Behavioral neurophysiology of the motor cortex
permalinkJournal of Laboratory and Clinical Medicine - 1994-12-01Georgopoulos AP
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...read more
Movement Parameters and Neural Activity in Motor Cortex and Area 5
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Overlapping neural networks for multiple motor engrams
permalinkProceedings of the National Academy of Sciences - 1994-08-30Lukashin A, Wilcox GL, Georgopoulos AP10.1073/pnas.91.18.8651
The hypothesis was tested that learned movement trajectories of different shapes can be stored in, and generated by, largely overlapping neural networks. Indeed, it was possible to train a massively interconnected neural network to generate different shapes of internally stored, dynamically evolving movement trajectories using a general-purpose core part, common to all networks, and a special-purpose part, specific for a particular trajectory. The weights of connections between the core units do not carry any information about trajectories. The core network alone could generate externally instructed trajectories but not internally stored ones, for which both the core and the trajectory-specific part were needed. All information about the movements is stored in the weights of connections between the core part and the specialized units and between the specialized units themselves. Due to these connections the core part reveals specific dynamical behavior for a particular trajectory and, as the result, discriminates different tasks. The...read more
New concepts in generation of movement
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Directional operations in the motor cortex modeled by a neural network of spiking neurons
Measuring Synaptic Interactions
Representations of movement and representations in movement
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A Neural Network for Coding of Trajectories by Time Series of Neuronal Population Vectors
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Mechanisms of Eye-Hand Coordination
permalinkDefense Technical Information Center - 1993-11-29Georgopoulos AP
We studied the capacities of human subjects to localize tactile stimuli in 3D space. For that purpose, five subjects (3 women and 2 men) were asked to make a pointing movement to a visual stimulus in otherwise complete darkness. At some random time before, during or after this initial movement, a tactile probe was presented to the tip of the subject's index finger. The probe (1-mm diameter, 0.75-mm extent, 5-ms duration) was applied by a lightweight (80 g) tactile stimulator worn on the subject's hand. To complete the task, the subject was required to point to the 3D spatial location at which the probe was applied. Hand position was monitored (200 Hz) by a video-based motion analysis system. In each subject, probes presented just before or during the initial movement were systematically mislocalized in the direction of that movement so that subjects perceived the probe to be at the location occupied...read more
A dynamical neural network model for motor cortical activity during movement: population coding of movement trajectories
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Motor cortical activity preceding a memorized movement trajectory with an orthogonal bend
permalinkExperimental Brain Research - 1993-07-01Ashe J, Taira M, Smyrnis N, Pellizzer G, Georgakopoulos T, Lurito JT, Georgopoulos AP10.1007/BF00229661
Two monkeys were trained to make an arm movement with an orthogonal bend, first up and then to the left (◹), following a waiting period. They held a two-dimensional manipulandum over a spot of light at the center of a planar working surface. When this light went off, the animals were required to hold the manipulandum there for 600-700 ms and then move the handle up and to the left to receive a liquid reward. There were no external signals concerning the "go" time or the trajectory of the movement. It was hypothesized that during that period signs of directional processing relating to the upcoming movement would be identified in the motor cortex. Following 20 trials of the memorized movement trajectory, 40 trials of visually triggered movements in radially arranged directions were performed. The activity of 137 single cells in the motor cortex was recorded extracellularly during performance of the task....read more
Functional Magnetic Resonance ImagingFunctional Magnetic Resonance Imaging (fMRI)
A functional neuroimaging procedure using MRI technology that measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases.[citation needed] The primary form of fMRI uses the blood-oxygen-level dependent (BOLD) contrast, discovered by Seiji Ogawa. This is a type of specialized brain and body scan used to map neural activity in the brain or spinal cord of humans or other animals by imaging the change in blood flow (hemodynamic response) related to energy use by brain cells. Since the early 1990s, fMRI has come to dominate brain mapping research because it does not require people to undergo shots, surgery, or to ingest substances, or be exposed to ionising radiation, etc. of motor cortex: hemispheric asymmetry and handedness
Functional Magnetic Resonance Imaging (fMRI)
A functional neuroimaging procedure using MRI technology that measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases.[citation needed] The primary form of fMRI uses the blood-oxygen-level dependent (BOLD) contrast, discovered by Seiji Ogawa. This is a type of specialized brain and body scan used to map neural activity in the brain or spinal cord of humans or other animals by imaging the change in blood flow (hemodynamic response) related to energy use by brain cells. Since the early 1990s, fMRI has come to dominate brain mapping research because it does not require people to undergo shots, surgery, or to ingest substances, or be exposed to ionising radiation, etc.permalinkScience - 1993-07-01Kim SG, Ashe J, Hendrich K, Ellermann JM, Merkle H, Ugurbil K, Georgopoulos AP10.1126/science.8342027
A hemispheric asymmetry in the functional activation of the human motor cortex during contralateral (C) and ipsilateral (I) finger movements, especially in right-handed subjects, was documented with nuclear magnetic resonance imaging at high field strength (4 tesla). Whereas the right motor cortex was activated mostly during contralateral finger movements in both right-handed (C/I mean area of activation = 36.8) and left-handed (C/I = 29.9) subjects, the left motor cortex was activated substantially during ipsilateral movements in left-handed subjects (C/I = 5.4) and even more so in right-handed subjects (C/I = 1.3).Spatiotemporal motor processing
permalinkAnnals of the New york Academy of Sciences - 1993-06-01Ashe J, Georgopoulos AP10.1111/j.1749-6632.1993.tb22968.x
Many studies of motor function deal with essentially static aspects of motor control; for example, the representation of motor output in maps, the encoding of motor parameters in the discharge of single cells, and the effect of behavioral context on neuronal activity. These questions do not encompass time as a crucial variable. However, actual motor performance always evolves in time. Moreover, daily activities, from eat to playing, depend critically on efficient processing of sensorimotor information. The devastating effect of a general slowness of this processing can be seen in patients with Parkinson's disease, who, without medication, are quite incapacitated in practically all everyday activities. In this paper we focus on the spatiotemporal processing of sensory-motor information in the motor cortex and the basal ganglia within the context of simple motor acts, such as movements to a target, as well as in more complicated tasks, such as mental rotation. Moreover, we treat...read more
Cortical cell types from spike trains
Structural models of captivity trauma, resilience, and trauma response among former prisoners of war 20 to 40 years after release
permalinkSocial Psychiatry and Psychiatric Epidemiology - 1993-05-01Engdahl B, Harkness AR, Eberly RE, Page WF, Bielinkski J10.1007/BF00801740
Long-term responses to captivity trauma were measured in a national sample of American former prisoners of war. Their responses included negative affect, positive affect, and somatic symptoms as assessed by the Cornell Medical Index in 1967 and the Center for Epidemiological Study Depression Scale in 1985. These responses were strongly associated with captivity trauma (as indexed by captivity weight loss, torture, and disease) and resilience (as indexed by age and education at capture). Symptoms reported in 1967 were related to symptoms reported in 1985, suggesting symptom stability. These results are consistent with a model of trauma response that incorporates both trauma exposure and individual resilience. The findings are interpreted within a theoretical view of trauma response as adaptive when viewed from an evolutionary perspective.Cognitive neurophysiology of the motor cortex.
Mental rotation of the intended direction of movement
permalinkCurrent Directions in Psychological Science - 1993-02-01Pellizzer G, Georgopoulos AP10.1111/1467-8721.ep10770546
Reviews studies of mental rotation (MR), neural coding of the direction of movement, and neural activity during a mental transformation of the intended direction of movement. In a study of similarities between MR of the direction of movement and mental images, the authors (in press) compared the performances of human Ss in a visuomotor MR and a visual MR task. The processing rates (PRs) in both tasks were correlated, but neither rate correlated significantly with the PR in a visuomotor memory scanning task. These results suggest that visuomotor and visual Magnetic Resonance Spectroscopy
possess common processing constraints that could not be ascribed to general PR performances. (PsycINFO Database Record (c) 2016 APA, all rights reserved)Magnetic Resonance Spectroscopy (MRS)
Used to roughly assess neuron health. Typically, we consider the ratios of N-acetyl aspartate, glutamine+glutamate, and choline over creatine.Common processing constraints for visuomotor and visual mental rotations
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Functional imaging of human motor cortex at high magnetic field
permalinkJournal of Neurophysiology - 1993-01-01Kim SG, Ashe J, Georgopoulos AP, Merkle H, Ellermann JM, Menon RS, Ogawa S, Ugurbil K10.1152/jn.1993.69.1.297
1. We used conventional gradient echo magnetic resonance imaging (MRI) at high field strength (4 Tesla) to functionally image the right motor cortex in six normal human subjects during the performance of a sequence of self-paced thumb to digit oppositions with the left hand (contralateral task), the right hand (ipsilateral task), and both hands (bilateral task). 2. A localized increase in activity in the lateral motor cortex was observed in all subjects during the task. The area of activation was similar in the contralateral and bilateral tasks but 20 times smaller in the ipsilateral task. The intensity of activation was 2.3 times greater in the contralateral than the ipsilateral task.Cortical Representation of Intended Movements
permalinkNeuroscience: From Neural Networks to Artificial Intelligence - 1993-01-01Georgopoulos AP10.1007/978-3-642-78102-5_24
The neural representation of reaching movements in the motor cortex of the monkey is discussed with respect to the coding of the direction of movement in the activity of single cells and neuronal populations. This code is then used to monitor the processing of directional information in various contexts involving delayed movements or directional transformations. Finally, some implications of these findings for the role of the motor cortex in planning and execution of reaching movements are discussed.Pages:
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