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.

Relationship and factor structure in multisystem neurodegeneration in Parkinson's disease.

Abstract: Objectives Parkinson's disease (PD) is a multisystem neurodegenerative disease. We aimed to identify the relationship and factor structure among its different features. Materials & methods Motor, olfactory and cognitive function, and cardiac sympathetic denervation were evaluated in 125 patients with PD using the Unified Parkinson's Disease Rating Scale (UPDRS) part III score, odor stick identification test for the Japanese (OSIT-J), Mini-Mental State Examination (MMSE), and [123I] meta-iodobenzylguanidine (MIBG) cardiac scintigraphy (heart-to-mediastinum (H/M) ratio). Pearson's correlation and multiple regression analysis were used to evaluate the association among the four measures with age, gender, and disease duration as the covariates. Exploratory factor analysis was used to identify the underlying factor structure among the measures and covariates. Results Pearson's correlation and multiple regression analysis showed correlations between OSIT-J score and MIBG H/M ratio, OSIT-J and MMSE scores, UPDRS part III score and MIBG H/M ratio, UPDRS part III score and disease duration, and MMSE score and age. Factor analysis identified three factors: (i) age and MMSE score; (ii) MIBG H/M ratio and OSIT-J score; and (iii) UPDRS part III score and disease duration. Conclusions Our results suggest that aging, PD-related pathogenesis, and disease duration underlie the multisystem neurodegeneration present in PD. Moreover, age and disease duration are the major risk factors for cognitive impairment and motor symptoms, respectively. Olfactory impairment and cardiac sympathetic denervation are strongly associated in PD.

Urethral narrowing in region of external sphincter: radiologic-urodynamic correlations in boys with myelodysplasia.

Abstract: Narrowing of the urethra in the region of the external sphincter as seen during voiding cystourethrography has routinely been termed sphincter spasm. This diagnosis was found to be incorrect in a significant percentage of boys with myelodysplasia. Thirty boys with myelodysplasia and dysfunction of the lower urinary tract, in whom voiding cystourethrography revealed narrowing in the area of the external sphincter, underwent urodynamic evaluation. Incoordination of the bladder and the sphincter (sphincter spasm) was found in only 16 (52%). In the other 14 (48%), there was either relaxation of the sphincter or absent electrical activity; atrophy and fibrosis of the striated muscle of the external sphincter (documented in six patients) probably resulted from chronic denervation. Thus, voiding cystourethrography only reveals narrowing of the urethra in the region of the external sphincter. However, when it is combined with urodynamic evaluation, the dynamics of the function of the sphincter can be defined and a rational approach to treatment planned.

Reply: The cerebellum in Parkinson's disease and parkinsonism in cerebellar disorders.

Abstract: ARTICLE Sir, We thank Pedroso et al. (2013) for their interest in our paper (Wu and Hallett, 2013), in which we discussed the role of the cerebellum in Parkinson’s disease; other types of parkinsonism were not included. Such parkinsonian disorders often contain overt pathological changes in both basal ganglia and cerebellar systems. The origin of these changes is generally thought to be primary in both locations, but it is conceivable that the primary pathology is in one location and secondary in the other. It is important to recognize that genetic mutations can cause different phenotypes and that the nomenclature …

Dysfunction of Ib (autogenic) spinal inhibition in patients with progressive supranuclear palsy.

Abstract: We compared the activity of Ib spinal interneurons in five patients with progressive supranuclear palsy (PSP) with six age-matched control subjects. Stimulation of the medial gastrocnemius nerve at motor threshold intensity activated Ib afferents that in turn inhibit H reflexes from the soleus muscle. Maximum inhibition occurred at interstimulus intervals of 6 and 8 ms for both control subjects and PSP patients and was significantly greater in the PSP patients. Increased Ib activity of PSP patients may be caused by loss of inhibition of Ib interneurons through degeneration of the medullary reticulospinal pathway. The corticospinal pathways, unopposed by the medullary reticulospinal tract, may excessively activate Ib interneurons.

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