Title: Socioeconomic status differences in children’s resting state EEG are correlated to vocabulary size Authors: Julie M. Schneider and Mandy J. Maguire Background: On average, children from low socioeconomic (LSES) homes exhibit significantly smaller vocabularies and poorer working memory skills when compared with their peers from middle or higher (MSES) homes (Hackman, Farah, & Meaney, 2011; Hoff, 2013). Known changes in resting state EEG are correlated to the development and mastery of vocabulary and working memory. In adults with a history of childhood poverty, brain activation during resting state was reduced, suggesting a relationship between less efficient cognitive processing, poverty, and brain activation (Sripada et. al., 2014). The current study aims to clarify the development of those differences during childhood poverty, by identifying if 8-15 year old children from LSES homes demonstrate decreases in resting state activation, and if these decreases are related to poor vocabulary or working memory. Methods: Twenty LSES children (8-14 years, Mage=10.7, SDage=2.1; 8 males) and twenty age- and gender-matched MSES peers (Mage=10.7, SDage=2.1; 8 males) participated in a resting state task. LSES was determined by parental reports of eligibility for free or reduced lunch, which places the family at 185% of the US poverty level or below. Children alternated between having their eyes open and closed (resting state) for one minute each, for a total of 8 minutes, while their EEG was recorded. Behaviorally, all children completed the Peabody Picture Vocabulary Task (PPVT) and a reverse digit span task, to measure vocabulary and working memory, respectively. Tasks were counterbalanced. Analysis: Using time frequency analysis of the EEG, we investigated changes in the neural signal during resting state within the alpha band, which has been considered a marker of cortical activity (Goldman et al., 2002). Within the minute window in such eyes were closed, data was cleaned using Independent Components Analysis and epoched from 0-5000 msec. Results: Based on a monte-carlo cluster correction permutation analysis LSES children demonstrated a significantly greater increase in alpha power during resting state when compared to MSES children at left parietal electrodes (p<0.05). To investigate the relationship between resting state, vocabulary and working memory, we computed a linear regression. This revealed that alpha amplitude predicted vocabulary, b=.02, t(39)=-2.58, p=.02, but not working memory b=-.03, t(39)=-.56, p=.58, when accounting for age. Specifically, children who exhibited lower alpha amplitudes were from LSES homes and exhibited lower scores on a standardized measure of vocabulary knowledge. Discussion. Our findings suggest that children from LSES homes demonstrate less alpha activation over left hemisphere areas during resting state than children from MSES homes. This decreased cortical activity statistically predicts vocabulary knowledge. Interestingly, no relationship was found between SES, working memory, and resting state. This research supports and expands upon previous findings that an early childhood in poverty results in differences in neurological activity, influencing language outcomes.