was acquired using RNA-seq and RT-qPCR. Custom signal processing, correlation, and PCSA analyses were performed using MATLAB and R. Results: Our results showed that effective DBS increased STN-LFP root- mean-square amplitude, decreased cortico-subthalamic phase-amplitude- coupling, decreased cortical LFP synchronization, and modulated a set of genes involved in plasticity, proliferation, and calcium signaling. Genes differentially transcribed in stimulated animals compared to controls included striatal nestin (Nes), cortical doublecortin (Dcx), and hippocam- pal S100a4. PCSA analysis identified region-specific optimal sets of fea- tures associated with effective DBS. Conclusions: Brain-wide signatures of effective stimulation as well as negative side effects can be identified through quantitative assessment of electrophysiology and transcriptome measures. These signatures enable analysis of both immediate and potential long-term effects of stimulation. We illustrate how these signatures can be identified in an animal model ABSTRACT #24: TRANSCRANIAL DIRECT CURRENT STIMULATION (TDCS) ELECTRIC FIELD MODELING IN CHILDREN AFTER PERINATAL STROKE H.L. Carlson* 1, 2, 3 , A. Giuffre 3, 4 , P. Ciechanski 3, 5 , A. Kirton 1, 2, 3, 6, 7 . 1 Department of Pediatrics, University of Calgary, Canada; 2 Alberta Children's Hospital Research Institute, University of Calgary, Canada; 3 Calgary Paediatric Stroke Program, Alberta Children's Hospital, Canada; 4 Department of Neuroscience, University of Calgary, Canada; 5 Faculty of Dentistry and Medicine, University of Alberta, Canada; 6 Cumming School of Medicine, University of Calgary, Canada; 7 Hotchkiss Brain Institute, University of Calgary, Canada Abstract: Background: Perinatal stroke (PS), the leading cause of hemiparetic ce- rebral palsy (HCP), typically results from occlusion of the middle cerebral artery (arterial ischemic stroke, AIS). Subsequent motor impairments last a lifetime and improving function is difficult. Transcranial direct-current stimulation (tDCS) is a form of non-invasive brain stimulation that may facilitate neuroplasticity and improve function. How current moves through the developing brain is different from adults. Modeling tDCS- induced electric fields (EF) is feasible but individual idiosyncrasies in lesion topology, white (WM) and grey matter (GM) architecture, and skull thickness are undefined in this population. Such subject-specific current modeling is imperative to maximize the safety profile and therapeutic potential of tDCS in hemiparetic children. Aims: We created models of tDCS-induced EF, using a motor cortex (M1)- targeting cathodal tDCS montage, in typically developing (TD) children and those with PS. We hypothesized that EF strength would be higher in PS children compared to TD due to neuroanatomical differences in perile- sional areas. Methods: PS participants aged 6-19 years with disabling HCP were recruited via the Alberta Perinatal Stroke Project as well as TD children of comparable age and gender. Brain MRIs were conducted on a 3T GE MR750w scanner. EF strength was modeled with ROAST (Realistic, vOlu- metric Approach to Simulate Transcranial electric stimulation, Huang 2018) using T1-weighted images (1mm3 voxels). Modeling consisted of T1 tissue segmentation, tetrahedral mesh generation and EF strength simu- lations using a 1mA cathodal montage targeting motor function in the paretic (or non-dominant) hand. The cathode was centered over non- lesioned M1, and anode over contralateral orbit. PeakEFs were extracted for WM and GM and compared between TD and AIS. Results: EF modeling was performed in 25 TDC (mean age (SD)¼13.2(3.6) years) and 26 AIS participants (mean age¼13.0(3.6) years). PeakEFs were higher in WM for AIS (mean (SD)¼0.325(0.06) V/m) compared to TD (mean(SD)¼0.297(0.04) V/m) though not significantly so (p¼0.067). Pea- kEFs in GM were not different from TD. PeakEF was not correlated with age. Conclusions: Individualized modeling of tDCS-induced EFs is feasible in children including those with large perinatal stroke lesions. PeakEF strength in WM may be higher in PS participants compared to TD children. Differences in EF strength were particularly apparent in areas near tissue boundaries. Individualized current modeling may help customize therapeutic tDCS to achieve more personalized rehabilitation in- terventions in future clinical trials. Acknowledgement This study was supported by the Canadian Institutes of Health Research ABSTRACT #25: CURRENT MODELING HIGH DEFINITION AND CONVENTIONAL TDCS-ENHANCED MOTOR LEARNING IN CHILDREN A. Giuffre* 1, 2, 4 , H.L. Carlson 1, 3, 4 , A. Kirton 1, 2,3, 5, 6,4 . 1 Calgary Paediatric Stroke Program, Alberta Children's Hospital, Canada; 2 Department of Neuroscience, University of Calgary, Canada; 3 Department of Pediatrics, University of Calgary, Canada; 4 Alberta Children's Hospital Research Institute, University of Calgary, Canada; 5 Cumming School of Medicine, University of Calgary, Canada; 6 Hotchkiss Brain Institute, University of Calgary, Canada Abstract: Background: Transcranial direct current stimulation (tDCS) can enhance motor learning in healthy children. We have also modelled higher peak electric fields (EF) and larger current spread in children compared to adults receiving primary motor cortex (M1) targeted tDCS montages (anodal, cathodal, bihemispheric). The behavioural effects and accompanying cur- rent models of high-definition (HD-tDCS) of motor cortex have not been defined in the developing brain. Such models may offer insight toward the mechanisms of enhanced motor learning in children. Methods: Healthy, right-handed children (n¼24, median age 15.5 years, range 12-18, 52% female) were recruited from the Healthy Infant and Children Research Program (HICCUP), a population-based research cohort. Participants received 20 minutes of 1mA right hemispheric M1 anodal tDCS (n¼8), HD-tDCS (n¼8), or sham (n¼8) for five consecutive days while training their left hand with the Purdue Pegboard Task (PPT). The HD-tDCS montage used five electrodes in a ring-like orientation (anode at C4, four cathodes FC2, FC6, CP2, CP6) while the tDCS montages has the anode placed at C4 and the cathode at FP1. 3T MRI T1-weighted anatomical im- ages were acquired. Current modeling of the same stimulation was per- formed using ROAST (Realistic vOlumetric Approach to Simulate Transcranial electric stimulation, Huang 2018). All 24 subjects were modelled for both montages with subsequent comparisons by treatment group. Primary outcome was the peak EF (V/m). Correlations with age, gender, and change in PPT were explored (Pearson correlation). Results: Both tDCS and HD-tDCS enhanced motor learning with moderate effect sizes (Cohen’sd >0.8) and sustained effects at 6 weeks. Peak EF was lower for HD-tDCS (mean¼0.238, SD¼0.08) as compared to tDCS (mean¼0.395, SD¼0.08, p<0.001). No correlation was observed between peak EF and age for either conventional (r¼-0.32, p¼0.12) or HD-tDCS (r¼- 0.05,p¼0.78). There were no association between gender and tDCS peak EF (p¼0.94, mean¼0.40, SD¼0.02 females; mean¼0.39, SD¼0.08 males) or HD peak EF (p¼0.85, mean¼0.25, SD¼0.08 females; mean¼0.22, SD¼0.08 males). Peak EF was not associated with change in PPT scores between baseline and post-training for tDCS (r¼-0.19, p¼0.65) or HD-tDCS (r¼0.501, p¼0.21). Conclusion: tDCS and HD-tDCS currents can be successfully modeled within a pediatric interventional trial. Peak EF are higher with tDCS as compared to HD-tDCS. Larger samples are required to accurately deter- mine if peak EF is associated with behavioural effects of stimulation. ABSTRACT #26: TRANSCRANIAL, CLOSED-LOOP TERMINATION OF TEMPORAL LOBE SEIZURES: INTERSECTIONAL SHORT-PULSE (ISP) STIMULATION Andr as Kisp al 1 ,G abor Koz ak 1 , Mih aly V€ or€ oslakos 1, 2 , Anett J. Nagy 1 , Tam as Gyurkovics 1, 3 , Gy€ orgy Buzs aki 2 , Antal Ber enyi* 1, 2, 3 . 1 MTA-SZTE “Momentum” Oscillatory Neuronal Networks Research Group, Dept. of Physiology, Univ. of Szeged, Szeged, Hungary; 2 Neuroscience Institute, New York University, School of Medicine, New York, NY, USA; 3 Neunos Ltd, Szeged, Hungary Abstracts / Brain Stimulation 12 (2019) e1ee55 e9