br Method br Results br Discussion

Method
Results
Discussion Our aim was to investigate whether differences in infants’ socioeconomic background were associated with resting EEG power at birth, and if those differences were correlated with later memory and language performance at 15 months of age. We found no correlations between resting EEG power at birth and any of our SES variables (i.e., parental educational attainment, family income, family income-to-needs). Had we found differences in resting EEG at birth, it eph receptor would have suggested that these differences were likely the result of socioeconomic differences in the prenatal environment (e.g., maternal diet, stress) and/or genetic differences (Monk et al., 2013; Turkheimer et al., 2003). Of course, this study cannot rule out those possibilities. However, in the context of previous work reporting SES disparities in resting EEG power as early as 6–9 months in a similar sample size of infants (Tomalski et al., 2013), the present null findings suggest the possibility that differences in postnatal experience lead to the emergence of these disparities in the first year of life. A longitudinal study assessing both the prenatal and postnatal environments would be necessary to formally test this hypothesis. Furthermore, no significant correlations were found between family SES and our memory and language outcomes of interest at 15 months. A recent study by Noble and colleagues (2015) reported socioeconomic disparities in both language and declarative memory emerging between 15 and 21 months of age; significant correlations between SES and language scores were reported at 15 months (r=0.18), but significant correlations between SES and memory scores were not reported until 21 months of age (r=0.31). The lack of a correlation between SES and memory is consistent with this past study, and our smaller sample size (N=66 compared to N=179) may have restricted our ability to find SES correlations with language. Consistent with previous research examining infants with congenital heart disease (Williams et al., 2012), we found significant associations between neonatal EEG power and later cognitive abilities, specifically declarative memory and auditory comprehension, in our sample of typically developing full-term infants. These individual differences in EEG power at birth could be due to a host of variables including genetics (Zietsch et al., 2007), developmental programming (Pluess and Belsky, 2011), differences in the prenatal environment (Monk et al., 2013), placental function (Schulkin et al., 2005), or hypoxia (Murray et al., 2009). As with past studies examining EEG power and early global cognitive development (Benasich et al., 2008; Gou et al., 2011), these associations between EEG power and later cognitive activity were limited to the low-gamma (24–35Hz) and higher-gamma frequency ranges (36–48Hz). Past work with adults has also reported associations between gamma oscillations and specific perceptual and cognitive processes. For example, in adults the gamma rhythm (30–100Hz) has been linked to object perception (Gruber and Muller, 2005; Gruber et al., 2002), attention (Muller et al., 2005; Ray et al., 2008), memory (Miltner et al., 1999; Hermann et al., 2010) and language-related processes (Eulitz et al., 1996; Pulvermuller et al., 1996). In both adults and infants, gamma oscillations have been proposed to reflect the active maintenance of object representations in memory (Kaufman et al., 2005; Tallon-Baudry et al., 1998) and may be closely tied to attention capabilities as positive correlations between gamma activity and attention measures have been reported (Muller et al., 2000; Reid et al., 2007). Gamma power has even been correlated with a parent report measure of concurrent attention (Toddler Behavior Assessment Questionnaire: TBAQ) at 24-months of age (Benasich et al., 2008). Our results contribute to this literature by extending findings between resting EEG activity in the gamma frequency collected in the newborn period and specific neurocognitive processes (i.e., declarative memory and language).