Biomedical subjects

J F Kalaska

Publications and source records attributed to J F Kalaska.

At least 19 recordsLinked to original sources

PubMed2000

Covariation of primate dorsal premotor cell activity with direction and amplitude during a memorized-delay reaching task.

Extensive behavioral evidence suggests that the direction and amplitude of reaching movements are planned as two independent parameters by the motor system. However, whereas direction-related activity has been well documented by neurophysiological studies in many motor structures including the dorsal premotor cortex (PMd), there is much less concensus about the prominence and timing of amplitude-related premotor activity. We studied this issue using an instructed-delay task in which prior information about target location (direction and distance) must be memorized before movement initiation. The results show that prior information about distance is reflected in PMd activity during the delay period well before movement initiation, and begins to be expressed as early as 150 ms after presentation of target location. The prominence of neural correlates with direction is relatively constant throughout the trial, but distance correlates become gradually more prominent with time, both during and after the delay period. A small majority of cells were modulated only by direction during the delay period, but very few were modulated only by distance, and most of the rest were modulated by both. Therefore PMd neurons usually process information about distance only in conjunction with directional information. These results do not support a separate neuronal substrate for distance in PMd, but do not preclude its existence elsewhere. The results also support a progressive change in the nature of the movement-related representation in PMd with time in an instructed-delay paradigm.

Analysis of Variance↗

PubMed2000

Prior information in motor and premotor cortex: activity during the delay period and effect on pre-movement activity.

In instructed-delay (ID) tasks, instructional cues provide prior information about the nature of a movement to execute after a delay. Neuronal responses in dorsal premotor cortex (PMd) during the instructed-delay period (IDP) between the CUE and subsequent GO signals are presumed to reflect early planning stages initiated by the prior information. In contrast, in multiple-choice reaction-time (RT) tasks, all motor planning and execution processes must occur after the GO signal. These assumptions predict that neuronal planning correlates recorded during the IDP of ID trials should share common features with early post-GO activity in RT trials, and that those response components need not be recapitulated after the GO signal of ID trials. These two predictions were tested by comparing activity recorded in RT and ID tasks from 503 neurons in PMd and caudal (MIc) and rostral (MIr) primary motor cortex. The incidence and strength of directionally tuned IDP activity declined progressively from PMd to MIc. The directional tuning of activity during the IDP of ID trials was more similar to that in the reaction-time epoch (RTE) of RT trials than after movement onset, especially in PMd. A modulation of post-GO activity was often observed between RT and ID trials and was confined mainly to the RTE. This effect was also most prominent in PMd. The most common change was a reduction in intensity of short-latency phasic responses to the GO signal between RT and ID trials, especially in PMd cells with a short-latency phasic response to CUE signals. However, the largest group of cells in each area showed no large change in peak RTE activity between RT and ID trials, whether they were active in the IDP or not. Since early phasic CUE-related responses are least likely to be recapitulated after the GO signal in ID trials, they may be a neuronal correlate of an early planning stage such as response selection. Tonic IDP responses, which are not as strongly associated with a post-GO reduction in activity, may be related to other aspects of motor planning and preparation. Finally, a major component of the movement-related activity in both MI and PMd is not susceptible to modification by prior information and is indivisibly coupled temporally to movement execution.

Analysis of Variance↗

PubMed1999

Comparison of variability of initial kinematics and endpoints of reaching movements.

The accuracy of reaching movements to memorized visual target locations is presumed to be determined largely by central planning processes before movement onset. If so, then the initial kinematics of a pointing movement should predict its endpoint. Our study examined this hypothesis by testing the correlation between peak acceleration, peak velocity, and movement amplitude and the correspondence between the respective spatial positions of these kinematic landmarks. Subjects made planar horizontal reaching movements to targets located at five different distances and along five radially arrayed directions without visual feedback during the movements. The spatial dispersion of the positions of peak acceleration, peak velocity, and endpoint all tended to form ellipses oriented along the movement trajectory. However, whereas the peaks of acceleration and velocity scaled strongly with movement amplitude for all of the movements made at the five target distances in any one direction, the correlations with movement amplitude were more modest for trajectories aimed at each target separately. Furthermore, the spatial variability in direction and extent of the distribution of positions of peak acceleration and peak velocity did not scale differently with target distance, whereas they did for endpoint distributions. Therefore, certain features of the final kinematics are evident in the early kinematics of the movements as predicted by the hypothesis that they reflect planning processes. However, endpoint distributions were not completely predetermined by the Initial kinematics. In contrast, multivariate analysis suggests that adjustments to movement duration help compensate for the variability of the initial kinematics to achieve desired movement amplitude. These compensatory adjustments do not contradict the general conclusion that the systematic patterns in the spatial variability observed in this study reflect planning processes. On the contrary, and consistent with that conclusion, our results provide further evidence that direction and extent of reaching movements are planned and determined in parallel over time.

Adult↗

PubMed1998

Cortical control of whole-arm motor tasks.

Making an arbitrary motor response to a sensory signal would appear to require at least two sequential steps--planning the appropriate response and generating a motor command to implement it. However, neuronal correlates of these two putative steps do not occur in strict serial order, nor are they subserved by separate cortical regions. Instead, they are distributed in a continuous, overlapping and non-uniform manner across the cerebral cortex, including primary motor, premotor and parietal regions. These processes take the form of temporal and spatial gradients of cell activity that are distributed within and across cortical regions. Instead of two serial steps, these neuronal events may be better described in terms of two parallel functions--action specification and action selection. These processes occur continuously, both before and during movement. Recent studies show that the activity of single cells in the caudal part of the primary motor cortex is strongly modulated by arm geometry and by task dynamics during whole-arm isometric and reaching tasks. This indicates that these cells contribute to the transformation between neural representations of the global attributes of motor actions and of the mechanical details of their implementation.

Arm↗

PubMed1998

Changes in the temporal pattern of primary motor cortex activity in a directional isometric force versus limb movement task.

We recorded the activity of 75 proximal-arm-related cells in caudal primary motor cortex (MI) while a monkey generated either isometric forces or limb movements against an inertial load. The forces and movements were in eight directions in a horizontal plane. The isometric force generated at the hand increased monotonically in the direction of the target force level. The force exerted against the load in the movement task was more complex, including a transient decelerative phase during the movement as the hand approached the target. Electromyographic (EMG) activity of proximal-arm muscles reflected the task-dependent changes in dynamics, showing a ramp increase in activity during the isometric task and a reciprocal triphasic burst pattern in the movement task. A sliding 50-ms window analysis showed that the directionality of the EMG, when expressed in hand-centered spatial coordinates, remained stable throughout the isometric ramp but often showed a significant transient shift during the limb movements. Many cells in M1 showed corresponding significant changes in activity pattern and instantaneous directionality between the two tasks. This momentary dissociation of discharge from the directional kinematics of hand displacement is evidence that the activity of many single proximal-arm related M1 cells is not coupled only to the direction and velocity of hand motion.

Animals↗

PubMed1997

Differential effect of task conditions on errors of direction and extent of reaching movements.

Invariant patterns in the distribution of the endpoints of reaching movements have been used to suggest that two important movement parameters of reaching movements, direction and extent, are planned by two independent processing channels. This study examined this hypothesis by testing the effect of task conditions on variable errors of direction and extent of reaching movements. Subjects made reaching movements to 25 target locations in a horizontal workspace, in two main task conditions. In task 1, subjects looked directly at the target location on the horizontal workspace before closing their eyes and pointing to it. In task 2, arm movements were made to the same target locations in the same horizontal workspace, but target location was displayed on a vertical screen in front of the subjects. For both tasks, variable errors of movement extent (on-axis error) were greater than for movement direction (off-axis error). As a result, the spatial distributions of endpoints about a given target usually formed an ellipse, with the principal axis oriented in the mean movement direction. Also, both on- and off-axis errors increased with movement amplitude. However, the magnitude of errors, especially on-axis errors, scaled differently with movement amplitude in the two task conditions. This suggests that variable errors of direction and extent can be modified independently by changing the nature of the sensorimotor transformations required to plan the movements. This finding is further evidence that the direction and extent of reaching movements appear to be controlled independently by the motor system.

Adult↗

PubMed1997

Cortical control of reaching movements.

Recent studies provide further support for the hypothesis that spatial representations of limb position, target locations, and potential motor actions are expressed in the neuronal activity in parietal cortex. In contrast, precentral cortical activity more strongly expresses processes involved in the selection and execution of motor actions. As a general conceptual framework, these processes may be interpreted in terms of such formalisms as sensorimotor transformations and 'internal models'.

Animals↗

PubMed1997

Reaching movements with similar hand paths but different arm orientations. I. Activity of individual cells in motor cortex.

This study shows that the discharge of many motor cortical cells is strongly influenced by attributes of movement related to the geometry and mechanics of the arm and not only by spatial attributes of the hand trajectory. The activity of 619 directionally tuned cells was recorded from the motor cortex of two monkeys during reaching movements with the use of similar hand paths but two different arm orientations, in the natural parasagittal plane and abducted into the horizontal plane. Nearly all cells (588 of 619, 95%) showed statistically significant changes in activity between the two arm orientations [analysis of variance (ANOVA). P < 0.01]. A majority of cells showed a significant change in their overall level of activity (ANOVA, main effect of task, P < 0.01) between arm orientations before, during, and after movement. Many cells (433 of 619, 70%) also showed a significant change in the relation of their discharge with movement direction (ANOVA, task x direction interaction term, P < 0.01) during movement, including changes in the dynamic range of discharge with movement and changes in the directional preference of cells that were directionally tuned in both arm orientations. Similar effects were seen for the discharge of cells while the monkey maintained constant arm postures over the different peripheral targets with the use of different arm orientations. Repeated data files from the same cell with the use of the same arm orientation showed only small changes in the level of discharge or in directional tuning, suggesting that changes in cell discharge between arm orientations cannot be explained by random temporal variations in cell activity. The distribution of movement-related preferred directions of the whole sample differed between arm orientations, and also differed strongly between cells receiving passive input predominantly from the shoulder or elbow. The electromyographic activity of most prime mover muscles at the shoulder and elbow was also strongly affected by arm orientation, resulting in changes in overall level of activity and/or directional tuning that often resembled those of the proximal arm-related motor cortical cells. A mathematical model that represented movements in terms of movement direction centered on the hand could not account for any of the arm-orientation-related response changes seen in this task, whereas models in intrinsic parameter spaces of joint kinematics and joint torques predicted many of the effects.

Analysis of Variance↗

PubMed1997

Systematic changes in directional tuning of motor cortex cell activity with hand location in the workspace during generation of static isometric forces in constant spatial directions.

We examined the activity of 46 proximal-arm-related cells in the primary motor cortex (MI) during a task in which a monkey uses the arm to exert isometric forces at the hand in constant spatial directions while the hand is in one of nine different spatial locations on a plane. The discharge rate of all 46 cells was significantly affected by both hand location and by the direction of static force during the final static-force phase of the task. In addition, all cells showed a significant interaction between force direction and hand location. That is, there was a significant modulation in the relationship between cell activity and the direction of exerted force as a function of hand location. For many cells, this modulation was expressed in part as a systematic arclike shift in the cell's directional tuning at the different hand locations, even though the direction of static force output at the hand remained constant. These effects of hand location in the workspace indicate that the discharge of single MI cells does not covary exclusively with the level and direction of force output at the hand. Sixteen proximal-arm-related muscles showed similar effects in the task, reflecting their dependence on various mechanical factors that varied with hand location. The parallel changes found for both MI cell activity and muscle activity for static force production at different hand locations are further evidence that MI contributes to the transformation between extrinsic and intrinsic representations of limb movement.

Analysis of Variance↗

PubMed1997

Reaching movements with similar hand paths but different arm orientations. II. Activity of individual cells in dorsal premotor cortex and parietal area 5.

Reaching movements with similar hand paths but different arm orientations. II. Activity of individual cells in dorsal premotor cortex and parietal area 5. J. Neurophysiol. 78: 2413-2426, 1997. Neuronal activity in primary motor cortex (MI) is altered when monkeys make reaching movements along similar handpaths at shoulder level with two different arm orientations, either in the natural orientation with the elbow positioned below the level of the shoulder and hand or in an abducted orientation with the elbow abducted nearly to shoulder level. The present study examines to what degree two other cortical areas, the dorsal premotor (PMd) and parietal area 5, also show modulation of cell activity related to arm geometry during reaching. The activity of most (89%) of the 207 cells in PMd recorded while monkeys made reaching movements showed a statistically significant change in activity between orientations [analysis of variation (ANOVA), P < 0.01]. A common effect of arm orientation on cell activity was a change in the overall level of discharge either before, during, and/or after movement (67%, ANOVA, task main effect, P < 0.01). Many cells (76%) showed a statistical change in their response to movement direction (ANOVA, task x direction interaction term, P < 0.01), including changes in dynamic range and changes in the preferred direction of cells that were directionally tuned in both arm orientations. Overall, these effects were similar qualitatively but not as strong quantitatively as those observed in MI. A sample of cells was recorded in area 5 of one monkey. Most (95%) of the 79 area 5 cells showed a change in activity when reaching movements were performed using different arm orientations (ANOVA, P < 0.01). As in PMd and MI, many area 5 cells (56, 71%) showed changes in their tonic discharge before, during, and/or after movement, and 70 cells (89%) showed changes in their response to movement direction (ANOVA, task x direction interaction term, P < 0.01). The observed changes in neuronal activity related to posture and movement in MI, PMd and area 5 demonstrate that single-cell activity in these cortical areas is not simply related to the spatial attributes of hand trajectory but is also strongly influenced by attributes of movement related to arm geometry.

Analysis of Variance↗

PubMed1996

Differential relation of discharge in primary motor cortex and premotor cortex to movements versus actively maintained postures during a reaching task.

The activity of cells in primary motor cortex (MI) and dorsal premotor cortex (PMd) were compared during reaching movements in a reaction-time (RT) task, without prior instructions, which required precise control of limb posture before and after movement. MI neurons typically showed strong, directionally tuned activity prior to and during movement as well as large gradations of tonic activity while holding the limb over different targets. The directionality of their movement- and posture-related activity was generally similar. Proximal-arm muscles behaved similarly. This is consistent with a role for MI in the moment-to-moment control of motor output, including both movement and actively maintained postures, and suggests a common functional relation for MI cells to both aspects of motor behavior. In contrast, PMd cells were generally more phasic, frequently emitting only strong bursts of activity confined mainly to the behavioral reaction time before movement onset. PMd tonic activity during different postures was generally weaker than in MI, and showed a much more variable relation with their movement-related directional tuning. These results imply that the major contribution of PMd to this RT task occurred prior to the onset of movement itself, consistent with a role for PMd in the selection and planning of visually guided movements. Furthermore, the nature of the relative contribution of PMd to movement versus actively maintained postures appears to be fundamentally different from that in MI. Finally, there was a continuous gradient of changes in responses across the rostrocaudal extent of the precentral gyrus, with no abrupt transition in response properties between PMd and MI.

Animals↗

PubMed1996

Parietal cortex area 5 and visuomotor behavior.

For years, area 5 of the parietal cortex was thought to be a somatic sensory structure. This view was challenged by recordings during active movements in alert behaving monkeys, which suggested that area 5 also contained populations of neurons that issued nonspecific, context-dependent "commands" about intended motor responses. Recent studies have revealed that area 5 generates a representation of the spatiotemporal form of arm movements and arm postures, although the parameter space of that representation is still controversial. They also showed that many area 5 cells are recipient to centrally generated signals about the motor relevance of external sensory signals. These new results support the hypothesis that area 5 contributes to the sensorimotor guidance of motor behavior, by contributing to the somatomotor and visuomotor transformations presumed to underlie visually guided behavior. However, area 5 appears to be less directly implicated than the premotor cortex in the process of selecting the nature of the response to instructional signals.

Animals↗

PubMed1995

Changes in motor cortex activity during reaching movements with similar hand paths but different arm postures.

1. Neuronal activity was recorded in the motor cortex of a monkey that performed reaching movements with the use of two different arm postures. In the first posture (control), the monkey used its natural arm orientation, approximately in the sagittal plane. In the second posture (abducted), the monkey had to adduct its elbow nearly to shoulder level to grasp the handle. The path of the hand between targets was similar in both arm postures, but the joint kinematics and kinetics were different. 2. In both postures, the activity of single cells was often broadly tuned with movement direction and static arm posture over the targets. In a large proportion of cells, either the level of tonic activity, the directional tuning, or both, varied between the two postures during the movement and target hold periods. 3. For most directions of movement, there was a statistically significant difference in the direction of the population vector for the two arm postures. Furthermore, whereas the population vector tended to point in the direction of movement for the control posture, there was a poorer correspondence between the direction of movement and the population vector for the abducted posture. These observed changes are inconsistent with the notion that the motor cortex encodes purely hand trajectory in space.

Animals↗

PubMed1994

Central neural mechanisms of touch and proprioception.

The argument is made that somesthesia is not strictly passive process, and its central neuronal mechanisms cannot be studied in all their complexity and subtlety by applying passive stimuli to uninterested or unconscious animals. The case is clear for kinesthesia. Peripheral proprioceptive signals are altered by active muscle contractions, and the central mechanisms of kinesthetic sensations should be studied during active movements. A similar case can be made for tactile discrimination. Ascending tactile afferents are subject to modulation during movement. Moreover, the generation of a central neural representation of the mechanical stimulus is only part of the tactile perceptual process. It is also influenced by the behavioral, attentive, and motivational state of the animal, whose effects can only be revealed in awake animals actively participating in discrimination tasks.

Central Nervous System↗

PubMed1994

Tactile activity in primate primary somatosensory cortex during active arm movements: correlation with receptive field properties.

1. Five hundred ninety-five single neurons with tactile receptive fields (RFs) on the contralateral arm were isolated in the primary somatosensory cortex (SI) of awake, behaving monkeys. 2. Fifty-eight percent of the tactile cells showed significantly different levels of activity during active movements of the arm in eight directions or during active maintenance of the arm over the target endpoints. 3. The discharge of many of the active tactile cells was unimodally tuned with movement direction and the pattern of the tactile population activity varied in a meaningful fashion with arm movement direction and posture. 4. The intensity of the arm-movement-induced activity was typically less than that evoked by direct tactile stimulation of the cell's RF. 5. The probability of task-related activity was correlated with certain RF properties, in particular the sensitivity of the cell to lateral stretch of the skin and to passive arm movements that avoided direct contact of the RF on any surface. 6. This suggests that task-related activity results mainly from the activation of tactile receptors by mechanical deformation of the skin as the arm changes geometry during movement. 7. These results demonstrate that tactile activity containing potential proprioceptive information is generated in SI during active arm movements that avoid direct contact of the skin with external surfaces. Whether or not this input contributes to the kinesthetic sensations evoked by the movements cannot be resolved by this study.

Adaptation, Physiological↗

PubMed1994

Tactile activity in primate primary somatosensory cortex during active arm movements: cytoarchitectonic distribution.

1. Cells were recorded in areas 3b and 1 of the primary somatosensory cortex (SI) of three monkeys during active arm movements. Successful reconstructions were made of 46 microelectrode penetrations, and 298 cells with tactile receptive fields (RFs) were located as to cytoarchitectonic area, lamina, or both. 2. Area 3b contained a greater proportion of cells with slowly adapting responses to tactile stimuli and fewer cells with deep modality inputs than did area 1. Area 3b also showed a greater level of movement-related modulation in tactile activity than area 1. Other cell properties were equally distributed in the two areas. 3. The distribution of cells with low-threshold tactile RFs that also responded to lateral stretch of the skin or to passive arm movements was skewed toward deeper laminae than for tactile cells that did not respond to those manipulations. 4. The variation of activity of tactile neurons during arm movements in different directions was weaker in the superficial laminae than in deeper cortical laminae. 5. Cells with only increases in activity during arm movements were preferentially but not exclusively located in middle and superficial layers. Cells with reciprocal responses were found mainly in laminae III and V, whereas cells with only decreases in activity were concentrated in lamina V. 6. Overall, active arm movements evoke directionally tuned tactile and "deep" activity in areas 3b and 1, in particular in the deeper cortical laminae that are the source of the descending output pathways from SI.

Animals↗

PubMed1994

Modulation of preparatory neuronal activity in dorsal premotor cortex due to stimulus-response compatibility.

1. Neuronal activity was recorded in the dorsal premotor cortex (PMd) of two monkeys performing a multidirectional, instructed-delay (ID) reaching task in which visuospatial cues signaled the direction of movement either congruent with the instruction cue ("direct-delay" trials, DD) or redirected 180 degrees opposite to the cue ("redirected-delay" trials, RD). Therefore, this task had two degrees of stimulus-response (S-R) compatibility because in one-half of the trials the spatial attributes of the visual cue were incongruent with those of the intended movement. 2. The majority of PMd cells discharged both at short latency to the RD or DD cues and subsequently with sustained activity during the remaining ID period (IDP). The earliest responses (< 250 ms) in both DD and RD trials covaried with cue location and so could be either a "visuospatial" response or a neuronal correlate of the selection of action with highest S-R compatibility, namely move to the stimulus. In contrast, later IDP activity usually covaried with the direction of movement signaled by the cues, independent of their spatial location, supporting the hypothesis that IDP discharge in PMd ultimately encodes attributes of intended reaching movements.

Animals↗

PubMed1994

Proprioceptive activity in primate primary somatosensory cortex during active arm reaching movements.

1. We studied the activity of 254 cells in the primary somatosensory cortex (SI) responding to inputs from peripheral proprioceptors in a variety of tasks requiring active reaching movements of the contralateral arm. 2. The majority of cells with receptive fields on the proximal arm (shoulder and elbow) were broadly and unimodally tuned for movement direction, often with approximately sinusoidal tuning curves similar to those seen in motor and parietal cortex. 3. The predominant temporal response profiles were directionally tuned phasic bursts during movement and tonic activity that varied with different arm postures. 4. Most cells showed both phasic and tonic response components to differing degrees, and the population formed a continuum from purely phasic to purely tonic cells with no evidence of separate distinct phasic and tonic populations. This indicates that the initial cortical neuronal correlates of the introspectively distinguishable sensations of movement and position are represented in an overlapping or distributed manner in SI. 5. The directional tuning of the phasic and tonic response components of most cells was generally similar, although rarely identical. 6. We tested 62 cells during similar active and passive arm movements. Many cells showed large differences in their responses in the two conditions, presumably due to changes in peripheral receptor discharge during active muscle contractions. 7. We tested 86 cells in a convergent movement task in which monkeys made reaching movements to a single central target from eight peripheral starting positions. A majority of the cells (46 of 86, 53.5%) showed a movement direction-related hysteresis in which their tonic activity after movement to the central target varied with the direction by which the arm moved to the target. The directionality of this hysteresis was coupled with the movement-related directional tuning of the cells. 8. We recorded the discharge of 93 cells as the monkeys performed the task while compensating for loads in different directions. The large majority of cells showed a statistically significant modulation of activity as a function of load direction, which was qualitatively similar to that seen in motor cortex under similar task conditions. Quantitatively, however, the sensitivity of SI proprioceptive cells to loads was less than that seen in motor cortex but greater than in parietal cortex. 9. We interpret these results in terms of their implications for the central representation of the spatiotemporal form ("kinematics") of arm movements and postures. Most importantly, the results emphasize the important influence of muscle contractile activity on the central proprioceptive representation of active movements.

Afferent Pathways↗