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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.


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Journal ArticleDOI
TL;DR: The data support the notion of a limited flexible relationship between primary motor cortex and its target muscles following alterations of normal input-output patterns and suggest enhanced excitability of motor pathways targeting muscles rostral to the level of a spinal transection.
Abstract: To assess changes in the relationship between cortical motor representation areas and their target muscles following spinal cord lesions, we studied motor evoked potentials (MEPs) to transcranial magnetic stimulation in six patients with complete spinal cord injuries at low thoracic levels and eight healthy subjects. Magnetic stimulation at rest activated a larger fraction of the motoneuron pool and evoked MEPs with shorter latencies from a larger number of scalp positions in muscles immediately rostral to the level of a spinal cord injury than in corresponding muscles in controls. The MEPs associated with maximal voluntary activation were not significantly different in the two groups. These results suggest enhanced excitability of motor pathways targeting muscles rostral to the level of a spinal transection, reflecting reorganization of motor pathways either within cortical motor representation areas or at the level of the spinal cord. The data do not allow the determination of the contribution of spinal or cortical mechanisms. However, they support the notion of a limited flexible relationship between primary motor cortex and its target muscles following alterations of normal input-output patterns.

259 citations

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TL;DR: Cortical motor excitability is increased in dystonia, and transcranial magnetic stimuli delivered at different stimulus intensities and with different levels of muscle facilitation recorded motor evoked potentials from the flexor carpi radialis muscles bilaterally.
Abstract: To assess the excitability of the motor system, we studied 11 patients with task-specific dystonia and 11 age-matched normal subjects. The dominant side was affected in nine of the patients. We delivered transcranial magnetic stimuli at different stimulus intensities and with different levels of muscle facilitation to the side contralateral to the side of electromyographic recording, and recorded motor evoked potentials (MEPs) from the flexor carpi radialis muscles bilaterally. The threshold intensity for eliciting MEPs at rest did not differ between patients and normal subjects. We compared the affected side in patients with the dominant side in normal subjects. With facilitation, the percentage of the area of the MEP to the M wave (MEP area%) was similar in both groups at low stimulus intensities, but with increasing stimulus intensity the increase in the MEP area% was greater in patients than in normal subjects (ANOVA, p < 0.001). The increase in MEP area% was similar in both groups with increasing facilitation levels. The duration of the silent period was similar in patients and normal subjects. We conclude that cortical motor excitability is increased in dystonia.

257 citations

Journal ArticleDOI
TL;DR: The physiological abnormalities support the interpretation that hand cramp is a focal dystonia, characterized by both excessive muscle activity and defective fine motor control.
Abstract: We studied 19 patients with hand cramps, including writer's cramp, typist's cramp, piano, and guitar player's cramp. EMGs were recorded while patients performed the task triggering the cramps. Ten patients with dystonic cramps had EMGs with generalized muscle spasms with co-contraction of agonist and antagonist muscles. In three patients with simple cramps that involved one to three fingers, specific muscle groups showed co-contracting bursts that lasted longer than normal. The physiological abnormalities support the interpretation that hand cramp is a focal dystonia, characterized by both excessive muscle activity and defective fine motor control.

256 citations

01 Jan 1984
TL;DR: It is concluded that the associated postural adjustments are pre-programmed motor activity linked to the focal movement, specific for the focalmovement including anticipated events and the postural set.
Abstract: Normal subjects made bilaterally symmetric rapid elbow flexions or extensions ("focal movement") while free standing or when supported by being strapped to a firm wall behind them (different "postural set"). In some trials a load opposed the movement two thirds of the way into its course. Electromyographic activity in leg and trunk muscles ("associated postural adjustments") demonstrated specific patterns for each type of movement. Activity in these muscles began prior to activity in the arm muscles and demonstrated a distal-to-proximal order of activation. The EMG patterns were characterised by alternating activity in the antagonist pairs similar to the triphasic pattern seen in the arm muscles. When the movement type was changed change of the pattern of the postural muscles occurred over several trials. It is concluded that the associated postural adjustments are pre-programmed motor activity linked to the focal movement, specific for the focal movement including anticipated events and the postural set.

256 citations

Journal ArticleDOI
TL;DR: Electrophysiological studies provide useful information for its diagnosis and classification, and about its generator mechanisms, and the electroencephalogram–electromyogram polygraph reveals the most important information about the myoclonus of interest.
Abstract: As myoclonus is often associated with abnormally increased excitability of cortical structures, electrophysiological studies provide useful information for its diagnosis and classification, and about its generator mechanisms. The electroencephalogram-electromyogram polygraph reveals the most important information about the myoclonus of interest. Jerk-locked back-averaging and evoked potential studies combined with recording of the long-latency, long-loop reflexes are useful to investigate the pathophysiology of myoclonus further, especially that of cortical myoclonus. Recent advances in magnetoencephalography and transcranial magnetic stimulation have contributed significantly to the understanding of some of the cortical mechanisms underlying myoclonus. Elucidation of physiological mechanisms underlying myoclonus in individual patients is important for selecting the most appropriate treatment.

251 citations


Cited by
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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