Anterior Intraparietal Cortex Research Articles

Recovered grasping performance after stroke depends on interhemispheric frontoparietal connectivity.

Activity changes in the ipsi- and contralesional parietal cortex and abnormal interhemispheric connectivity between these regions are commonly observed after stroke, however, their significance for motor recovery remains poorly understood. We here assessed the contribution of ipsilesional and contralesional anterior intraparietal cortex (aIPS) for hand motor function in 18 recovered chronic stroke patients and 18 healthy control subjects using a multimodal assessment consisting of resting-state functional MRI, motor task functional MRI, online-repetitive transcranial magnetic stimulation (rTMS) interference, and 3D movement kinematics. Effects were compared against two control stimulation sites, i.e. contralesional M1 and a sham stimulation condition. We found that patients with good motor outcome compared to patients with more substantial residual deficits featured increased resting-state connectivity between ipsilesional aIPS and contralesional aIPS as well as between ipsilesional aIPS and dorsal premotor cortex. Moreover, interhemispheric connectivity between ipsilesional M1 and contralesional M1 as well as ipsilesional aIPS and contralesional M1 correlated with better motor performance across tasks. TMS interference at individual aIPS and M1 coordinates led to differential effects depending on the motor task that was tested, i.e. index finger-tapping, rapid pointing movements, or a reach-grasp-lift task. Interfering with contralesional aIPS deteriorated the accuracy of grasping, especially in patients featuring higher connectivity between ipsi- and contralesional aIPS. In contrast, interference with the contralesional M1 led to impaired grasping speed in patients featuring higher connectivity between bilateral M1. These findings suggest differential roles of contralesional M1 and aIPS for distinct aspects of recovered hand motor function, depending on the reorganization of interhemispheric connectivity.

Motor impairment evoked by direct electrical stimulation of human parietal cortex during object manipulation

In primates, the parietal cortex plays a crucial role in hand-object manipulation. However, its involvement in object manipulation and related hand-muscle control has never been investigated in humans with a direct and focal electrophysiological approach. To this aim, during awake surgery for brain tumors, we studied the impact of direct electrical stimulation (DES) of parietal lobe on hand-muscles during a hand-manipulation task (HMt). Results showed that DES applied to fingers-representation of postcentral gyrus (PCG) and anterior intraparietal cortex (aIPC) impaired HMt execution. Different types of EMG-interference patterns were observed ranging from a partial (task-clumsy) or complete (task-arrest) impairment of muscles activity. Within PCG both patterns coexisted along a medio (arrest)–lateral (clumsy) distribution, while aIPC hosted preferentially the task-arrest. The interference patterns were mainly associated to muscles suppression, more pronounced in aIPC with respect to PCG. Moreover, within PCG were observed patterns with different level of muscle recruitment, not reported in the aIPC. Overall, EMG-interference patterns and their probabilistic distribution suggested the presence of different functional parietal sectors, possibly playing different roles in hand-muscle control during manipulation. We hypothesized that task-arrest, compared to clumsy patterns, might suggest the existence of parietal sectors more closely implicated in shaping the motor output.

Decoding motor imagery and action planning in the early visual cortex: Overlapping but distinct neural mechanisms

Recent evidence points to a role of the primary visual cortex that goes beyond visual processing into high-level cognitive and motor-related functions, including action planning, even in absence of feedforward visual information. It has been proposed that, at the neural level, motor imagery is a simulation based on motor representations, and neuroimaging studies have shown overlapping and shared activity patterns for motor imagery and action execution in frontal and parietal cortices. Yet, the role of the early visual cortex in motor imagery remains unclear. Here we used multivoxel pattern analyses on functional magnetic resonance imaging (fMRI) data to examine whether the content of motor imagery and action intention can be reliably decoded from the activity patterns in the retinotopic location of the target object in the early visual cortex. Further, we investigated whether the discrimination between specific actions generalizes across imagined and intended movements. Eighteen right-handed human participants (11 females) imagined or performed delayed hand actions towards a centrally located object composed of a small shape attached on a large shape. Actions consisted of grasping the large or small shape, and reaching to the center of the object. We found that despite comparable fMRI signal amplitude for different planned and imagined movements, activity patterns in the early visual cortex, as well as dorsal premotor and anterior intraparietal cortex, accurately represented action plans and action imagery. However, movement content is similar irrespective of whether actions are actively planned or covertly imagined in parietal but not early visual or premotor cortex, suggesting a generalized motor representation only in regions that are highly specialized in object directed grasping actions and movement goals. In sum, action planning and imagery have overlapping but non identical neural mechanisms in the cortical action network.

Connectivity of the Human Number Form Area Reveals Development of a Cortical Network for Mathematics.

The adult brain contains cortical areas thought to be specialized for the analysis of numbers (the putative number form area, NFA) and letters (the visual word form area, VWFA). Although functional development of the VWFA has been investigated, it is largely unknown when and how the NFA becomes specialized and connected to the rest of the brain. One hypothesis is that NFA and VWFA derive their special functions through differential connectivity, but the development of this differential connectivity has not been shown. Here, we mapped the resting state connectivity of NFA and VWFA to the rest of the brain in a large sample (n = 437) of individuals (age 3.2–21 years). We show that within NFA-math network and within VWFA-reading network the strength of connectivity increases with age. The right NFA is significantly connected to the right intraparietal cortex already at the earliest age tested (age 3), before formal mathematical education has begun. This connection might support or enable an early understanding of magnitude or numerosity In contrast, the functional connectivity from NFA to the left anterior intraparietal cortex and to the right dorsolateral prefrontal cortex is not different from the functional connectivity of VWFA to these regions until around 12–14 years of age. The increase in connectivity to these regions was associated with a gradual increase in mathematical ability in an independent sample. In contrast, VWFA connects significantly to Broca’s region around age 6, and this connectivity is correlated with reading ability. These results show how the differential connectivity of the networks for mathematics and reading slowly emerges through years of training and education.

The neural basis of hand choice: An fMRI investigation of the Posterior Parietal Interhemispheric Competition model

The current study investigates a new neurobiological model of human hand choice: The Posterior Parietal Interhemispheric Competition (PPIC) model. The model specifies that neural populations in bilateral posterior intraparietal and superior parietal cortex (pIP-SPC) encode actions in hand-specific terms, and compete for selection across and within hemispheres. Actions with both hands are encoded bilaterally, but the contralateral hand is overrepresented. We use a novel fMRI paradigm to test the PPIC model. Participants reach to visible targets while in the scanner, and conditions involving free choice of which hand to use (Choice) are compared with when hand-use is instructed. Consistent with the PPIC model, bilateral pIP-SPC is preferentially responsive for the Choice condition, and for actions made with the contralateral hand. In the right pIP-SPC, these effects include anterior intraparietal and superior parieto-occipital cortex. Left dorsal premotor cortex, and an area in the right lateral occipitotemporal cortex show the same response pattern, while the left inferior parietal lobule is preferentially responsive for the Choice condition and when using the ipsilateral hand. Behaviourally, hand choice is biased by target location – for targets near the left/right edges of the display, the hand in ipsilateral hemispace is favoured. Moreover, consistent with a competitive process, response times are prolonged for choices to more ambiguous targets, where hand choice is relatively unbiased, and fMRI responses in bilateral pIP-SPC parallel this pattern. Our data provide support for the PPIC model, and reveal a selective network of brain areas involved in free hand choice, including bilateral posterior parietal cortex, left-lateralized inferior parietal and dorsal premotor cortices, and the right lateral occipitotemporal cortex.

Grasping with a new hand: Improved performance and normalized grasp-selective brain responses despite persistent functional changes in primary motor cortex and low-level sensory and motor impairments

Hand loss can now be reversed through surgical transplantation years or decades after amputation. Remarkably, these patients come to use their new hand to skilfully grasp and manipulate objects. The brain mechanisms that make this possible are unknown. Here we test the hypothesis that the anterior intraparietal cortex (aIPC) – a multimodal region implicated in hand preshaping and error correction during grasping – plays a key role in this compensatory grasp control. Motion capture and fMRI are used to characterize hand kinematics and brain responses during visually guided grasping with a transplanted hand at 26 and 41 months post-transplant in patient DR, a former hand amputee of 13 years. Compared with matched controls, DR shows increasingly normal grasp kinematics paralleled by increasingly robust grasp-selective fMRI responses within the very same brain areas that show grasp-selectivity in controls, including the aIPC, premotor and cerebellar cortices. Paradoxically, over this same time DR exhibits significant limitations in basic sensory and motor functions, and persistent amputation-related functional reorganization of primary motor cortex. Movements of the non-transplanted hand positively activate the ipsilateral primary motor hand area – a functional marker of persistent interhemispheric amputation-related reorganization. Our data demonstrate for the first time that even after more than a decade of living as an amputee the normative functional brain organization governing the control of grasping can be restored. We propose that the aIPC and interconnected premotor and cerebellar cortices enable grasp normalization by compensating for the functional impact of reorganizational changes in primary sensorimotor cortex and targeting errors in regenerating peripheral nerves.

Partially Mixed Selectivity in Human Posterior Parietal Association Cortex

To clarify the organization of motor representations in posterior parietal cortex, we test how three motor variables (body side, body part, cognitive strategy) are coded in the human anterior intraparietal cortex. All tested movements were encoded, arguing against strict anatomical segregation of effectors. Single units coded for diverse conjunctions of variables, with different dimensions anatomically overlapping. Consistent with recent studies, neurons encoding body parts exhibited mixed selectivity. This mixed selectivity resulted in largely orthogonal coding of body parts, which "functionally segregate" the effector responses despite the high degree of anatomical overlap. Body side and strategy were not coded in a mixed manner as effector determined their organization. Mixed coding of some variables over others, what we term "partially mixed coding," argues that the type of functional encoding depends on the compared dimensions. This structure is advantageous for neuroprosthetics, allowing a single array to decode movements of a large extent of the body.

State-Dependent TMS Reveals Representation of Affective Body Movements in the Anterior Intraparietal Cortex.

In humans, recognition of others' actions involves a cortical network that comprises, among other cortical regions, the posterior superior temporal sulcus (pSTS), where biological motion is coded and the anterior intraparietal sulcus (aIPS), where movement information is elaborated in terms of meaningful goal-directed actions. This action observation system (AOS) is thought to encode neutral voluntary actions, and possibly some aspects of affective motor repertoire, but the role of the AOS' areas in processing affective kinematic information has never been examined. Here we investigated whether the AOS plays a role in representing dynamic emotional bodily expressions. In the first experiment, we assessed behavioral adaptation effects of observed affective movements. Participants watched series of happy or fearful whole-body point-light displays (PLDs) as adapters and were then asked to perform an explicit categorization of the emotion expressed in test PLDs. Participants were slower when categorizing any of the two emotions as long as it was congruent with the emotion in the adapter sequence. We interpreted this effect as adaptation to the emotional content of PLDs. In the second experiment, we combined this paradigm with TMS applied over either the right aIPS, pSTS, and the right half of the occipital pole (corresponding to Brodmann's area 17 and serving as control) to examine the neural locus of the adaptation effect. TMS over the aIPS (but not over the other sites) reversed the behavioral cost of adaptation, specifically for fearful contents. This demonstrates that aIPS contains an explicit representation of affective body movements.SIGNIFICANCE STATEMENT In humans, a network of areas, the action observation system, encodes voluntary actions. However, the role of these brain regions in processing affective kinematic information has not been investigated. Here we demonstrate that the aIPS contains a representation of affective body movements. First, in a behavioral experiment, we found an adaptation after-effect for emotional PLDs, indicating the existence of a neural representation selective for affective information in biological motion. To examine the neural locus of this effect, we then combined the adaptation paradigm with TMS. Stimulation of the aIPS (but not over pSTS and control site) reversed the behavioral cost of adaptation, specifically for fearful contents, demonstrating that aIPS contains a representation of affective body movements.

Hand-independent representation of tool-use pantomimes in the left anterior intraparietal cortex.

Previous neuropsychological studies of ideomotor apraxia (IMA) indicated impairments in pantomime actions for tool use for both right and left hands following lesions of parieto-premotor cortices in the left hemisphere. Using functional magnetic resonance imaging (fMRI) with multi-voxel pattern analysis (MVPA), we tested the hypothesis that the left parieto-premotor cortices are involved in the storage or retrieval of hand-independent representation of tool-use actions. In the fMRI scanner, one of three kinds of tools was displayed in pictures or letters, and the participants made pantomimes of the use of these tools using the right hand for the picture stimuli or with the left hand for the letters. We then used MVPA to classify which kind of tool the subjects were pantomiming. Whole-brain searchlight analysis revealed successful decoding using the activities largely in the contralateral primary sensorimotor region, ipsilateral cerebellum, and bilateral early visual area, which may reflect differences in low-level sensorimotor components for three types of pantomimes. Furthermore, a successful cross-classification between the right and left hands was possible using the activities of the left inferior parietal lobule (IPL) near the junction of the anterior intraparietal sulcus. Our finding indicates that the left anterior intraparietal cortex plays an important role in the production of tool-use pantomimes in a hand-independent manner, and independent of stimuli modality.

EP 8. The role of contralesional motor areas in early motor recovery – evidence from event-related (“online”) TMS

Background TMS studies examining the role of the unaffected hemisphere in motor function after stroke have mainly focused on the contralesional primary motor cortex (M1), revealing both supporting ( Lotze et al., 2006 , Rehme et al., 2011 ) as well as disturbing ( Vollmer et al., 2015 , Nowak et al., 2008 ) influence for recovery of function. However, the relevance of other contralesional motor areas for paretic hand function has rarely been examined, especially with respect to motor recovery in the first days and weeks after stroke. Therefore, we tested the effects of online-TMS applied to contralesional primary motor cortex, anterior intraparietal sulcus (aIPS) and dorsal premotor cortex (dPMC) while stroke patients performed different motor tasks with their paretic hand. Methods Patients with first-ever ischemic left hemispheric stroke performed motor tasks of different complexities with their paretic right hand while being stimulated with ‘online TMS’: (i) index finger tapping, (ii) hand tapping, (iii) visuomotor pointing task (pointing back and forth between two defined targets) and (iv) simple reaction time task. Performance was measured using a three-dimensional motion analyzer system (Zebris). Patients were measured in the acute stage after stroke. Results Compared to healthy controls, acute stroke patients showed reduced finger tapping amplitudes during TMS interference with ipsilateral (=contralesional) aIPS. Likewise, reaction times deteriorated upon contralesional aIPS stimulation in stroke patients but not in controls. Finally, accuracy in the 3D pointing task not only deteriorated upon aIPS stimulation (like in controls) but in addition also during interference with contralesional M1, which was exclusively found in the stroke patients group. Conclusion We here found evidence that especially anterior intraparietal cortex –an area critically engaged in hand motor function by means of parieto-frontal loops– has a relevant influence on motor performance of the paretic hand early after stroke. Therefore, aIPS might constitute an interesting stimulation target for excitability enhancing brain stimulation protocols in order to support recovery of function after stroke.

Spatial Representations in Local Field Potential Activity of Primate Anterior Intraparietal Cortex (AIP).

The execution of reach-to-grasp movements in order to interact with our environment is an important subset of the human movement repertoire. To coordinate such goal-directed movements, information about the relative spatial position of target and effector (in this case the hand) has to be continuously integrated and processed. Recently, we reported the existence of spatial representations in spiking-activity of the cortical fronto-parietal grasp network (Lehmann & Scherberger 2013), and in particular in the anterior intraparietal cortex (AIP). To further investigate the nature of these spatial representations, we explored in two rhesus monkeys (Macaca mulatta) how different frequency bands of the local field potential (LFP) in AIP are modulated by grip type, target position, and gaze position, during the planning and execution of reach-to-grasp movements. We systematically varied grasp type, spatial target, and gaze position and found that both spatial and grasp information were encoded in a variety of frequency bands (1–13Hz, 13–30Hz, 30–60Hz, and 60–100Hz, respectively). Whereas the representation of grasp type strongly increased towards and during movement execution, spatial information was represented throughout the task. Both spatial and grasp type representations could be readily decoded from all frequency bands. The fact that grasp type and spatial (reach) information was found not only in spiking activity, but also in various LFP frequency bands of AIP, might significantly contribute to the development of LFP-based neural interfaces for the control of upper limb prostheses.

Action observation network in childhood: a comparative fMRI study with adults.

Very little is known about the action observation network and the mirror neuron system (AON/MNS) in children and its age-related properties compared with those observed in adults. In the present fMRI study we explored the activation of areas belonging to the AON/MNS in children and adults during observation of complex hand-grasping actions, as compared to observation of simple grasping acts executed with the left and the right hand, seen from a first person perspective. The results indicate that during the action observation tasks in children there was activation of a cortical network similar to that found in adults, including the premotor cortex, the posterior part of the inferior frontal gyrus and the posterior parietal lobe. However, the activation in children was more widespread and showed a higher inter-subject variability compared with adults. Furthermore, the activated network seems more lateralized to the left hemisphere in adults and more bilateral in children, with a linear growth of lateralization index as a function of age. Finally, in children the activation in the anterior intraparietal cortex (AIP) of each hemisphere was higher during observation of the contralateral hand (hand identity effect) and during the observation of complex actions relative to simple grasping acts, confirming the role of AIP for action-related hand identity previously described in adults. These results support the assumption that structure and size of action representations are sensitive to mechanisms of development and show physiological plasticity. These properties of the AON/MNS could constitute a powerful tool for spontaneous reorganization and recovery of motor deficits after brain injury in children and in adults, as well as for specific rehabilitation programmes.

Effects of Microstimulation in the Anterior Intraparietal Area during Three-Dimensional Shape Categorization.

The anterior intraparietal area (AIP) of rhesus monkeys is part of the dorsal visual stream and contains neurons whose visual response properties are commensurate with a role in three-dimensional (3D) shape perception. Neuronal responses in AIP signal the depth structure of disparity-defined 3D shapes, reflect the choices of monkeys while they categorize 3D shapes, and mirror the behavioral variability across different stimulus conditions during 3D-shape categorization. However, direct evidence for a role of AIP in 3D-shape perception has been lacking. We trained rhesus monkeys to categorize disparity-defined 3D shapes and examined AIP's contribution to 3D-shape categorization by microstimulating in clusters of 3D-shape selective AIP neurons during task performance. We find that microstimulation effects on choices (monkey M1) and reaction times (monkey M1 and M2) depend on the 3D-shape preference of the stimulated site. Moreover, electrical stimulation of the same cells, during either the 3D-shape-categorization task or a saccade task, could affect behavior differently. Interestingly, in one monkey we observed a strong correlation between the strength of choice-related AIP activity (choice probabilities) and the influence of microstimulation on 3D-shape-categorization behavior (choices and reaction time). These findings propose AIP as part of the network responsible for 3D-shape perception. The results also show that the anterior intraparietal cortex contains cells with different tuning properties, i.e. 3D-shape- or saccade-related, that can be dynamically read out depending on the requirements of the task at hand.

P 82. Dose-dependent effects of theta-burst rTMS on the cortical excitability and fMRI-connectivity of the primary motor cortex

Introduction Theta Burst Stimulation (TBS) is an effective rTMS-protocol to modulate the excitability of cortical motor regions (Huang et al., 2005). However, the effects between subjects are rather variable (Hamda et al., 2012). The reason for this variability is still unclear (Thickbroom, 2007). Recently, animal studies showed that there are dose-dependent effects of TBS on the expression of cellular proteins (Volz et al., 2010). In contrast, studies with human subjects did not find a consistent dose–effect after applying two TBS sessions serially at different intersession intervals (Gamboa et al., 2010, 2011). Objectives The aim of our study was to investigate the effect of a triple TBS session on the cortical excitability compared to a control-stimulation. By combining TBS with functional magnetic resonance imaging (fMRI) measurements we sought to reveal stimulation effects on cortical connectivity. Methods 15 healthy subjects received three stimulations according to the iTBS-protocol (600 pulses per stimulation, (Huang et al., 2005)). iTBS sessions were applied in a serial fashion spaced by intervals of 15min. Two different stimulation sites were tested at different days: primary motor cortex (M1) and the parieto-occipital cortex (control). Stimulation after-effects on cortical excitability were tested via stimulus–response curves. In separate stimulation sessions, the iTBS effects on fMRI-connectivity were tested for two conditions: (i) resting-state measurements and (ii) during thumb movements. The following motor areas were included in the network analysis: M1, supplementary motor area (SMA), dorsal and ventral premotor cortex (dPMC, vPMC), anterior intraparietal cortex, putamen, thalamus and cerebellum. Results We found a dose-dependent effect of iTBS on the height of the stimulus–response-curve with significantly higher MEPs after applying iTBS over M1 compared to the control-stimulation. The connectivity-analyses revealed that after M1 stimulation with 1800 pulses the effective connectivity of the ipsilateral dPMC to the stimulated M1 was significantly enhanced while the control-stimulation had no differential effect on cortical connectivity ( p Conclusions Our results suggest that the after-effects of iTBS are dose-dependent. Furthermore, our data show that iTBS of M1 leads to a higher integration of the stimulated area with premotor areas.

Unexpected novelty and familiarity orienting responses in lateral parietal cortex during recognition judgment

The role of lateral parietal cortex during recognition memory is heavily debated. We examined parietal activation during an Explicit Memory Cueing recognition paradigm that biases participants towards expecting novel or familiar stimuli on a trial-by-trial basis using anticipatory cues (“Likely Old”, “Likely New”), compared to trials with neutral cues (“????”). Three qualitatively distinct patterns were observed in the left lateral parietal cortex. An unexpected novelty response occurred in left anterior intraparietal cortex (IPS)/post-central gyrus (PoCG) in which greater activation was observed for new vs. old materials following the “Likely Old” cue, but not following the “Likely New” cue. In contrast, anterior angular gyrus demonstrated an unexpected familiarity response with greater activation for old vs. new materials following the “Likely New” cue, but not the “Likely Old” cue. Thus these two regions demonstrated increased responses that were selective for either new or old materials respectively, but only when they were unexpected. In contrast, a mid IPS area demonstrated greater response for whichever class of memoranda was unanticipated given the cue condition (an unexpected memory response). Analogous response patterns in regions outside of parietal cortex, and the results of a resting state connectivity analysis, suggested these three response patterns were associated with visuo-spatial orienting following unexpected novelty, source monitoring operations following unexpected familiarity, and general executive control processes following violated expectations. These findings support a Memory Orienting Model of the left lateral parietal cortex in which the region is linked to the investigation of unexpected novelty or familiarity in the environment.

Preference for Orientations Commonly Viewed for One’s Own Hand in the Anterior Intraparietal Cortex

Brain regions in the intraparietal and the premotor cortices selectively process visual and multisensory events near the hands (peri-hand space). Visual information from the hand itself modulates this processing potentially because it is used to estimate the location of one’s own body and the surrounding space. In humans specific occipitotemporal areas process visual information of specific body parts such as hands. Here we used an fMRI block-design to investigate if anterior intraparietal and ventral premotor ‘peri-hand areas’ exhibit selective responses to viewing images of hands and viewing specific hand orientations. Furthermore, we investigated if the occipitotemporal ‘hand area’ is sensitive to viewed hand orientation. Our findings demonstrate increased BOLD responses in the left anterior intraparietal area when participants viewed hands and feet as compared to faces and objects. Anterior intraparietal and also occipitotemporal areas in the left hemisphere exhibited response preferences for viewing right hands with orientations commonly viewed for one’s own hand as compared to uncommon own hand orientations. Our results indicate that both anterior intraparietal and occipitotemporal areas encode visual limb-specific shape and orientation information.

Human Parietofrontal Networks Related to Action Observation Detected at Rest

Recent data show a broad correspondence between human resting-state and task-related brain networks. We performed a functional magnetic resonance imaging (fMRI) study to compare, in the same subjects, the spatial independent component analysis (ICA) maps obtained at rest and during the observation of either reaching/grasping hand actions or matching static pictures. Two parietofrontal networks were identified by ICA from action observation task data. One network, specific to reaching/grasping observation, included portions of the anterior intraparietal cortex and of the dorsal and ventral lateral premotor cortices. A second network included more posterior portions of the parietal lobe, the dorsomedial frontal cortex, and more anterior and ventral parts, respectively, of the dorsal and ventral premotor cortices, extending toward Broca's area; this network was more generally related to the observation of hand action and static pictures. A good spatial correspondence was found between the 2 observation-related ICA maps and 2 ICA maps identified from resting-state data. The anatomical connectivity among the identified clusters was tested in the same volunteers, using persistent angular structure-MRI and deterministic tractography. These findings extend available knowledge of human parietofrontal circuits and further support the hypothesis of a persistent coherence within functionally relevant networks during rest.

Grasp Movement Decoding from Premotor and Parietal Cortex

Despite recent advances in harnessing cortical motor-related activity to control computer cursors and robotic devices, the ability to decode and execute different grasping patterns remains a major obstacle. Here we demonstrate a simple Bayesian decoder for real-time classification of grip type and wrist orientation in macaque monkeys that uses higher-order planning signals from anterior intraparietal cortex (AIP) and ventral premotor cortex (area F5). Real-time decoding was based on multiunit signals, which had similar tuning properties to cells in previous single-unit recording studies. Maximum decoding accuracy for two grasp types (power and precision grip) and five wrist orientations was 63% (chance level, 10%). Analysis of decoder performance showed that grip type decoding was highly accurate (90.6%), with most errors occurring during orientation classification. In a subsequent off-line analysis, we found small but significant performance improvements (mean, 6.25 percentage points) when using an optimized spike-sorting method (superparamagnetic clustering). Furthermore, we observed significant differences in the contributions of F5 and AIP for grasp decoding, with F5 being better suited for classification of the grip type and AIP contributing more toward decoding of object orientation. However, optimum decoding performance was maximal when using neural activity simultaneously from both areas. Overall, these results highlight quantitative differences in the functional representation of grasp movements in AIP and F5 and represent a first step toward using these signals for developing functional neural interfaces for hand grasping.

Resonance of cortico–cortical connections of the motor system with the observation of goal directed grasping movements

Goal directed movements require the activation of parietal, premotor and primary motor areas. In monkeys, neurons of these areas become active also during the observation of movements performed by others, especially for coding the goal of the action (mirror system). Using bifocal transcranial magnetic stimulation (TMS) in healthy subjects, we tested whether the observation of goal directed reach to grasp actions may lead to specific changes in the short-latency connections linking key areas of the mirror system, such as the anterior intraparietal cortex (AIP) and the ventral premotor cortex (PMv), with the primary motor cortex (M1). We found that AIP-M1 and PMv-M1 cortico–cortical interactions were specifically activated when observing successful reaching to grasp goal directed actions, in which the hand posture was congruent with the goal of the action performed by the actor. On the other hand they were not modified when the same goal directed actions were performed wrongly with an inappropriate grasping posture. A similar profile of excitability was observed when testing specific intracortical facilitatory circuits in M1 (I2-waves), known to reflect the activity in cortico–cortical pathways transmitting information from PMv. We conclude that the simple observation of others’ goal directed actions is able to induce specific neurophysiological changes in some cortico–cortical circuits of the human motor system.

Hemispheric Asymmetry in the Remapping and Maintenance of Visual Saliency Maps: A TMS Study

Parietal cortex has been implicated in the updating, after eye movements, of a salience map that is required for coherent visual experience and for the control of visually guided behavior. The current experiment investigated whether TMS over anterior intraparietal cortex (AIPCx), just after a saccade, would affect the ability to update and maintain a salience map. In order to generate a salience map, we employed a paradigm in which an uninformative cue was presented at one object in a display to generate inhibition of return (IOR)-an inhibitory tag that renders the cued object less salient than others in the display, and that slows subsequent responses to visual transients at its location. Following the cue, participants made a saccade to either left or right, and we then probed for updating of the location of IOR by measuring manual reaction time to targets appearing at cued location of the cued compared to an uncued object. Between the time of saccade initiation and target appearance, dual-pulse TMS was targeted over right (Experiment 1) or left AIPCx (Experiment 2), and a vertex control side. Updating of the location of IOR was eliminated by TMS over right, but not the left, AIPCx, suggesting that right parietal cortex is involved in the remapping of IOR. Remapping was eliminated by right AIPCx, regardless of whether the saccade was made to the left (contralateral), or right (ipsilateral) visual field, and regardless of which field the target appeared in. We conclude that right AIPCx is the neural substrate for maintaining a salience map across saccades, and not simply for propagating an efference copy of saccade commands.