Neural activity correlated with the preparation and execution of visually guided arm movements in the cingulate motor area of the monkey

Recent anatomical and physiological studies have suggested that parts of the cingulate cortex are involved in the control of movement. These areas have been collectively termed the cingulate motor area (CMA). Currently almost nothing is known, however, about how neurons in the CMA actually participate in the control of movement. Therefore, we investigated the role of cells in the dorsal and ventral banks of the CMA (CMAd and CMAv, respectively) in the preparation and execution of visually guided arm movements. We recorded the activity of neurons while a monkey performed a visually guided, two-dimensional instructed delay task. A monkey was required to operate a joystick that moved a cursor from a centrally located hold target to one of four peripheral targets. Neurons were classified as exhibiting preparatory activity if the neural discharge during the postinstruction delay period was significantly higher than the preinstruction activity. Neurons were classified as exhibiting movement activity if the neural discharge was significantly elevated around the time of the movement. Of the 115 task-related neurons studied, 18 (16%) exhibited only preparatory activity, 48 (42%) exhibited only movement activity, and 49 (43%) exhibited both preparatory and movement activity. Neurons were further classified in terms of their directional tuning. For 51% of neurons with preparatory activity, that activity was directional. A significantly larger proportion of movement-related activity was directional (78%). For neurons with both directional preparatory and movement activity, the preferred directions were highly correlated (r=0.83). The median onset of movement activity was 10 ms before the beginning of movement (range -200 to 200 ms). The patterns and directionality of task-related activity of CMA neurons observed in this study are similar to those previously reported for other cortical motor areas. Together, these data provide preliminary evidence that neurons in CMAd and CMAv play a role in both the preparation and execution of visually guided arm movements.     

Changes in motor cortical activity during visuomotor adaptation

We examined neuronal activity in three motor cortical areas while a rhesus monkey adapted to novel visuomotor transforms. The monkey moved a joystick that controlled a cursor on a video screen. Each trial began with the joystick centered. Next, the cursor appeared in one of eight positions, arranged in a circle around a target stimulus at the center of the screen. To receive reinforcement, the monkey moved the joystick so that the cursor contacted the target continuously for 1s. The video monitor provided continuous visual feedback of both cursor and target position. With those elements of the task constant, we modified the transform between joystick movement and that of the cursor at the beginning of a block of trials. Neuronal activity was studied as the monkey adapted to these novel joystick-cursor transforms. Some novel tasks included spatial transforms such as single-axis inversions, asymmetric double-axis inversions and angular deviations (also known as rotations). Other tasks involved changes in the spatiotemporal pattern and magnitude of joystick movement. As the monkey adapted to various visuomotor tasks, 209 task-related neurons (selected for stable background activity) showed significant changes in their task-related activity: 88 neurons in the primary motor cortex (M1), 32 in the supplementary motor cortex (M2), and 89 in the caudal part of the dorsal premotor cortex (PMdc). Slightly more than half of the sample in each area showed significant changes in the magnitude of activity modulation during adaptation, with the number of increases approximately equaling the number of decreases. These data support the prediction that changes in task-related neuronal activity can be observed in M1 during motor adaptation, but fail to support the hypothesis that M1 and PMdc differ in this regard. When viewed in population averages, motor cortex continued to change its activity for at least dozens of trials after performance reached a plateau. This slow, apparently continuing change in the pattern and magnitude of task-related activity may reflect the initial phases of consolidating the motor memory for preparing and executing visuomotor skills.     

Preparation for movement: neural representations of intended direction in three motor areas of the monkey

1. The purpose of this study was to compare the functional properties of neurons in three interrelated motor areas that have been implicated in the planning and execution of visually guided limb movements. All three structures, the supplementary motor area (SMA), primary motor cortex (MC), and the putamen, are components of the basal ganglia-thalamocortical "motor circuit." The focus of this report is on neuronal activity related to the preparation for movement. 2. Five rhesus monkeys were trained to perform a visuomotor step-tracking task in which elbow movements were made both with and without prior instruction concerning the direction of the forthcoming movement. To dissociate the direction of preparatory set (and limb movement) from the task-related patterns of tonic (and phasic) muscular activation, some trials included the application of a constant torque load that either opposed or assisted the movements required by the behavioral paradigm. Single-cell activity was recorded from the arm regions of the SMA, MC, and putamen contralateral to the working arm. 3. A total of 741 task-related neurons were studied, including 222 within the SMA, 202 within MC, and 317 within the putamen. Each area contained substantial proportions of neurons that manifested preparatory activity, i.e., cells that showed task-related changes in discharge rate during the postinstruction (preparatory) interval. The SMA contained a larger proportion of such cells (55%) than did MC (37%) or the putamen (33%). The proportion of cells showing only preparatory activity was threefold greater in the SMA (32%) than in MC (11%). In all three areas, cells that showed only preparatory activity tended to be located more rostrally than cells with movement-related activity. Within the arm region of the SMA, the distribution of sites from which movements were evoked by microstimulation showed just the opposite tendency: i.e., microexcitable sites were largely confined to the caudal half of this region. 4. The majority of cells with task-related preparatory activity showed selective activation in anticipation of elbow movements in a particular direction (SMA, 86%; MC, 87%; putamen, 78%), and in most cases the preparatory activity was found to be independent of the loading conditions (80% in SMA, 83% in MC, and 84% in putamen).(ABSTRACT TRUNCATED AT 400 WORDS)     

Neuronal activity in the cingulate motor areas during adaptation to a new dynamic environment

Neurons in the cingulate motor areas (CMA) have been shown to be involved in many aspects of sensorimotor behavior, although their role in motor learning has received less attention. Here, we recorded single-cell activity in the CMA of monkeys while they adapted reaching movements to different dynamic environments. Specifically, we analyzed CMA activity during normal reaching to visual targets and during reaching in the presence of an applied velocity-dependent force field. We found that the cingulate neuronal activity was modulated during each phase of the task and in response to the applied forces. The neurons' involvement in the visuomotor transformation was influenced by their rostrocaudal location in the cingulate sulcus. Rostral CMA (CMAr) neurons were modulated by the visual instruction to a greater extent than caudal CMA (CMAc) neurons. In contrast, CMAc neurons had a greater amount of phasic and directionally tuned activity during movement than CMAr cells. Furthermore, compared with CMAr cells, the movement-related activity of CMAc cells was more frequently modulated by the applied force fields. The magnitude of the force-field–related neuronal response scaled with the amount of perturbation in each reaching direction. However, contrary to previous results from other cortical motor areas, force-field adaptation was not correlated with a shift in directional tuning of the CMA population. Based on these results, we suggest that although the CMA is clearly sensitive to applied forces, it is less involved in generating anticipatory responses to predictable forces than other cortical motor areas.     

An event-related potential evoked by movement planning is modulated by performance and learning in visuomotor control

Based on a previous exploratory study, the functionality of event-related potentials related to visuomotor processing and learning was investigated. Three pursuit tracking tasks (cursor control either mouse, joystick, or bimanually) revealed the greatest tracking error and greatest learning effect in the bimanual task. The smallest error without learning was found in the mouse task. Error reduction reflected visuomotor learning. In detail, target–cursor distance was reduced continuously, indicating a better fit to a changed direction, whereas response time remained at 300 ms. A central positive ERP component with an activity onset 100 ms after a directional change of the target and most likely generated in premotor areas could be assigned to response planning and execution. The magnitude of this component was modulated by within-and-between-task difficulty and size of the tracking error. Most importantly, the size of this component was sensitive to between-subject performance and increased with visuomotor learning. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sustained seizures cause circumscribed cerebral changes in glial fibrillary acidic protein,neurofilament and laminin immunofluorescence

Summary Single cell activity was examined in the three motor fields of the monkey frontal cortex with the aim of comparing the neuronal activity preceding movements triggered by a visual signal to that preceding nontriggered (self-paced) movements. The following findings emerged from this study. 1. Neuronal activity changes were observed at two different phases in relation to the movement onset; the shortlead type observed within 480 ms prior to the movement onset and the long-lead type, beginning earlier (typically 1 to 2 s). 2. Neurons in both the supplementary motor area (SMA) and premotor area (PM) exhibited the short-lead activity changes prior to the triggered and self-paced movement. Their magnitudes were similar in 63% of SMA and in 36% of PM neurons, whether the movement was triggered or self-paced. 3. SMA neurons, as a whole, were not less active before the triggered than self-paced movement. 4. On the other hand, as many as 92 PM neurons (61%) were related exclusively or peferentially to the triggered movement. 5. The majority of precentral motor cortex (MC) neurons exhibited similar activity changes before the two modes of movement initiation. 6. The long lead type of activity changes were observed mainly prior to the self-paced and much less frequently before the triggered movement. They were particularly abundant among SMA neurons. These results do not support the simple dichotomy hypothesis that SMA primarily takes part in self-paced movement and PM is only involved in visually triggered movement. However, PM neurons show relatively more prominent responses to the visual trigger signal and SMA neurons are intimately related to a long-lasting process leading to initiation of the self-paced movement.Supported by Special Coordination Funds for Promoting Science and Technology from Science and Technology Agency of Japan (Research on the development of basic technologies for brain function analysis)     

猴大脑内侧皮质运动区投射到运动前区的神经元的分布

目的定性和定量解析内侧皮质运动区投射到运动前区不同部位神经元的分布。方法采用多重标记法在同一只猴运动前区(PM)的三个不同部位即吻背侧部(PMdr)、尾背侧部(PMdc)及腹侧部(PMv)分别注入DY、FB、WGA-HRP三种不同的逆行标记物,对在内侧皮质运动区(MMC)逆行标记神经元的分布进行精确的定位和定量分析。结果投射到PMdr的神经元主要分布在前辅助运动区(prp-SMA)及前扣带回皮质运动区(CMAr);投射到PMdc的神经元,在MMC均有不同的分布,但在后扣带回皮质运动区(CMAc)被标记的神经元量明显多于其它部位;投射到PMv的神经元主要分布在辅助运动区(SMA)和CMAc,在CMAr也有少量标记神经元。结论SMA和CMAc主要投射到PMv,PMdr多接受pre-SMA和CMAr的投射。     

Movement-related potentials preceding voluntary movement are modulated by the mode of movement selection

In two experiments movement-related cortical potentials preceding voluntary movement were recorded. In experiment 1, subjects performed four motor tasks involving joystick movements. The four tasks differed in complexity (single vs sequential movements) and in the mode of movement selection, i.e., whether a movement or movement sequence was made in fixed or in self-determined directions. The choice of these tasks was based, firstly, on previous electrophysiological studies suggesting an effect of task-complexity on the amplitude of the readiness potential (RP) and, secondly, on previous positron emission tomography (PET) studies showing that activity of the supplementary motor area (SMA) is influenced by the mode of movement selection. The results show that, for single movements, RP amplitude is higher preceding freely selected movements than preceding movements in a fixed direction. In experiment 2 this effect was replicated using button presses instead of joystick movements. The results converge with PET evidence obtained in similar tasks and establish that the RP is modulated by the mode of movement selection. This modulation is probably related to differential involvement of the SMA.     

Allocation of attention for dissociated visual and motor goals

In daily life, selecting an object visually is closely intertwined with processing that object as a potential goal for action. Since visual and motor goals are typically identical, it remains unknown whether attention is primarily allocated to a visual target, a motor goal, or both. Here, we dissociated visual and motor goals using a visuomotor adaptation paradigm, in which participants reached toward a visual target using a computer mouse or a stylus pen, while the direction of the cursor was rotated 45° counter-clockwise from the direction of the hand movement. Thus, as visuomotor adaptation was accomplished, the visual target was dissociated from the movement goal. Then, we measured the locus of attention using an attention-demanding rapid serial visual presentation (RSVP) task, in which participants detected a pre-defined visual stimulus among the successive visual stimuli presented on either the visual target, the motor goal, or a neutral control location. We demonstrated that before visuomotor adaptation, participants performed better when the RSVP stream was presented at the visual target than at other locations. However, once visual and motor goals were dissociated following visuomotor adaptation, performance at the visual and motor goals was equated and better than performance at the control location. Therefore, we concluded that attentional resources are allocated both to visual target and motor goals during goal-directed reaching movements.     

Effect of visuomotor-map uncertainty on visuomotor adaptation

Vision and proprioception contribute to generating hand movement. If a conflict between the visual and proprioceptive feedback of hand position is given, reaching movement is disturbed initially but recovers after training. Although previous studies have predominantly investigated the adaptive change in the motor output, it is unclear whether the contributions of visual and proprioceptive feedback controls to the reaching movement are modified by visuomotor adaptation. To investigate this, we focused on the change in proprioceptive feedback control associated with visuomotor adaptation. After the adaptation to gradually introduce visuomotor rotation, the hand reached the shifted position of the visual target to move the cursor to the visual target correctly. When the cursor feedback was occasionally eliminated (probe trial), the end point of the hand movement was biased in the visual-target direction, while the movement was initiated in the adapted direction, suggesting the incomplete adaptation of proprioceptive feedback control. Moreover, after the learning of uncertain visuomotor rotation, in which the rotation angle was randomly fluctuated on a trial-by-trial basis, the end-point bias in the probe trial increased, but the initial movement direction was not affected, suggesting a reduction in the adaptation level of proprioceptive feedback control. These results suggest that the change in the relative contribution of visual and proprioceptive feedback controls to the reaching movement in response to the visuomotor-map uncertainty is involved in visuomotor adaptation, whereas feedforward control might adapt in a manner different from that of the feedback control.     

Dissociation of visual, motor and predictive signals in parietal cortex during visual guidance

The role of the posterior parietal cortex (PPC) in the visual guidance of movements was studied in monkeys trained to use a joystick to guide a spot to a target. Visual and motor influences were dissociated by transiently occluding the spot and by varying the relationship between the direction of joystick and spot movements. We found a strong segregation of function in PPC during visual guidance. Neurons in area MST were selectively modulated by the direction of visible moving stimuli, whereas neurons in area MIP were selectively modulated by the direction of hand movement. In contrast, the selectivity of cells in the lateral intraparietal area (LIP) did not directly depend on either visual input or motor output, but rather seemed to encode a predictive representation of stimulus movement. These predictive signals may be an important link in visuomotor transformations.     

The role of proprioception and attention in a visuomotor adaptation task

The role of proprioception in the control and adaptation of visuomotor relationships is still unclear. We have studied a deafferented subject, IW, and control subjects in a task in which they used single joint elbow extension to move to a visual target, with visual feedback of the terminal position provided by a cursor displayed in the plane of their movements. We report the differences in movement accuracy between the deafferented subject and controls in the normal task and when challenged with a cognitive load, counting backwards. All subjects were less accurate when counting; this was a small effect for the controls (<10% change) but much greater for the deafferented subject (>60% change). We also examined changes in movement kinematics when the instructed amplitude was altered via a changed gain between final arm position and presentation of the feedback cursor. The deafferented subject maintained temporal movement parameters stable and altered amplitude by scaling force (i.e. changed peak velocity), whereas the controls scaled both movement velocity and duration. Finally, we compared the subjects' adaptation of movement amplitude after a period of exposure to the changed visuomotor gain. The deafferented subject was able to adapt, but his adaptation was severely impaired by the counting task. These results suggest that proprioception is not an absolute requirement for adaptation to occur. Instead, proprioception has a more subtle role to play in the adjustment to visuomotor perturbations. It has an important role in the control of reaching movements, while in the absence of proprioception, attention appears necessary to monitor movements.     

A motor area rostral to the supplementary motor area (presupplementary motor area) in the monkey: neuronal activity during a learned motor task.

1. The rostromesial agranular frontal cortex of macaque monkey (Macaca fuscata), traditionally defined as the supplementary motor area (SMA), was studied using various physiological techniques to delineate two different areas rostrocaudally. 2. Field and unitary responses to electrical stimulation of the primary motor cortex were distinct in the caudal part, but minimal or absent in the rostral part. Intracortical microstimulation readily evoked limb or orofacial movements in the caudal part, but only infrequently in the rostral part. Neuronal responses to visual stimuli prevailed in the rostral part, but somatosensory responses were rare. The opposite was true in the caudal part. 3. The rostral part, roughly corresponding to area 6a beta, was operationally defined as the presupplementary motor area (pre-SMA). The caudal part was redefined as the SMA proper. 4. Single-cell activity in the pre-SMA was quantitatively compared with that in the SMA proper in relation to a trained motor task. 5. Phasic responses to visual cue signals indicating the direction of forthcoming arm-reaching movement were more abundant in the pre-SMA. 6. Activity changes during the preparatory period, which lasted until the occurrence of the trigger signal for the reaching movement, were more frequent in the pre-SMA. 7. Phasic, movement-related activity was more frequent in the SMA, and its onset was often time locked to the movement onset. In the pre-SMA, the occurrences of response time locked to the movement-trigger signal were more frequent than in the SMA. 8. Among neurons in both areas, directional selectivity was found in all the cue, preparatory, and movement-related responses.     

Role of primate basal ganglia and frontal cortex in the internal generation of movements

Summary This study is a part of a project investigating neuronal activity in the basal ganglia and frontal cortex and describes externally and internally induced preparatory activity in the supplementary motor area (SMA), which forms a closed neuronal loop with the striatum. Monkeys made self-initiated arm reaching movements toward a constant target in the absence of phasic external stimuli. In separate blocks of trials, animals performed in a delayed go no-go task in which an instruction cue prepared for subsequent movement or no-movement to a trigger stimulus. A total of 328 neurons were tested in the delay task. Of these, 91 responded transiently to the instruction light with a median latency of 262 ms. Three quarters of these responses were restricted to the instruction preparing for arm movement, as opposed to with-holding it, and thus may be involved in movement preparation processes. Sustained activation during the instruction-trigger interval was found for 67 neurons and occurred nearly exclusively in movement trials. Activation usually increased gradually after the cue and ended abruptly upon movement onset and thus could be related to the setting and maintenance of processes underlying the preparation of movement. Time-locked responses to the trigger stimulus were found in 38 neurons and were usually restricted to movement trials (median latency 80 ms). Activity time-locked to movement execution occurred in 67 neurons, beginning up to 252 ms before movement onset. A total of 266 neurons were tested with self-initiated arm movements. Of these, 43 showed premovement activity beginning 610–3030 ms before movement onset (median 1430 ms). The activity increased slowly and reached its peak at 370 ms before movement onset. It ended before movement onset or continued until the arm began to move or reached the target. This activity appears to reflect neuronal processes related to the internal generation of movements. Two thirds of activations preceding self-initiated movements occurred in neurons not activated before externally instructed movements, suggesting a selectivity for the internal generation process. Activity related to the execution of self-initiated movements occurred in 67 neurons: it began during and up to 420 ms before movement onset and was usually not associated with pre-movement activity. Most of these neurons were also activated with stimulus-triggered movements, suggesting a lack of selectivity for the execution of self-initiated movements. In comparison with the striatum, more SMA neurons showed preparatory activity preceding externally instructed movements (transient 27% vs 16%, sustained 20% vs 12%) and self-initiated movements (16% vs 11%). Whereas transient responses showed similar latencies and durations in the two structures, sustained preparatory activity preceding externally instructed or self-initiated movements began and reached its peak earlier in SMA compared to striatal neurons. However, due to the long durations, sustained activation largely overlapped in the two structures, and thus essentially occurred simultaneously. Instruction-induced or internally generated preparatory activity may originate outside of the SMA and striatum or may derive from activity reverberating in cortico-basal ganglia loops, possibly in conjunction with other, closely associated cortical and subcortical structures. These data would favor a conjoint role for SMA and striatum in the internal generation of individual behavioral acts and the preparation of behavioral reactions.     

Distribution of eye- and arm-movement-related neuronal activity in the SEF and in the SMA and Pre-SMA of monkeys

We analyzed neuronal activity in the supplementary eye field (SEF), supplementary motor area (SMA), and presupplementary motor area (pre-SMA) during the performance of three motor tasks: capturing a visual target with a saccade, reaching one arm to a target while gazing at a visual fixation point, or capturing a target with a saccade and arm-reach together. Our data demonstrated that each area was involved in controlling the arm and eye movements in a different manner. Saccade-related neurons were found mainly in the SEF. In contrast, arm-movement-related neurons were found primarily in the SMA and pre-SMA. In addition, we found that the activity of both arm-movement- and saccade-related neurons differed depending on the presence or absence of an accompanying saccade or arm movement. Such context dependency was found in all three areas. We also discovered that activity preceding eye or arm movement alone, and eye and arm movement combined, appeared more often in the pre-SMA and SEF, suggesting their involvement in effector-independent aspects of motor behavior. Subsequent analysis revealed that the laterality of arm representation differed in the three areas: it was predominantly contralateral in the SMA but largely bilateral in the pre-SMA and SEF.     

Primate basal ganglia activity in a precued reaching task: preparation for movement

Single cell activity was recorded from the primate putamen, caudate nucleus, and globus pallidus during a precued reaching movement task. Two monkeys were trained to touch one of several target knobs mounted in front of them after an LED was lighted on the correct target. A precue was presented prior to this target go cue by a randomly varied delay interval, giving the animals partial or complete advance information about the target for the movement task. The purpose of this design was to examine neuronal activity in the major structures of the basal ganglia during the preparation phase of limb movements when varying amounts of advance information were provided to the animals. The reaction times were shortest with complete precues, intermediate with partial precues, and longest with precues containing no information, demonstrating that the animals used precue information to prepare partly or completely for the reaching movement before the target go cue was given. Changes in activity were seen in the basal ganglia during the preparatory period in 30% of neurons in putamen, 31% in caudate nucleus, and 27% in globus pallidus. Preparatory changes were stronger and more closely linked to the time of movement initiation in putamen than in caudate nucleus. Although the amount of information contained in the precues had no significant effect on preparatory activity preceding the target go cue, a directional selectivity during this period was observed for a subset of neurons with preparatory changes (15% in putamen, 11% in caudate nucleus, 14% in globus pallidus) when the precue contained information about the upcoming direction of movement. A smaller subset of neurons showed selectivity for the preparation of movement amplitude. A larger number of preparatory changes showed selectivity for the direction or amplitude of movement following the target go cue than in the delay period before the cue. The intensity of preparatory changes in activity in many cases depended on the length of the delay interval preceding the target go cue. Even following the target go cue, the intensity of the preparatory changes in activity continued to be significantly influenced by the length of the preceding delay interval for 11% of changes in putamen, 8% in caudate nucleus, and 18% in globus pallidus. This finding suggests that preparatory activity in the basal ganglia takes part in a process termed motor readiness. Behaviorally, this process was seen as a shortening of reaction time regardless of precue information for trials in which the delay interval was long and the animals showed an increased readiness to move. Preparatory activity in putamen following the target go cue was most intense in trials with a short delay interval, in which motor readiness had not achieved its maximum level prior to the go cue. The results of this study indicate that the basal ganglia are involved in multiple aspects of preparatory processing for limb movement. Preparatory processing is therefore unlikely to be divided anatomically along the functional lines examined in this study. In the basal ganglia, preparatory processing reflects both preparation for target selection and control of timing the onset of movement (motor readiness). These characteristics can be integrated in a functional scheme in which the basal ganglia are predominantly responsible for the automated execution of well-trained behavior.     

Movement-related neuronal activity selectively coding either direction or muscle pattern in three motor areas of the monkey

1. Movement-related neuronal activity in the supplementary motor area (SMA), primary motor cortex (MC), and putamen was studied in monkeys performing a visuomotor tracking task designed to determine 1) the extent to which neuronal activity in each of these areas represented the direction of visually guided arm movements versus the pattern of muscle activity required to achieve those movements and 2) the relative timing of different types of movement-related activity in these three motor areas. 2. A total of 455 movement-related neurons in the three motor areas were tested with a behavioral paradigm, which dissociated the direction of visually guided elbow movements from the accompanying pattern of muscular activity by the application of opposing and assisting torque loads. The movement-related activity described in this report was collected in the same animals performing the same behavioral paradigm used to study preparatory activity described in the preceding paper. Of the total sample, 87 neurons were located within the arm region of the SMA, 150 within the arm region of the MC, and 218 within the arm region of the putamen. 3. Movement-related cells were classified as "directional" if they showed an increase in discharge rate predominantly or exclusively during movements in one direction and did not have significant static or dynamic load effects. A cell was classified as "muscle-like" if its directional movement-related activity was associated with static and/or dynamic load effects whose pattern was similar to that of flexors or extensors of the forearm. Both directional and muscle-like cells were found in all three motor areas. The largest proportion of directional cells was located in the putamen (52%), with significantly smaller proportions in the SMA (38%) and MC (41%). Conversely, a smaller proportion of muscle-like cells was seen in the putamen (24%) than in the SMA (41%) or MC (36%). 4. The time of onset of movement-related discharge relative to the onset of movement ("lead time") was computed for each cell. On average, SMA neurons discharged significantly earlier (SMA lead times 47 +/- 8 ms, mean +/- SE) than those in MC (23 +/- 6 ms), which in turn were earlier than those in putamen (-33 +/- 6 ms). However, the degree of overlap of the distributions of lead times for the three areas was extensive.(ABSTRACT TRUNCATED AT 400 WORDS)     

Movement-related potentials in Huntington's disease: movement preparation and execution

Movement-related potentials (MRPs) reflect increasing cortical activity related to the preparation and execution of voluntary movement. Execution and preparatory components may be separated by comparing MRPs recorded from actual and imagined movement. Imagined movement initiates preparatory processes, but not motor execution activity. MRPs are maximal over the supplementary motor area (SMA), an area of the cortex involved in the planning and preparation of movement. The SMA receives input from the basal ganglia, which are affected in Huntington's disease (HD), a hyperkinetic movement disorder. In order to further elucidate the effects of the disorder upon the cortical activity relating to movement, MRPs were recorded from ten HD patients, and ten age-matched controls, whilst they performed and imagined performing a sequential button-pressing task. HD patients produced MRPs of significantly reduced size both for performed and imagined movement. The component relating to movement execution was obtained by subtracting the MRP for imagined movement from the MRP for performed movement, and was found to be normal in HD. The movement preparation component was found by subtracting the MRP found for a control condition of watching the visual cues from the MRP for imagined movement. This preparation component in HD was reduced in early slope, peak amplitude, and post-peak slope. This study therefore reported abnormal MRPs in HD, particularly in terms of the components relating to movement preparation, and this finding may further explain the movement deficits reported in the disease. Electronic Publication     

Movement-related and preparatory activity in the reticulospinal system of the monkey

Three monkeys (M. fascicularis) performed a center-out, two-dimensional reaching task that included an instructed delay interval based on a color-coded visuospatial cue. Neural activity in the medial pontomedullary reticular formation (mPMRF) was recorded along with hand movement. Of 176 neurons with movement-related activity, 109 (62%) had movement-related but not preparatory activity (M cells), and 67 (38%) had both movement-related and preparatory activity (MP cells). EOG analyses indicated that the preparatory activity was not consistent with control of eye movements. There were slight changes in electromyograms (EMG) late in the instructed delay period before the Go cue, but these were small compared with the movement-related EMG activity. Preparatory activity, like the EMG activity, was also confined to the end of the instructed delay period for 14 MP cells, but the remaining 53 MP cells (30%) had preparatory activity that was not reflected in the EMG. Peri-movement neural activity varied with movement direction for 70% of the cells, but this variation rarely fit circular statistics commonly used for studies of directional tuning; directional tuning was even less common in the preparatory activity. These data show that neurons in the mPMRF are strongly modulated during small reaching movements, but this modulation was rarely correlated with the trajectory of the hand. In accord with findings in the literature from other regions of the CNS, evidence of activity related to motor preparation in these cells indicates that this function is distributed in the nervous system and is not a feature limited to the cerebral cortex.     

Selective coding of motor sequence in the supplementary motor area of the monkey cerebral cortex

Summary We describe a property of neurons in the supplementary motor area (SMA) of the cerebral cortex of monkey that is different from those in the primary motor area (MI) in relation to execution of a sequential motor task. A group of SMA neurons was active when the animal remembered and pressed three touch-pads in a predetermined sequence but inactive when the same movement was guided by sequentially presented visual signals. This finding indicates that the SMA is involved in the performance of sequential movements on the basis of the information stored inside the brain.