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Corcia P, Bede P, Pradat PF, Couratier P, Vucic S, de Carvalho M. Split-hand and split-limb phenomena in amyotrophic lateral sclerosis: pathophysiology, electrophysiology and clinical manifestations. J Neurol Neurosurg Psychiatry 2021; 92:1126-1130. [PMID: 34285065 DOI: 10.1136/jnnp-2021-326266] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/01/2021] [Accepted: 07/05/2021] [Indexed: 11/03/2022]
Abstract
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder affecting the upper and lower motor neurons. A key clinical feature of ALS is the absence of accurate, early-stage diagnostic indicators. 'Split-hand syndrome' was first described in ALS at the end of the last century and a considerable body of literature suggests that the split-hand phenomenon may be an important clinical feature of ALS. Considering the published investigations, it is conceivable that the 'split-hand syndrome' results from the associated upper and lower motor neuron degeneration, whose interaction remains to be fully clarified. Additionally, other split syndromes have been described in ALS involving upper or lower limbs, with a nuanced description of clinical and neurophysiological manifestations that may further aid ALS diagnosis. In this review, we endeavour to systematically present the spectrum of the 'split syndromes' in ALS from a clinical and neurophysiology perspective and discuss their diagnostic and pathogenic utility.
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Affiliation(s)
- Philippe Corcia
- Centre Constitutif de Référence SLA, CHU Bretonneau, Tours, France
| | - Peter Bede
- Computational Neuroimaging Group, Trinity College Dublin, Ireland.,Pitié-Salpêtrière University Hospital, Sorbonne University, Paris, France
| | - Pierre-François Pradat
- Neurology, Hopital Pitie-Salpetriere, Paris, France.,LIB, Université Pierre et Marie Curie Faculté de Médecine, Paris, Île-de-France, France
| | | | - Steve Vucic
- Westmead Clinical School, Westmead Hospital, University of Sydney, Sydney, New South Wales, Australia.,Sydney Medical School, The University of Sydney, Sydney, New South Wales, Australia
| | - Mamede de Carvalho
- Instituto de Fisiologia, Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisbon, Lisbon, Portugal.,Department of Neurosciences and Mental Health, Hospital de Santa Maria, Lisboa, Portugal
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2
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Vucic S, Pavey N, Haidar M, Turner BJ, Kiernan MC. Cortical hyperexcitability: Diagnostic and pathogenic biomarker of ALS. Neurosci Lett 2021; 759:136039. [PMID: 34118310 DOI: 10.1016/j.neulet.2021.136039] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 03/04/2021] [Accepted: 06/01/2021] [Indexed: 02/06/2023]
Abstract
Cortical hyperexcitability is an early and intrinsic feature of both sporadic and familial forms of amyotrophic lateral sclerosis (ALS).. Importantly, cortical hyperexcitability appears to be associated with motor neuron degeneration, possibly via an anterograde glutamate-mediated excitotoxic process, thereby forming a pathogenic basis for ALS. The presence of cortical hyperexcitability in ALS patients may be readily determined by transcranial magnetic stimulation (TMS), a neurophysiological tool that provides a non-invasive and painless method for assessing cortical function. Utilising the threshold tracking TMS technique, cortical hyperexcitability has been established as a robust diagnostic biomarker that distinguished ALS from mimicking disorders at early stages of the disease process. The present review discusses the pathophysiological and diagnostic utility of cortical hyperexcitability in ALS.
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Affiliation(s)
- Steve Vucic
- Western Clinical School, University of Sydney, Sydney, Australia.
| | - Nathan Pavey
- Western Clinical School, University of Sydney, Sydney, Australia
| | - Mouna Haidar
- Florey Institute of Neuroscieace and Mental Health, University of Melbourne, Parkville, Victoria, Australia
| | - Bradley J Turner
- Florey Institute of Neuroscieace and Mental Health, University of Melbourne, Parkville, Victoria, Australia
| | - Matthew C Kiernan
- Brain and Mind Centre, University of Sydney and Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney, Australia
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3
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Rossi M, Sciortino T, Conti Nibali M, Gay L, Viganò L, Puglisi G, Leonetti A, Howells H, Fornia L, Cerri G, Riva M, Bello L. Clinical Pearls and Methods for Intraoperative Motor Mapping. Neurosurgery 2021; 88:457-467. [PMID: 33476393 PMCID: PMC7884143 DOI: 10.1093/neuros/nyaa359] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Accepted: 04/26/2020] [Indexed: 12/13/2022] Open
Abstract
Resection of brain tumors involving motor areas and pathways requires the identification and preservation of various cortical and subcortical structures involved in motor control at the time of the procedure, in order to maintain the patient's full motor capacities. The use of brain mapping techniques has now been integrated into clinical practice for many years, as they help the surgeon to identify the neural structures involved in motor functions. A common definition of motor function, as well as knowledge of its neural organization, has been continuously evolving, underlining the need for implementing intraoperative strategies at the time of the procedure. Similarly, mapping strategies have been subjected to continuous changes, enhancing the likelihood of preservation of full motor capacities. As a general rule, the motor mapping strategy should be as flexible as possible and adapted strictly to the individual patient and clinical context of the tumor. In this work, we present an overview of current knowledge of motor organization, indications for motor mapping, available motor mapping, and monitoring strategies, as well as their advantages and limitations. The use of motor mapping improves resection and outcomes in patients harboring tumors involving motor areas and pathways, and should be considered the gold standard in the resection of this type of tumor.
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Affiliation(s)
- Marco Rossi
- Neurosurgery , Department of Oncology and Hemato-Oncology, Università degli Studi di Milano, Milano, Italy
| | - Tommaso Sciortino
- Neurosurgery , Department of Oncology and Hemato-Oncology, Università degli Studi di Milano, Milano, Italy
| | - Marco Conti Nibali
- Neurosurgery , Department of Oncology and Hemato-Oncology, Università degli Studi di Milano, Milano, Italy
| | - Lorenzo Gay
- Neurosurgery , Department of Oncology and Hemato-Oncology, Università degli Studi di Milano, Milano, Italy
| | - Luca Viganò
- Neurosurgery , Department of Oncology and Hemato-Oncology, Università degli Studi di Milano, Milano, Italy
| | - Guglielmo Puglisi
- Neurosurgery , Department of Oncology and Hemato-Oncology, Università degli Studi di Milano, Milano, Italy.,Laboratory of Motor Control, Department of Biotechnology and Translational Medicine, Università degli Studi di Milano Milano, Italy
| | - Antonella Leonetti
- Neurosurgery , Department of Oncology and Hemato-Oncology, Università degli Studi di Milano, Milano, Italy.,Laboratory of Motor Control, Department of Biotechnology and Translational Medicine, Università degli Studi di Milano Milano, Italy
| | - Henrietta Howells
- Laboratory of Motor Control, Department of Biotechnology and Translational Medicine, Università degli Studi di Milano Milano, Italy
| | - Luca Fornia
- Laboratory of Motor Control, Department of Biotechnology and Translational Medicine, Università degli Studi di Milano Milano, Italy
| | - Gabriella Cerri
- Laboratory of Motor Control, Department of Biotechnology and Translational Medicine, Università degli Studi di Milano Milano, Italy
| | - Marco Riva
- Neurosurgery , Department of Oncology and Hemato-Oncology, Università degli Studi di Milano, Milano, Italy
| | - Lorenzo Bello
- Neurosurgery , Department of Oncology and Hemato-Oncology, Università degli Studi di Milano, Milano, Italy
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4
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Lemon R, Kraskov A. Starting and stopping movement by the primate brain. Brain Neurosci Adv 2019; 3:2398212819837149. [PMID: 32166180 PMCID: PMC7058194 DOI: 10.1177/2398212819837149] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Indexed: 01/13/2023] Open
Abstract
We review the current knowledge about the part that motor cortex plays in the preparation and generation of movement, and we discuss the idea that corticospinal neurons, and particularly those with cortico-motoneuronal connections, act as ‘command’ neurons for skilled reach-to-grasp movements in the primate. We also review the increasing evidence that it is active during processes such as action observation and motor imagery. This leads to a discussion about how movement is inhibited and stopped, and the role in these for disfacilitation of the corticospinal output. We highlight the importance of the non-human primate as a model for the human motor system. Finally, we discuss the insights that recent research into the monkey motor system has provided for translational approaches to neurological diseases such as stroke, spinal injury and motor neuron disease.
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Affiliation(s)
- Roger Lemon
- Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London (UCL), London, UK
| | - Alexander Kraskov
- Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London (UCL), London, UK
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5
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Abstract
The last few years have seen major advances in our understanding of the organisation and function of the corticospinal tract (CST). These have included studies highlighting important species-specific variations in the different functions mediated by the CST. In the primate, the most characteristic feature is direct cortico-motoneuronal (CM) control of muscles, particularly of hand and finger muscles. This system, which is unique to dexterous primates, is probably at its most advanced level in humans. We now know much more about the origin of the CM system within the cortical motor network, and its connectivity within the spinal cord has been quantified. We have learnt much more about how the CM system works in parallel with other spinal circuits receiving input from the CST and how the CST functions alongside other brainstem motor pathways. New work in the mouse has provided fascinating insights into the contribution of the CM system to dexterity. Finally, accumulating evidence for the involvement of CM projections in motor neuron disease has highlighted the importance of advances in basic neuroscience for our understanding and possible treatment of a devastating neurological disease.
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Affiliation(s)
- Roger Lemon
- Department of Clinical and Motor Neuroscience, Queen Square Institute of Neurology, Box 28 National Hospital, Queen Square, London, WC1N 3BG, UK
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Eisen A, Braak H, Del Tredici K, Lemon R, Ludolph AC, Kiernan MC. Cortical influences drive amyotrophic lateral sclerosis. J Neurol Neurosurg Psychiatry 2017; 88:917-924. [PMID: 28710326 DOI: 10.1136/jnnp-2017-315573] [Citation(s) in RCA: 131] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Revised: 04/26/2017] [Accepted: 05/02/2017] [Indexed: 11/04/2022]
Abstract
The early motor manifestations of sporadic amyotrophic lateral sclerosis (ALS), while rarely documented, reflect failure of adaptive complex motor skills. The development of these skills correlates with progressive evolution of a direct corticomotoneuronal system that is unique to primates and markedly enhanced in humans. The failure of this system in ALS may translate into the split hand presentation, gait disturbance, split leg syndrome and bulbar symptomatology related to vocalisation and breathing, and possibly diffuse fasciculation, characteristic of ALS. Clinical neurophysiology of the brain employing transcranial magnetic stimulation has convincingly demonstrated a presymptomatic reduction or absence of short interval intracortical inhibition, accompanied by increased intracortical facilitation, indicating cortical hyperexcitability. The hallmark of the TDP-43 pathological signature of sporadic ALS is restricted to cortical areas as well as to subcortical nuclei that are under the direct control of corticofugal projections. This provides anatomical support that the origins of the TDP-43 pathology reside in the cerebral cortex itself, secondarily in corticofugal fibres and the subcortical targets with which they make monosynaptic connections. The latter feature explains the multisystem degeneration that characterises ALS. Consideration of ALS as a primary neurodegenerative disorder of the human brain may incorporate concepts of prion-like spread at synaptic terminals of corticofugal axons. Further, such a concept could explain the recognised widespread imaging abnormalities of the ALS neocortex and the accepted relationship between ALS and frontotemporal dementia.
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Affiliation(s)
- Andrew Eisen
- Division of Neurology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Heiko Braak
- Clinical Neuroanatomy Section, Department of Neurology, Center for Biomedical Research, University of Ulm, Ulm, Baden-Württemberg, Germany
| | - Kelly Del Tredici
- Clinical Neuroanatomy Section, Department of Neurology, Center for Biomedical Research, University of Ulm, Ulm, Baden-Württemberg, Germany
| | - Roger Lemon
- Sobell Department of Motor Neuroscience and Movement Disorders, Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, Queen Square, London, UK
| | | | - Matthew C Kiernan
- Brain and Mind Centre, The University of Sydney, Sydney, NSW, Australia
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7
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Fregosi M, Contestabile A, Hamadjida A, Rouiller EM. Corticobulbar projections from distinct motor cortical areas to the reticular formation in macaque monkeys. Eur J Neurosci 2017; 45:1379-1395. [PMID: 28394483 DOI: 10.1111/ejn.13576] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 03/31/2017] [Accepted: 04/03/2017] [Indexed: 12/31/2022]
Abstract
Corticospinal and corticobulbar descending pathways act in parallel with brainstem systems, such as the reticulospinal tract, to ensure the control of voluntary movements via direct or indirect influences onto spinal motoneurons. The aim of this study was to investigate the corticobulbar projections from distinct motor cortical areas onto different nuclei of the reticular formation. Seven adult macaque monkeys were analysed for the location of corticobulbar axonal boutons, and one monkey for reticulospinal neurons' location. The anterograde tracer BDA was injected in the premotor cortex (PM), in the primary motor cortex (M1) or in the supplementary motor area (SMA), in 3, 3 and 1 monkeys respectively. BDA anterograde labelling of corticobulbar axons were analysed on brainstem histological sections and overlapped with adjacent Nissl-stained sections for cytoarchitecture. One adult monkey was analysed for retrograde CB tracer injected in C5-C8 hemispinal cord to visualise reticulospinal neurons. The corticobulbar axons formed bilateral terminal fields with boutons terminaux and en passant, which were quantified in various nuclei belonging to the Ponto-Medullary Reticular Formation (PMRF). The corticobulbar projections from both PM and SMA tended to end mainly ipsilaterally in PMRF, but contralaterally when originating from M1. Furthermore, the corticobulbar projection was less dense when originating from M1 than from non-primary motor areas (PM, SMA). The main nuclei of bouton terminals corresponded to the regions where reticulospinal neurons were located with CB retrograde tracing. In conclusion, the corticobulbar projection differs according to the motor cortical area of origin in density and laterality.
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Affiliation(s)
- Michela Fregosi
- Department of Medecine, University of Fribourg, Chemin du Musée 5, 1700, Fribourg, Switzerland
| | - Alessandro Contestabile
- Department of Medecine, University of Fribourg, Chemin du Musée 5, 1700, Fribourg, Switzerland
| | - Adjia Hamadjida
- Department of Medecine, University of Fribourg, Chemin du Musée 5, 1700, Fribourg, Switzerland
| | - Eric M Rouiller
- Department of Medecine, University of Fribourg, Chemin du Musée 5, 1700, Fribourg, Switzerland
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Pathological TDP-43 changes in Betz cells differ from those in bulbar and spinal α-motoneurons in sporadic amyotrophic lateral sclerosis. Acta Neuropathol 2017; 133:79-90. [PMID: 27757524 PMCID: PMC5209403 DOI: 10.1007/s00401-016-1633-2] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2016] [Revised: 09/22/2016] [Accepted: 10/10/2016] [Indexed: 01/31/2023]
Abstract
Two nerve cells types, Betz cells in layer Vb of the primary motor neocortex and α-motoneurons of the lower brainstem and spinal cord, become involved at the beginning of the pathological cascade underlying sporadic amyotrophic lateral sclerosis (sALS). In both neuronal types, the cell nuclei forfeit their normal (non-phosphorylated) expression of the 43-kDa transactive response DNA-binding protein (TDP-43). Here, we present initial evidence that in α-motoneurons the loss of normal nuclear TDP-43 expression is followed by the formation of phosphorylated TDP-43 aggregates (pTDP-43) within the cytoplasm, whereas in Betz cells, by contrast, the loss of normal nuclear TDP-43 expression remains mostly unaccompanied by the development of cytoplasmic aggregations. We discuss some implications of this phenomenon of nuclear clearing in the absence of cytoplasmic inclusions, namely, abnormal but soluble (and, thus, probably toxic) cytoplasmic TDP-43 could enter the axoplasm of Betz cells, and following its transmission to the corresponding α-motoneurons in the lower brainstem and spinal cord, possibly contribute in recipient neurons to the dysregulation of the normal nuclear protein. Because the cellular mechanisms that possibly inhibit the aggregation of TDP-43 in the cytoplasm of involved Betz cells are unknown, insight into such mechanisms could disclose a pathway by which the development of aggregates in this cell population could be accelerated, thereby opening an avenue for a causally based therapy.
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Eisen A, Lemon R, Kiernan MC, Hornberger M, Turner MR. Does dysfunction of the mirror neuron system contribute to symptoms in amyotrophic lateral sclerosis? Clin Neurophysiol 2015; 126:1288-94. [DOI: 10.1016/j.clinph.2015.02.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Revised: 02/03/2015] [Accepted: 02/10/2015] [Indexed: 01/10/2023]
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10
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Menon P, Geevasinga N, Yiannikas C, Howells J, Kiernan MC, Vucic S. Sensitivity and specificity of threshold tracking transcranial magnetic stimulation for diagnosis of amyotrophic lateral sclerosis: a prospective study. Lancet Neurol 2015; 14:478-84. [PMID: 25843898 DOI: 10.1016/s1474-4422(15)00014-9] [Citation(s) in RCA: 138] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Revised: 01/28/2015] [Accepted: 03/10/2015] [Indexed: 01/12/2023]
Abstract
BACKGROUND Diagnosis of amyotrophic lateral sclerosis (ALS) remains problematic, with substantial diagnostic delays. We assessed the sensitivity and specificity of a threshold tracking transcranial magnetic stimulation (TMS) technique, which might allow early detection of upper motor neuron dysfunction, for the diagnosis of the disorder. METHODS We did a prospective study of patients referred to three neuromuscular centres in Sydney, Australia, in accordance with the Standards for Reporting of Diagnostic Accuracy. Participants had definite, probable, or possible ALS, as defined by the Awaji criteria; or pure motor disorder with clinical features of upper and lower motor neuron dysfunction in at least one body region, progressing over a 6 month follow-up period; or muscle wasting and weakness for at least 6 months. All patients underwent threshold tracking TMS at recruitment (index test), with application of the reference standard, the Awaji criteria, to differentiate patients with ALS from those with non-ALS disorders. The investigators who did the index test were masked to the results of the reference test and all other investigations. The primary outcome measures were the sensitivity and specificity of TMS in differentiating ALS from non-ALS disorders; these measures were derived from receiver operator curve analysis. FINDINGS Between Jan 1, 2010, and March 1, 2014, we screened 333 patients; 281 met our inclusion criteria. We eventually diagnosed 209 patients with ALS and 68 with non-ALS disorders; the diagnosis of four patients was inconclusive. The threshold tracking TMS technique differentiated ALS from non-ALS disorders with a sensitivity of 73·21% (95% CI 66·66-79·08) and specificity of 80·88% (69·53-89·40) at an early stage in the disease. All patients tolerated the study well, and we did not record any adverse events from performance of the index test. INTERPRETATION The threshold tracking TMS technique reliably distinguishes ALS from non-ALS disorders and, if these findings are replicated in larger studies, could represent a useful diagnostic investigation when combined with the Awaji criteria to prove upper motor neuron dysfunction at early stages of ALS. FUNDING Motor Neuron Disease Research Institute of Australia, National Health and Medical Research Council of Australia, and Pfizer.
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Affiliation(s)
- Parvathi Menon
- Derek Craig Motor Neuron Disease Research Centre, Western Clinical School, University of Sydney, NSW, Australia
| | - Nimeshan Geevasinga
- Derek Craig Motor Neuron Disease Research Centre, Western Clinical School, University of Sydney, NSW, Australia
| | - Con Yiannikas
- Westmead Hospital, Westmead, Royal North Shore Hospital, University of Sydney, NSW, Australia
| | - James Howells
- Brain and Mind Research Institute, Royal Prince Alfred Hospital, University of Sydney, NSW, Australia
| | - Matthew C Kiernan
- Brain and Mind Research Institute, Royal Prince Alfred Hospital, University of Sydney, NSW, Australia
| | - Steve Vucic
- Derek Craig Motor Neuron Disease Research Centre, Western Clinical School, University of Sydney, NSW, Australia; Department of Neurology, University of Sydney, NSW, Australia.
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Abstract
While task‐dependent changes in motor cortical outputs have been previously reported, the issue of whether such changes are specific for complex hand tasks remains unresolved. The aim of the present study was to determine whether cortical inhibitory tone and cortical output were greater during precision grip and power grip. Motor cortex excitability was undertaken by using the transcranial magnetic stimulation threshold tracking technique in 15 healthy subjects. The motor‐evoked potential (MEP) responses were recorded over the abductor pollicis brevis (APB), with the hand in the following positions: (1) rest, (2) precision grip and (3) power grip. The MEP amplitude (MEP amplitude REST 23.6 ± 3.3%; MEP amplitude PRECISIONGRIP 35.2 ± 5.6%; MEP amplitude POWERGRIP 19.6 ± 3.4%, F = 2.4, P < 0.001) and stimulus‐response gradient (SLOPEREST 0.06 ± 0.01; SLOPEPRCISIONGRIP 0.15 ± 0.04; SLOPE POWERGRIP 0.07 ± 0.01, P < 0.05) were significantly increased during precision grip. Short interval intracortical inhibition (SICI) was significantly reduced during the precision grip (SICI REST 15.0 ± 2.3%; SICI PRECISIONGRIP 9.7 ± 1.5%, SICI POWERGRIP 15.9 ± 2.7%, F = 2.6, P < 0.05). The present study suggests that changes in motor cortex excitability are specific for precision grip, with functional coupling of descending corticospinal pathways controlling thumb and finger movements potentially forming the basis of these cortical changes. This manuscript establishes that specific cortical mechanisms underlie the maintenance of the precision grip. The mechanisms appear distinct to the processes maintaining the power grip.
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Affiliation(s)
- Nimeshan Geevasinga
- Sydney Medical School Westmead, University of Sydney, Sydney, NSW, Australia
| | - Parvathi Menon
- Sydney Medical School Westmead, University of Sydney, Sydney, NSW, Australia
| | - Matthew C Kiernan
- The Brain and Mind Research Institute, University of Sydney, Sydney, NSW, Australia
| | - Steve Vucic
- Sydney Medical School Westmead, University of Sydney, Sydney, NSW, Australia
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de Carvalho M, Eisen A, Krieger C, Swash M. Motoneuron firing in amyotrophic lateral sclerosis (ALS). Front Hum Neurosci 2014; 8:719. [PMID: 25294995 PMCID: PMC4170108 DOI: 10.3389/fnhum.2014.00719] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Accepted: 08/27/2014] [Indexed: 01/09/2023] Open
Abstract
Amyotrophic lateral sclerosis is an inexorably progressive neurodegenerative disorder involving the classical motor system and the frontal effector brain, causing muscular weakness and atrophy, with variable upper motor neuron signs and often an associated fronto-temporal dementia. The physiological disturbance consequent on the motor system degeneration is beginning to be well understood. In this review we describe aspects of the motor cortical, neuronal, and lower motor neuron dysfunction. We show how studies of the changes in the pattern of motor unit firing help delineate the underlying pathophysiological disturbance as the disease progresses. Such studies are beginning to illuminate the underlying disordered pathophysiological processes in the disease, and are important in designing new approaches to therapy and especially for clinical trials.
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Affiliation(s)
- Mamede de Carvalho
- Institute of Physiology and Institute of Molecular Medicine, Faculty of Medicine, University of Lisbon Lisbon, Portugal ; Department of Neurosciences, Hospital Santa Maria, Faculty of Medicine, University of Lisbon Lisbon, Portugal
| | - Andrew Eisen
- Emeritus Professor of Neurology, University of British Columbia Vancouver, BC, Canada
| | - Charles Krieger
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby BC, Canada ; Department of Medicine (Neurology), University of British Columbia, Vancouver BC, Canada
| | - Michael Swash
- Institute of Physiology and Institute of Molecular Medicine, Faculty of Medicine, University of Lisbon Lisbon, Portugal ; Department of Neurosciences, Hospital Santa Maria, Faculty of Medicine, University of Lisbon Lisbon, Portugal ; Institute of Neuroscience, Barts and The London School of Medicine, Queen Mary University of London London, UK
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13
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Kiritani T, Wickersham IR, Seung HS, Shepherd GMG. Hierarchical connectivity and connection-specific dynamics in the corticospinal-corticostriatal microcircuit in mouse motor cortex. J Neurosci 2012; 32:4992-5001. [PMID: 22492054 PMCID: PMC3329752 DOI: 10.1523/jneurosci.4759-11.2012] [Citation(s) in RCA: 137] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2011] [Revised: 01/30/2012] [Accepted: 02/23/2012] [Indexed: 11/21/2022] Open
Abstract
The generation of purposive movement by mammals involves coordinated activity in the corticospinal and corticostriatal systems, which are involved in different aspects of motor control. In the motor cortex, corticospinal and corticostriatal neurons are closely intermingled, raising the question of whether and how information flows intracortically within and across these two channels. To explore this, we developed an optogenetic technique based on retrograde transfection of neurons with deletion-mutant rabies virus encoding channelrhodopsin-2, and used this in conjunction with retrograde anatomical labeling to stimulate and record from identified projection neurons in mouse motor cortex. We also used paired recordings to measure unitary connections. Both corticospinal and callosally projecting corticostriatal neurons in layer 5B formed within-class (recurrent) connections, with higher connection probability among corticostriatal than among corticospinal neurons. In contrast, across-class connectivity was extraordinarily asymmetric, essentially unidirectional from corticostriatal to corticospinal. Corticostriatal neurons in layer 5A and corticocortical neurons (callosal projection neurons similar to corticostriatal neurons) similarly received a paucity of corticospinal input. Connections involving presynaptic corticostriatal neurons had greater synaptic depression, and those involving postsynaptic corticospinal neurons had faster decaying EPSPs. Consequently, the three connections displayed a diversity of dynamic properties reflecting the different combinations of presynaptic and postsynaptic projection neurons. Collectively, these findings delineate a four-way specialized excitatory microcircuit formed by corticospinal and corticostriatal neurons. The "rectifying" corticostriatal-to-corticospinal connectivity implies a hierarchical organization and functional compartmentalization of corticospinal activity via unidirectional signaling from higher-order (corticostriatal) to lower-order (corticospinal) output neurons.
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Affiliation(s)
- Taro Kiritani
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, and
| | - Ian R. Wickersham
- Howard Hughes Medical Institute and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - H. Sebastian Seung
- Howard Hughes Medical Institute and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Gordon M. G. Shepherd
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, and
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