Planning Ahead: Object-Directed Sequential Actions Decoded from Human Frontoparietal and Occipitotemporal Networks

Neural Correlates of Online Action Preparation

When performing movements in rapid succession, the brain needs to coordinate ongoing execution with the preparation of an upcoming action. Here we identify the processes and brain areas involved in this ability of online preparation. Human participants (both male and female) performed pairs of single-finger presses or three-finger chords in rapid succession, while 7T fMRI was recorded. In the overlap condition, they could prepare the second movement during the first response and in the nonoverlap condition only after the first response was completed. Despite matched perceptual and movement requirements, fMRI revealed increased brain activity in the overlap condition in regions along the intraparietal sulcus and ventral visual stream. Multivariate analyses suggested that these areas are involved in stimulus identification and action selection. In contrast, the dorsal premotor cortex, known to be involved in planning upcoming movements, showed no discernible signs of heightened activity. This observation suggests that the bottleneck during simultaneous action execution and preparation arises at the level of stimulus identification and action selection, whereas movement planning in the premotor cortex can unfold concurrently with the execution of a current action without requiring additional neural activity.

Distinct Neural Components of Visually Guided Grasping during Planning and Execution

Selecting suitable grasps on three-dimensional objects is a challenging visuomotor computation, which involves combining information about an object (e.g., its shape, size, and mass) with information about the actor's body (e.g., the optimal grasp aperture and hand posture for comfortable manipulation). Here, we used functional magnetic resonance imaging to investigate brain networks associated with these distinct aspects during grasp planning and execution. Human participants of either sex viewed and then executed preselected grasps on L-shaped objects made of wood and/or brass. By leveraging a computational approach that accurately predicts human grasp locations, we selected grasp points that disentangled the role of multiple grasp-relevant factors, that is, grasp axis, grasp size, and object mass. Representational Similarity Analysis revealed that grasp axis was encoded along dorsal-stream regions during grasp planning. Grasp size was first encoded in ventral stream areas during grasp planning then in premotor regions during grasp execution. Object mass was encoded in ventral stream and (pre)motor regions only during grasp execution. Premotor regions further encoded visual predictions of grasp comfort, whereas the ventral stream encoded grasp comfort during execution, suggesting its involvement in haptic evaluation. These shifts in neural representations thus capture the sensorimotor transformations that allow humans to grasp objects.SIGNIFICANCE STATEMENT Grasping requires integrating object properties with constraints on hand and arm postures. Using a computational approach that accurately predicts human grasp locations by combining such constraints, we selected grasps on objects that disentangled the relative contributions of object mass, grasp size, and grasp axis during grasp planning and execution in a neuroimaging study. Our findings reveal a greater role of dorsal-stream visuomotor areas during grasp planning, and, surprisingly, increasing ventral stream engagement during execution. We propose that during planning, visuomotor representations initially encode grasp axis and size. Perceptual representations of object material properties become more relevant instead as the hand approaches the object and motor programs are refined with estimates of the grip forces required to successfully lift the object.

Object representation in a gravitational reference frame

When your head tilts laterally, as in sports, reaching, and resting, your eyes counterrotate less than 20%, and thus eye images rotate, over a total range of about 180°. Yet, the world appears stable and vision remains normal. We discovered a neural strategy for rotational stability in anterior inferotemporal cortex (IT), the final stage of object vision in primates. We measured object orientation tuning of IT neurons in macaque monkeys tilted +25 and -25° laterally, producing ~40° difference in retinal image orientation. Among IT neurons with consistent object orientation tuning, 63% remained stable with respect to gravity across tilts. Gravitational tuning depended on vestibular/somatosensory but also visual cues, consistent with previous evidence that IT processes scene cues for gravity's orientation. In addition to stability across image rotations, an internal gravitational reference frame is important for physical understanding of a world where object position, posture, structure, shape, movement, and behavior interact critically with gravity.

Grasping with a Twist: Dissociating Action Goals from Motor Actions in Human Frontoparietal Circuits

In daily life, prehension is typically not the end goal of hand-object interactions but a precursor for manipulation. Nevertheless, functional MRI (fMRI) studies investigating manual manipulation have primarily relied on prehension as the end goal of an action. Here, we used slow event-related fMRI to investigate differences in neural activation patterns between prehension in isolation and prehension for object manipulation. Sixteen (seven males and nine females) participants were instructed either to simply grasp the handle of a rotatable dial (isolated prehension) or to grasp and turn it (prehension for object manipulation). We used representational similarity analysis (RSA) to investigate whether the experimental conditions could be discriminated from each other based on differences in task-related brain activation patterns. We also used temporal multivoxel pattern analysis (tMVPA) to examine the evolution of regional activation patterns over time. Importantly, we were able to differentiate isolated prehension and prehension for manipulation from activation patterns in the early visual cortex, the caudal intraparietal sulcus (cIPS), and the superior parietal lobule (SPL). Our findings indicate that object manipulation extends beyond the putative cortical grasping network (anterior intraparietal sulcus, premotor and motor cortices) to include the superior parietal lobule and early visual cortex.SIGNIFICANCE STATEMENT A simple act such as turning an oven dial requires not only that the CNS encode the initial state (starting dial orientation) of the object but also the appropriate posture to grasp it to achieve the desired end state (final dial orientation) and the motor commands to achieve that state. Using advanced temporal neuroimaging analysis techniques, we reveal how such actions unfold over time and how they differ between object manipulation (turning a dial) versus grasping alone. We find that a combination of brain areas implicated in visual processing and sensorimotor integration can distinguish between the complex and simple tasks during planning, with neural patterns that approximate those during the actual execution of the action.

Dynamic spatial coding in parietal cortex mediates tactile-motor transformation

Movements towards touch on the body require integrating tactile location and body posture information. Tactile processing and movement planning both rely on posterior parietal cortex (PPC) but their interplay is not understood. Here, human participants received tactile stimuli on their crossed and uncrossed feet, dissociating stimulus location relative to anatomy versus external space. Participants pointed to the touch or the equivalent location on the other foot, which dissociates sensory and motor locations. Multi-voxel pattern analysis of concurrently recorded fMRI signals revealed that tactile location was coded anatomically in anterior PPC but spatially in posterior PPC during sensory processing. After movement instructions were specified, PPC exclusively represented the movement goal in space, in regions associated with visuo-motor planning and with regional overlap for sensory, rule-related, and movement coding. Thus, PPC flexibly updates its spatial codes to accommodate rule-based transformation of sensory input to generate movement to environment and own body alike.

Loss of action-related function and connectivity in the blind extrastriate body area

The Extrastriate Body Area (EBA) participates in the visual perception and motor actions of body parts. We recently showed that EBA’s perceptual function develops independently of visual experience, responding to stimuli with body-part information in a supramodal fashion. However, it is still unclear if the EBA similarly maintains its action-related function. Here, we used fMRI to study motor-evoked responses and connectivity patterns in the congenitally blind brain. We found that, unlike the case of perception, EBA does not develop an action-related response without visual experience. In addition, we show that congenital blindness alters EBA’s connectivity profile in a counterintuitive way—functional connectivity with sensorimotor cortices dramatically decreases, whereas connectivity with perception-related visual occipital cortices remains high. To the best of our knowledge, we show for the first time that action-related functions and connectivity in the visual cortex could be contingent on visuomotor experience. We further discuss the role of the EBA within the context of visuomotor control and predictive coding theory.

HD-tDCS of primary and higher-order motor cortex affects action word processing

The contribution of action-perception systems of the brain to lexical semantics remains controversial. Here, we used high-definition transcranial direct current stimulation (HD-tDCS) in healthy adults to examine the role of primary (left hand motor area; HMA) and higher-order (left anterior inferior parietal lobe; aIPL) action areas in action-related word processing (action verbs and manipulable nouns) compared to non-action-related control words (non-action verbs and non-manipulable nouns). We investigated stimulation-related effects at three levels of semantic processing: subliminal, implicit, and explicit. Broadly, we found that stimulation of HMA and aIPL resulted in relative facilitation of action-related language processing compared to non-action. HMA stimulation facilitated action verb processing in subliminal and implicit task contexts, suggesting that HMA helps represent action verbs even in semantically shallow tasks. HMA stimulation also facilitated manipulable noun comprehension in an explicit semantic task, suggesting that HMA contributes to manipulable noun comprehension when semantic demands are high. aIPL stimulation facilitated both manipulable noun and action verb processing during an implicit task. We suggest that both HMA and aIPL play a functional role in action semantics. HMA plays a general role in the semantics of actions and manipulable objects, while aIPL is important only when visuo-motor coordination is required for the action.

The role of the anterior temporal cortex in action: evidence from fMRI multivariate searchlight analysis during real object grasping

Intelligent manipulation of handheld tools marks a major discontinuity between humans and our closest ancestors. Here we identified neural representations about how tools are typically manipulated within left anterior temporal cortex, by shifting a searchlight classifier through whole-brain real action fMRI data when participants grasped 3D-printed tools in ways considered typical for use (i.e., by their handle). These neural representations were automatically evocated as task performance did not require semantic processing. In fact, findings from a behavioural motion-capture experiment confirmed that actions with tools (relative to non-tool) incurred additional processing costs, as would be suspected if semantic areas are being automatically engaged. These results substantiate theories of semantic cognition that claim the anterior temporal cortex combines sensorimotor and semantic content for advanced behaviours like tool manipulation.

Linking Pain and Motor Control: Conceptualization of Movement Deficits in Patients With Painful Conditions

When people experience or expect pain, they move differently. Pain-altered movement strategies, collectively described here as pain-related movement dysfunction (PRMD), may persist well after pain resolves and, ultimately, may result in altered kinematics and kinetics, future reinjury, and disability. Although PRMD may manifest as abnormal movements that are often evident in clinical assessment, the underlying mechanisms are complex, engaging sensory-perceptual, cognitive, psychological, and motor processes. Motor control theories provide a conceptual framework to determine, assess, and target processes that contribute to normal and abnormal movement and thus are important for physical therapy and rehabilitation practice. Contemporary understanding of motor control has evolved from reflex-based understanding to a more complex task-dependent interaction between cognitive and motor systems, each with distinct neuroanatomic substrates. Though experts have recognized the importance of motor control in the management of painful conditions, there is no comprehensive framework that explicates the processes engaged in the control of goal-directed actions, particularly in the presence of pain. This Perspective outlines sensory-perceptual, cognitive, psychological, and motor processes in the contemporary model of motor control, describing the neural substrates underlying each process and highlighting how pain and anticipation of pain influence motor control processes and consequently contribute to PRMD. Finally, potential lines of future inquiry-grounded in the contemporary model of motor control-are outlined to advance understanding and improve the assessment and treatment of PRMD.

IMPACT

This Perspective proposes that approaching PRMD from a contemporary motor control perspective will uncover key mechanisms, identify treatment targets, inform assessments, and innovate treatments across sensory-perceptual, cognitive, and motor domains, all of which have the potential to improve movement and functional outcomes in patients with painful conditions.

Motor planning brings human primary somatosensory cortex into action-specific preparatory states

Motor planning plays a critical role in producing fast and accurate movement. Yet, the neural processes that occur in human primary motor and somatosensory cortex during planning, and how they relate to those during movement execution, remain poorly understood. Here, we used 7T functional magnetic resonance imaging and a delayed movement paradigm to study single finger movement planning and execution. The inclusion of no-go trials and variable delays allowed us to separate what are typically overlapping planning and execution brain responses. Although our univariate results show widespread deactivation during finger planning, multivariate pattern analysis revealed finger-specific activity patterns in contralateral primary somatosensory cortex (S1), which predicted the planned finger action. Surprisingly, these activity patterns were as informative as those found in contralateral primary motor cortex (M1). Control analyses ruled out the possibility that the detected information was an artifact of subthreshold movements during the preparatory delay. Furthermore, we observed that finger-specific activity patterns during planning were highly correlated to those during execution. These findings reveal that motor planning activates the specific S1 and M1 circuits that are engaged during the execution of a finger press, while activity in both regions is overall suppressed. We propose that preparatory states in S1 may improve movement control through changes in sensory processing or via direct influence of spinal motor neurons.

Human Somatosensory Cortex Is Modulated during Motor Planning

Recent data and motor control theory argues that movement planning involves preparing the neural state of primary motor cortex (M1) for forthcoming action execution. Theories related to internal models, feedback control, and predictive coding also emphasize the importance of sensory prediction (and processing) before (and during) the movement itself, explaining why motor-related deficits can arise from damage to primary somatosensory cortex (S1). Motivated by this work, here we examined whether motor planning, in addition to changing the neural state of M1, changes the neural state of S1, preparing it for the sensory feedback that arises during action. We tested this idea in two human functional MRI studies (N = 31, 16 females) involving delayed object manipulation tasks, focusing our analysis on premovement activity patterns in M1 and S1. We found that the motor effector to be used in the upcoming action could be decoded, well before movement, from neural activity in M1 in both studies. Critically, we found that this effector information was also present, well before movement, in S1. In particular, we found that the encoding of effector information in area 3b (S1 proper) was linked to the contralateral hand, similarly to that found in M1, whereas in areas 1 and 2 this encoding was present in both the contralateral and ipsilateral hemispheres. Together, these findings suggest that motor planning not only prepares the motor system for movement but also changes the neural state of the somatosensory system, presumably allowing it to anticipate the sensory information received during movement.SIGNIFICANCE STATEMENT Whereas recent work on motor cortex has emphasized the critical role of movement planning in preparing neural activity for movement generation, it has not investigated the extent to which planning also modulates the activity in the adjacent primary somatosensory cortex. This reflects a key gap in knowledge, given that recent motor control theories emphasize the importance of sensory feedback processing in effective movement generation. Here, we find through a convergence of experiments and analyses, that the planning of object manipulation tasks, in addition to modulating the activity in the motor cortex, changes the state of neural activity in different subfields of the human S1. We suggest that this modulation prepares the S1 for the sensory information it will receive during action execution.

Hand-Selective Visual Regions Represent How to Grasp 3D Tools: Brain Decoding during Real Actions

Most neuroimaging experiments that investigate how tools and their actions are represented in the brain use visual paradigms where tools or hands are displayed as 2D images and no real movements are performed. These studies discovered selective visual responses in occipitotemporal and parietal cortices for viewing pictures of hands or tools, which are assumed to reflect action processing, but this has rarely been directly investigated. Here, we examined the responses of independently visually defined category-selective brain areas when participants grasped 3D tools (N = 20; 9 females). Using real-action fMRI and multivoxel pattern analysis, we found that grasp typicality representations (i.e., whether a tool is grasped appropriately for use) were decodable from hand-selective areas in occipitotemporal and parietal cortices, but not from tool-, object-, or body-selective areas, even if partially overlapping. Importantly, these effects were exclusive for actions with tools, but not for biomechanically matched actions with control nontools. In addition, grasp typicality decoding was significantly higher in hand than tool-selective parietal regions. Notably, grasp typicality representations were automatically evoked even when there was no requirement for tool use and participants were naive to object category (tool vs nontools). Finding a specificity for typical tool grasping in hand-selective, rather than tool-selective, regions challenges the long-standing assumption that activation for viewing tool images reflects sensorimotor processing linked to tool manipulation. Instead, our results show that typicality representations for tool grasping are automatically evoked in visual regions specialized for representing the human hand, the primary tool of the brain for interacting with the world.

Motor Planning Modulates Neural Activity Patterns in Early Human Auditory Cortex

It is well established that movement planning recruits motor-related cortical brain areas in preparation for the forthcoming action. Given that an integral component to the control of action is the processing of sensory information throughout movement, we predicted that movement planning might also modulate early sensory cortical areas, readying them for sensory processing during the unfolding action. To test this hypothesis, we performed 2 human functional magnetic resonance imaging studies involving separate delayed movement tasks and focused on premovement neural activity in early auditory cortex, given the area's direct connections to the motor system and evidence that it is modulated by motor cortex during movement in rodents. We show that effector-specific information (i.e., movements of the left vs. right hand in Experiment 1 and movements of the hand vs. eye in Experiment 2) can be decoded, well before movement, from neural activity in early auditory cortex. We find that this motor-related information is encoded in a separate subregion of auditory cortex than sensory-related information and is present even when movements are cued visually instead of auditorily. These findings suggest that action planning, in addition to preparing the motor system for movement, involves selectively modulating primary sensory areas based on the intended action.

Selective Modulation of Early Visual Cortical Activity by Movement Intention

The primate visual system contains myriad feedback projections from higher- to lower-order cortical areas, an architecture that has been implicated in the top-down modulation of early visual areas during working memory and attention. Here we tested the hypothesis that these feedback projections also modulate early visual cortical activity during the planning of visually guided actions. We show, across three separate human functional magnetic resonance imaging (fMRI) studies involving object-directed movements, that information related to the motor effector to be used (i.e., limb, eye) and action goal to be performed (i.e., grasp, reach) can be selectively decoded-prior to movement-from the retinotopic representation of the target object(s) in early visual cortex. We also find that during the planning of sequential actions involving objects in two different spatial locations, that motor-related information can be decoded from both locations in retinotopic cortex. Together, these findings indicate that movement planning selectively modulates early visual cortical activity patterns in an effector-specific, target-centric, and task-dependent manner. These findings offer a neural account of how motor-relevant target features are enhanced during action planning and suggest a possible role for early visual cortex in instituting a sensorimotor estimate of the visual consequences of movement.

Reduced competition between tool action neighbors in left hemisphere stroke

When pantomiming the use of tools, patients with limb apraxia after left hemisphere stroke (LCVA) produce more spatiotemporal hand action errors with tools associated with conflicting actions for use versus grasp-to-pick-up (e.g., corkscrew) than tools having a single action for both use and grasp (e.g., hammer). There are two possible accounts for this pattern of results. Reduced performance with 'conflict' tools may simply reflect weakened automaticity of use action activation, which is evident only when the use and grasp actions are not redundant. Alternatively, poor use performance may reflect a reduced ability of appropriate tool use actions to compete with task-inappropriate action representations. To address this issue, we developed a Stroop-like experiment in which 21 LCVA and 8 neurotypical participants performed pantomime actions in blocks containing two tools that were similar ("neighbors") in terms of hand action or function, or were unrelated on either dimension. In a congruent condition, they pantomimed the use action associated with the visually presented tool, whereas in an incongruent condition, they pantomimed the use action for the other tool in the block. Relative to controls and other task conditions, LCVA participants showed reductions in hand action errors in incongruent relative to congruent action trials; furthermore, the degree of reduction in this incongruence effect was related to the participants' susceptibility to grasp-on-use conflict in a separate test of pantomime to the sight of tools. Support vector regression lesion-symptom mapping analyses identified the left inferior frontal gyrus, supramarginal gyrus, and superior longitudinal fasciculus as core neuroanatomical sites associated with abnormal performance. Collectively, the results indicate that weakened activation of tool use actions in limb apraxia gives rise to reduced ability of these actions to compete for task-appropriate selection when competition arises within single tools (grasp-on-use conflict) as well as between two tools (reduced neighborhood effects).

Differential neural dynamics underling pragmatic and semantic affordance processing in macaque ventral premotor cortex

Premotor neurons play a fundamental role in transforming physical properties of observed objects, such as size and shape, into motor plans for grasping them, hence contributing to “pragmatic” affordance processing. Premotor neurons can also contribute to “semantic” affordance processing, as they can discharge differently even to pragmatically identical objects depending on their behavioural relevance for the observer (i.e. edible or inedible objects). Here, we compared the response of monkey ventral premotor area F5 neurons tested during pragmatic (PT) or semantic (ST) visuomotor tasks. Object presentation responses in ST showed shorter latency and lower object selectivity than in PT. Furthermore, we found a difference between a transient representation of semantic affordances and a sustained representation of pragmatic affordances at both the single neuron and population level. Indeed, responses in ST returned to baseline within 0.5 s whereas in PT they showed the typical sustained visual-to-motor activity during Go trials. In contrast, during No-go trials, the time course of pragmatic and semantic information processing was similar. These findings suggest that premotor cortex generates different dynamics depending on pragmatic and semantic information provided by the context in which the to-be-grasped object is presented.

Unraveling the spatiotemporal brain dynamics during a simulated reach-to-eat task

The reach-to-eat task involves a sequence of action components including looking, reaching, grasping, and feeding. While cortical representations of individual action components have been mapped in human functional magnetic resonance imaging (fMRI) studies, little is known about the continuous spatiotemporal dynamics among these representations during the reach-to-eat task. In a periodic event-related fMRI experiment, subjects were scanned while they reached toward a food image, grasped the virtual food, and brought it to their mouth within each 16-s cycle. Fourier-based analysis of fMRI time series revealed periodic signals and noise distributed across the brain. Independent component analysis was used to remove periodic or aperiodic motion artifacts. Time-frequency analysis was used to analyze the temporal characteristics of periodic signals in each voxel. Circular statistics was then used to estimate mean phase angles of periodic signals and select voxels based on the distribution of phase angles. By sorting mean phase angles across regions, we were able to show the real-time spatiotemporal brain dynamics as continuous traveling waves over the cortical surface. The activation sequence consisted of approximately the following stages: (1) stimulus related activations in occipital and temporal cortices; (2) movement planning related activations in dorsal premotor and superior parietal cortices; (3) reaching related activations in primary sensorimotor cortex and supplementary motor area; (4) grasping related activations in postcentral gyrus and sulcus; (5) feeding related activations in orofacial areas. These results suggest that phase-encoded design and analysis can be used to unravel sequential activations among brain regions during a simulated reach-to-eat task.

Repetitive Transcranial Magnetic Stimulation Over the Left Posterior Middle Temporal Gyrus Reduces Wrist Velocity During Emblematic Hand Gesture Imitation

Results from neuropsychological studies, and neuroimaging and behavioural experiments with healthy individuals, suggest that the imitation of meaningful and meaningless actions may be reliant on different processing routes. The left posterior middle temporal gyrus (pMTG) is one area that might be important for the recognition and imitation of meaningful actions. We studied the role of the left pMTG in imitation using repetitive transcranial magnetic stimulation (rTMS) and two-person motion-tracking. Participants imitated meaningless and emblematic meaningful hand and finger gestures performed by a confederate actor whilst both individuals were motion-tracked. rTMS was applied during action observation (before imitation) over the left pMTG or a vertex control site. Since meaningless action imitation has been previously associated with a greater wrist velocity and longer correction period at the end of the movement, we hypothesised that stimulation over the left pMTG would increase wrist velocity and extend the correction period of meaningful actions (i.e., due to interference with action recognition). We also hypothesised that imitator accuracy (actor-imitator correspondence) would be reduced following stimulation over the left pMTG. Contrary to our hypothesis, we found that stimulation over the pMTG, but not the vertex, during action observation reduced wrist velocity when participants later imitated meaningful, but not meaningless, hand gestures. These results provide causal evidence for a role of the left pMTG in the imitation of meaningful gestures, and may also be in keeping with proposals that left posterior temporal regions play a role in the production of postural components of gesture.

Task- and domain-specific modulation of functional connectivity in the ventral and dorsal object-processing pathways

A whole-brain network of regions collectively supports the ability to recognize and use objects-the Tool Processing Network. Little is known about how functional interactions within the Tool Processing Network are modulated in a task-dependent manner. We designed an fMRI experiment in which participants were required to either generate object pantomimes or to carry out a picture matching task over the same images of tools, while holding all aspects of stimulus presentation constant across the tasks. The Tool Processing Network was defined with an independent functional localizer, and functional connectivity within the network was measured during the pantomime and picture matching tasks. Relative to tool picture matching, tool pantomiming led to an increase in functional connectivity between ventral stream regions and left parietal and frontal-motor areas; in contrast, the matching task was associated with an increase in functional connectivity among regions in ventral temporo-occipital cortex, and between ventral temporal regions and the left inferior parietal lobule. Graph-theory analyses over the functional connectivity data indicated that the left premotor cortex and left lateral occipital complex were hub-like (exhibited high betweenness centrality) during tool pantomiming, while ventral stream regions (left medial fusiform gyrus and left posterior middle temporal gyrus) were hub-like during the picture matching task. These results demonstrate task-specific modulation of functional interactions among a common set of regions, and indicate dynamic coupling of anatomically remote regions in task-dependent manner.

Action and semantic tool knowledge - Effective connectivity in the underlying neural networks

Evidence from neuropsychological and imaging studies indicate that action and semantic knowledge about tools draw upon distinct neural substrates, but little is known about the underlying interregional effective connectivity. With fMRI and dynamic causal modeling (DCM) we investigated effective connectivity in the left-hemisphere (LH) while subjects performed (i) a function knowledge and (ii) a value knowledge task, both addressing semantic tool knowledge, and (iii) a manipulation (action) knowledge task. Overall, the results indicate crosstalk between action nodes and semantic nodes. Interestingly, effective connectivity was weakened between semantic nodes and action nodes during the manipulation task. Furthermore, pronounced modulations of effective connectivity within the fronto-parietal action system of the LH (comprising lateral occipito-temporal cortex, intraparietal sulcus, supramarginal gyrus, inferior frontal gyrus) were observed in a bidirectional manner during the processing of action knowledge. In contrast, the function and value knowledge tasks resulted in a significant strengthening of the effective connectivity between visual cortex and fusiform gyrus. Importantly, this modulation was present in both semantic tasks, indicating that processing different aspects of semantic knowledge about tools evokes similar effective connectivity patterns. Data revealed that interregional effective connectivity during the processing of tool knowledge occurred in a bidirectional manner with a weakening of connectivity between areas engaged in action and semantic knowledge about tools during the processing of action knowledge. Moreover, different semantic tool knowledge tasks elicited similar effective connectivity patterns.

Spatial eye-hand coordination during bimanual reaching is not systematically coded in either LIP or PRR

When we reach for something, we also look at it. If we reach for two objects at once, one with each hand, we look first at one and then the other. It is not known which brain areas underlie this coordination. We studied two parietal areas known to be involved in eye and arm movements. Neither area was sensitive to the order in which the targets were looked at. This implies that coordinated saccades are driven by downstream areas and not by the parietal cortex as is commonly assumed.

We often orient to where we are about to reach. Spatial and temporal correlations in eye and arm movements may depend on the posterior parietal cortex (PPC). Spatial representations of saccade and reach goals preferentially activate cells in the lateral intraparietal area (LIP) and the parietal reach region (PRR), respectively. With unimanual reaches, eye and arm movement patterns are highly stereotyped. This makes it difficult to study the neural circuits involved in coordination. Here, we employ bimanual reaching to two different targets. Animals naturally make a saccade first to one target and then the other, resulting in different patterns of limb–gaze coordination on different trials. Remarkably, neither LIP nor PRR cells code which target the eyes will move to first. These results suggest that the parietal cortex plays at best only a permissive role in some aspects of eye–hand coordination and makes the role of LIP in saccade generation unclear.

Task-Relevant Information Modulates Primary Motor Cortex Activity Before Movement Onset

Monkey neurophysiology research supports the affordance competition hypothesis (ACH) proposing that cognitive information useful for action selection is integrated in sensorimotor areas. In this view, action selection would emerge from the simultaneous representation of competing action plans, in parallel biased by relevant task factors. This biased competition would take place up to primary motor cortex (M1). Although ACH is plausible in environments affording choices between actions, its relevance for human decision making is less clear. To address this issue, we designed an functional magnetic resonance imaging (fMRI) experiment modeled after monkey neurophysiology studies in which human participants processed cues conveying predictive information about upcoming button presses. Our results demonstrate that, as predicted by the ACH, predictive information (i.e., the relevant task factor) biases activity of primary motor regions. Specifically, first, activity before movement onset in contralateral M1 increases as the competition is biased in favor of a specific button press relative to activity in ipsilateral M1. Second, motor regions were more tightly coupled with fronto-parietal regions when competition between potential actions was high, again suggesting that motor regions are also part of the biased competition network. Our findings support the idea that action planning dynamics as proposed in the ACH are valid both in human and non-human primates.

Recruitment of Foveal Retinotopic Cortex During Haptic Exploration of Shapes and Actions in the Dark

The role of the early visual cortex and higher-order occipitotemporal cortex has been studied extensively for visual recognition and to a lesser degree for haptic recognition and visually guided actions. Using a slow event-related fMRI experiment, we investigated whether tactile and visual exploration of objects recruit the same "visual" areas (and in the case of visual cortex, the same retinotopic zones) and if these areas show reactivation during delayed actions in the dark toward haptically explored objects (and if so, whether this reactivation might be due to imagery). We examined activation during visual or haptic exploration of objects and action execution (grasping or reaching) separated by an 18 s delay. Twenty-nine human volunteers (13 females) participated in this study. Participants had their eyes open and fixated on a point in the dark. The objects were placed below the fixation point and accordingly visual exploration activated the cuneus, which processes retinotopic locations in the lower visual field. Strikingly, the occipital pole (OP), representing foveal locations, showed higher activation for tactile than visual exploration, although the stimulus was unseen and location in the visual field was peripheral. Moreover, the lateral occipital tactile-visual area (LOtv) showed comparable activation for tactile and visual exploration. Psychophysiological interaction analysis indicated that the OP showed stronger functional connectivity with anterior intraparietal sulcus and LOtv during the haptic than visual exploration of shapes in the dark. After the delay, the cuneus, OP, and LOtv showed reactivation that was independent of the sensory modality used to explore the object. These results show that haptic actions not only activate "visual" areas during object touch, but also that this information appears to be used in guiding grasping actions toward targets after a delay.SIGNIFICANCE STATEMENT Visual presentation of an object activates shape-processing areas and retinotopic locations in early visual areas. Moreover, if the object is grasped in the dark after a delay, these areas show "reactivation." Here, we show that these areas are also activated and reactivated for haptic object exploration and haptically guided grasping. Touch-related activity occurs not only in the retinotopic location of the visual stimulus, but also at the occipital pole (OP), corresponding to the foveal representation, even though the stimulus was unseen and located peripherally. That is, the same "visual" regions are implicated in both visual and haptic exploration; however, touch also recruits high-acuity central representation within early visual areas during both haptic exploration of objects and subsequent actions toward them. Functional connectivity analysis shows that the OP is more strongly connected with ventral and dorsal stream areas when participants explore an object in the dark than when they view it.

Is the extrastriate body area part of the dorsal visuomotor stream?

The extrastriate body area (EBA) processes visual information about body parts, and it is considered one among a series of category-specific perceptual modules distributed across the occipito-temporal cortex. However, recent evidence raises the possibility that EBA might also provide an interface between perception and action, linking the ventral and dorsal streams of visual information processing. Here, we assess anatomical evidence supporting this possibility. We localise EBA in individual subjects using a perceptual task and compare the characteristics of its functional and structural connectivity to those of two perceptual areas, the lateral occipital complex (LOC) and the fusiform body area (FBA), separately for each hemisphere. We apply complementary analyses of resting-state fMRI and diffusion-weighted MRI data in a group of healthy right-handed human subjects (N = 31). Functional and structural connectivity profiles indicate that EBA interacts more strongly with dorsal-stream regions compared to other portions of the occipito-temporal cortex involved in processing body parts (FBA) and object identification (LOC). These findings provide anatomical ground for a revision of the functional role of EBA. Building on a number of recent observations, we suggest that EBA contributes to planning goal-directed actions, possibly by specifying a desired postural configuration to parieto-frontal areas involved in computing movement parameters.

Integration of Visual and Proprioceptive Limb Position Information in Human Posterior Parietal, Premotor, and Extrastriate Cortex

The brain constructs a flexible representation of the body from multisensory information. Previous work on monkeys suggests that the posterior parietal cortex (PPC) and ventral premotor cortex (PMv) represent the position of the upper limbs based on visual and proprioceptive information. Human experiments on the rubber hand illusion implicate similar regions, but since such experiments rely on additional visuo-tactile interactions, they cannot isolate visuo-proprioceptive integration. Here, we independently manipulated the position (palm or back facing) of passive human participants' unseen arm and of a photorealistic virtual 3D arm. Functional magnetic resonance imaging (fMRI) revealed that matching visual and proprioceptive information about arm position engaged the PPC, PMv, and the body-selective extrastriate body area (EBA); activity in the PMv moreover reflected interindividual differences in congruent arm ownership. Further, the PPC, PMv, and EBA increased their coupling with the primary visual cortex during congruent visuo-proprioceptive position information. These results suggest that human PPC, PMv, and EBA evaluate visual and proprioceptive position information and, under sufficient cross-modal congruence, integrate it into a multisensory representation of the upper limb in space.

SIGNIFICANCE STATEMENT

The position of our limbs in space constantly changes, yet the brain manages to represent limb position accurately by combining information from vision and proprioception. Electrophysiological recordings in monkeys have revealed neurons in the posterior parietal and premotor cortices that seem to implement and update such a multisensory limb representation, but this has been difficult to demonstrate in humans. Our fMRI experiment shows that human posterior parietal, premotor, and body-selective visual brain areas respond preferentially to a virtual arm seen in a position corresponding to one's unseen hidden arm, while increasing their communication with regions conveying visual information. These brain areas thus likely integrate visual and proprioceptive information into a flexible multisensory body representation.

Stereoscopically Observing Manipulative Actions

The purpose of this study was to investigate the contribution of stereopsis to the processing of observed manipulative actions. To this end, we first combined the factors "stimulus type" (action, static control, and dynamic control), "stereopsis" (present, absent) and "viewpoint" (frontal, lateral) into a single design. Four sites in premotor, retro-insular (2) and parietal cortex operated specifically when actions were viewed stereoscopically and frontally. A second experiment clarified that the stereo-action-specific regions were driven by actions moving out of the frontoparallel plane, an effect amplified by frontal viewing in premotor cortex. Analysis of single voxels and their discriminatory power showed that the representation of action in the stereo-action-specific areas was more accurate when stereopsis was active. Further analyses showed that the 4 stereo-action-specific sites form a closed network converging onto the premotor node, which connects to parietal and occipitotemporal regions outside the network. Several of the specific sites are known to process vestibular signals, suggesting that the network combines observed actions in peripersonal space with gravitational signals. These findings have wider implications for the function of premotor cortex and the role of stereopsis in human behavior.

Resilience to the contralateral visual field bias as a window into object representations

Viewing images of manipulable objects elicits differential blood oxygen level-dependent (BOLD) contrast across parietal and dorsal occipital areas of the human brain that support object-directed reaching, grasping, and complex object manipulation. However, it is unknown which object-selective regions of parietal cortex receive their principal inputs from the ventral object-processing pathway and which receive their inputs from the dorsal object-processing pathway. Parietal areas that receive their inputs from the ventral visual pathway, rather than from the dorsal stream, will have inputs that are already filtered through object categorization and identification processes. This predicts that parietal regions that receive inputs from the ventral visual pathway should exhibit object-selective responses that are resilient to contralateral visual field biases. To test this hypothesis, adult participants viewed images of tools and animals that were presented to the left or right visual fields during functional magnetic resonance imaging (fMRI). We found that the left inferior parietal lobule showed robust tool preferences independently of the visual field in which tool stimuli were presented. In contrast, a region in posterior parietal/dorsal occipital cortex in the right hemisphere exhibited an interaction between visual field and category: tool-preferences were strongest contralateral to the stimulus. These findings suggest that action knowledge accessed in the left inferior parietal lobule operates over inputs that are abstracted from the visual input and is contingent on analysis by the ventral visual pathway, consistent with its putative role in supporting object manipulation knowledge.

Decoding Internally and Externally Driven Movement Plans

During movement planning, brain activity within parietofrontal networks encodes information about upcoming actions that can be driven either externally (e.g., by a sensory cue) or internally (i.e., by a choice/decision). Here we used multivariate pattern analysis (MVPA) of fMRI data to distinguish between areas that represent (1) abstract movement plans that generalize across the way in which these were driven, (2) internally driven movement plans, or (3) externally driven movement plans. In a delayed-movement paradigm, human volunteers were asked to plan and execute three types of nonvisually guided right-handed reaching movements toward a central target object: using a precision grip, a power grip, or touching the object without hand preshaping. On separate blocks of trials, movements were either instructed via color cues (Instructed condition), or chosen by the participant (Free-Choice condition). Using ROI-based and whole-brain searchlight-based MVPA, we found abstract representations of planned movements that generalize across the way these movements are selected (internally vs externally driven) in parietal cortex, dorsal premotor cortex, and primary motor cortex contralateral to the acting hand. In addition, we revealed representations specific for internally driven movement plans in contralateral ventral premotor cortex, dorsolateral prefrontal cortex, supramarginal gyrus, and in ipsilateral posterior parietotemporal regions, suggesting that these regions are recruited during movement selection. Finally, we observed representations of externally driven movement plans in bilateral supplementary motor cortex and a similar trend in presupplementary motor cortex, suggesting a role in stimulus-response mapping.

SIGNIFICANCE STATEMENT

The way the human brain prepares the body for action constitutes an essential part of our ability to interact with our environment. Previous studies demonstrated that patterns of neuronal activity encode upcoming movements. Here we used multivariate pattern analysis of human fMRI data to distinguish between brain regions containing movement plans for instructed (externally driven) movements, areas involved in movement selection (internally driven), and areas containing abstract movement plans that are invariant to the way these were generated (i.e., that generalize across externally and internally driven movement plans). Our findings extend our understanding of the neural basis of movement planning and have the potential to contribute to the development of brain-controlled neural prosthetic devices.

Shared and Distinct Neuroanatomic Regions Critical for Tool-related Action Production and Recognition: Evidence from 131 Left-hemisphere Stroke Patients

The inferior frontal gyrus and inferior parietal lobe have been characterized as human homologues of the monkey "mirror neuron" system, critical for both action production (AP) and action recognition (AR). However, data from brain lesion patients with selective impairment on only one of these tasks provide evidence of neural and cognitive dissociations. We sought to clarify the relationship between AP and AR, and their critical neural substrates, by directly comparing performance of 131 chronic left-hemisphere stroke patients on both tasks--to our knowledge, the largest lesion-based experimental investigation of action cognition to date. Using voxel-based lesion-symptom mapping, we found that lesions to primary motor and somatosensory cortices and inferior parietal lobule were associated with disproportionately impaired performance on AP, whereas lesions to lateral temporo-occipital cortex were associated with a relatively rare pattern of disproportionately impaired performance on AR. In contrast, damage to posterior middle temporal gyrus was associated with impairment on both AP and AR. The distinction between lateral temporo-occipital cortex, critical for recognition, and posterior middle temporal gyrus, important for both tasks, suggests a rough gradient from modality-specific to abstract representations in posterior temporal cortex, the first lesion-based evidence for this phenomenon. Overall, the results of this large patient study help to bring closure to a long-standing debate by showing that tool-related AP and AR critically depend on both common and distinct left hemisphere neural substrates, most of which are external to putative human mirror regions.

Functional subdivisions of medial parieto-occipital cortex in humans and nonhuman primates using resting-state fMRI

Based on its diverse and wide-spread patterns of connectivity, primate posteromedial cortex (PMC) is well positioned to support roles in several aspects of sensory-, cognitive- and motor-related processing. Previous work in both humans and non-human primates (NHPs) using resting-state functional MRI (rs-fMRI) suggests that a subregion of PMC, the medial parieto-occipital cortex (mPOC), by virtue of its intrinsic functional connectivity (FC) with visual cortex, may only play a role in higher-order visual processing. Recent neuroanatomical tracer studies in NHPs, however, demonstrate that mPOC also has prominent cortico-cortical connections with several frontoparietal structures involved in movement planning and control, a finding consistent with increasing observations of reach- and grasp-related activity in the mPOC of both NHPs and humans. To reconcile these observations, here we used rs-fMRI data collected from both awake humans and anesthetized macaque monkeys to more closely examine and compare parcellations of mPOC across species and explore the FC patterns associated with these subdivisions. Seed-based and voxel-wise hierarchical cluster analyses revealed four broad spatially separated functional boundaries that correspond with graded differences in whole-brain FC patterns in each species. The patterns of FC observed are consistent with mPOC forming a critical hub of networks involved in action planning and control, spatial navigation, and working memory. In addition, our comparison between species indicates that while there are several similarities, there may be some species-specific differences in functional neural organization. These findings and the associated theoretical implications are discussed.

The lateral occipitotemporal cortex in action

Understanding and responding to other people's actions is fundamental for social interactions. Whereas many studies emphasize the importance of parietal and frontal regions for these abilities, several lines of recent research show that the human lateral occipitotemporal cortex (LOTC) represents varied aspects of action, ranging from perception of tools and bodies and the way they typically move, to understanding the meaning of actions, to performing overt actions. Here, we highlight common themes across these lines of work, which have informed theories related to high-level vision, concepts, social cognition, and apraxia. We propose that patterns of activity in LOTC form representational spaces, the dimensions of which capture perceptual, semantic, and motor knowledge of how actions change the state of the world.