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.

Task‐dependent intracortical inhibition is impaired in focal hand dystonia

Abstract: We tested whether task-dependent modulation of inhibition within the motor cortex is impaired in patients with dystonia. Paired-pulse transcranial magnetic stimulation (TMS) at an interstimulus interval of 2 msec was used to measure the effect of two different tasks on short ISI intracortical inhibition (SICI) in dystonic and normal subjects. In two experiments, SICI of the fourth dorsal interosseus (4DIO) and abductor pollicis brevis (APB) muscles were measured before and at the end of the training task. In the first experiment, subjects performed a nonselective task consisting of abducting the thumb, where the APB acted as agonist and the 4DIO as synergist. In the second experiment, the function of the 4DIO was changed as the subjects were asked to consciously inhibit this muscle while abducting the thumb (selective task). Therefore, while the APB was activated in both tasks, the 4DIO was activated in the nonselective task but was in the inhibitory surround in the selective task. We found that performance of the selective but not the nonselective task resulted in increased SICI in the 4DIO of normal but not in dystonic subjects. We conclude that task-dependent SICI is disturbed in patients with dystonia.

Adaptation motor learning of arm movements in patients with cerebellar disease.

Abstract: OBJECTIVE--To design a test of motor learning using arm movements in normal subjects and patients with cerebellar disease. METHODS--Elbow angle was continuously displayed as a cursor (a dot) on a computer screen, and subjects made ballistic elbow flexion and extension movements to try to move the cursor between two targets on the screen. The relation between the arm movement and its visual feedback was changed, and the subjects reacted by adapting the amplitude of their movements in subsequent trials. RESULTS--The consecutive errors showed exponential learning curves during adaptation, which were quantified by their steepness. Ten patients with isolated cerebellar or olivopontocerebellar degeneration had less steep learning curves than normal subjects, indicating a failure of adaptation motor learning in cerebellar disease. The results show that this test may be useful for the analysis of motor learning.

Physiologic studies of spinal inhibitory circuits in patients with stiff-person syndrome.

Abstract: Objective: To test inhibitory spinal circuits in patients with stiff-person syndrome(SPS). Background: Patients with SPS have fluctuating muscle stiffness and spasms, and most have antibodies against GABAergic neurons. We predicted they would also have abnormalities of spinal GABAergic circuits. Design/Methods: Physiologic methods using H-reflexes were used to test reciprocal inhibition in the forearm and thigh, vibration-induced inhibition of flexor carpi radialis and soleus H-reflexes, recurrent inhibition, and nonreciprocal(1b) inhibition of soleus H-reflexes. Results: Vibration-induced inhibition of H-reflexes was diminished in eight of nine patients tested, but the presynaptic period of reciprocal inhibition was normal in most patients. Both circuits are presumed to involve presynaptic inhibition and GABAergic interneurons. Presumed glycinergic circuits, including the first period of reciprocal inhibition and nonreciprocal (1b) inhibition, showed occasional abnormalities. Recurrent inhibition was normal in all five patients tested. Conclusion: Differences between the two presumptive GABAergic circuits may indicate that not all populations of GABAergic neurons are uniformly affected in SPS. The involvement of presumptive glycinergic circuits in some patients could point to impairment of nonGABAergic neurons, unrecognized involvement of GABAergic neurons in these inhibitory circuits, or, more likely, alterations of supraspinal systems that exert descending control over spinal circuits.

The nature of postural tremor in Parkinson disease

Abstract: Objective To disentangle the different forms of postural tremors in Parkinson disease (PD). Methods In this combined observational and intervention study, we measured resting and postural tremor characteristics in 73 patients with tremulous PD by using EMG of forearm muscles. Patients were measured both “off” medication (overnight withdrawal) and after dispersible levodopa-benserazide 200/50 mg. We performed an automated 2-step cluster analysis on 3 postural tremor characteristics: the frequency difference with resting tremor, the degree of tremor suppression after posturing, and the dopamine response. Results The cluster analysis revealed 2 distinct postural tremor phenotypes: 81% had re-emergent tremor (amplitude suppression, frequency difference with resting tremor 0.4 Hz, clear dopamine response) and 19% had pure postural tremor (no amplitude suppression, frequency difference with resting tremor 3.5 Hz, no dopamine response). This finding was manually validated (accuracy of 93%). Pure postural tremor was not associated with clinical signs of essential tremor or dystonia, and it was not influenced by weighing. Conclusion There are 2 distinct postural tremor phenotypes in PD, which have a different pathophysiology and require different treatment. Re-emergent tremor is a continuation of resting tremor during stable posturing, and it has a dopaminergic basis. Pure postural tremor is a less common type of tremor that is inherent to PD, but has a largely nondopaminergic basis.

Coil for magnetic stimulation and methods for using the same

Abstract: A magnetic stimulator (11), which may be used as a transcranial magnetic stimulation (TMS) device, and a method for its use are disclosed. The stimulator comprises a frame and an electrically conductive coil having a partially toroidal or ovate base (12) and an outwardly projecting extension portion (14). The frame may be a flexible or malleable material and may be non-conductive. The electrically conductive coil may comprise one or more windings of electrically conductive material (such as a wire) coupled to the frame. The coil is electrically connected to a power supply. The device (11) may be place adjacent to or in contact with the body of a subject, such as on the head (100) of a subject. The device may be used on humans for treating certain physiological conditions, such as cardiovascular or neurophysiological conditions, or for studying the physiology of the body. This device is useful in studying or treating neurophysiological conditions associated with the deep regions of the brain, such as drug addiction and depression.

The Brain's Default Network Anatomy, Function, and Relevance to 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

Parallel Organization of Functionally Segregated Circuits Linking Basal Ganglia and 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

FieldTrip: open source software for advanced analysis of MEG, EEG, and invasive electrophysiological 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.

Principles of Neural Science

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