Seeing or moving in parallel: the premotor cortex does both during bimanual coordination, while the cerebellum monitors the behavioral instability of symmetric movements

The underlying neural mechanisms of a perceptual bias for in-phase bimanual coordination movements are not well understood. In the present study, we measured brain activity with functional magnetic resonance imaging in healthy subjects during a task, where subjects performed bimanual index finger adduction–abduction movements symmetrically or in parallel with real-time congruent or incongruent visual feedback of the movements. One network, consisting of bilateral superior and middle frontal gyrus and supplementary motor area (SMA), was more active when subjects performed parallel movements, whereas a different network, involving bilateral dorsal premotor cortex (PMd), primary motor cortex, and SMA, was more active when subjects viewed parallel movements while performing either symmetrical or parallel movements. Correlations between behavioral instability and brain activity were present in right lateral cerebellum during the symmetric movements. These findings suggest the presence of different error-monitoring mechanisms for symmetric and parallel movements. The results indicate that separate areas within PMd and SMA are responsible for both perception and performance of ongoing movements and that the cerebellum supports symmetric movements by monitoring deviations from the stable coordination pattern.     

Unraveling interlimb interactions underlying bimanual coordination

Three sources of interlimb interactions have been postulated to underlie the stability characteristics of bimanual coordination but have never been evaluated in conjunction: integrated timing of feedforward control signals, phase entrainment by contralateral afference, and timing corrections based on the perceived error of relative phase. In this study, the relative contributions of these interactions were discerned through systematic comparisons of five tasks involving rhythmic flexion-extension movements about the wrist, performed bimanually (in-phase and antiphase coordination) or unimanually with or without comparable passive movements of the contralateral hand. The main findings were the following. 1) Contralateral passive movements during unimanual active movements induced phase entrainment to interlimb phasing of either 0 degrees (in-phase) or 180 degrees (antiphase). 2) Entrainment strength increased with the passive movements' amplitude, but was similar for in-phase and antiphase movements. 3) Coordination of unimanual active movements with passive movements of the contralateral hand (kinesthetic tracking) was characterized by similar bilateral EMG activity as observed in active bimanual coordination. 4) During kinesthetic tracking the timing of the movements of the active hand was modulated by afference-based error corrections, which were more pronounced during in-phase coordination. 5) Indications of in-phase coordination being more stable than antiphase coordination were most prominent during active bimanual coordination and marginal during kinesthetic tracking. Together the results indicated that phase entrainment by contralateral afference contributed equally to the stability of in-phase and antiphase coordination, and that differential stability of these patterns depended predominantly on integrated timing of feedforward signals, with only a minor role for afference-based error corrections.     

Coordination disorders in patients with Parkinson's disease: a study of paced rhythmic forearm movements

Whereas the consequences of Parkinson's disease (PD) for the performance of single-limb movements are well documented (i.e., bradykinesia, akinesia, rigidity, and tremor), fairly little is known about its implications for the coordination between limb movements. To help resolve this situation an experiment was conducted in which 11 PD patients and 11 control subjects performed rhythmic forearm movements at a comfortable amplitude in the in-phase, antiphase, and single-arm mode at pacing frequencies ranging from 0.5 to 3 Hz. The PD group displayed marked coordination problems over and above the known clinical motor symptoms of PD. The performance of both the in-phase and antiphase modes was significantly affected in the PD group compared to the control group; furthermore, the variability of relative phase was significantly increased in this group. These observations were not caused by problems to synchronize the movements with the external pacing signal. In addition to the bimanual coordination problems, involuntary mirror movements (MM) were observed in the single-arm control trials that were significantly larger in the PD group (4.4% of the amplitude of the moving arm) than in the control group (2.3%), suggesting a reduced ability to suppress a basic in-phase coupling of the arms. In the PD group, MM were largest during movements of the least-affected arm. These parkinsonian coordination problems are interpreted in terms of recent evidence on the neural organization of bimanual coordination, suggesting that they are due to cortical rather than callosal dysfunction.     

Effect of transcranial magnetic stimulation on bimanual movements

Transcranial magnetic stimulation (TMS) of the motor cortex can interrupt voluntary contralateral rhythmic limb movements. Using the method of "resetting index" (RI), our study investigated the TMS effect on different types of bimanual movements. Six normal subjects participated. For unimanual movement, each subject tapped either the right or left index finger at a comfortable rate. For bimanual movement, index fingers of both hands tapped in the same (in-phase) direction or in the opposite (antiphase) direction. TMS was applied to each hemisphere separately at various intensities from 0.5 to 1.5 times motor threshold (MT). TMS interruption of rhythm was quantified by RI. For the unimanual movements, TMS disrupted both contralateral and ipsilateral rhythmic hand movements, although the effect was much less in the ipsilateral hand. For the bimanual in-phase task, TMS could simultaneously reset the rhythmic movements of both hands, but the effect on the contralateral hand was less and the effect on the ipsilateral hand was more compared with the unimanual tasks. Similar effects were seen from right and left hemisphere stimulation. TMS had little effect on the bimanual antiphase task. The equal effect of right and left hemisphere stimulation indicates that neither motor cortex is dominant for simple bimanual in-phase movement. The smaller influence of contralateral stimulation and the greater effect of ipsilateral stimulation during bimanual in-phase movement compared with unimanual movement suggest hemispheric coupling. The antiphase movements were resistant to TMS disruption, and this suggests that control of rhythm differs in the 2 tasks. TMS produced a transient asynchrony of movements on the 2 sides, indicating that both motor cortices might be downstream of the clocking command or that the clocking is a consequence of the 2 hemispheres communicating equally with each other.     

The effect of tapping finger and mode differences on cortical and subcortical activities: a PET study

Using positron emission tomography (PET), the brain regions recruited for the tapping movement by different fingers and different tapping modes were investigated in ten young healthy volunteers without specific finger training. Auditory-paced (2 Hz) tapping movements were performed by the index (I) or ring (R) finger alone (single-finger tapping) and by the alternate use of the I and middle (M) fingers or the R and little (L) fingers (double-finger tapping). Each subject also provided subjective rankings of perceived task difficulty, as well as muscular fatigue, among the tapping tasks. The activated areas of the brain during tapping by the R finger were more extensive in the frontal and temporal areas, as well as the cerebellum, than during tapping by the I finger. A similar result was revealed for the comparison of the RL and IM finger pairs. The perceived task difficulty, as well as muscular fatigue, was also higher for the R finger or RL finger pair than the I finger or IM finger pair. These results indicate that movement of individual fingers or finger pairs with different levels of task difficulty is represented differently in the structures of cortical and subcortical systems. A comparison of the single- and double-finger modes revealed that in addition to the brain areas activated during single-finger mode, the bilateral dorsal premotor and left primary motor/sensory areas and the right anterior cerebellum were also activated during the double-finger mode. These additional areas could be essential structures for the execution and motor sequence operation of the two fingers.     

Resource-demanding versus cost-effective bimanual interaction in the brain

When two hands require different information in bimanual asymmetric movements, interference can occur via callosal connections and ipsilateral corticospinal pathways. This interference could potentially work as a cost-effective measure in symmetric movements, allowing the same information to be commonly available to both hands at once. Using functional magnetic resonance imaging, we investigated supra-additive and sub-additive neural interactions in bimanual movements during the initiation and continuation phases of movement. We compared activity during bimanual asymmetric and symmetric movements with the sum of activity during unimanual right and left finger-tapping. Supra-additive continuation-related activation was found in the right dorsal premotor cortex and left cerebellum (lobule V) during asymmetric movements. In addition, for unimanual movements, the right dorsal premotor cortex and left cerebellum (lobule V) showed significant activation only for left-hand (non-dominant) movements, but not for right-hand movements. These results suggest that resource-demanding interactions in bimanual asymmetric movements are involved in a non-dominant hand motor network that functions to keep non-dominant hand movements stable. We found sub-additive continuation-related activation in the supplementary motor area (SMA), bilateral cerebellum (lobule VI) in symmetric movements, and the SMA in asymmetric movements. This suggests that no extra demands were placed on these areas in bimanual movements despite the conventional notion that they play crucial roles in bimanual coordination. Sub-additive initiation-related activation in the left anterior putamen suggests that symmetric movements place lower demands on motor programming. These findings indicate that, depending on coordination patterns, the neural substrates of bimanual movements either exhibit greater effort to keep non-dominant hand movements stable, or save neural cost by sharing information commonly to both hands.     

Error correction in bimanual coordination benefits from bilateral muscle activity: evidence from kinesthetic tracking

Although previous studies indicated that the stability properties of interlimb coordination largely result from the integrated timing of efferent signals to both limbs, they also depend on afference-based interactions. In the present study, we examined contributions of afference-based error corrections to rhythmic bimanual coordination using a kinesthetic tracking task. Furthermore, since we found in previous research that subjects activated their muscles in the tracked (motor-driven) arm, we examined the functional significance of this activation to gain more insight into the processes underlying this phenomenon. To these aims, twelve subjects coordinated active movements of the right hand with motor-driven oscillatory movements of the left hand in two coordinative patterns: in-phase (relative phase 0°) and antiphase (relative phase 180°). They were either instructed to activate the muscles in the motor-driven arm as if moving along with the motor (active condition), or to keep these muscles as relaxed as possible (relaxed condition). We found that error corrections were more effective in in-phase than in antiphase coordination, resulting in more adequate adjustments of cycle durations to compensate for timing errors detected at the start of each cycle. In addition, error corrections were generally more pronounced in the active than in the relaxed condition. This activity-related difference was attributed to the associated bilateral neural control signals (as estimated using electromyography), which provided an additional reference (in terms of expected sensory consequences) for afference-based error corrections. An intimate relation was revealed between the (integrated) motor commands to both limbs and the processing of afferent feedback.

Suppression of the non-dominant motor cortex during bimanual symmetric finger movement: a functional magnetic resonance imaging study

Patterns of bimanual coordination in which homologous muscles are simultaneously active are more stable than those in which homologous muscles are engaged in an alternating fashion. This may be attributable to the stronger involvement of the dominant motor cortex in ipsilateral hand movements via interaction with the non-dominant motor system, known as neural crosstalk. We used functional magnetic resonance imaging to investigate the neural representation of the interhemispheric interaction during bimanual mirror movements. Thirteen right-handed subjects completed four conditions: sequential finger tapping using the right and left index and middle fingers, bimanual mirror and parallel finger tapping. Auditory cues (3 Hz) were used to keep the tapping frequency constant. Task-related activation in the right primary motor cortex was significantly less prominent during mirror than unimanual left-handed movements. This was mirror- and non-dominant side-specific; parallel movements did not cause such a reduction, and the left primary motor cortex showed no such differential activation across the unimanual right, bimanual mirror, and bimanual parallel conditions. Reducing the contralateral innervation of the left hand may increase the fraction of the force command to the left hand coming from the left primary motor cortex, enhancing the neural crosstalk.     

Characteristics of instructed and uninstructed interpersonal coordination while walking side-by-side

We examined how people synchronize their leg movements while walking side-by-side on a treadmill. Walker pairs were either instructed to synchronize their steps in in-phase or in antiphase or received no coordination instructions. Frequency and phase analysis revealed that instructed in-phase and antiphase coordination were equally stable and independent of walking speed and the difference in individually preferred stride frequencies. Without instruction we found episodes of frequency locking in three pairs and episodes of phase locking in four pairs, albeit not always at (or near) 0 degrees or 180 degrees. Again, we found no difference in the stability of in-phase and antiphase coordination and no systematic effects of walking speed and the difference in individually preferred stride frequencies. These results suggest that the Haken-Kelso-Bunz model for rhythmic interlimb coordination does not apply to interpersonal coordination during gait in a straightforward manner. When the typically involved parameter constraints are relaxed, however, this model may largely account for the observed dynamical characteristics.     

Slowing fastest finger movements of the dominant hand with low-frequency rTMS of the hand area of the primary motor cortex

Neuroimaging studies suggest that the primary hand motor area and the cerebellum play a pivotal role in the control of finger tapping, but their differential contribution in this task is unknown. We used therefore repetitive transcranial magnetic stimulation (rTMS) in its virtual lesion mode (1 Hz, 10 min, 90% of motor threshold) to study the effects of transient disruption of the right lateral cerebellum (CB), the left primary hand motor area (M1), and the right brachial plexus (PL, control site) on various finger tapping tasks (paced finger tapping task: PFT; tapping with maximum speed: TAPMAX, and tapping with convenient speed: TAPCON) in healthy right-handed subjects. RTMS of the left M1 slowed finger tapping speed of the right hand in the TAPMAX task. This effect eliminated the right hand superiority in the TAPMAX task. In addition, rTMS of the left M1 resulted in slower tapping speeds for both hands during TAPCON. There were no other effects of rTMS on tapping speed or tapping variability. Findings indicate that M1 is essential for generating fastest finger movements.     

Temporal feature of BOLD responses varies with temporal patterns of movement

Which brain sites represent the final form of motor commands that encode temporal patterns of muscle activities? Here, we show the possible brain sites which have activity equivalent to the motor commands with functional magnetic resonance imaging (fMRI). We hypothesized that short-temporal patterns of movements or stimuli are reflected in blood-oxygenation-level-dependent (BOLD) responses and we searched for regions representing the response. Participants performed two temporal patterns of tapping and/or listened to the same patterns of auditory stimuli in a 3T fMRI. The patterns were designed to have the same number (11) of events and the same duration, but different temporal distribution of events. The 11 events were divided into two parts (10 repetitive taps and one stand-alone tap) and the interval of the two parts was 3s. The two patterns had reverse order of the two parts. The results revealed that different temporal patterns of auditory stimuli were represented in different temporal features of BOLD responses in the bilateral auditory cortex, whereas different temporal patterns of tapping were reflected in contralateral primary motor cortex and the ipsilateral anterior cerebellum. In bilateral premotor cortex, supplementary motor area, visual cortex, and posterior cerebellum, task-related BOLD responses were exhibited, but their responses did not reflect the temporal patterns of the movement and/or stimuli. One possible explanation is that the neuronal activities were similar for the two patterns in these regions. The sensitivity of the BOLD response to the temporal patterns reflects local differences in functional contributions to the tasks. The present experimental design and analysis may be useful to reveal particular brain regions that participate in multiple functions.     

Brain Activation Patterns Characterizing Different Phases of Motor Action: Execution,Choice and Ideation

Motor behaviour is controlled by a large set of interacting neural structures, subserving the different components involved in hierarchical motor processes. Few studies have investigated the neural substrate of higher-order motor ideation, i.e. the mental operation of conceiving a movement. The aim of this functional magnetic resonance imaging study was to segregate the neural structures involved in motor ideation from those involved in movement choice and execution. An index finger movement paradigm was adopted, including three different conditions: performing a pre-specified movement, choosing and executing a movement and ideating a movement of choice. The tasks involved either the right or left hand, in separate runs. Neuroimaging results were obtained by comparing the different experimental conditions and computing conjunction maps of the right and left hands for each contrast. Pre-specified movement execution was supported by bilateral fronto-parietal motor regions, the cerebellum and putamen. Choosing and executing finger movement involved mainly left fronto-temporal areas and the anterior cingulate. Motor ideation activated almost exclusively left hemisphere regions, including the inferior, middle and superior frontal regions, middle temporal and middle occipital gyri. These findings show that motor ideation is controlled by a cortical network mainly involved in abstract thinking, cognitive and motor control, semantic and visual imagery processes.     

Age-related reduction in the differential pathways involved in internal and external movement generation

Age-related differences in regional brain activation during two different movement generation modes were examined. Old and young volunteers were scanned while performing cyclical hand-foot flexion-extension movements in the presence and the absence of augmented visual feedback, referring to external and internal movements generation, respectively. Performing the coordination task under both conditions resulted in the activation of two distinct neural networks in the young adults, i.e., the hMT/V5+, and parietal and premotor cortices were typically involved during the visually guided mode, whereas the supplementary motor area (SMA), cingulate motor area (CMA), frontal operculum (FO) and secondary somatosensory area (S2) were typically involved during internally guided movements. Remarkably, much less differentiation between both feedback dependent networks was observed in the seniors, i.e., they exhibited high activity in the SMA, CMA, FO and S2 during both modes, suggesting that the typical network differentiation was largely diminished. This is hypothesized to reflect a general increase in processing resources within areas contributing to motor control and associated sensory processing, supporting motor performance in the elderly.     

Instabilities during antiphase bimanual movements: are ipsilateral pathways involved?

The spatial and temporal coupling between the hands is known to be very robust during movements which use homologous muscles (in-phase or symmetric movements). In contrast, movements using nonhomologous muscles (antiphase or asymmetric movements) are less stable and exhibit a tendency to undergo a phase transition to in-phase movements as movement frequency increases. The instability during antiphase movements has been modeled in terms of signal interference mediated by the ipsilateral corticospinal pathways. In this study we report that participants in whom distal ipsilateral motor-evoked potentials could be elicited with transcranial magnetic stimulation (TMS), exhibited higher variability during a bimanual circling task than participants whose ipsilateral pathways could not be transcranially activated. These results suggest that ipsilateral control of the limb affects the level of bimanual coupling, and may contribute to uncoupling phenomena observed during asymmetric coordination.     

Interactions between new and pre-existing dynamics in bimanual movement control

Motor skills are commonly acquired through practice. This process not only involves acquisition of the particular task demands but also requires overcoming pre-existing modes. In the present study, interactions between new and intrinsic dynamics were evaluated. Accordingly, bimanual finger tapping with a 2:1 ratio was performed according to two training schedules: continuous (consecutive trials) and interrupted (non-consecutive trials with intermediate 1:1 in-phase performances). In addition, in-phase and anti-phase were probed before and after training. Behavioral output was assessed by means of temporal accuracy and variability, whereas neural activation patterns were determined by EEG coherence. Results showed that continuous practice resulted in improved performance with reduced coherence across the motor network. For interrupted practice, behavioral execution ameliorated, although it was inferior to performance with continuous practice. In terms of neural changes, the degree of intrahemispheric and midline connectivity did not reduce with interrupted practice, whereas interhemispheric connectivity increased. This signifies that short-term motor consolidation of the 2:1 task was disrupted due to intermediate performance of the in-phase mode. Furthermore, the probed in-phase and anti-phase pattern showed no behavioral changes, although neural alterations occurred that depended on training schedule and coordination mode. Overall, the observations illustrate bidirectional interactions between new and inherent dynamics during motor acquisition, raising issues about effective methods for learning skills and scheduling of practices in neurorehabilitation.     

Effects of interlimb and intralimb constraints on bimanual shoulder-elbow and shoulder-wrist coordination patterns

The present study addressed the interactions between interlimb and intralimb constraints during the control of bimanual multi-joint movements. Participants performed eight coordination tasks involving bilateral shoulder-elbow (expt I) and shoulder-wrist (expt II) movements. Three principal findings were obtained. First, the principle of muscle homology (in-phase coordination), giving rise to mirror symmetrical movements with respect to the midsagittal plane, had a powerful influence on the quality of interlimb coordination. In both experiments, the accuracy and stability of inter- and/or intralimb coordination deteriorated as soon as the antiphase mode was introduced in one or both joint pairs. However, the mutual influences between bilateral distal and proximal joint pairs varied across coordination tasks and effectors. Second, the impact of intralimb coordination modes on the quality of intralimb coordination was inconsistent between adjacent (expt I) and non-adjacent joint (expt II) combinations. Third, the mode of interlimb coordination affected the quality of intralimb coordination, whereas strong support for the converse effect was not obtained. Taken together, these observations point to a hierarchical control structure whereby interlimb coordination constraints have a stronger impact on the global coordination of the system than intralimb constraints, whose impact is substantially dependent on effector and task. The finding that intralimb coordination is subordinate to interlimb coordination during the production of bimanual multi-joint coordination patterns indicates that symmetry is a major organizational principle in the neural control of complex movement.     

Bilateral phase entrainment by movement-elicited afference contributes equally to the stability of in-phase and antiphase coordination

This study examined if and how phase entrainment by movement-related afference-- induced by passive movements of the contralateral hand-- contributes to the coordinative stability of rhythmic bimanual movements. The results revealed that phase-shifted passive movements of the dominant or the nondominant hand induced similar entrainment effects on the active movements of the contralateral hand. In terms of the phase relations between the hands only two attractors of equal strength were present, corresponding to relative phase shifts of 0 degrees and 180 degrees , respectively, i.e., to in-phase and antiphase coordination. The attractors were separated by two repellors located at relative phase shifts of +90 degrees and -90 degrees . EMG analysis indicated that the entrainment effects indeed resulted from contralateral afference, because no related changes in muscle activation were observed in the passively moved hand. It was concluded that phase entrainment by contralateral afference contributed equally to the stable performance of the bimanual in-phase and antiphase patterns, thereby enhancing the stability of these patterns relative to other phase relations between the limbs.     

Neuromuscular and biomechanical factors codetermine the solution to motor redundancy in rhythmic multijoint arm movement

How the CNS deals with the issue of motor redundancy remains a central question for motor control research. Here we investigate the means by which neuromuscular and biomechanical factors interact to resolve motor redundancy in rhythmic multijoint arm movements. We used a two-df motorised robot arm to manipulate the dynamics of rhythmic flexion–extension (FE) and supination–pronation (SP) movements at the elbow-joint complex. Participants were required to produce rhythmic FE and SP movements, either in isolation, or in combination (at the phase relationship of their choice), while we recorded the activity of key bi-functional muscles. When performed in combination, most participants spontaneously produced an in-phase pattern of coordination in which flexion is synchronised with supination. The activity of the Biceps Brachii (BB), the strongest arm muscle which also has the largest moment arms in both flexion and supination was significantly higher for FE and SP performed in combination than in isolation, suggesting optimal exploitation of the mechanical advantage of this muscle. In a separate condition, participants were required to produce a rhythmic SP movement while a rhythmic FE movement was imposed by the motorised robot. Simulations based upon a musculoskeletal model of the arm demonstrated that in this context, the most efficient use of the force–velocity relationship of BB requires that an anti-phase pattern of coordination (flexion synchronized with pronation) be produced. In practice, the participants maintained the in-phase behavior, and BB activity was higher than for SP performed in isolation. This finding suggests that the neural organisation underlying the exploitation of bifunctional muscle properties, in the natural context, constrains the system to maintain the “natural” coordination pattern in an altered dynamic environment, even at the cost of reduced biomechanical efficiency. We suggest an important role for afference from the imposed movement in promoting the “natural” pattern. Practical implications for the emerging field of robot-assisted therapy and rehabilitation are briefly mentioned.     

Evaluation of Cortical Connectivity During Real and Imagined Rhythmic Finger Tapping

Accumulating evidence suggests the existence of a shared neural substrate between imagined and executed movements. However, a better understanding of the mechanisms involved in the motor execution and motor imagery requires knowledge of the way the co-activated brain regions interact to each other during the particular (real or imagined) motor task. Within this general framework, the aim of the present study is to investigate the cortical activation and connectivity sub-serving real and imaginary rhythmic finger tapping, from the analysis of multi-channel electroencephalogram (EEG) scalp recordings. A sequence of 250 auditory pacing stimuli has been used for both the real and imagined right finger tapping task, with a constant inter-stimulus interval of 1.5 s length. During the motor execution, healthy subjects were asked to tap in synchrony with the regular sequence of stimulus events, whereas in the imagery condition subjects imagined themselves tapping in time with the auditory cue. To improve the spatial resolution of the scalp fields and suppress unwanted interferences, the EEG data have been spatially filtered. Further, event related synchronization and desynchronization phenomena and phase synchronization analysis have been employed for the study of functionally active brain areas and their connectivity during real and imagery finger tapping. Our results show a fronto-parietal co-activation during both real and imagined movements and similar connectivity patterns among contralateral brain areas. The results support the hypothesis that functional connectivity over the contralateral hemisphere during finger tapping is preserved in imagery. The approach and results can be regarded as indicative evidences of a new strategy for recognizing imagined movements in EEG-based brain computer interface research.     

High Resolution DC-EEG Analysis of the Bereitschaftspotential and Post Movement Onset Potentials Accompanying Uni- or Bilateral Voluntary Finger Movements

Movement-related potentials (MRPs, including Bereitschaftspotential, BP) were recorded using a 64 channel DC-EEG amplifier (High Resolution DC-EEG, Nunez et al. 1994) in 18 subjects (Ss) to explore functions of the supplementary, the cingulate, and the primary motor area (SMA, CMA and MI). Spatial and temporal resolutions on single trials, single subject and grand average data were evaluated for preparation and execution of self-initiated index finger extensions (bilateral, right and left unilateral). Results showed that [1] MRPs consisted of six waves: Early component (BP1) of the MRPs, late component (BP2) of the MRPs, Motor potential (MP), Post movement positive potential (PMPP), Movement-evoked potential I (MEP I) and Movement-evoked potential II (MEPII). [2] Onset of BP1 was earliest in the mesial wall motor areas, SMA/CMA, then in the contralateral MI (conMI) and latest in the ipsilateral MI (ipsMI). [3] MRP amplitudes were maximum in the SMA/CMA in all three tasks. In the unilateral tasks, MRP amplitudes were higher in the conMI than they were in the ipsMI. [4] The early BP component (BP1) was always localized in the fronto-central midline (overlying the mesial wall motor areas SMA and CMA). BP2, MP, PMPP, MEP1 and MEP II showed clear lateralized distributions (contralaterally larger) for unilateral movement but not for bilateral movement. [5] BP2, MP, PMPP, MEPI and MEPII in bilateral movement are not just the mathematical sum of right and left unilateral movements on both hemispheres. [6] The three tasks influenced all six MRP components. [7] Current source density maps, which were relatively robust between different tasks, further demonstrated that BP1 stemmed from the fronto-central midline (mesial wall motor areas). [8] MANOVA showed that there were several statistically significant differences (p<0.001) across the multiple combinations between time points of the epoch (20), electrodes (56) and tasks (3). Conclusions: [1] SMA/CMA participates in preparation and initiation of volitional index finger extensions, while MI participates in their execution and performance. [2] BP1 stems primarily from the mesial wall motor areas, SMA and CMA. [3] SMA/CMA subserves the temporal organization of sequential movements and bimanual coordination.