Three of the most common internal sources of artifact include eye blinks, saccades, and contraction of face, jaw or neck muscles (electromyographic noise or EMG). Unlike studies in adults where recording duration often exceed 10 minutes (Barry et al., 2007 Bonfiglio et al., 2013 Hagemann and Naumann, 2001 Leuchter et al., 2012), in infants and children a total of 2 minutes of data are often gathered, with fewer than 30 seconds of clean data remaining after artifact rejection ( John et al., 1980 Marshall et al., 2002 Tierney et al., 2012).
However, these practical benefits also lead to greater challenges in data acquisition and quality, as the target populations of interest (infants, young children, atypically developing children) may also generate the most artifact, resulting in an insufficient amount of useable, clean EEG data ( Slifer et al., 2008 Webb et al., 2013). Moreover, cognitive processes such as attention, memory, cognitive inhibition, and feature binding can be characterized without requiring an overt behavioral response. Scientific merits notwithstanding, it is the practical benefits of QEEG that often motivate its use in the study of developmental populations, as it is non-invasive, less vulnerable to motion artifact, and more readily available in clinical settings ( Keil et al., 2014 Saby and Marshall, 2012 Webb et al., 2013). QEEG holds particular appeal as a metric of individual variability in neurodevelopmental disorders, such as autism spectrum disorder (ASD), where behavioral output is limited and sometimes unable to capture phenotypic and functional heterogeneity ( Cantor and Chabot, 2009 Saby and Marshall, 2012). With a temporal resolution that facilitates quantification of subtle changes in state and function over time, QEEG holds tremendous promise as a quantitative biomarker of clinical phenomenon such as the change in brain function over discrete time points in development ( Marshall et al., 2002), the effects of intervention in developmental disorders ( Dawson et al., 2012), prediction of functional outcomes ( Gou et al., 2011), early disorder detection ( Bosl et al., 2011), disease progression ( Luckhaus et al., 2008), and subgroup ( Clarke et al., 2011) and group ( Barry et al., 2010) differences in childhood psychiatric disorders.
Quantitative electrocenphalography (QEEG) has served as a powerful tool to study both typical and atypical brain development and function, informing the understanding of processes such as perception, cognition, and cortical connectivity (For review see: Saby and Marshall, 2012 Uhlhaas et al., 2010).
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