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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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TL;DR: There is a loss of inhibition in these patients and recent studies show abnormalities in brain GABA and dopamine function and dopamine blocking agents are effective therapy, and in severe drug-refractory patients, deep brain stimulation can be effective.
Abstract: Tourette Syndrome is a disorder characterized by tics. It typically begins in childhood and often improves in adult life. Tics are best described as voluntary movements made automatically so that volition is not ordinarily appreciated. There is frequently an urge, sometimes in the form of a specific sensory feeling (sensory tic), that precedes the tic. Patients say that they make the tic in order to reduce the urge, although shortly after the tic, the urge recurs. The sensory feeling may arise due to defective sensory habituation. Since tics relieve the urge, this can be considered rewarding, and repetition of this behavior may perpetuate the tic as a habit. Tourette Syndrome affects boys more than girls and is associated with attention deficit hyperactivity disorder and obsessive compulsive disorder. Although Tourette Syndrome often appears to be autosomal recessive in inheritance, it has been difficult to find any abnormal genes. There is a loss of inhibition in these patients and recent studies show abnormalities in brain GABA. Certainly there is also an abnormality in dopamine function and dopamine blocking agents are effective therapy. In severe drug-refractory patients, deep brain stimulation can be effective.

92 citations

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TL;DR: This is the first study to offer evidence that patients with primary insomnia have objectively definable features during wakefulness that clearly distinguish them from normal subjects.
Abstract: Objective: In the absence of clear distinctions in alertness between patients with primary insomnia and normal subjects, the goal of this study was to identify psychometric and electrophysiological measures that would distinguish these two groups. Method: The daytime alertness of 20 primary insomnia patients and 20 normal subjects was investigated through their scores on a 26-item hyperarousal scale and measurement ofauditory evoked potentials and alpha and nonalpha band EEG activity. Statisticalanalysis ofthe data included correlation of the hyperarousal scores and the electrophysiological measures. Results: The hyperarousal scores showed clearly higher daytime alertness in the insomnia patients compared with the normal subjects. In addition, during wakefulness, the insomnia patients showed greater amplitudes ofP1N1, a durable, intrinsic, late (cortical) component ofthe auditory evoked potential, as well as greater EEG activity across the frequency spectrum. The hyperarousal scores correlated positively with the amplitude of P1N1 at each of three sound intensities. Conclusigns: To the authors’ knowledge, this is the first study to offer evidence that patients with primary insomnia have objectively definable features during wakefulness that clearly distinguish them from normal subjects. The measurement of hyperarousal might be used to refine descriptions of insomnia populations in experimental studies. (Am J Psychiatry 1993; 150:1529-1534)

91 citations

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TL;DR: This paper examines existing methods to study the "Human Brain Connectome" with a specific focus on the neurophysiological ones, including the most commonly used structural and functional MRI, EEG, MEG and non-invasive brain stimulation techniques and measures of local and global brain connectivity.

91 citations

Journal ArticleDOI
TL;DR: The battery found 100% abnormality in the definite patients and 82% in the indefinite patients and somatosensory evoked potentials were most often abnormal: 86% in definite patients, 58% in indefinite patients, and 77% in asymptomatic definite patients.
Abstract: Thirty patients with definite multiple sclerosis and 50 patients in whom the diagnosis was suspected but not proved (indefinite multiple sclerosis) were studied with visual evoked potentials from each eye, somatosensory evoked potentials from each limb, brainstem auditory evoked potentials from each ear, and the blink reflex. The purpose was to organize a battery of clinically practical tests. The battery found 100% abnormality in the definite patients and 82% in the indefinite patients. Of the individual tests, somatosensory evoked potentials were most often abnormal: 86% in definite patients, 58% in indefinite patients, and 77% in asymptomatic definite patients. Visual evoked potentials were abnormal in 76%, 55%, and 40% of the same three categories. Brainstem auditory evoked potentials and the blink reflex were abnormal less often but contributed to the efficacy of the battery.

91 citations

Journal ArticleDOI
TL;DR: It is concluded that cutaneous stimuli to the fingers activate a complex motor pattern that tends to withdraw the hand at the same time the grasp is released, similar to that of the E2 component of the cutaneomuscular reflex evoked in these same muscles during contraction.
Abstract: We characterized reflexes of the upper limb elicited by electrical stimulation of the fingers. Surface electromyogram (EMG) was recorded from several upper extremity muscles, and a finger was stimulated through paired ring electrodes. A train of 4-10 shocks at a frequency of 300 Hz and an intensity 4-6 times the perceptual threshold was the most effective stimulus for evoking EMG activity in relaxed arm muscles. Habituation was prominent. Latencies of EMG activity were <100 ms for most proximal and forearm muscles, and at least 40 ms prior to voluntary withdrawal movements. The timing of EMG activity in arm muscles was similar to that of the E2 component of the cutaneomuscular reflex evoked in these same muscles during contraction, and coincided with a silent period in active hand muscles. We conclude that cutaneous stimuli to the fingers activate a complex motor pattern that tends to withdraw the hand at the same time the grasp is released.

91 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

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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