受病变累及的运动中枢fMR表现

目的观察正常及受病变累及的运动中枢的脑功能核磁共振成像(fMR)表现.方法通过双手对指运动使运动中枢功能活跃,然后对14例正常志愿者和36例运动中枢受累的病人进行运动功能区血氧水平依赖法(BOLD)fMR成像.结果通过双手对指运动使运动中枢功能活跃,正常志愿者和病人脑内产生了相应的功能信号,表现为功能区信号增高.在正常志愿者中,双侧半球运动功能区的位置基本对称,但大部分志愿者左侧半球功能信号稍强于对侧半球.在累及运动中枢病变的病人中,病变侧功能信号全部位于病变外或病变边缘,病变内未见功能信号.病侧功能区主要表现为功能信号降低、移位.结论BOLD法fMR可以很好的显示正常和病变的运动中枢,是评价运动中枢的有效方法.     

rTMS reveals premotor cortex dysfunction in frontal lobe epilepsy

PURPOSE: Studies of motor cortex excitability provided evidence that focal epilepsies may alter the excitability of cortical areas distant from the epileptogenic zone. In order to explore this hypothesis we studied the functional connectivity between premotor and motor cortex in seven patients with frontal lobe epilepsy and seizure onset zone outside the premotor or motor cortex. METHODS: Low-frequency subthreshold repetitive transcranial magnetic stimulation was applied to the premotor cortex and its impact on motor cortex excitability was measured by the amplitude of motor-evoked potentials in response to direct suprathreshold stimulation of the motor cortex. RESULTS: Stimulation of the premotor cortex of the non-epileptogenic hemisphere resulted in a progressive and significant inhibition of the motor cortex as evidenced by a reduction of motor evoked potential amplitude. On the other hand, stimulation of the premotor cortex of the epileptogenic hemisphere failed to inhibit the motor cortex. The reduced inhibition of the motor cortex by remote areas was additionally supported by the significantly shorter cortical silent periods obtained after stimulation of the motor cortex of the epileptogenic hemisphere. CONCLUSION: These results show that the functional connectivity between premotor and motor cortex or motor cortex interneuronal excitability is impaired in the epileptogenic hemisphere in frontal lobe epilepsy while it is normal in the nonepileptogenic hemisphere.     

Asymmetry of cortical excitability revealed by transcranial stimulation in a patient with focal motor epilepsy and cortical myoclonus

Motor cortex excitability was analyzed with transcranial stimulation in a patient with motor focal epilepsy and cortical myoclonus originating from the right motor cortex. The motor threshold to single transcranial magnetic shocks, but not to electric stimuli, was higher in the epileptic motor cortex than the normal left motor cortex. Single magnetic shocks elicited a short cortical silent period (50 ms) in the epileptic motor cortex. Paired magnetic stimuli also showed reduced cortico-cortical inhibition. These findings reveal an asymmetry in cortical excitability presumably due to impaired inhibition in the epileptic motor cortex.     

功能磁共振对脑卒中患者拇指运动时大脑活动的初步研究

目的：观察偏瘫患者拇指在不同运动形式下,大脑半球相关区域血氧水平的变化情况。方法：让患者分别进行健侧和患者拇指被动运动、主动运动和加阻力下的主动运动。在患运运动时行功能磁共振（F－MRI）检查,观察上述不同运动形式下大脑半球相关区域血氧水平的变化。结果：在健侧分别进行主动、被动及加阻力的主动运动时,皮层信号区均集中于中央前回第一运动区和中央后回本体感觉附近,重复性强。而当患侧行上述3种动作模式时,在其病变区信号活动明显增强,而且可见大 皮层及皮层下其他部位有兴奋性信号出现。结论：在脑卒中恢复期,大脑半球其他部位对其运动功能的改善发挥了作用,而且不同的运动模式其参与的部位也不同,运动疗法中的各种手法确实能引起脑组织内的某些信号变化,对大脑半球的功能重组产生了积极的作用。     

Ipsilateral cortical connections of motor, premotor, frontal eye, and posterior parietal fields in a prosimian primate, Otolemur garnetti

The ipsilateral connections of motor areas of galagos were determined by injecting tracers into primary motor cortex (M1), dorsal premotor area (PMD), ventral premotor area (PMV), supplementary motor area (SMA), and frontal eye field (FEF). Other injections were placed in frontal cortex and in posterior parietal cortex to define the connections of motor areas further. Intracortical microstimulation was used to identify injection sites and map motor areas in the same cases. The major connections of M1 were with premotor cortex, SMA, cingulate motor cortex, somatosensory areas 3a and 1, and the rostral half of posterior parietal cortex. Less dense connections were with the second (S2) and parietal ventral (PV) somatosensory areas. Injections in PMD labeled neurons across a mediolateral belt of posterior parietal cortex extending from the medial wall to lateral to the intraparietal sulcus. Other inputs came from SMA, M1, PMV, and adjoining frontal cortex. PMV injections labeled neurons across a large zone of posterior parietal cortex, overlapping the region projecting to PMD but centered more laterally. Other connections were with M1, PMD, and frontal cortex and sparsely with somatosensory areas 3a, 1-2, S2, and PV. SMA connections were with medial posterior parietal cortex, cingulate motor cortex, PMD, and PMV. An FEF injection labeled neurons in the intraparietal sulcus. Injections in posterior parietal cortex revealed that the rostral half receives somatosensory inputs, whereas the caudal half receives visual inputs. Thus, posterior parietal cortex links visual and somatosensory areas with motor fields of frontal cortex.     

The role of the premotor cortex and the primary motor cortex in action verb comprehension: evidence from Granger causality analysis

Although numerous studies find the premotor cortex and the primary motor cortex are involved in action language comprehension, so far the nature of these motor effects is still in controversy. Some researchers suggest that the motor effects reflect that the premotor cortex and the primary motor cortex make functional contributions to the semantic access of action verbs, while other authors argue that the motor effects are caused by comprehension. In the current study, we used Granger causality analysis to investigate the roles of the premotor cortex and the primary motor cortex in processing of manual-action verbs. Regions of interest were selected in the primary motor cortex (M1) and the premotor cortex based on a hand motion task, and in the left posterior middle temporal gyrus (lexical semantic area) based on the reading task effect. We found that (1) the left posterior middle temporal gyrus had a causal influence on the left M1; and (2) the left posterior middle temporal gyrus and the left premotor cortex had bidirectional causal relations. These results suggest that the premotor cortex and the primary motor cortex play different roles in manual verb comprehension. The premotor cortex may be involved in motor simulation that contributes to action language processing, while the primary motor cortex may be engaged in a processing stage influenced by the meaning access of manual-action verbs. Further investigation combining effective connectivity analysis and technique with high temporal resolution is necessary for better clarification of the roles of the premotor cortex and the primary motor cortex in action language comprehension.     

Interhemispheric effects of high and low frequency rTMS in healthy humans.

OBJECTIVE: We investigated whether repetitive transcranial magnetic stimulation (rTMS) applied to the right motor cortex modified the excitability of the unstimulated left motor cortex. METHODS: Interhemispheric effects of 0.5 and 5 Hz subthreshold rTMS over the right motor cortex were examined by single pulse and paired pulse TMS and by transcranial electrical stimulation (TES) applied to the unstimulated left motor cortex. The effects of (a) 1800 pulses real and sham rTMS with 5 Hz, (b) 180 pulses real and sham rTMS with 0.5 Hz and (c) 1800 pulses real rTMS with 0.5 Hz were studied. RESULTS: Following 5 Hz right motor rTMS motor evoked potential (MEP) amplitudes induced by single pulse TMS over the left motor cortex increased significantly. Intracortical inhibition (ICI) and facilitation (ICF) and MEP amplitudes evoked by TES were unchanged. Sham stimulation had no influence on motor cortex excitability. After 180 pulses right motor cortex rTMS with 0.5 Hz a significant decrease of left motor ICF, but no change in single pulse MEP amplitudes was found. A similar trend was observed with 1800 pulses rTMS with 0.5 Hz. CONCLUSIONS: High frequency right motor rTMS can increase left motor cortex excitability whereas low frequency right motor rTMS can decrease it. These effects outlast the rTMS by several minutes. The underlying mechanisms mediating interhemispheric excitability changes are likely to be frequency dependent.     

A change in injured corticospinal tract originating from the premotor cortex to the primary motor cortex in a patient with intracerebral hemorrhage

Many studies have attempted to elucidate the motor recovery mechanism of stroke,but the majority of these studies focus on cerebral infarct and relatively little is known about the motor recovery mechanism of intracerebral hemorrhage.In this study,we report on a patient with intracerebral hemorrhage who displayed a change in injured corticospinal tract originating from the premotor cortex to the primary motor cortex on diffusion tensor imaging.An 86-year-old woman presented with complete paralysis of the right extremities following spontaneous intracerebral hemorrhage in the left frontoparietal cortex.The patient showed motor recovery,to the extent of being able to extend affected fingers against gravity and to walk independently on even ground at 5 months after onset.Diffusion tensor imaging showed that the left corticospinal tract originated from the premotor cortex at 1 month after intracerebral hemorrhage and from the left primary motor cortex and premotor cortex at 5 months after intracerebral hemorrhage.The change of injured corticospinal tract originating from the premotor cortex to the primary motor cortex suggests motor recovery of intracerebral hemorrhage.     

Functionally specific changes in resting-state sensorimotor networks after motor learning

Motor learning changes the activity of cortical motor and subcortical areas of the brain, but does learning affect sensory systems as well? We examined in humans the effects of motor learning using fMRI measures of functional connectivity under resting conditions and found persistent changes in networks involving both motor and somatosensory areas of the brain. We developed a technique that allows us to distinguish changes in functional connectivity that can be attributed to motor learning from those that are related to perceptual changes that occur in conjunction with learning. Using this technique, we identified a new network in motor learning involving second somatosensory cortex, ventral premotor cortex, and supplementary motor cortex whose activation is specifically related to perceptual changes that occur in conjunction with motor learning. We also found changes in a network comprising cerebellar cortex, primary motor cortex, and dorsal premotor cortex that were linked to the motor aspects of learning. In each network, we observed highly reliable linear relationships between neuroplastic changes and behavioral measures of either motor learning or perceptual function. Motor learning thus results in functionally specific changes to distinct resting-state networks in the brain.     

Crossed inhibition of sensory cortex by 0.3 Hz transcranial magnetic stimulation of motor cortex.

Low-frequency repetitive transcranial magnetic stimulation (rTMS) of motor cortex causes persistent inhibitory effects in the targeted area. rTMS of motor cortex impairs sensory perception and results in a persistent change in cortical function at remote sites. The ability of rTMS to induce sustained changes in cortical function has led to studies testing its therapeutic efficacy in neurologic disorders, including epilepsy. Studies on the effect of low-frequency rTMS of motor cortex on the contralateral motor cortex have provided evidence for both inhibitory and excitatory changes. This study was designed to determine the effect of low-frequency rTMS of the right motor cortex on the contralateral sensory cortex. Before and after 0.3-Hz rTMS of right motor cortex, perception of ipsilateral threshold of cutaneous stimuli was assessed and somatosensory evoked potentials (SEPs) recorded after stimulation of the right thumb in eight normal subjects. In a control group of six subjects, sensory responses were assessed after rTMS anterior to the right motor cortex. After rTMS of motor cortex, detection of threshold sensory stimuli decreased by more than 50% compared with pre-rTMS (P < 0.05). The change in sensory perception lasted at least 30 minutes. No change was detected in the control group. Amplitude of the N20-P25 waveform of the SEP decreased from a mean of 0.84 muV before rTMS to 0.54 muV immediately after rTMS of motor cortex (P < 0.05). 0.3 Hz rTMS of motor cortex inhibits the contralateral sensory cortex.     

The transcranial magnetic stimulation motor threshold depends on the distance from coil to underlying cortex: a replication in healthy adults comparing two methods of assessing the distance to cortex.

Using transcranial magnetic stimulation (TMS), a handheld electrified copper coil against the scalp produces a powerful and rapidly oscillating magnetic field, which in turn induces electrical currents in the brain. The amount of electrical energy needed for TMS to induce motor movement (called the motor threshold [MT]), varies widely across individuals. The intensity of TMS is dosed relative to the MT. Kozel et al observed in a depressed cohort that MT increases as a function of distance from coil to cortex. This article examines this relationship in a healthy cohort and compares the two methods of assessing distance to cortex. Seventeen healthy adults had their TMS MT determined and marked with a fiducial. Magnetic resonance images showed the fiducials marking motor cortex, allowing researchers to measure distance from scalp to motor and prefontal cortex using two methods: 1) measuring a line from scalp to the nearest cortex and 2) sampling the distance from scalp to cortex of two 18-mm-square areas. Confirming Kozel's previous finding, we observe that motor threshold increases as distance to motor cortex increased for both methods of measuring distance and that no significant correlation exists between MT and prefontal cortex distance. Distance from TMS coil to motor cortex is an important determinant of MT in healthy and depressed adults. Distance to prefontal cortex is not correlated with MT, raising questions about the common practice of dosing prefontal stimulation using MT determined over motor cortex.     

Disengagement of Motor Cortex during Long-Term Learning Tracks the Performance Level of Learned Movements

Not all movements require the motor cortex for execution. Intriguingly, dependence on motor cortex of a given movement is not fixed, but instead can dynamically change over the course of long-term learning. For instance, rodent forelimb movements that initially require motor cortex can become independent of the motor cortex after an extended period of training. However, it remains unclear whether long-term neural changes rendering the motor cortex dispensable are a simple function of the training length. To address this issue, we trained mice (both male and female) to perform two distinct forelimb movements, forward versus downward reaches with a joystick, concomitantly over several weeks, and then compared the involvement of the motor cortex between the two movements. Most mice achieved different levels of motor performance between the two movements after long-term training. Of the two movements, the one that achieved higher trial-to-trial consistency (i.e., consistent-direction movement) was significantly less affected by inactivation of motor cortex than the other (i.e., variable-direction movement). Two-photon calcium imaging of motor cortical neurons revealed that the consistent-direction movement activates fewer neurons, producing weaker and less consistent population activity than the variable-direction movement. Together, the motor cortex was less engaged and less necessary for learned movements that achieved higher levels of consistency. Thus, the long-term reorganization of neural circuits that frees the motor cortex from the learned movement is not a mere function of training length. Rather, this reorganization tracks the level of motor performance that the animal achieves during training.SIGNIFICANCE STATEMENT Long-term training of a movement reshapes motor circuits, disengaging motor cortex potentially for automatized execution of the learned movement. Acquiring new motor skills often involves learning of multiple movements (e.g., forehand and backhand strokes when learning tennis), but different movements do not always improve at the same time nor reach the same level of proficiency. Here we showed that the involvement of motor cortex after long-term training differs between similar yet distinct movements that reached different levels of expertise. Motor cortex was less engaged and less necessary for the more proficient movement. Thus, disengagement of motor cortex is not a simple function of training time, but instead tracks the level of expertise of a learned movement.     

Modulating activity in the motor cortex affects performance for the two hands differently depending upon which hemisphere is stimulated

We modulated neural excitability in the human motor cortex to investigate behavioral effects for both hands. In a previous study, we showed that decreasing excitability in the dominant motor cortex led to a decline in performance for the contralateral hand and an improvement for the ipsilateral hand; increasing excitability produced the opposite effects. Research suggests that the ipsilateral effects were mediated by interhemispheric inhibition. Physiological evidence points to an asymmetry in interhemispheric inhibition between the primary motor cortices, with stronger inhibitory projections coming from the dominant motor cortex. In the present study, we examined whether there is a hemispheric asymmetry in the effects on performance when modulating excitability in the motor cortex. Anodal and cathodal transcranial direct current stimulation were applied to the motor cortex of 17 participants, targeting the non-dominant hemisphere on one day and the dominant hemisphere on another day, along with one sham session. Participants performed a finger-sequence coordination task with each hand before and after stimulation. The dependent variable was calculated as the percentage of change in the number of correct keystrokes. We found that the effects of transcranial direct current stimulation depended upon which hemisphere was stimulated; modulating excitability in the dominant motor cortex significantly affected performance for the contralateral and ipsilateral hands, whereas modulating excitability in the non-dominant motor cortex only had a significant impact for the contralateral hand. These results provide evidence for a hemispheric asymmetry in the ipsilateral effects of modulating excitability in the motor cortex and may be important for clinical research on motor recovery.     

Organization of the projections from the posterior parietal cortex to the rostral and caudal regions of the motor cortex of the cat

The posterior parietal cortex (PPC) is an important source of input to the motor cortex in both the primate and the cat. However, the available evidence from the cat suggests that the projection from the PPC to those rostral areas of the motor cortex that project to the intermediate and ventral parts of the spinal gray matter is relatively small. This leaves in question the importance of the contribution of the PPC to the initiation and modulation of voluntary movements in the cat. As this anatomical evidence is not entirely compatible with the physiological data, we reinvestigated the PPC projection to the motor cortex by injecting dextran amine tracers either into the proximal or distal representations of the forelimb in the rostral motor cortex, into the representation of the forelimb in the caudal motor cortex, or into the hindlimb representation. The results show strong projections from the PPC to each of these regions. However, projections to the rostral motor cortex were observed primarily from the caudal bank of the ansate sulcus and the adjacent gyrus, whereas those to the caudal motor cortex were generally located more rostrally. There was also evidence of some topographic organization with the distal limb being located progressively more laterally and rostrally in the PPC than the areas projecting to more proximal regions. In contrast to previous anatomical investigations, these results suggest that the PPC can potentially modulate motor activity via its strong projection to the more rostral regions of the motor cortex.     

The involvement of primary motor cortex in mental rotation revealed by transcranial magnetic stimulation

We used single‐pulse transcranial magnetic stimulation of the left primary hand motor cortex and motor evoked potentials of the contralateral right abductor pollicis brevis to probe motor cortex excitability during a standard mental rotation task. Based on previous findings we tested the following hypotheses. (i) Is the hand motor cortex activated more strongly during mental rotation than during reading aloud or reading silently? The latter tasks have been shown to increase motor cortex excitability substantially in recent studies. (ii) Is the recruitment of the motor cortex for mental rotation specific for the judgement of rotated but not for nonrotated Shepard & Metzler figures? Surprisingly, motor cortex activation was higher during mental rotation than during verbal tasks. Moreover, we found strong motor cortex excitability during the mental rotation task but significantly weaker excitability during judgements of nonrotated figures. Hence, this study shows that the primary hand motor area is generally involved in mental rotation processes. These findings are discussed in the context of current theories of mental rotation, and a likely mechanism for the global excitability increase in the primary motor cortex during mental rotation is proposed.     

Primary motor cortex involvement in Alzheimer disease

In Alzheimer disease (AD) the involvement of entorhinal cortex, hippocampus, and associative cortical areas is well established. Regarding the involvement of the primary motor cortex the reported data are contradictory. In order to determine whether the primary motor cortex is involved in AD, the brains of 29 autopsy cases were studied, including, 17 cases with severe cortical AD-type changes with definite diagnoses of AD, 7 age-matched cases with discrete to moderate cortical AD-type changes, and 5 control cases without any AD-type cortical changes. Morphometric analysis of the cortical surface occupied by senile plaques (SPs) on beta-amyloid-immunostained sections and quantitative analysis of neurofibrillary tangles (NFTs) on Gallyas-stained sections was performed in 5 different cortical areas including the primary motor cortex. The percentage of cortical surface occupied by SPs was similar in all cortical areas, without significant difference and corresponded to 16.7% in entorhinal cortex, 21.3% in frontal associative, 16% in parietal associative, and 15.8% in primary motor cortex. The number of NFTs in the entorhinal cortex was significantly higher (41 per 0.4 mm2), compared with those in other cortical areas (20.5 in frontal, 17.9 in parietal and 11.5 in the primary motor cortex). Our findings indicate that the primary motor cortex is significantly involved in AD and suggest the appearance of motor dysfunction in late and terminal stages of the disease.     

Investigation of the normal proximal somatomotor system using magnetoencephalography.

OBJECTIVE: The role of the ipsilateral cortex in proximal muscle control in normal human subjects is still under debate. One clinical finding, rapid recovery of proximal muscle relative to distal muscle use following stroke, has led to the suggestion that the ipsilateral as well as the contralateral motor cortex may be involved in normal proximal muscle control. The primary goal of this project was to identify contralateral and ipsilateral motor cortex activation associated with proximal muscle movement in normal subjects using magnetoencephalography (MEG). METHODS: We developed protocols for a self-paced bicep motor task and a deltoid, electrical-stimulation somatosensory task. The MEG data were analyzed using automated multi-dipole spatiotemporal modeling techniques to localize the sources and characterize the associated timing of these sources. RESULTS: Reliable contralateral primary motor and somatosensory sources localized to areas consistent with the homunculus. Ipsilateral M1 activation was only found in 2/12 hemispheres. CONCLUSIONS: Robust contralateral motor cortex activation and sparse ipsilateral motor cortex activation suggest that the ipsilateral motor cortex is not involved in normal proximal muscle control. SIGNIFICANCE: The results suggest that proximal and distal muscle control is similar in normal subjects in the sense that proximal muscle control is primarily governed by the contralateral motor cortex.     

Microstimulation and architectonics of frontoparietal cortex in common marmosets (Callithrix jacchus)

We investigated the organization of frontoparietal cortex in the common marmoset (Callithrix jacchus) by using intracortical microstimulation and an architectonic analysis. Primary motor cortex (M1) was identified as an area that evoked visible movements at low levels of electric current and had a full body representation of the contralateral musculature. Primary motor cortex represented the contralateral body from hindlimb to face in a mediolateral sequence, with individual movements such as jaw and wrist represented in multiple nearby locations. Primary motor cortex was coextensive with an agranular area of cortex marked by a distinct layer V of large pyramidal cells that gradually decreased in size toward the rostral portion of the area and was more homogenous in appearance than other New World primates. In addition to M1, stimulation also evoked movements from several other areas of frontoparietal cortex. Caudal to primary motor cortex, area 3a was identified as a thin strip of cortex where movements could be evoked at thresholds similar to those in M1. Rostral to primary motor cortex, supplementary motor cortex and premotor areas responded to higher stimulation currents and had smaller layer V pyramidal cells. Other areas evoking movements included primary somatosensory cortex (area 3b), two lateral somatosensory areas (areas PV and S2), and a caudal somatosensory area. Our results suggest that frontoparietal cortex in marmosets is organized in a similar fashion to that of other New World primates.     

Charting the excitability of premotor to motor connections while withholding or initiating a selected movement

In 19 healthy volunteers, we used transcranial magnetic stimulation (TMS) to probe the excitability in pathways linking the left dorsal premotor cortex and right primary motor cortex and those linking the left and right motor cortex during the response delay and the reaction time period while subjects performed a delayed response [symbol 1 (S1) - symbol 2 (S2)] Go-NoGo reaction time task with visual cues. Conditioning TMS pulses were applied to the left premotor or left motor cortex 8 ms before a test pulse was given to the right motor cortex at 300 or 1800 ms after S1 or 150 ms after S2. S1 coded for right-hand or left-hand movement, and S2 for release or stopping the prepared movement. Conditioning of the left premotor cortex led to interhemispheric inhibition at 300 ms post-S1, interhemispheric facilitation at 150 ms post-S2, and shorter reaction times in the move-left condition. Conditioning of the left motor cortex led to inhibition at 1800 ms post-S1 and 150 ms post-S2, and slower reaction times for move-right conditions, and inhibition at 300 and 1800 ms post-S1 for move-left conditions. Relative motor evoked potential amplitudes following premotor conditioning at 150 ms post-S2 were significantly smaller in 'NoGo' than in 'Go' trials for move-left instructions. We conclude that the excitability in left premotor/motor right motor pathways is context-dependent and affects motor behaviour. Thus, the left premotor cortex is engaged not only in action selection but also in withholding and releasing a preselected movement generated by the right motor cortex.     

The organization of the rat motor cortex: a microstimulation mapping study

In conclusion, the rat primary motor cortex appears to be organized into irregularly shaped patches of cortex devoted to particular movements. The location of major subdivisions such as the forelimb or hindlimb areas is somatotopic and is consistent from animal to animal, but the internal organization of the pattern of movements represented within major subdivisions varies significantly between animals. The motor cortex includes both agranular primary motor cortex (AgL) and, in addition, a significant amount of the bordering granular somatic sensory cortex (Gr(SI)), as well as the rostral portion of the taste sensory insular or claustrocortex (Cl). The rat frontal cortex also contains a second, rostral motor representation of the forelimb, trunk and hindlimb, which is somatotopically organized and may be the rat's supplementary motor area. Both of these motor representations give rise to direct corticospinal projections, some of which may make monosynaptic connections with cervical enlargement motoneurons. Medial to the primary motor cortex, in cytoarchitectonic field AgM, is what appears to be part of the rat's frontal eye fields, a region which also includes the vibrissae motor representation. The somatic motor cortical output organization pattern in the rat is remarkably similar to that seen in the primate, whose primary, supplementary and frontal eye field cortical motor regions have been extensively studied.