Motor planning: effect of directional uncertainty with continuous spatial cues

Experimental Brain Research - 2004-01-01Pellizzer G, Hedges J10.1007/s00221-003-1669-0
We have investigated the effect of directional uncertainty on the planning of reaching movements. For this purpose, we have used sections of annuli as spatial cues to indicate the directional range within which the target would be presented. The results showed that the reaction time of the reaching response increased with cue range and with the angle between the center of the cue and the target. In addition, the initial direction of movement was biased toward the center of the cue. These results conformed to the predictions of the capacity-sharing model. This model assumes that the processing resources used for motor planning are limited and distributed as a function of the range of directions indicated by the cue, and that when the target appears, these resources are reallocated to represent the response to be executed.

Cerebellar Activation During Copying Geometrical Shapes

Journal of Neurophysiology - 2003-12-01Lewis S, Jerde T, Tzagarakis C, Georgopoulos MA, Tsekos N, Amirikian B, Kim SG, Ugurbil K, Georgopoulos AP10.1152/jn.00009.2003
We studied functional MRI activation in the cerebellum during copying 9 geometrical shapes (equilateral triangle, isosceles triangle, square, diamond, vertical trapezoid, pentagon, hexagon, circle, and vertical lemniscate). Twenty subjects were imaged during 3 consecutive 45-s periods (rest, visual presentation, and copying). First, there was a positive relation between cerebellar activation and the peak speed of individual movements. This effect was strongest in the lateral and posterior ipsilateral cerebellum but it was also present in the paramedian zones of both cerebellar hemispheres and in the vermis. A finer grain analysis of the relations between the time course of the blood oxygenation level-dependent activation and movement parameters revealed a significant relation to hand position and speed but not to acceleration. Second, there was a significant relation between the intensity of voxel activation during visual presentation and the speed of the upcoming movement. The spatial distribution of these voxels was very similar to that...

Modular organization of directionally tuned cells in the motor cortex: Is there a short-range order?

Proceedings of the National Academy of Sciences of the United States of America - 2003-10-14Amirikian B, Georgopoulos AP10.1073/pnas.2037719100
We investigated the presence of short-range order (>600 μm) in the directional properties of neurons in the motor cortex of the monkey. For that purpose, we developed a quantitative method for the detection of functional cortical modules and used it to examine such potential modules formed by directionally tuned cells. In the functional domain, we labeled each cell by its preferred direction (PD) vector in 3D movement space; in the spatial domain, we used the position of the tip of the recording microelectrode as the cell's coordinate. The images produced by this method represented two orthogonal dimensions in the cortex; one was parallel ("horizontal") and the other perpendicular ("vertical") to the cortical layers. The distribution of directionally tuned cells in these dimensions was nonuniform and highly structured. Specifically, cells with similar PDs tended to segregate into vertically oriented minicolumns 50-100 μm wide and at least 500 μm high. Such minicolumns aggregated...

Interception of real and apparent motion targets: psychophysics in humans and monkeys

Human subjects and monkeys intercepted real (RM) and apparent (AM) moving targets that traveled through a low contrast circular path. The subjects intercepted the targets at 6 o'clock by applying a net force pulse on a semi-isometric joystick which controlled a cursor on the screen. Eight target speeds (180-560°/s) were used. The starting points of the moving target were systematically placed around the circle in order to determine the effect of the target travel time and velocity on the decision to initiate the interception movement and on the interception accuracy. It was found that the probability of interception in the first revolution varied as a function of the target travel time, which followed an S-shaped psychometric curve. The minimum processing time (MPT) was defined as the target travel that corresponded to a 75% probability of interception in the first revolution on the psychometric curve. The MPT decreased slightly as a function...

Functional Organization of Parietal Neuronal Responses to Optic-Flow Stimuli

We analyzed the dissimilarity matrix of neuronal responses to moving visual stimuli using tree clustering and multidimensional scaling (MDS). Single-cell activity was recorded in area 7a while random dots moving coherently in eight different kinds of motion (right-, left-, up-, and downward, clockwise, counterclockwise, expansion, contraction) were presented to behaving monkeys with eyes fixated. Tree clustering analyses showed that the {rightward, leftward}, {upward, downward}, and {clockwise, counterclockwise]} motions were clustered in three separate branches (i.e., horizontal, vertical, and rotatory motion, respectively). In contrast, expansion was in a lone branch, whereas contraction was also separate but within a larger cluster. The distances among these clusters were then subjected to an MDS analysis to identify the dimensions underlying the tree clustering observed. This analysis revealed two major factors in operation. The first factor separated expansion from all other stimulus motions, which seems to reflect the prominence of expansion during the common activity of...

The internal structure of the phenomenology of auditory verbal hallucinations

Schizophrenia Research - 2003-06-01Stephane M, Thuras P, Nasrallah H, Georgopoulos AP10.1016/S0920-9964(03)00013-6
Background: Auditory verbal hallucinations (AVH) do not have uniform pathological significance. They affect patients with different brain disorders, and vary along multiple phenomenological dimensions. Evidence indicates that some of the phenomenological variables have specific neural substrates. Therefore, a comprehensive characterization of the phenomenological variations of AVH and the interrelationship between these variables was undertaken. Method: Twenty phenomenological variables were identified; on each AVH had a binary value (present or absent). Information about 11 of these variables were obtained from 30 patients. Hierarchical cluster (HC) and multidimensional scaling (MDS) analyses were performed to investigate the hidden structure and dimensions of these variables. Results: HC yielded two main clusters with further sub-clusters in each. The first cluster included hallucinations with low linguistic complexity, repetitive content, attributed to self, located in outer space, and associated with different kinds of control strategies. The second cluster included hallucinations with high linguistic complexity, systematized content, multiple voices,...

Motor planning: effect of directional uncertainty with discrete spatial cues

Experimental Brain Research - 2003-06-01Pellizzer G10.1007/s00221-003-1453-1
We investigated the effect of spatial uncertainty on motor planning by using the cueing method in a reaching task (experiment 1). Discrete spatial cues indicated the different locations in which the target could be presented. The number of cues as well as their direction changed from trial to trial. We tested the adequacy of two models of motor planning to account for the data. The switching model assumes that only one motor response can be planned at a time, whereas the capacity-sharing model assumes that multiple motor responses can be planned in parallel. Both models predict the same relation between average reaction time (RT) and number of cues, but they differ in their prediction of the shape of the distribution of the reaction time. The results showed that RT increased with the number of cues independently from their spatial dispersion. This relation was well described by the function predicted by both...

Neural activity in prefrontal cortex during copying geometrical shapes II. Decoding shape segments from neural ensembles

We trained two monkeys to draw copies of geometrical shapes (e.g. squares, triangles) using a joystick, and found that several variables describing the arm trajectories were encoded in the activity of individual prefrontal neurons (Averbeck et al. 2003). Copy trajectories were drawn as sequences of segments, identified by the serial order in which they were drawn and the shape that they together produced. Here we use linear discriminant analysis to test how well the segments of copied shapes could be decoded from the neural activity patterns of small ensembles (3-22 neurons) of simultaneously recorded cells in prefrontal cortex. Using this analysis, the proper segment (drawn by the monkey) was correctly decoded from the ensemble activity pattern during the drawing of that segment in 60-80% of the cases when the largest ensembles were considered. The information transmitted by these ensembles, as well as by single neurons, was also calculated. We found that...

Neural activity in prefrontal cortex during copying geometrical shapes I. Single cells encode shape, sequence and metric parameters

In drawing a copy of a geometrical shape, a sequence of movements must be produced to represent the sides of the object in the proper spatial relationship. We investigated neural mechanisms of this process by training monkeys to draw (using a joystick) copies of geometrical shapes (triangles, squares, trapezoids and inverted triangles) presented on a video monitor while recording single cell activity in prefrontal cortex. The drawing trajectories monkeys produced were divided into a series of discrete segments, varying in direction and length. We performed a stepwise multiple linear regression analysis to identify those copy parameters significantly influencing cell activity. The copied shape (e.g., triangle, square) and the serial position of the segment within each trajectory were the most prevalent effects (in 46% and 43% of cells, respectively), followed by segment direction (32%) and length (16%). Effects of temporal factors (maximum segment speed and time to maximum segment speed) were less...

Neural Mechanisms of Catching: Translating Moving Target Information into Hand Interception Movement

Taking Action: Cognitive Neuroscience Perspectives on Intentional Acts - 2003-01-01Kruse W, Port NL, Lee D, Georgopoulos AP
The neural mechanisms underlying the visuomotor coordination of arm movements have been intensely investigated over the past 20-odd years (Georgopoulos, 1990; Kalaska and Crarnmond, 1992; Caminiti et al., 1996; Schwartz, 1994b). Most of the tasks used have involved movement of the arm toward stationary targets. Because the visual information about the target in such tasks is static, consisting simply of the target's location in space, the key corresponding movement parameters are the direction and amplitude of the movement. In real life, however, the visual target may change location, involving a dynamic aspect of visuomotor coordination.Previous studies addressed this issue partially by shifting the target location at various times during the reaction or movement time (Georgopoulos et al., 1981, 1983). With respect to monkey behavior, it was found that the hand moved first toward the first target for a period of time and then changed direction to move toward the second target....

Cognitive motor control: spatial and temporal aspects

Current Opinion in Neurobiology - 2002-12-01Georgopoulos AP10.1016/S0959-4388(02)00382-3
Cognitive motor control refers to processes that blend cognitive and motor functions in a seamless, interwoven fashion. Such functions evolve in space and time at various levels of complexity. This article focuses on conceptual issues regarding spatial and temporal aspects of motor control as well as on methods suitable for extracting information from neuronal ensembles.

Parallel processing of serial movements in prefrontal cortex

Proceedings of the National Academy of Sciences of the United States of America - 2002-10-01Averbeck B, Chafee M, Crowe D, Georgopoulos AP10.1073/pnas.162485599
A key idea in Lashley's formulation of the problem of serial order in behavior is the postulated neural representation of all serial elements before the action begins. We studied this question by recording the activity of individual neurons simultaneously in small ensembles in prefrontal cortex while monkeys copied geometrical shapes shown on a screen. Monkeys drew the shapes as sequences of movement segments, and these segments were associated with distinct patterns of neuronal ensemble activity. Here we show that these patterns were present during the time preceding the actual drawing. The rank of the strength of representation of a segment in the neuronal population during this time, as assessed by discriminant analysis, predicted the serial position of the segment in the motor sequence. An analysis of errors in copying and their neural correlates supplied additional evidence for this code and provided a neural basis for Lashley's hypothesis that errors in motor...

Analysis of
Functional Magnetic Resonance Imaging

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.
and finger tracking training in subjects with chronic stroke

Journal of Neurology - 2002-04-01Carey JR, Kimberley TJ, Lewis S, Auerbach EJ, Dorsey L, Rundquist P, Ugurbil K10.1093/brain/awf091
Hand movement recovery and cortical reorganization were studied in 10 subjects with chronic stroke using functional MRI (
Functional Magnetic Resonance Imaging

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.
) before and after training with an intensive finger movement tracking programme. Subjects were assigned randomly to a treatment or control group. The treatment group received 18-20 sessions of finger tracking training using target waveforms under variable conditions. The control group crossed over to receive the same treatment after the control period. For comparison with a healthy population, nine well elderly females were also studied; however, the well elderly controls did not cross over after the control period. The dependent variables consisted of a Box and Block score to measure prehensile ability (subjects with stroke only), a tracking accuracy score and quantification of active cortical areas using
fMRI

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.
. For the tracking tests, the subjects tracked a sine wave target on a computer screen with extension and flexion movements of the paretic index finger. Functional...

Impact of path parameters on maze solution time

Archives Italiennes de Biologie - 2002-01-01Chafee M, Averbeck B, Crowe D, Georgopoulos AP10.4449/aib.v140i3.473
In order to compare spatial attention and visual processing capabilities of humans and rhesus macaques, we developed a visual maze task both could perform. Maze stimuli were constructed of orthogonal line segments displayed on a monitor. Each was octagonal in outline and contained a central square (the 'start box'). A single ('main') path, containing a random number of turns, extended outward from the start box, and either reached an exit in the maze's perimeter, or a blind ending within the maze. Subjects maintained ocular fixation within the start box, and indicated their judgment whether the path reached an exit or not by depressing one of two keys (humans) or foot pedals (monkeys). Successful maze solution by human subjects required a minimum viewing time. Replacing the maze with a masking stimulus after a variable interval revealed that the percent correct performance increased systematically with greater viewing time, reaching a plateau of approximately...

Behavioral and neural aspects of motor topology: following Bernstein's thread

Progress in Motor Control: Structure-function relations in voluntary movements - 2002-01-01Georgopoulos AP
In his article "The Problem of the Interrelation of Co-ordination and Lateralization," Bernstein (1935) drew attention to invariance in the shape of drawings made under very different conditions, such as using different effectors or different combinations of muscles and joints. He called these invariances "topological" and contrasted them with other "metric" aspects of movement, such as size and location in space. He then speculated on the brain representation of motor topology, as follows:
There is the deeply seated inherent indifference of the motor control centre to the scale and position of the movement effected. ... it is clear that each of the variations of a movement (for example, drawing a circle large or small...) demands a quite different muscular formula; and even more than this, involves a completely different set of muscles in the action. The almost equal facility and accuracy with which all these variations can be performed is evidence...

Effects of Optic Flow in Motor Cortex and Area 7a

Moving visual stimuli were presented to behaving monkeys who fixated their eyes and did not move their arm. The stimuli consisted of random dots moving coherently in eight different kinds of motion (right, left, up, downward, expansion, contraction, clockwise, and counterclockwise) and were presented in 25 square patches on a liquid crystal display projection screen. Neuronal activity in the arm area of the motor cortex and area 7a was significantly influenced by the visual stimulation, as assessed using an ANOVA. The percentage of cells with a statistically significant effect of visual stimulation was 3 times greater in area 7a (370/587, 63%) than in motor cortex (148/693, 21.4%). With respect to stimulus properties, its location and kind of motion had differential effects on cell activity in the two areas. Specifically, the percentage of cells with a significant stimulus location effect was ∼2.5 times higher in area 7a (311/370, 84%) than in motor...

Guiding contact by coupling the taus of gaps

Experimental Brain Research - 2001-07-01Lee D, Georgopoulos AP, Clark MJO, Craig CM, Port NL10.1007/s002210100725
Animals control contact with surfaces when locomoting, catching prey, etc. This requires sensorily guiding the rate of closure of gaps between effectors such as the hands, feet or jaws and destinations such as a ball, the ground and a prey. Control is generally rapid, reliable and robust, even with small nervous systems: the sensorimotor processes are therefore probably rather simple. We tested a hypothesis, based on general τ theory, that closing two gaps simultaneously, as required in many actions, might be achieved simply by keeping the taus of the gaps coupled in constant ratio. τ of a changing gap is defined as the time-to-closure of the gap at the current closure-rate. General τ theory shows that τ of a gap could, in principle, be directly sensed without needing to sense either the gap size or its rate of closure. In our experiment, subjects moved an effector (computer cursor) to a destination...

Neuronal Clusters in the Primate Motor Cortex during Interceptin of Moving Targets

Journal of Cognitive Neuroscience - 2001-04-01Lee D, Port NL, Kruse W, Georgopoulos AP10.1162/08989290151137377
Two rhesus monkeys were trained to intercept a moving target at a fixed location with a feedback cursor controlled bya 2-D manipulandum. The direction from which the target appeared, the time from the target onset to its arrival at the interception point, and the target acceleration were randomized for each trial, thus requiring the animal to adjust its movement according to the visual input on a trail-by-trail basis. The two animals adopted different strategies, similar to those identified previously in human subjects. Single-cell activity was recorded from the arm area of the primary motor cortex in these two animals, and the neurons were classified based on the temporal patterns in their activity, using a nonhierarchical cluster analysis. Results of this analysis revealed differences in the complexity and diversity of motor cortical activity between the two animals that paralleled those of behavioral strategies. Most clusters displayed activity closedly related to the kinematics...

Motor Cortical Activity during Interception of Moving Targets

Journal of Cognitive Neuroscience - 2001-04-01Port NL, Kruse W, Lee D, Georgopoulos AP10.1162/08989290151137368
The single-unit activity of 831 cells was recorded in the arm area of the motor cortex of tow monkeys while the monkeys intercepted a moving visual stimulus (interception task) or remained immobile during presentation of the same moving stimulus (no-go task). The moving target traveled on an oblique path from either lower corner of a screen toward the vertical meridian, and its movement time (0.5,1.0, or 1.5 sec) and velocity profile (accelerating, decelerating, or constant velocity) were pseudorandomly varied. The moving target had to be intercepted within 130 msec of target arrival at an interception point. By comparing motor cortical activity at the single-neuron tasks, we tested whether information about parameters of moving target is represented in the primary motor cortex to generate appropriate motor responses. A substantial number of neurons displayed modulation of their activity during the no-go task, and this activity was often affected by the stimulus parameters. These...

Functional Magnetic Resonance Imaging

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.
of Visual Object Construction and Shape Discrimination: Relations among Task, Hemispheric Lateralization, and Gender

Journal of Cognitive Neuroscience - 2001-01-01Georgopoulos AP, Whang K, Georgopoulos MA, Tagaris GA, Amirikian B, Richter W, Kim SG, Ugurbil K10.1162/089892901564180
We studied the brain activation patterns in two visual image processing tasks requiring judgements on object construction (FIT task) or object sameness (SAME task). Eight right-handed healthy human subjects (four women and four men) performed the two tasks in a randomized block design while 5-mm, multislice functional images of the whole brain were acquired using a 4-tesla system using blood oxygenation dependent (BOLD) activation. Pairs of objects were picked randomly from a set of 25 oriented fragments of a square and presented to the subjects approximately every 5 sec. In the FIT task, subjects had to indicate, by pushing one of two buttons, whether the two fragments could match to form a perfect square, whereas in the SAME task they had to decide whether they were the same or not. In a control task, preceding and following each of the two tasks above, a single square was presented at the same...

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