Tool use kinematics across different modes of execution. Implications for action representation and apraxia

The social cognitive dimension of pantomime

Pantomime production is commonly interpreted as reflecting tool-use-related cognitive processes. Yet, in everyday life, pantomime deserves a communication function and the exaggeration of amplitude found during pantomime compared to real tool use may reflect the individual's attempt to communicate the intended gesture. Therefore, the question arises about whether pantomime is a communicative behavior that is nevertheless supported only by non-social cognitive processes. We contribute to answering this question by using kinematic analyses. Participants performed the pantomime of using a saw or a hammer from visual presentation in three conditions: Free (no specific instructions), Self (focus on the real tool-use action), and Others (focus on the communicative dimension). Finally, they used the tool with the corresponding object (Actual condition). Participants' social cognition were assessed using gold standard questionnaires. Our results indicated that the manipulation of instructions had a minor effect on the exaggeration of amplitude during pantomime. We reported a link between the social cognition score and the amplitude in the Others condition for the hammer, which suggests that social cognitive processes could take part in pantomime production in some conditions. Nevertheless, this result does not alter our conclusion that social cognitive processes might be far from necessary for pantomime production.

Pantomime of tool use: looking beyond apraxia

Pantomime has a long tradition in clinical neuropsychology of apraxia. It has been much more used by researchers and clinicians to assess tool-use disorders than real tool use. Nevertheless, it remains incompletely understood and has given rise to controversies, such as the involvement of the left inferior parietal lobe or the nature of the underlying cognitive processes. The present article offers a comprehensive framework, with the aim of specifying the neural and cognitive bases of pantomime. To do so, we conducted a series of meta-analyses of brain-lesion, neuroimaging and behavioural studies about pantomime and other related tasks (i.e. real tool use, imitation of meaningless postures and semantic knowledge). The first key finding is that the area PF (Area PF complex) within the left inferior parietal lobe is crucially involved in both pantomime and real tool use as well as in the kinematics component of pantomime. The second key finding is the absence of a well-defined neural substrate for the posture component of pantomime (both grip errors and body-part-as-tool responses). The third key finding is the role played by the intraparietal sulcus in both pantomime and imitation of meaningless postures. The fourth key finding is that the left angular gyrus seems to be critical in the production of motor actions directed towards the body. The fifth key finding is that performance on pantomime is strongly correlated with the severity of semantic deficits. Taken together, these findings invite us to offer a neurocognitive model of pantomime, which provides an integrated alternative to the two hypotheses that dominate the field: The gesture-engram hypothesis and the communicative hypothesis. More specifically, this model assumes that technical reasoning (notably the left area PF), the motor-control system (notably the intraparietal sulcus), body structural description (notably the left angular gyrus), semantic knowledge (notably the polar temporal lobes) and potentially theory of mind (notably the middle prefrontal cortex) work in concert to produce pantomime. The original features of this model open new avenues for understanding the neurocognitive bases of pantomime, emphasizing that pantomime is a communicative task that nevertheless originates in specific tool-use (not motor-related) cognitive processes.

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Brain Stimulation and Group Therapy to Improve Gesture and Social Skills in Schizophrenia-The Study Protocol of a Randomized, Sham-Controlled, Three-Arm, Double-Blind Trial

An important component of nonverbal communication is gesture performance, which is strongly impaired in 2/3 of patients with schizophrenia. Gesture deficits in schizophrenia are linked to poor social functioning and reduced quality of life. Therefore, interventions that can help alleviate these deficits in schizophrenia are crucial. Here, we describe an ongoing randomized, double-blind 3-arm, sham-controlled trial that combines two interventions to reduce gesture deficits in schizophrenia patients. The combined interventions are continuous theta burst stimulation (cTBS) and social cognitive remediation therapy (SCRT). We will randomize 72 patients with schizophrenia spectrum disorders in three different groups of 24 patients. The first group will receive real cTBS and real SCRT, the second group will receive sham cTBS and real SCRT, and finally the third group will receive sham SCRT. Here, the sham treatments are, as per definition, inactive interventions that mimic as closely as possible the real treatments (similar to placebo). In addition, 24 age- and gender-matched controls with no interventions will be added for comparison. Measures of nonverbal communication, social cognition, and multimodal brain imaging will be applied at baseline and after intervention. The main research aim of this project will be to test whether the combination of cTBS and SCRT improves gesture performance and social functioning in schizophrenia patients more than standalone cTBS, SCRT or sham psychotherapy. We hypothesize that the patient group receiving the combined interventions will be superior in improving gesture performance.

CLINICAL TRIAL REGISTRATION

[www.ClinicalTrials.gov], identifier [NCT04106427].

Distinct cognitive components and their neural substrates underlying praxis and language deficits following left hemisphere stroke

Apraxia is characterised by multiple deficits of higher motor functions, primarily caused by left hemisphere (LH) lesions to parietal-frontal praxis networks. While previous neuropsychological and lesion studies tried to relate the various apraxic deficits to specific lesion sites, a comprehensive analysis of the different apraxia profiles and the related (impaired) motor-cognitive processes as well as their differential neural substrates in LH stroke is lacking. To reveal the cognitive mechanisms that underlie the different patterns of praxis and (related) language deficits, we applied principal component analysis (PCA) to the scores of sub-acute LH stroke patients (n = 91) in several tests of apraxia and aphasia. Voxel-based lesion-symptom mapping (VLSM) analyses were then used to investigate the neural substrates of the identified components. The PCA yielded a first component related to language functions and three components related to praxis functions, with each component associated with specific lesion patterns. Regarding praxis functions, performance in imitating arm/hand gestures was accounted for by a second component related to the left precentral gyrus and the inferior parietal lobule. Imitating finger configurations, pantomiming the use of objects related to the face, and actually using objects loaded on component 3, related to the left anterior intraparietal sulcus and angular gyrus. The last component represented the imitation of bucco-facial gestures and was linked to the basal ganglia and LH white matter tracts. The results further revealed that pantomime of (limb-related) object use depended on both the component 2 and 3, which were shared with gesture imitation and actual object use. Data support and extend the notion that apraxia represents a multi-componential syndrome comprising different (impaired) motor-cognitive processes, which dissociate - at least partially - from language processes. The distinct components might be disturbed to a varying degree following LH stroke since they are associated with specific lesion patterns within the LH.

Improvement of Apraxia With Augmented Reality: Influencing Pantomime of Tool Use via Holographic Cues

Background: Defective pantomime of tool use is a hall mark of limb apraxia. Contextual information has been demonstrated to improve tool use performance. Further, knowledge about the potential impact of technological aids such as augmented reality for patients with limb apraxia is still scarce. Objective: Since augmented reality offers a new way to provide contextual information, we applied it to pantomime of tool use. We hypothesize that the disturbed movement execution can be mitigated by holographic stimulation. If visual stimuli facilitate the access to the appropriate motor program in patients with apraxia, their performance should improve with increased saliency, i.e., should be better when supported by dynamic and holographic cues vs. static and screen-based cues. Methods: Twenty one stroke patients and 23 healthy control subjects were randomized to mime the use of five objects, presented in two Environments (Screen vs. Head Mounted Display, HMD) and two Modes (Static vs. Dynamic) resulting in four conditions (ScreenStat, ScreenDyn, HMDStat, HMDDyn), followed by a real tool demonstration. Pantomiming was analyzed by a scoring system using video recordings. Additionally, the sense of presence was assessed using a questionnaire. Results: Healthy control participants performed close to ceiling and significantly better than patients. Patients achieved significantly higher scores with holographic or dynamic cues. Remarkably, when their performance was supported by animated holographic cues (e.g., striking hammer), it did not differ significantly from real tool demonstration. As the sense of presence increases with animated holograms, so does the pantomiming. Conclusion: Patients' performance improved with visual stimuli of increasing saliency. Future assistive technology could be implemented upon this knowledge and thus, positively impact the rehabilitation process and a patient's autonomy.

Treating limb apraxia via action semantics: a preliminary study

Limb apraxia is evident in approximately 50% of patients after left hemisphere cerebral vascular accident (LCVA) and increases disability and caregiver dependence. Individuals with apraxia exhibit abnormalities in spatio-temporal aspects of gesture production and/or in knowledge of tool-related actions (action semantics). This preliminary study of three LCVA participants aimed to (i) explore the efficacy of a novel Action Network Treatment (ANT) that focused on improving the semantic association between tool actions and other types of tool knowledge, an intervention inspired by successful semantic network treatments in aphasia (e.g., Edmonds et al., 2009), and (ii) explore whether there are individuals with apraxia who benefit from ANT relative to a version of a comparatively well-studied existing apraxia treatment (Smania et al., 2006; Smania et al., 2000) that shapes gesture via focus on practicing the spatio-temporal aspects of gesture production (Tool Use Treatment or TUT). One participant demonstrated treatment benefits from both ANT and TUT, while another only benefited from TUT. These findings indicate that our novel semantic network strengthening approach to gesture training may be efficacious in at least some individuals with apraxia, and provide a foundation for future study of the characteristics of people with apraxia who benefit from each approach.

The challenge of apraxia: Toward an operational definition?

The diagnosis of limb apraxia relies mainly on exclusion criteria (e.g., elementary motor or sensory deficits, aphasia). Due to the diversity of apraxia definitions and assessment methods, patients may or may not show apraxia depending on the chosen assessment method or theory, making the definition of apraxia somewhat arbitrary. As a result, "apraxia" may be diagnosed in patients with different cognitive impairments. Based on a quantitative and critical review of the literature, it is argued that this situation has its roots in the evolution from a task-based approach (i.e., the use of gold standard tests to detect apraxia) toward a process-based approach, namely, the deconstruction of the conceptual or production systems of action into multiple cognitive processes: language, executive functions, working memory, semantic memory, body schema, body image, visual-spatial skills, social cognition, visual-kinesthetic engrams, manipulation knowledge, technical reasoning, structural inference, and categorical apprehension. The coexistence of both approaches in the current literature is a major challenge that stands in the way of a scientific definition of apraxia. As a step toward a solution, we suggest to focus on symptoms, and on two complementary definition criteria (in addition with traditional exclusion criteria): Specificity (i.e., is apraxia explained by the alteration of cognitive processes specifically dedicated to gesture production?), and consistency (i.e., is the gesture production impairment consistent across tasks?). Two categories of limb apraxia are proposed: symptomatic apraxia (i.e., gesture production deficits that are secondary to more general cognitive impairments) and idiopathic apraxia (i.e., gesture production deficits that can be observed in isolation). It turns out that the only apraxia subtype that fulfills exclusion, specificity, and consistency criteria is limb-kinetic apraxia. A century after Liepmann's demonstration of the autonomy of apraxia toward language, the autonomy of this syndrome toward the rest of cognition remains an open question, while it poses new challenges to apraxia studies.

Structural organization of the praxis network predicts gesture production: Evidence from healthy subjects and patients with schizophrenia

Hand gestures are an integral part of social interactions and communication. Several imaging studies in healthy subjects and lesion studies in patients with apraxia suggest the praxis network for gesture production, involving mainly left inferior frontal, posterior parietal and temporal regions. However, little is known about the structural connectivity underlying gesture production. We recruited 41 healthy participants and 39 patients with schizophrenia. All participants performed a gesture production test, the Test of Upper Limb Apraxia, and underwent diffusion tensor imaging. We hypothesized that gesture production is associated with structural network connectivity as well as with tract integrity. We defined the praxis network as an undirected graph comprised of 13 bilateral regions of interest and derived measures of local and global structural connectivity and tract integrity from Finsler geometry. We found an association of gesture deficit with reduced global and local efficiency of the praxis network. Furthermore, reduced tract integrity, for example in the superior longitudinal fascicle, arcuate fascicle or corpus callosum were related to gesture deficits. Our findings contribute to the understanding of structural correlates of gesture production as they first present diffusion tensor imaging data in a combined sample of healthy subjects and a patient cohort with gestural deficits.

Limb and face apraxias in frontotemporal dementia: A systematic scoping review

PURPOSE

To investigate the literature for frequencies, profiles and neural correlates of limb and face apraxias in frontotemporal dementia (FTD).

METHOD

The search conducted in Ovid Medline, PsycINFO and Scopus yielded 487 non-duplicate records, and 43 were included in the final analysis.

RESULTS

Apraxias are evident in diverse forms in all clinical variants of FTD within the first four years of the disease. Face apraxia and productive limb apraxia co-occur in the behavioural and nonfluent variants. The logopenic variant resembles Alzheimer's disease in terms of pronounced parietal limb apraxia and absence of face apraxia. The semantic variant exhibits conceptual praxis deficits together with relatively preserved imitation skills. Concerning the genetic variants of FTD, productive limb apraxia is common among carriers of the progranulin gene mutation, and subtle gestural alterations have been documented among carriers of the chromosome 9 open reading frame 72 gene mutation before the expected disease onset. The data on neural correlations suggest that the breakdown of praxis results from bilateral cortical and subcortical damage in FTD and that Alzheimer-type pathology of the cerebrospinal fluid increases the severity of limb apraxia in all of the variants. Face apraxia correlates with degeneration of the medial and superior frontal cortices.

CONCLUSIONS

Each of the clinical variants of FTD exhibits a characteristic profile of apraxias that may support early differentiation between the variants and from Alzheimer's disease. However, the screening procedures developed for stroke populations seem insufficient, and a multifaceted assessment tool is needed. Although valid and practical tests already exist for dementia populations, a concise selection of test items that covers all of the critical domains is called for.

Action Observation for Neurorehabilitation in Apraxia

Neurorehabilitation and brain stimulation studies of post-stroke patients suggest that action-observation effects can lead to rapid improvements in the recovery of motor functions and long-term motor cortical reorganization. Apraxia is a clinically important disorder characterized by marked impairment in representing and performing skillful movements [gestures], which limits many daily activities and impedes independent functioning. Recent clinical research has revealed errors of visuo-motor integration in patients with apraxia. This paper presents a rehabilitative perspective focusing on the possibility of action observation as a therapeutic treatment for patients with apraxia. This perspective also outlines impacts on neurorehabilitation and brain repair following the reinforcement of the perceptual-motor coupling. To date, interventions based primarily on action observation in apraxia have not been undertaken.

Functional fixedness and body-part-as-object production in pantomime

In pantomiming the use of tools, it is possible to use a body part as the object (BPO) or imagine the object (IO). The present four studies test how conceptualizing the functions of objects may underlie BPO production in a non-clinical adult population. We showed that familiar vs. unfamiliar tools (Study 1) and visual experience only vs. visual + motor experience with novel tools (Study 2) made no difference in BPO production. In Study 3, participants showed a trend for higher BPO production for tools presented in two-dimensional pictures rather than in reality. In Study 4, participants' functional fixedness was experimentally manipulated: participants were told unfamiliar tools had either five functions or only one function. Participants produced significantly more BPOs in the one-function condition. These results suggest that conceptualizing objects as having a fixed function is a predictor of BPO production.

Distortion of Visuo-Motor Temporal Integration in Apraxia: Evidence From Delayed Visual Feedback Detection Tasks and Voxel-Based Lesion-Symptom Mapping

Limb apraxia is a higher brain dysfunction that typically occurs after left hemispheric stroke and its cause cannot be explained by sensory disturbance or motor paralysis. The comparison of motor signals and visual feedback to generate errors, i.e., visuo-motor integration, is important in motor control and motor learning, which may be impaired in apraxia. However, in apraxia after stroke, it is unknown whether there is a specific deficit in visuo-motor temporal integration compared to visuo-tactile and visuo-proprioceptive temporal integration. We examined the precision of visuo-motor temporal integration and sensory-sensory (visuo-tactile and visuo-proprioception) temporal integration in apraxia after stroke by using a delayed visual feedback detection task with three different conditions (tactile, passive movement, and active movement). The delay detection threshold and the probability curve for delay detection obtained in this task were quantitative indicators of the respective temporal integration functions. In addition, we performed subtraction and voxel-based lesion-symptom mapping to identify the brain lesions responsible for apraxia and deficits in visuo-motor temporal integration. The behavioral experiments showed that the delay detection threshold was extended and that the probability curve for delay detection was less steep in apraxic patients compared to controls (pseudo-apraxic patients and unaffected patients), only for the active movement condition, and not for the tactile and passive movement conditions. Furthermore, the severity of apraxia was significantly correlated with the delay detection threshold and the steepness of the probability curve in the active movement condition. These results indicated that multisensory (i.e., visual, tactile, and proprioception) feedback was normally temporally integrated, but motor prediction and visual feedback were not correctly temporally integrated in apraxic patients. That is, apraxic patients had difficulties with visuo-motor temporal integration. Lesion analyses revealed that both apraxia and the distortion of visuo-motor temporal integration were associated with lesions in the fronto-parietal motor network, including the left inferior parietal lobule and left inferior frontal gyrus. We suppose that damage to the left inferior fronto-parietal network could cause deficits in motor prediction for visuo-motor temporal integration, but not for sensory-sensory (visuo-tactile and visuo-proprioception) temporal integration, leading to the distortion of visuo-motor temporal integration in patients with apraxia.

The effect of aging and contextual information on manual asymmetry in tool use

Healthy aging affects manual asymmetries in simple motor tasks, such as unilateral reaching and aiming. The effects of aging on manual asymmetries in the performance of a complex, naturalistic task are unknown, but are relevant for investigating the praxis system. This study examined how aging influences manual asymmetry in different contexts in a tool manipulation task. Fifty healthy, right-hand-dominant young (N = 29; 21.41 ± 2.87 years), and elderly (N = 21; mean: 74.14 ± 6.64 years) participants performed a 'slicing' gesture in response to a verbal command in two contexts: with (tool) and without the tool (pantomime). For interjoint relationships between shoulder plane of elevation and elbow flexion, a HAND × AGE × CONTEXT interaction existed (F_1,43 = 4.746, p = 0.035). In pantomime, interjoint control deviated more in the left (non-dominant) than the right (dominant) limb in the elderly adult group (Wilcoxon, p = 0.010). No such differences existed in the young adult group (Wilcoxon, p = 0.471). Furthermore, contextual information reduced interjoint deviation in young adults when the task was performed with the right (dominant) hand (Wilcoxon, p = 0.001) and in the elderly adults when the task was performed with the left (non-dominant) hand (Wilcoxon, p = 0.012). The presence of the tool did not reduce interjoint deviation for the right hand in the elderly group (Wilcoxon, p = 0.064) or the left hand in the young group (Wilcoxon, p = 0.044). Deviation within trials (i.e., intrasubject deviation) in elbow flexion was higher in the elderly relative to the young adult group (p = 0.003). Finally, resultant peak velocities were smaller (p = 0.002) and cycle duration longer (p < 0.0001) in the elderly adult group. This study provides novel evidence that aging affects manual asymmetries and sensorimotor control in a naturalistic task and warrants that aging research considers the context in which the task is performed.

Come together: human-avatar on-line interactions boost joint-action performance in apraxic patients

Limb apraxia (LA) is a high-order motor disorder linked to left-hemisphere damage. It is characterized by defective execution of purposeful actions upon delayed imitation, or verbal command when the actions are performed in isolated, non-naturalistic, conditions. Whether interpersonal interactions provide social affordances that activate neural resources different from those requested by individual action execution, which may improve LA performance, is unknown. To fill this gap, we measured interaction performance, behavioral and kinematic indexes of left-brain damaged patients with/without LA in a social reach-to-grasp task involving two different degrees of spatio-temporal interactivity with an avatar. We found that LA patients' impairment in coordinating with the virtual partner was abolished in highly interactive conditions (where patients selected their actions on-line based on the behavior of the virtual partner) with respect to low interactive conditions (where actions were selected beforehand based on abstract instructions). Voxel-based-Lesion-Symptom-Mapping indicated that impairments in low-interactive conditions were underpinned by lesions of premotor, motor and insular areas, and of the basal ganglia. Our approach expands current understanding of the behavioral and neural correlates of interactive motor performance by highlighting the important role of social affordances, and provides novel, potentially important, views on rehabilitation of higher-order motor cognition disorders.

Evolution of Cognitive Rehabilitation After Stroke From Traditional Techniques to Smart and Personalized Home-Based Information and Communication Technology Systems: Literature Review

Background

Neurological patients after stroke usually present cognitive deficits that cause dependencies in their daily living. These deficits mainly affect the performance of some of their daily activities. For that reason, stroke patients need long-term processes for their cognitive rehabilitation. Considering that classical techniques are focused on acting as guides and are dependent on help from therapists, significant efforts are being made to improve current methodologies and to use eHealth and Web-based architectures to implement information and communication technology (ICT) systems that achieve reliable, personalized, and home-based platforms to increase efficiency and level of attractiveness for patients and carers.

Objective

The goal of this work was to provide an overview of the practices implemented for the assessment of stroke patients and cognitive rehabilitation. This study puts together traditional methods and the most recent personalized platforms based on ICT technologies and Internet of Things.

Methods

A literature review has been distributed to a multidisciplinary team of researchers from engineering, psychology, and sport science fields. The systematic review has been focused on published scientific research, other European projects, and the most current innovative large-scale initiatives in the area. A total of 3469 results were retrieved from Web of Science, 284 studies from Journal of Medical Internet Research, and 15 European research projects from Community Research and Development Information Service from the last 15 years were reviewed for classification and selection regarding their relevance.

Results

A total of 7 relevant studies on the screening of stroke patients have been presented with 6 additional methods for the analysis of kinematics and 9 studies on the execution of goal-oriented activities. Meanwhile, the classical methods to provide cognitive rehabilitation have been classified in the 5 main techniques implemented. Finally, the review has been finalized with the selection of 8 different ICT–based approaches found in scientific-technical studies, 9 European projects funded by the European Commission that offer eHealth architectures, and other large-scale activities such as smart houses and the initiative City4Age.

Conclusions

Stroke is one of the main causes that most negatively affect countries in the socioeconomic aspect. The design of new ICT-based systems should provide 4 main features for an efficient and personalized cognitive rehabilitation: support in the execution of complex daily tasks, automatic error detection, home-based performance, and accessibility. Only 33% of the European projects presented fulfilled those requirements at the same time. For this reason, current and future large-scale initiatives focused on eHealth and smart environments should try to solve this situation by providing more complete and sophisticated platforms.

Efficiency in Rule- vs. Plan-Based Movements Is Modulated by Action-Mode

The rule/plan motor cognition (RPMC) paradigm elicits visually indistinguishable motor outputs, resulting from either plan- or rule-based action-selection, using a combination of essentially interchangeable stimuli. Previous implementations of the RPMC paradigm have used pantomimed movements to compare plan- vs. rule-based action-selection. In the present work we attempt to determine the generalizability of previous RPMC findings to real object interaction by use of a grasp-to-rotate task. In the plan task, participants had to use prospective planning to achieve a comfortable post-handle rotation hand posture. The rule task used implementation intentions (if-then rules) leading to the same comfortable end-state. In Experiment A, we compare RPMC performance of 16 healthy participants in pantomime and real object conditions of the experiment, within-subjects. Higher processing efficiency of rule- vs. plan-based action-selection was supported by diffusion model analysis. Results show a significant response-time increase in the pantomime condition compared to the real object condition and a greater response-time advantage of rule-based vs. plan-based actions in the pantomime compared to the real object condition. In Experiment B, 24 healthy participants performed the real object RPMC task in a task switching vs. a blocked condition. Results indicate that plan-based action-selection leads to longer response-times and less efficient information processing than rule-based action-selection in line with previous RPMC findings derived from the pantomime action-mode. Particularly in the task switching mode, responses were faster in the rule compared to the plan task suggesting a modulating influence of cognitive load. Overall, results suggest an advantage of rule-based action-selection over plan-based action-selection; whereby differential mechanisms appear to be involved depending on the action-mode. We propose that cognitive load is a factor that modulates the advantageous effect of implementation intentions in motor cognition on different levels as illustrated by the varying speed advantages and the variation in diffusion parameters per action-mode or condition, respectively.

Early dysfunctions of fronto-parietal praxis networks in Parkinson's disease

In Parkinson’s disease (PD) the prevalence of apraxia increases with disease severity implying that patients in early stages may already have subclinical deficits. The aim of this exploratory fMRI study was to investigate if subclinical aberrations of the praxis network are already present in patients with early PD. In previous functional imaging literature only data on basal motor functions in PD exists. Thirteen patients with mild parkinsonian symptoms and without clinically diagnosed apraxia and 14 healthy controls entered this study. During fMRI participants performed a pantomime task in which they imitated the use of visually presented objects. Patients were measured ON and OFF dopaminergic therapy to evaluate a potential medication effect on praxis abilities and related brain functions. Although none of the patients was apraxic according to De Renzi ideomotor scores (range 62–72), patients OFF showed significantly lower praxis scores than controls. Patients exhibited significant hyperactivation in left fronto-parietal core areas of the praxis network. Frontal activations were clearly dominant in patients and were correlated with lower individual praxis scores. We conclude that early PD patients already show characteristic signs of praxis network dysfunctions and rely on specific hyperactivations to avoid clinically evident apraxic symptoms. Subclinical apraxic deficits were shown to correlate with an activation shift from left parietal to left frontal areas implying a prospective individual imaging marker for incipient apraxia.

Limb apraxia and the left parietal lobe

Limb apraxia is a heterogeneous disorder of skilled action and tool use that has long perplexed clinicians and researchers. It occurs after damage to various loci in a densely interconnected network of regions in the left temporal, parietal, and frontal lobes. Historically, a highly classificatory approach to the study of apraxia documented numerous patterns of performance related to two major apraxia subtypes: ideational and ideomotor apraxia. More recently, there have been advances in our understanding of the functional neuroanatomy and connectivity of the left-hemisphere "tool use network," and the patterns of performance that emerge from lesions to different loci within this network. This chapter focuses on the left inferior parietal lobe, and its role in tool and body representation, action prediction, and action selection, and how these functions relate to the deficits seen in patients with apraxia subsequent to parietal lesions. Finally, suggestions are offered for several future directions that will benefit the study of apraxia, including increased attention to research on rehabilitation of this disabling disorder.

The cortical signature of impaired gesturing: Findings from schizophrenia

Schizophrenia is characterized by deficits in gesturing that is important for nonverbal communication. Research in healthy participants and brain-damaged patients revealed a left-lateralized fronto-parieto-temporal network underlying gesture performance. First evidence from structural imaging studies in schizophrenia corroborates these results. However, as of yet, it is unclear if cortical thickness abnormalities contribute to impairments in gesture performance. We hypothesized that patients with deficits in gesture production show cortical thinning in 12 regions of interest (ROIs) of a gesture network relevant for gesture performance and recognition. Forty patients with schizophrenia and 41 healthy controls performed hand and finger gestures as either imitation or pantomime. Group differences in cortical thickness between patients with deficits, patients without deficits, and controls were explored using a multivariate analysis of covariance. In addition, the relationship between gesture recognition and cortical thickness was investigated. Patients with deficits in gesture production had reduced cortical thickness in eight ROIs, including the pars opercularis of the inferior frontal gyrus, the superior and inferior parietal lobes, and the superior and middle temporal gyri. Gesture recognition correlated with cortical thickness in fewer, but mainly the same, ROIs within the patient sample. In conclusion, our results show that impaired gesture production and recognition in schizophrenia is associated with cortical thinning in distinct areas of the gesture network.

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Impairments in gesture production and recognition in schizophrenia are related to altered brain structure.

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Brain alterations in schizophrenia are located in areas that are generally damaged in apraxia.

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Schizophrenia patients with gesture deficits show cortical thinning of several regions in the gesture network.

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Deficits of gesture production and recognition are both related to a fronto-parieto-temporal gesture network.

Mental imagery of gravitational motion

There is considerable evidence that gravitational acceleration is taken into account in the interaction with falling targets through an internal model of Earth gravity. Here we asked whether this internal model is accessed also when target motion is imagined rather than real. In the main experiments, naïve participants grasped an imaginary ball, threw it against the ceiling, and caught it on rebound. In different blocks of trials, they had to imagine that the ball moved under terrestrial gravity (1g condition) or under microgravity (0g) as during a space flight. We measured the speed and timing of the throwing and catching actions, and plotted ball flight duration versus throwing speed. Best-fitting duration-speed curves estimate the laws of ball motion implicit in the participant's performance. Surprisingly, we found duration-speed curves compatible with 0g for both the imaginary 0g condition and the imaginary 1g condition, despite the familiarity with Earth gravity effects and the added realism of performing the throwing and catching actions. In a control experiment, naïve participants were asked to throw the imaginary ball vertically upwards at different heights, without hitting the ceiling, and to catch it on its way down. All participants overestimated ball flight durations relative to the durations predicted by the effects of Earth gravity. Overall, the results indicate that mental imagery of motion does not have access to the internal model of Earth gravity, but resorts to a simulation of visual motion. Because visual processing of accelerating/decelerating motion is poor, visual imagery of motion at constant speed or slowly varying speed appears to be the preferred mode to perform the tasks.

Learning, remembering, and predicting how to use tools: Distributed neurocognitive mechanisms: Comment on Osiurak and Badets (2016)

The reasoning-based approach championed by Francois Osiurak and Arnaud Badets (Osiurak & Badets, 2016) denies the existence of sensory-motor memories of tool use except in limited circumstances, and suggests instead that most tool use is subserved solely by online technical reasoning about tool properties. In this commentary, I highlight the strengths and limitations of the reasoning-based approach and review a number of lines of evidence that manipulation knowledge is in fact used in tool action tasks. In addition, I present a "two route" neurocognitive model of tool use called the "Two Action Systems Plus (2AS+)" framework that posits a complementary role for online and stored information and specifies the neurocognitive substrates of task-relevant action selection. This framework, unlike the reasoning based approach, has the potential to integrate the existing psychological and functional neuroanatomic data in the tool use domain. (PsycINFO Database Record

Effects of Stroke on Ipsilesional End-Effector Kinematics in a Multi-Step Activity of Daily Living

Background: Stroke frequently impairs activities of daily living (ADL) and deteriorates the function of the contra- as well as the ipsilesional limbs. In order to analyze alterations of higher motor control unaffected by paresis or sensory loss, the kinematics of ipsilesional upper limb movements in patients with stroke has previously been analyzed during prehensile movements and simple tool use actions. By contrast, motion recording of multi-step ADL is rare and patient-control comparisons for movement kinematics are largely lacking. Especially in clinical research, objective quantification of complex externally valid tasks can improve the assessment of neurological impairments. Methods: In this preliminary study we employed three-dimensional motion recording and applied kinematic analysis in a multi-step ADL (tea-making). The trials were examined with respect to errors and sub-action structure, durations, path lengths (PLs), peak velocities, relative activity (RA) and smoothness. In order to check for specific burdens the sub-actions of the task were extracted and compared. To examine the feasibility of the approach, we determined the behavioral and kinematic metrics of the (ipsilesional) unimanual performance of seven chronic stroke patients (64a ± 11a, 3 with right/4 with left brain damage (LBD), 2 with signs of apraxia, variable severity of paresis) and compared the results with data of 14 neurologically healthy age-matched control participants (70a ± 7a). Results: T-tests revealed that while the quantity and structure of sub-actions of the task were similar. The analysis of end-effector kinematics was able to detect clear group differences in the associated parameters. Specifically, trial duration (TD) was increased (Cohen's d = 1.77); the RA (Cohen's d = 1.72) and the parameters of peak velocities (Cohen's d = 1.49/1.97) were decreased in the patient group. Analysis of the task's sub-actions repeated measures analysis of variance (rmANOVA) revealed no impact of the different demands of the sub-actions on the relative performance of the patient group. Conclusion: The analyses revealed kinematic peculiarities in the performance with the ipsilesional hand. These deficits apparently arose from the cognitive demands like sequencing rather than motor constraints. End-effector kinematics proved as a sensitive method to detect and quantify aspects of disturbed multi-step ADL performance after stroke. If standardized, the examination and the analysis are quick and deliver objective data supporting clinical research.

Gender differences in non-standard mapping tasks: A kinematic study using pantomimed reach-to-grasp actions

Comparison between real and pantomimed actions is used in neuroscience to dissociate stimulus-driven (real) as compared to internally driven (pantomimed) visuomotor transformations, with the goal of testing models of vision (Milner & Goodale, 1995) and diagnosing neuropsychological deficits (apraxia syndrome). Real actions refer to an overt movement directed toward a visible target whereas pantomimed actions refer to an overt movement directed either toward an object that is no longer available. Although similar, real and pantomimed actions differ in their kinematic parameters and in their neural substrates. Pantomimed-reach-to-grasp-actions show reduced reaching velocities, higher wrist movements, and reduced grip apertures. In addition, seminal neuropsychological studies and recent neuroimaging findings confirmed that real and pantomimed actions are underpinned by separate brain networks. Although previous literature suggests differences in the praxis system between males and females, no research to date has investigated whether or not gender differences exist in the context of real versus pantomimed reach-to-grasp actions. We asked ten male and ten female participants to perform real and pantomimed reach-to-grasp actions toward objects of different sizes, either with or without visual feedback. During pantomimed actions participants were required to pick up an imaginary object slightly offset relative to the location of the real one (which was in turn the target of the real reach-to-grasp actions). Results demonstrate a significant difference between the kinematic parameters recorded in male and female participants performing pantomimed, but not real reach-to-grasp tasks, depending on the availability of visual feedback. With no feedback both males and females showed smaller grip aperture, slower movement velocity and lower reach height. Crucially, these same differences were abolished when visual feedback was available in male, but not in female participants. Our results suggest that male and female participants should be evaluated separately in the clinical environment and in future research in the field.

Tool-use: An open window into body representation and its plasticity

Over the last decades, scientists have questioned the origin of the exquisite human mastery of tools. Seminal studies in monkeys, healthy participants and brain-damaged patients have primarily focused on the plastic changes that tool-use induces on spatial representations. More recently, we focused on the modifications tool-use must exert on the sensorimotor system and highlighted plastic changes at the level of the body representation used by the brain to control our movements, i.e., the Body Schema. Evidence is emerging for tool-use to affect also more visually and conceptually based representations of the body, such as the Body Image. Here we offer a critical review of the way different tool-use paradigms have been, and should be, used to try disentangling the critical features that are responsible for tool incorporation into different body representations. We will conclude that tool-use may offer a very valuable means to investigate high-order body representations and their plasticity.

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 connectivity associated with hand shape generation: Imitating novel hand postures and pantomiming tool grips challenge different nodes of a shared neural network

Clinical research suggests that imitating meaningless hand postures and pantomiming tool-related hand shapes rely on different neuroanatomical substrates. We investigated the BOLD responses to different tasks of hand posture generation in 14 right handed volunteers. Conjunction and contrast analyses were applied to select regions that were either common or sensitive to imitation and/or pantomime tasks. The selection included bilateral areas of medial and lateral extrastriate cortex, superior and inferior regions of the lateral and medial parietal lobe, primary motor and somatosensory cortex, and left dorsolateral prefrontal, and ventral and dorsal premotor cortices. Functional connectivity analysis revealed that during hand shape generation the BOLD-response of every region correlated significantly with every other area regardless of the hand posture task performed, although some regions were more involved in some hand postures tasks than others. Based on between-task differences in functional connectivity we predict that imitation of novel hand postures would suffer most from left superior parietal disruption and that pantomiming hand postures for tools would be impaired following left frontal damage, whereas both tasks would be sensitive to inferior parietal dysfunction. We also unveiled that posterior temporal cortex is committed to pantomiming tool grips, but that the involvement of this region to the execution of hand postures in general appears limited. We conclude that the generation of hand postures is subserved by a highly interconnected task-general neural network. Depending on task requirements some nodes/connections will be more engaged than others and these task-sensitive findings are in general agreement with recent lesion studies.

A distributed network critical for selecting among tool-directed actions

Tools pose a challenge to the need to select actions appropriate for task goals and environmental constraints. For many tools (e.g., calculator), actions for "using" and "grasping-to-move" conflict with each other and may compete during selection. To date, little is known about the mechanisms that enable selection between possible tool actions or their neural substrates. The study of patients with chronic left hemisphere stroke, many of whom are deficient in tool-use action (apraxic), provides an opportunity to elucidate these issues. Here, 31 such patients pantomimed or recognized tool use actions for "conflict" and "non-conflict" tools. Voxel-based lesion-symptom mapping (VLSM), lesion subtraction, and tractographic overlap analyses were used to determine brain regions necessary for selecting among tool-directed actions. Lesions to posterior middle temporal gyrus (pMTG) and anterior intraparietal sulcus (aIPS) tended to impair production of use actions similarly for both conflict and non-conflict tools. By contrast, lesions to the supramarginal gyrus (SMG), inferior frontal gyrus (IFG)/anterior insula, and superior longitudinal fasciculus (SLF) specifically impaired production of use actions for conflict tools. Patients' errors on conflict tools suggested inappropriate selection of grasping actions and difficulty selecting single actions. Use/grasp conflict had no effect on action recognition. We suggest that the SMG/SLF/IFG pathway implements biased competition between possible tool actions, while aIPS and pMTG compute the structure-based and skilled use actions, respectively, that constitute input to this competitive process. This is the first study to demonstrate a reliable link between a characteristic of single tools (i.e., their association with different use and grasp actions) and action selection difficulties. Additionally, the data allow us to posit an SMG-involved subtype of apraxia characterized by an inability to resolve action competition.

Conceptual- and production-related predictors of pantomimed tool use deficits in apraxia

Apraxia following left hemisphere stroke disrupts pantomimed tool use (PTU), a task that requires the integrity of a number of cognitive and motor processes. Although previous studies have identified that apraxics have deficits in (1) the integrity of/access to stored tool-use gesture representations, (2) deficits in intrinsic (body-based) coordinate control, and (3) abnormal reliance on visual feedback, no study to date has simultaneously tested the relative contribution of these three deficits to poor PTU performance. In this study we assessed 38 chronic left hemisphere stroke survivors on tests of PTU and the 3 component processes. We then attempted to predict PTU with the component scores using hierarchical regression to control for overall stroke severity and the possibility of correlated component scores. Results showed that over half of the variability in PTU was predictable, with the strongest independent predictor being a test of intrinsic coordinate control without visual feedback. A test of the integrity of/access to stored representations also predicted PTU. These results confirm and extend previous claims that conceptual- and production-related factors affect PTU, even after considering that deficits in both factors are commonly observed to varying degrees in apraxic patients.

Apraxia, pantomime and the parietal cortex

Apraxia, a disorder of higher motor cognition, is a frequent and outcome-relevant sequel of left hemispheric stroke. Deficient pantomiming of object use constitutes a key symptom of apraxia and is assessed when testing for apraxia. To date the neural basis of pantomime remains controversial. We here review the literature and perform a meta-analysis of the relevant structural and functional imaging (fMRI/PET) studies. Based on a systematic literature search, 10 structural and 12 functional imaging studies were selected. Structural lesion studies associated pantomiming deficits with left frontal, parietal and temporal lesions. In contrast, functional imaging studies associate pantomimes with left parietal activations, with or without concurrent frontal or temporal activations. Functional imaging studies that selectively activated parietal cortex adopted the most stringent controls. In contrast to previous suggestions, current analyses show that both lesion and functional studies support the notion of a left-hemispheric fronto-(temporal)-parietal network underlying pantomiming object use. Furthermore, our review demonstrates that the left parietal cortex plays a key role in pantomime-related processes. More specifically, stringently controlled fMRI-studies suggest that in addition to storing motor schemas, left parietal cortex is also involved in activating these motor schemas in the context of pantomiming object use. In addition to inherent differences between structural and functional imaging studies and consistent with the dedifferentiation hypothesis, the age difference between young healthy subjects (typically included in functional imaging studies) and elderly neurological patients (typically included in structural lesion studies) may well contribute to the finding of a more distributed representation of pantomiming within the motor-dominant left hemisphere in the elderly.

Tool use disorders after left brain damage

In this paper we review studies that investigated tool use disorders in left-brain damaged (LBD) patients over the last 30 years. Four tasks are classically used in the field of apraxia: Pantomime of tool use, single tool use, real tool use and mechanical problem solving. Our aim was to address two issues, namely, (1) the role of mechanical knowledge in real tool use and (2) the cognitive mechanisms underlying pantomime of tool use, a task widely employed by clinicians and researchers. To do so, we extracted data from 36 papers and computed the difference between healthy subjects and LBD patients. On the whole, pantomime of tool use is the most difficult task and real tool use is the easiest one. Moreover, associations seem to appear between pantomime of tool use, real tool use and mechanical problem solving. These results suggest that the loss of mechanical knowledge is critical in LBD patients, even if all of those tasks (and particularly pantomime of tool use) might put differential demands on semantic memory and working memory.

The tool in the brain: apraxia in ADL. Behavioral and neurological correlates of apraxia in daily living

Humans differ from other animals in the way they can skilfully and precisely operate or invent tools to facilitate their everyday life. Tools have dominated our home, travel and work environment, becoming an integral step for our motor skills development. What happens when the part of the brain responsible for tool use is damaged in our adult life due to a cerebrovascular accident? How does daily life change when we lose the previously mastered ability to make use of the objects around us? How do patients suffering from compromised tool use cope with food preparation, personal hygiene, grooming, housework, or use of home appliances? In this literature review we present a state of the art for single and multiple tool use research, with a focus on the impact that apraxia (impaired ability to perform tool-based actions) and action disorganization syndrome (ADS; impaired ability to carry out multi-step actions) have on activities of daily living (ADL). Firstly, we summarize the behavioral studies investigating the impact of apraxia and other comorbidity syndromes, such as neglect or visual extinction, on ADL. We discuss the hallmarks of the compromised tool use in terms of the sequencing of action steps, conceptual errors committed, spatial motor control, and temporal organization of the movement. In addition, we present an up-to-date overview of the neuroimaging and lesion analyses studies that provide an insight into neural correlates of tool use in the human brain and functional changes in the neural organization following a stroke, in the context of ADL. Finally we discuss the current practice in neurorehabilitation of ADL in apraxia and ADS aiming at increasing patients' independence.

Tool use without a tool: kinematic characteristics of pantomiming as compared to actual use and the effect of brain damage

Movement goals and task mechanics differ substantially between actual tool use and corresponding pantomimes. In addition, apraxia seems to be more severe during pantomime than during actual tool use. Comparisons of these two modes of action execution using quantitative methods of movement analyses are rare. In the present study, repetitive scooping movements with a ladle from a bowl into a plate were recorded and movement kinematics was analyzed. Brain-damaged patients using their ipsilesional hand and healthy control subjects were tested in three conditions: pantomime, demonstration with the tool only, and actual use in the normal context. Analysis of the hand trajectories during the transport component revealed clear differences between the tasks, such as slower actual use and moderate deficits in patients with left brain damage (LBD). LBD patients were particularly impaired in the scooping component: LBD patients with apraxia exhibited reduced hand rotation at the bowl and the plate. The deficit was most obvious during pantomime but actual use was also affected, and reduced hand rotation was consistent across conditions as indicated by strong pair-wise correlations between task conditions. In healthy control subjects, correlations between movement parameters were most evident between the pantomime and demonstration conditions but weak in correlation pairs involving actual use. From these findings and published neuroimaging evidence, we conclude that for a specific tool-use action, common motor schemas are activated but are adjusted and modified according to the actual task constraints and demands. An apraxic LBD individual can show a deficit across all three action conditions, but the severity can differ substantially between conditions.