Mark Hallett

Govind Ballabh Pant Hospital, New Dilli, NCT, India

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Publications (364)1825.77 Total impact

  • Sanjay Pandey, Debra L Byler, Mark Hallett
    JAMA Neurology 10/2014; · 7.58 Impact Factor
  • Movement Disorders Clinical Practice. 10/2014;
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    ABSTRACT: Objective Praxis, the performance of complex motor gestures, is crucial to the development of motor and social/communicative capacities. Praxis relies on a network consisting of inferior parietal and premotor regions, particularly on the left, and is thought to require transformation of spatio-temporal representations (parietal) into movement sequences (premotor). Method We examined praxis network dynamics by measuring EEG effective connectivity while healthy subjects performed a praxis task. Results Propagation from parietal to frontal regions was not statistically greater on the left than the right. However, propagation from left parietal regions to all other regions was significantly greater during gesture preparation than execution. Moreover, during gesture preparation only, propagation from the left parietal region to bilateral frontal regions was greater than reciprocal propagations to the left parietal region. This directional specificity was not observed for the right parietal region. Conclusions These findings represent direct electrophysiological evidence for directionally predominant propagation in left frontal-parietal networks during praxis behavior, which may reflect neural mechanisms by which representations in the human brain select appropriate motor sequences for subsequent execution. Significance In addition to bolstering the classic view of praxis network function, these results also demonstrate the relevance of additional information provided by directed connectivity measures.
    Clinical Neurophysiology 09/2014; · 3.14 Impact Factor
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    ABSTRACT: In the pursuit to better understand the neural underpinnings of oculomotor deficits following concussion we performed a battery of oculomotor tests while performing simultaneous functional magnetic resonance imaging (fMRI). Based on the increasing evidence that concussion can disrupt multiple brain functional networks, including the oculomotor control networks, a series of classic saccadic and smooth pursuit tasks were implemented. Nine concussed athletes were tested within seven days of injury along with nine age and sex matched healthy normal volunteers. Both behavioral and fMRI data revealed differential results between the concussed and normal volunteer groups. Concussed subjects displayed longer latency time in the saccadic tasks, worse position errors, and fewer numbers of self-paced saccades compared to normal volunteer subjects. Furthermore, the concussed group showed recruitment of additional brain regions and larger activation sites as evidenced by fMRI. As a potential diagnostic and management tool for concussion, oculomotor testing shows promise, and here we try to understand the reasons for this disrupted performance with the aide of advanced neuroimaging tools.
    Brain Imaging and Behavior 09/2014; · 2.67 Impact Factor
  • Kathrin LaFaver, Mark Hallett
    Movement Disorders 09/2014; · 5.63 Impact Factor
  • Movement Disorders Clinical Practice. 09/2014;
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    ABSTRACT: Although less severe than a full blown concussive episode, subconcuussive impacts happen much more frequent and current research has suggested this form of head trauma may have an accumulative effect and lead to neurological impairment later in life. To investigate the acute effects that subconcussive head trauma may have on the default mode network of the brain resting state functional magnetic resonance was performed. Twenty-four current collegiate rugby players were recruited and all subjects underwent initial scanning twenty-four hours prior to a scheduled full contact game to provide a baseline. Follow-up scanning of the rugby players happened within twenty-four hours following that game to assess acute effects from subconcussive head trauma. Differences between pregame and postgame scans showed both increased connectivity from the left supramarginal gyrus to bilateral orbitofrontal cortex and decreased connectivity from the retrosplenial cortex and dorsal posterior cingulate cortex. To assess whether or not a history of previous concussion may lead to a differential response following subconcussive impacts, subjects were further divided into two subgroups based upon history of previous concussion. Individuals with a prior history of concussion exhibited only decreased functional connectivity following exposure to subconcussive head trauma, while those with no history showed increased connectivity. Even acute exposure to subconcussive head trauma demonstrates the ability to alter functional connectivity and there is possible evidence of a differential response in the brain for those with and without a history of concussion.
    Journal of neurotrauma. 07/2014;
  • Yanan Hou, Xuemin Wu, Mark Hallett, Piu Chan, Tao Wu
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    ABSTRACT: The brainstem and basal ganglia are important in the pathophysiology of Parkinson's disease (PD). Reliable and sensitive detection of neural activity changes in these regions should be helpful in scientific and clinical research on PD. In this study, we used resting state functional MRI and amplitude of low frequency fluctuation (ALFF) methods to examine spontaneous neural activity in 109 patients with PD. We examined activity in two frequency bands, slow-4 (between 0.027 and 0.073 Hz) and slow-5 (0.010–0.027 Hz). Patients had decreased ALFF in the striatum and increased ALFF in the midbrain, and changes were more significant in slow-4. Additionally, changes in slow-4 in both basal ganglia and midbrain correlated with the severity of the parkinsonism. The ALFF in the caudate nucleus positively correlated with the dose of levodopa, while the ALFF in the putamen negatively correlated with the disease duration in both slow-4 and slow-5 bands. In addition, the ALFF in the rostral supplementary motor area negatively correlated with bradykinesia subscale scores. Our findings show that with a large cohort of patients and distinguishing frequency bands, neural modulations in the brainstem and striatum in PD can be detected and may have clinical relevance. The physiological interpretation of these changes needs to be determined. Hum Brain Mapp, 2014. © 2014 Wiley Periodicals, Inc.
    Human Brain Mapping 07/2014; · 6.88 Impact Factor
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    ABSTRACT: Tourette syndrome (TS) is a neuropsychiatric disorder characterized by motor and vocal tics. Most patients describe uncomfortable premonitory sensations preceding the tics and a subjective experience of increased sensitivity to tactile stimuli. These reports indicate that a sensory processing disturbance is an important component of TS together with motor phenomena. Thus, we focused our investigation on the role of the sensorimotor cortex (SMC) in TS using multimodal neuroimaging techniques. We measured the gamma-aminobutyric acid (GABA)+/Creatine (Cre) ratio in the SMC using GABA 1H magnetic resonance spectroscopy. We recorded the baseline beta activity in the SMC using magnetoencephalography and correlated GABA+/Cre ratio with baseline beta band power. Finally, we examined the resting state functional connectivity (FC) pattern of the SMC using functional magnetic resonance imaging (fMRI). GABA+/Cre ratio in the SMC did not differ between patients and controls. Correlation between the baseline beta band power and GABA+/Cre ratio was abnormal in patients. The anterior insula showed increased FC with the SMC in patients. These findings suggest that altered limbic input to the SMC and abnormal GABA-mediated beta oscillations in the SMC may underpin some of the sensorimotor processing disturbances in TS and contribute to tic generation. Hum Brain Mapp, 2014. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.
    Human Brain Mapping 07/2014; · 6.88 Impact Factor
  • M. Hallett
    European Journal of Neurology 07/2014; · 4.16 Impact Factor
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    ABSTRACT: The aim of the study was to investigate the effect of botulinum toxin (BoNT) on blink rate (BR) in patients with blepharospasm (BSP) and increased blinking (IB).
    Journal of neurology, neurosurgery, and psychiatry. 06/2014;
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    ABSTRACT: We investigated neural correlates when attending to a movement that could be made automatically in healthy subjects and Parkinson's disease (PD) patients. Subjects practiced a visuomotor association task until they could perform it automatically, and then directed their attention back to the automated task. Functional MRI was obtained during the early-learning, automatic stage, and when re-attending. In controls, attention to automatic movement induced more activation in the dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex, and rostral supplementary motor area. The motor cortex received more influence from the cortical motor association regions. In contrast, the pattern of the activity and connectivity of the striatum remained at the level of the automatic stage. In PD patients, attention enhanced activity in the DLPFC, premotor cortex, and cerebellum, but the connectivity from the putamen to the motor cortex decreased. Our findings demonstrate that, in controls, when a movement achieves the automatic stage, attention can influence the attentional networks and cortical motor association areas, but has no apparent effect on the striatum. In PD patients, attention induces a shift from the automatic mode back to the controlled pattern within the striatum. The shifting between controlled and automatic behaviors relies in part on striatal function.
    Cerebral cortex (New York, N.Y. : 1991). 06/2014;
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    ABSTRACT: The purpose of this study is to develop a method to reliably characterize multiple features of the corticospinal system in a more efficient manner than typically done in transcranial magnetic stimulation studies.
    Journal of clinical neurophysiology: official publication of the American Electroencephalographic Society 06/2014; 31(3):246-252. · 1.47 Impact Factor
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    ABSTRACT: Peripheral trauma may be a trigger for the development of various movement disorders, though the pathophysiology remains controversial and some of these patients have a functional (psychogenic) disorder. We report on 3 cases of shoulder movement disorders subsequent to trauma to the shoulder region. Physiology was done in all the patients to extend the physical examination. Two patients had a history of recurrent shoulder dislocation and were diagnosed with Ehlers-Danlos syndrome. One patient had shoulder injury after repeated falls while performing as a cheerleader. In 2 patients, there were some clinical features suggesting a functional etiology, but physiological studies in all 3 failed to produce objective evidence of a functional nature. Shoulder movement after trauma is uncommon. Diagnosis in such cases is challenging, considering the complex pathophysiology. The movements can be associated with prolonged pain and handicap, and once established, they appear resistant to treatment.
    Movement Disorders Clinical Practice. 05/2014;
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    ABSTRACT: The authors hypothesized that a deficient premotor-motor inhibitory network contributes to the unwanted involuntary movements in dystonia. The authors studied nine controls and nine patients with writer's cramp (WC). Dorsal premotor-motor cortical inhibition (dPMI) was tested by applying conditioning transcranial magnetic stimulation (TMS) to the dorsal premotor cortex and then a test pulse to the ipsilateral motor cortex at an interval of 6 ms. The authors used an H-reflex in flexor carpi radialis paired with TMS over the premotor cortex to assess for spinal cord excitability change. Finally, the authors interrupted a choice reaction time task with TMS over dorsal premotor cortex to assess performance in a nondystonic task. The results showed that WC patients exhibited dPMI at rest (88.5%, the ratio of conditioned to unconditioned test pulse), in contrast to controls, who did not show dPMI (109.6%) (P = 0.0198). This difference between patients and controls persisted during contraction (100% vs. 112%) and pen-holding (95.6% vs. 111%). The H-reflex in the arm was not modulated by the premotor cortex stimulation. The WC patients made more errors, and the error rate improved with TMS over the premotor cortex. These results suggest that abnormal premotor-motor interactions may play a role in the pathophysiology of focal dystonia. The dPMI was not modulated by task in either group, but was constantly greater in the patients. The significance of the increased inhibition is likely to be compensatory. It appears to be a robust finding and, in combination with other features, could be further explored as a biomarker. © 2014 International Parkinson and Movement Disorder Society.
    Movement Disorders 04/2014; · 5.63 Impact Factor
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    ABSTRACT: Palatal tremor (PT) is an uncommon movement disorder that has been subdivided into essential and symptomatic forms. A distinct subgroup of the symptomatic form presents with progressive ataxia and PT. The histopathology of progressive ataxia and PT has not been previously determined. This study consisted of a clinical review, histopathology, and electron microscopy of the brain of a man with progressive ataxia and PT. The inferior olivary hypertrophy was symmetrical and homogenous, and no focal pathologic lesions could be identified in the brainstem. Insoluble tau deposits were found in neurons, exclusively infratentorially. We present the clinical and pathological evaluation of a case of progressive ataxia and PT that provide evidence for a unique form of 4R tauopathy.
    Movement Disorders Clinical Practice. 04/2014; 1(1).
  • Movement Disorders 03/2014; · 5.63 Impact Factor
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    ABSTRACT: Sensory tricks are various manoeuvres that can ameliorate dystonia. Common characteristics are well known, but their variety is wide, sensory stimulation is not necessarily the critical feature, and their physiology is unknown. To enumerate the various forms of sensory tricks and describe their nature, research findings and theories that may elucidate their neurophysiologic mechanism, we reviewed the literature pertaining to sensory tricks, including variants like motor tricks, imaginary tricks, forcible tricks and reverse sensory tricks. On the basis of this information, we propose a new classification of sensory tricks to include its variants. We highlight neurophysiologic evidence suggesting that sensory tricks work by decreasing abnormal facilitation. We tie this with established dystonia pathogenesis and postulate that sensory tricks decrease abnormally increased facilitation to inhibition ratios in the dystonic brain. It appears worthwhile for patients to search for possible sensory tricks.
    Journal of neurology, neurosurgery, and psychiatry 01/2014; · 4.87 Impact Factor
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    ABSTRACT: The authors assessed bilateral motor and sensory function in individuals with upper limb dystonia due to unilateral perinatal stroke and explored interrelationships of motor function and sensory ability. Reach kinematics and tactile sensation were measured in 7 participants with dystonia and 9 healthy volunteers. The dystonia group had poorer motor (hold time, reach time, shoulder/elbow correlation) and sensory (spatial discrimination, stereognosis) outcomes than the control group on the nondominant side. On the dominant side, only sensation (spatial discrimination, stereognosis) was poorer in the dystonia group compared with the control group. In the dystonia group, although sensory and motor outcomes were uncorrelated, dystonia severity was related to poorer stereognosis, longer hold and reach times, and decreased shoulder/elbow coordination. Findings of bilateral sensory deficits in dystonia can be explained by neural reorganization. Visual compensation for somatosensory changes in the nonstroke hemisphere may explain the lack of bilateral impairments in reaching.
    Journal of child neurology 01/2014; · 1.59 Impact Factor
  • Neepa Patel, Joseph Jankovic, Mark Hallett
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    ABSTRACT: Movement disorders, which include disorders such as Parkinson's disease, dystonia, Tourette's syndrome, restless legs syndrome, and akathisia, have traditionally been considered to be disorders of impaired motor control resulting predominantly from dysfunction of the basal ganglia. This notion has been revised largely because of increasing recognition of associated behavioural, psychiatric, autonomic, and other non-motor symptoms. The sensory aspects of movement disorders include intrinsic sensory abnormalities and the effects of external sensory input on the underlying motor abnormality. The basal ganglia, cerebellum, thalamus, and their connections, coupled with altered sensory input, seem to play a key part in abnormal sensorimotor integration. However, more investigation into the phenomenology and physiological basis of sensory abnormalities, and about the role of the basal ganglia, cerebellum, and related structures in somatosensory processing, and its effect on motor control, is needed.
    The Lancet Neurology 01/2014; 13(1):100-112. · 23.92 Impact Factor

Publication Stats

11k Citations
1,825.77 Total Impact Points


  • 2014
    • Govind Ballabh Pant Hospital
      New Dilli, NCT, India
  • 1992–2014
    • National Institutes of Health
      • Division of Intramural Research (Dental Research)
      Maryland, United States
  • 2013
    • Northumbria University
      • Faculty of Health and Life Sciences
      Newcastle-on-Tyne, England, United Kingdom
    • San Raffaele Scientific Institute
      Milano, Lombardy, Italy
    • University of Washington Seattle
      • Department of Neurology
      Seattle, WA, United States
  • 2012–2013
    • George Washington University
      Washington, Washington, D.C., United States
    • Chung-Ang University Hospital
      Sŏul, Seoul, South Korea
    • Johns Hopkins Medicine
      • Department of Neurology
      Baltimore, Maryland, United States
    • Copenhagen University Hospital Hvidovre
      Hvidovre, Capital Region, Denmark
    • University Hospital of Lausanne
      Lausanne, Vaud, Switzerland
    • Catholic University of the Sacred Heart
      Milano, Lombardy, Italy
    • U.S. Department of Health and Human Services
      • Food and Drug Administration (FDA)
      Washington, D. C., DC, United States
  • 2010–2013
    • University of Cambridge
      • • Department of Psychology
      • • Behavioural and Clinical Neurosciences Institute (BCNI)
      Cambridge, England, United Kingdom
    • Hallym University Medical Center
      Sŏul, Seoul, South Korea
    • University of Cologne
      • Department of Neurology
      Köln, North Rhine-Westphalia, Germany
    • University of Hamburg
      • Department of Neurology
      Hamburg, Hamburg, Germany
    • University of Toronto
      Toronto, Ontario, Canada
  • 2007–2013
    • Xuanwu hospital
      Peping, Beijing, China
    • CUNY School of Law
      New York City, New York, United States
    • Sungkyunkwan University
      • Samsung Medical Center
      Seoul, Seoul, South Korea
  • 2011–2012
    • Pennsylvania State University
      • Department of Kinesiology
      University Park, MD, United States
    • Emory University
      • Department of Neurology
      Atlanta, Georgia, United States
    • University of Colorado
      • Department of Neurology
      Denver, CO, United States
    • University of Freiburg
      Freiburg, Baden-Württemberg, Germany
  • 2010–2012
    • University of Miami Miller School of Medicine
      • Department of Neurology
      Miami, FL, United States
  • 2004–2012
    • Yonsei University Hospital
      • Department of Internal Medicine
      Sŏul, Seoul, South Korea
    • University Hospital RWTH Aachen
      Aachen, North Rhine-Westphalia, Germany
  • 2009–2011
    • Università degli Studi di Siena
      Siena, Tuscany, Italy
    • Università degli Studi di Messina
      • Dipartimento di Neuroscienze
      Messina, Sicily, Italy
    • FLENI Fundation
      Buenos Aires, Buenos Aires F.D., Argentina
    • Baylor College of Medicine
      • Department of Neurology
      Houston, TX, United States
  • 2008–2011
    • Virginia Commonwealth University
      • Biomedical Engineering
      Richmond, VA, United States
    • Università degli Studi di Milano-Bicocca
      Milano, Lombardy, Italy
    • University of New Mexico
      Albuquerque, New Mexico, United States
  • 2007–2011
    • Christian-Albrechts-Universität zu Kiel
      • Unit of Neurobiology
      Kiel, Schleswig-Holstein, Germany
  • 2005–2011
    • National Eye Institute
      Maryland, United States
    • Hampton University
      • Department of Physical Therapy
      Hampton, Virginia, United States
    • Weizmann Institute of Science
      • Department of Neurobiology
  • 2008–2010
    • East Carolina University
      • Department of Exercise and Sport Science
      Greenville, NC, United States
  • 2007–2009
    • Università degli Studi di Bari Aldo Moro
      • Dipartimento di Scienze Biomediche ed Oncologia Umana (DIMO)
      Bari, Apulia, Italy
  • 2006–2009
    • University of Lisbon
      • Faculdade de Ciências
      Lisbon, Lisbon, Portugal
    • Yonsei University
      Sŏul, Seoul, South Korea
    • University of Tuebingen
      • Department of Neurology
      Tübingen, Baden-Wuerttemberg, Germany
  • 2003
    • Minneapolis Veterans Affairs Hospital
      Minneapolis, Minnesota, United States
  • 1994
    • Howard Hughes Medical Institute
      Ashburn, Virginia, United States