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Handbook of Clinical Neurology 2019This review presents the neurophysiologic principles and clinical applications of transcranial magnetic stimulation (TMS) and other related techniques of noninvasive... (Review)
Review
This review presents the neurophysiologic principles and clinical applications of transcranial magnetic stimulation (TMS) and other related techniques of noninvasive cortical stimulation. TMS can serve various purposes for diagnosis or treatment. Regarding diagnosis, TMS is mainly dedicated to the recording of motor evoked potentials (MEPs). MEP recording allows investigation of corticospinal conduction time and cortical motor control in clinical practice. Especially when using image-guided neuronavigation methods, MEP recording is a reliable method to perform functional mapping of muscle representation within the motor cortex. Using various types of paired-pulse paradigms, TMS allows the assessment of brain circuit excitability or plastic changes affecting these circuits. In particular, paired-pulse TMS paradigms are able to appraise the intracortical balance between inhibitory controls mediated by GABAergic neurotransmission and excitatory controls mediated by glutamatergic neurotransmission. Finally, TMS delivered as repetitive trains of stimulation (rTMS) may activate, inhibit, or otherwise interfere with the activity of neuronal cortical networks, depending on stimulus frequency and intensity, and brain-induced electric field configuration. Therefore by modifying brain functions, with after-effects lasting beyond the time of stimulation, rTMS opens exciting perspectives for therapeutic applications, especially in the domain of depression and chronic pain syndromes.
Topics: Evoked Potentials, Motor; Humans; Motor Cortex; Nerve Net; Nervous System Diseases; Transcranial Magnetic Stimulation
PubMed: 31277876
DOI: 10.1016/B978-0-444-64032-1.00037-0 -
Current Opinion in Neurobiology Apr 2018Neurons in motor cortex and connected brain regions fire in anticipation of specific movements, long before movement occurs. This neural activity reflects internal... (Review)
Review
Neurons in motor cortex and connected brain regions fire in anticipation of specific movements, long before movement occurs. This neural activity reflects internal processes by which the brain plans and executes volitional movements. The study of motor planning offers an opportunity to understand how the structure and dynamics of neural circuits support persistent internal states and how these states influence behavior. Recent advances in large-scale neural recordings are beginning to decipher the relationship of the dynamics of populations of neurons during motor planning and movements. New behavioral tasks in rodents, together with quantified perturbations, link dynamics in specific nodes of neural circuits to behavior. These studies reveal a neural network distributed across multiple brain regions that collectively supports motor planning. We review recent advances and highlight areas where further work is needed to achieve a deeper understanding of the mechanisms underlying motor planning and related cognitive processes.
Topics: Animals; Executive Function; Humans; Motor Cortex; Movement; Neural Pathways; Neurons; Psychomotor Performance
PubMed: 29172091
DOI: 10.1016/j.conb.2017.10.023 -
Philosophical Transactions of the Royal... Dec 2021Humans are vocal modulators par excellence. This ability is supported in part by the dual representation of the laryngeal muscles in the motor cortex. Movement, however,... (Review)
Review
Humans are vocal modulators par excellence. This ability is supported in part by the dual representation of the laryngeal muscles in the motor cortex. Movement, however, is not the product of motor cortex alone but of a broader motor network. This network consists of brain regions that contain somatotopic maps that parallel the organization in motor cortex. We therefore present a novel hypothesis that the dual laryngeal representation is repeated throughout the broader motor network. In support of the hypothesis, we review existing literature that demonstrates the existence of network-wide somatotopy and present initial evidence for the hypothesis' plausibility. Understanding how this uniquely human phenotype in motor cortex interacts with broader brain networks is an important step toward understanding how humans evolved the ability to speak. We further suggest that this system may provide a means to study how individual components of the nervous system evolved within the context of neuronal networks. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.
Topics: Brain; Brain Mapping; Larynx; Magnetic Resonance Imaging; Motor Cortex; Movement
PubMed: 34719252
DOI: 10.1098/rstb.2020.0392 -
Progress in Brain Research 2015Following damage to the motor system (e.g., after stroke or spinal cord injury), recovery of upper limb function exploits the multiple pathways which allow motor... (Review)
Review
Following damage to the motor system (e.g., after stroke or spinal cord injury), recovery of upper limb function exploits the multiple pathways which allow motor commands to be sent to the spinal cord. Corticospinal fibers originate from premotor as well as primary motor cortex. While some corticospinal fibers make direct monosynaptic connections to motoneurons, there are also many connections to interneurons which allow control of motoneurons indirectly. Such interneurons may be placed within the cervical enlargement, or more rostrally (propriospinal interneurons). In addition, connections from cortex to the reticular formation in the brainstem allow motor commands to be sent over the reticulospinal tract to these spinal centers. In this review, we consider the relative roles of these different routes for the control of hand function, both in healthy primates and after recovery from lesion.
Topics: Afferent Pathways; Animals; Functional Laterality; Humans; Motor Cortex; Motor Neurons; Movement Disorders; Neuronal Plasticity; Recovery of Function
PubMed: 25890147
DOI: 10.1016/bs.pbr.2014.12.010 -
International Review of Neurobiology 2021Medial secondary motor cortex (MOs or M2) constitutes the dorsal aspect of the rodent medial frontal cortex. We previously proposed that the function of MOs is to link... (Review)
Review
Medial secondary motor cortex (MOs or M2) constitutes the dorsal aspect of the rodent medial frontal cortex. We previously proposed that the function of MOs is to link antecedent conditions, including sensory stimuli and prior choices, to impending actions. In this review, we focus on the long-range pathways between MOs and other cortical and subcortical regions. We highlight three circuits: (1) connections with visual and auditory cortices that are essential for predictive coding of perceptual inputs; (2) connections with motor cortex and brainstem that are responsible for top-down, context-dependent modulation of movements; (3) connections with retrosplenial cortex, orbitofrontal cortex, and basal ganglia that facilitate reward-based learning. Together, these long-range circuits allow MOs to broadcast choice signals for feedback and to bias decision-making processes.
Topics: Animals; Bias; Decision Making; Motor Cortex
PubMed: 33785155
DOI: 10.1016/bs.irn.2020.11.008 -
Current Opinion in Neurobiology Oct 2014Our ability to learn and control the motor aspects of complex laryngeal behaviors, such as speech and song, is modulated by the laryngeal motor cortex (LMC), which is... (Review)
Review
Our ability to learn and control the motor aspects of complex laryngeal behaviors, such as speech and song, is modulated by the laryngeal motor cortex (LMC), which is situated in the area 4 of the primary motor cortex and establishes both direct and indirect connections with laryngeal motoneurons. In contrast, the LMC in monkeys is located in the area 6 of the premotor cortex, projects only indirectly to laryngeal motoneurons and its destruction has essentially no effect on production of species-specific calls. These differences in cytoarchitectonic location and connectivity may be a result of hominid evolution that led to the LMC shift from the phylogenetically 'old' to 'new' motor cortex in order to fulfill its paramount function, that is, voluntary motor control of human speech and song production.
Topics: Brain Mapping; Humans; Larynx; Motor Cortex; Motor Neurons; Neural Pathways
PubMed: 24929930
DOI: 10.1016/j.conb.2014.05.006 -
Neuroscience and Biobehavioral Reviews Sep 2017In recent years, sheep (Ovis aries) have emerged as a useful animal model for neurological research due to their relatively large brain and blood vessel size, their... (Review)
Review
In recent years, sheep (Ovis aries) have emerged as a useful animal model for neurological research due to their relatively large brain and blood vessel size, their cortical architecture, and their docile temperament. However, the functional anatomy of sheep brain is not as well studied as that of non-human primates, rodents, and felines. For example, while the location of the sheep motor cortex has been known for many years, there have been few studies of the somatotopy of the motor cortex and there were a range of discrepancies across them. The motivation for this review is to provide a definitive resource for studies of the sheep motor cortex. This work critically reviews the literature examining the organization of the motor cortex in sheep, utilizing studies that have applied direct electrical stimulation and histological methods A clearer understanding of the sheep brain will facilitate and progress the use of this species as a scientific animal model for neurological research.
Topics: Animals; Brain Mapping; Motor Cortex; Neurons; Sheep
PubMed: 28595827
DOI: 10.1016/j.neubiorev.2017.06.002 -
The Journal of Neuroscience : the... Oct 2018In the 1960s, Evarts first recorded the activity of single neurons in motor cortex of behaving monkeys (Evarts, 1968). In the 50 years since, great effort has been... (Review)
Review
In the 1960s, Evarts first recorded the activity of single neurons in motor cortex of behaving monkeys (Evarts, 1968). In the 50 years since, great effort has been devoted to understanding how single neuron activity relates to movement. Yet these single neurons exist within a vast network, the nature of which has been largely inaccessible. With advances in recording technologies, algorithms, and computational power, the ability to study these networks is increasing exponentially. Recent experimental results suggest that the dynamical properties of these networks are critical to movement planning and execution. Here we discuss this dynamical systems perspective and how it is reshaping our understanding of the motor cortices. Following an overview of key studies in motor cortex, we discuss techniques to uncover the "latent factors" underlying observed neural population activity. Finally, we discuss efforts to use these factors to improve the performance of brain-machine interfaces, promising to make these findings broadly relevant to neuroengineering as well as systems neuroscience.
Topics: Animals; Brain-Computer Interfaces; Humans; Motor Cortex; Movement; Neurons; Time Factors
PubMed: 30381431
DOI: 10.1523/JNEUROSCI.1669-18.2018 -
Neuroscience Mar 2022The primary motor cortex, a dynamic center for overall motion control and decision making, undergoes significant alterations upon neural stimulation. Over the last few... (Review)
Review
The primary motor cortex, a dynamic center for overall motion control and decision making, undergoes significant alterations upon neural stimulation. Over the last few decades, data from numerous studies using rodent models have improved our understanding of the morphological and functional plasticity of the primary motor cortex. In particular, spatially specific formation of dendritic spines and their maintenance during distinct behaviors is considered crucial for motor learning. However, whether the modifications of specific synapses are associated with motor learning should be studied further. In this review, we summarized the findings of prior studies on the features and dynamics of the primary motor cortex in rodents.
Topics: Animals; Dendritic Spines; Motor Cortex; Neuronal Plasticity; Rodentia; Synapses
PubMed: 35051529
DOI: 10.1016/j.neuroscience.2022.01.009 -
Frontiers in Neural Circuits 2017Elaboration of appropriate responses to behavioral situations rests on the ability of selecting appropriate motor outcomes in accordance to specific environmental... (Review)
Review
Elaboration of appropriate responses to behavioral situations rests on the ability of selecting appropriate motor outcomes in accordance to specific environmental inputs. To this end, the primary motor cortex (M1) is a key structure for the control of voluntary movements and motor skills learning. Subcortical loops regulate the activity of the motor cortex and thus contribute to the selection of appropriate motor plans. Monoamines are key mediators of arousal, attention and motivation. Their firing pattern enables a direct encoding of different states thus promoting or repressing the selection of actions adapted to the behavioral context. Monoaminergic modulation of motor systems has been extensively studied in subcortical circuits. Despite evidence of converging projections of multiple neurotransmitters systems in the motor cortex pointing to a direct modulation of local circuits, their contribution to the execution and learning of motor skills is still poorly understood. Monoaminergic dysregulation leads to impaired plasticity and motor function in several neurological and psychiatric conditions, thus it is critical to better understand how monoamines modulate neural activity in the motor cortex. This review aims to provide an update of our current understanding on the monoaminergic modulation of the motor cortex with an emphasis on motor skill learning and execution under physiological conditions.
Topics: Animals; Biogenic Monoamines; Humans; Motor Cortex; Neurons
PubMed: 29062274
DOI: 10.3389/fncir.2017.00072