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.

Modulation of vastus medialis motoneuronal excitability by sciatic nerve afferents.

Abstract: We activated the sciatic nerve afferents by either the discharge of a magnetic coil or a needle inserted near the nerve. Both types of stimulation induced facilitation of the vastus medialis (VM) H reflex, and of the VM response to transcranial magnetic stimulation, at the joint time of arrival of conditioning and test volleys, while a subsequent inhibition was induced only in the H reflex. We conclude that sciatic nerve afferents induce reciprocal inhibition of VM motoneurons presynaptically on the la afferent terminals.

Cortical control of brainstem motor systems.

Abstract: Cranial Nerve Motor Nuclei The general principle for cortical control of cranial nerve motor nuclei 5, 7, 9, 10, 11, and 12 is that there is predominant contralateral influence and variable, but important, ipsilateral influence as well. The importance of the bilaterality of innervation is clearly different than for limb motor control and is helpful in understanding clinical phenomena such as recovery from stroke. The best understood situation is the 7th nerve, thanks in part to a new anatomical study in the rhesus monkey by Morecraft and colleagues. The corticobulbar projection was defined by injecting anterograde tracers into the face representation of each motor cortex, and in the same animals, the musculotopic organization of the facial nucleus was defined by injecting fluorescent retrograde tracers into individual muscles of the upper and lower face. Perioral muscles, prototypical for the lower face, are innervated largely contralaterally from the primary motor cortex (M1); lateral premotor cortex, ventral and dorsal (LPMCv, LPMCd); and caudal cingulate (M4). For upper face muscles, orbicularis oculi are innervated mostly by rostral cingulate (M3) and auricular muscles by the supplementary motor area (M2), both bilaterally. Such a pattern explains the upper face sparing in typical middle cerebral artery stroke. Recovery from stroke in any location is explained by at least a minimal projection from all cortical face areas to all parts of the face. In addition, that one component of the corticofacial projection arises from the limbic proisocortices (M3 and M4) and another component arises from frontal isocortices (M1, M2, LPMCv, and LPMCd) suggests an anatomical substrate which may contribute to the clinical dissociation of emotional and volitional facial movement. Transcranial magnetic stimulation (TMS) and transcranial electrical stimulation studies have explored cortical connections to muscles of both the lower and upper face. Only a few studies have reported data for orbicularis oculi in the upper face. Latencies are reported to be about 10 msec and bilateral in nature, but given that the R1 component of the blink reflex has about the same latency, this response may well be contaminated by the blink reflex. Additionally, stimulation was done over M1 regions for the face, and, as noted in the study by Morecraft and associates, there is only very sparse projection to the eyelid muscles from M1. TMS studies of the orbicularis oris in the lower face are much better documented. The effects here are primarily contralateral with latencies of 9 to 10 msec. Studies of single motor unit latency histograms show that the earliest responses, which ranged from 9.2 to 16.5 msec, are very likely to be monosynaptic. The relative slowness of this projection is due to slow central conduction and a relatively longer length of the 7th nerve than other cranial motor nerves. It is also possible to find inhibitory responses in orbicular oris, and these can be seen even without a preceding motor evoked potential. Because the facial muscles remain responsive to trigeminal stimulation during this silent period, the origin of the inhibition must be intracortical. Muscles of the 5th cranial nerve have also been studied with TMS. Responses in the masseter muscle are heavily contralateral, but with some ipsilateral influence. The latency for the contracting masseter muscle is approximately 6 msec. The ipsilateral response can be inhibitory as well as excitatory. Poststimulus time histograms of single motor unit responses show the earliest

Chapter 42 Topics in transcranial magnetic stimulation

Abstract: Publisher Summary This chapter reviews the important areas regarding transcranial magnetic stimulation (TMS), which is making a significant impact in neuroscience, neurology, clinical neurophysiology, and psychiatry. Using the method in different ways, it can be used to measure central motor conduction times, determine physiological processes in the brain, and potentially treat various disorders. TMS has extra ordinary potential as a tool to investigate the pathophysiology of psychiatric disorders and as a therapeutic intervention for psychiatric illness. Examples in the study of schizophrenia are illustrated in the chapter. By far, the greatest focus in the field has been on using repetitive TMS (rTMS) as a potential antidepressant treatment. Conventional rTMS is intended to be non-convulsive and it is believed that daily administration of rTMS may result in significant therapeutic effects in major depression. Recently, it has been established that at very high intensity, rTMS may reliably produce generalized seizures in primates. This development offers a different approach to the treatment of severe major depression—that is, the replacement of transcranial electrical stimulation to induce seizures (electroconvulsive therapy (ECT)) with magnetic induction.

Corticolimbic Modulation via Intermittent Theta Burst Stimulation as a Novel Treatment for Functional Movement Disorder: A Proof-of-Concept Study.

Abstract: Neuroimaging studies suggest that corticolimbic dysfunctions, including increased amygdala reactivity to emotional stimuli and heightened fronto-amygdala coupling, play a central role in the pathophysiology of functional movement disorders (FMD). Transcranial magnetic stimulation (TMS) has the potential to probe and modulate brain networks implicated in neuropsychiatric disorders, including FMD. Therefore, the objective of this proof-of-concept study was to investigate the safety, tolerability and preliminary efficacy of fronto-amygdala neuromodulation via targeted left prefrontal intermittent theta burst stimulation (iTBS) on brain and behavioral manifestations of FMD. Six subjects with a clinically defined diagnosis of FMD received three open-label iTBS sessions per day for two consecutive study visits. Safety and tolerability were assessed throughout the trial. Amygdala reactivity to emotionally valenced stimuli presented during an fMRI task and fronto-amygdala connectivity at rest were evaluated at baseline and after each stimulation visit, together with subjective levels of arousal and valence in response to affective stimuli. The FMD symptom severity was assessed at baseline, during treatment and 24 h after the last iTBS session. Multiple doses of iTBS were well-tolerated by all participants. Intermittent TBS significantly decreased fronto-amygdala connectivity and influenced amygdala reactivity to emotional stimuli. These neurocircuitry changes were associated to a marked reduction in FMD symptom severity. Corticolimbic modulation via iTBS represents a promising treatment for FMD that warrants additional research.

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