Modulation of Frontoparietal Dynamics Underlying Adolescent Working Memory Deficits

The objective of this project is to examine the contributing roles of the PPC and PFC in WM processes and relatedly, develop optimal targets for modulating WM-related neural oscillations. Patient Arm: In a 2x2 factorial double-blind design, we will randomize a sample of adolescents (13-18 years) with WM deficits to intermittent theta burst stimulation (iTBS) at the left dorsolateral prefrontal cortex (DLPFC) or inferior parietal lobule (IPL), based on each participant's structural brain MRI. Control Arm: A sample of healthy young adults (18-25 years) will receive an individualized theta-gamma parameters protocol of iTBS to the left DLPFC. Participants in both arms will complete an active iTBS session and a sham iTBS session. The primary outcome will be theta-gamma coupling during WM demands, as measured via electroencephalography (EEG) during a Sternberg spatial WM task (SWMT) immediately before and after iTBS. The central hypothesis is that the PFC and PPC regions have complimentary roles in executing WM processes. Further, iTBS can modulate theta-gamma coupling in these regions to improve behavioral performance. Our central hypothesis is formulated based on our preliminary data on the critical role of theta-gamma coupling in WM processes. To attain the overall objectives, the following specific aims will be pursued: Aim 1: Examine the effect of iTBS to the PPC on the encoding stage of WM. Hypothesis: Compared to sham and DLPFC conditions, iTBS to the IPL will increase theta-gamma coupling during encoding. Modulation of theta-gamma coupling will correlate with improved behavioral performance. Aim 2: Examine the effect of iTBS to the PFC on the maintenance stage of WM. Hypothesis: Compared to sham and IPL conditions, iTBS to the DLPFC will increase theta-gamma coupling during maintenance. Modulation of theta-gamma coupling will correlate with improved behavioral performance. Aim 3: Examine the feasibility and preliminary effect of individualized iTBS to the PFC. Hypothesis: It will be feasible to utilize peak theta-gamma coupling during the SWMT to identify optimal iTBS parameters. Individualized iTBS will increase theta-gamma coupling during WM demands and improve behavioral performance. Exploratory Aim: Identify the neocortical circuitry underlying oscillatory modulation. Computational modeling designed for neural interpretation of EEG will translate obtained recordings into cellular/circuit-level activity delineating the neural mechanism of the observed modulation. Hypothesis: pyramidal-interneuron mechanisms within the PPC/PFC will underlie the theta/gamma oscillatory modulation.