zBMI scales with multispectral alterations in the neural oscillatory dynamics serving verbal working memory in youth

Pediatric obesity is one of the most serious public health issues the world faces today. Deleterious behavioral effects scaling with obesity and body mass have been demonstrated in cognitive tasks in children and adults, yet the neural oscillatory dynamics underlying these effects remain largely unstudied. In this study, 88 youth (6-13 years old) performed a verbal working memory task during high-density magnetoencephalography (MEG). The MEG data were transformed into the time-frequency domain and oscillatory responses during encoding and maintenance phases were imaged separately using a beamformer approach. Each participant's height, weight, sex, and age were used to create age- and-sex-adjusted body mass index (i.e., zBMI) measures and BMI-for-age percentiles. Whole-brain correlation maps were examined for effects of body mass on neural dynamics serving encoding and maintenance. According to the BMI-for-age percentiles, 21 subjects were classified as overweight/obese. Behaviorally, our results indicated that task accuracy and reaction time were strongly correlated with age but not zBMI, such that older youth were faster and more accurate than their younger peers. Neural oscillatory activity in the theta (4-7 Hz) and alpha (8-12 Hz) range scaled with zBMI in several left-hemispheric regions across occipital, temporal, and frontal cortices. During the encoding phase, elevated zBMI was associated with weaker theta and stronger alpha oscillations. In the maintenance phase, higher zBMIs were associated with stronger alpha oscillatory activity. Taken together, these results suggest that oscillatory dynamics in brain regions central to working memory processing are vulnerable to deviations from normal body mass in specific spectral bands. The stronger alpha and weaker theta oscillations may point to opposing compensatory and deleterious effects of elevated zBMI on working memory, respectively.