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Role of Motor Cortex in Voluntary Movements in Primates

Edward V. Evarts

10.1002/cphy.cp010223

Source: Supplement 2: Handbook of Physiology, The Nervous System, Motor Control

Originally published: 1981

Published online: January 2011

Full Article on Wiley Online Library



Abstract

The sections in this article are:

1 Historical Considerations
2 Boundaries of Mi in Primates
3 Reviews of MI
4 Activity of MI in Relation to Input and Output
4.1 Coding of MI Output in Relation to Parameters of Movement
4.2 Responses of MI Neurons to Afferent Input
4.3 Hierarchical Organization Within Sensorimotor Cortex
4.4 Summary
5 Transcortical Reflexes
5.1 Criteria for Assessing Functional Significance of MI Outputs
5.2 Transcortical Reflexes
5.3 Reflexes of MI in Course of Volitional Movements
5.4 Foci in MI for Afferent Submodalities
5.5 Parallels Between Servo Responses in Humans and Subhuman Primates
5.6 Functional Analogies Between Segmental and Suprasegmental Reflexes
5.7 Summary
6 Centrally Programmed Movement
6.1 Contrasting Patterns of MI Activity With Different Movement Strategies
6.2 Pathways Transmitting Central Programs to MI
6.3 Summary
7 Conceptual Issues in Sensorimotor Integration
7.1 Contrasts Between MI and SI in Relation to Voluntary Movement
7.2 Corollary Discharge and Efference Copy in Sensorimotor Cortex
7.3 Precision, Fractionation, and Dynamic Range of Motor Control
7.4 Topography of MI and Spatial Distribution of Its Functional Components in Relation to Generation of Different Movements
Figure 1. Figure 1.

Diagram of monkey cortex showing locations of precentral motor (MI; Ms I and II on figure) and postcentral tactile (SI; Sm I and II on figure) areas.

From Woolsey 180
Figure 2. Figure 2.

Composite diagram of histologically verified recording sites (filled circles) from which wave and unitary responses were evoked by stimulating group I muscle afferents in deep radial nerve or in deep palmar branch of ulnar nerve. They are superimposed on a single diagram; location of each point in relation to cytoarchitectonics and lamination of areas 3b, 3a, and 4 was verified for each experiment.

From Phillips et al. 132
Figure 3. Figure 3.

Relation between tonic firing rate and static torque for 14 corticomotoneuronal (CM) cells related to wrist extension and 11 CM cells related to wrist flexion. Cells were selected solely on the basis of the strength of their postspike facilitation and the adequacy of the range of load studied. Firing rate of all plotted cells was measured from response averages, compiled for at least 4 load levels. Compared with extension CM cells, flexion cells showed a similar range of firing rates but extended over approximately twice the torque range.

From Cheney and Fetz 29
Figure 4. Figure 4.

Distribution of spindle (left) and motor cortex (right) inputs to motoneurons of different muscles and muscle groups of baboon hand. Thicknesses of arrow shafts measure mean quantities of monosynaptic excitatory action (MV scale at left). EDC, extensor digitorum communis; R, remaining dorsiflexors of wrist; Uh, hypothenar muscles, in‐terossei, ulnar lumbricals, intrinsic flexor, and adductor of thumb; Mh, remaining intrinsic hand muscles; FDS, flexor digitorum sublimis; PL, palmaris longus.

From Clough et al. 31
Figure 5. Figure 5.

Changes of movement and discharge of precentral unit during flexion loading (middle column, n = 18) and flexion unloading torque pulse (right column, n = 17) compared with flexions without torque pulse (left column, n = 20). Uppermost trace: overplot of position signals computed with programmed data processor (PDP‐12) at a sampling rate of 200 Hz. Hatched boxes indicate 2 target zones. Second trace: overplot of computed velocities. Two middle traces: intramuscularly recorded EMG activity in triceps and biceps as photographed from superimposed traces on storage oscilloscope. Raster plots of sequentially displayed unit discharges; bin width = 1 ms. Time histograms: bin width = 10 ms. Vertical lines indicate time when velocity reached 60°/s, taken as zero reference point for averaging procedure and when torque pulses were applied.

From Conrad et al. 33
Figure 6. Figure 6.

Electromyographic activity following a suddenly applied and maintained stretching force in normal biceps (A), quadriceps (B), and gastrocnemius (C). In each muscle, the stretch (onset of which, denoted by arrow, triggered the sweep) produced a tendon jerk response, followed after a silent period by a large, asynchronous burst of activity termed the functional stretch reflex. Time between onsets of tendon jerk and functional stretch reflex is sequentially related to segmental level of muscular innervation. Five traces were superimposed in each example. All records were from same subject.

From Chan et al. 27
Figure 7. Figure 7.

Electromyographic responses in biceps (upper traces) and gastrocnemius (lower traces) to sudden and maintained stretching force in normal (A) and spastic paraplegic (B) subjects. Biceps response evoked in spastic subject (upper trace in B), being above level of cord transection, has a similar pattern to that of normal subject (upper trace in A). In contrast early discharge is prolonged in spastic gastrocnemius (lower trace in B), but no EMG activity is evident in time bracket normally occupied by functional stretch reflex in intact subject, which in this instance occurred about 100 ms after stimulus (lower trace in A).

From Chan et al. 27
Figure 8. Figure 8.

Comparison of electromyographic (EMG) response evoked by sudden and sustained stretch in biceps (upper trace) and gastrocnemius (lower trace) between normal (A) and affected (B) side of hemiplegic patients. Biceps response is obtained from one patient; gastrocnemius response from another. Note that response of affected muscles (B) showed a prolonged early discharge, but no EMG burst can be observed in time gate normally occupied by functional stretch reflex in corresponding unaffected muscles (A), although in some subjects a late burst can be seen marking the beginning of clonus (e.g., lower trace in B).

From Chan et al. 27
Figure 9. Figure 9.

Three displays are shown: 1) superimposed position traces, 2) histograms of unit discharge, and 3) rasters of unit discharge. Attention is directed to several points. 1) Unperturbed small pronation (top left) is preceded by more prolonged unit discharge than unperturbed ballistic movement (top right). 2) Inhibitory effect of torque pulse is greater when delivered during a small pronation (top, small + torque) than when delivered during holding (top, torque pulse holding). 3) There is a corresponding accentuation of excitatory effects of supinating torque pulse when this is delivered during small movement (bottom, small + torque) compared with holding (bottom, torque pulse holding). 4) There is attentuation of torque pulse response when pulse is delivered immediately before ballistic movement (preballistic torque).

From Evarts and Fromm 47
Figure 10. Figure 10.

Superimposed average handle displacement traces. For half the trials, a monkey was given prior instruction to prepare to push; for the other half, it was instructed to prepare to pull. Load change in both cases moved handle toward monkey. Traces follow same trajectory for approximately 90 ms (period between dashed lines). Since peripheral input during this period should be very similar, the influence of motor preparation on a short‐latency response to load change could be analyzed in this period.

From Strick 146
Figure 11. Figure 11.

Biceps electromyographic (EMG) activity in paradigm involving a prior instruction and a kinesthetic trigger. A lamp (red or green) indicated to the monkey what to do, and a perturbation of the handle indicated when to do it. Instructions to pull or push and perturbations toward or away from the monkey could be combined in 4 possible ways, as shown in the 4 pairs of traces in this figure. Each pair of traces shows biceps EMG activity and output of a potentiometer coupled to the handle, with upward deflection of potentiometer trace indicating movement of handle toward monkey, and downward deflection of potentiometer trace indicating movement of handle away from monkey. For set of traces at upper left, prior instruction was pull, calling for biceps contraction, and perturbing stimulus (indicated by potentiometer trace) moved handle away from the monkey, thereby stretching the biceps. At lower right, instruction was push, and initial perturbation was a movement of the handle toward the monkey, resulting in shortening of biceps.

From Evarts and Tanji 50
Figure 12. Figure 12.

Raster displays of activity of pyramidal tract neuron show activity occurring 500 ms before and 500 ms after a perturbation that occurred at center line of display. Single heavy dot in each row following perturbation shows when handle reached intended push or pull zone. This PTN was one that discharged with intended push movement and fell silent with intended pull movement. In raster at top, heavy dot marking completion of push movement is followed by PTN silence as monkey pulls back into “hold zone” to initiate a new trial. In the raster at bottom, the heavy dot occurs during PTN silence as monkey pulls, and discharge recommences as monkey pushes back to hold zone to start a new trial.

From Evarts and Tanji 51
Figure 13. Figure 13.

Proposed roles of several brain structures in movement. Dashed line represents pathway of unknown importance. Short dashed lines at A and B represent lesions described in text. It is proposed that the basal ganglia and cerebellar hemisphere (cbm) are involved with the association cortex (assn cx) in programming volitional movements. When the motor command descends to motoneurons, engaging the movement, the pars intermedia updates the intended movement based on the motor command and somatosensory description of limb position and velocity on which the movement is to be superimposed. Follow‐up correction can be performed by the motor cortex (motor cx) when the cerebellar hemisphere and pars intermedia do not effectively perform their functions.

From Allen and Tsukahara 2
Figure 14. Figure 14.

Influence of motor preparation on short‐latency response of dentate neuron to load changes. Neural response averages (A1, B1), rasters of individual trials (A2, B2), and average displacement traces (A3, B3) of same dentate neuron recorded under 2 conditions. Load change in A panels and B panels moved handle away from monkey. In A, animal was instructed to prepare to push and in B, to prepare to pull. Each line in the rasters (A2, B2) represents an individual trial, and each dot a single neural discharge. Both rasters and response averages show that same direction of load change evoked a short‐latency increase in activity when animal was prepared to push and a short‐latency decrease in activity when animal was prepared to pull. Maximum scale in A1 equals 512 pulses/s and in B1, 256 pulses/s.

From Strick 146
Figure 15. Figure 15.

Above: surface reconstruction made from sagittal sections at approximately 200‐μm intervals showing striplike distribution of labeled corticospinal cells (dots) in fields of sensorimotor and parietal cortex after large injection of HRP into contralateral thoracic spinal cord. Cynomolgus monkey. Below: representative sagittal sections from levels indicated showing positions of labeled cell clusters. In both parts of figure, each dot represents 1 cell.

From Jones and Wise 91
Figure 16. Figure 16.

Discharge of precentral motor cortex pyramidal tract neuron (same neuron as illustrated in Fig. 9) for slow movement (left) and rapid movement (right). Displays are centered on detection of movement onset (a change of position of approximately 1°) and include 500 ms before and 500 ms after detection of movement onset. Further details concerning position display (top), histograms of unit discharge (middle), and rasters (bottom) are given in legend of Figure 9.

From Evarts and Fromm 48
Figure 17. Figure 17.

Two possible schemata that might have the functional properties Jackson assigned to each unit of corpus striatum. At left is a unit in which pyramidal tract neurons (a, b, and c) projecting to motoneurons (Ma, Mb, and Mc) are intermingled. Relative strengths of representation of 3 muscles (A, B, and C) in this unit are in the ratio of 4:2:1. Electrical stimulation of a group of units such as this at threshold for motoneuronal discharge would excite Ma. At right is shown a different arrangement, one in which axon of a single PTN (4a + 2b + c) has a divergent projection onto motoneurons of 3 different muscles. Like the unit at left, this unit represents muscles A, B, and C in a ratio of 4:2:1. Electrical stimulation of a group of units such as this at threshold for motoneuron discharge would excite Ma without exciting Mb or Mc.

From Evarts 41
Figure 18. Figure 18.

Five variants of organization of corticomotoneuronal projections. Large circles denote 2 different motor nuclei; small circles denote pyramidal tract cells; lines around them indicate cortical areas of projection to different motor nuclei; columns above them show cortical network with fibers terminating on pyramidal cells. A: mosaiclike organization of pyramidal tract cells; B: overlapping organization of pyramidal tract cells with projections of single pyramidal tract cells to only 1 motor nucleus; C: overlapping organization of pyramidal tract cells with projections of some pyramidal tract cells to more than 1 motor nucleus; D: pseudomosaic organization of cortical output with overlapping organization of pyramidal tract cells and selective activation of pyramidal tract cells projecting to different motor nuclei; E: patterned organization of cortical output with overlapping organization of pyramidal tract cells and coactivation of pyramidal tract cells projecting to different motor nuclei.

From Jankowska et al. 85


Figure 1.

Diagram of monkey cortex showing locations of precentral motor (MI; Ms I and II on figure) and postcentral tactile (SI; Sm I and II on figure) areas.

From Woolsey 180


Figure 2.

Composite diagram of histologically verified recording sites (filled circles) from which wave and unitary responses were evoked by stimulating group I muscle afferents in deep radial nerve or in deep palmar branch of ulnar nerve. They are superimposed on a single diagram; location of each point in relation to cytoarchitectonics and lamination of areas 3b, 3a, and 4 was verified for each experiment.

From Phillips et al. 132


Figure 3.

Relation between tonic firing rate and static torque for 14 corticomotoneuronal (CM) cells related to wrist extension and 11 CM cells related to wrist flexion. Cells were selected solely on the basis of the strength of their postspike facilitation and the adequacy of the range of load studied. Firing rate of all plotted cells was measured from response averages, compiled for at least 4 load levels. Compared with extension CM cells, flexion cells showed a similar range of firing rates but extended over approximately twice the torque range.

From Cheney and Fetz 29


Figure 4.

Distribution of spindle (left) and motor cortex (right) inputs to motoneurons of different muscles and muscle groups of baboon hand. Thicknesses of arrow shafts measure mean quantities of monosynaptic excitatory action (MV scale at left). EDC, extensor digitorum communis; R, remaining dorsiflexors of wrist; Uh, hypothenar muscles, in‐terossei, ulnar lumbricals, intrinsic flexor, and adductor of thumb; Mh, remaining intrinsic hand muscles; FDS, flexor digitorum sublimis; PL, palmaris longus.

From Clough et al. 31


Figure 5.

Changes of movement and discharge of precentral unit during flexion loading (middle column, n = 18) and flexion unloading torque pulse (right column, n = 17) compared with flexions without torque pulse (left column, n = 20). Uppermost trace: overplot of position signals computed with programmed data processor (PDP‐12) at a sampling rate of 200 Hz. Hatched boxes indicate 2 target zones. Second trace: overplot of computed velocities. Two middle traces: intramuscularly recorded EMG activity in triceps and biceps as photographed from superimposed traces on storage oscilloscope. Raster plots of sequentially displayed unit discharges; bin width = 1 ms. Time histograms: bin width = 10 ms. Vertical lines indicate time when velocity reached 60°/s, taken as zero reference point for averaging procedure and when torque pulses were applied.

From Conrad et al. 33


Figure 6.

Electromyographic activity following a suddenly applied and maintained stretching force in normal biceps (A), quadriceps (B), and gastrocnemius (C). In each muscle, the stretch (onset of which, denoted by arrow, triggered the sweep) produced a tendon jerk response, followed after a silent period by a large, asynchronous burst of activity termed the functional stretch reflex. Time between onsets of tendon jerk and functional stretch reflex is sequentially related to segmental level of muscular innervation. Five traces were superimposed in each example. All records were from same subject.

From Chan et al. 27


Figure 7.

Electromyographic responses in biceps (upper traces) and gastrocnemius (lower traces) to sudden and maintained stretching force in normal (A) and spastic paraplegic (B) subjects. Biceps response evoked in spastic subject (upper trace in B), being above level of cord transection, has a similar pattern to that of normal subject (upper trace in A). In contrast early discharge is prolonged in spastic gastrocnemius (lower trace in B), but no EMG activity is evident in time bracket normally occupied by functional stretch reflex in intact subject, which in this instance occurred about 100 ms after stimulus (lower trace in A).

From Chan et al. 27


Figure 8.

Comparison of electromyographic (EMG) response evoked by sudden and sustained stretch in biceps (upper trace) and gastrocnemius (lower trace) between normal (A) and affected (B) side of hemiplegic patients. Biceps response is obtained from one patient; gastrocnemius response from another. Note that response of affected muscles (B) showed a prolonged early discharge, but no EMG burst can be observed in time gate normally occupied by functional stretch reflex in corresponding unaffected muscles (A), although in some subjects a late burst can be seen marking the beginning of clonus (e.g., lower trace in B).

From Chan et al. 27


Figure 9.

Three displays are shown: 1) superimposed position traces, 2) histograms of unit discharge, and 3) rasters of unit discharge. Attention is directed to several points. 1) Unperturbed small pronation (top left) is preceded by more prolonged unit discharge than unperturbed ballistic movement (top right). 2) Inhibitory effect of torque pulse is greater when delivered during a small pronation (top, small + torque) than when delivered during holding (top, torque pulse holding). 3) There is a corresponding accentuation of excitatory effects of supinating torque pulse when this is delivered during small movement (bottom, small + torque) compared with holding (bottom, torque pulse holding). 4) There is attentuation of torque pulse response when pulse is delivered immediately before ballistic movement (preballistic torque).

From Evarts and Fromm 47


Figure 10.

Superimposed average handle displacement traces. For half the trials, a monkey was given prior instruction to prepare to push; for the other half, it was instructed to prepare to pull. Load change in both cases moved handle toward monkey. Traces follow same trajectory for approximately 90 ms (period between dashed lines). Since peripheral input during this period should be very similar, the influence of motor preparation on a short‐latency response to load change could be analyzed in this period.

From Strick 146


Figure 11.

Biceps electromyographic (EMG) activity in paradigm involving a prior instruction and a kinesthetic trigger. A lamp (red or green) indicated to the monkey what to do, and a perturbation of the handle indicated when to do it. Instructions to pull or push and perturbations toward or away from the monkey could be combined in 4 possible ways, as shown in the 4 pairs of traces in this figure. Each pair of traces shows biceps EMG activity and output of a potentiometer coupled to the handle, with upward deflection of potentiometer trace indicating movement of handle toward monkey, and downward deflection of potentiometer trace indicating movement of handle away from monkey. For set of traces at upper left, prior instruction was pull, calling for biceps contraction, and perturbing stimulus (indicated by potentiometer trace) moved handle away from the monkey, thereby stretching the biceps. At lower right, instruction was push, and initial perturbation was a movement of the handle toward the monkey, resulting in shortening of biceps.

From Evarts and Tanji 50


Figure 12.

Raster displays of activity of pyramidal tract neuron show activity occurring 500 ms before and 500 ms after a perturbation that occurred at center line of display. Single heavy dot in each row following perturbation shows when handle reached intended push or pull zone. This PTN was one that discharged with intended push movement and fell silent with intended pull movement. In raster at top, heavy dot marking completion of push movement is followed by PTN silence as monkey pulls back into “hold zone” to initiate a new trial. In the raster at bottom, the heavy dot occurs during PTN silence as monkey pulls, and discharge recommences as monkey pushes back to hold zone to start a new trial.

From Evarts and Tanji 51


Figure 13.

Proposed roles of several brain structures in movement. Dashed line represents pathway of unknown importance. Short dashed lines at A and B represent lesions described in text. It is proposed that the basal ganglia and cerebellar hemisphere (cbm) are involved with the association cortex (assn cx) in programming volitional movements. When the motor command descends to motoneurons, engaging the movement, the pars intermedia updates the intended movement based on the motor command and somatosensory description of limb position and velocity on which the movement is to be superimposed. Follow‐up correction can be performed by the motor cortex (motor cx) when the cerebellar hemisphere and pars intermedia do not effectively perform their functions.

From Allen and Tsukahara 2


Figure 14.

Influence of motor preparation on short‐latency response of dentate neuron to load changes. Neural response averages (A1, B1), rasters of individual trials (A2, B2), and average displacement traces (A3, B3) of same dentate neuron recorded under 2 conditions. Load change in A panels and B panels moved handle away from monkey. In A, animal was instructed to prepare to push and in B, to prepare to pull. Each line in the rasters (A2, B2) represents an individual trial, and each dot a single neural discharge. Both rasters and response averages show that same direction of load change evoked a short‐latency increase in activity when animal was prepared to push and a short‐latency decrease in activity when animal was prepared to pull. Maximum scale in A1 equals 512 pulses/s and in B1, 256 pulses/s.

From Strick 146


Figure 15.

Above: surface reconstruction made from sagittal sections at approximately 200‐μm intervals showing striplike distribution of labeled corticospinal cells (dots) in fields of sensorimotor and parietal cortex after large injection of HRP into contralateral thoracic spinal cord. Cynomolgus monkey. Below: representative sagittal sections from levels indicated showing positions of labeled cell clusters. In both parts of figure, each dot represents 1 cell.

From Jones and Wise 91


Figure 16.

Discharge of precentral motor cortex pyramidal tract neuron (same neuron as illustrated in Fig. 9) for slow movement (left) and rapid movement (right). Displays are centered on detection of movement onset (a change of position of approximately 1°) and include 500 ms before and 500 ms after detection of movement onset. Further details concerning position display (top), histograms of unit discharge (middle), and rasters (bottom) are given in legend of Figure 9.

From Evarts and Fromm 48


Figure 17.

Two possible schemata that might have the functional properties Jackson assigned to each unit of corpus striatum. At left is a unit in which pyramidal tract neurons (a, b, and c) projecting to motoneurons (Ma, Mb, and Mc) are intermingled. Relative strengths of representation of 3 muscles (A, B, and C) in this unit are in the ratio of 4:2:1. Electrical stimulation of a group of units such as this at threshold for motoneuronal discharge would excite Ma. At right is shown a different arrangement, one in which axon of a single PTN (4a + 2b + c) has a divergent projection onto motoneurons of 3 different muscles. Like the unit at left, this unit represents muscles A, B, and C in a ratio of 4:2:1. Electrical stimulation of a group of units such as this at threshold for motoneuron discharge would excite Ma without exciting Mb or Mc.

From Evarts 41


Figure 18.

Five variants of organization of corticomotoneuronal projections. Large circles denote 2 different motor nuclei; small circles denote pyramidal tract cells; lines around them indicate cortical areas of projection to different motor nuclei; columns above them show cortical network with fibers terminating on pyramidal cells. A: mosaiclike organization of pyramidal tract cells; B: overlapping organization of pyramidal tract cells with projections of single pyramidal tract cells to only 1 motor nucleus; C: overlapping organization of pyramidal tract cells with projections of some pyramidal tract cells to more than 1 motor nucleus; D: pseudomosaic organization of cortical output with overlapping organization of pyramidal tract cells and selective activation of pyramidal tract cells projecting to different motor nuclei; E: patterned organization of cortical output with overlapping organization of pyramidal tract cells and coactivation of pyramidal tract cells projecting to different motor nuclei.

From Jankowska et al. 85
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Article Title: Role of Motor Cortex in Voluntary Movements in Primates
 

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Edward V. Evarts. Role of Motor Cortex in Voluntary Movements in Primates. Compr Physiol 2011, Supplement 2: Handbook of Physiology, The Nervous System, Motor Control: 1083-1120. First published in print 1981. doi: 10.1002/cphy.cp010223