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Trends in Neurosciences Dec 2013The agranular architecture of motor cortex lacks a functional interpretation. Here, we consider a 'predictive coding' account of this unique feature based on asymmetries... (Review)
Review
The agranular architecture of motor cortex lacks a functional interpretation. Here, we consider a 'predictive coding' account of this unique feature based on asymmetries in hierarchical cortical connections. In sensory cortex, layer 4 (the granular layer) is the target of ascending pathways. We theorise that the operation of predictive coding in the motor system (a process termed 'active inference') provides a principled rationale for the apparent recession of the ascending pathway in motor cortex. The extension of this theory to interlaminar circuitry also accounts for a sub-class of 'mirror neuron' in motor cortex--whose activity is suppressed when observing an action--explaining how predictive coding can gate hierarchical processing to switch between perception and action.
Topics: Animals; Humans; Models, Neurological; Motor Activity; Motor Cortex; Nerve Net; Neural Pathways; Neurons; Perception
PubMed: 24157198
DOI: 10.1016/j.tins.2013.09.004 -
Annual Review of Neuroscience 2006Motor cortex in the primate brain was once thought to contain a simple map of the body's muscles. Recent evidence suggests, however, that it operates at a radically more... (Review)
Review
Motor cortex in the primate brain was once thought to contain a simple map of the body's muscles. Recent evidence suggests, however, that it operates at a radically more complex level, coordinating behaviorally useful actions. Specific subregions of motor cortex may emphasize different ethologically relevant categories of behavior, such as interactions between the hand and the mouth, reaching motions, or defensive maneuvers to protect the body surface from impending impact. Single neurons in motor cortex may contribute to these behaviors by means of their broad tuning to idiosyncratic, multijoint actions. The mapping from cortex to muscles is not fixed, as was once thought, but instead is fluid, changing continuously on the basis of feedback in a manner that could support the control of higher-order movement parameters. These findings suggest that the motor cortex participates directly in organizing and controlling the animal's behavioral repertoire.
Topics: Animals; Behavior; Brain Mapping; Humans; Motor Cortex; Motor Neurons; Movement
PubMed: 16776581
DOI: 10.1146/annurev.neuro.29.051605.112924 -
Journal of Neuroscience Research Feb 2006The excitability of the motor cortex is a function of single cell excitability, synaptic strength, and the balance between excitatory cells and inhibitory cells.... (Review)
Review
The excitability of the motor cortex is a function of single cell excitability, synaptic strength, and the balance between excitatory cells and inhibitory cells. Sustained periods of sensory stimulation enhance the excitability in the motor cortex. This adaptation, which represents an early change in cortical network function effective in motor learning and recovery from a motor deficit, is followed by longer-lasting changes, such as modifications in cortical somatotopy, and by structural plasticity. Interventions aiming at increasing excitability also positively affect learning processes. Recent studies highlight that the cerebellum, especially the interpositus nucleus, plays a key function in the adaptation of the motor cortex to repeated trains of peripheral stimulation. Interpositus neurons, which receive inputs from the sensorimotor cortex and the spinal cord, are involved in somesthetic reflex behaviors and assist the cerebral cortex in transforming sensory signals to motor-oriented commands by acting via the cerebello-thalamo-cortical projections. Moreover, climbing fibers originating in the inferior olivary complex and innervating the nucleus interpositus mediate highly integrated sensorimotor information derived from spinal modules. The intermediate cerebellum allows the motor cortex to tune the gain of polysynaptic responses originating from the spinal cord after repetitive trains of peripheral stimulation, allowing an online calibration of cutaneo-muscular responses.
Topics: Adaptation, Physiological; Animals; Cerebellum; Humans; Motor Cortex; Neuronal Plasticity; Neurons
PubMed: 16385580
DOI: 10.1002/jnr.20733 -
Philosophical Transactions of the Royal... Apr 2005The agranular cortex is an important landmark-anatomically, as the architectural flag of mammalian motor cortex, and historically, as a spur to the development of... (Review)
Review
The agranular cortex is an important landmark-anatomically, as the architectural flag of mammalian motor cortex, and historically, as a spur to the development of theories of localization of function. But why, exactly, do agranularity and motor function go together? To address this question, it should be noted that not only does motor cortex lack granular layer four, it also has a relatively thinner layer three. Therefore, it is the two layers which principally constitute the ascending pathways through the sensory (granular) cortex that have regressed in motor cortex: simply stated, motor cortex does not engage in serial reprocessing of incoming sensory data. But why should a granular architecture not be demanded by the downstream relay of motor instructions through the motor cortex? The scant anatomical evidence available regarding laminar patterns suggests that the pathways from frontal and premotor areas to the primary motor cortex actually bear a greater resemblance to the descending, or feedback connections of sensory cortex that avoid the granular layer. The action of feedback connections is generally described as "modulatory" at a cellular level, or "selective" in terms of systems analysis. By contrast, ascending connections may be labelled "driving" or "instructive". Where the motor cortex uses driving inputs, they are most readily identified as sensory signals instructing the visual location of targets and the kinaesthetic state of the body. Visual signals may activate motor concepts, e.g. "mirror neurons", and the motor plan must select the appropriate muscles and forces to put the plan into action, if the decision to move is taken. This, perhaps, is why "driving" motor signals might be inappropriate-the optimal selection and its execution are conditional upon both kinaesthetic and motivational factors. The argument, summarized above, is constructed in honour of Korbinian Brodmann's centenary, and follows two of the fundamental principles of his school of thought: that uniformities in cortical structure, and development imply global conservation of some aspects of function, whereas regional variations in architecture can be used to chart the "organs" of the cortex, and perhaps to understand their functional differences.
Topics: Brain Mapping; Feedback, Physiological; Humans; Models, Neurological; Motor Cortex; Neural Pathways; Visual Cortex
PubMed: 15937013
DOI: 10.1098/rstb.2005.1630 -
Frontiers in Neural Circuits 2013The brain has to analyze and respond to external events that can change rapidly from time to time, suggesting that information processing by the brain may be essentially... (Review)
Review
The brain has to analyze and respond to external events that can change rapidly from time to time, suggesting that information processing by the brain may be essentially dynamic rather than static. The dynamical features of neural computation are of significant importance in motor cortex that governs the process of movement generation and learning. In this paper, we discuss these features based primarily on our recent findings on neural dynamics and information coding in the microcircuit of rat motor cortex. In fact, cortical neurons show a variety of dynamical behavior from rhythmic activity in various frequency bands to highly irregular spike firing. Of particular interest are the similarity and dissimilarity of the neuronal response properties in different layers of motor cortex. By conducting electrophysiological recordings in slice preparation, we report the phase response curves (PRCs) of neurons in different cortical layers to demonstrate their layer-dependent synchronization properties. We then study how motor cortex recruits task-related neurons in different layers for voluntary arm movements by simultaneous juxtacellular and multiunit recordings from behaving rats. The results suggest an interesting difference in the spectrum of functional activity between the superficial and deep layers. Furthermore, the task-related activities recorded from various layers exhibited power law distributions of inter-spike intervals (ISIs), in contrast to a general belief that ISIs obey Poisson or Gamma distributions in cortical neurons. We present a theoretical argument that this power law of in vivo neurons may represent the maximization of the entropy of firing rate with limited energy consumption of spike generation. Though further studies are required to fully clarify the functional implications of this coding principle, it may shed new light on information representations by neurons and circuits in motor cortex.
Topics: Action Potentials; Animals; Humans; Motor Cortex; Movement; Nerve Net; Neurons
PubMed: 23653596
DOI: 10.3389/fncir.2013.00085 -
Neuron Apr 2003In this issue of Neuron, Jackson and colleagues describe a functional correlate of neural synchrony related to movement control. Synchrony strength in... (Review)
Review
In this issue of Neuron, Jackson and colleagues describe a functional correlate of neural synchrony related to movement control. Synchrony strength in cortico-motoneuronal output neurons in primary motor cortex depended upon similarity of these neurons' connectivity pattern with the spinal cord. These results could form the foundation for subsequent investigations of motor binding.
Topics: Animals; Motor Cortex; Motor Neurons; Spinal Cord
PubMed: 12691657
DOI: 10.1016/s0896-6273(03)00203-4 -
The Journal of Laboratory and Clinical... Dec 1994The study of the motor cortex in behaving monkeys during the past 20 years has provided important information on the brain mechanisms underlying motor control. With... (Review)
Review
The study of the motor cortex in behaving monkeys during the past 20 years has provided important information on the brain mechanisms underlying motor control. With respect to reaching movements in space, several aspects of motor cortical function concerning the specification of the direction of movement have now been elucidated and are reviewed in this article. The activity of single cells in the motor cortex is broadly tuned with respect to the direction of reaching, so that the discharge rate is highest with movements in a preferred direction and decreases progressively with movements made in directions more and more away from the preferred one. Thus the neural command for the direction of reaching can be regarded as an ensemble of cell vectors, with each vector pointing in the cell's preferred direction and having a length proportional to the change in cell activity. The outcome of this population code can be visualized as a vector that points in the direction of the upcoming movement during the reaction time, during an instructed delay period, and during a memorized delay period. Moreover, when a mental transformation is required for the generation of a reaching movement in a different direction from a reference direction, the population vector provides a direct insight into the nature of the cognitive process by which the required transformation is achieved.
Topics: Animals; Behavior, Animal; Cognition; Hand; Motor Cortex; Neurons; Psychomotor Performance
PubMed: 7798788
DOI: No ID Found -
Trends in Neurosciences May 2015The stratified motor cortex is variously thought to either lack or contain layer 4. Yamawaki et al. described a functional layer 4 in mouse motor cortex with properties...
The stratified motor cortex is variously thought to either lack or contain layer 4. Yamawaki et al. described a functional layer 4 in mouse motor cortex with properties and connections similar to layer 4 in sensory areas. Their results bolster a theoretical framework suggesting all primary cortical areas are equivalent.
Topics: Animals; Humans; Motor Cortex
PubMed: 25868984
DOI: 10.1016/j.tins.2015.03.005 -
Advances in Anatomy, Embryology, and... 2004When we voluntarily interact with our environment, the agranular frontal cortex (Brodmann's areas 4 and 6) plays a pivotal role in cortical motor control. The primary... (Review)
Review
When we voluntarily interact with our environment, the agranular frontal cortex (Brodmann's areas 4 and 6) plays a pivotal role in cortical motor control. The primary motor cortex (area 4) influences kinematic and dynamic parameters of movements, whereas the rostrally adjoining nonprimary motor cortex (area 6) uses external (e.g., sensory) or internal cues to trigger and guide movements. Once thought to be homogeneous, data from nonhuman primates have shown that area 6 is a mosaic of areas, each with distinct structural and functional properties: the supplementary motor areas "SMA proper" and "pre-SMA" on the mesial cortical surface, and the dorso- and ventrolateral premotor cortex on the cortical convexity. Dorso- and ventrolateral premotor areas are specifically connected with posterior parietal areas. These parieto-frontal circuits work in parallel and tranform different aspects of sensory information into appropriate motor commands. The rostral border of area 6 is very important for functional neuroimaging studies in humans since it separates the "motor domain" of the supplementary motor/premotor cortex from the "cognitive domain" of the prefrontal cortex. Can the topography of this border be inferred from the gyral pattern of the frontal lobe? To answer this, ten postmorterm brains were scanned with a T1-weighted magnetic resonance sequence. The brains were serially sectioned at 20 micro M and area 6 was defined by subjective and objective cytoarchitectonic analysis. Each brain's histological volume (with the representation of area 6) was reconstructed in 3-D and spatially normalized to the reference brain of a computerized atlas. The ten normalized volumes were superimposed and a population map was generated that describes, for each voxel, how many brains have a representation of area 6. On the mesial coetical surface, the rostral border of area 6 lies rostral to the anterior commissure-- though the distance varies across different brains. On the lateral convexity, the border recedes in a caudal direction-- again to a varying degree in different brains-- and lies on the precentral gyrus close to the sylvian fissure. No macroanatomical landmark indicates the border between area 6 and the prefrontal cortex. The question whether a motor task engages only the "motor domain" of the supplementary motor/premotor cortex or in addition the "cognitive domain" of the prefrontal cortex can only be answered by superimposing the functional activation map with the microstructural population map of area 6.
Topics: Animals; Brain Mapping; Cognition; Humans; Motor Cortex; Movement
PubMed: 14750415
DOI: 10.1007/978-3-642-18910-4 -
Scientific Reports Oct 2022Spontaneous brain activity, measured with resting state fMRI (R-fMRI), is correlated among regions that are co-activated by behavioral tasks. It is unclear, however,...
Spontaneous brain activity, measured with resting state fMRI (R-fMRI), is correlated among regions that are co-activated by behavioral tasks. It is unclear, however, whether spatial patterns of spontaneous activity within a cortical region correspond to spatial patterns of activity evoked by specific stimuli, actions, or mental states. The current study investigated the hypothesis that spontaneous activity in motor cortex represents motor patterns commonly occurring in daily life. To test this hypothesis 15 healthy participants were scanned while performing four different hand movements. Three movements (Grip, Extend, Pinch) were ecological involving grip and grasp hand movements; one control movement involving the rotation of the wrist was not ecological and infrequent (Shake). They were also scanned at rest before and after the execution of the motor tasks (resting-state scans). Using the task data, we identified movement-specific patterns in the primary motor cortex. These task-defined patterns were compared to resting-state patterns in the same motor region. We also performed a control analysis within the primary visual cortex. We found that spontaneous activity patterns in the primary motor cortex were more like task patterns for ecological than control movements. In contrast, there was no difference between ecological and control hand movements in the primary visual area. These findings provide evidence that spontaneous activity in human motor cortex forms fine-scale, patterned representations associated with behaviors that frequently occur in daily life.
Topics: Brain Mapping; Hand; Humans; Magnetic Resonance Imaging; Motor Cortex; Movement; Psychomotor Performance
PubMed: 36207360
DOI: 10.1038/s41598-022-20866-5