Browsing by Author "Sheth, Sameer A."
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Item A biophysically constrained brain connectivity model based on stimulation-evoked potentials.(Elsevier, 2024) Schmid, William; Danstrom, Isabel A.; Crespo Echevarria, Maria; Adkinson, Joshua; Mattar, Layth; Banks, Garrett P.; Sheth, Sameer A.; Watrous, Andrew J.; Heilbronner, Sarah R.; Bijanki, Kelly R.; Alabastri, Alessandro; Bartoli, EleonoraBackground Single-pulse electrical stimulation (SPES) is an established technique used to map functional effective connectivity networks in treatment-refractory epilepsy patients undergoing intracranial-electroencephalography monitoring. While the connectivity path between stimulation and recording sites has been explored through the integration of structural connectivity, there are substantial gaps, such that new modeling approaches may advance our understanding of connectivity derived from SPES studies. New method Using intracranial electrophysiology data recorded from a single patient undergoing stereo-electroencephalography (sEEG) evaluation, we employ an automated detection method to identify early response components, C1, from pulse-evoked potentials (PEPs) induced by SPES. C1 components were utilized for a novel topology optimization method, modeling 3D electrical conductivity to infer neural pathways from stimulation sites. Additionally, PEP features were compared with tractography metrics, and model results were analyzed with respect to anatomical features. Results The proposed optimization model resolved conductivity paths with low error. Specific electrode contacts displaying high error correlated with anatomical complexities. The C1 component strongly correlated with additional PEP features and displayed stable, weak correlations with tractography measures. Comparison with existing method Existing methods for estimating neural signal pathways are imaging-based and thus rely on anatomical inferences. Conclusions These results demonstrate that informing topology optimization methods with human intracranial SPES data is a feasible method for generating 3D conductivity maps linking electrical pathways with functional neural ensembles. PEP-estimated effective connectivity is correlated with but distinguished from structural connectivity. Modeled conductivity resolves connectivity pathways in the absence of anatomical priors.Item Beta activity in human anterior cingulate cortex mediates reward biases(Springer Nature, 2024) Xiao, Jiayang; Adkinson, Joshua A.; Myers, John; Allawala, Anusha B.; Mathura, Raissa K.; Pirtle, Victoria; Najera, Ricardo; Provenza, Nicole R.; Bartoli, Eleonora; Watrous, Andrew J.; Oswalt, Denise; Gadot, Ron; Anand, Adrish; Shofty, Ben; Mathew, Sanjay J.; Goodman, Wayne K.; Pouratian, Nader; Pitkow, Xaq; Bijanki, Kelly R.; Hayden, Benjamin; Sheth, Sameer A.The rewards that we get from our choices and actions can have a major influence on our future behavior. Understanding how reward biasing of behavior is implemented in the brain is important for many reasons, including the fact that diminution in reward biasing is a hallmark of clinical depression. We hypothesized that reward biasing is mediated by the anterior cingulate cortex (ACC), a cortical hub region associated with the integration of reward and executive control and with the etiology of depression. To test this hypothesis, we recorded neural activity during a biased judgment task in patients undergoing intracranial monitoring for either epilepsy or major depressive disorder. We found that beta (12–30 Hz) oscillations in the ACC predicted both associated reward and the size of the choice bias, and also tracked reward receipt, thereby predicting bias on future trials. We found reduced magnitude of bias in depressed patients, in whom the beta-specific effects were correspondingly reduced. Our findings suggest that ACC beta oscillations may orchestrate the learning of reward information to guide adaptive choice, and, more broadly, suggest a potential biomarker for anhedonia and point to future development of interventions to enhance reward impact for therapeutic benefit.Item Computational modeling and minimization of unintended neuronal excitation in a LIFU stimulation(Springer Nature, 2023) Fan, Boqiang; Goodman, Wayne; Cho, Raymond Y.; Sheth, Sameer A.; Bouchard, Richard R.; Aazhang, BehnaamThe neuromodulation effect of low-intensity focused ultrasound (LIFU) is highly target-specific. Unintended off-target neuronal excitation can be elicited when the beam focusing accuracy and resolution are limited, whereas the resulted side effect has not been evaluated quantitatively. There is also a lack of methods addressing the minimization of such side effects. Therefore, this work introduces a computational model of unintended neuronal excitation during LIFU neuromodulation, which evaluates the off-target activation area (OTAA) by integrating an ultrasound field model with the neuronal spiking model. In addition, a phased array beam focusing scheme called constrained optimal resolution beamforming (CORB) is proposed to minimize the off-target neuronal excitation area while ensuring effective stimulation in the target brain region. A lower bound of the OTAA is analytically approximated in a simplified homogeneous medium, which could guide the selection of transducer parameters such as aperture size and operating frequency. Simulations in a human head model using three transducer setups show that CORB markedly reduces the OTAA compared with two benchmark beam focusing methods. The high neuromodulation resolution demonstrates the capability of LIFU to effectively limit the side effects during neuromodulation, allowing future clinical applications such as treatment of neuropsychiatric disorders.Item Decoding Depression Severity From Intracranial Neural Activity(Elsevier, 2023) Xiao, Jiayang; Provenza, Nicole R.; Asfouri, Joseph; Myers, John; Mathura, Raissa K.; Metzger, Brian; Adkinson, Joshua A.; Allawala, Anusha B.; Pirtle, Victoria; Oswalt, Denise; Shofty, Ben; Robinson, Meghan E.; Mathew, Sanjay J.; Goodman, Wayne K.; Pouratian, Nader; Schrater, Paul R.; Patel, Ankit B.; Tolias, Andreas S.; Bijanki, Kelly R.; Pitkow, Xaq; Sheth, Sameer A.Background Disorders of mood and cognition are prevalent, disabling, and notoriously difficult to treat. Fueling this challenge in treatment is a significant gap in our understanding of their neurophysiological basis. Methods We recorded high-density neural activity from intracranial electrodes implanted in depression-relevant prefrontal cortical regions in 3 human subjects with severe depression. Neural recordings were labeled with depression severity scores across a wide dynamic range using an adaptive assessment that allowed sampling with a temporal frequency greater than that possible with typical rating scales. We modeled these data using regularized regression techniques with region selection to decode depression severity from the prefrontal recordings. Results Across prefrontal regions, we found that reduced depression severity is associated with decreased low-frequency neural activity and increased high-frequency activity. When constraining our model to decode using a single region, spectral changes in the anterior cingulate cortex best predicted depression severity in all 3 subjects. Relaxing this constraint revealed unique, individual-specific sets of spatiospectral features predictive of symptom severity, reflecting the heterogeneous nature of depression. Conclusions The ability to decode depression severity from neural activity increases our fundamental understanding of how depression manifests in the human brain and provides a target neural signature for personalized neuromodulation therapies.Item Unknown EMvelop stimulation: minimally invasive deep brain stimulation using temporally interfering electromagnetic waves(IOP Publishing, 2022) Ahsan, Fatima; Chi, Taiyun; Cho, Raymond; Sheth, Sameer A.; Goodman, Wayne; Aazhang, BehnaamObjective. Recently, the temporal interference stimulation (TIS) technique for focal noninvasive deep brain stimulation (DBS) was reported. However, subsequent computational modeling studies on the human brain have shown that while TIS achieves higher focality of electric fields than state-of-the-art methods, further work is needed to improve the stimulation strength. Here, we investigate the idea of EMvelop stimulation, a minimally invasive DBS setup using temporally interfering gigahertz (GHz) electromagnetic (EM) waves. At GHz frequencies, we can create antenna arrays at the scale of a few centimeters or less that can be endocranially implanted to enable longitudinal stimulation and circumvent signal attenuation due to the scalp and skull. Furthermore, owing to the small wavelength of GHz EM waves, we can optimize both amplitudes and phases of the EM waves to achieve high intensity and focal stimulation at targeted regions within the safety limit for exposure to EM waves. Approach. We develop a simulation framework investigating the propagation of GHz EM waves generated by line current antenna elements and the corresponding heat generated in the brain tissue. We propose two optimization flows to identify antenna current amplitudes and phases for either maximal intensity or maximal focality transmission of the interfering electric fields with EM waves safety constraint. Main results. A representative result of our study is that with two endocranially implanted arrays of size × each, we can achieve an intensity of 12 V m−1 with a focality of at a target deep in the brain tissue. Significance. In this proof-of-principle study, we show that the idea of EMvelop stimulation merits further investigation as it can be a minimally invasive way of stimulating deep brain targets and offers benefits not shared by prior methodologies of electrical or magnetic stimulation.Item Unknown Epileptic seizure prediction using spectral width of the covariance matrix(IOP Publishing, 2022) EPMoghaddam, Dorsa; Sheth, Sameer A.; Haneef, Zulfi; Gavvala, Jay; Aazhang, BehnaamObjective. Epilepsy is a common neurological disorder in which patients suffer from sudden and unpredictable seizures. Seizures are caused by excessive and abnormal neuronal activity. Different methods have been employed to investigate electroencephalogram (EEG) data in patients with epilepsy. This paper introduces a simple yet accurate array-based method to study and predict seizures. Approach. We use the CHB-MIT dataset (all 24 cases), which includes scalp EEG recordings. The proposed method is based on the random matrix theory. After applying wavelet decomposition to denoise the data, we analyze the spatial coherence of the epileptic recordings by looking at the width of the covariance matrix eigenvalue distribution at different time and frequency bins. Main results. We train patient-specific support vector machine classifiers to distinguish between interictal and preictal data with high performance and a false prediction rate as low as 0.09 h−1. The proposed technique achieves an average accuracy, specificity, sensitivity, and area under the curve of 99.05%, 93.56%, 99.09%, and 0.99, respectively. Significance. Our proposed method outperforms state-of-the-art works in terms of sensitivity while maintaining a low false prediction rate. Also, in contrast to neural networks, which may achieve high performance, this work provides high sensitivity without compromising interpretability.Item Unknown Miniature battery-free epidural cortical stimulators(AAAS, 2024) Woods, Joshua E.; Singer, Amanda L.; Alrashdan, Fatima; Tan, Wendy; Tan, Chunfeng; Sheth, Sunil A.; Sheth, Sameer A.; Robinson, Jacob T.; Applied Physics ProgramMiniaturized neuromodulation systems could improve the safety and reduce the invasiveness of bioelectronic neuromodulation. However, as implantable bioelectronic devices are made smaller, it becomes difficult to store enough power for long-term operation in batteries. Here, we present a battery-free epidural cortical stimulator that is only 9 millimeters in width yet can safely receive enough wireless power using magnetoelectric antennas to deliver 14.5-volt stimulation bursts, which enables it to stimulate cortical activity on-demand through the dura. The device has digitally programmable stimulation output and centimeter-scale alignment tolerances when powered by an external transmitter. We demonstrate that this device has enough power and reliability for real-world operation by showing acute motor cortex activation in human patients and reliable chronic motor cortex activation for 30 days in a porcine model. This platform opens the possibility of simple surgical procedures for precise neuromodulation.Item Unknown Sub-scalp electroencephalography: A next-generation technique to study human neurophysiology(Elsevier, 2022) Haneef, Zulfi; Yang, Kaiyuan; Sheth, Sameer A.; Aloor, Fuad Z.; Aazhang, Behnaam; Krishnan, Vaishnav; Karakas, CemalSub-scalp electroencephalography (ssEEG) is emerging as a promising technology in ultra-long-term electroencephalography (EEG) recordings. Given the diversity of devices available in this nascent field, uncertainty persists about its utility in epilepsy evaluation. This review critically dissects the many proposed utilities of ssEEG devices including (1) seizure quantification, (2) seizure characterization, (3) seizure lateralization, (4) seizure localization, (5) seizure alarms, (6) seizure forecasting, (7) biomarker discovery, (8) sleep medicine, and (9) responsive stimulation. The different ssEEG devices in development have individual design philosophies with unique strengths and limitations. There are devices offering primarily unilateral recordings (24/7 EEGTM SubQ, NeuroviewTM, Soenia® UltimateEEG™), bilateral recordings (Minder™, Epios™), and even those with responsive stimulation capability (EASEE®). We synthesize the current knowledge of these ssEEG systems. We review the (1) ssEEG devices, (2) use case scenarios, (3) challenges and (4) suggest a roadmap for ideal ssEEG designs.Item Unknown Towards objective, temporally resolved neurobehavioral predictors of emotional state(Elsevier, 2024) Kabotyanski, Katherine E.; Yi, Han G.; Hingorani, Rahul; Robinson, Brian S.; Cowley, Hannah P.; Fifer, Matthew S.; Wester, Brock A.; Lamichhane, Bishal; Sabharwal, Ashutosh; Allawala, Anusha B.; Rajesh, Sameer V.; Diab, Nabeel; Mathura, Raissa K.; Pirtle, Victoria; Adkinson, Joshua; Watrous, Andrew J.; Bartoli, Eleonora; Xiao, Jiayang; Banks, Garrett P.; Mathew, Sanjay J.; Goodman, Wayne K.; Pitkow, Xaq; Pouratian, Nader; Hayden, Benjamin Y.; Provenza, Nicole R.; Sheth, Sameer A.