Weight-specific anticipatory coding of grip force in human dorsal premotor cortex

The dorsal premotor cortex (PMd) uses prior sensory information for motor preparation. Here, we used a conditioning-and-map approach in 11 healthy male humans (mean age 27 years) to further clarify the role of PMd in anticipatory motor control. We transiently disrupted neuronal processing in PMd, using either continuous theta burst stimulation (cTBS) at 80% (inhibitory cTBS) or 30% (sham cTBS) of active motor threshold. The conditioning effects of cTBS on preparatory brain activity were assessed with functional MRI, while participants lifted a light or heavy weight in response to a go-cue (S2). An additional pre-cue (S1) correctly predicted the weight in 75% of the trials. Participants were asked to use this prior information to prepare for the lift. In the sham condition, grip force showed a consistent undershoot, if the S1 incorrectly prompted the preparation of a light lift. Likewise, an S1 that falsely announced a heavy weight produced a consistent overshoot in grip force. In trials with incorrect S1, preparatory activity in left PMd during the S1-S2 delay period predicted grip force undershoot but not overshoot. Real cTBS selectively abolished this undershoot in grip force. Furthermore, preparatory S1-S2 activity in left PMd no longer predicted the individual undershoot after real cTBS. Our results provide converging evidence for a causal involvement of PMd in anticipatory downscaling but not upscaling of grip force, suggesting an inhibitory role of PMd in anticipatory grip force control during object lifting.     

Signal-, set-, and movement-related activity in the human premotor cortex

Single unit recording studies in non-human premotor cortex have revealed neurons with motor-related activity. Other neurons, however, seem to be involved in prior movement selection and preparation processes, and have activity related to visual instruction signals or movement preparation ('set'). We have used single pulse transcranial magnetic stimulation (TMS) to identify similar processes in human subjects. In Experiment 1 subjects performed a cued movement task while being stimulated with TMS over three sites: sensorimotor cortex, posterior premotor cortex and anterior premotor cortex. TMS slowed movements when applied at 140 ms after the visual cue over the anterior premotor site, at 180 ms after the visual cue over the posterior premotor site, and at 220 ms and later after the visual cue over the sensorimotor cortex. The results are consistent with a change from signal to movement-related processing when moving from premotor to motor cortex. In Experiment 2 there was a preparatory set period between the instruction signal that informed subjects which movement to make and the 'go' signal that informed them when to actually make the movement. TMS was applied over the anterior premotor site and the sensorimotor site during the set period. At both sites TMS had similar effects on slowing subsequent movements. The results suggest set activity in both premotor and motor cortices in human subjects.     

Multisynaptic projections from the ventrolateral prefrontal cortex to the dorsal premotor cortex in macaques – anatomical substrate for conditional visuomotor behavior

Lines of evidence indicate that both the ventrolateral prefrontal cortex (vlPFC) (areas 45/12) and dorsal premotor cortex (PMd) (rostral F2 in area 6) are crucially involved in conditional visuomotor behavior, in which it is required to determine an action based on an associated visual object. However, virtually no direct projections appear to exist between the vlPFC and PMd. In the present study, to elucidate possible multisynaptic networks linking the vlPFC to the PMd, we performed a series of neuroanatomical tract‐tracing experiments in macaque monkeys. First, we identified cortical areas that send projection fibers directly to the PMd by injecting Fast Blue into the PMd. Considerable retrograde labeling occurred in the dorsal prefrontal cortex (dPFC) (areas 46d/9/8B/8Ad), dorsomedial motor cortex (dmMC) (F7 and presupplementary motor area), rostral cingulate motor area, and ventral premotor cortex (F5 and area 44), whereas the vlPFC was virtually devoid of neuronal labeling. Second, we injected the rabies virus, a retrograde transneuronal tracer, into the PMd. At 3 days after the rabies injections, second‐order neurons were labeled in the vlPFC (mainly area 45), indicating that the vlPFC disynaptically projects to the PMd. Finally, to determine areas that connect the vlPFC to the PMd indirectly, we carried out an anterograde/retrograde dual‐labeling experiment in single monkeys. By examining the distribution of axon terminals labeled from the vlPFC and cell bodies labeled from the PMd, we found overlapping labels in the dPFC and dmMC. These results indicate that the vlPFC outflow is directed toward the PMd in a multisynaptic fashion through the dPFC and/or dmMC.     

Spatial orienting of attention: a study of reaction time during pointing movement]

AIM: The aim of this study was to investigate how advance information both explicit and implicit provided prior to movement may affect the spatial orientation and the internal attention control processes in normal adult subjects. The originality of this work compared to the test of Posner, lies essentially in the methodology used to study the attentional systems. The use of three procedures of reaction time (RT) allowed us to study the setting concerned of the specific and non-specific components of the attention in the motor preparation. By associating of these three procedures of RT, we have evaluated the effects of the explicit and implicit components of advance information on motor preparation. The use of advance information to the movement requires the implication of the attentional systems. MATERIAL AND METHODS: Experiments were carried out using a simple reaction time (RT) procedure involving the use of an orientation cue and two choice reaction time situations: one with a neutral preparatory cue and one with a priming cue giving the likelihood of the preparatory stimulus (S1) being compatible with the imperative stimulus (S2). The mechanisms underlying the subjects' vigilance and the orientation of their attention were studied by assessing the effects on their reaction times of the preparatory signal and those of the cue giving the likelihood of S1 and S2 being compatible. The preparatory signal was designed to explicitly attract the subjects' attention towards the position of the forthcoming pointing target, whereas the cue giving the compatibility between S1 and S2 was intended to mobilize the subject's attention more implicitly. Prior to performing the pointing movement towards a visual target, the subjects' attention was therefore mobilized by the advance information containing two components: the explicit information about the position of S1 and the implicit information about the probability of S1 and S2 being compatible. RESULTS AND CONCLUSION: The results obtained here on 17 normal adult subjects show that the subjects significantly improved their RTs by using the explicit component of the information provided. The implicit information available was also used in the choice reaction situations: a priming effect was found to occur, which resulted in the shortening of the primed "compatible cue" reaction times in comparison with the "neutral cue" reaction times, and in the correlation which was found to exist between the reaction time performances and the degree of compatibility between the preparatory signal and the imperative signal. These results suggest that various components of the attentional system may participate in processing the advance information provided prior to the movement in reaction time tasks of the kind used here. The explicit information provided prior to the movement may mobilize the subject's vigilance and spatially orients his attention; whereas the implicit information available may rather subserve the internal control of the subject's attention.     

Rostrocaudal functional gradient among the pre‐dorsal premotor cortex,dorsal premotor cortex and primary motor cortex in goal‐directed motor behaviour

The dorsal premotor cortex residing in the dorsolateral aspect of area 6 is a rostrocaudally elongated area that is rostral to the primary motor cortex (M1) and caudal to the prefrontal cortex. This region, which is subdivided into rostral [pre‐dorsal premotor cortex (pre‐PMd)] and caudal [dorsal premotor cortex proper (PMd)] components, probably plays a central role in planning and executing actions to achieve a behavioural goal. In the present study, we investigated the functional specializations of the pre‐PMd, PMd, and M1, because the synthesis of the specific functions performed by each area is considered to be essential. Neurons were recorded while monkeys performed a conditional visuo‐goal task designed to include separate processes for determining a behavioural goal (reaching towards a right or left potential target) on the basis of visual object instructions, specifying actions (direction of reaching) to be performed on the basis of the goal, and preparing and executing the action. Neurons in the pre‐PMd and PMd retrieved and maintained behavioural goals without encoding the visual features of the visual object instructions, and subsequently specified the actions by multiplexing the goals with the locations of the targets. Furthermore, PMd and M1 neurons played a major role in representing the action during movement preparation and execution, whereas the contribution of the pre‐PMd progressively decreased as the time of the actual execution of the movement approached. These findings revealed that the multiple processing stages necessary for the realization of an action to accomplish a goal were implemented in an area‐specific manner across a functional gradient from the pre‐PMd to M1 that included the PMd as an intermediary.     

Fronto-parietal networks activation during the contingent negative variation period

The preparation for stimuli and responses in which the position and required finger to respond are cued, produces the preparatory activation of the specific neural resources that are going to be needed for the completion of the task. The focus of the present report is to evaluate if the fronto-parietal networks activated in fMRI studies during endogenous attention are also activated during the CNV period using EEG recording. The behavioural responses and 64 EEG channels were recorded during an S1-S2 paradigm similar to Posner central cue paradigms. The LORETA analysis based in the averaging of the z-LORETA values showed that the Brodmann's areas with the highest activation during the CNV period were in the medial and superior frontal areas, fronto-parietal lateral areas (including the premotor cortex) and extrastriate visual cortex. These results suggest that in addition to the previously described activation in premotor-motor, posterior sensory and superior and medial frontal areas, the activation of fronto-parietal networks is a main contributor to the CNV, indicating the endogenous attentional effort during the CNV period.     

The primary motor and premotor areas of the human cerebral cortex.

Brodmann's cytoarchitectonic map of the human cortex designates area 4 as cortex in the anterior bank of the precentral sulcus and area 6 as cortex encompassing the precentral gyrus and the posterior portion of the superior frontal gyrus on both the lateral and medial surfaces of the brain. More than 70 years ago, Fulton proposed a functional distinction between these two areas, coining the terms primary motor area for cortex in Brodmann area 4 and premotor area for cortex in Brodmann area 6. The parcellation of the cortical motor system has subsequently become more complex. Several nonprimary motor areas have been identified in the brain of the macaque monkey, and associations between anatomy and function in the human brain are being tested continuously using brain mapping techniques. In the present review, the authors discuss the unique properties of the primary motor area (M1), the dorsal portion of the premotor cortex (PMd), and the ventral portion of the premotor cortex (PMv). They end this review by discussing how the premotor areas influence M1.     

Synchronization of parietal and premotor areas during preparation and execution of praxis hand movements.

OBJECTIVE: We sought to determine temporal patterns of functional connectivity between the parietal, premotor, and motor cortices during preparation and execution of praxis hand movements. METHODS: Normal subjects were instructed to perform six transitive (tool use) and intransitive (communicative gesture) self-paced pantomimes with the right hand while recording 64-channel electroencephalography (EEG) and electromyography (EMG) from right thumb and forearm flexors. Focusing on corticocortical coherence, we explored the time-course of synchronously active parietal and premotor circuits involved in these motor tasks. Trials were marked for EMG onset and averaged across subjects to determine changes in coherence relative to baseline between parietal, premotor, and motor areas. RESULTS: Coherence of homologous electrode pairs was similar when comparing transitive and intransitive movements. During preparation, beta band (18-22 Hz) coherence was maximal between electrodes over the left parietal lobe and left premotor electrodes. Additionally during preparation, the premotor area showed high coherence to the motor hand area and the parietal cortex. Electrodes over the supplementary motor area also showed coherence to the motor and parietal, but not the premotor area. Before and during execution, a second peak of high coherence increase was present in each area that demonstrated coherence increases during preparation. There was no coherence increase between parietal and motor areas. Coherence rapidly diminished 1.5-2.0 s after movement onset. CONCLUSIONS: Patterns of increased corticocortical coupling within a parietal, premotor, and motor network are present during preparation and execution of praxis movements. SIGNIFICANCE: This study adds to evidence that parietofrontal networks may be critical for integrating preparatory and motor-related activity for praxis movements.     

Interhemispheric connections of the ventral premotor cortex in a new world primate

This study describes the pattern of interhemispheric connections of the ventral premotor cortex (PMv) distal forelimb representation (DFL) in squirrel monkeys. Our objectives were to describe qualitatively and quantitatively the connections of PMv with contralateral cortical areas. Intracortical microstimulation techniques (ICMS) guided the injection of the neuronal tract tracers biotinylated dextran amine or Fast blue into PMv DFL. We classified the interhemispheric connections of PMv into three groups. Major connections were found in the contralateral PMv and supplementary motor area (SMA). Intermediate interhemispheric connections were found in the rostral portion of the primary motor cortex, the frontal area immediately rostral and ventral to PMv (FR), cingulate motor areas (CMAs), and dorsal premotor cortex (PMd). Minor connections were found inconsistently across cases in the anterior operculum (AO), posterior operculum/inferior parietal cortex (PO/IP), and posterior parietal cortex (PP), areas that consistently show connections with PMv in the ipsilateral hemisphere. Within-case comparisons revealed that the percentage of PMv connections with contralateral SMA and PMd are higher than the percentage of PMv connections with these areas in the ipsilateral hemisphere; percentages of PMv connections with contralateral M1 rostral, FR, AO, and the primary somatosensory cortex are lower than percentages of PMv connections with these areas in the ipsilateral hemisphere. These studies increase our knowledge of the pattern of interhemispheric connection of PMv. They help to provide an anatomical foundation for understanding PMv's role in motor control of the hand and interhemispheric interactions that may underlie the coordination of bimanual movements.     

Neural correlates of object size and object location during grasping actions

The visuo‐motor channel hypothesis (Jeannerod, 1981) postulates that grasping movements consist of a grip and a transport component differing in their reliance on intrinsic vs. extrinsic object properties (e.g. size vs. location, respectively). While recent neuroimaging studies have revealed separate brain areas implicated in grip and transport components within the parietal lobe, less is known about the neural processing of extrinsic and intrinsic properties of objects for grasping actions. We used functional magnetic resonance imaging adaptation to examine the cortical areas involved in processing object size, object location or both. Participants grasped (using the dominant right hand) or passively viewed sequential pairs of objects that could differ in size, location or both. We hypothesized that if intrinsic and extrinsic object properties are processed separately, as suggested by the visuo‐motor channel hypothesis, we would observe adaptation to object size in areas that code the grip and adaptation to location in areas that code the transport component. On the other hand, if intrinsic and extrinsic object properties are not processed separately, brain areas involved in grasping may show adaptation to both object size and location. We found adaptation to object size for grasping movements in the left anterior intraparietal sulcus (aIPS), in agreement with the idea that object size is processed separately from location. In addition, the left superior parietal occipital sulcus (SPOC), primary somatosensory and motor area (S1/M1), precuneus, dorsal premotor cortex (PMd), and supplementary motor area (SMA) showed non‐additive adaptation to both object size and location. We propose different roles for the aIPS as compared with the SPOC, S1/M1, precuneus, PMd and SMA. In particular, while the aIPS codes intrinsic object properties, which are relevant for hand preshaping and force scaling, area SPOC, S1/M1, precuneus, PMd and SMA code intrinsic as well as extrinsic object properties, both of which are relevant for digit positioning during grasping.     

Beyond the “Bereitschaftspotential”: Action preparation behind cognitive functions

Research on preparatory brain processes taking place before acting shows unexpected connections with cognitive processing. From 50 years, we know that motor-related brain activity can be measured by electrocortical recordings 1–3 s before voluntary actions. This readiness potential has been associated with increasing excitably of premotor and motor areas and directly linked to the kinematic of the upcoming action. Now we know that the mere motor preparation is only one function of a more complex preparatory activity. Recent research shows that before any action many cognitive processes may occur depending on various aspects of the action, such as complexity, meaning, emotional valence, fatigue and consequences of the action itself. In addition to studies on self-paced action, the review considers also studies on externally-triggered paradigms showing differences in preparation processes related to age, physical exercise, and task instructions. Evidences from electrophysiological and neuroimaging recording indicate that in addition to the motor areas, the prefrontal, parietal and sensory cortices may be active during action preparation to anticipate future events and calibrate responses.     

Comparison of unilateral and bilateral complex finger tapping-related activation in premotor and primary motor cortex

Sixteen healthy right-handed subjects performed a complex finger-tapping task that broadly activates the motor and premotor regions, including primary motor (M1), ventral premotor (PMv), and dorsal premotor (PMd) cortex. This task was performed with the right hand only, left hand only and both hands simultaneously. Behavioral performance and the possibility of mirror movements were controlled through the use of MRI-compatible gloves to monitor finger movements. Using spatially normalized ROIs from the Human Motor Area Template (HMAT), comparisons were made of the spatial extent and location of activation in the left and right motor regions between all three tasks. During unilateral right and left hand tapping, ipsilateral precentral gyrus activation occurred in all subjects, mainly in the PMv and PMd. Ipsilateral M1 activation was less consistent and shifted anteriorly within M1, towards the border of M1 and premotor cortex. Regions of ipsilateral activation were also activated during contralateral and bilateral tasks. Overall, 83%/70%/58% of the ipsilaterally activated voxels in M1/PMd/PMv were also activated during contralateral and bilateral tapping. The mean percent signal change of spatially overlapping activated voxels was similar in PMv and PMd between all three tasks. However, the mean percent signal change of spatially overlapping M1 activation was significantly less during ipsilateral tapping compared with contra- or bilateral tapping. Results suggest that the ipsilateral fMRI activation in unilateral motor tasks may not be inhibitory in nature, but rather may reflect part of a bilateral network involved in the planning and/or execution of tapping in the ipsilateral hand.     

Identification of multiple nonprimary motor cortical areas with simple movements

The human cortex reportedly contains at least five nonprimary motor areas: in the frontolateral convexity, the dorsal and ventral premotor cortex (PMd and PMv), and in the frontomesial wall, the presupplementary and supplementary motor areas (pre-SMA and SMA), and the rostral, dorsal and ventral cingulate areas (CMAr, CMAd, and CMAv). Activation of these regions in neuroimaging studies has been generally associated either with the performance of complex motor tasks or with reorganization occurring with motor recovery in the presence of pathology. Recent evidence from neuroimaging studies suggests that the same areas are activated with well controlled simple movements in healthy subjects providing support to the observation that their contribution may be more quantitative rather than exclusively specific to a certain aspect of motor behaviour. An important consequence of this observation is that activation of multiple nonprimary motor areas during simple motor tasks should not be considered unique to patients with upper or lower motoneuron lesions but rather as a normal physiological process.     

Compensatory activity in the extrastriate body area of Parkinson's disease patients

Compensatory mechanisms are a crucial component of the cerebral changes triggered by neurodegenerative disorders. Identifying such compensatory mechanisms requires at least two complementary approaches: localizing candidate areas using functional imaging, and showing that interference with these areas has behavioral consequences. Building on recent imaging evidence, we use this approach to test whether a visual region in the human occipito-temporal cortex-the extrastriate body area-compensates for altered dorsal premotor activity in Parkinson's disease (PD) during motor-related processes. We separately inhibited the extrastriate body area and dorsal premotor cortex in 11 PD patients and 12 healthy subjects, using continuous theta burst stimulation. Our goal was to test whether these areas are involved in motor compensatory processes. We used motor imagery to isolate a fundamental element of motor planning, namely subjects' ability to incorporate the current state of their body into a motor plan (mental hand rotation). We quantified this ability through a posture congruency effect (i.e., the improvement in subjects' performance when their current body posture is congruent to the imagined movement). Following inhibition of the right extrastriate body area, the posture congruency effect was lost in PD patients, but not in healthy subjects. In contrast, inhibition of the left dorsal premotor cortex reduced the posture congruency effect in healthy subjects, but not in PD patients. These findings suggest that the right extrastriate body area plays a compensatory role in PD by supporting a function that is no longer performed by the dorsal premotor cortex.     

Disrupting Short-Term Memory Maintenance in Premotor Cortex Affects Serial Dependence in Visuomotor Integration

Human behavior is biased by past experience. For example, when intercepting a moving target, the speed of previous targets will bias responses in future trials. Neural mechanisms underlying this so-called serial dependence are still under debate. Here, we tested the hypothesis that the previous trial leaves a neural trace in brain regions associated with encoding task-relevant information in visual and/or motor regions. We reasoned that injecting noise by means of transcranial magnetic stimulation (TMS) over premotor and visual areas would degrade such memory traces and hence reduce serial dependence. To test this hypothesis, we applied bursts of TMS pulses to right visual motion processing region hV5/MT+ and to left dorsal premotor cortex (PMd) during intertrial intervals of a coincident timing task performed by twenty healthy human participants (15 female). Without TMS, participants presented a bias toward the speed of the previous trial when intercepting moving targets. TMS over PMd decreased serial dependence in comparison to the control Vertex stimulation, whereas TMS applied over hV5/MT+ did not. In addition, TMS seems to have specifically affected the memory trace that leads to serial dependence, as we found no evidence that participants'' behavior worsened after applying TMS. These results provide causal evidence that an implicit short-term memory mechanism in premotor cortex keeps information from one trial to the next, and that this information is blended with current trial information so that it biases behavior in a visuomotor integration task with moving objects.SIGNIFICANCE STATEMENT Human perception and action are biased by the recent past. The origin of such serial bias is still not fully understood, but a few components seem to be fundamental for its emergence: the brain needs to keep previous trial information in short-term memory and blend it with incoming information. Here, we present evidence that a premotor area has a potential role in storing previous trial information in short-term memory in a visuomotor task and that this information is responsible for biasing ongoing behavior. These results corroborate the perspective that areas associated with processing information of a stimulus or task also participate in maintaining that information in short-term memory even when this information is no longer relevant for current behavior.     

Sub-second "temporal attention" modulates alpha rhythms. A high-resolution EEG study

In the present high-resolution electroencephalographic (EEG) study, event-related desynchronization/synchronization (ERD/ERS) of alpha rhythms was computed during an S1-S2 paradigm, in which a visual cue (S1) predicted a SHORT (600 ms) or LONG (1400 ms) foreperiod, preceding a visual go stimulus (S2) triggering right or left finger movement. Could orienting attention to a selective point in time influence the alpha rhythms as a function of the SHORT vs. LONG foreperiod? Stronger selective attentional modulations were predicted for the SHORT than LONG condition. EEG data from 54 channels were "depurated" from phase-locked visual evoked potentials and spatially enhanced by surface Laplacian estimation (i.e., final data analysis was conducted on 16 subjects having a sufficient number of artifact-free EEG single trials). Low-band alpha rhythms (about 6-10 Hz) were supposed to be related to anticipatory attentional processes, whereas high-band alpha rhythms (10-12 Hz) would indicate task-specific visuo-motor processes. Compared to the LONG condition (foreperiod), the SHORT condition induced a quicker and stronger ERS at low-band alpha rhythm (about 6-8 Hz) over midline and bilateral prefrontal, sensorimotor, and posterior parietal areas. In contrast, the concomitant high-band alpha (about 10-12 Hz) ERD/ERS showed no significant difference between the two conditions. In conclusion, temporal attention for a sub-second delay (800 ms) did modulate low-band alpha rhythm over large regions of both cortical hemispheres.     

Corticocortical projections to area 1 in squirrel monkeys (Saimiri sciureus)

Cortical area 1 is a non‐primary somatosensory area in the primate anterior parietal cortex that is critical to tactile discrimination. The corticocortical projections to area 1 in squirrel monkeys were determined by placing multiple injections of anatomical tracers into separate body part representations defined by multiunit microelectrode mapping in area 1. The pattern of labeled cells in the cortex indicated that area 1 has strong intrinsic connections within each body part representation and has inputs from somatotopically matched regions of areas 3b, 3a, 2 and 5. Somatosensory areas in the lateral sulcus, including the second somatosensory area (S2), the parietal ventral area (PV), and the presumptive parietal rostral (PR) and ventral somatosensory (VS) areas, also project to area 1. Topographically organized projections to area 1 also came from the primary motor cortex (M1), the dorsal and ventral premotor areas (PMd and PMv), and the supplementary motor area (SMA). Labeled cells were also found in cingulate motor and sensory areas on the medial wall of the hemisphere. Previous studies revealed a similar pattern of projections to area 1 in Old World macaque monkeys, suggesting a pattern of cortical inputs to area 1 that is common across anthropoid primates.     

Callosal connections of dorso-lateral premotor cortex

This study investigated the organization of the callosal connections of the two subdivisions of the monkey dorsal premotor cortex (PMd), dorso-rostral (F7) and dorso-caudal (F2). In one animal, Fast blue and Diamidino yellow were injected in F7 and F2, respectively; in a second animal, the pattern of injections was reversed. F7 and F2 receive a major callosal input from their homotopic counterpart. The heterotopic connections of F7 originate mainly from F2, with smaller contingent from pre-supplementary motor area (pre-SMA, F6), area 8 (frontal eye fields), and prefrontal cortex (area 46), while those of F2 originate from F7, with smaller contributions from ventral premotor areas (F5, F4), SMA-proper (F3), and primary motor cortex (M1). Callosal cells projecting homotopically are mostly located in layers II-III, those projecting heterotopically occupy layers II-III and V-VI. A spectral analysis was used to characterize the spatial fluctuations of the distribution of callosal neurons, in both F7 and F2, as well as in adjacent cortical areas. The results revealed two main periodic components. The first, in the domain of the low spatial frequencies, corresponds to periodicities of cell density with peak-to-peak distances of approximately 10 mm, and suggests an arrangement of callosal cells in the form of 5-mm wide bands. The second corresponds to periodicities of approximately 2 mm, and probably reflects a 1-mm columnar-like arrangement. Coherency and phase analyses showed that, although similar in their spatial arrangements, callosal cells projecting to dorsal premotor areas are segregated in the tangential cortical domain.     

Transcallosal connection patterns of opposite dorsal premotor regions support a lateralized specialization for action and perception

Lateralization of higher brain functions requires that a dominant hemisphere collects relevant information from both sides. The right dorsal premotor cortex (PMd), particularly implicated in visuomotor transformations, was hypothesized to be optimally located to converge visuospatial information from both hemispheres for goal‐directed movement. This was assessed by probabilistic tractography and a novel analysis enabling group comparisons of whole‐brain connectivity distributions of the left and right PMd in standard space (16 human subjects). The resulting dominance of contralateral PMd connections was characterized by right PMd connections with left visual and parietal areas, indeed supporting a dominant role in visuomotor transformations, while the left PMd showed dominant contralateral connections with the frontal lobe. Ipsilateral right PMd connections were also stronger with posterior parietal regions, relative to the left PMd connections, while ipsilateral connections of the left PMd were stronger with, particularly, the anterior cingulate, the ventral premotor and anterior parietal cortex. The pattern of dominant right PMd connections thus points to a specific role in guiding perceptual information into the motor system, while the left PMd connections are consistent with action dominance based on a lead in motor intention and fine precision skills.     

Attention and movement-related motor cortex activation: a high-density EEG study of spatial stimulus-response compatibility

Visual spatial attentional activation of motor areas has been documented in single cell neurophysiology and functional imaging studies of the brain. Here, we investigate a candidate event-related brain potential representing visuospatial attentional activity in motor areas of the cortex. The investigation aimed to elucidate the neural origin and the functional characteristics of this brain potential, which has been labelled N2cc and is typically observed in spatial stimulus-response compatibility tasks. High-density EEG was recorded in 10 subjects while they performed a Simon-type spatial stimulus-response compatibility task and a control task where the same stimuli were assigned to Go-Nogo response alternatives. The N2cc showed a time course parallel to the posteriorly distributed N2pc, associated with visuospatial selection. Scalp distribution and current source density reconstructions allowed a spatial separation of N2pc and centrally distributed N2cc and were compatible with a source for the N2cc in the lateral premotor cortex. Comparisons across tasks demonstrated that the N2cc depends on bilateral response readiness, ruling out an exclusively attentional interpretation. Instead, the activity appears associated with visuospatial attentional processes that serve the selection and suppression of competing responses, in accord with a function of the dorsal premotor cortex in response selection. Together, the results consolidate the N2cc as a new ERP component relevant to the investigation of visuospatial motor processes.