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The effects of healthy aging on auditory processing in humans as indexed by transient brain responses Laura E. Matilainen a,b , Sanna S. Talvitie a,b , Eero Pekkonen b,d , Paavo Alku c , Patrick J.C. May a,b , Hannu Tiitinen a,b, * a Department of Biomedical Engineering and Computational Science, Aalto University, School of Science and Technology, Finland b BioMag Laboratory, Hospital District of Helsinki and Uusimaa HUSLAB, Helsinki University Central Hospital, Finland c Department of Signal Processing and Acoustics, Aalto University, School of Science and Technology, Finland d Department of Neurology, Helsinki University Central Hospital, Finland article info Article history: Accepted 8 January 2010 Available online 31 March 2010 Keywords: Aging Auditory Human Magnetoencephalography MEG Transient brain response 1. Introduction abstract In Western countries, life expectancies are getting longer and the number of elderly will grow rapidly in the near future. However, the causes of perceptual and cognitive deteriorations experienced by aged people are still unclear. Normal, healthy aging causes anatomical and physiological changes in the human brain (Tisserand et al., 2002; Alexander et al., 2006) and, consequently, deficits in behaviorally assessed cognitive functions (Ylikoski et al., 1998; Kennedy and Raz, 2009). Also, in the cortical processing of auditory stimuli, various aging-related changes have been found when studied with electro- and magnetoencephalography * Corresponding author. Address: Department of Biomedical Engineering and Computational Science, P.O. Box 12200 (Otakaari 3), FI-00076 AALTO, Finland. Tel.: +358 503014985. E-mail address: hannu.tiitinen@tkk.fi (H. Tiitinen). Clinical Neurophysiology 121 (2010) 902–911 Contents lists available at ScienceDirect Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph Objective: The aim of the study was to investigate the effects of aging on human cortical auditory processing of rising-intensity sinusoids and speech sounds. We also aimed to evaluate the suitability of a recently discovered transient brain response for applied research. Methods: In young and aged adults, magnetic fields produced by cortical activity elicited by a 570-Hz pure-tone and a speech sound (Finnish vowel /a/) were measured using MEG. The stimuli rose smoothly in intensity from an inaudible to an audible level over 750 ms. We used both the active (attended) and the passive recording condition. In the attended condition, behavioral reaction times were measured. Results: The latency of the transient brain response was prolonged in the aged compared to the young and the accuracy of behavioral responses to sinusoids was diminished among the aged. In response amplitudes, no differences were found between the young and the aged. In both groups, spectral complexity of the stimuli enhanced response amplitudes. Conclusions: Aging seems to affect the temporal dynamics of cortical auditory processing. The transient brain response is sensitive both to spectral complexity and aging-related changes in the timing of cortical activation. Significance: The transient brain responses elicited by rising-intensity sounds could be useful in revealing differences in auditory cortical processing in applied research. Ó 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. (EEG and MEG; e.g., Pekkonen et al., 1995; Bellis et al., 2000; Geal-Dor et al., 2006). Recent studies (Mäkinen et al., 2004; Tiitinen et al., 2005) have introduced a new method for the objective assessment of human sound detection through MEG measurements. When presented with sounds whose intensity increases linearly from inaudible to audible over a period of up to 2 s, subjects display a transient brain response. This response is not time-locked to the onset of the stimulus but, rather, has a latency which increases with shallower intensity slopes and can occur as late as 1 s from the onset of the stimulus (Mäkinen et al., 2004). Importantly, this response predicts behavioral sound detection with almost 100% accuracy: it precedes behavioral reaction time by approximately 200 ms, and can already be observed in single subjects after 3 min of recording time. It is more prominent and spatially constrained over the right hemisphere and is generated in areas which coincide with the auditorycortex generators of the N1m response elicited by short-duration ( 100-ms) stimuli. Contrasting the N1m, typically elicited by 50–200 ms stimuli and occurring at approximately 100 ms from 1388-2457/$36.00 Ó 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2010.01.007