Arm movements in monkeys: behavior and neurophysiology
A simulated actuator driven by motor cortical signals
Intercepting real and path-guided apparent motion targets
permalinkExperimental Brain Research - 1996-07-01Port NL, Pellizzer G, Georgopoulos AP10.1007/BF00228560Human subjects were instructed to intercept with a cursor real and apparent motion targets presented on a computer screen. Targets traveled counterclockwise (CCW) in a circle at one of five angular velocities (180, 300, 420, 480 and 540 deg/s), either smoothly (real motion) or in path-guided apparent motion. Subjects operated a computer mouse and were instructed to intercept targets at the 12 o'clock position; there were no constraints on when to initiate the response, which was a movement from the center of the screen towards and past 12 o'clock. We found the following: (a) for both motion conditions and all target velocities, subjects were late in intercepting the target, especially at higher target velocities; (b) for both motion conditions, the directional variability of the response increased as a linear function of the target velocity; (c) the directional variability of the response was systematically higher for the apparent than the real motion...
On the relations between single cell activity in the motor cortex and the direction and magnitude of three-dimensional static isometric force
permalinkExperimental Brain Research - 1996-06-01Taira M, Boline J, Smyrnis N, Georgopoulos AP, Ashe J10.1007/BF00229620We examined the relations between the steady-state frequency of discharge of cells in the arm area of the motor cortex of the monkey and the direction and magnitude of the three-dimensional static force exerted by the arm on an isometric manipulandum. Data were analyzed from two monkeys (n=188 cells) using stepwise multiple linear regression. In 154 of 188 (81.9%) cells the regression model was statistically significant (P<0.05). In 121 of 154 (78.6%) cells the direction but not the magnitude of force had a statistically significant effect on cell activity; in 11 of 154 (7.1%) cells only the magnitude effect was significant; and in 22 of 154 (14.3%) cells both the direction and magnitude effects were significant. The same analysis was used to assess the effect of the direction and magnitude of force on the electromyographic activity of 9 muscles of the arm and shoulder girdle. The regression model was statistically significant....
Neural computations underlying the exertion of force: a model
permalinkBiological Cybernetics - 1996-05-01Lukashin A, Amirikian B, Georgopoulos AP10.1007/BF00206713We have developed a model that simulates possible mechanisms by which supraspinal neuronal signals coding forces could converge in the spinal cord and provide an ongoing integrated signal to the motoneuronal pools whose activation results in the exertion of force. The model consists of a three-layered neural network connected to a two-joint-six-muscle model of the arm. The network layers represent supraspinal populations, spinal cord interneurons, and motoneuronal pools. We propose an approach to train the network so that, after the synaptic connections between the layers are adjusted, the performance of the model is consistent with experimental data obtained on different organisms using different experimental paradigms: the stiffness characteristics of human arm; the structure of force fields generated by the stimulation of the frog's spinal cord; and a correlation between motor cortical activity and force exerted by monkey against an immovable object. The model predicts a specific pattern of connections between supraspinal...
Modeling of directional operations in the motor cortex: A noisy network of spiking neurons is trained to generate a neural-vector trajectory
permalinkNeural Networks - 1996-04-01Lukashin A, Wilcox GL, Georgopoulos AP10.1016/0893-6080(95)00138-7A fully connected network of spiking neurons modeling motor cortical directional operations is presented and analyzed. The model allows for the basic biological requirements stemming from the results of experimental studies. The dynamical evolution of the network's output is interpreted as the sequential generation of neuronal population vectors representing the combined directional tendency of the ensemble. Adding these population vectors tip-to-tail yields the neural-vector trajectory that describes the upcoming movement trajectory. The key point of the model is that the intra-network interactions provide sustained dynamics, whereas external inputs are only required to initiate the population. The network is trained to generate neural-vector trajectories corresponding to basic types of two-dimensional movements (the network with specified connections can store one trajectory). A simple modification of the simulated annealing algorithm enables training of the network in the presence of noise. Training in the presence of noise yields robustness of the learned dynamical behaviors. Another...
Visuo-manual Aiming Movements in 6- to 10-Year-Old Children: Evidence for an Asymmetric and Asynchronous Development of Information Processes
On the translation of directional motor cortical commands to activation of muscles via spinal interneuronal systems
Modeling motor cortical operations by an attractor network of stochastic neurons
permalinkBiological Cybernetics - 1996-03-01Lukashin A, Amirikian B, Mozhaev VL, Wilcox GL, Georgopoulos AP10.1007/BF00652226Understanding the neural computations performed by the motor cortex requires biologically plausible models that account for cell discharge patterns revealed by neurophysiological recordings. In the present study the motor cortical activity underlying movement generation is modeled as the dynamic evolution of a large fully recurrent network of stochastic spiking neurons with noise superimposed on the synaptic transmission. We show that neural representations of the learned movement trajectories can be stored in the connectivity matrix in such a way that, when activated, a particular trajectory evolves in time as a dynamic attractor of the system while individual neurons fire irregularly with large variability in their interspike intervals. Moreover, the encoding of trajectories as attractors ensures high stability of the ensemble dynamics in the presence of synaptic noise. In agreement with neurophysiological findings, the suggested model can provide a wide repertoire of specific motor behaviors, whereas the number of specialized cells and specific...
Quantitative relations between parietal activation and performance in mental rotation
Changing the intended direction of movement
Assessment of Posttraumatic Stress Disorder in World War II Veterans
permalinkPsychological Assessment - 1996-01-01Engdahl B, Eberly RE, Blake JD10.1037/1040-35126.96.36.1995Four
Posttraumatic Stress Disorderscales were compared in a community sample of 330 American former prisoners of war and combat veterans of World War II. The Mississippi Scale for Combat-Related
PTSD), the Minnesota Multiphasic Personality Inventory-2 Pk
PTSDscale, and the Impact of Event Scale (IES) all demonstrated moderate relationships with
PTSDas defined by the Structured Clinical Interview for DSM-III-R. Comparative validities were similar to those observed in Vietnam veteran samples. Confirmatory factor analysis indicated that the 3 scales loaded significantly on 1 factor. The impact of Diagnostic and Statistical Manual of Mental Disorders (4th ed.)
PTSDcriteria changes was examined and found to be minimal. Implications for the use of the M-
PTSD, Pk, and IES in combat-related
PTSDassessment are discussed.
The mental and the neural: Psychological and neural studies of mental rotation and memory scanning
System for projection of a three-dimensional, moving virtual target for studies of eye-hand coordination
permalinkJournal of Neuroscience Methods - 1995-11-01Schneider W, Harris TJ, Feldberg IE, Massey JT, Georgopoulos AP, Meyer RA10.1016/0165-0270(95)00068-2Eye-hand tracking of moving visual objects in three-dimensional (3D) space is common in the behavioral repertoire of primates. However, behavioral and/or neurophysiological studies of this function are lacking mainly because devices do not exist that allow its investigation. We describe a device by which a spot of light can be presented in the immediate extrapersonal space of a subject and can be moved in various trajectories in 3D space. The target is a real image of a circular aperture produced by a system consisting of a light source, aperture, filters, several lenses and fold mirros, and a large concave mirror to focus the final real image. Rapid, computer-controlled movement of the image is obtained by tilting a gimbal-mounted guide mirror (for x and y motion) and by translating a lens (for motion in the z direction). A second configuration of the system allows movement of a 3D image in the 3D...
Current issues in directional motor control
Colon cancer: Personality factors predictive of onset and stage of presentation
permalinkJournal of Psychosomatic Research - 1995-11-01Kavan MG, Engdahl B, Kay S10.1016/0022-3999(95)00523-4This study examined premorbid personality correlates of colon cancer and stage of presentation of colon cancer to health care providers. Sixty-one male veterans who completed the MMPI between 1947 and 1975 and were then diagnosed with colon cancer between 1977 and 1988 were matched with control patients. A 21-factor solution of the MMPI  was used to seek potential personality differences between colon cancer cases and their controls in terms of presence of colon cancer and stage of presentation for this disease. A stepwise conditional regression analysis found significant differences between the colon cancer and control groups on the Aggressive Hostility variable (p<0.018). A multivariate analysis of variance conducted across the stages of colon cancer presentation found that patients who presented later on for colon cancer had higher Phobia scores (p<0.05). Religious Fundamentalism who also related to presentation (p<0.05), but in a nonlinear manner. Discussion is related to previous findings regarding...
Motor cortical activity in a context-recall task
Motor cortex and cognitive processing
Image and Brain: The Resolution of the Imagery Debate
Population activity in the control of movement