Neural plasticity activities associated with neuropathic pain have been found in multiple deep nuclei, which mainly involve different frequency band oscillations and their dynamic features. Therefore, the dynamics state of these nuclei characterized based on neural activity may reflect the state of neuropathic pain. In this study, multiple oscillations in the sensory thalamus local field potentials (LFPs) were extracted and distinguished to synchronization state and de-synchronization state according to their synchronization level. Then neural states of the sensory thalamus were defined rely on the synchronization state of at least one oscillation using binary coding. Two dynamic features were used to characterize neural states: switch rate and average duration. The switch rate is the total number of times the neural state switches from one neural state to other any neural states within 50 seconds. The average duration is average of the time that neural state continues to be in a certain state. Results show switch rate of the low-beta-based the sensory thalamus neural state was significantly related to pain relief after 12 months DBS surgery (p<0.01) and this relationship became more significant when combine low-beta with other any oscillations to define neural states (P<0.001). Moreover, even average duration of the low-beta-based neural state was not signif- icant related to pain relief, but it became significant when combine low- beta with other oscillations (p<0.001). On the contrary, mean duration of high-beta-based neural state was significantly related to pain relief. But it did not further enhance when combine high-beta with other oscillations. These results indicated that oscillations play different roles in neuropathic pain. Low-beta oscillation co-works with other oscillations to encode neuropathic pain by generate a neural oscillation network, while high-beta oscillation independently from other oscillations. These findings contribute to the understanding of neural plasticity in the sensory thal- amus of neuropathic pain. Keywords: plasticity, neuropathic pain, sensory thalamus 801 DESIGN AND EVALUATION OF VARIOUS TDCS ELECTRODES AND ELECTRODE PLACEMENT TO UNDERSTAND OPTIMAL CONFIGURATION FOR TREATMENT OF DEPRESSION A. Sadeghi 1, 2 , A. Zalli 3 , R. Jalili Khoshnoud 3 , K. Bajelani 1, 4 , F. Tondnevis 1, 4 , M. Aboulhasani 1, 5 , R. Vaez Ghaemi 6 . 1 Department of Biomedical Engineering (Center of Excellence), Amirkabir University of Technology, Islamic Republic of Iran; 2 Neurological division, Medtronic, Tehran, Islamic Republic of Iran; 3 Neurofunctional Research Center, Shohada Tajrish Neurosurgical Comprehensive Center of Excellence, Shahid Beheshti University of Medical Science, Tehran, Islamic Republic of Iran; 4 Neurological division, Medtronic, Tehran, Islamic Republic of Iran; 5 Neurological division, Medtronic, Iran, Islamic Republic of Iran; 6 Department of Biomedical Engineering, University of British Columbia, Vancouver, Canada Depression is a common serious mood disorder. Major depressive disorder is a leading cause of disability worldwide, affecting more than 100 million people. An emerging problem in treating depression is the development of resistance to the treatment. Brain stimulation therapy is a novel approach to overcome the treatment resistance, and replaces pharmacotherapy and psychotherapy. Transcranial Direct-Current Stimulation (tDCS) is a mini- mally invasive form of brain stimulation therapy which applies a weak electrical direct current. This current would modulate spontaneous firing rates of the cortical neurons by depolarizing or hyperpolarizing the neural resting membrane potential. tDCS has been suggested as a therapeutic method to influence pathologic mood states in patients with depressive disorders. Several studies have been conducted to examine the efficacy of tDCS in treating depression. Most of these studies demonstrate that active tDCS reduces depressive symptoms. More recently research had focused on optimization of parameters such as electrode placement, electrode size, stimulation time and frequency for tDCS treatment. However, there is still a lack of consensus on the placement of electrodes that leads to optimal treatment outcomes. The depressive symptoms have been reduced using anodal stimulation of the left dorsolateral prefrontal cortex, as well as cathodal stimulation of the right dorsolateral prefrontal cortex, and anodal stimulation of the left dorsolateral prefrontal cortex with a neutral region. In our study we try to find out the optimal electrode placement and electrode properties to induce appropriate stimulation. According to this we prepare various type of electrode with different sizes to study the treatment response and patient relief. Keywords: tDCS, Brain stimulation, Brain phantom, electrode replace- ment, electrode size 802 FROM DEEP BRAIN STIMULATION IN PARKINSON  S DISEASE AND TREATMENT-RESISTANT DEPRESSION TO A NEW PERSPECTIVE TO UNDERSTAND DEPRESSION A. Silva Dos Santos 1, 2 , M. Sales 1 . 1 Psychiatry Department, Hospital Vila Franca de Xira, Portugal; 2 Neuroscience and Pharmacology Institute, Institute of Molecular Medicine, University of Lisbon, Portugal Brain stimulation therapies, such as Deep Brain Stimulation (DBS) have emerged from an idea entertained by science fiction into a mainstream medical treatment, which constantly finds new applications. DBS was first introduced to medical practice by Benabid and his colleagues in 1987 when they discovered that high frequency stimulation of the thalamus diminished tremor. Later, guided by the neurophysiological studies of Delong and his colleagues on the neural circuits involved in Parkinson  s Disease, Benabid stimulated the subthalamic nucleus with high frequency current and achieved significant improvement of PD symptoms. PD has been linked to degeneration of dopaminergic neurons in the substantia nigra, which eventually results in an abnormal neuronal activity in the basal ganglia circuitry. This abnormal activity is characterized by syn- chronous bursts, which resemble epileptiform activity. DBS has thera- peutic effect on PD because it disrupts the abnormal bursting in the basal ganglia e corticothalamic loops. Regarding the application of DBS in Depression, in 2005, Mayberg  s group reported that DBS was effective for the treatment of patients with depression who were resistant to medica- tion and/or electroconvulsive therapy. The idea of such treatment was based on the neuroimaging studies that revealed an abnormal hyperac- tivity of the subcallosalcingulate cortex (SCC) also known by area 25 of Broadman (BA25) or subgenualcingulated (Cg25) in some patients with depression. Based on a literature review, we discuss a possible mechanism that may cause, at least in part, some of the abnormal brain oscillation in some types of depression. This hypothesis is based on an approach that we call an Integrative Perspective to understand Mental Disorders that uses prag- matic clinical-psychiatric inputs as well as the contribution of DBS, com- bined with modern perspectives from neuroscience, neuroanatomy, neurochemistry, neuroimaging, and neurophysiology. Keywords: deep brain stimulation, parkinson  s disease, depression,neur- ophysiology 803 HYPERACTIVATION OF THE SUBGENUAL CINGULATE IN DEPRESSED PATIENTS THAT IS NORMALIZED WITH RTMS TREATMENT I. Hadas, D. Blumberger, Z. Daskalakis . CAMH, Canada Background:Hyperactivity in the subgenual cingulate (SGC) has been demonstrated in major depressive disorder (MDD). These findings suggest that the DLPFC-SGC connectivity is important for understanding the rTMS therapeutic mechanism in MDD, and MDD pathophysiology in general. Methods: 30 healthy volunteers and 43 MDD patients were recruited as part of an rTMS trial. DLPFC targeted TMS-EEG responses and Hamilton Depression Rating Scale (HRSD-17) was taken before and after Active or Sham rTMS treatment. The SGC activity was quantified using the signifi- cant current density (SCD), and the effective connectivity between the DLPFC and SGC was computed using significant current scattering (SCS). Both measures were computed around TMS evoked potentials (TEP) standard peak times before rTMS treatment for healthy (N¼30) and MDD (N¼30), and after rTMS treatment comparing sham (N¼18) and active (N¼25) treated MDD participants. Results: Before rTMS treatment we found that the SGC SCD was higher in MDD participants around 30 ms (P < 0.01), 100 ms (P < 0.005), and 200 ms (P < 0.006) after the TMS pulse, also the SCS between the SGC and the DLPFC in MDD patients was significantly higher compared to healthy Abstracts / Brain Stimulation 12 (2019) 385e592 541