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Biomedical subjects

M H Schieber

Publications and source records attributed to M H Schieber.

26 records · Page 2Linked to original sources
PubMed1991

Individuated finger movements of rhesus monkeys: a means of quantifying the independence of the digits.

1. Two rhesus monkeys were trained to perform flexion and extension movements of each digit of the right hand and of the wrist. Movements of all five digits and the wrist were monitored simultaneously. During each instructed movement, the instructed digit (or wrist) had the greatest excursion; other, noninstructed digits moved to varying degrees. 2. To assess the degree of independence of the different digits during these movements, I plotted, as a function of the instructed digit's position, the position of each noninstructed digit. The resulting trajectories typically were linear, with consistent slopes from trial to trial. 3. The slopes of these noninstructed digit versus instructed digit trajectories were used to calculate an individuation index for each instructed movement and a stationarity index for each digit. These indexes quantified two different aspects of independence. The individuation index reflects the degree to which other digits remained still during instructed movement of a given digit. The stationarity index reflects the degree to which a given digit remained still whenever it was a noninstructed digit. 4. In accordance with casual observation, thumb flexion and wrist flexion and extension consistently had both high individuation and stationarity and therefore can be said to be independent of the fingers. Although the same cannot be said of the other fingers, the present analysis provides a means of quantifying the degree of independence of these digits as well. 5. Factors are discussed that might contribute to the motion of noninstructed digits and to the trajectory linearity.

Animals↗
PubMed1990

How might the motor cortex individuate movements?

The ability to individuate movements--that is, the ability to move one or more body parts independently of the movement or posture of other contiguous body parts--imparts an increasing flexibility to the motor repertoire of higher mammals. The movements used in walking, grasping, or eating contrast greatly with the phylogenetically more recent movements of the same body parts used, respectively, in dancing, playing a musical instrument, or talking. The movements used in the latter functions depend critically on the primary motor cortex (area 4). With advances in our understanding of the output organization of the motor cortex (reviewed recently by Roger Lemon), which have been based largely on studies of the hand area in primates, we can now consider more fully certain problems inherent in moving body parts individually, and some ways in which the motor cortex might accomplish this feat.

Animals↗
PubMed1985

Trained slow tracking. I. Muscular production of wrist movement.

Electromyographic (EMG) activity was recorded from those forearm muscles that act across the wrist as highly trained monkeys tracked slow hold-ramp-hold target trajectories with angular wrist position. During performance of this task, the forearm flexors and extensors had a common "basic pattern" of EMG activity. Flexor digitorum sublimis (FDS) and extensor digitorum communis (EDC), though commonly classified as prime movers of the fingers, were the most active flexor and extensor muscles during these movements at the wrist. The basic pattern of EMG activity was analyzed by varying independently 1) the movement direction, 2) the initial and final held wrist positions, 3) the ramp-movement velocity, and 4) the direction and magnitude of maintained external torque load. Most of the modulation of the basic pattern was related to wrist position: EMG amplitude was greatest at the extreme of muscle shortening. There was a slight difference in EMG activity between flexion and extension ramps that was related purely to the direction of movements, independent of wrist position, velocity, and external load; EMG amplitude was greater when a muscle was shortening and less when it was lengthening. During ramp movement, there was little or no observed EMG activity related to velocity (8-28 degrees/s). The magnitude of EMG activity varied in proportion to the external torque load, but this load-related component was additive, and the basic pattern of activity (related to direction and position) did not change with load. From these results we infer that a muscle's EMG activity was determined by 1) passive elastic properties of the wrist and the active length-tension characteristics of the muscle itself (position), 2) asymmetries in the muscle's contractile force depending on whether it was lengthening or shortening (direction), and 3) magnitude of the external torque load (force). By contrast, since no EMG activity was related to velocity in these slow movements, passive viscous properties and velocity-related cross-bridge kinetics were apparently so slight as to make undetectable the small additional EMG activity and contractile force presumably required to overcome them. A model of the muscle forces acting at the wrist incorporates these experimental observations.

Animals↗
PubMed1985

Trained slow tracking. II. Bidirectional discharge patterns of cerebellar nuclear, motor cortex, and spindle afferent neurons.

Single-unit discharge was recorded in the dentate and interposed cerebellar nuclei, motor cortex, and C7 and C8 dorsal root ganglia during trained, slow hold-ramp-hold tracking, rapid alternating movement, torque-pulse perturbation, and action tremor of the monkey's wrist. Fifty-seven dentate and 45 interposed neurons were found in two monkeys that discharged in relation to slow tracking movement. Nearly all neurons had a distinct bidirectional pattern of discharge consisting of an abrupt increase (or decrease) in firing frequency at or before the onset of movement that was variably maintained throughout the ramp and was independent of movement direction. None of the neurons showed a clear relationship to direction, position, velocity, or load during the performance of this task. Nevertheless, many of these neurons discharged in relation to rapid alternation and (for interpositus) torque pulses in patterns that were directionally reciprocal. Some interpositus neurons showed a modulation related to tremor superimposed on the bidirectional discharge related to slow ramps. Twenty-nine neurons in motor cortex of one monkey discharged during slow hold-ramp-hold tracking in two patterns. Class I neurons (14 of 29) showed gradually changing, directionally reciprocal modulations of firing frequency for movements in opposite directions. These neurons were often related to torque load and/or to wrist position but not to velocity. The discharge pattern was similar to the pattern of activity of forearm muscles. Class II neurons (15 of 29) showed an abrupt change in firing frequency that was bidirectional. They were often related to torque load and/or to velocity but not to position. Motor cortex neurons discharged in relation to rapid alternating movements, torque pulses, and tremor in similar patterns that did not distinguish the two classes. Five units in dorsal root ganglia were identified as muscle spindle afferents. During ramps, their pattern of discharge was bidirectional and resembled the bidirectional discharge patterns of neurons in motor cortex (class II) and cerebellum. For some cells the bidirectional pattern varied slightly in relation to the direction and velocity of movement and the amount of torque load, but it was not related to the large changes in wrist position (muscle length). Modulation in relation to tremor was superimposed on the bidirectional pattern related to ramps. The comparison of spindle afferent discharge with the concurrent electromyogram (EMG) of the parent muscle suggested that spindles were driven by gamma-fusimotor activity dissociated from that of homonymous alpha-skeletomotor neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Activity of muscle spindles, motor cortex and cerebellar nuclei during action tremor.

Repeated electrode penetration of the dentate and interpositus nuclei in a rhesus monkey transformed an 11-13 Hz physiologic tremor into a much larger action tremor at 5-7 Hz. This tremor was associated with muscle spindle spike train modulation and reflexly evoked tremor modulation of interpositus and motor cortex neurons as well as electromyogram (EMG). No tremor modulation was observed in spike trains recorded from dentate. The timing relationships of the spindle, EMG, and interpositus tremor discharges suggest that the interpositus plays a direct role in tremor suppression. Dentate, by contrast, may function indirectly by setting optimal transcortical long loop reflex dynamics concerned with intended voluntary movement.

Animals↗
PubMed1980

Alpha-gamma dissociation during slow tracking movements of the monkey's wrist: preliminary evidence from spinal ganglion recording.

Conventional glass-coated Pt-Ir microelectrode technique was adapted for use in recording single unit activity in the cervical dorsal root ganglia of chronic awake behaving monkeys. The activity of one fully identified and four putative afferents from forearm muscle spindles was recorded as a trained monkey performed wrist movements, guided by a visual display, in pursuit tracking of slow predictable hold-ramp-hold target trajectories. Comparison of spindle afferent discharge with parent muscle EMG provided evidence of gamma fusimotor activity dissociated from the activity of homonymous a motoneurons. This appears to maintain a uniform pattern of afferent activity in the face of widely varying parent muscle activity.

Afferent Pathways↗
PubMedDate not supplied

Neural coding of finger and wrist movements.

Previous work (Schieber and Hibbard, 1993) has shown that single motor cortical neurons do not discharge specifically for a particular flexion-extension finger movement but instead are active with movements of different fingers. In addition, neuronal populations active with movements of different fingers overlap extensively in their spatial locations in the motor cortex. These data suggested that control of any finger movement utilizes a distributed population of neurons. In this study we applied the neuronal population vector analysis (Georgopoulos et al., 1983) to these same data to determine (1) whether single cells are tuned in an abstract, three-dimensional (3D) instructed finger and wrist movement space with hand-like geometry and (2) whether the neuronal population encodes specific finger movements. We found that the activity of 132/176 (75%) motor cortical neurons related to finger movements was indeed tuned in this space. Moreover, the population vector computed in this space predicted well the instructed finger movement. Thus, although single neurons may be related to several disparate finger movements, and neurons related to different finger movements are intermingled throughout the hand area of the motor cortex, the neuronal population activity does specify particular finger movements.

Finger Joint↗