Methods/Results : Syncope may be neurally mediated (for example reflex syncope or vasovagal syncope). The most relevant differential diagnosis of syncope and second most common cause of non-traumatic TLOC are pri- mary or secondary generalized epileptic seizures. Rapid recovery with full orientation, very shortly after TLOC, supports the diagnosis of syncope. Other causes of TLOC are ’pseudoseizures’ and ‘pseudosyncope’, conditions during which patients seem to be unconscious although they have not lost consciousness. Misdiagnoses may be frequent and require careful history taking, monitoring of blood pressure, heart rate, respiration and, when possible, also electroencephalography. Conclusions : Together with the key clinical aspects, the history often supports the differential diagnosis and helps to determine whether the patient experienced an epileptic loss of consciousness, syncope or func- tional (“psychogenic”) loss of consciousness, conditions that are not un- common in clinical routine. Keywords: syncope, seizure, epileptic discharge 785 FUNCTIONAL CONNECTIVITY CHANGES WITH TARGETED RTMS OF THE DORSAL ATTENTION NETWORK IN TBI-ASSOCIATED DEPRESSION S. Siddiqi 1, 2, 3 , N. Trapp 4 , C. Hacker 2 , S. Kandala 2 , E. Leuthardt 2 , A. Carter 2 , D. Brody 3 . 1 Harvard Medical School, Berenson-Allen Center for Noninvasive Brain Stimulation, USA; 2 Washington University School of Medicine, USA; 3 Center for Neuroscience & Regenerative Medicine, USUHS, USA; 4 University of Iowa, USA Objective: To modulate specific brain network interactions using rTMS in a clinical trial for depression following traumatic brain injury (TBI). Background: While rTMS is believed to induce functional connectivity (FC) changes, this is challenging to study due to inter-individual variability in brain network architecture. Advances in resting-state fMRI (rsfMRI) technology have led to the recent advent/validation of individualized resting-state network (RSN) mapping, which may help to overcome this hurdle. Methods: As part of a pilot randomized-controlled trial, 9 subjects with TBI-associated depression received sequential left-sided excitatory and right-sided inhibitory rTMS, while 5 received sham. 17 minutes of rsfMRI was collected before and after treatment. Treatment was targeted to an individualized node with strong anti-correlation between dorsal attention network (DAN) and default mode network (DMN). A general linear model (GLM) was used to assess differences between active/sham, change in connectivity, and antidepressant efficacy (change in MADRS). Results: Mean MADRS improvement was 54% (SD 25%) with active treat- ment and 25% (SD 34%) with sham. Antidepressant efficacy was inversely related to baseline subgenual anterior cingulate cortex (sgACC) connec- tivity with the right stimulation site (r¼ -0.68, p¼0.04). Treatment led to significant increase in DMN-sgACC connectivity (standardized b effect size¼1.2, 95% CI [0.1,2.3]), left stimulation site-sgACC anti-correlation (b¼- 1.0 [-1.9,-0.1]), and interhemispheric stimulation site connectivity (b¼1.2 [0.1,2.3]). Antidepressant response further covaried with changes in DMN- sgACC connectivity (b¼1.7 [0.4,3.0]), within-sgACC connectivity (b¼1.4 [0.1,2.7]), left stimulation site anti-correlation with sgACC (b¼ -1.8 [-3.0,- 0.7]), connectivity within the left stimulation site (b¼1.4 [0.02,2.9]), con- nectivity within the right stimulation site (b¼1.6 [0.2,2.9]), and inter- hemispheric stimulation site connectivity (b¼1.7 [0.4,3.0]). Conclusions: rTMS targeted with individualized RSN mapping enables successful modulation of DLPFC-sgACC-DMN interactions, which may underlie its antidepressant efficacy. Keywords: TMS, TBI, fMRI, connectivity 786 THERAPY-ORIENTED INDUCTION OF SEIZURES J. Daskalakis . University of Toronto, Canada In any given year, 2.5 percent of the population experiences treatment resistant depression (TRD). TRD is estimated to cost 60-100 billion per year to treat in the US. Electroconvulsive therapy (ECT) is effective for TRD with remission rates ranging from 50 to 75 percent. However, ECT use in TRD is limited to fewer than 1 percent of patients due to fear, stigma and memory side effects. Repetitive transcranial magnetic stimulation (rTMS) and magnetic seizure therapy (MST) offer a viable alternative to ECT with treatment results suggesting significant mood improvement in TRD. These treatments are also associated with significant rates of remission of sui- cidal ideation (SI). In this presentation, rTMS and MST will be discussed in detail. Novel rTMS and MST treatment approaches will also be discussed Keywords: Seizure, transcranial magnetic stimulation, epilepsy 787 MOTOR CORTICAL EXCITABILITY: A CLINICAL MARKER FOR MEMORY DYSFUNCTION IN TYPE 2 DIABETES MELLITUS S. Zadey 1, 2 , A. Pascual-Leone 2, 3 , P. Fried 2 , S. Buss 2 . 1 Indian Institute of Science Education and Research, Pune, India; 2 Beth Israel Deaconess Medical Center, Harvard Medical School, USA; 3 Institut Guttman, Spain Background: Type 2 Diabetes Mellitus (T2DM) accelerates cognitive aging and increases the risk for Alzheimer’s disease (AD). Even non-demented older adults with T2DM show learning and memory impairments. Prior research has linked cortical hyperexcitability to memory dysfunction in AD. Our aim was to investigate if a similar association exists in T2DM. Methods: Data from 28 individuals with T2DM (aged: 50-80 years; 12 females) and 19 healthy controls (HC) (aged: 50-75, 10 females) were analyzed retrospectively. Cortical excitability was indexed with the resting motor threshold (RMT)dassessed with transcranial magnetic stimulation (TMS) of the left motor cortex. Individual scores from the Rey Auditory Verbal Learning Test and the Logical Memory Story Test were normalized and averaged together to create a composite memory score (CMS). Mul- tiple linear regression analyses were used to assess the relationship be- tween RMT and CMS with coil-to-cortex distance (CCD) as a covariate. Results: RMT, CCD and demographic measures were equivalent between groups (p-values > 0.05). The linear model demonstrated significant variance in CMS by group (F [1,44] ¼ 19.03, p < 0.001), indicating reduced memory function in T2DM. After controlling for CCD, in the full model, group (F [1,30] ¼ 22.27, p < 0.001), RMT (F [1,30] ¼ 8.55, p ¼ 0.007) and the interaction between them (F [1,30] ¼ 4.75, p ¼ 0.037) accounted for sig- nificant amount of variance in CMS. Follow-up linear regression within each group, controlled for CCD, demonstrated that RMT was significantly correlated with CMS (r [13] ¼ 0.62, p ¼ 0.014) in T2DM, but not in HC (r [16] ¼ 0.38, p ¼ 0.123). Significance: The relationship between cortical excitability and memory dysfunction in T2DM provides further neurophysiological evidence to support the epidemiological link between T2DM and AD. RMT is an objective, reliable, and easy-to-capture clinical marker of neurophysio- logical alterations underlying memory decline in T2DM. Keywords: transcranial magnetic stimulation, resting motor threshold, type 2 diabetes mellitus, memory dysfunction 788 ACCELERATED INTERMITTENT THETA BURST STIMULATION FOR ACUTE SUICIDALITY IN AN INPATIENT SETTING N. Williams . Stanford University, USA Background: There are no procedures currently approved for the treat- ment of suicidal thinking during an inpatient psychiatric hospitalization. Recent studies have demonstrated both the safety and possible increased efficacy of accelerated iTBS (aiTBS). The shorter duration of aiTBS protocols could allow treatment to be delivered during an acute psychiatric hospitalization. Objectives: Evaluate the preliminary safety and efficacy of inpatient aiTBS targeting the L-DLPFC for the treatment of suicidal thinking. Methods: Six psychiatric inpatients with suicidal thinking completed a treatment course of aiTBS targeting the L-DLPFC. Patients received treat- ment on five consecutive days, each day consisting of 10 sessions of iTBS (1800 pulses per session) delivered over the course of 10 minutes at 80% resting motor threshold with 50-minute inter-session intervals. In total, patients received 50 iTBS sessions and 90,000 pulses over the course of the five days. Suicidal thinking was assessed before and immediately after with the Scale for Suicidal Ideation (SSI). Abstracts / Brain Stimulation 12 (2019) 385e592 538