@article{kim_wittenberg_nam_2017, title={Behavioral and Neural Correlates of Executive Function: Interplay between Inhibition and Updating Processes}, volume={11}, ISSN={1662-453X}, url={http://dx.doi.org/10.3389/fnins.2017.00378}, DOI={10.3389/fnins.2017.00378}, abstractNote={This study investigated the interaction between two executive function processes, inhibition and updating, through analyses of behavioral, neurophysiological, and effective connectivity metrics. Although, many studies have focused on behavioral effects of executive function processes individually, few studies have examined the dynamic causal interactions between these two functions. A total of twenty participants from a local university performed a dual task combing flanker and n-back experimental paradigms, and completed the Operation Span Task designed to measure working memory capacity. We found that both behavioral (accuracy and reaction time) and neurophysiological (P300 amplitude and alpha band power) metrics on the inhibition task (i.e., flanker task) were influenced by the updating load (n-back level) and modulated by working memory capacity. Using independent component analysis, source localization (DIPFIT), and Granger Causality analysis of the EEG time-series data, the present study demonstrated that manipulation of cognitive demand in a dual executive function task influenced the causal neural network. We compared connectivity across three updating loads (n-back levels) and found that experimental manipulation of working memory load enhanced causal connectivity of a large-scale neurocognitive network. This network contains the prefrontal and parietal cortices, which are associated with inhibition and updating executive function processes. This study has potential applications in human performance modeling and assessment of mental workload, such as the design of training materials and interfaces for those performing complex multitasking under stress.}, journal={Frontiers in Neuroscience}, publisher={Frontiers Media SA}, author={Kim, Na Young and Wittenberg, Ellen and Nam, Chang S.}, year={2017}, month={Jun} }
 @article{wittenberg_thompson_nam_franz_2017, title={Neuroimaging of Human Balance Control: A Systematic Review}, volume={11}, ISSN={1662-5161}, url={http://dx.doi.org/10.3389/fnhum.2017.00170}, DOI={10.3389/fnhum.2017.00170}, abstractNote={This review examined 83 articles using neuroimaging modalities to investigate the neural correlates underlying static and dynamic human balance control, with aims to support future mobile neuroimaging research in the balance control domain. Furthermore, this review analyzed the mobility of the neuroimaging hardware and research paradigms as well as the analytical methodology to identify and remove movement artifact in the acquired brain signal. We found that the majority of static balance control tasks utilized mechanical perturbations to invoke feet-in-place responses (27 out of 38 studies), while cognitive dual-task conditions were commonly used to challenge balance in dynamic balance control tasks (20 out of 32 studies). While frequency analysis and event related potential characteristics supported enhanced brain activation during static balance control, that in dynamic balance control studies was supported by spatial and frequency analysis. Twenty-three of the 50 studies utilizing EEG utilized independent component analysis to remove movement artifacts from the acquired brain signals. Lastly, only eight studies used truly mobile neuroimaging hardware systems. This review provides evidence to support an increase in brain activation in balance control tasks, regardless of mechanical, cognitive, or sensory challenges. Furthermore, the current body of literature demonstrates the use of advanced signal processing methodologies to analyze brain activity during movement. However, the static nature of neuroimaging hardware and conventional balance control paradigms prevent full mobility and limit our knowledge of neural mechanisms underlying balance control.}, journal={Frontiers in Human Neuroscience}, publisher={Frontiers Media SA}, author={Wittenberg, Ellen and Thompson, Jessica and Nam, Chang S. and Franz, Jason R.}, year={2017}, month={Apr} }