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International Journal of Molecular... Aug 2020Rodent neocortical neurons undergo prominent postnatal development and maturation. The process is associated with structural and functional maturation of the axon...
Rodent neocortical neurons undergo prominent postnatal development and maturation. The process is associated with structural and functional maturation of the axon initial segment (AIS), the site of action potential initiation. In this regard, cell size and optimal AIS length are interconnected. In sensory cortices, developmental onset of sensory input and consequent changes in network activity cause phasic AIS plasticity that can also control functional output. In non-sensory cortices, network input driving phasic events should be less prominent. We, therefore, explored the relationship between postnatal functional maturation and AIS maturation in principal neurons of the primary motor cortex layer V (M1LV), a non-sensory area of the rat brain. We hypothesized that a rather continuous process of AIS maturation and elongation would reflect cell growth, accompanied by progressive refinement of functional output properties. We found that, in the first two postnatal weeks, cell growth prompted substantial decline of neuronal input resistance, such that older neurons needed larger input current to reach rheobase and fire action potentials. In the same period, we observed the most prominent AIS elongation and significant maturation of functional output properties. Alternating phases of AIS plasticity did not occur, and changes in functional output properties were largely justified by AIS elongation. From the third postnatal week up to five months of age, cell growth, AIS elongation, and functional output maturation were marginal. Thus, AIS maturation in M1LV is a continuous process that attunes the functional output of pyramidal neurons and associates with early postnatal development to counterbalance increasing electrical leakage due to cell growth.
Topics: Action Potentials; Age Factors; Animals; Axon Initial Segment; Cell Differentiation; Cells, Cultured; Growth; Models, Neurological; Motor Cortex; Motor Neurons; Neurogenesis; Neuronal Plasticity; Rats
PubMed: 32847128
DOI: 10.3390/ijms21176101 -
Human Brain Mapping May 2022Sensorimotor coordination requires orchestrated network activity in the brain, mediated by inter- and intra-hemispheric interactions that may be affected by...
Sensorimotor coordination requires orchestrated network activity in the brain, mediated by inter- and intra-hemispheric interactions that may be affected by aging-related changes. We adopted a theoretical model, according to which intra-hemispheric inhibition from premotor to primary motor cortex is mandatory to compensate for inter-hemispheric excitation through the corpus callosum. To test this as a function of age we acquired electroencephalography (EEG) simultaneously with functional magnetic resonance imaging (fMRI) in two groups of healthy adults (younger N = 13: 20-25 year and older N = 14: 59-70 year) while learning a unimanual motor task. On average, quality of performance of older participants stayed significantly below that of the younger ones. Accompanying decreases in motor-event-related EEG β-activity were lateralized toward contralateral motor regions, albeit more so in younger participants. In this younger group, the mean β-power during motor task execution was significantly higher in bilateral premotor areas compared to the older adults. In both groups, fMRI blood oxygen level dependent (BOLD) signals were positively correlated with source-reconstructed β-amplitudes: positive in primary motor and negative in premotor cortex. This suggests that β-amplitude modulation is associated with primary motor cortex "activation" (positive BOLD response) and premotor "deactivation" (negative BOLD response). Although the latter results did not discriminate between age groups, they underscore that enhanced modulation in primary motor cortex may be explained by a β-associated excitatory crosstalk between hemispheres.
Topics: Aged; Aging; Cohort Studies; Electroencephalography; Humans; Magnetic Resonance Imaging; Motor Cortex
PubMed: 35133058
DOI: 10.1002/hbm.25791 -
Journal of Neurophysiology Apr 2016Changes in the environment require rapid modification or inhibition of ongoing behavior. We used the stop-signal paradigm and intracranial recordings to investigate...
Changes in the environment require rapid modification or inhibition of ongoing behavior. We used the stop-signal paradigm and intracranial recordings to investigate response preparation, inhibition, and monitoring of task-relevant information. Electrocorticographic data were recorded in eight patients with electrodes covering frontal, temporal, and parietal cortex, and time-frequency analysis was used to examine power differences in the beta (13-30 Hz) and high-gamma bands (60-180 Hz). Over motor cortex, beta power decreased, and high-gamma power increased during motor preparation for both go trials (Go) and unsuccessful stops (US). For successful stops (SS), beta increased, and high-gamma was reduced, indexing the cancellation of the prepared response. In the middle frontal gyrus (MFG), stop signals elicited a transient high-gamma increase. The MFG response occurred before the estimated stop-signal reaction time but did not distinguish between SS and US trials, likely signaling attention to the salient stop stimulus. A postresponse high-gamma increase in MFG was stronger for US compared with SS and absent in Go, supporting a role in behavior monitoring. These results provide evidence for differential contributions of frontal subregions to response inhibition, including motor preparation and inhibitory control in motor cortex and cognitive control and action evaluation in lateral prefrontal cortex.
Topics: Adult; Attention; Beta Rhythm; Drug Resistant Epilepsy; Female; Gamma Rhythm; Humans; Male; Motor Cortex; Neural Inhibition; Psychomotor Performance
PubMed: 26864760
DOI: 10.1152/jn.00708.2015 -
Journal of Neurophysiology Jul 2017Transcallosal fibers facilitate interhemispheric networks involved in motor tasks. Despite their clinical relevance, interhemispheric motor control systems have not been...
Transcallosal fibers facilitate interhemispheric networks involved in motor tasks. Despite their clinical relevance, interhemispheric motor control systems have not been completely defined in the developing brain. The objective of this study was to examine the developmental profile of transcallosal inhibition in healthy children and adolescents. Nineteen typically developing right-handed participants were recruited. Two transcranial magnetic stimulation (TMS) paradigms assessed transcallosal inhibition: ipsilateral silent periods (iSP) and paired-pulse interhemispheric inhibition (IHI). TMS was applied to the motor hotspot of the first dorsal interosseous muscle. Resting motor threshold (RMT), iSP latency, duration and suppression strength, and paired-pulse IHI were measured from both hemispheres. The Purdue Pegboard Test assessed unimanual motor function. Hemispheric differences were evident for RMT and iSP latency and suppression strength, where the left hemisphere had a lower RMT, prolonged latency, and greater suppression strength. iSP duration showed hemispheric symmetry. RMT and iSP latency decreased with age, whereas iSP suppression strength increased. Girls showed shorter iSP latency. Children typically displayed IHI, although hemispheric differences were observed. iSP suppression strength was uniquely associated with IHI within individuals. iSP duration correlated with motor performance. TMS can characterize transcallosal inhibition in normal children and adolescents with effects of age, directionality, sex, and motor performance. Establishing this developmental profile of interhemispheric interactions may advance understanding and therapeutic strategies for pediatric motor disorders such as cerebral palsy. Here we demonstrate that transcranial magnetic stimulation can characterize transcallosal inhibition in normal children and adolescents with effects of age, directionality, handedness, and motor performance. Interestingly, we also demonstrated sex effects, possibly related to the differing developmental profiles of boys and girls. Establishing this developmental profile of interhemispheric interactions may advance understanding and therapeutic strategies for pediatric motor disorders such as cerebral palsy.
Topics: Adolescent; Child; Corpus Callosum; Female; Functional Laterality; Humans; Male; Motor Cortex; Neural Inhibition; Reaction Time; Transcranial Magnetic Stimulation
PubMed: 28381485
DOI: 10.1152/jn.00076.2017 -
Journal of Neuroengineering and... Nov 2019Transcranial Direct Current Stimulation (tDCS) is a non-invasive technique used to modulate neural tissue. Neuromodulation apparently improves cognitive functions in... (Review)
Review
Transcranial Direct Current Stimulation (tDCS) is a non-invasive technique used to modulate neural tissue. Neuromodulation apparently improves cognitive functions in several neurologic diseases treatment and sports performance. In this study, we present a comprehensive, integrative review of tDCS for motor rehabilitation and motor learning in healthy individuals, athletes and multiple neurologic and neuropsychiatric conditions. We also report on neuromodulation mechanisms, main applications, current knowledge including areas such as language, embodied cognition, functional and social aspects, and future directions. We present the use and perspectives of new developments in tDCS technology, namely high-definition tDCS (HD-tDCS) which promises to overcome one of the main tDCS limitation (i.e., low focality) and its application for neurological disease, pain relief, and motor learning/rehabilitation. Finally, we provided information regarding the Transcutaneous Spinal Direct Current Stimulation (tsDCS) in clinical applications, Cerebellar tDCS (ctDCS) and its influence on motor learning, and TMS combined with electroencephalography (EEG) as a tool to evaluate tDCS effects on brain function.
Topics: Athletes; Healthy Volunteers; Humans; Learning; Motor Cortex; Nervous System Diseases; Transcranial Direct Current Stimulation
PubMed: 31730494
DOI: 10.1186/s12984-019-0581-1 -
Cerebral Cortex (New York, N.Y. : 1991) Jun 2022Motor behavior results in complex exchanges of motor and sensory information across cortical regions. Therefore, fully understanding the cerebral cortex's role in motor...
Motor behavior results in complex exchanges of motor and sensory information across cortical regions. Therefore, fully understanding the cerebral cortex's role in motor behavior requires a mesoscopic-level description of the cortical regions engaged, their functional interactions, and how these functional interactions change with behavioral state. Mesoscopic Ca2+ imaging through transparent polymer skulls in mice reveals elevated activation of the dorsal cerebral cortex during locomotion. Using the correlations between the time series of Ca2+ fluorescence from 28 regions (nodes) obtained using spatial independent component analysis (sICA), we examined the changes in functional connectivity of the cortex from rest to locomotion with a goal of understanding the changes to the cortical functional state that facilitate locomotion. Both the transitions from rest to locomotion and from locomotion to rest show marked increases in correlation among most nodes. However, once a steady state of continued locomotion is reached, many nodes, including primary motor and somatosensory nodes, show decreases in correlations, while retrosplenial and the most anterior nodes of the secondary motor cortex show increases. These results highlight the changes in functional connectivity in the cerebral cortex, representing a series of changes in the cortical state from rest to locomotion and on return to rest.
Topics: Animals; Brain Mapping; Calcium; Diagnostic Imaging; Locomotion; Magnetic Resonance Imaging; Mice; Motor Cortex; Neural Pathways
PubMed: 34689209
DOI: 10.1093/cercor/bhab373 -
The Journal of Physiology Mar 2020Discrete and rhythmic dynamics are inherent components of (human) movements. We provide evidence that distinct human motor cortex circuits contribute to discrete and...
KEY POINTS
Discrete and rhythmic dynamics are inherent components of (human) movements. We provide evidence that distinct human motor cortex circuits contribute to discrete and rhythmic movements. Excitability of supragranular layer circuits of the human motor cortex was higher during discrete movements than during rhythmic movements. Conversely, more complex corticospinal circuits showed higher excitability during rhythmic movements than during discrete movements. No task-specific differences existed for corticospinal output neurons at infragranular layers. The excitability differences were found to be time(phase)-specific and could not be explained by the kinematic properties of the movements. The same task-specific differences were found between the last cycle of a rhythmic movement period and ongoing rhythmic movements.
ABSTRACT
Human actions entail discrete and rhythmic movements (DM and RM, respectively). Recent insights from human and animal studies indicate different neural control mechanisms for DM and RM, emphasizing the intrinsic nature of the task. However, how distinct human motor cortex circuits contribute to these movements remains largely unknown. In the present study, we tested distinct primary motor cortex and corticospinal circuits and proposed that they show differential excitability between DM and RM. Human subjects performed either 1) DM or 2) RM using their right wrist. We applied an advanced electrophysiological approach involving transcranial magnetic stimulation and peripheral nerve stimulation to test the excitability of the neural circuits. Probing was performed at different movement phases: movement initiation (MI, 20 ms after EMG onset) and movement execution (ME, 200 ms after EMG onset) of the wrist flexion. At MI, excitability at supragranular layers was significantly higher in DM than in RM. Conversely, excitability of more complex corticospinal circuits was significantly lower in DM than RM at ME. No task-specific differences were found for direct corticospinal output neurons at infragranular layers. The neural differences could not be explained by the kinematic properties of the movements and also existed between ongoing RM and the last cycle of RM. Our results therefore strengthen the hypothesis that different neural control mechanisms engage in DM and RM.
Topics: Electromyography; Humans; Motor Cortex; Movement; Transcranial Magnetic Stimulation; Wrist
PubMed: 32057108
DOI: 10.1113/JP278779 -
Human Brain Mapping Jun 2019Sensorimotor control of neck muscles differs between individuals with and without pain. Differences in the primary motor cortex (M1) maps of these muscles may be...
Sensorimotor control of neck muscles differs between individuals with and without pain. Differences in the primary motor cortex (M1) maps of these muscles may be involved. This study compared M1 representations of deep (DNF) and superficial (SNF) neck flexor muscles between 10 individuals with neck pain (NP) and 10 painfree controls. M1 organisation was studied using transcranial magnetic stimulation (TMS) applied to a grid over the skull and surface electromyography of DNF (pharyngeal electrode) and SNF. Three-dimensional maps of M1 representation of each muscle were generated. Peaks in the SNF map that represented the sternocleidomastoid (SCM) and platysma muscles were identified. Unique centre of gravity (CoG)/map peaks were identified for the three muscles. In comparison to painfree controls, NP participants had more medial location of the CoG/peak of DNF, SCM, and platysma, greater mediolateral variation in DNF CoG (p = 0.02), fewer SNF and DNF map peaks (p = 0.01). These data show that neck flexor muscle M1 maps relate to trunk, neck, and face areas of the motor homunculus. Differences in M1 representation in NP have some similarities and some differences with observations for other musculoskeletal pain conditions. Despite the small sample size, our data did reveal differences and is comparable to other similar studies. The results of this study should be interpreted with consideration of methodological issues.
Topics: Adult; Electromyography; Female; Humans; Male; Motor Cortex; Neck Muscles; Neck Pain; Transcranial Magnetic Stimulation
PubMed: 30835902
DOI: 10.1002/hbm.24558 -
Neuroscience Bulletin Jul 2022In contrast to traditional representational perspectives in which the motor cortex is involved in motor control via neuronal preference for kinetics and kinematics, a... (Review)
Review
In contrast to traditional representational perspectives in which the motor cortex is involved in motor control via neuronal preference for kinetics and kinematics, a dynamical system perspective emerging in the last decade views the motor cortex as a dynamical machine that generates motor commands by autonomous temporal evolution. In this review, we first look back at the history of the representational and dynamical perspectives and discuss their explanatory power and controversy from both empirical and computational points of view. Here, we aim to reconcile the above perspectives, and evaluate their theoretical impact, future direction, and potential applications in brain-machine interfaces.
Topics: Biomechanical Phenomena; Brain-Computer Interfaces; Motor Cortex; Neurons
PubMed: 35298779
DOI: 10.1007/s12264-022-00832-x -
NeuroImage Oct 2021Vocal flexibility is a hallmark of the human species, most particularly the capacity to speak and sing. This ability is supported in part by the evolution of a direct...
Vocal flexibility is a hallmark of the human species, most particularly the capacity to speak and sing. This ability is supported in part by the evolution of a direct neural pathway linking the motor cortex to the brainstem nucleus that controls the larynx the primary sound source for communication. Early brain imaging studies demonstrated that larynx motor cortex at the dorsal end of the orofacial division of motor cortex (dLMC) integrated laryngeal and respiratory control, thereby coordinating two major muscular systems that are necessary for vocalization. Neurosurgical studies have since demonstrated the existence of a second larynx motor area at the ventral extent of the orofacial motor division (vLMC) of motor cortex. The vLMC has been presumed to be less relevant to speech motor control, but its functional role remains unknown. We employed a novel ultra-high field (7T) magnetic resonance imaging paradigm that combined singing and whistling simple melodies to localise the larynx motor cortices and test their involvement in respiratory motor control. Surprisingly, whistling activated both 'larynx areas' more strongly than singing despite the reduced involvement of the larynx during whistling. We provide further evidence for the existence of two larynx motor areas in the human brain, and the first evidence that laryngeal-respiratory integration is a shared property of both larynx motor areas. We outline explicit predictions about the descending motor pathways that give these cortical areas access to both the laryngeal and respiratory systems and discuss the implications for the evolution of speech.
Topics: Adult; Female; Humans; Larynx; Least-Squares Analysis; Magnetic Resonance Imaging; Male; Motor Cortex; Neural Pathways; Respiration; Respiratory Mechanics; Rest; Singing; Speech; Young Adult
PubMed: 34216772
DOI: 10.1016/j.neuroimage.2021.118326