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Mark Hallett

Bio: Mark Hallett is an academic researcher from National Institutes of Health. The author has contributed to research in topics: Transcranial magnetic stimulation & Motor cortex. The author has an hindex of 186, co-authored 1170 publications receiving 123741 citations. Previous affiliations of Mark Hallett include Government of the United States of America & Armed Forces Institute of Pathology.


Papers
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Journal ArticleDOI
01 Apr 2016-Brain
TL;DR: The connectivity patterns observed in this study suggest that the modulation of white matter tracts directed to the superior frontal gyrus and the thalamus is associated with favourable clinical outcomes and may contribute to the therapeutic effects of deep brain stimulation.
Abstract: Deep brain stimulation therapy is an effective symptomatic treatment for Parkinson's disease, yet the precise mechanisms responsible for its therapeutic effects remain unclear. Although the targets of deep brain stimulation are grey matter structures, axonal modulation is known to play an important role in deep brain stimulation's therapeutic mechanism. Several white matter structures in proximity to the subthalamic nucleus have been implicated in the clinical benefits of deep brain stimulation for Parkinson's disease. We assessed the connectivity patterns that characterize clinically beneficial electrodes in Parkinson's disease patients, after deep brain stimulation of the subthalamic nucleus. We evaluated 22 patients with Parkinson's disease (11 females, age 57 ± 9.1 years, disease duration 13.3 ± 6.3 years) who received bilateral deep brain stimulation of the subthalamic nucleus at the National Institutes of Health. During an initial electrode screening session, one month after deep brain stimulation implantation, the clinical benefits of each contact were determined. The electrode was localized by coregistering preoperative magnetic resonance imaging and postoperative computer tomography images and the volume of tissue activated was estimated from stimulation voltage and impedance. Brain connectivity for the volume of tissue activated of deep brain stimulation contacts was assessed using probabilistic tractography with diffusion-tensor data. Areas most frequently connected to clinically effective contacts included the thalamus, substantia nigra, brainstem and superior frontal gyrus. A series of discriminant analyses demonstrated that the strength of connectivity to the superior frontal gyrus and the thalamus were positively associated with clinical effectiveness. The connectivity patterns observed in our study suggest that the modulation of white matter tracts directed to the superior frontal gyrus and the thalamus is associated with favourable clinical outcomes and may contribute to the therapeutic effects of deep brain stimulation. Our method can be further developed to reliably identify effective deep brain stimulation contacts and aid in the programming process.

119 citations

Journal ArticleDOI
TL;DR: Risk of hearing loss from the acoustic artifact of magnetic stimulation, as evaluated by audiograms, tympanograms, acoustic reflexes, and auditory evoked potentials, seems to be small in humans.
Abstract: Prompted by the description of hearing loss in rabbits exposed to the acoustic artifact of magnetic stimulation, we compared the results of audiologic studies before and after exposure to transcranial magnetic stimulation in humans. We found no evidence of temporary or permanent threshold shifts in any of the subjects, even in those exposed to transcranial magnetic stimulation repeatedly for several years. Risk of hearing loss from the acoustic artifact of magnetic stimulation, as evaluated by audiograms, tympanograms, acoustic reflexes, and auditory evoked potentials, seems to be small in humans.

119 citations

Journal Article
TL;DR: Myoclonus appears to be generated by a brief transient activation of a focal region of motor cortex that gives rise to a transient depression of function that would lead to a brief lapse in muscle activation that would be interpreted as either asterixis or negative myOClonus.
Abstract: Myoclonus appears to be generated by a brief transient activation of a focal region of motor cortex. Activation of a focal region of motor cortex can also give rise to a transient depression of function. If a subject, or patient, is trying to produce movement, this depression would lead to a brief lapse in muscle activation that would be interpreted as either asterixis or negative myoclonus. Both positive events and negative events can occur either individually or together. The physiological substrate in the cortex appears to be different for the two phenomena, and the pharmacology may differ as well.

119 citations

Journal ArticleDOI
TL;DR: The question arises as to how a movement can be produced with voluntary mechanisms, but not be considered voluntary, and the good clinical neurophysiological methods available suggest that PMDs share voluntary mechanisms for movement production.

119 citations

Book
01 Jan 2003
TL;DR: This work presents recordings of the Bereitschaftspotential and related potentials in cortical and subcortical structures in human subjects from epicortical recording in patients with intractable partial epilepsy, and discusses distributed source modeling in the analysis of movement-related activity.
Abstract: Introduction. The Bereitschaftspotential: What does it measure and where does it come from? M. Jahanshahi, M. Hallett. From Surface to Depth Electrodes. Surface recordings of the Bereitschaftspotential in normals W. Lang. The Bereitschaftspotential and the conscious will/intention to act B. Libet. Generator mechanisms of the Bereitschaftspotentials as studied by epicortical recording in patients with intractable partial epilepsy A. Ikeda, H. Shibasaki. Intracerebral recordings of the Bereitschaftspotential and related potentials in cortical and subcortical structures in human subjects I. Rektor. Dipole Source Modeling and the Generators of the Bereitschaftspotential. Distributed source modeling in the analysis of movement-related activity R. Kristeva-Feige. Recordings of the movement-related potentials combined with PET, fMRI or MEG C.D. MacKinnon. Generators of the movement-related cortical potentials and dipole source analysis K. Toma, M. Hallett. The Bereitschaftspotential in Patient Groups. Surface recordings in patients with movement disorders and the impact of subcortical surgery P. Praamstra, M. Jahanshahi, J.C. Rothwell. The Bereitschaftspotential in schizophrenia and depression K.P. Westphal. Movement-related cortical potentials in patients with focal brain lesions C. Gerloff. Other Related EEG Measures. Movement and ERD/ERS G. Pfurtscheller, C. Neuper. CNV and SPN: Indices of anticipatory behavior C.H.M. Brunia. The lateralized readiness potential M. Eimer, M.G.H. Coles. Other Approaches to Measuring Motor Preparation. Movement selection, preparation, and the decision to act: neurophysiological studies in nonhuman primates S. Wise. Movement preparation: neuroimaging studies I. Toni, R. Passingham. Finale. Human freedom, reasoned will, and the brain: the Bereitschaftspotential story L. Deecke, H.H. Kornhuber. Index.

117 citations


Cited by
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Journal ArticleDOI
TL;DR: Past observations are synthesized to provide strong evidence that the default network is a specific, anatomically defined brain system preferentially active when individuals are not focused on the external environment, and for understanding mental disorders including autism, schizophrenia, and Alzheimer's disease.
Abstract: Thirty years of brain imaging research has converged to define the brain’s default network—a novel and only recently appreciated brain system that participates in internal modes of cognition Here we synthesize past observations to provide strong evidence that the default network is a specific, anatomically defined brain system preferentially active when individuals are not focused on the external environment Analysis of connectional anatomy in the monkey supports the presence of an interconnected brain system Providing insight into function, the default network is active when individuals are engaged in internally focused tasks including autobiographical memory retrieval, envisioning the future, and conceiving the perspectives of others Probing the functional anatomy of the network in detail reveals that it is best understood as multiple interacting subsystems The medial temporal lobe subsystem provides information from prior experiences in the form of memories and associations that are the building blocks of mental simulation The medial prefrontal subsystem facilitates the flexible use of this information during the construction of self-relevant mental simulations These two subsystems converge on important nodes of integration including the posterior cingulate cortex The implications of these functional and anatomical observations are discussed in relation to possible adaptive roles of the default network for using past experiences to plan for the future, navigate social interactions, and maximize the utility of moments when we are not otherwise engaged by the external world We conclude by discussing the relevance of the default network for understanding mental disorders including autism, schizophrenia, and Alzheimer’s disease

8,448 citations

Journal ArticleDOI
TL;DR: The basal ganglia serve primarily to integrate diverse inputs from the entire cerebral cortex and to "funnel" these influences, via the ventrolateral thalamus, to the motor cortex.
Abstract: Information about the basal ganglia has accumulated at a prodigious pace over the past decade, necessitating major revisions in our concepts of the structural and functional organization of these nuclei. From earlier data it had appeared that the basal ganglia served primarily to integrate diverse inputs from the entire cerebral cortex and to "funnel" these influences, via the ventrolateral thalamus, to the motor cortex (Allen & Tsukahara 1974, Evarts & Thach 1969, Kemp & Powell 1971). In particular, the basal

8,111 citations

Journal ArticleDOI
TL;DR: FieldTrip is an open source software package that is implemented as a MATLAB toolbox and includes a complete set of consistent and user-friendly high-level functions that allow experimental neuroscientists to analyze experimental data.
Abstract: This paper describes FieldTrip, an open source software package that we developed for the analysis of MEG, EEG, and other electrophysiological data. The software is implemented as a MATLAB toolbox and includes a complete set of consistent and user-friendly high-level functions that allow experimental neuroscientists to analyze experimental data. It includes algorithms for simple and advanced analysis, such as time-frequency analysis using multitapers, source reconstruction using dipoles, distributed sources and beamformers, connectivity analysis, and nonparametric statistical permutation tests at the channel and source level. The implementation as toolbox allows the user to perform elaborate and structured analyses of large data sets using the MATLAB command line and batch scripting. Furthermore, users and developers can easily extend the functionality and implement new algorithms. The modular design facilitates the reuse in other software packages.

7,963 citations

Journal ArticleDOI
06 Jun 1986-JAMA
TL;DR: The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or her own research.
Abstract: I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

7,563 citations