title: Human posterior auditory cortex gates novel sounds to consciousness.
abstract: Life or death in hostile environments depends crucially on one's ability to detect and gate novel sounds to awareness, such as that of a twig cracking under the paw of a stalking predator in a noisy jungle. Two distinct auditory cortex processes have been thought to underlie this phenomenon: (i) attenuation of the so-called N1 response with repeated stimulation and (ii) elicitation of a mismatch negativity response (MMN) by changes in repetitive aspects of auditory stimulation. This division has been based on previous studies suggesting that, unlike for the N1, repetitive "standard" stimuli preceding a physically different "novel" stimulus constitute a prerequisite to MMN elicitation, and that the source loci of MMN and N1 are different. Contradicting these findings, our combined electromagnetic, hemodynamic, and psychophysical data indicate that the MMN is generated as a result of differential adaptation of anterior and posterior auditory cortex N1 sources by preceding auditory stimulation. Early ( approximately 85 ms) neural activity within posterior auditory cortex is adapted as sound novelty decreases. This alters the center of gravity of electromagnetic N1 source activity, creating an illusory difference between N1 and MMN source loci when estimated by using equivalent current dipole fits. Further, our electroencephalography data show a robust MMN after a single standard event when the interval between two consecutive novel sounds is kept invariant. Our converging findings suggest that transient adaptation of feature-specific neurons within human posterior auditory cortex filters superfluous sounds from entering one's awareness.
authors.affiliation: Massachusetts General Hospital, Massachusetts Institute of Technology, Harvard Medical School, Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA 02129, USA. iiro@nmr.mgh.harvard.edu
authors.forename: Iiro P
authors.initials: IP
authors.lastname: Jääskeläinen
authors.forename: Jyrki
authors.initials: J
authors.lastname: Ahveninen
authors.forename: Giorgio
authors.initials: G
authors.lastname: Bonmassar
authors.forename: Anders M
authors.initials: AM
authors.lastname: Dale
authors.forename: Risto J
authors.initials: RJ
authors.lastname: Ilmoniemi
authors.forename: Sari
authors.initials: S
authors.lastname: Levänen
authors.forename: Fa-Hsuan
authors.initials: FH
authors.lastname: Lin
authors.forename: Patrick
authors.initials: P
authors.lastname: May
authors.forename: Jennifer
authors.initials: J
authors.lastname: Melcher
authors.forename: Steven
authors.initials: S
authors.lastname: Stufflebeam
authors.forename: Hannu
authors.initials: H
authors.lastname: Tiitinen
authors.forename: John W
authors.initials: JW
authors.lastname: Belliveau
mesh_terms: D000328:Adult; D001303:Auditory Cortex / Q000502:physiology*; D001307:Auditory Perception; D003243:Consciousness; D004569:Electroencephalography; D004574:Electromagnetic Fields; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D011601:Psychophysics