COGNITIVE NEUROSCIENCE Development of auditory-specific brain rhythm in infants Takako Fujioka, 1,2 Nasser Mourad 3 and Laurel J. Trainor 1,2 1 Department of Psychology, Neuroscience & Behaviour, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4K1, Canada 2 Rotman Research Institute, Baycrest, University of Toronto, 3560 Bathurst St, Toronto, ON, M6A 2E1, Canada 3 Department of Electrical Engineering, Aswan Faculty of Engineering, South Valley University, Aswan, Egypt Keywords: auditory cortex, cortical plasticity, EEG frequency band analysis, event-related oscillations, maturation Abstract Human infants rapidly develop their auditory perceptual abilities and acquire culture-specific knowledge in speech and music in the second 6 months of life. In the adult brain, neural rhythm around 10 Hz in the temporal lobes is thought to reflect sound analysis and subsequent cognitive processes such as memory and attention. To study when and how such rhythm emerges in infancy, we examined electroencephaolgram (EEG) recordings in infants 4 and 12 months of age during sound stimulation and silence. In the 4-month-olds, the amplitudes of narrowly tuned 4-Hz brain rhythm, recorded from bilateral temporal electrodes, were modulated by sound stimuli. In the 12-month-olds, the sound-induced modulation occurred at faster 6-Hz rhythm at temporofrontal locations. The brain rhythms in the older infants consisted of more complex components, as even evident in individual data. These findings suggest that auditory-specific rhythmic neural activity, which is already established before 6 months of age, involves more speed-efficient long-range neural networks by the age of 12 months when long-term memory for native phoneme representation and for musical rhythmic features is formed. We suggest that maturation of distinct rhythmic components occurs in parallel, and that sensory-specific functions bound to particular thalamo-cortical networks are transferred to newly developed higher-order networks step by step until adult hierarchical neural oscillatory mechanisms are achieved across the whole brain. Introduction The human auditory system starts developing in utero (Kisilevsky & Low, 1998) and plays a fundamental role in acquisition of linguistic and musical knowledge in infancy. Six-month-old infants can discriminate phonetic contrasts (Werker & Lalonde, 1988), detect rhythmic pattern differences (Hannon & Trehub, 2005) and recognize a melody played at different pitch levels (Plantinga & Trainor, 2005). However, 12-month-olds do not recognize acoustic contrasts that are no longer meaningful in their native culture (Werker & Lalonde, 1988; Hannon & Trehub, 2005). Thus, infants appear to develop neural networks for higher-order sensory information processing in the second 6 months after birth. Neural correlates of such perceptual skills have been probed using electroencephalography (EEG) or magnetoencephalography (MEG) rhythms, which are thought to reflect global and local neural networks operating at different frequency ranges (Varela et al., 2001; Buzsa ´ki & Draguhn, 2004). In adults, alpha-band rhythm around 10 Hz (8– 12 Hz) is dominant and most pronounced across the brain in resting states, while its power decreases selectively at specific brain regions, according to sensory (visual ⁄ auditory ⁄ somatosensory), motor and cognitive (attention and memory) task demands (Klimesch, 1999). These modulations are hypothesized to reflect selective activation and inhibition in specific neural networks regarding sensory processing and subsequent cognitive processes (Knyazev, 2007). However, development of neural rhythms is not fully understood, mainly because to determine which infant rhythms correspond to those in adults, functional and spatial information should be taken into account (Kuhlman, 1980). Recent studies, using modern quantification methods with multiple electrodes, have shown that in infants between 8 and 12 months of age, the occipital-alpha rhythm is blocked by attending to visual stimuli (Stroganova et al., 1999), and that the central-mu rhythm is blocked by movements (Orekhova et al., 2006), both in a lower frequency range than in adults. These studies also confirmed earlier findings (Smith, 1939, 1941) that, as age increases, these rhythms gradually accelerate and become more spatially segregated. Here, we examined for the first time in infants the development of ‘temporal-tau’ rhythm, the one remaining alpha-band rhythm origi- nating from auditory cortex that is suppressed by sounds in adults (Tiihonen et al., 1991; Lehtela et al., 1997; Niedermeyer, 1997), and in 4- to 6-year-old children with already adult-like frequency (Fujioka & Ross, 2008). During the first 4 months the auditory system rapidly changes the way it processes acoustic inputs (Lutter et al., 2006; Rivera-Gaxiola et al., 2007), simple acoustic contrasts (C ˇ eponiene et al., 2000; Kushnerenko et al., 2002), and more complex acoustic features such as periodicity pitch (He & Trainor, 2009) and sequential patterns (He et al., 2009). EEG activity at rest also changes in spectral components (Mizuno et al., 1970) and topography (Marshall et al., Correspondence: Dr T. Fujioka, 2 Rotman Research Institute, as above. E-mail: tfujioka@rotman-baycrest.on.ca Received 21 July 2010, revised 1 October 2010, accepted 28 October 2010 European Journal of Neuroscience, Vol. 33, pp. 521–529, 2011 doi:10.1111/j.1460-9568.2010.07544.x ª 2011 The Authors. European Journal of Neuroscience ª 2011 Federation of European Neuroscience Societies and Blackwell Publishing Ltd European Journal of Neuroscience