organization of the human auditory cortex revealed by transient auditory evoked magnetic fields. , 1988, Electroencephalography and clinical neurophysiology.

[11]  D. Poeppel,et al.  Peri‐threshold encoding of stimulus frequency and intensity in the M100 latency , 1998, Neuroreport.

[12]  Christoph E. Schreiner,et al.  Spatial Distribution of Responses to Simple and Complex Sounds in the Primary Auditory Cortex , 1998, Audiology and Neurotology.

[13]  Lloyd Kaufman,et al.  Advantages and limitations of magnetic source imaging , 2005, Brain Topography.

[14]  S. Knecht,et al.  Latency of Auditory Evoked Field Deflection N100m Ruled by Pitch or Spectrum? , 2001, Audiology and Neurotology.

[15]  M Hoke,et al.  The auditory evoked sustained field: origin and frequency dependence. , 1994, Electroencephalography and clinical neurophysiology.

[16]  Matthias M. Müller,et al.  Expansion of the Tonotopic Area in the Auditory Cortex of the Blind , 2002, The Journal of Neuroscience.

[17]  J. Eggermont,et al.  The Neurophysiology of Auditory Perception: From Single Units to Evoked Potentials , 2002, Audiology and Neurotology.

[18]  A. Papanicolaou,et al.  Multiple Bilaterally Asymmetric Cortical Sources Account for the Auditory N1m Component , 2004, Brain Topography.

[19]  S. Baumann,et al.  Neuromagnetic evidence of a dynamic excitation pattern generating the N100 auditory response. , 1990, Electroencephalography and clinical neurophysiology.

[20]  P. Heil,et al.  Frequency and periodicity are represented in orthogonal maps in the human auditory cortex: evidence from magnetoencephalography , 1997, Journal of Comparative Physiology A.

[21]  J. Kaas,et al.  Architectonic identification of the core region in auditory cortex of macaques, chimpanzees, and humans , 2001, The Journal of comparative neurology.

[22]  Ingrid S. Johnsrude,et al.  Functional Imaging of the Auditory System: The Use of Positron Emission Tomography , 2002, Audiology and Neurotology.

[23]  C. C. Wood,et al.  Scalp distribution of human auditory evoked potentials. II. Evidence for overlapping sources and involvement of auditory cortex. , 1982, Electroencephalography and clinical neurophysiology.

[24]  B. Lutkenhoner.  Dipole separability in a neuromagnetic source analysis , 1998, IEEE Transactions on Biomedical Engineering.

[25]  M. Scherg,et al.  A Source Analysis of the Late Human Auditory Evoked Potentials , 1989, Journal of Cognitive Neuroscience.

[26]  L. McEvoy,et al.  Temporal characteristics of auditory sensory memory: neuromagnetic evidence. , 1997, Psychophysiology.

[27]  B. Lütkenhöner.  Dipole source localization by means of maximum likelihood estimation. II. Experimental evaluation. , 1998, Electroencephalography and clinical neurophysiology.

[28]  J. E. Hind,et al.  Auditory cortex on the human posterior superior temporal gyrus , 2000, The Journal of comparative neurology.

[29]  T. Elbert,et al.  Reorganization of auditory cortex in tinnitus. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[30]  H. Sauer,et al.  Tonotopy of the Auditory-Evoked Field Component N100m in Patients with Schizophrenia , 2000 .

[31]  E. Cassetta,et al.  Tonotopic cortical changes following stapes substitution in otosclerotic patients: A magnetoencephalographic study , 2000, Human brain mapping.

[32]  Bernd Lütkenhöner,et al.  High-Precision Neuromagnetic Study of the Functional Organization of the Human Auditory Cortex , 1998, Audiology and Neurotology.

[33]  Ernst Terhardt,et al.  Binaural fusion and the representation of virtual pitch in the human auditory cortex , 1996, Hearing Research.

[34]  P. Teale,et al.  Alterations in tonotopy and auditory cerebral asymmetry in schizophrenia , 2002, Biological Psychiatry.

[35]  C. Pantev,et al.  Cortical reorganization in patients with high frequency cochlear hearing loss , 2001, Hearing Research.

[36]  M Hoke,et al.  Tonotopic organization of the auditory cortex: pitch versus frequency representation. , 1989, Science.

[37]  D. Yves von Cramon,et al.  Is It Tonotopy after All? , 2002, NeuroImage.

[38]  H. Sauer,et al.  Stimulus Duration Influences the Dipole Location Shift Within the Auditory Evoked Field Component N100m , 2002, Brain Topography.

[39]  M Steinschneider,et al.  Temporal encoding of the voice onset time phonetic parameter by field potentials recorded directly from human auditory cortex. , 1999, Journal of neurophysiology.

[40]  S. Williamson,et al.  Tonotopic organization of human auditory association cortex , 1994, Brain Research.

[41]  M Steinschneider,et al.  Consonance and dissonance of musical chords: neural correlates in auditory cortex of monkeys and humans. , 2001, Journal of neurophysiology.

[42]  J. Kaas,et al.  Subdivisions of AuditoryCortex and Levels of Processing in Primates , 1998, Audiology and Neurotology.

[43]  C. Elberling,et al.  Auditory magnetic fields: source location and 'tonotopical organization' in the right hemisphere of the human brain. , 1982, Scandinavian audiology.