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

The purpose of these studies was to investigate neuronal activity in the basal ganglia and frontal cortex in relation to the internal generation of goal-directed movements. Monkeys performed goal-directed arm movements at a self-chosen moment in the absence of phasic stimuli providing external temporal reference. They were rewarded with a small morsel of food for each movement, although automatic or repetitive behavior was not reinforced. For reasons of comparison, animals were also trained in a delayed go no-go task in which visual cues instructed them to perform or refrain from an arm movement reaction to a subsequent trigger stimulus. This report describes the activity of neurons in the head of the caudate nucleus and rostral putamen preceding self-initiated arm movements and compares it with instruction-induced preparatory activity preceding movements in the delay task. A total of 497 caudate and 354 putamen neurons were tested in the delay task. Two types of preparatory activity were observed: (1) transient responses to the instruction cue, and (2) sustained activity preceding the trigger stimulus or movement onset. Transient responses were found in 48 caudate and 50 putamen neurons, occurring twice as often in movement ('go') as compared to no-movement ('no-go') trials, but rarely in both. These responses may code the information contained in the instruction relative to the forthcoming behavioral reaction. Sustained activity began after instruction onset and lasted until the trigger stimulus or the arm movement occurred, this being for periods of 2-7 s, 12-35 s, or up to 80 s, depending on the task requirements. This activity was seen in 47 caudate and 45 putamen neurons, was largely confined to go trials, and was unrelated to the preparation of saccadic eye movements. In some cases, this activity began as direct responses to the instruction stimulus, but in the majority of cases developed more gradually before the movement. Thus, both transient and sustained activations appear to be related to the preparation of movements. A total of 390 caudate and 293 putamen neurons were tested during self-initiated movements. Activity preceding earliest movement-related muscle activity was found in 32 caudate and 42 putamen neurons. This premovement activity began 0.5-5.0 s before movement onset (median 1160 ms), increased slowly, reached its peak close to movement onset, and subsided rapidly thereafter. It was unrelated to the preparation of saccadic eye movements. Comparisons between the two tasks were made on 53 neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

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

In order to more comprehensively assess the role of the basal ganglia in the internal generation of movements, we studied the activity of neurons in the head of the caudate and in the rostral putamen in relation to the execution of movements. Monkeys performed self-initiated and stimulus-triggered arm reaching movements in separate blocks of trials. With stimulus-triggered movements, 217 striatal neurons increased their activity after the trigger stimulus (127 in caudate, 90 in putamen). Of these, 68 neurons showed time-locked responses to the trigger stimulus, with a median latency of 60 ms, that were independent of visual or auditory stimulus modalities. Three quarters of responses were conditional on a movement being performed. These responses may participate in neuronal processes through which the reception of a stimulus is translated into the execution of a behavioral reaction. Further, 44 neurons increased their activity before the earliest muscle activity without being clearly time-locked to the stimulus (148-324 ms before movement onset), 55 neurons were activated later before the movement, and 50 neurons were activated after movement onset. With self-initiated movements, 106 striatal neurons showed movement-related activity beginning up to 460 ms before movement onset (52 in caudate, 54 in putamen). Comparisons between the two types of movement were made on 53 neurons with premovement activity beginning more than 500 ms before self-initiated movements. Only one fifth of them also showed movement-related activity with stimulus-triggered movements, including trigger responses. Comparisons among 39 neurons with movement-related activity during self-initiated arm movements showed that about half of them also showed movement-related activity with stimulus-triggered movements. These data demonstrate a considerably segregated population of striatal neurons engaged in the internal generation of movements, whereas processes underlying the execution of movements appear to involve overlapping neuronal populations.     

Neuronal activity preceding self-initiated or externally timed arm movements in area 6 of monkey cortex

Summary Several lines of evidence suggest that the supplementary motor area (SMA) and the premotor cortex (PM) may participate in neuronal mechanisms for the initiation of movements. We recorded the impulse activity of single neurons in monkeys that were trained in two behavioral tasks employing, respectively, self-initiated and externally timed movements. Neurons in both areas were activated up to 2.6 s in advance of self-initiated, reward-related arm reaching movements. In the externally timed task, changes occurred during light instructions that preceded movements by 2 s. Neurons also responded to the trigger stimulus for movement. In view of similar premovement activity in the basal ganglia, these cortical regions appear to be parts of a distributed neuronal system for movement initiation.     

Neuronal activity in the monkey striatum during the initiation of movements

Summary The sources of afferent input to the striatum (caudate nucleus and putamen) suggest that this structure may be engaged in neuronal processes related to the initiation of movement. We found that 26% of 508 neurons in both parts of the striatum were activated during the presentation of visual signals which prepared the animals for the execution or withholding of individual arm reaching movements. In a second task, 20% of 382 striatal neurons were activated up to 3 s before self-initiated, non automatic and purposive arm movements which were performed in the complete absence of phasic external stimuli. The data demonstrate an involvement of the striatum in externally and internally generated processes which are related to presetting mechanisms during the initiation of behavioral acts.     

Differential roles of neuronal activity in the supplementary and presupplementary motor areas: from information retrieval to motor planning and execution

We explored functional differences between the supplementary and presupplementary motor areas (SMA and pre-SMA, respectively) systematically with respect to multiple behavioral factors, ranging from the retrieval and processing of associative visual signals to the planning and execution of target-reaching movement. We analyzed neuronal activity while monkeys performed a behavioral task in which two visual instruction cues were given successively with a delay: one cue instructed the location of the reach target, and the other instructed arm use (right or left). After a second delay, the monkey received a motor-set cue to be prepared to make the reaching movement as instructed. Finally, after a GO signal, it reached for the instructed target with the instructed arm. We found the following apparent differences in activity: 1) neuronal activity preceding the appearance of visual cues was more frequent in the pre-SMA; 2) a majority of pre-SMA neurons, but many fewer SMA neurons, responded to the first or second cue, reflecting what was shown or instructed; 3) in addition, pre-SMA neurons often reflected information combining the instructions in the first and second cues; 4) during the motor-set period, pre-SMA neurons preferentially reflected the location of the target, while SMA neurons mainly reflected which arm to use; and 5) when executing the movement, a majority of SMA neurons increased their activity and were largely selective for the use of either the ipsilateral or contralateral arm. In contrast, the activity of pre-SMA neurons tended to be suppressed. These findings point to the functional specialization of the two areas, with respect to receiving associative cues, information processing, motor behavior planning, and movement execution.     

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.     

Movement preparation in self-initiated versus externally triggered movements: an event-related fMRI-study

In the present study, we used fMRI to investigate whether event-related preparatory processes of self-initiated and externally triggered movements differ. Twenty subjects were examined with 1000 T2*-weighted images in two consecutive sessions. During the first session subjects performed self-initiated abductions of the right index finger. For the second session subjects were instructed to perform the movements in response to visual cues. Number and timing of movements were matched between conditions. For statistical inference on multisubject level, random effects analyses were performed. Significantly enhanced activity during self-initiated compared to externally triggered movements was found within the left SMA, the left pre- and sensorimotor cortex, the right putamen, the left anterior cingulate gyrus, and the left inferior parietal lobe. The significantly increased activity during self-initiated in comparison to externally triggered movements might represent differential demands of the two conditions on the neuronal motor net during movement preparation, reflecting utilization of precise knowledge when to move in self-initiated movements. Our results emphasize a possible role of the primary motor cortex for movement preparation as observed in electrophysiological studies, but do not support a specific involvement of the dorsolateral prefrontal cortex as suggested by former block design studies.     

Neuronal activity in monkey striatum related to the expectation of predictable environmental events.

1. This study investigated neuronal activity in the striatum preceding predictable environmental events and behavioral reactions. Monkeys performed in a delayed go-nogo task that included separate time periods during which animals expected signals of behavioral significance, prepared for execution or inhibition of arm reaching movements, and expected the delivery of reward. In the task, animals were instructed by a green light cue to perform an arm reaching movement when a trigger stimulus came on approximately 3 s later (go situation). Movement was withheld after the same trigger light when the instruction cue had been red (nogo situation). Liquid reward was delivered on correct performance in both situations. 2. A total of 1,173 neurons were studied in the striatum (caudate nucleus and putamen) of 3 animals, of which 615 (52%) showed some change in activity during task performance. This report describes how the activity of 193 task-related neurons increased in advance of at least 1 component of the task, namely the instruction cue, the trigger stimulus, or the delivery of liquid reward. These neurons were found in dorsal and anterior parts of caudate and putamen and were slightly more frequent in the proximity of the internal capsule. 3. The activity of 16 neurons increased in both go and nogo trials before the onset of the instruction and subsided shortly after this signal. These activations may be related to the expectation of the instruction as the first signal in each trial. 4. The activity of 15 neurons increased between the instruction and the trigger stimulus in both go and nogo trials. These activations may be related to the expectation of the trigger stimulus independent of an arm movement. Further 56 neurons showed sustained activations only when the instruction requested a movement reaction. Activations were absent in trials in which the movement was withheld. Twenty-one of these neurons were tested with 2 different movement targets, 5 of which showed activity related to the direction of movement. These activations may be related to the preparation of movement or expectation of the specific movement triggering signal. The activity of an additional 20 neurons was unmodulated before the trigger stimulus in movement trials but increased in the interval between the no-movement instruction and the trigger stimulus for withholding the movement. These activations may be related to the preparation of movement inhibition as specific nogo reaction.(ABSTRACT TRUNCATED AT 400 WORDS)     

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)     

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)     

Activity of digital area neurons of the primary somatosensory cortex in relation to sensorially triggered and self-initiated digital movements of monkeys

Single-cell activity was examined in digital areas of the primary somatosensory cortex (SI) of monkeys performing sensorially triggered and self-initiated digital movements with the aim of rigorously determining the relative timing of onset of the neuronal activity with respect to movement onset. The activity of prime mover muscles for execution of a key-press movement was recorded simultaneously with the neuronal activity; movement onset was defined as the onset of muscle activity. Neuronal receptive fields were also identified. The following findings emerged from this study: (1) Few neurons, if any, in the SI(areas 3b, 1, 2), including pyramidal tract neurons, were active prior to movement onset. (2) The movement-related activity of SI neurons was basically similar in cases of signal-triggered and self-initiated movement. (3) No neuron in the SI showed activity associated with ipsilateral digital movement. (4) A majority of movement-related neurons in the precentral motor cortex, in contrast, started their activity before movement onset. These findings suggest that SI neuronal activity participates little in providing information necessary for developing motor responses in the initial phase of simple digital movements.     

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)     

Decoding higher-order motor information from primate non-primary motor cortices.

To investigate the involvement of primate non-primary motor cortices in bimanual sequential movements, we recorded neuronal activity in the supplementary motor area (SMA) and presupplementary motor area (pre-SMA) while an animal was performing bimanual motor tasks that required two sequential arm movements consisting of either pronation or supination of the right or left arms with delay periods. We also recorded electromyograms (EMGs) from the arm while the animal performed the bimanual task to compare muscle and neuronal activity. This paper focuses on the neuronal activity before the onset of sequential movements. We found that the prime-mover forelimb muscles were selectively active when an impending arm movement involved recorded muscles, but was not dependent on whether the arm movements were bimanual or unimanual. In contrast, we found that neurons in the non-primary motor cortices showed different activity depending on whether the forthcoming sequential arm movements were unimanual or bimanual. Our results suggest that neuronal activity in the SMA and pre-SMA reflects higher-order information about arm use before motor execution. By extracting this type of information, we can use it to control prosthetic arms in a more intelligent manner through a brain-machine interface.     

Target-, limb-, and context-dependent neural activity in the cingulate and supplementary motor areas of the monkey

Very little is known about the role of the cingulate motor area (CMA) in visually guided reaching compared to other cortical motor areas. To investigate the hierarchical role of the caudal CMA (CMAc) during reaching we recorded the activity of neurons in CMAc in comparison to the supplementary motor area proper (SMA) while a monkey performed an instructed delay task that required it to position a cursor over visual targets on a computer screen using two-dimensional (2D) joystick movements. The direction of the monkeys arm movement was dissociated from the direction of the visual target by periodically reversing the relationship between the direction of movement of the joystick and that of the cursor. Neurons that responded maximally with a particular limb movement direction regardless of target location were classified as limb-dependent, whereas neurons that responded maximally to a particular target direction regardless of the direction of limb movement were classified as target-dependent. Neurons whose activity was directional in one of the two visuomotor mapping conditions and non-directional or inactive in the other were categorized as context-dependent. Limb-dependent activity was observed more frequently than target-dependent activity in both CMAc and SMA proper during both the delay period (preparatory activity; CMAc, 17%; SMA, 31%) and during movement execution (CMAc, 49%, SMA, 48%). A modest percentage of neurons with preparatory activity were target-dependent in both CMAc (11%) and SMA proper (8%) and a similar percentage of neurons in both areas demonstrated target-dependent, movement activity (CMAc, 8%; SMA, 10%). The surprising finding was that a very large percentage of neurons in both areas displayed context-dependent activity either during the preparatory (CMAc, 72%; SMA, 61%) or movement (CMAc, 43%, SMA 42%) epochs of the task. These results show that neural activity in both CMAc and SMA can directly represent movement direction in either limb-centered or target-centered coordinates. The presence of target-dependent activity in CMAc, as well as SMA, suggests that both are involved in the transformation of visual target information into appropriate motor commands. Target-dependent activity has been found in the putamen, SMA, CMAc, dorsal and ventral premotor cortex, as well as primary motor cortex. This indicates that the visuomotor transformations required for visually guided reaching are carried out by a distributed network of interconnected motor areas. The large proportion of neurons with context-dependent activity suggests, however, that while both CMAc and SMA may play a role in the visuomotor transformation of target information into movement parameters, their activity is not solely coding parameters of movement, since their involvement in this process is highly condition-dependent.     

Neural activity in monkey dorsal and ventral cingulate motor areas: comparison with the supplementary motor area

The cingulate motor areas are a recently discovered group of discrete cortical regions located in the cingulate sulcus with direct connections to the primary motor cortex and spinal cord. Although much is known about their anatomical relationship with other motor areas, relatively little is known about their functional neurophysiology. We investigated neural mechanisms of motor processing in the dorsal and ventral cingulate motor areas (CMAd and CMAv) during two-dimensional visually guided arm movements. Single-neuron activity in CMAd and CMAv was recorded during an instructed delay task requiring combined elbow and shoulder movements. Neural activity associated with the onset of a visual cue (signal activity), delay (set activity), and motor response (movement activity) were assessed, and their onset time, duration, magnitude, and parameters of directional specificity were calculated. To determine how CMAd and CMAv compared with other premotor areas, we also analyzed the activity of neurons in the supplementary motor area (SMA) during the same task in the same monkeys. Comparison of CMAd, CMAv, and SMA revealed remarkably similar response properties. All three areas contained signal, set, and movement activity in similar proportions and in all possible combinations within single neurons. The average onset time of signal and set activity and the duration of signal activity were not significantly different across areas. The directional tuning of activities in all three areas were uniformly distributed and highly correlated within the same neuron. There were, however, some notable differences in movement activity between motor areas. Neurons with only movement activity were more numerous in CMAd and CMAv, whereas neurons with both set and movement activity were more prevalent in SMA. Furthermore, movement activity in SMA began earlier and had a shorter duration than movement activity in CMAd and CMAv, although there was substantial overlap in their distributions. These results indicate that CMAd and CMAv participate in the visual guidance of limb movements using similar neurophysiological mechanisms as SMA. The earlier average onset and shorter duration of movement activity in SMA suggest a more prominent role for this area in movement initiation, whereas the later onset and longer duration of movement activity in CMAd and CMAv suggest a more influential role in movement execution. Notwithstanding these differences, however, the remarkable similarities in response types and their combinatorial organization within single neurons across all cortical areas attests to the parallel organization and distributed nature of information processing in these three motor areas.     

Reorganization of activity in the supplementary motor area associated with motor learning and functional recovery

Summary The supplementary motor area (SMA) of primates has been implicated in the initiation and execution of limb movements. However, when a motor task was extensively overlearned, few SMA neurons, if any, were active before the movement onset. Subsequent lesions of the primary motor cortex gave rise to the appearance of premovement activity changes, indicating usedependent reorganization of the neuronal activity in SMA.     

Neuronal activity in nuclei pontis and reticularis tegmenti pontis related to forelimb movements of the monkey

The activity of the pontine nucleus (PN) neuron was recorded in 3 monkeys moving a handle alternately from start to target zones in a simple extension-flexion movement at the wrist. Of 73 PN neurons related to the task, 44 were related to movement, 19 to handle holding and 5 to both movement and holding of the handle. Of the 44 movement-related neurons, 16 were related to flexion, 22 to extension, and 6 to both. In 37 of 54 analyzed movements of the PN neurons which were related to movements, or to both movements and handle holding, the change of the activity occurred before the movement. However, in most of these cases (24/37), discharge occurred less than 100 ms earlier than the start of the movement. In the remaining one-third of movements (17/54), neurons discharged after the onset of the movement. Locations of the 73 neurons were histologically verified in the pontine nucleus. Somewhat similar observations were made of 14 cells located in the nucleus reticularis tegmenti pontis (NRTP). Considering that the majority of movement-related PN and NRTP neurons discharged immediately before or even after the onset of movement, these neurons may play a role in the execution of movement, at least of a simple movement, rather than in the initiation or planning of movement.     

Activity properties and location of neurons in the motor thalamus that project to the cortical motor areas in monkeys

The activity of neurons in the motor nuclei of the thalamus that project to the cortical motor areas (the primary motor cortex, the ventral and dorsal premotor cortex, and the supplementary motor area) was investigated in monkeys that were performing a task in which wrist extension and flexion movements were instructed by visuospatial cues before the onset of movement. Movement was triggered by a visual, auditory, or somatosensory stimulus. Thalamocortical neurons were identified by a spike collision, and exhibited 2 distinct types of task-related activity: 1) a sustained change in activity during the instructed preparation period in response to the instruction cues (set-related activity); and 2) phasic changes in activity during the reaction and movement time periods (movement-related activity). A number of set- and moment-related neurons exhibited direction selectivity. Most movement-related neurons were similarly active, irrespective of the different sensory modalities of the cue for movement. These properties of neuronal activity were similar, regardless of their target cortical motor areas. There were no significant differences in the antidromic latencies of neurons that projected to the primary and nonprimary motor areas. These results suggest that the thalamocortical neurons play an important role in the preparation for, and initiation and execution of, the movements, but are less important than neurons of the nonprimary cortical motor areas in modality-selective sensorimotor transformation. It is likely that such transformations take place within the nonprimary cortical motor areas, but not through thalamocortical information channels.     

Time-resolved fMRI of activation patterns in M1 and SMA during complex voluntary movement

The aim of this study was to use time-resolved functional magnetic resonance imaging (fMRI) to investigate temporal differences in the activation of the supplementary motor area (SMA) and the primary motor cortex (M1). We report data from eight human volunteers who underwent fMRI examinations in a 1.5T Philips Gyroscan ACS-NT MRI scanner. While wearing a contact glove, subjects executed a complex automated sequence of finger movements either spontaneously or in response to external auditory cues. Based on the result of a functional scout scan, a single slice that included the M1 and the SMA was selected for image acquisition (echo planar imaging, repetition time 100 ms, echo time 50 ms, 64 x 64 matrix, 1,000 images). Data were analyzed with a shifting cross-correlation approach using the STIMULATE program and in-house programs written in Interactive Data Language (IDL(TM)). Time-course data were generated for regions of interest in the M1 as well as in the rostral and caudal SMA. Mean time between onset of the finger movement sequence and half-maximum of the signal change in M1 was 3.6 s for the externally cued execution (SD 0.5) and 3.5 s for the spontaneous execution (SD 0.6). Activation in the rostral section of the SMA occurred 0.7 s earlier than it did in the M1 during the externally cued execution and 2.0 s earlier during the spontaneous execution, a difference significant at the P < 0.01 level. Our results indicate that rostral SMA activation precedes M1 activation by varying time intervals in the sub-second range that are determined by the mode of movement initialization. By applying a paradigm that exerts a differential influence on temporal activation, we could ensure that the observed timing differences were not the result of differences in hemodynamic response function.     

Neuronal activity in cortical motor areas related to ipsilateral, contralateral, and bilateral digit movements of the monkey

1. Single cell activity was studied in the precentral (PCM), premotor (PM), and supplementary (SMA) motor cortex of the monkey to compare magnitudes of activity changes in relation to ipsilateral, contralateral, and bilateral digit movements. 2. Three Japanese monkeys were trained to press a small key with the right or left hand, or with both hands, in accordance with visual instruction signals given 2.6-5.4 s before a visual movement-trigger signal. Great care was taken to train the animal to use only the required part of the limb. As a result of extensive training, electromyographic (EMG) studies revealed that muscle activities before the key press were limited to the digit and hand muscles of the limb instructed to move. No overt increase or decrease in activity was detectable in the proximal limb or body muscles in relation to the key-press movements or instructions. 3. Even though the movement was thus limited to distal forelimb, distinct ipsilateral relationships were observed in 8.2% of the task-related PCM neurons. They changed their activity before ipsilateral and bilateral (but not before contralateral) key press. 4. A majority of the neurons recorded from the digit area of PCM (mostly limited to the anterior bank of the central sulcus) exhibited a contralateral relationship; namely the activity increased or decreased before the onset of the contralateral and bilateral key-press movements. In most of them, the magnitudes of the activity changes before the contralateral and bilateral movements were similar. 5. In proximal limb and trunk areas of PCM and also in the somatosensory cortex, no neurons were found to exhibit distinct relations to any of the key-press movements. 6. In both SMA and PM, a number of neurons exhibited relationships of the type never or only rarely observed in the primary motor cortex. Thirty-seven percent of SMA and 62% of PM neurons exhibited premovement activity changes before all of the key-press movements. The movement-specific type of activity was observed in 28% of SMA and 16% of PM neurons. In these neurons, the activity changes were observed in relation to only one of the right or left key-press movements or exclusively in relation to the bilateral key press. Neuronal activity resembling the majority of the PCM neurons (contralateral type) was observed in 31% of SMA and 13% of PM neurons. 7. Instruction-induced changes in activity were more often found in the secondary than in the primary motor area.(ABSTRACT TRUNCATED AT 400 WORDS)