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ELife Jul 2020Pyramidal tract neurons (PTNs) within macaque rostral ventral premotor cortex (F5) and (M1) provide direct input to spinal circuitry and are critical for skilled...
Pyramidal tract neurons (PTNs) within macaque rostral ventral premotor cortex (F5) and (M1) provide direct input to spinal circuitry and are critical for skilled movement control. Contrary to initial hypotheses, they can also be active during action observation, in the absence of any movement. A population-level understanding of this phenomenon is currently lacking. We recorded from single neurons, including identified PTNs, in (M1) (n = 187), and F5 (n = 115) as two adult male macaques executed, observed, or withheld (NoGo) reach-to-grasp actions. F5 maintained a similar representation of grasping actions during both execution and observation. In contrast, although many individual M1 neurons were active during observation, M1 population activity was distinct from execution, and more closely aligned to NoGo activity, suggesting this activity contributes to withholding of self-movement. M1 and its outputs may dissociate initiation of movement from representation of grasp in order to flexibly guide behaviour.
Topics: Animals; Electromyography; Hand Strength; Macaca mulatta; Male; Mirror Neurons; Motor Cortex; Movement; Reaction Time
PubMed: 32628107
DOI: 10.7554/eLife.54139 -
Frontiers in Neural Circuits 2013Rodent whisking is an exploratory behavior that can be modified by sensory feedback. Consistent with this, many whisker-sensitive cortical regions project to agranular...
Rodent whisking is an exploratory behavior that can be modified by sensory feedback. Consistent with this, many whisker-sensitive cortical regions project to agranular motor [motor cortex (MI)] cortex, but the relative topography of these afferent projections has not been established. Intracortical microstimulation (ICMS) evokes whisker movements that are used to map the functional organization of MI, but no study has compared the whisker-related inputs to MI with the ICMS sites that evoke whisker movements. To elucidate this relationship, anterograde tracers were placed in posterior parietal cortex (PPC) and in the primary somatosensory (SI) and secondary somatosensory (SII) cortical areas so that their labeled projections to MI could be analyzed with respect to ICMS sites that evoke whisker movements. Projections from SI and SII terminate in a narrow zone that marks the transition between the medial agranular (AGm) and lateral agranular (AGl) cortical areas, but PPC projects more medially and terminates in AGm proper. Paired recordings of MI neurons indicate that the region between AGm and AGl is highly responsive to whisker deflections, but neurons in AGm display negligible responses to whisker stimulation. By contrast, AGm microstimulation is more effective in evoking whisker movements than microstimulation of the transitional region between AGm and AGl. The AGm region was also found to contain a larger concentration of corticotectal neurons, which could convey whisker-related information to the facial nucleus. These results indicate that rat whisker MI is comprised of at least two functionally distinct subregions: a sensory processing zone in the transitional region between AGm and AGl, and a motor-output region located more medially in AGm proper.
Topics: Animals; Male; Motor Cortex; Rats; Rats, Sprague-Dawley; Sensory Receptor Cells; Somatosensory Cortex; Vibrissae
PubMed: 23372545
DOI: 10.3389/fncir.2013.00004 -
Journal of Neurophysiology Feb 2021The mammalian motor cortex is topographically organized into representations of discrete body parts (motor maps). Studies in adult rats using long-duration intracortical...
The mammalian motor cortex is topographically organized into representations of discrete body parts (motor maps). Studies in adult rats using long-duration intracortical microstimulation (LD-ICMS) reveal that forelimb motor cortex is functionally organized into several spatially distinct areas encoding complex, multijoint movement sequences: elevate, advance, grasp, and retract. The topographical arrangement of complex movements during development and the influence of skilled learning are unknown. Here, we determined the emergence and topography of complex forelimb movement representations in rats between () and . We further investigated the expression of the maps for complex movements under conditions of reduced cortical inhibition and whether skilled forelimb motor training could alter their developing topography. We report that simple forelimb movements are first evoked at and are confined to the caudal forelimb area (CFA), whereas complex movements first reliably appear at and are observed in both the caudal and rostral forelimb areas (RFA). During development, the topography of complex movement representations undergoes reorganization with "grasp" and "elevate" movements predominantly observed in the RFA and all four complex movements observed in CFA. Under reduced cortical inhibition, simple and complex movements were first observed in the CFA on and , respectively, and the topography is altered relative to a saline control. Further, skilled motor learning was associated with increases in "grasp" and "retract" representations specific to the trained limb. Our results demonstrate that early-life motor experience during development can modify the topography of complex forelimb movement representations. The motor cortex is topographically organized into maps of different body parts. We used to think that the function of motor cortex was to drive individual muscles, but more recently we have learned that it is also organized to make complex movements. However, the development and plasticity of those complex movements is completely unknown. In this paper, the emergence and topography of complex movement representation, as well as their plasticity during development, is detailed.
Topics: Animals; Evoked Potentials, Motor; Forelimb; Male; Motor Cortex; Motor Skills; Neural Inhibition; Neurogenesis; Neuronal Plasticity; Rats; Rats, Long-Evans
PubMed: 33471611
DOI: 10.1152/jn.00531.2020 -
Brain Stimulation 2020Deep brain stimulation (DBS) is an effective treatment for movement disorders, yet its mechanisms of action remain unclear. One method used to study its circuit-wide...
BACKGROUND
Deep brain stimulation (DBS) is an effective treatment for movement disorders, yet its mechanisms of action remain unclear. One method used to study its circuit-wide neuromodulatory effects is functional magnetic resonance imaging (fMRI) which measures hemodynamics as a proxy of neural activity. To interpret functional imaging data, we must understand the relationship between neural and vascular responses, which has never been studied with the high frequencies used for DBS.
OBJECTIVE
To measure neurovascular coupling in the rat motor cortex during thalamic DBS.
METHOD
Simultaneous intrinsic optical imaging and extracellular electrophysiology was performed in the motor cortex of urethane-anesthetized rats during thalamic DBS at 7 different frequencies. We related Maximum Change in Reflectance (MCR) from the imaging data to Integrated Evoked Potential (IEP) and change in broadband power of multi-unit (MU) activity, computing Spearman's correlation to determine the strength of these relationships. To determine the source of these effects, we studied the contributions of antidromic versus orthodromic activation in motor cortex perfusion using synaptic blockers.
RESULTS
MCR, IEP and change in MU power increased linearly to 60 Hz and saturated at higher frequencies of stimulation. Blocking orthodromic transmission only reduced the DBS-induced change in optical signal by ∼25%, suggesting that activation of corticofugal fibers have a major contribution in thalamic-induced cortical activation.
CONCLUSION
DBS-evoked vascular response is related to both evoked field potentials as well as multi-unit activity.
Topics: Animals; Deep Brain Stimulation; Evoked Potentials; Magnetic Resonance Imaging; Male; Motor Cortex; Neurovascular Coupling; Rats; Rats, Sprague-Dawley; Thalamus
PubMed: 32289725
DOI: 10.1016/j.brs.2020.03.005 -
NeuroImage Oct 2018The relevance of human primary motor cortex (M1) for motor actions has long been established. However, it is still unknown how motor actions are represented, and whether...
The relevance of human primary motor cortex (M1) for motor actions has long been established. However, it is still unknown how motor actions are represented, and whether M1 contains an ordered somatotopy at the mesoscopic level. In the current study we show that a detailed within-limb somatotopy can be obtained in M1 during finger movements using Gaussian population Receptive Field (pRF) models. Similar organizations were also obtained for primary somatosensory cortex (S1), showing that individual finger representations are interconnected throughout sensorimotor cortex. The current study additionally estimates receptive field sizes of neuronal populations, showing differences between finger digit representations, between M1 and S1, and additionally between finger digit flexion and extension. Using the Gaussian pRF approach, the detailed somatotopic organization of M1 can be obtained including underlying characteristics, allowing for the in-depth investigation of cortical motor representation and sensorimotor integration.
Topics: Brain Mapping; Female; Fingers; Humans; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Male; Motor Cortex; Movement; Somatosensory Cortex; Young Adult
PubMed: 29940282
DOI: 10.1016/j.neuroimage.2018.06.062 -
Arthritis Research & Therapy Jun 2015The aim of this study was to investigate possible differences in the organisation of the motor cortex in people with knee osteoarthritis (OA) and whether there is an... (Comparative Study)
Comparative Study
INTRODUCTION
The aim of this study was to investigate possible differences in the organisation of the motor cortex in people with knee osteoarthritis (OA) and whether there is an association between cortical organisation and accuracy of a motor task.
METHODS
fMRI data were collected while 11 participants with moderate/severe right knee OA (6 male, 69 ± 6 (mean ± SD) years) and seven asymptomatic controls (5 male, 64 ± 6 years) performed three visually guided, variable force, force matching motor tasks involving isolated isometric muscle contractions of: 1) quadriceps (knee), 2) tibialis anterior (ankle) and, 3) finger/thumb flexor (hand) muscles. fMRI data were used to map the loci of peak activation in the motor cortex during the three tasks and to assess whether there were differences in the organisation of the motor cortex between the groups for the three motor tasks. Root mean square of the difference between target and generated forces during muscle contraction quantified task accuracy.
RESULTS
A 4.1 mm anterior shift in the representation of the knee (p = 0.03) and swap of the relative position of the knee and ankle representations in the motor cortex (p = 0.003) were found in people with knee OA. Poorer performance of the knee task was associated with more anterior placement of motor cortex loci in people with (p = 0.05) and without (p = 0.02) knee OA.
CONCLUSIONS
Differences in the organisation of the motor cortex in knee OA was demonstrated in relation to performance of knee and ankle motor tasks and was related to quality of performance of the knee motor task. These results highlight the possible mechanistic link between cortical changes and modified motor behavior in people with knee OA.
Topics: Aged; Female; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Motor Cortex; Osteoarthritis, Knee; Psychomotor Performance; Quadriceps Muscle
PubMed: 26080802
DOI: 10.1186/s13075-015-0676-4 -
Brain Research Reviews Oct 2007In this review we bring together three different lines of evidence to bear on the issue of local shaping of function in the motor cortex. The first line of evidence... (Review)
Review
In this review we bring together three different lines of evidence to bear on the issue of local shaping of function in the motor cortex. The first line of evidence comes from the description by Cajal (1904) of the recurrent collaterals of pyramidal cell axons in the precentral gyrus. The second line of evidence comes from the electrophysiological study of the functional effects of these collaterals [Stefanis, C., Jasper, H. 1964a. Intracellular microelectrode studies of antidromic responses in cortical pyramidal tract neurons. J. Neurophysiol. 27, 828-854.; Stefanis, C., Jasper, H. 1964b. Recurrent collateral inhibition in pyramidal tract neurons. J. Neurophysiol. 27, 855-877.] and associated interneurons [Stefanis, C. 1969. Interneuronal mechanisms in the cortex. In: The Interneuron, Brazier, M.A.B. (ed.), Berkeley, CA: University of California Press, pp. 497-526.] using intracellular recordings. And third came the discovery of directional tuning in the motor cortex [Georgopoulos, A.P., Kalaska, J.F., Caminiti, R., Massey, J.T. 1982. On the relations between the direction of two-dimensional arm movements and cell discharge in primate motor cortex. J. Neurosci. 2, 1527-1537.] in the behaving monkey. We hazard the hypothesis that the bell-shaped directional tuning curve is the outcome of orderly, local neuronal interactions in the motor cortex in which the recurrent pyramidal cell collaterals play a crucial role. Specifically, we propose that these collaterals and the intercalated interneurons they impinge upon serve to spatially sharpen the motor cortical activation to a locus corresponding to the direction of the intended movement. Thus, the originally proposed role of the pyramidal cell collaterals in enhancing "motor contrast" [Stefanis, C. 1969. Interneuronal mechanisms in the cortex. In: The Interneuron, Brazier, M.A.B. (ed.), Berkeley, CA: University of California Press, pp. 497-526.] would translate to creating a "directional tuning field" on the motor cortical surface, where the enhanced motor contrast would correspond to high activity at the center of directional field, and the suppression of the fringe would correspond to lower activity at the periphery of the field, resulting, together in spatial tuning.
Topics: Animals; Humans; Models, Neurological; Motor Cortex; Motor Neurons; Movement; Nerve Net; Orientation
PubMed: 17543390
DOI: 10.1016/j.brainresrev.2007.05.001 -
Physiological Reports Apr 2021Transcranial magnetic stimulation (TMS) motor mapping can characterize the neurophysiology of the motor system. Limitations including human error and the challenges of... (Randomized Controlled Trial)
Randomized Controlled Trial
INTRODUCTION
Transcranial magnetic stimulation (TMS) motor mapping can characterize the neurophysiology of the motor system. Limitations including human error and the challenges of pediatric populations may be overcome by emerging robotic systems. We aimed to show that neuronavigated robotic motor mapping in adolescents could efficiently produce discrete maps of individual upper extremity muscles, the characteristics of which would correlate with motor behavior.
METHODS
Typically developing adolescents (TDA) underwent neuronavigated robotic TMS mapping of bilateral motor cortex. Representative maps of first dorsal interosseous (FDI), abductor pollicis brevis (APB), and abductor digiti minimi (ADM) muscles in each hand were created. Map features including area (primary), volume, and center of gravity were analyzed across different excitability regions (R100%, R75%, R50%, R25%). Correlations between map metrics and validated tests of hand motor function (Purdue Pegboard Test as primary) were explored.
RESULTS
Twenty-four right-handed participants (range 12-18 years, median 15.5 years, 52% female) completed bilateral mapping and motor assessments with no serious adverse events or dropouts. Gender and age were associated with hand function and motor map characteristics. Full motor maps (R100%) for FDI did not correlate with motor function in either hand. Smaller excitability subset regions demonstrated reduced variance and dose-dependent correlations between primary map variables and motor function in the dominant hemisphere.
CONCLUSIONS
Hand function in TDA correlates with smaller subset excitability regions of robotic TMS motor map outcomes. Refined motor maps may have less variance and greater potential to quantify interventional neuroplasticity. Robotic TMS mapping is safe and feasible in adolescents.
Topics: Adolescent; Female; Functional Laterality; Hand; Humans; Magnetic Resonance Imaging; Male; Motor Cortex; Robotics
PubMed: 33817998
DOI: 10.14814/phy2.14801 -
Current Opinion in Neurobiology Feb 2011Dendritic spines are the postsynaptic sites of the majority of excitatory synapses in the mammalian central nervous system. The morphology and dynamics of dendritic... (Review)
Review
Dendritic spines are the postsynaptic sites of the majority of excitatory synapses in the mammalian central nervous system. The morphology and dynamics of dendritic spines change throughout the lifespan of animals, in response to novel experiences and neuropathologies. New spines form rapidly as animals learn new tasks or experience novel sensory stimulations. This is followed by a selective elimination of previously existing spines, leading to significant synaptic remodeling. In the brain damaged by injuries or neurological diseases, spines in surviving cortical regions turn over substantially, potentially forming new synaptic connections to adopt the function lost in the damaged region. These findings suggest that spine plasticity plays important roles in the formation and maintenance of a functional neural circuitry.
Topics: Animals; Dendritic Spines; Humans; Motor Cortex; Neuronal Plasticity
PubMed: 20728341
DOI: 10.1016/j.conb.2010.07.010 -
ELife Feb 2022The primary motor cortex (M1) is known to be a critical site for movement initiation and motor learning. Surprisingly, it has also been shown to possess reward-related...
The primary motor cortex (M1) is known to be a critical site for movement initiation and motor learning. Surprisingly, it has also been shown to possess reward-related activity, presumably to facilitate reward-based learning of new movements. However, whether reward-related signals are represented among different cell types in M1, and whether their response properties change after cue-reward conditioning remains unclear. Here, we performed longitudinal in vivo two-photon Ca imaging to monitor the activity of different neuronal cell types in M1 while mice engaged in a classical conditioning task. Our results demonstrate that most of the major neuronal cell types in M1 showed robust but differential responses to both the conditioned cue stimulus (CS) and reward, and their response properties undergo cell-type-specific modifications after associative learning. PV-INs' responses became more reliable to the CS, while VIP-INs' responses became more reliable to reward. Pyramidal neurons only showed robust responses to novel reward, and they habituated to it after associative learning. Lastly, SOM-INs' responses emerged and became more reliable to both the CS and reward after conditioning. These observations suggest that cue- and reward-related signals are preferentially represented among different neuronal cell types in M1, and the distinct modifications they undergo during associative learning could be essential in triggering different aspects of local circuit reorganization in M1 during reward-based motor skill learning.
Topics: Animals; Female; Learning; Male; Mice; Motor Cortex; Neurons
PubMed: 35113017
DOI: 10.7554/eLife.72549