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Neurobiology of Aging Oct 2022Effective connectivity between the cerebellum and primary motor cortex (M1) is critical for motor learning and motor control. Despite evidence of cerebellar atrophy and...
Effective connectivity between the cerebellum and primary motor cortex (M1) is critical for motor learning and motor control. Despite evidence of cerebellar atrophy and declines in motor learning and motor control with advanced age, recent behavioral studies indicate that cerebellar-dependent motor learning processes are preserved or even enhanced in older adults. However, physiological evidence of heightened cerebellar excitability leading to strengthened cerebellar-M1 connectivity with advanced age is lacking. Here, we used transcranial magnetic stimulation to assess age-related effects on cerebellar inhibition, a measure of cerebellar-M1 connectivity, in 20 young and 19 older adults. We observed stronger cerebellar inhibition in older compared with young adults. The behavioral implications of strengthened cerebellar inhibition with advanced age found in this study remain to be determined.
Topics: Aged; Cerebellum; Evoked Potentials, Motor; Humans; Learning; Motor Cortex; Transcranial Magnetic Stimulation
PubMed: 35810524
DOI: 10.1016/j.neurobiolaging.2022.04.016 -
Cerebral Cortex (New York, N.Y. : 1991) Jun 2022Deciphering the physiological patterns of motor network connectivity is a prerequisite to elucidate aberrant oscillatory transformations and elaborate robust...
Deciphering the physiological patterns of motor network connectivity is a prerequisite to elucidate aberrant oscillatory transformations and elaborate robust translational models of movement disorders. In the proposed translational approach, we studied the connectivity between premotor (PMC) and primary motor cortex (M1) by recording high-density electroencephalography in humans and between caudal (CFA) and rostral forelimb (RFA) areas by recording multi-site extracellular activity in mice to obtain spectral power, functional and effective connectivity. We identified a significantly higher spectral power in β- and γ-bands in M1compared to PMC and similarly in mice CFA layers (L) 2/3 and 5 compared to RFA. We found a strong functional β-band connectivity between PMC and M1 in humans and between CFA L6 and RFA L5 in mice. We observed that in both humans and mice the direction of information flow mediated by β- and γ-band oscillations was predominantly from PMC toward M1 and from RFA to CFA, respectively. Combining spectral power, functional and effective connectivity, we revealed clear similarities between human PMC-M1 connections and mice RFA-CFA network. We propose that reciprocal connectivity of mice RFA-CFA circuitry presents a suitable model for analysis of motor control and physiological PMC-M1 functioning or pathological transformations within this network.
Topics: Animals; Electroencephalography; Forelimb; Mice; Motor Cortex; Neural Pathways
PubMed: 34689188
DOI: 10.1093/cercor/bhab369 -
Nature Human Behaviour Apr 2024The most prominent characteristic of motor cortex is its activation during movement execution, but it is also active when we simply imagine movements in the absence of...
The most prominent characteristic of motor cortex is its activation during movement execution, but it is also active when we simply imagine movements in the absence of actual motor output. Despite decades of behavioural and imaging studies, it is unknown how the specific activity patterns and temporal dynamics in motor cortex during covert motor imagery relate to those during motor execution. Here we recorded intracortical activity from the motor cortex of two people who retain some residual wrist function following incomplete spinal cord injury as they performed both actual and imagined isometric wrist extensions. We found that we could decompose the population activity into three orthogonal subspaces, where one was similarly active during both action and imagery, and the others were active only during a single task type-action or imagery. Although they inhabited orthogonal neural dimensions, the action-unique and imagery-unique subspaces contained a strikingly similar set of dynamic features. Our results suggest that during motor imagery, motor cortex maintains the same overall population dynamics as during execution by reorienting the components related to motor output and/or feedback into a unique, output-null imagery subspace.
Topics: Humans; Motor Cortex; Imagination; Male; Spinal Cord Injuries; Adult; Movement; Female; Wrist; Motor Activity; Middle Aged; Psychomotor Performance
PubMed: 38287177
DOI: 10.1038/s41562-023-01804-5 -
Nature Communications Apr 2023Suppressing responses to distractor stimuli is a fundamental cognitive function, essential for performing goal-directed tasks. A common framework for the neuronal...
Suppressing responses to distractor stimuli is a fundamental cognitive function, essential for performing goal-directed tasks. A common framework for the neuronal implementation of distractor suppression is the attenuation of distractor stimuli from early sensory to higher-order processing. However, details of the localization and mechanisms of attenuation are poorly understood. We trained mice to selectively respond to target stimuli in one whisker field and ignore distractor stimuli in the opposite whisker field. During expert task performance, optogenetic inhibition of whisker motor cortex increased the overall tendency to respond and the detection of distractor whisker stimuli. Within sensory cortex, optogenetic inhibition of whisker motor cortex enhanced the propagation of distractor stimuli into target-preferring neurons. Single unit analyses revealed that whisker motor cortex (wMC) decorrelates target and distractor stimulus encoding in target-preferring primary somatosensory cortex (S1) neurons, which likely improves selective target stimulus detection by downstream readers. Moreover, we observed proactive top-down modulation from wMC to S1, through the differential activation of putative excitatory and inhibitory neurons before stimulus onset. Overall, our studies support a contribution of motor cortex to sensory selection, in suppressing behavioral responses to distractor stimuli by gating distractor stimulus propagation within sensory cortex.
Topics: Mice; Animals; Somatosensory Cortex; Motor Cortex; Parietal Lobe; Neurons; Vibrissae
PubMed: 37055425
DOI: 10.1038/s41467-023-37848-4 -
Brain Structure & Function Dec 2023The cortex contains multiple motor areas, including the primary motor cortex (M1) and supplementary motor area (SMA). Many muscles are represented in both the M1 and... (Review)
Review
The cortex contains multiple motor areas, including the primary motor cortex (M1) and supplementary motor area (SMA). Many muscles are represented in both the M1 and SMA, but the reason for this dual representation remains unclear. Previous work has shown that the M1 and SMA representations of a specific human muscle can be differentiated according to their functional connectivity with different brain areas located outside of the motor cortex. It is our perspective that this differential functional connectivity may be the neural substrate that allows an individual muscle to be accessed by distinct neural processes, such as those implementing volitional vs. postural task control. Here, we review existing human and animal literature suggesting how muscles are represented in the M1 and SMA and how these brain regions have distinct functions. We also discuss potential studies to further elucidate the distinct roles of the SMA and M1 in normal and dysfunctional motor control.
Topics: Animals; Humans; Motor Cortex; Muscles; Neural Pathways; Brain Mapping
PubMed: 37709903
DOI: 10.1007/s00429-023-02703-1 -
Proceedings of the National Academy of... Jun 2021Learning motor skills commonly requires repeated execution to achieve gains in performance. Motivated by memory reactivation frameworks predominantly originating from... (Clinical Trial)
Clinical Trial
Learning motor skills commonly requires repeated execution to achieve gains in performance. Motivated by memory reactivation frameworks predominantly originating from fear-conditioning studies in rodents, which have extended to humans, we asked the following: Could motor skill learning be achieved by brief memory reactivations? To address this question, we had participants encode a motor sequence task in an initial test session, followed by brief task reactivations of only 30 s each, conducted on separate days. Learning was evaluated in a final retest session. The results showed that these brief reactivations induced significant motor skill learning gains. Nevertheless, the efficacy of reactivations was not consistent but determined by the number of consecutive correct sequences tapped during memory reactivations. Highly continuous reactivations resulted in higher learning gains, similar to those induced by full extensive practice, while lower continuity reactivations resulted in minimal learning gains. These results were replicated in a new independent sample of subjects, suggesting that the quality of memory reactivation, reflected by its continuity, regulates the magnitude of learning gains. In addition, the change in noninvasive brain stimulation measurements of corticospinal excitability evoked by transcranial magnetic stimulation over primary motor cortex between pre- and postlearning correlated with retest and transfer performance. These results demonstrate a unique form of rapid motor skill learning and may have far-reaching implications, for example, in accelerating motor rehabilitation following neurological injuries.
Topics: Adolescent; Adult; Female; Humans; Learning; Male; Motor Cortex; Motor Skills; Transcranial Magnetic Stimulation
PubMed: 34088842
DOI: 10.1073/pnas.2102242118 -
Experimental Brain Research Aug 2020I-waves represent high-frequency (~ 600 Hz) repetitive discharge of corticospinal fibers elicited by single-pulse stimulation of motor cortex. First detected and...
I-waves represent high-frequency (~ 600 Hz) repetitive discharge of corticospinal fibers elicited by single-pulse stimulation of motor cortex. First detected and examined in animal preparations, this multiple discharge can also be recorded in humans from the corticospinal tract with epidural spinal electrodes. The exact underpinning neurophysiology of I-waves is still unclear, but there is converging evidence that they originate at the cortical level through synaptic input from specific excitatory interneuronal circuitries onto corticomotoneuronal cells, controlled by GABAAergic interneurons. In contrast, there is at present no supportive evidence for the alternative hypothesis that I-waves are generated by high-frequency oscillations of the membrane potential of corticomotoneuronal cells upon initial strong depolarization. Understanding I-wave physiology is essential for understanding how TMS activates the motor cortex.
Topics: Animals; Evoked Potentials, Motor; Humans; Interneurons; Membrane Potentials; Motor Cortex; Pyramidal Tracts; Transcranial Magnetic Stimulation
PubMed: 32185405
DOI: 10.1007/s00221-020-05764-4 -
ELife Sep 2022Neural plasticity allows us to learn skills and incorporate new experiences. What happens when our lived experiences fundamentally change, such as after a severe injury?...
Neural plasticity allows us to learn skills and incorporate new experiences. What happens when our lived experiences fundamentally change, such as after a severe injury? To address this question, we analyzed intracortical population activity in the posterior parietal cortex (PPC) of a tetraplegic adult as she controlled a virtual hand through a brain-computer interface (BCI). By attempting to move her fingers, she could accurately drive the corresponding virtual fingers. Neural activity during finger movements exhibited robust representational structure similar to fMRI recordings of able-bodied individuals' motor cortex, which is known to reflect able-bodied usage patterns. The finger representational structure was consistent throughout multiple sessions, even though the structure contributed to BCI decoding errors. Within individual BCI movements, the representational structure was dynamic, first resembling muscle activation patterns and then resembling the anticipated sensory consequences. Our results reveal that motor representations in PPC reflect able-bodied motor usage patterns even after paralysis, and BCIs can re-engage these stable representations to restore lost motor functions.
Topics: Adult; Brain-Computer Interfaces; Female; Fingers; Humans; Magnetic Resonance Imaging; Motor Cortex; Movement; Paralysis
PubMed: 36125116
DOI: 10.7554/eLife.74478 -
Nature Reviews. Neuroscience Apr 2024The study of the cortical control of movement experienced a conceptual shift over recent decades, as the basic currency of understanding shifted from single-neuron... (Review)
Review
The study of the cortical control of movement experienced a conceptual shift over recent decades, as the basic currency of understanding shifted from single-neuron tuning towards population-level factors and their dynamics. This transition was informed by a maturing understanding of recurrent networks, where mechanism is often characterized in terms of population-level factors. By estimating factors from data, experimenters could test network-inspired hypotheses. Central to such hypotheses are 'output-null' factors that do not directly drive motor outputs yet are essential to the overall computation. In this Review, we highlight how the hypothesis of output-null factors was motivated by the venerable observation that motor-cortex neurons are active during movement preparation, well before movement begins. We discuss how output-null factors then became similarly central to understanding neural activity during movement. We discuss how this conceptual framework provided key analysis tools, making it possible for experimenters to address long-standing questions regarding motor control. We highlight an intriguing trend: as experimental and theoretical discoveries accumulate, the range of computational roles hypothesized to be subserved by output-null factors continues to expand.
Topics: Humans; Motor Cortex; Movement; Neurons
PubMed: 38443626
DOI: 10.1038/s41583-024-00796-z -
Journal of Motor Behavior 2021The predominant role of the primary motor cortex (M1) in motor execution is well acknowledged. However, additional roles of M1 are getting evident in humans owing to... (Review)
Review
The predominant role of the primary motor cortex (M1) in motor execution is well acknowledged. However, additional roles of M1 are getting evident in humans owing to advances in noninvasive brain stimulation (NIBS) techniques. This review collates such studies in humans and proposes that M1 also plays a key role in higher cognitive processes. The review commences with the studies that have investigated the nature of connectivity of M1 with other cortical regions in light of studies based on NIBS. The review then moves on to discuss the studies that have demonstrated the role of M1 in higher cognitive processes such as attention, motor learning, motor consolidation, movement inhibition, somatomotor response, and movement imagery. Overall, the purpose of the review is to highlight the additional role of M1 in motor cognition besides motor control, which remains unexplored.
Topics: Attention; Cognition; Humans; Learning; Motor Cortex; Movement; Transcranial Magnetic Stimulation
PubMed: 32194004
DOI: 10.1080/00222895.2020.1738992