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J F Kalaska

Publications and source records attributed to J F Kalaska.

At least 37 records · Page 2Linked to original sources
PubMed1993

Comparison of cerebellar and motor cortex activity during reaching: directional tuning and response variability.

1. The responses of 262 motor cortex cells and 223 cerebellar neurons were recorded during whole-arm reaching movements toward targets lights in eight evenly distributed directions radiating from a common central starting position. The reaching movements were followed by a 2-s target hold period where a fixed arm posture was actively maintained to stabilize the hand over the target light. 2. Cerebellar neurons had a higher mean tonic discharge rate while holding over the starting position (22.9 imp/s) than did motor cortex cells (12.5 imp/s). The mean population response curve describing the changes in activities with movement direction was likewise shifted toward higher frequencies in the cerebellum compared with the motor cortex, but the amplitude of the two curves was about equal. Therefore, the baseline discharges of cerebellar neurons were higher, but their changes in activity during movement were similar to those of motor cortical cells. 3. Motor cortex neurons were more strongly related to active maintenance of different arm postures than were cerebellar units. This was shown by a larger posture-related population response curve in the motor cortex (half-wave amplitude of cosine function was 11.2 imp/s, compared with 7.0 imp/s for cerebellar neurons), which represented the average response curve calculated from all the cells of the population. Furthermore, the motor cortex population had a higher percentage of single cells with tonic responses while the hand was held over different targets (tonic and phasic-tonic cells composed 57% of motor cortex population, compared with 38% of cerebellar population). Proportionately more cerebellar cells were phasically related to the movements. 4. The majority of motor cortex cells (58%) showed reciprocal changes relative to the center-hold time activity where the activity increased for movements in the preferred direction and decreased for movements in the opposite direction. Most of the remaining cells (40%) showed graded changes where the activity increased gradually as reaching was directed closer to the preferred direction. In contrast, the most common cerebellar response pattern was graded (38%). Only 26% were reciprocal and 18% were non-directional. The remaining 2% of motor cortical cells and 18% of cerebellar neurons could not be readily assigned to any of these three response classes. 5. Sector widths were calculated to measure the dispersion of individual cerebellar and motor cortical cell activities about the eight movement directions. Sector widths calculated from the absolute activities were always broader for cerebellar neurons (i.e., the cells were more broadly tuned).(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1992

Cerebral cortical mechanisms of reaching movements.

Because reaching movements have a clear objective--to bring the hand to the spatial location of an object--they are well suited to study how the central nervous system plans a purposeful act from sensory input to motor output. Most models of movement planning propose a serial hierarchy of analytic steps. However, the central nervous system is organized into densely interconnected populations of neurons. This paradox between the apparent serial order of central nervous system function and its complex internal organization is strikingly demonstrated by recent behavioral, modeling, and neurophysiological studies of reaching movements.

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PubMed1990

Parietal area 5 neuronal activity encodes movement kinematics, not movement dynamics.

A previous study reported that proximal-arm related area 5 neurons showed continuously-graded changes in activity during unloaded arm movements in different directions (Kalaska et al. 1983), which resembled the responses of primary motor cortex cells in several respects (Georgopoulos et al. 1982). We report here that loading the arm reveals an important difference between cell activity in the two areas. Loads were continuously applied to the arm in different directions. The loads produced large continuously-graded changes in muscle activity but did not alter the handpath or joint angle changes of the arm during the movements. The activity of most area 5 cells was only weakly affected by the loads, and the overall pattern of population activity was virtually unaltered under all load conditions. This indicates that area 5 activity encodes the invariant spatial parameters (kinematics) of the movements. In contrast, many motor cortex cells showed large changes in activity during loading, and so signal the changing forces, torques or muscle activity (movement dynamics; Kalaska et al. 1989).

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PubMed1989

Neuronal activity in primate parietal cortex area 5 varies with intended movement direction during an instructed-delay period.

A monkey was trained to make arm movements to visual targets immediately after presentation of a GO signal, either in a visual reaction-time paradigm (CONTROL task), or after an instructed-delay period of variable duration, during which a CUE stimulus signalled the direction of the impending movement (DELAY task). The activity of 98 area 5 cells recorded in 2 hemispheres varied with movement direction in the CONTROL task. This included 60 "early" cells which showed directional activity changes prior to movement onset. In the DELAY task, 54/98 cells (55%) showed activity changes during the instructed-delay period which varied with the direction of the impending movement. Most of these (45/54, 83%) were "early" cells. Forty proximal arm-related cells were recorded in adjacent area 2. In contrast to area 5, only 2/40 area 2 cells showed any evidence of changes in activity varying with intended movement direction during the instructed-delay period. The origin of area 5 activity changes during an instructed-delay period which are related to intended direction of a delayed movement is uncertain, but its presence is consistent with a number of proposed roles for area 5.

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PubMed1989

Cerebellar neuronal activity related to whole-arm reaching movements in the monkey.

1. Three monkeys were trained to make whole-arm reaching movements from a common central starting position toward eight radially arranged targets disposed at 45 degrees intervals. A sample of 312 cerebellar neurons with proximal-arm receptive fields or discharge related to shoulder or elbow movements was studied in the task. The sample included 69 Purkinje cells, 115 unidentified cortical cells, 65 interpositus neurons, and 63 dentate units. 2. The reaching task was divided into three movement-related epochs: a reaction time, a movement time, and holding over the target. All neurons demonstrated significant changes in discharge during one or more of these three epochs. Almost all of the cells (95%) showed a significant change in activity during the movement, whereas 68-69% of the cells showed significant changes from premovement activity during the reaction time and holding periods. 3. During the combined reaction time-movement period, 231/312 cells were strongly active in the task. Of these, 151 cells (65.4%) demonstrated unimodal directional responses. Sixty-three had a reciprocal relation to movement direction, whereas 88 showed only graded increases or decreases in activity. A further 37 cells (16.0%) were nondirectional, with statistically uniform changes in discharge in all eight directions. The remaining 43 cells (18.6%) showed significant differences in activity for different directions of movement, but their response patterns were not readily classifiable. 4. The proportion of directional versus nondirectional cells was consistent across the four cell populations. However, graded response patterns were more common and reciprocal responses less common among Purkinje and dentate neurons than among unidentified cortical cells and interpositus neurons. 5. The distribution of preferred directions of the population of cerebellar neurons covered all possible movement directions away from the common central starting position in the horizontal plane. When the preferred direction of each cell in the sample population was aligned, the mean direction-related activity of the cerebellar population formed a bell-shaped tuning curve for the activity recorded during both the reaction time and the movement, as well as during the time the arm maintained a fixed posture over the targets. A vector representation also showed that the overall activity of the cerebellar population during normal reaching arm movements generated a signal that varied with movement direction. 6. These results demonstrate that the cerebellum generates a signal that varies with the direction of movement of the proximal arm during normal aimed reaching movements and is consistent with a role in the control of the activity of muscles or muscle groups generating these movements.

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PubMed1989

A comparison of movement direction-related versus load direction-related activity in primate motor cortex, using a two-dimensional reaching task.

Shoulder joint-related motor cortex cells show continuously graded changes in activity, centered on a preferred movement direction, during active arm movements in 8 directions away from a central starting position (Georgopoulos et al., 1982). We demonstrate here that many of these cells show similar large continuously graded changes in discharge when the monkey compensates for inertial loads which pull the arm in 8 different directions. These load-dependent discharge variations are typically unimodal, centered on one load direction called the cell's load axis, and are often sufficiently continuous, symmetric, and broad as to show a good fit to a sinusoidal curve. A vectorial representation of cell activity indicates that the pattern of load-dependent activity changes in the population forms a signal whose direction is appropriate to compensate for the loads. The responses of single cells to different combinations of movement and load direction are often complex. Nevertheless, the mean activity of the sample population under any condition of movement direction and load direction can be described reasonably well by a simple linear summation of the movement-related discharge without any loads, and the change in tonic activity of the population caused by the load, measured prior to movement. The strength of the load-dependent discharge variation differs among cells. Cells can be sorted into 2 phasic and 2 tonic groups that show differing degrees of sensitivity to loads. In particular, it was found that the greater the degree of cell discharge variation associated with different actively maintained limb postures, the greater the activity changes caused by loads. No similar correlation was found for the degree of discharge variation during movement. Preliminary evidence suggests that phasic and tonic cell groups may be spatially segregated in the motor cortex. These observations are consistent with the idea that there exists in the motor cortex activity encoding aspects of movement kinematics, as well as movement dynamics. These observations are in agreement with studies of more distal arm joints, showing that the activity of certain motor cortex cells varies with the patterns of muscle activity and output forces required to produce a movement. These experiments extend the description of the control of the direction of movement of a multiple degree-of-freedom joint into the spatial (direction) domain to a greater extent than previously achieved.

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PubMed1988

The representation of arm movements in postcentral and parietal cortex.

Considerable experimental evidence supports the hypothesis that the neocortical processes underlying kinesthetic sensation form a hierarchical series of cells signalling increasingly complex patterns of movement of the body. However, this view has been criticized and the data lack quantitative verification under controlled conditions. These studies have also typically used one-dimensional (reciprocal) movements, even of multiple degree-of-freedom joints such as the wrist or shoulder, and have been restricted to passive movements. This latter limitation is particularly critical, since the response of many muscle receptors is affected by fusimotor activity while that of many articular receptors is sensitive to the level of muscle contractile activity. Both factors introduce significant kinesthetic ambiguity to the signals arising from these receptors during active movement. This ambiguity is evident in the discharge of primary somatosensory cortex proprioceptive cells. Studies in area 5 show that single cells signal shoulder joint movements in the form of broad directional tuning curves. The pattern of activity of the entire population encodes movement direction. The cells appear to encode spatial aspects of movement unambiguously, since their discharge is relatively insensitive to the changes in muscle activity required to produce the same movements under different load conditions. It is not yet certain whether the somesthetic activity in area 5 is a kinesthetic representation that is sequential to and hierarchically superior to that in SI, or whether it is a parallel representation with separate and distinct function.

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PubMed1985

Area 4 and area 5: differences between the load direction-dependent discharge variability of cells during active postural fixation.

Previous experiments have shown that the activity of cells in both areas 4 and 5 is strongly modulated in a continuously-graded manner for movements of the arm in 8 different directions away from a central starting position. However, it is reported here that there is a clear difference between these two areas during postural fixation of the arm in one position against loads applied in 8 different directions. Area 4 cell activity shows large variations when the monkey holds its arm at the central position by exerting forces in different directions to counteract the loads. The activity of cells in area 5 is much less strongly modulated under the same isometric conditions. These observations suggest that cell activity in area 5 is less related to the level and pattern of force output than are cells in area 4. Area 5 may produce instead a signal related more to the limb position, per se, during actively maintained posture.

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PubMed1985

Cerebellar nuclear cell activity during antagonist cocontraction and reciprocal inhibition of forearm muscles.

Monkeys were trained to exert a maintained isometric pinch with the thumb and forefinger. This task reliably elicited a simultaneous cocontraction of the forearm muscles. The same monkeys were also taught to insert the open hand into a manipulandum, flex and extend the wrist 35 and 15 degrees, respectively, and maintain an isometric wrist position against a mechanical stop for 1 s. This second task comprised two conditions: a dynamic or movement phase and a static or isometric phase. Movement always involved a wrist displacement of 50 degrees. Although some forearm muscles demonstrated bidirectional activity during the wrist displacement phase, all the wrist and finger muscles were alternatively active in isometric flexion or extension. Of the neurons in the dentate and interposed nuclei that consistently changed discharge during repeated isometric prehension, over 90% (61/67) of the neurons increased activity during this cocontraction of forearm muscles. About 70% (47/67) of these same nuclear cells discharged with a reciprocal pattern of firing during alternating wrist flexion-extension movements. Forty-six neurons had sustained and reciprocal discharge during the maintained isometric wrist postures. No differences were seen between the activity patterns of dentate and interposed cells with respect to either the prehension task or the reciprocal wrist-movement task. The discharge frequency of some dentate and interpositus neurons could be correlated with prehensile force as well as velocity of wrist movement and torque developed by wrist muscles. Correlation coefficients were calculated between nuclear cell discharge and the amplitude of the surface EMGs of the flexors and extensors of the wrist and fingers during the wrist-movement task. Sixteen nuclear cells showed low-order, but reliably positive, correlations with one of the two forearm muscle groups (mean r = 0.33). In contrast, a sample of seven Purkinje cells recorded during the same task demonstrated low-order correlations that were negative in sign (mean r = -0.30) between discharge frequency and one of the two forearm EMGs.

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PubMed1984

Static spatial effects in motor cortex and area 5: quantitative relations in a two-dimensional space.

We describe the relations between active maintenance of the hand at various positions in a two-dimensional space and the frequency of single cell discharge in motor cortex (n = 185) and area 5 (n = 128) of the rhesus monkey. The steady-state discharge rate of 124/185 (67%) motor cortical and 105/128 (82%) area 5 cells varied with the position in which the hand was held in space ("static spatial effect"). The higher prevalence of this effect in area 5 was statistically significant. In both structures, static effects were observed at similar frequencies for cells that possessed as well as for those that lacked passive driving from the limb. The results obtained by a quantitative analysis were similar for neurons of the two cortical areas studied. It was found that of the neurons with a static effect, the steady-state discharge rate of 78/124 (63%) motor cortical and 63/105 (60%) area 5 cells was a linear function of the position of the hand across the two-dimensional space, so that the neuronal "response surface" was adequately described by a plane (R2 greater than or equal to 0.7, p less than 0.05, F-test in analysis of variance). The preferred orientations of these response planes differed for different cells. These results indicate that individual cells in these areas do not relate uniquely a particular position of the hand in space. Instead, they seem to encode spatial gradients at certain orientations.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1984

Cerebellar cortical activity during antagonist cocontraction and reciprocal inhibition of forearm muscles.

Monkeys were trained to perform a maintained isometric grip of the thumb and forefinger that elicited a simultaneous cocontraction of the antagonist muscles of the forearm. The same monkeys were also trained to flex and extend the wrist against a stop with the fingers extended and to maintain an isometric wrist position for 1.0-1.5 s. During wrist movement, some of the synergist forearm muscles contracted during both flexion and extension. However, during the maintained isometric wrist position, the prime mover and synergist muscles were reciprocally active or silent. In the culmen-simplex region of the cerebellar cortex bordering on the primary fissure, 62% of the Purkinje cells that were identified by the climbing fiber discharge and that changed firing frequency decreased activity during maintained prehension. Almost all of these same Purkinje cells were reciprocally active during isometric wrist flexion and extension, although three neurons had similar discharge patterns during movements in both directions. In contrast, 79% of the unidentified neurons recorded from the same region of the cerebellar cortex increased discharge frequency during prehension. In general, most of these same neurons had reciprocal patterns of discharge during wrist movement even though a few cells were active during the dynamic phase in both directions. Together, the Purkinje cells and the unidentified neurons with bidirectional response patterns were thought to be related to muscles active during both flexion and extension wrist movements. No cells were found that increased discharge with the static isometric wrist torque exerted in both directions. The discharge frequency of some Purkinje and some unidentified neurons could be shown to be related to prehensile force as well as wrist movement velocity and isometric wrist torque. These data suggest that the discharge of about two-thirds of the Purkinje cells related to forearm muscles located along the borders of the primary fissure may depend on whether antagonist muscles are activated reciprocally or coactively. As a consequence, these cells may play a role in the selection or alternation between either of these two modes of muscular contraction. The increased discharge of the remaining one-third of the Purkinje cells excited during antagonist coactivation may provide inhibition of nuclear cells to stabilize the posture at joints other than the wrist and fingers or, alternatively, they may act to reduce nuclear cell discharge in proportion to the intensity of cutaneous stimulation.

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PubMed1983

Cortical mechanisms related to the direction of two-dimensional arm movements: relations in parietal area 5 and comparison with motor cortex.

The relations between the direction of two-dimensional arm movements and single cell discharge in area 5 were investigated during 49 penetrations into the superior parietal lobule of 3 monkeys. A significant variation of cell discharge with the direction of movement was observed in 182 of 212 cells that were related to arm movements. In 151/182 of these cells the frequency of discharge was highest during movements in a preferred direction, and decreased in an orderly fashion with movements made in directions farther and farther away from the preferred one; in 112/151 cells this variation in discharge was a sinusoidal function of the direction of movement. Preferred directions differed for different cells so that directional tuning curves overlapped partially. These results are similar to those described for cells in the motor cortex (Georgopoulos et al. 1982): this suggests that directional information may be processed in a similar way in these structures. Many cells in area 5 changed activity before the onset of movement, and several did so before the earliest electromyographic changes (63% and 35%, respectively, of the cells that showed an increase in activity with movements in the preferred direction). However, the distribution of onset times of the parietal cells lagged the corresponding one of the motor cortical cells by about 60 ms. This suggests that the early changes observed in the parietal cortex might represent a corollary discharge from the precentral motor fields, whereas later activity might reflect peripheral as well as central events.

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PubMed1983

Interruption of motor cortical discharge subserving aimed arm movements.

Can evolving motor commands be interrupted by changes in sensory signals that triggered them? We investigated this problem by observing the changes in single cell activity in the motor cortex of monkeys, changes that preceded movement of the hand toward a visual target. We found that this activity was interrupted following a shift of the target during the reaction or movement time and replaced by the pattern activity related to the movement towards the new target. This suggests that motor cortical commands subserving aimed arm movements are processes that can be interrupted in the course of their formation and/or execution by changes in afferent controlling inputs.

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PubMed1982

On the relations between the direction of two-dimensional arm movements and cell discharge in primate motor cortex.

The activity of single cells in the motor cortex was recorded while monkeys made arm movements in eight directions (at 45 degrees intervals) in a two-dimensional apparatus. These movements started from the same point and were of the same amplitude. The activity of 606 cells related to proximal arm movements was examined in the task; 323 of the 606 cells were active in that task and were studied in detail. The frequency of discharge of 241 of the 323 cells (74.6%) varied in an orderly fashion with the direction of movement. Discharge was most intense with movements in a preferred direction and was reduced gradually when movements were made in directions farther and farther away from the preferred one. This resulted in a bell-shaped directional tuning curve. These relations were observed for cell discharge during the reaction time, the movement time, and the period that preceded the earliest changes in the electromyographic activity (approximately 80 msec before movement onset). In about 75% of the 241 directionally tuned cells, the frequency of discharge, D, was a sinusoidal function of the direction of movement, theta: D = b0 + b1 sin theta + b2cos theta, or, in terms of the preferred direction, theta 0: D = b0 + c1cos (theta - theta0), where b0, b1, b2, and c1 are regression coefficients. Preferred directions differed for different cells so that the tuning curves partially overlapped. The orderly variation of cell discharge with the direction of movement and the fact that cells related to only one of the eight directions of movement tested were rarely observed indicate that movements in a particular direction are not subserved by motor cortical cells uniquely related to that movement. It is suggested, instead, that a movement trajectory in a desired direction might be generated by the cooperation of cells with overlapping tuning curves. The nature of this hypothetical population code for movement direction remains to be elucidated.

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