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Farooqi H, Vitek JL, Escobar Sanabria D. Deep brain stimulation pulse sequences to optimally modulate frequency-specific neural activity. J Neural Eng 2024; 21:036045. [PMID: 38843788 PMCID: PMC11191056 DOI: 10.1088/1741-2552/ad54f0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Revised: 05/27/2024] [Accepted: 06/06/2024] [Indexed: 06/21/2024]
Abstract
Objective. Precise neuromodulation systems are needed to identify the role of neural oscillatory dynamics in brain function and to advance the development of brain stimulation therapies tailored to each patient's signature of brain dysfunction. Low-frequency, local field potentials (LFPs) are of increasing interest for the development of these systems because they can reflect the synaptic inputs to a recorded neuronal population and can be chronically recorded in humans. In this computational study, we aim to identify stimulation pulse patterns needed to optimally maximize the suppression or amplification of frequency-specific neural activity.Approach. We derived DBS pulse patterns to minimize or maximize the 2-norm of frequency-specific neural oscillations using a generalized mathematical model of spontaneous and stimulation-evoked LFP activity, and a subject-specific model of neural dynamics in the pallidum of a Parkinson's disease patient. We leveraged convex and mixed-integer optimization tools to identify these pulse patterns, and employed constraints on the pulse frequency and amplitude that are required to keep electrical stimulation within its safety envelope.Main results. Our analysis revealed that a combination of phase, amplitude, and frequency pulse modulation is needed to attain optimal suppression or amplification of the targeted oscillations. Phase modulation is sufficient to modulate oscillations with a constant amplitude envelope. To attain optimal modulation for oscillations with a time-varying envelope, a trade-off between frequency and amplitude pulse modulation is needed. The optimized pulse sequences were invariant to changes in the dynamics of stimulation-evoked neural activity, including changes in damping and natural frequency or complexity (i.e. generalized vs. patient-specific model).Significance. Our results provide insight into the structure of pulse patterns for future closed-loop brain stimulation strategies aimed at controlling neural activity precisely and in real-time.
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Affiliation(s)
- Hafsa Farooqi
- Department of Neurology, Medical School, University of Minnesota, Minneapolis, MN 55455, United States of America
| | - Jerrold L Vitek
- Department of Neurology, Medical School, University of Minnesota, Minneapolis, MN 55455, United States of America
| | - David Escobar Sanabria
- Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, United States of America
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2
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Hu J, Anderson W, Hayes E, Strauss EA, Lang J, Bacos J, Simacek N, Vu HH, McCarty OJT, Kim H, Kang YA. The development, use, and challenges of electromechanical tissue stimulation systems. Artif Organs 2024. [PMID: 38887912 DOI: 10.1111/aor.14808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2024] [Revised: 05/15/2024] [Accepted: 06/02/2024] [Indexed: 06/20/2024]
Abstract
BACKGROUND Tissue stimulations greatly affect cell growth, phenotype, and function, and they play an important role in modeling tissue physiology. With the goal of understanding the cellular mechanisms underlying the response of tissues to external stimulations, in vitro models of tissue stimulation have been developed in hopes of recapitulating in vivo tissue function. METHODS Herein we review the efforts to create and validate tissue stimulators responsive to electrical or mechanical stimulation including tensile, compression, torsion, and shear. RESULTS Engineered tissue platforms have been designed to allow tissues to be subjected to selected types of mechanical stimulation from simple uniaxial to humanoid robotic stain through equal-biaxial strain. Similarly, electrical stimulators have been developed to apply selected electrical signal shapes, amplitudes, and load cycles to tissues, lending to usage in stem cell-derived tissue development, tissue maturation, and tissue functional regeneration. Some stimulators also allow for the observation of tissue morphology in real-time while cells undergo stimulation. Discussion on the challenges and limitations of tissue simulator development is provided. CONCLUSIONS Despite advances in the development of useful tissue stimulators, opportunities for improvement remain to better reproduce physiological functions by accounting for complex loading cycles, electrical and mechanical induction coupled with biological stimuli, and changes in strain affected by applied inputs.
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Affiliation(s)
- Jie Hu
- Department of Mechanical Engineering, University of Massachusetts, Lowell, Massachusetts, USA
| | - William Anderson
- Department of Mechanical, Civil, and Biomedical Engineering, George Fox University, Newberg, Oregon, USA
| | - Emily Hayes
- Department of Mechanical, Civil, and Biomedical Engineering, George Fox University, Newberg, Oregon, USA
| | - Ellie Annah Strauss
- Department of Mechanical, Civil, and Biomedical Engineering, George Fox University, Newberg, Oregon, USA
| | - Jordan Lang
- Department of Mechanical, Civil, and Biomedical Engineering, George Fox University, Newberg, Oregon, USA
| | - Josh Bacos
- Department of Mechanical, Civil, and Biomedical Engineering, George Fox University, Newberg, Oregon, USA
| | - Noah Simacek
- Department of Mechanical, Civil, and Biomedical Engineering, George Fox University, Newberg, Oregon, USA
| | - Helen H Vu
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, Oregon, USA
| | - Owen J T McCarty
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, Oregon, USA
- Cell, Developmental and Cancer Biology, Oregon Health & Science University, Portland, Oregon, USA
| | - Hoyeon Kim
- Department of Engineering, Loyola University Maryland, Baltimore, Maryland, USA
| | - Youngbok Abraham Kang
- Department of Mechanical, Civil, and Biomedical Engineering, George Fox University, Newberg, Oregon, USA
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3
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Noor MS, Steina AK, McIntyre CC. Dissecting deep brain stimulation evoked neural activity in the basal ganglia. Neurotherapeutics 2024; 21:e00356. [PMID: 38608373 PMCID: PMC11019280 DOI: 10.1016/j.neurot.2024.e00356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 03/26/2024] [Accepted: 04/01/2024] [Indexed: 04/14/2024] Open
Abstract
Deep brain stimulation (DBS) is an established therapeutic tool for the treatment of Parkinson's disease (PD). The mechanisms of DBS for PD are likely rooted in modulation of the subthalamo-pallidal network. However, it can be difficult to electrophysiologically interrogate that network in human patients. The recent identification of large amplitude evoked potential (EP) oscillations from DBS in the subthalamic nucleus (STN) or globus pallidus internus (GPi) are providing new scientific opportunities to expand understanding of human basal ganglia network activity. In turn, the goal of this review is to provide a summary of DBS-induced EPs in the basal ganglia and attempt to explain various components of the EP waveforms from their likely network origins. Our analyses suggest that DBS-induced antidromic activation of globus pallidus externus (GPe) is a key driver of these oscillatory EPs, independent of stimulation location (i.e. STN or GPi). This suggests a potentially more important role for GPe in the mechanisms of DBS for PD than typically assumed. And from a practical perspective, DBS EPs are poised to become clinically useful electrophysiological biomarker signals for verification of DBS target engagement.
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Affiliation(s)
- M Sohail Noor
- Department of Biomedical Engineering, Duke University, Durham, NC, USA
| | - Alexandra K Steina
- Institute of Clinical Neuroscience and Medical Psychology, Heinrich Heine University, Düsseldorf, Germany
| | - Cameron C McIntyre
- Department of Biomedical Engineering, Duke University, Durham, NC, USA; Department of Neurosurgery, Duke University, Durham, NC, USA.
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4
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Zeng Z, Huang P, Lin Z, Pan Y, Wan X, Zhang C, Sun B, Li D. Rescue subthalamic stimulation after unsatisfactory outcome of pallidal stimulation in Parkinson's disease: a case series and review. Front Aging Neurosci 2024; 15:1323541. [PMID: 38264547 PMCID: PMC10803461 DOI: 10.3389/fnagi.2023.1323541] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Accepted: 12/20/2023] [Indexed: 01/25/2024] Open
Abstract
Background Subthalamic nucleus (STN) and globus pallidus interna (GPi) are two main structures primarily targeted by deep brain stimulation (DBS) to treat advanced Parkinson's disease (PD). A subset of cases with unsatisfactory outcomes may benefit from rescue DBS surgery targeting another structure, while these patients' characteristics have not been well described and this phenomenon has not been well reviewed. Methods This monocentric retrospective study included patients with PD, who underwent rescue STN DBS following an unsatisfactory outcome of the initial bilateral GPi DBS in a retrospective manner. A short review of the current literature was conducted to report the clinical outcome of rescue DBS surgeries. Results Eight patients were identified, and six of them were included in this study. The rescue STN DBS was performed 19.8 months after the initial GPi DBS. After 8.8 months from the rescue STN DBS, patients showed a significant off-medication improvement by 29.2% in motor symptoms compared to initial GPi DBS. Non-motor symptoms and the health-related quality of life were also significantly improved. Conclusion Our findings suggest that the rescue STN DBS may improve off-medication motor and non-motor symptoms and quality of life in patients with failure of initial GPi DBS. The short review of the current literature showed that the target switching from GPi to STN was mainly due to poor initial outcomes and was performed by target substitution, whereas the switching from STN to GPi was mainly due to a gradual waning of benefits, long-term axial symptoms, dyskinesia, and dystonia and was performed by target addition.
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Affiliation(s)
| | | | | | | | | | | | | | - Dianyou Li
- Department of Neurosurgery, Center for Functional Neurosurgery, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
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Palopoli-Trojani K, Schmidt SL, Baringer KD, Slotkin TA, Peters JJ, Turner DA, Grill WM. Temporally non-regular patterns of deep brain stimulation (DBS) enhance assessment of evoked potentials while maintaining motor symptom management in Parkinson's disease (PD). Brain Stimul 2023; 16:1630-1642. [PMID: 37863388 PMCID: PMC10872419 DOI: 10.1016/j.brs.2023.10.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Revised: 09/25/2023] [Accepted: 10/11/2023] [Indexed: 10/22/2023] Open
Abstract
BACKGROUND Traditional deep brain stimulation (DBS) at fixed regular frequencies (>100 Hz) is effective in treating motor symptoms of Parkinson's disease (PD). Temporally non-regular patterns of DBS are a new parameter space that may help increase efficacy and efficiency. OBJECTIVE To compare the effects of temporally non-regular patterns of DBS to traditional regularly-spaced pulses. METHODS We simultaneously recorded local field potentials (LFP) and monitored motor symptoms (tremor and bradykinesia) in persons with PD during DBS in subthalamic nucleus (STN). We quantified both oscillatory activity and DBS local evoked potentials (DLEPs) from the LFP. RESULTS Temporally non-regular patterns were as effective as traditional pulse patterns in modulating motor symptoms, oscillatory activity, and DLEPs. Moreover, one of our novel patterns enabled recording of longer duration DLEPs during clinically effective stimulation. CONCLUSIONS Stimulation gaps of 50 ms can be used to increase efficiency and to enable regular assessment of long-duration DLEPs while maintaining effective symptom management. This may be a promising paradigm for closed-loop DBS with biomarker assessment during the gaps.
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Affiliation(s)
| | - Stephen L Schmidt
- Department of Biomedical Engineering, Duke University, Durham, NC, USA
| | - Karley D Baringer
- Department of Biomedical Engineering, Duke University, Durham, NC, USA
| | - Theodore A Slotkin
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, USA
| | - Jennifer J Peters
- Department of Biomedical Engineering, Duke University, Durham, NC, USA
| | - Dennis A Turner
- Department of Biomedical Engineering, Duke University, Durham, NC, USA; Department of Neurobiology and Department of Neurosurgery, Duke University, Durham, NC, USA
| | - Warren M Grill
- Department of Biomedical Engineering, Duke University, Durham, NC, USA; Department of Neurobiology and Department of Neurosurgery, Duke University, Durham, NC, USA; Department of Electrical and Computer Engineering, Duke University, Durham, NC, USA.
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Zapata Amaya V, Aman JE, Johnson LA, Wang J, Patriat R, Hill ME, MacKinnon CD, Cooper SE, Darrow D, McGovern R, Harel N, Molnar GF, Park MC, Vitek JL, Escobar Sanabria D. Low-frequency deep brain stimulation reveals resonant beta-band evoked oscillations in the pallidum of Parkinson's Disease patients. Front Hum Neurosci 2023; 17:1178527. [PMID: 37810764 PMCID: PMC10556241 DOI: 10.3389/fnhum.2023.1178527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Accepted: 08/28/2023] [Indexed: 10/10/2023] Open
Abstract
Introduction Evidence suggests that spontaneous beta band (11-35 Hz) oscillations in the basal ganglia thalamocortical (BGTC) circuit are linked to Parkinson's disease (PD) pathophysiology. Previous studies on neural responses in the motor cortex evoked by electrical stimulation in the subthalamic nucleus have suggested that circuit resonance may underlie the generation of spontaneous and stimulation-evoked beta oscillations in PD. Whether these stimulation-evoked, resonant oscillations are present across PD patients in the internal segment of the globus pallidus (GPi), a primary output nucleus in the BGTC circuit, is yet to be determined. Methods We characterized spontaneous and stimulation-evoked local field potentials (LFPs) in the GPi of four PD patients (five hemispheres) using deep brain stimulation (DBS) leads externalized after DBS implantation surgery. Results Our analyses show that low-frequency (2-4 Hz) stimulation in the GPi evoked long-latency (>50 ms) beta-band neural responses in the GPi in 4/5 hemispheres. We demonstrated that neural sources generating both stimulation-evoked and spontaneous beta oscillations were correlated in their frequency content and spatial localization. Discussion Our results support the hypothesis that the same neuronal population and resonance phenomenon in the BGTC circuit generates both spontaneous and evoked pallidal beta oscillations. These data also support the development of closed-loop control systems that modulate the GPi spontaneous oscillations across PD patients using beta band stimulation-evoked responses.
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Affiliation(s)
| | - Joshua E Aman
- Department of Neurology, University of Minnesota, Minneapolis, MN, United States
| | - Luke A Johnson
- Department of Neurology, University of Minnesota, Minneapolis, MN, United States
| | - Jing Wang
- Department of Neurology, University of Minnesota, Minneapolis, MN, United States
| | - Remi Patriat
- Department of Radiology, University of Minnesota, Minneapolis, MN, United States
| | - Meghan E Hill
- Department of Neurology, University of Minnesota, Minneapolis, MN, United States
| | - Colum D MacKinnon
- Department of Neurology, University of Minnesota, Minneapolis, MN, United States
| | - Scott E Cooper
- Department of Neurology, University of Minnesota, Minneapolis, MN, United States
| | - David Darrow
- Department of Neurosurgery, University of Minnesota, Minneapolis, MN, United States
| | - Robert McGovern
- Department of Neurosurgery, University of Minnesota, Minneapolis, MN, United States
| | - Noam Harel
- Department of Radiology, University of Minnesota, Minneapolis, MN, United States
| | - Gregory F Molnar
- Department of Neurology, University of Minnesota, Minneapolis, MN, United States
| | - Michael C Park
- Department of Neurosurgery, University of Minnesota, Minneapolis, MN, United States
| | - Jerrold L Vitek
- Department of Neurology, University of Minnesota, Minneapolis, MN, United States
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Najera RA, Mahavadi AK, Khan AU, Boddeti U, Del Bene VA, Walker HC, Bentley JN. Alternative patterns of deep brain stimulation in neurologic and neuropsychiatric disorders. Front Neuroinform 2023; 17:1156818. [PMID: 37415779 PMCID: PMC10320008 DOI: 10.3389/fninf.2023.1156818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Accepted: 06/06/2023] [Indexed: 07/08/2023] Open
Abstract
Deep brain stimulation (DBS) is a widely used clinical therapy that modulates neuronal firing in subcortical structures, eliciting downstream network effects. Its effectiveness is determined by electrode geometry and location as well as adjustable stimulation parameters including pulse width, interstimulus interval, frequency, and amplitude. These parameters are often determined empirically during clinical or intraoperative programming and can be altered to an almost unlimited number of combinations. Conventional high-frequency stimulation uses a continuous high-frequency square-wave pulse (typically 130-160 Hz), but other stimulation patterns may prove efficacious, such as continuous or bursting theta-frequencies, variable frequencies, and coordinated reset stimulation. Here we summarize the current landscape and potential clinical applications for novel stimulation patterns.
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Affiliation(s)
- Ricardo A. Najera
- Department of Neurosurgery, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Anil K. Mahavadi
- Department of Neurosurgery, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Anas U. Khan
- Department of Neurosurgery, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Ujwal Boddeti
- Department of Neurosurgery, University of Maryland School of Medicine, Baltimore, MD, United States
| | - Victor A. Del Bene
- Department of Neurology, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Harrison C. Walker
- Department of Neurology, University of Alabama at Birmingham, Birmingham, AL, United States
| | - J. Nicole Bentley
- Department of Neurosurgery, University of Alabama at Birmingham, Birmingham, AL, United States
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Wiest C, He S, Duchet B, Pogosyan A, Benjaber M, Denison T, Hasegawa H, Ashkan K, Baig F, Bertaina I, Morgante F, Pereira EA, Torrecillos F, Tan H. Evoked resonant neural activity in subthalamic local field potentials reflects basal ganglia network dynamics. Neurobiol Dis 2023; 178:106019. [PMID: 36706929 PMCID: PMC7614125 DOI: 10.1016/j.nbd.2023.106019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2022] [Revised: 01/11/2023] [Accepted: 01/23/2023] [Indexed: 01/25/2023] Open
Abstract
Evoked resonant neural activity (ERNA) is induced by subthalamic deep brain stimulation (DBS) and was recently suggested as a marker of lead placement and contact selection in Parkinson's disease. Yet, its underlying mechanisms and how it is modulated by stimulation parameters are unclear. Here, we recorded local field potentials from 27 Parkinson's disease patients, while leads were externalised to scrutinise the ERNA. First, we show that ERNA in the time series waveform and spectrogram likely represent the same activity, which was contested before. Second, our results show that the ERNA has fast and slow dynamics during stimulation, consistent with the synaptic failure hypothesis. Third, we show that ERNA parameters are modulated by different DBS frequencies, intensities, medication states and stimulation modes (continuous DBS vs. adaptive DBS). These results suggest the ERNA might prove useful as a predictor of the best DBS frequency and lowest effective intensity in addition to contact selection. Changes with levodopa and DBS mode suggest that the ERNA may indicate the state of the cortico-basal ganglia circuit making it a putative biomarker to track clinical state in adaptive DBS.
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Affiliation(s)
- Christoph Wiest
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Shenghong He
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Benoit Duchet
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Alek Pogosyan
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Moaad Benjaber
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Timothy Denison
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Harutomo Hasegawa
- Department of Neurosurgery, King’s College Hospital, Denmark Hill, London, UK
| | - Keyoumars Ashkan
- Department of Neurosurgery, King’s College Hospital, Denmark Hill, London, UK
| | - Fahd Baig
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK,Neurosciences Research Centre, Molecular and Clinical Sciences Institute, St. George’s, University of London, London, UK
| | - Ilaria Bertaina
- Neurosciences Research Centre, Molecular and Clinical Sciences Institute, St. George’s, University of London, London, UK,Neurology Department, Neurocenter of Southern Switzerland, Ente Ospedaliero Cantonale, Lugano, Switzerland
| | - Francesca Morgante
- Neurosciences Research Centre, Molecular and Clinical Sciences Institute, St. George’s, University of London, London, UK
| | - Erlick A. Pereira
- Neurosciences Research Centre, Molecular and Clinical Sciences Institute, St. George’s, University of London, London, UK
| | - Flavie Torrecillos
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Huiling Tan
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
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Wiest C, Morgante F, Torrecillos F, Pogosyan A, He S, Baig F, Bertaina I, Hart MG, Edwards MJ, Pereira EA, Tan H. Subthalamic Nucleus Stimulation-Induced Local Field Potential Changes in Dystonia. Mov Disord 2023; 38:423-434. [PMID: 36562479 PMCID: PMC7614354 DOI: 10.1002/mds.29302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 12/02/2022] [Accepted: 12/05/2022] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND Subthalamic nucleus (STN) stimulation is an effective treatment for Parkinson's disease and induced local field potential (LFP) changes that have been linked with clinical improvement. STN stimulation has also been used in dystonia although the internal globus pallidus is the standard target where theta power has been suggested as a physiomarker for adaptive stimulation. OBJECTIVE We aimed to explore if enhanced theta power was also present in STN and if stimulation-induced spectral changes that were previously reported for Parkinson's disease would occur in dystonia. METHODS We recorded LFPs from 7 patients (12 hemispheres) with isolated craniocervical dystonia whose electrodes were placed such that inferior, middle, and superior contacts covered STN, zona incerta, and thalamus. RESULTS We did not observe prominent theta power in STN at rest. STN stimulation induced similar spectral changes in dystonia as in Parkinson's disease, such as broadband power suppression, evoked resonant neural activity (ERNA), finely-tuned gamma oscillations, and an increase in aperiodic exponents in STN-LFPs. Both power suppression and ERNA localize to STN. Based on this, single-pulse STN stimulation elicits evoked neural activities with largest amplitudes in STN, which are relayed to the zona incerta and thalamus with changing characteristics as the distance from STN increases. CONCLUSIONS Our results show that STN stimulation-induced spectral changes are a nondisease-specific response to high-frequency stimulation, which can serve as placement markers for STN. This broadens the scope of STN stimulation and makes it an option for other disorders with excessive oscillatory peaks in STN. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.
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Affiliation(s)
- Christoph Wiest
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical NeurosciencesJohn Radcliffe Hospital, University of OxfordOxfordUnited Kingdom
| | - Francesca Morgante
- Neurosciences Research CentreMolecular and Clinical Sciences Institute, St. George's, University of LondonLondonUnited Kingdom
| | - Flavie Torrecillos
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical NeurosciencesJohn Radcliffe Hospital, University of OxfordOxfordUnited Kingdom
| | - Alek Pogosyan
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical NeurosciencesJohn Radcliffe Hospital, University of OxfordOxfordUnited Kingdom
| | - Shenghong He
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical NeurosciencesJohn Radcliffe Hospital, University of OxfordOxfordUnited Kingdom
| | - Fahd Baig
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical NeurosciencesJohn Radcliffe Hospital, University of OxfordOxfordUnited Kingdom
- Neurosciences Research CentreMolecular and Clinical Sciences Institute, St. George's, University of LondonLondonUnited Kingdom
| | - Ilaria Bertaina
- Neurosciences Research CentreMolecular and Clinical Sciences Institute, St. George's, University of LondonLondonUnited Kingdom
| | - Michael G. Hart
- Neurosciences Research CentreMolecular and Clinical Sciences Institute, St. George's, University of LondonLondonUnited Kingdom
| | - Mark J. Edwards
- Institute of Psychiatry, Psychology and NeurosciencesKing's College LondonLondonUnited Kingdom
| | - Erlick A. Pereira
- Neurosciences Research CentreMolecular and Clinical Sciences Institute, St. George's, University of LondonLondonUnited Kingdom
| | - Huiling Tan
- Medical Research Council Brain Network Dynamics Unit, Nuffield Department of Clinical NeurosciencesJohn Radcliffe Hospital, University of OxfordOxfordUnited Kingdom
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10
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Madadi Asl M, Valizadeh A, Tass PA. Decoupling of interacting neuronal populations by time-shifted stimulation through spike-timing-dependent plasticity. PLoS Comput Biol 2023; 19:e1010853. [PMID: 36724144 PMCID: PMC9891531 DOI: 10.1371/journal.pcbi.1010853] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Accepted: 01/05/2023] [Indexed: 02/02/2023] Open
Abstract
The synaptic organization of the brain is constantly modified by activity-dependent synaptic plasticity. In several neurological disorders, abnormal neuronal activity and pathological synaptic connectivity may significantly impair normal brain function. Reorganization of neuronal circuits by therapeutic stimulation has the potential to restore normal brain dynamics. Increasing evidence suggests that the temporal stimulation pattern crucially determines the long-lasting therapeutic effects of stimulation. Here, we tested whether a specific pattern of brain stimulation can enable the suppression of pathologically strong inter-population synaptic connectivity through spike-timing-dependent plasticity (STDP). More specifically, we tested how introducing a time shift between stimuli delivered to two interacting populations of neurons can effectively decouple them. To that end, we first used a tractable model, i.e., two bidirectionally coupled leaky integrate-and-fire (LIF) neurons, to theoretically analyze the optimal range of stimulation frequency and time shift for decoupling. We then extended our results to two reciprocally connected neuronal populations (modules) where inter-population delayed connections were modified by STDP. As predicted by the theoretical results, appropriately time-shifted stimulation causes a decoupling of the two-module system through STDP, i.e., by unlearning pathologically strong synaptic interactions between the two populations. Based on the overall topology of the connections, the decoupling of the two modules, in turn, causes a desynchronization of the populations that outlasts the cessation of stimulation. Decoupling effects of the time-shifted stimulation can be realized by time-shifted burst stimulation as well as time-shifted continuous simulation. Our results provide insight into the further optimization of a variety of multichannel stimulation protocols aiming at a therapeutic reshaping of diseased brain networks.
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Affiliation(s)
- Mojtaba Madadi Asl
- School of Biological Sciences, Institute for Research in Fundamental Sciences (IPM), Tehran, Iran
- Pasargad Institute for Advanced Innovative Solutions (PIAIS), Tehran, Iran
| | - Alireza Valizadeh
- Pasargad Institute for Advanced Innovative Solutions (PIAIS), Tehran, Iran
- Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran
| | - Peter A. Tass
- Department of Neurosurgery, Stanford University School of Medicine, Stanford, CA, United States of America
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11
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Johnson KA, Cagle JN, Lopes JL, Wong JK, Okun MS, Gunduz A, Shukla AW, Hilliard JD, Foote KD, de Hemptinne C. Globus pallidus internus deep brain stimulation evokes resonant neural activity in Parkinson's disease. Brain Commun 2023; 5:fcad025. [PMID: 36895960 PMCID: PMC9989134 DOI: 10.1093/braincomms/fcad025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 10/07/2022] [Accepted: 02/06/2023] [Indexed: 02/10/2023] Open
Abstract
Globus pallidus internus deep brain stimulation is an established therapy for patients with medication-refractory Parkinson's disease. Clinical outcomes are highly dependent on applying stimulation to precise locations in the brain. However, robust neurophysiological markers are needed to determine the optimal electrode location and to guide postoperative stimulation parameter selection. In this study, we evaluated evoked resonant neural activity in the pallidum as a potential intraoperative marker to optimize targeting and stimulation parameter selection to improve outcomes of deep brain stimulation for Parkinson's disease. Intraoperative local field potential recordings were acquired in 22 patients with Parkinson's disease undergoing globus pallidus internus deep brain stimulation implantation (N = 27 hemispheres). A control group of patients undergoing implantation in the subthalamic nucleus (N = 4 hemispheres) for Parkinson's disease or the thalamus for essential tremor (N = 9 patients) were included for comparison. High-frequency (135 Hz) stimulation was delivered from each electrode contact sequentially while recording the evoked response from the other contacts. Low-frequency stimulation (10 Hz) was also applied as a comparison. Evoked resonant neural activity features, including amplitude, frequency and localization were measured and analysed for correlation with empirically derived postoperative therapeutic stimulation parameters. Pallidal evoked resonant neural activity elicited by stimulation in the globus pallidus internus or externus was detected in 26 of 27 hemispheres and varied across hemispheres and across stimulating contacts within individual hemispheres. Bursts of high-frequency stimulation elicited evoked resonant neural activity with similar amplitudes (P = 0.9) but a higher frequency (P = 0.009) and a higher number of peaks (P = 0.004) than low-frequency stimulation. We identified a 'hotspot' in the postero-dorsal pallidum where stimulation elicited higher evoked resonant neural activity amplitudes (P < 0.001). In 69.6% of hemispheres, the contact that elicited the maximum amplitude intraoperatively matched the contact empirically selected for chronic therapeutic stimulation by an expert clinician after 4 months of programming sessions. Pallidal and subthalamic nucleus evoked resonant neural activity were similar except for lower pallidal amplitudes. No evoked resonant neural activity was detected in the essential tremor control group. Given its spatial topography and correlation with postoperative stimulation parameters empirically selected by expert clinicians, pallidal evoked resonant neural activity shows promise as a potential marker to guide intraoperative targeting and to assist the clinician with postoperative stimulation programming. Importantly, evoked resonant neural activity may also have the potential to guide directional and closed-loop deep brain stimulation programming for Parkinson's disease.
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Affiliation(s)
- Kara A Johnson
- Norman Fixel Institute for Neurological Diseases, University of Florida, Gainesville, FL, USA.,Department of Neurology, University of Florida, Gainesville, FL, USA
| | - Jackson N Cagle
- Norman Fixel Institute for Neurological Diseases, University of Florida, Gainesville, FL, USA.,Department of Neurology, University of Florida, Gainesville, FL, USA
| | - Janine Lobo Lopes
- Norman Fixel Institute for Neurological Diseases, University of Florida, Gainesville, FL, USA.,Department of Neurology, University of Florida, Gainesville, FL, USA
| | - Joshua K Wong
- Norman Fixel Institute for Neurological Diseases, University of Florida, Gainesville, FL, USA.,Department of Neurology, University of Florida, Gainesville, FL, USA
| | - Michael S Okun
- Norman Fixel Institute for Neurological Diseases, University of Florida, Gainesville, FL, USA.,Department of Neurology, University of Florida, Gainesville, FL, USA
| | - Aysegul Gunduz
- Norman Fixel Institute for Neurological Diseases, University of Florida, Gainesville, FL, USA.,J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, USA
| | - Aparna Wagle Shukla
- Norman Fixel Institute for Neurological Diseases, University of Florida, Gainesville, FL, USA.,Department of Neurology, University of Florida, Gainesville, FL, USA
| | - Justin D Hilliard
- Norman Fixel Institute for Neurological Diseases, University of Florida, Gainesville, FL, USA.,Department of Neurosurgery, University of Florida, Gainesville, FL, USA
| | - Kelly D Foote
- Norman Fixel Institute for Neurological Diseases, University of Florida, Gainesville, FL, USA.,Department of Neurosurgery, University of Florida, Gainesville, FL, USA
| | - Coralie de Hemptinne
- Norman Fixel Institute for Neurological Diseases, University of Florida, Gainesville, FL, USA.,Department of Neurology, University of Florida, Gainesville, FL, USA
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12
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Johnson BP, Cohen LG. Applied strategies of neuroplasticity. HANDBOOK OF CLINICAL NEUROLOGY 2023; 196:599-609. [PMID: 37620093 DOI: 10.1016/b978-0-323-98817-9.00011-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/26/2023]
Abstract
Various levels of somatotopic organization are present throughout the human nervous system. However, this organization can change when needed based on environmental demands, a phenomenon known as neuroplasticity. Neuroplasticity can occur when learning a new motor skill, adjusting to life after blindness, or following a stroke. Following an injury, these neuroplastic changes can be adaptive or maladaptive, and often occur regardless of whether rehabilitation occurs or not. But not all movements produce neuroplasticity, nor do all rehabilitation interventions. Here, we focus on research regarding how to maximize adaptive neuroplasticity while also minimizing maladaptive plasticity, known as applied neuroplasticity. Emphasis is placed on research exploring how best to apply neuroplastic principles to training environments and rehabilitation protocols. By studying and applying these principles in research and clinical practice, it is hoped that learning of skills and regaining of function and independence can be optimized.
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Affiliation(s)
- Brian P Johnson
- Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States
| | - Leonardo G Cohen
- Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States.
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13
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Saberi M, Khosrowabadi R, Khatibi A, Misic B, Jafari G. Pattern of frustration formation in the functional brain network. Netw Neurosci 2022; 6:1334-1356. [PMID: 38800463 PMCID: PMC11117102 DOI: 10.1162/netn_a_00268] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Accepted: 07/05/2022] [Indexed: 05/29/2024] Open
Abstract
The brain is a frustrated system that contains conflictual link arrangements named frustration. The frustration as a source of disorder prevents the system from settling into low-energy states and provides flexibility for brain network organization. In this research, we tried to identify the pattern of frustration formation in the brain at the levels of region, connection, canonical network, and hemisphere. We found that frustration formation has no uniform pattern. Some subcortical elements have an active role in frustration formation, despite low contributions from many cortical elements. Frustrating connections are mostly between-network connections, and triadic frustrations are mainly formed between three regions from three distinct canonical networks. We did not find any significant differences between brain hemispheres or any robust differences between the frustration formation patterns of various life-span stages. Our results may be interesting for those who study the organization of brain links and promising for those who want to manipulate brain networks.
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Affiliation(s)
- Majid Saberi
- Institute for Cognitive and Brain Sciences, Shahid Beheshti University, G.C. Tehran, Iran
| | - Reza Khosrowabadi
- Institute for Cognitive and Brain Sciences, Shahid Beheshti University, G.C. Tehran, Iran
| | - Ali Khatibi
- Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK
| | - Bratislav Misic
- McConnell Brain Imaging Centre, Montréal Neurological Institute, McGill University, Montréal, QC, Canada
| | - Gholamreza Jafari
- Institute for Cognitive and Brain Sciences, Shahid Beheshti University, G.C. Tehran, Iran
- Physics Department, Shahid Beheshti University, Tehran, Iran
- Institute of Information Technology and Data Science, Irkutsk National Research Technical University, Irkutsk, Russia
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14
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Campbell BA, Favi Bocca L, Escobar Sanabria D, Almeida J, Rammo R, Nagel SJ, Machado AG, Baker KB. The impact of pulse timing on cortical and subthalamic nucleus deep brain stimulation evoked potentials. Front Hum Neurosci 2022; 16:1009223. [PMID: 36204716 PMCID: PMC9532054 DOI: 10.3389/fnhum.2022.1009223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Accepted: 08/31/2022] [Indexed: 11/13/2022] Open
Abstract
The impact of pulse timing is an important factor in our understanding of how to effectively modulate the basal ganglia thalamocortical (BGTC) circuit. Single pulse low-frequency DBS-evoked potentials generated through electrical stimulation of the subthalamic nucleus (STN) provide insight into circuit activation, but how the long-latency components change as a function of pulse timing is not well-understood. We investigated how timing between stimulation pulses delivered in the STN region influence the neural activity in the STN and cortex. DBS leads implanted in the STN of five patients with Parkinson's disease were temporarily externalized, allowing for the delivery of paired pulses with inter-pulse intervals (IPIs) ranging from 0.2 to 10 ms. Neural activation was measured through local field potential (LFP) recordings from the DBS lead and scalp EEG. DBS-evoked potentials were computed using contacts positioned in dorsolateral STN as determined through co-registered post-operative imaging. We quantified the degree to which distinct IPIs influenced the amplitude of evoked responses across frequencies and time using the wavelet transform and power spectral density curves. The beta frequency content of the DBS evoked responses in the STN and scalp EEG increased as a function of pulse-interval timing. Pulse intervals <1.0 ms apart were associated with minimal to no change in the evoked response. IPIs from 1.5 to 3.0 ms yielded a significant increase in the evoked response, while those >4 ms produced modest, but non-significant growth. Beta frequency activity in the scalp EEG and STN LFP response was maximal when IPIs were between 1.5 and 4.0 ms. These results demonstrate that long-latency components of DBS-evoked responses are pre-dominantly in the beta frequency range and that pulse interval timing impacts the level of BGTC circuit activation.
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Affiliation(s)
- Brett A. Campbell
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States
- Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Leonardo Favi Bocca
- Center for Neurological Restoration, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
| | - David Escobar Sanabria
- Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Julio Almeida
- Center for Neurological Restoration, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Richard Rammo
- Center for Neurological Restoration, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
- Department of Neurosurgery, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Sean J. Nagel
- Center for Neurological Restoration, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
- Department of Neurosurgery, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Andre G. Machado
- Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
- Center for Neurological Restoration, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
- Department of Neurosurgery, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Kenneth B. Baker
- Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
- Center for Neurological Restoration, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
- *Correspondence: Kenneth B. Baker
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15
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Dale J, Schmidt SL, Mitchell K, Turner DA, Grill WM. Evoked potentials generated by deep brain stimulation for Parkinson's disease. Brain Stimul 2022; 15:1040-1047. [DOI: 10.1016/j.brs.2022.07.048] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Revised: 04/18/2022] [Accepted: 07/20/2022] [Indexed: 11/29/2022] Open
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16
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Bingham CS, McIntyre CC. Subthalamic deep brain stimulation of an anatomically detailed model of the human hyperdirect pathway. J Neurophysiol 2022; 127:1209-1220. [PMID: 35320026 PMCID: PMC9054256 DOI: 10.1152/jn.00004.2022] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Revised: 03/14/2022] [Accepted: 03/15/2022] [Indexed: 11/22/2022] Open
Abstract
The motor hyperdirect pathway (HDP) is considered a key target in the treatment of Parkinson's disease with subthalamic deep brain stimulation (DBS). This hypothesis is partially derived from the association of HDP activation with evoked potentials (EPs) generated in the motor cortex and subthalamic nucleus (STN) after a DBS pulse. However, the biophysical details of how and when DBS-induced action potentials (APs) in HDP neurons reach their terminations in the cortex or STN remain unclear. Therefore, we used an anatomically detailed representation of the motor HDP, as well as the internal capsule (IC), in a model of human subthalamic DBS to explore AP activation and transmission in the HDP and IC. Our results show that small diameter HDP axons exhibited AP initiation in their subthalamic terminal arbor, which resulted in relatively long transmission latencies to cortex (∼3.5-8 ms). Alternatively, large diameter HDP axons were most likely to be directly activated in the capsular region, which resulted in short transmission times to the cortex (∼1-3 ms). However, those large diameter HDP antidromic APs would be indistinguishable from any other IC axons that were also activated by the stimulus. Conversely, DBS-induced APs in both small and large diameter HDP axons reached their synaptic boutons in the STN with similar timings, but both spanned a wide temporal range (∼0.5-5 ms). We also found that using anodic or bipolar stimulation helped to bias activation of the HDP over the IC. These computational results provide useful information for linking HDP activation with EP recordings in clinical experiments.NEW & NOTEWORTHY We used biophysical models to study pathway recruitment and conduction latencies of the hyperdirect pathway (HDP) in response to subthalamic deep brain stimulation (DBS). The model system allowed us to assess the influence of increased anatomical realism on pathway activity and the possibility of identifying HDP activity in evoked potentials (EPs) recorded in either the subthalamic nucleus (STN) or cortex. The model predicts that HDP activation is accentuated by complex axonal branching in the STN.
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Affiliation(s)
- Clayton S Bingham
- Department of Biomedical Engineering, Duke University, Durham, North Carolina
| | - Cameron C McIntyre
- Department of Biomedical Engineering, Duke University, Durham, North Carolina
- Department of Neurosurgery, Duke University, Durham, North Carolina
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17
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Bahners BH, Waterstraat G, Kannenberg S, Curio G, Schnitzler A, Nikulin V, Florin E. Electrophysiological characterization of the hyperdirect pathway and its functional relevance for subthalamic deep brain stimulation. Exp Neurol 2022; 352:114031. [PMID: 35247373 DOI: 10.1016/j.expneurol.2022.114031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 02/01/2022] [Accepted: 02/28/2022] [Indexed: 11/04/2022]
Abstract
The subthalamic nucleus (STN) receives input from various cortical areas via hyperdirect pathway (HDP) which bypasses the basal-ganglia loop. Recently, the HDP has gained increasing interest, because of its relevance for STN deep brain stimulation (DBS). To understand the HDP's role cortical responses evoked by STN-DBS have been investigated. These responses have short (<2 ms), medium (2-15 ms), and long (20-70 ms) latencies. Medium-latency responses are supposed to represent antidromic cortical activations via HDP. Together with long-latency responses the medium responses can potentially be used as biomarker of DBS efficacy as well as side effects. We here propose that the activation sequence of the cortical evoked responses can be conceptualized as high frequency oscillations (HFO) for signal analysis. HFO might therefore serve as marker for antidromic activation. Using existing knowledge on HFO recordings, this approach allows data analyses and physiological modeling to advance the pathophysiological understanding of cortical DBS-evoked high-frequency activity.
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Affiliation(s)
- Bahne Hendrik Bahners
- Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany
| | - Gunnar Waterstraat
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Neurophysics Group, Department of Neurology, Berlin, Germany
| | - Silja Kannenberg
- Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany
| | - Gabriel Curio
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Neurophysics Group, Department of Neurology, Berlin, Germany; Bernstein Center for Computational Neuroscience, Berlin, Germany
| | - Alfons Schnitzler
- Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany; Department of Neurology, Center for Movement Disorders and Neuromodulation, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany
| | - Vadim Nikulin
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Esther Florin
- Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany.
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