19, 1.24-3.397). Racial/ethnic disparities differed considerably across frailty criteria, ranging from a twofold increase in odds of slowness to a 25-30% decrease in odds of self-reported exhaustion. CONCLUSIONS BMI and disease burden do not explain racial/ethnic frailty disparities. Black-white disparities are not restricted to low income groups. Racial/ethnic differences vary considerably by NHATS PFP criteria. Our findings support the need to better understand mechanisms underlying elevated frailty burden in older non-Hispanic black and Hispanic Americans, how phenotypic measures capture frailty in racial/ethnic subgroups and, potentially, how to create assessments more comparable by race/ethnicity. © The Author(s) 2020. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail journals.permissions@oup.com.The balance of excitation and inhibition is essential for cortical information processing, relying on the tight orchestration of the underlying subcellular processes. Dynamic transcriptional control by DNA methylation, catalyzed by DNA methyltransferases (DNMTs), and DNA demethylation, achieved by ten-eleven translocation (TET)-dependent mechanisms, is proposed to regulate synaptic function in the adult brain with implications for learning and memory. However, focus so far is laid on excitatory neurons. Given the crucial role of inhibitory cortical interneurons in cortical information processing and in disease, deciphering the cellular and molecular mechanisms of GABAergic transmission is fundamental. The emerging relevance of DNMT and TET-mediated functions for synaptic regulation irrevocably raises the question for the targeted subcellular processes and mechanisms. In this study, we analyzed the role dynamic DNA methylation has in regulating cortical interneuron function. We found that DNMT1 and TET1/TET3 contrarily modulate clathrin-mediated endocytosis. Moreover, we provide evidence that DNMT1 influences synaptic vesicle replenishment and GABAergic transmission, presumably through the DNA methylation-dependent transcriptional control over endocytosis-related genes. The relevance of our findings is supported by human brain sample analysis, pointing to a potential implication of DNA methylation-dependent endocytosis regulation in the pathophysiology of temporal lobe epilepsy, a disease characterized by disturbed synaptic transmission. © The Author(s) 2020. Published by Oxford University Press.The ability to detect short gaps in noise is an important tool for assessing the temporal resolution in the auditory cortex. However, the mere existence of responses to temporal gaps bounded by two short broadband markers is surprising, because of the expected short-term suppression that is prevalent in auditory cortex. Here, we used in-vivo intracellular recordings in anesthetized rats to dissect the synaptic mechanisms that underlie gap-related responses. When a gap is bounded by two short markers, a gap termination response was evoked by the onset of the second marker with minimal contribution from the offset of the first marker. Importantly, we show that the gap termination response was driven by a different (potentially partially overlapping) synaptic population than that underlying the onset response to the first marker. This recruitment of additional synaptic resources is a novel mechanism contributing to the important perceptual task of gap detection. APD334 © The Author(s) 2020. Published by Oxford University Press.Spinal ependymomas compose approximately 60% of spinal gliomas, the predominance occurring within adults. These tumors are generally benign, and maximal surgical resection with neurological preservation is the surgical goal. This patient had a large upper cervical ependymoma, which was approached through a cervical laminotomy. The surgical resection of this lesion demonstrates the principles of pial venous plexus preservation during posterior midline raphe identification and dissection. Gross total surgical resection was achieved with the preservation of the patient’s baseline neurological function. The patient gave informed consent for surgery and video recording. Institutional review board approval was deemed unnecessary. Used with permission from Barrow Neurological Institute, Phoenix, Arizona. Copyright © 2020 by the Congress of Neurological Surgeons.BACKGROUND Robotic-assisted stereotaxy has been increasingly adopted for lead implantation in stereoelectroencephalography based on its efficiency, accuracy, and precision. Despite initially being developed for use in deep brain stimulation (DBS) surgery, adoption for this indication has not been widespread. OBJECTIVE To describe a recent robotic-assisted stereotaxy experience and workflow for DBS lead implantation in awake patients with and without microelectrode recording (MER), including considerations for intraoperative research using electrocorticography (ECoG). METHODS A retrospective review of 20 consecutive patients who underwent simultaneous bilateral DBS lead implantation using robotic-assisted stereotaxy was performed. Radial error was determined by comparing the preoperative target with the DBS lead position in the targeting plane on postoperative computed tomography. Information regarding any postoperative complications was obtained by chart review. RESULTS A novel method for robot coregistration was developed. We describe a standard workflow that allows for MER and/or ECoG research, and a streamlined workflow for cases in which MER is not required. The overall radial error for lead placement across all 20 patients was 1.14 ± 0.11 mm. A significant difference (P = .006) existed between the radial error of the first 10 patients (1.46 ± 0.19 mm) as compared with the second 10 patients (0.86 ± 0.09 mm). No complications were encountered. CONCLUSION Robotic-assisted stereotaxy has the potential to increase precision and reduce human error, compared to traditional frame-based DBS surgery, without negatively impacting patient safety or the ability to perform awake neurophysiology research. Copyright © 2020 by the Congress of Neurological Surgeons.