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The Corticospinal System: A Structural Framework for the Central Control of Movement

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Abstract

The sections in this article are:

1 Historical Overview
2 Current Viewpoint
3 Functional Anatomy
3.1 Primary Motor Cortex
3.2 Premotor Areas in the Frontal Lobe
3.3 Corticospinal Terminations
4 Inputs to the Cortical Motor Areas
4.1 Inputs to Primary Motor Cortex
4.2 Inputs to the Premolar Areas
5 Physiological Overview
5.1 Common Activation of the Motor Areas
5.2 Specialization of Motor Processing in the Motor Areas
6 Conclusion
Figure 1. Figure 1.

Summary maps of the motor areas in the frontal lobe. A, Body representation in the frontal lobe based on surface stimulation. The medial wall is reflected upward to display the body map of the supplementary motor area (SMA) on the same figure as the body map of the precentral gyrus. According to Woolsey et al. , the SMA extends onto the dorsal bank of the cingulate sulcus. These authors did not explore the motor representation on either the ventral bank of the cingulate sulcus or the cingulate gyrus. B, An unfolded reconstruction of frontal lobe with the medial wall of the hemisphere reflected upward. The location of the arm representation in each motor area is indicated by the lettered ellipses. The boundaries between cytoarchitectonic areas are indicated by dotted lines. A dashed line indicates the fundus of the cingulate sulcus.

Adapted from He, Dum, and Strick . Reprinted by permission of the Society for Neuroscience.] ArSi, arcuate sulcus, inferior limb; ArSs, arcuate sulcus, superior limb; CC, corpus callosum; CgG, cingulate gyrus; CgSd, cingulate sulcus, dorsal bank; CgSv, cingulate sulcus, ventral bank; CMAd, caudal cingulate motor area, dorsal bank; CMAv, caudal cingulate motor area, ventral bank; CMAr, rostral cingulate motor area; M1, primary motor cortex; PMd, dorsal premotor area; PMv, ventral premotor area; pre‐SMA, pre‐supplementary motor area; SPcS, superior precentral sulcus; SGm, superior frontal gyrus, medial wall; SMA, supplementary motor area. Adapted from Woolsey, et al.
Figure 2. Figure 2.

Body map of the M1, lateral premotor cortex, and the SMA in an owl monkey as defined by intracortical stimulation. Electrode penetration sites that evoked movements at currents up to 30 μA are indicated by dots. The enclosed cortical regions indicate penetrations where movements of the same body part were evoked. K, knee; H, hip; ANK, ankle; W, wrist; EL, elbow; TR, trunk; FA, forearm; SH, shoulder; CH, chin; NO, nose; M, mouth; VIB, vibrissae; NE, neck.

From Gould, et al. , Copyright © 1986 by Wiley‐Liss, Inc. Reprinted by permission of John Wiley & Sons, Inc
Figure 3. Figure 3.

Terminal distribution of a single corticospinal axon to several spinal motor nuclei. A single corticospinal axon originating from the “hand area” of the primary motor cortex of the monkey was reconstructed from 12 serial transverse sections at C7. Motoneurons in the two upper motor nuclei were identified by retrograde transport of HRP from the ulnar nerve. The branches of this corticospinal axon projected to at least four different motoneuron groups. Terminal boutons in close contact with the proximal dendrites of some HRP‐filled motoneurons could be identified in three of them.

From Shinoda, Yokata, and Futami . Reprinted by permission of Elsevier Science, Ireland
Figure 4. Figure 4.

Postspike facilitation by corticomotoneuronal cells. A, Summary of experimental technique for compiling spike‐triggered averages. The microelectrode recorded activity of a task‐related cell. Sample records show activity of an extension‐related corticomotoneuronal cell, a wrist extensor muscle, and wrist position during an extension movement. Fast sweep shows unit spikes with raw EMG and full‐wave rectified EMG. Full‐wave rectified EMG activity was averaged over an interval from 5 ms before to 25 ms after the trigger event. B, Postspike facilitation profiles evoked by a single corticomotoneuronal cell. This cell facilitated three of six wrist extensor muscles, with the strongest relationship being at the top.

Adapted from Cheney and Fetz . Adapted from Cheney and Fetz . Reprinted by permission of the American Physiological Society
Figure 5. Figure 5.

Diagram of the simplest circuits that may mediate the basic pattern of a corticomotoneuronal cell's influence on wrist flexor and extensor motoneurons. Correlational evidence indicates that cells may facilitate agonist muscles with no effect on antagonist muscle (A, C); facilitate agonist muscles and simultaneously suppress antagonist muscles through a reciprocal inhibitory pathway (B, E, and F); or suppress certain muscles with no effect on their antagonists (D). Clustering and interconnection of cells with common targets is also suggested by these experiments.

From Cheney, Fetz, and Palmer . Reprinted by permission of the American Physiological Society
Figure 6. Figure 6.

Sensorimotor map in the primary motor cortex. A, The cortical region explored with intracortical stimulation is indicated on a lateral view of a squirrel monkey's brain. CF, central fissure. B, Map of the movements evoked by intracortical stimulation and the modality of the somatosensory input at the same sites within the arm representation of the primary motor cortex of a squirrel monkey. Microelectrode penetrations that encountered neurons receiving somatosensory input from “deep” receptors are indicated by filled symbols. Those sites that received peripheral input from “cutaneous” receptors are indicated by open symbols. Circles indicate penetrations where finger movements were evoked, and squares represent wrist movement sites. No movements were elicited at less than 30 μA at sites indicated by triangles. Major surface blood vessels are shaded. Histological analysis showed that the area 3a‐4 border was located just rostral to the region containing triangles. Dotted lines indicate borders between physiologically defined cortical regions. M1/c, caudal region of the primary motor cortex; M1/r, rostral region of the primary motor cortex.

Adapted from Strick and Preston . Reprinted by permission of the American Physiological Society
Figure 7. Figure 7.

Map of cortical neurons projecting from premotor areas on medial wall to arm region of primary motor cortex. WGA‐HRP was injected into the arm region of the primary motor cortex. The spread of tracer is indicated on the flattened reconstruction of the frontal lobe (inset at upper right). Xs mark the site of needle penetration into the cortex. A heavy line encircles the densest region of reaction product, and a lighter line indicates the “halo” that surrounded it. The dashed line encircles the region of almost continuous cell labeling that surrounded the injection site. Every fourth section was used to reconstruct the distribution of labeled neurons (dots) on the medial wall. The genu of the arcuate sulcus (left arrow) and the junction of the central sulcus with the midline (right arrow) are indicated. ArSi, arcuate sulcus, inferior limb; ArSs, arcuate sulcus, superior limb; CgG, cingulate gyrus; CgSd, singulate sulcus, dorsal bank; CgSv, singulate sulcus, ventral bank; SPcS, superior precentral sulcus; SGm, superior frontal gyrus, medial wall. Note that neurons projecting to the arm region of the primary motor cortex are located in the same regions that project to cervical segments of the spinal cord (cf. Fig. ).

From Dum and Strick . Reprinted by permission of the Society of Neuroscience
Figure 8. Figure 8.

Map of corticospinal neurons in the frontal lobe projecting to the cervical segments of the spinal cord. The WGAHRP injection site included all segments located between the fourth cervical and the second thoracic segments. Each labeled cell is represented by a dot. Every fourth section was used to construct this map. ArSi, arcuate sulcus, inferior limb; ArSs, arcuate sulcus, superior limb; CgG, cingulate gyrus; CgSd, singulate sulcus, dorsal bank; CgSv, singulate sulcus, ventral bank; SPcS, superior precentral sulcus; SGm, superior frontal gyrus, medial wall.

From Dum and Strick . Reprinted by permission of the Society for Neuroscience
Figure 9. Figure 9.

Summary of “arm” and “leg” representation in each motor area in the frontal lobe. In this map, the arm representations are based on the location of neurons that project to upper and lower cervical segments. The leg representations are based on the location of neurons that project to lower lumbosacral segments. ArSi, arcuate sulcus, inferior limb; ArSs, arcuate sulcus, superior limb; CgG, cingulate gyrus; CgSd, singulate sulcus, dorsal bank; CgSv, singulate sulcus, ventral bank; SPcS, superior precentral sulcus; SGm, superior frontal gyrus, medial wall.

Adapted from He, Dum, and Strick . Reprinted by permission of the Society for Neuroscience
Figure 10. Figure 10.

Map of the body movements evoked by intracortical stimulation of the motor areas on the medial wall of the hemisphere of a macaque monkey. All movements were contralateral to the stimulated hemisphere. Key to movements—diamonds, face; diamonds with dot, eye; filled circles, arm; open circles, arm movements evoked with long train stimulation; open squares, leg; open triangles, neck and upper truck; inverted triangles, lower trunk and tail; dash, no response; dot, penetration site. ArSi, arcuate sulcus, inferior limb; ArSs, arcuate sulcus, superior limb; CgG, cingulate gyrus; CgSd, singulate sulcus, dorsal bank; CgSv, singulate sulcus, ventral bank; SPcS, superior precentral sulcus; SGm, superior frontal gyrus, medial wall.

Adapted from Luppino et al. . Copyright © 1991 by Wiley‐Liss, Inc. Reprinted by permission of John Wiley & Sons, Inc
Figure 11. Figure 11.

Corticospinal terminations in cebus and squirrel monkeys. These images were “captured” using a digital imaging system and were taken under darkfield illumination with polarized light. A, Cebus monkey, C8. B, Squirrel monkey, C8. Arrows point to regions of dense termination at C8. Note that dense terminations are present in three regions in the cebus monkey, and only two in the squirrel monkey.

Adapted from Bortoff and Strick . Reprinted by permission of the Society for Neuroscience
Figure 12. Figure 12.

Corticospinal terminations in C7 of a macaque monkey. These images were “captured” using a digital imaging system and were taken under darkfield illumination with polarized light. The outline of the gray matter and spinal laminae are indicated. A, SMA efferents terminate densely in intermediate zone of the gray matter of the cervical spinal cord. Arrow points to terminations in the dorsolateral part of lamina IX, which contains motoneurons. B, M1 efferents terminate in the same regions as do SMA efferents. Compared to SMA terminations, M1 terminations generally are more dense, are somewhat more extensive in lamina IX, and extend farther into the base of the dorsal horn (laminae V–VI).

Figure 13. Figure 13.

Origin of parietal lobe projections from the postcentral cortex and the anterior bank of the intraparietal sulcus to the arm areas of the primary motor cortex (MC), the arcuate premotor area (APA; termed the PMv in this chapter), and the SMA. Upper left, The dashed lines on the small view of the brain indicate the region of parietal lobe that is enlarged in each of the other panels. The cytoarchitectonic areas are labeled with numbers or small lettering on the unfolded reconstruction of these regions. In the remaining panels, each dash represents a neuron labeled following tracer injection into the arm area of the designated cortical region. Note that MC receives dense input from a lateral region of area 5 (PEa) buried in the anterior bank of the intraparietal sulcus, and the SMA receives input from more medial regions of area 5. CgS, cingulate sulcus; IpS, intraparietal sulcus; PcS, postcentral sulcus.

From Dum and Strick . Copyright © 1991 by Wiley‐Liss, Inc. Reprinted by permission by John Wiley & Sons, Inc
Figure 14. Figure 14.

Summary diagram of the “loops” between the primary motor cortex and two subcortical structures, the basal ganglia and the cerebellum. Coronal sections of the thalamus (center) show the location of neurons (dots) that project from the ventrolateral thalamus to the surface and sulcus of the primary motor cortex. The shading in the primary motor cortex indicates, from dark to light, the hand, elbow, and shoulder representations. The cortical efferent terminations in the putamen are shaded according to the intensity of anterograde labeling (see ). The location of the labeled cells in the globus pallidus was determined by retrograde transneuronal transport of virus. The shading in the diagram of the pontine nuclei indicate the location of terminations from the primary motor cortex. The location of labeled neurons in the deep cerebellar nuclei was determined by retrograde transneuronal transport of virus. See text for further explanation.

Adapted from Holsapple, Preston, and Strick . Reprinted by permission of the Society for Neuroscience. Adapted from Hoover and Strick , © 1993 American Association for the Advancement of Science. Reprinted by permission. Adapted from Brodal . Reprinted by permission of Oxford University Press. Adapted from Strick, Hoover, and Mushiake . Reprinted by permission of Elsevier Science
Figure 15. Figure 15.

Location of globus pallidus neurons that innervate thalamic nuclei projecting to the SMA, M1, and PMv. Neurons in the internal segment of the globus pallidus (GPi) were labeled by retrograde transneuronal transport of herpes simplex virus type 1 (HSV‐1) following injections into the arm representations of the SMA, M1, or PMv of monkeys. The dots indicate the position of labeled cells observed in two or three coronal sections near the same stereotaxic level (A 14.0). For comparison, the dotted line indicates the region of the GPi containing neurons labeled from M1. The thick solid line indicates the outline of the globus pallidus. The thin solid line indicates the border between the internal and external (E) segments of GP. The dashed line indicates the border between the inner and outer portions of the GPi. i, inner portion of the GPi; o, outer portion of GPi; D, dorsal; M, medial.

Adapted from Hoover and Strick . © 1993 American Association for the Advancement of Science. Reprinted by permission
Figure 16. Figure 16.

The discharge pattern of a shoulder joint‐related neuron in M1 of a monkey is shown for reaching movements in eight directions. Rasters of cell activity (left) are illustrated for eight radial directions of movement from the center hold zone (x). Rasters are aligned to the onset of movement (arrowheads below dotted lines). The appearance of the target light in each trial is indicated by the heavy tick mark to the left of the arrow, and the end of the movement is designated by the heavy tick mark to the right of the arrow. In the polar plot (right), the mean discharge of the cell during movement time (from the appearance of the target light to the end of movement) is indicated by the length of the axis corresponding to each direction of movement. This response may be compared to the cell's mean discharge during the control period (all center hold epochs averaged together), which is equal to the radius of the circle. The cell's preferred direction of discharge is toward the upper left and decreases continuously to reach a minimum in the downward direction. The cell's activity during the movement time period showed an excellent fit (R2 = 0.94) to a sinusoidal curve.

From Kalaska et al. . Reprinted by permission of the Society for Neuroscience
Figure 17. Figure 17.

Representation of movement direction by a neuronal population code. The directional vectors for neurons (thin lines) in M1 of a monkey are illustrated for each of eight directions of reaching movements (diagram at center). The population vector (interrupted lines with arrows) calculated from the individual cell vectors is closely aligned to its corresponding movement direction. The cell vectors producing each population vector are symmetrically distributed around it.

From Georgopoulos et al. . © 1983 Springer‐Verlag. Reprinted by permission
Figure 18. Figure 18.

A set‐related neuron in the PMd of the monkey. This unit had a sustained increase in activity during an instructed delay period when the upcoming movement direction was to the left. Unit activity is aligned on the appearance of the visual instruction signal (left) and on movement onset (right). The unit's activity is shown as a reciprocal interval plot for the summed trials (top), in a histogram (middle), and as rasters (bottom). In the rasters, each dot represents an action potential and each line of the raster represents one movement trial.

Adapted from Weinrich and Wise . Reprinted by permission of the Society for Neuroscience
Figure 19. Figure 19.

Discharge of a PMv neuron during visually guided reaching and grasping. Individual rasters and histograms are aligned with the hand's contact with the object (central vertical line). This neuron was classified as a “grasping‐with‐the‐hand” neuron. A and B, Neuronal discharge was related to grasping with a precision grip. Note that the discharge was nearly identical during testing of the contralateral (A) or ipsilateral hands (B). C and D, Neuronal discharge was weakly related to grasping a cylinder with whole‐hand prehension. Bin width is 10 ms.

From Rizzolatti et al. . © 1988 Springer‐Verlag. Reprinted by permission
Figure 20. Figure 20.

A sequence‐specific neuron recorded in the SMA of a macaque monkey. This neuron increased its activity only when the animal performed a remembered sequence of movements (INT 1). The neuron was not active during different remembered sequences (INT 2 and 3), visually guided sequences (vis) or the transitional phase (transition) between visually guided and remembered sequences.

Adapted from Mushiake, Inase, and Tanji . Reprinted by permission of the American Physiological Society


Figure 1.

Summary maps of the motor areas in the frontal lobe. A, Body representation in the frontal lobe based on surface stimulation. The medial wall is reflected upward to display the body map of the supplementary motor area (SMA) on the same figure as the body map of the precentral gyrus. According to Woolsey et al. , the SMA extends onto the dorsal bank of the cingulate sulcus. These authors did not explore the motor representation on either the ventral bank of the cingulate sulcus or the cingulate gyrus. B, An unfolded reconstruction of frontal lobe with the medial wall of the hemisphere reflected upward. The location of the arm representation in each motor area is indicated by the lettered ellipses. The boundaries between cytoarchitectonic areas are indicated by dotted lines. A dashed line indicates the fundus of the cingulate sulcus.

Adapted from He, Dum, and Strick . Reprinted by permission of the Society for Neuroscience.] ArSi, arcuate sulcus, inferior limb; ArSs, arcuate sulcus, superior limb; CC, corpus callosum; CgG, cingulate gyrus; CgSd, cingulate sulcus, dorsal bank; CgSv, cingulate sulcus, ventral bank; CMAd, caudal cingulate motor area, dorsal bank; CMAv, caudal cingulate motor area, ventral bank; CMAr, rostral cingulate motor area; M1, primary motor cortex; PMd, dorsal premotor area; PMv, ventral premotor area; pre‐SMA, pre‐supplementary motor area; SPcS, superior precentral sulcus; SGm, superior frontal gyrus, medial wall; SMA, supplementary motor area. Adapted from Woolsey, et al.


Figure 2.

Body map of the M1, lateral premotor cortex, and the SMA in an owl monkey as defined by intracortical stimulation. Electrode penetration sites that evoked movements at currents up to 30 μA are indicated by dots. The enclosed cortical regions indicate penetrations where movements of the same body part were evoked. K, knee; H, hip; ANK, ankle; W, wrist; EL, elbow; TR, trunk; FA, forearm; SH, shoulder; CH, chin; NO, nose; M, mouth; VIB, vibrissae; NE, neck.

From Gould, et al. , Copyright © 1986 by Wiley‐Liss, Inc. Reprinted by permission of John Wiley & Sons, Inc


Figure 3.

Terminal distribution of a single corticospinal axon to several spinal motor nuclei. A single corticospinal axon originating from the “hand area” of the primary motor cortex of the monkey was reconstructed from 12 serial transverse sections at C7. Motoneurons in the two upper motor nuclei were identified by retrograde transport of HRP from the ulnar nerve. The branches of this corticospinal axon projected to at least four different motoneuron groups. Terminal boutons in close contact with the proximal dendrites of some HRP‐filled motoneurons could be identified in three of them.

From Shinoda, Yokata, and Futami . Reprinted by permission of Elsevier Science, Ireland


Figure 4.

Postspike facilitation by corticomotoneuronal cells. A, Summary of experimental technique for compiling spike‐triggered averages. The microelectrode recorded activity of a task‐related cell. Sample records show activity of an extension‐related corticomotoneuronal cell, a wrist extensor muscle, and wrist position during an extension movement. Fast sweep shows unit spikes with raw EMG and full‐wave rectified EMG. Full‐wave rectified EMG activity was averaged over an interval from 5 ms before to 25 ms after the trigger event. B, Postspike facilitation profiles evoked by a single corticomotoneuronal cell. This cell facilitated three of six wrist extensor muscles, with the strongest relationship being at the top.

Adapted from Cheney and Fetz . Adapted from Cheney and Fetz . Reprinted by permission of the American Physiological Society


Figure 5.

Diagram of the simplest circuits that may mediate the basic pattern of a corticomotoneuronal cell's influence on wrist flexor and extensor motoneurons. Correlational evidence indicates that cells may facilitate agonist muscles with no effect on antagonist muscle (A, C); facilitate agonist muscles and simultaneously suppress antagonist muscles through a reciprocal inhibitory pathway (B, E, and F); or suppress certain muscles with no effect on their antagonists (D). Clustering and interconnection of cells with common targets is also suggested by these experiments.

From Cheney, Fetz, and Palmer . Reprinted by permission of the American Physiological Society


Figure 6.

Sensorimotor map in the primary motor cortex. A, The cortical region explored with intracortical stimulation is indicated on a lateral view of a squirrel monkey's brain. CF, central fissure. B, Map of the movements evoked by intracortical stimulation and the modality of the somatosensory input at the same sites within the arm representation of the primary motor cortex of a squirrel monkey. Microelectrode penetrations that encountered neurons receiving somatosensory input from “deep” receptors are indicated by filled symbols. Those sites that received peripheral input from “cutaneous” receptors are indicated by open symbols. Circles indicate penetrations where finger movements were evoked, and squares represent wrist movement sites. No movements were elicited at less than 30 μA at sites indicated by triangles. Major surface blood vessels are shaded. Histological analysis showed that the area 3a‐4 border was located just rostral to the region containing triangles. Dotted lines indicate borders between physiologically defined cortical regions. M1/c, caudal region of the primary motor cortex; M1/r, rostral region of the primary motor cortex.

Adapted from Strick and Preston . Reprinted by permission of the American Physiological Society


Figure 7.

Map of cortical neurons projecting from premotor areas on medial wall to arm region of primary motor cortex. WGA‐HRP was injected into the arm region of the primary motor cortex. The spread of tracer is indicated on the flattened reconstruction of the frontal lobe (inset at upper right). Xs mark the site of needle penetration into the cortex. A heavy line encircles the densest region of reaction product, and a lighter line indicates the “halo” that surrounded it. The dashed line encircles the region of almost continuous cell labeling that surrounded the injection site. Every fourth section was used to reconstruct the distribution of labeled neurons (dots) on the medial wall. The genu of the arcuate sulcus (left arrow) and the junction of the central sulcus with the midline (right arrow) are indicated. ArSi, arcuate sulcus, inferior limb; ArSs, arcuate sulcus, superior limb; CgG, cingulate gyrus; CgSd, singulate sulcus, dorsal bank; CgSv, singulate sulcus, ventral bank; SPcS, superior precentral sulcus; SGm, superior frontal gyrus, medial wall. Note that neurons projecting to the arm region of the primary motor cortex are located in the same regions that project to cervical segments of the spinal cord (cf. Fig. ).

From Dum and Strick . Reprinted by permission of the Society of Neuroscience


Figure 8.

Map of corticospinal neurons in the frontal lobe projecting to the cervical segments of the spinal cord. The WGAHRP injection site included all segments located between the fourth cervical and the second thoracic segments. Each labeled cell is represented by a dot. Every fourth section was used to construct this map. ArSi, arcuate sulcus, inferior limb; ArSs, arcuate sulcus, superior limb; CgG, cingulate gyrus; CgSd, singulate sulcus, dorsal bank; CgSv, singulate sulcus, ventral bank; SPcS, superior precentral sulcus; SGm, superior frontal gyrus, medial wall.

From Dum and Strick . Reprinted by permission of the Society for Neuroscience


Figure 9.

Summary of “arm” and “leg” representation in each motor area in the frontal lobe. In this map, the arm representations are based on the location of neurons that project to upper and lower cervical segments. The leg representations are based on the location of neurons that project to lower lumbosacral segments. ArSi, arcuate sulcus, inferior limb; ArSs, arcuate sulcus, superior limb; CgG, cingulate gyrus; CgSd, singulate sulcus, dorsal bank; CgSv, singulate sulcus, ventral bank; SPcS, superior precentral sulcus; SGm, superior frontal gyrus, medial wall.

Adapted from He, Dum, and Strick . Reprinted by permission of the Society for Neuroscience


Figure 10.

Map of the body movements evoked by intracortical stimulation of the motor areas on the medial wall of the hemisphere of a macaque monkey. All movements were contralateral to the stimulated hemisphere. Key to movements—diamonds, face; diamonds with dot, eye; filled circles, arm; open circles, arm movements evoked with long train stimulation; open squares, leg; open triangles, neck and upper truck; inverted triangles, lower trunk and tail; dash, no response; dot, penetration site. ArSi, arcuate sulcus, inferior limb; ArSs, arcuate sulcus, superior limb; CgG, cingulate gyrus; CgSd, singulate sulcus, dorsal bank; CgSv, singulate sulcus, ventral bank; SPcS, superior precentral sulcus; SGm, superior frontal gyrus, medial wall.

Adapted from Luppino et al. . Copyright © 1991 by Wiley‐Liss, Inc. Reprinted by permission of John Wiley & Sons, Inc


Figure 11.

Corticospinal terminations in cebus and squirrel monkeys. These images were “captured” using a digital imaging system and were taken under darkfield illumination with polarized light. A, Cebus monkey, C8. B, Squirrel monkey, C8. Arrows point to regions of dense termination at C8. Note that dense terminations are present in three regions in the cebus monkey, and only two in the squirrel monkey.

Adapted from Bortoff and Strick . Reprinted by permission of the Society for Neuroscience


Figure 12.

Corticospinal terminations in C7 of a macaque monkey. These images were “captured” using a digital imaging system and were taken under darkfield illumination with polarized light. The outline of the gray matter and spinal laminae are indicated. A, SMA efferents terminate densely in intermediate zone of the gray matter of the cervical spinal cord. Arrow points to terminations in the dorsolateral part of lamina IX, which contains motoneurons. B, M1 efferents terminate in the same regions as do SMA efferents. Compared to SMA terminations, M1 terminations generally are more dense, are somewhat more extensive in lamina IX, and extend farther into the base of the dorsal horn (laminae V–VI).



Figure 13.

Origin of parietal lobe projections from the postcentral cortex and the anterior bank of the intraparietal sulcus to the arm areas of the primary motor cortex (MC), the arcuate premotor area (APA; termed the PMv in this chapter), and the SMA. Upper left, The dashed lines on the small view of the brain indicate the region of parietal lobe that is enlarged in each of the other panels. The cytoarchitectonic areas are labeled with numbers or small lettering on the unfolded reconstruction of these regions. In the remaining panels, each dash represents a neuron labeled following tracer injection into the arm area of the designated cortical region. Note that MC receives dense input from a lateral region of area 5 (PEa) buried in the anterior bank of the intraparietal sulcus, and the SMA receives input from more medial regions of area 5. CgS, cingulate sulcus; IpS, intraparietal sulcus; PcS, postcentral sulcus.

From Dum and Strick . Copyright © 1991 by Wiley‐Liss, Inc. Reprinted by permission by John Wiley & Sons, Inc


Figure 14.

Summary diagram of the “loops” between the primary motor cortex and two subcortical structures, the basal ganglia and the cerebellum. Coronal sections of the thalamus (center) show the location of neurons (dots) that project from the ventrolateral thalamus to the surface and sulcus of the primary motor cortex. The shading in the primary motor cortex indicates, from dark to light, the hand, elbow, and shoulder representations. The cortical efferent terminations in the putamen are shaded according to the intensity of anterograde labeling (see ). The location of the labeled cells in the globus pallidus was determined by retrograde transneuronal transport of virus. The shading in the diagram of the pontine nuclei indicate the location of terminations from the primary motor cortex. The location of labeled neurons in the deep cerebellar nuclei was determined by retrograde transneuronal transport of virus. See text for further explanation.

Adapted from Holsapple, Preston, and Strick . Reprinted by permission of the Society for Neuroscience. Adapted from Hoover and Strick , © 1993 American Association for the Advancement of Science. Reprinted by permission. Adapted from Brodal . Reprinted by permission of Oxford University Press. Adapted from Strick, Hoover, and Mushiake . Reprinted by permission of Elsevier Science


Figure 15.

Location of globus pallidus neurons that innervate thalamic nuclei projecting to the SMA, M1, and PMv. Neurons in the internal segment of the globus pallidus (GPi) were labeled by retrograde transneuronal transport of herpes simplex virus type 1 (HSV‐1) following injections into the arm representations of the SMA, M1, or PMv of monkeys. The dots indicate the position of labeled cells observed in two or three coronal sections near the same stereotaxic level (A 14.0). For comparison, the dotted line indicates the region of the GPi containing neurons labeled from M1. The thick solid line indicates the outline of the globus pallidus. The thin solid line indicates the border between the internal and external (E) segments of GP. The dashed line indicates the border between the inner and outer portions of the GPi. i, inner portion of the GPi; o, outer portion of GPi; D, dorsal; M, medial.

Adapted from Hoover and Strick . © 1993 American Association for the Advancement of Science. Reprinted by permission


Figure 16.

The discharge pattern of a shoulder joint‐related neuron in M1 of a monkey is shown for reaching movements in eight directions. Rasters of cell activity (left) are illustrated for eight radial directions of movement from the center hold zone (x). Rasters are aligned to the onset of movement (arrowheads below dotted lines). The appearance of the target light in each trial is indicated by the heavy tick mark to the left of the arrow, and the end of the movement is designated by the heavy tick mark to the right of the arrow. In the polar plot (right), the mean discharge of the cell during movement time (from the appearance of the target light to the end of movement) is indicated by the length of the axis corresponding to each direction of movement. This response may be compared to the cell's mean discharge during the control period (all center hold epochs averaged together), which is equal to the radius of the circle. The cell's preferred direction of discharge is toward the upper left and decreases continuously to reach a minimum in the downward direction. The cell's activity during the movement time period showed an excellent fit (R2 = 0.94) to a sinusoidal curve.

From Kalaska et al. . Reprinted by permission of the Society for Neuroscience


Figure 17.

Representation of movement direction by a neuronal population code. The directional vectors for neurons (thin lines) in M1 of a monkey are illustrated for each of eight directions of reaching movements (diagram at center). The population vector (interrupted lines with arrows) calculated from the individual cell vectors is closely aligned to its corresponding movement direction. The cell vectors producing each population vector are symmetrically distributed around it.

From Georgopoulos et al. . © 1983 Springer‐Verlag. Reprinted by permission


Figure 18.

A set‐related neuron in the PMd of the monkey. This unit had a sustained increase in activity during an instructed delay period when the upcoming movement direction was to the left. Unit activity is aligned on the appearance of the visual instruction signal (left) and on movement onset (right). The unit's activity is shown as a reciprocal interval plot for the summed trials (top), in a histogram (middle), and as rasters (bottom). In the rasters, each dot represents an action potential and each line of the raster represents one movement trial.

Adapted from Weinrich and Wise . Reprinted by permission of the Society for Neuroscience


Figure 19.

Discharge of a PMv neuron during visually guided reaching and grasping. Individual rasters and histograms are aligned with the hand's contact with the object (central vertical line). This neuron was classified as a “grasping‐with‐the‐hand” neuron. A and B, Neuronal discharge was related to grasping with a precision grip. Note that the discharge was nearly identical during testing of the contralateral (A) or ipsilateral hands (B). C and D, Neuronal discharge was weakly related to grasping a cylinder with whole‐hand prehension. Bin width is 10 ms.

From Rizzolatti et al. . © 1988 Springer‐Verlag. Reprinted by permission


Figure 20.

A sequence‐specific neuron recorded in the SMA of a macaque monkey. This neuron increased its activity only when the animal performed a remembered sequence of movements (INT 1). The neuron was not active during different remembered sequences (INT 2 and 3), visually guided sequences (vis) or the transitional phase (transition) between visually guided and remembered sequences.

Adapted from Mushiake, Inase, and Tanji . Reprinted by permission of the American Physiological Society
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Richard P. Dum, Peter L. Strick. The Corticospinal System: A Structural Framework for the Central Control of Movement. Compr Physiol 2011, Supplement 29: Handbook of Physiology, Exercise: Regulation and Integration of Multiple Systems: 217-254. First published in print 1996. doi: 10.1002/cphy.cp120106