Age trends and sex differences of alpha rhythms including split alpha peaks A.K.I. Chiang a,b,⇑ , C.J. Rennie a,b,c , P.A. Robinson a,b , S.J. van Albada a,b,d , C.C. Kerr a,b,e a School of Physics, University of Sydney, NSW 2006, Australia b Brain Dynamics Centre, Westmead Millennium Institute, Sydney Medical School – Western, University of Sydney, Westmead, Australia c Department of Medical Physics, Westmead Hospital, Westmead, NSW 2145, Australia d Institute of Neuroscience and Medicine – Neuromodulation INM-7, Research Center Jülich, Leo-Brandt-Straße, D-52425 Jülich, Germany e Neurosimulation Laboratory, Downstate Medical Center, State University of New York, Brooklyn, NY 11203, USA article info Article history: Accepted 18 January 2011 Available online 23 February 2011 Keywords: Development Aging EEG Alpha rhythm Split alpha Double alpha highlights  Single and double alpha peaks characterized in a sample of 1498 subjects.  Systematic age trends found in alpha frequency, position, and power.  Results are consistent with all subjects having posterior and frontal alpha, often with distinguishable frequencies. abstract Objective: To investigate age trends, sex differences, and splitting of alpha peaks of the EEG spectrum in the healthy population. Methods: An automated multi-site algorithm was used to parametrize the alpha rhythm in 1498 healthy subjects aged 6–86 years. Alpha peaks identified from multiple electrode sites were organized into clus- ters of similar frequencies whose sex differences and age trends were investigated. Results: Significant age-related trends were observed for frequency, position, and amplitude of dominant alpha peaks. Occipital sites had alpha clusters of higher average frequency, higher power, and greater presence across the scalp. Frequency and power differences were found between the sexes. Conclusion: Observed increases in alpha frequency in children and decreases in the elderly were consis- tent with those from earlier studies. A large fraction of participants (44%) showed multiple distinct alpha rhythm thus investigations which only examine the alpha frequency with the highest peak power can produce misleading results. The strong dependence of alpha frequency on age and anterior–posterior position indicates use of a fixed alpha frequency band is insufficient to capture the full characteristics of the alpha rhythm. Significance: This study establishes alpha rhythm parameter ranges (including power and frequency) in the healthy population, and quantifies the variation in alpha frequency across the scalp. The automated characterization enables objective evaluations of alpha band activities over large samples. These findings are potentially useful in testing theories of alpha generation, where splitting of the alpha rhythm has been theoretically predicted to occur in individuals with large differences in axon length between ante- rior and posterior corticothalamic loops. Crown Copyright Ó 2011 Published by Elsevier Ireland Ltd. on behalf of International Federation of Clinical Neurophysiology. All rights reserved. 1. Introduction The alpha rhythm is the most prominent feature observed in the human electroencephalogram (EEG), and is strongest when the subject is in an eyes-closed relaxed state (Niedermeyer and Lopes da Silva, 2004). It is suppressed by attention or mental effort, though this attenuation varies greatly between individuals and experimental conditions (Shaw, 2003). The normal alpha rhythm varies in amplitude from one individual to another, and a small minority of people with normal brain function do not show an al- pha rhythm (Niedermeyer and Lopes da Silva, 2004). An alpha-free low voltage EEG may also develop in adult life in certain clinical conditions such as Huntington’s chorea (Scott et al., 1972). Activity is still present in the alpha band, but there is not necessarily a spectral peak, which is required for the identification of the alpha rhythm. The frequency of the alpha rhythm increases from approx- imately 3–5 Hz at birth until an adult value near 10 Hz is reached 1388-2457/$36.00 Crown Copyright Ó 2011 Published by Elsevier Ireland Ltd. on behalf of International Federation of Clinical Neurophysiology. All rights reserved. doi:10.1016/j.clinph.2011.01.040 ⇑ Corresponding author. Address: Physics Annexe, University of Sydney, NSW 2006, Australia. Tel.: +61 4 02950186; fax: +61 2 93517726. E-mail address: chiang@physics.usyd.edu.au (A.K.I. Chiang). Clinical Neurophysiology 122 (2011) 1505–1517 Contents lists available at ScienceDirect Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph