Imitation Of Meaningless Gestures Research Articles

Visuo-spatial complexity potentiates the body-part effect in intransitive imitation of meaningless gestures.

Recent studies on the imitation of intransitive gestures suggest that the body part effect relies mainly upon the direct route of the dual-route model through a visuo-transformation mechanism. Here, we test the visuo-constructive hypothesis which posits that the visual complexity may directly potentiate the body part effect for meaningless gestures. We predicted that the difference between imitation of hand and finger gestures would increase with the visuo-spatial complexity of gestures. Second, we aimed to identify some of the visuo-spatial predictors of meaningless finger imitation skills. Thirty-eight participants underwent an imitation task containing three distinct set of gestures, that is, meaningful gestures, meaningless gestures with low visual complexity, and meaningless gestures with higher visual complexity than the first set of meaningless gestures. Our results were in general agreement with the visuo-constructive hypothesis, showing an increase in the difference between hand and finger gestures, but only for meaningless gestures with higher visuo-spatial complexity. Regression analyses confirm that imitation accuracy decreases with resource-demanding visuo-spatial factors. Taken together, our results suggest that the body part effect is highly dependent on the visuo-spatial characteristics of the gestures.

Localizing apraxia in corticobasal syndrome: a morphometric MRI study.

Apraxia localization has relied on voxel-based, lesion-symptom mapping studies in left hemisphere stroke patients. Studies on the neural substrates of different manifestations of apraxia in neurodegenerative disorders are scarce. The primary aim of this study was to look into the neural substrates of different manifestations of apraxia in a cohort of corticobasal syndrome patients (CBS) by use of cortical thickness. Twenty-six CBS patients were included in this cross-sectional study. The Goldenberg apraxia test (GAT) was applied. 3D-T1-weighted images were analyzed via the automated recon-all Freesurfer version 6.0 pipeline. Vertex-based multivariate General Linear Model analysis was applied to correlate GAT scores with cortical thickness. Deficits in imitation of meaningless gestures correlated with bilateral superior parietal atrophy, extending to the angular and supramarginal gyri, particularly on the left. Finger imitation relied predominantly on superior parietal lobes, whereas the left angular and supramarginal gyri, in addition to superior parietal lobes, were critical for hand imitation. The widespread bilateral clusters of atrophy in CBS related to apraxia indicate different pathophysiological mechanisms mediating praxis in neurodegenerative disorders compared to vascular lesions, with implications both for our understanding of praxis and for the rehabilitation approaches of patients with apraxia.

Gesture profiles distinguish primary progressive aphasia variants: a preliminary study

ABSTRACT Background Primary progressive aphasia (PPA) is a neurodegenerative syndrome characterized by progressive language deficits. The main variants of PPA – semantic (svPPA), logopenic (lvPPA), and nonfluent (nfvPPA) – can be challenging to distinguish. Limb apraxia often co-occurs with PPA, but it is unclear whether PPA variants are associated with different gesture deficits. Prior evidence from stroke indicates that temporal lobe lesions are associated with reduced benefit from meaning in gesture performance. Temporal lesions are also associated with greater deficits in hand postures compared to arm kinematics in gesture imitation. Aims We tested the hypothesis that svPPA, who primarily exhibit temporal lobe atrophy, would differentially show this pattern. In addition, we predicted that as a group, individuals with PPA would more accurately produce meaningful than meaningless gestures and kinematic components than hand postures, as found in neurotypical adults and individuals with stroke. Methods & Procedures Participants with PPA completed meaningful and meaningless gesture imitation tasks. Performance was scored for hand posture and arm kinematic components. Bayesian mixed-effect models examined trial-level gesture imitation accuracy, while controlling for dementia severity and random effects of subjects and items. Fixed effects included an interaction between PPA variant, task condition/meaning, and gesture component. Outcomes & Results We found a critical interaction between PPA variant, meaning, and gesture component. In particular, unlike lvPPA and nfvPPA, svPPA subjects’ hand postures failed to benefit from gesture meaning. This preliminary research extends prior findings on the role of the temporal lobe in action representations associated with manipulable objects, and is among the first to demonstrate distinct gesture imitation patterns between PPA variants. Conclusions Characterizing gesture deficits in PPA may help inform diagnostics, compensatory communication strategies, and models of praxis.

Shared and distinct routes in speech and gesture imitation: Evidence from stroke

Dual-route models of high-level (praxis) actions distinguish between an “indirect” semantic route mediating meaningful gesture imitation, and a “direct” sensory-motor route mediates meaningless gesture imitation. Similarly, dual-route language models distinguish between an indirect route mediating production and repetition of words, and a direct route mediating non-word repetition. Although aphasia and limb apraxia frequently co-occur following left-hemisphere cerebrovascular accident (LCVA), it is unclear which aspects of these functional-neuroanatomic dual-route architectures are shared across praxis and language domains. This study focused on gesture imitation to test the hypothesis that semantic information (and portions of the indirect route) are shared across domains, whereas two distinct dorsal routes mediate sensory-motor mapping. Forty chronic LCVA and 17 neurotypical controls completed semantic memory and language tasks and imitated 3 types of gesture stimuli: (1) labeled/“named” meaningful, (2) unnamed meaningful, and (3) meaningless gestures. The comparison of accuracy between meaningless versus unnamed meaningful gestures examined the benefits of semantic information, while the comparison of unnamed meaningful versus named meaningful imitation examined additional benefits of linguistic cueing. Mixed-effects models examined group by task interaction effects on gesture ability. We found that for patients with LCVA, unnamed meaningful gestures were imitated more accurately than meaningless gestures, suggesting that semantic information was beneficial, but there was no benefit of labeling. Reduced benefit of semantic information on gesture accuracy was associated with lesions to inferior frontal and posterior temporal regions as well as semantic memory performance on a pictorial (non-gesture) task. In contrast, there was no relationship between meaningless gesture imitation and nonword repetition, indicating that measures of direct route performance are not associated across language and action. These results provide preliminary evidence that portions of the indirect semantic route are shared across the language and action domains, while two direct sensory-motor mapping routes mediate word repetition and gesture imitation.

Imitation of meaningless gestures in the Alzheimer’s disease: influence of egocentric and allocentric spatial reference frames

Imitation of meaningless gestures is a frequently used task to assess praxis skills in Alzheimer’s disease (AD). The visuospatial analysis is considered to be one of the cognitive mechanisms most involved in perceiving the gestures of the other (i.e. model to imitate) in the imitation of meaningless gestures. However, in order to perform a classic gesture imitation task (i.e. face model), it is also necessary to transpose the representation of the other’s gestures to better represent one’s own gestures. This transposition can be superimposed on the dichotomy of egocentric spatial reference frames (i.e. self-gestures) and allocentric spatial reference frames (i.e. gestures of the other). Given previous researches on the relation between hippocampus and allocentric performance, we predicted that AD patients could have imitation difficulties specifically for the allocentric imitation. We thus propose a specific methodology to evaluate the imitation of meaningless gestures in both egocentric and allocentric conditions using unimanual ( i.e. one hand gestures) as well bimanual (i.e. two hand gestures) gest modalities for each condition. Our results show significant differences between the AD group and control group, except under the bimanualallocentric condition. Moreover, correlation analyses with visuospatial assessments do not validate the essential role of visuospatial abilities in our gestural imitation tasks. The comparison of the within-group results shows a significant difference between egocentric and allocentric conditions only for the elderly control group suggesting that the impact of spatial reference frames in gestural imitation would not be specific to AD. However, one should also be alert to within-pathological variability in AD, which would require a future study with several subgroups of AD patients.

Cognitive development of imitation of intransitive gestures: an analysis of hand and finger errors

ABSTRACT The dual-route model proposes that imitation of meaningful gestures relies on a lexical route whereas imitation of meaningless gestures relies on a sub-lexical route. The aim of the present study was to investigate the development of imitation of intransitive meaningful and meaningless gestures in children from 6 to 9 years old by exploring hand and finger errors. Despite lower performance, children showed similar patterns than adults with better imitation of meaningful compared to meaningless gestures. Concerning body part errors, children made more errors than adults. Moreover, children produced more hand errors than adults for meaningful gestures whereas they were no difference for meaningless gestures. These results suggest that the two routes are present but are still maturing. Moreover, several specific and non-specific factors may have impacted imitation skills. Further studies are needed to disentangle the role of these factors in imitation of intransitive gestures during development from childhood to adulthood.

Single-case disconnectome lesion-symptom mapping: Identifying two subtypes of limb apraxia

Influential theories of skilled action posit that distinct cognitive mechanisms and neuroanatomic substrates support meaningless gesture imitation and tool use pantomiming, and poor performance on these tasks are hallmarks of limb apraxia. Yet prior research has primarily investigated brain-behavior relations at the group level; thus, it is unclear whether we can identify individuals with isolated impairments in meaningless gesture imitation or tool use pantomiming whose performance is associated with a distinct neuroanatomic lesion profile. The goal of this study was to test the hypothesis that individuals with disproportionately worse performance in meaningless gesture imitation would exhibit cortical damage and white matter disconnection in left fronto-parietal brain regions, whereas individuals with disproportionately worse performance in tool use pantomiming would exhibit cortical damage and white matter disconnection in left temporo-parietal brain regions. Fifty-eight participants who experienced a left cerebrovascular accident took part in a meaningless gesture imitation task, a tool use pantomiming task, and a T1 structural MRI. Two participants were identified who had relatively small lesions and disproportionate impairments on one task relative to the other, as well as below-control-level performance on one task and not the other. Using these criteria, one participant was disproportionately impaired at meaningless gesture imitation, and the other participant was disproportionately impaired at pantomiming tool use. Graph theoretic analysis of each participant's structural disconnectome demonstrated that disproportionately worse meaningless gesture imitation performance was associated with disconnection among the left inferior parietal lobule, the left superior parietal lobule, and the left middle and superior frontal gyri, whereas disproportionately worse tool use pantomiming performance was associated with disconnection between left temporal and parietal regions. Our results demonstrate that relatively focal lesions to specific portions of the Tool Use Network can be associated with distinct limb apraxia subtypes.

100 years after Liepmann–Lesion correlates of diminished selection and application of familiar versus novel tools

100 years ago, Liepmann highlighted the role of left ventro-dorsal lesions for impairments in conceptual (rather ventral) and motor (more dorsal) related aspects of apraxia. Many studies thereafter attributed to an extended left fronto-temporo-parietal network. Yet, to date there are only few studies that looked at apraxic performance in the selection and application of familiar versus novel tools.In the current study we applied modern voxel-based lesion-symptom mapping (VLSM) to analyze neural correlates of impaired selection and application of familiar versus novel tools. 58 left (LBD) and 51 right brain damaged (RBD) stroke patients participated in the Novel Tools Test (NTT) and the Familiar Tools Test (FTT) of the Diagnostic Instrument for Limb Apraxia (DILA-S). We further assessed performance in control tasks, namely semantic knowledge (BOSU), visuo-spatial working memory (Corsi Block Tapping) and meaningless imitation of gestures (IML).Impaired tool use was most pronounced after LBD. Our VLSM results in the LBD group suggested that selection- versus application-related aspects of praxis and semantics of familiar versus novel tool use can be behaviorally and neuro-anatomically differentiated. For impairments in familiar tool tasks, the major focus of lesion maps was rather ventral while deficiencies in novel tool tasks went along with rather dorsal lesions. Affected selection processes were linked to rather anterior lesions, while impacted application processes went along with rather posterior lesion maps. In our study, particular tool selection processes were rather specific for familiar versus novel tools. Foci for lesion overlaps of experimental and control tasks were noticed ventrally for semantic knowledge and FTT, in fronto-parietal regions for working memory and NTT, and ventro-dorsally for imitation of meaningless gestures and the application of NTT and FTT.We visualized our current interpretation within a neuroanatomical model for apraxia of tool use.

Oscillatory entrainment of neural activity between inferior frontoparietal cortices alters imitation performance

The frontoparietal mirror network is activated when an individual performs a goal-directed action and observes another person's intentional action. It has been speculated that the distinct frontal and parietal regions might work together to participate in the imitation process, which translates an observed movement into an identical action. We aimed to determine the relationship between the frontoparietal mirror network and imitation by applying transcranial alternating current stimulation (tACS) to exogenously modulate oscillatory neural activity in the left inferior frontal gyrus and the left inferior parietal lobule. In total, 45 young adults participated in this study. The participants were randomly assigned to the three tACS groups (synchronous, desynchronous, and sham; 55 Hz enveloped by 6 Hz). Before and during tACS, the participants performed the gesture matching task and the gesture imitation task. Application of synchronous tACS over the left frontoparietal cortices significantly improved the performance of gesture matching and the meaningless gesture imitation relative to the baseline performance. Desynchronous tACS deteriorated the gesture matching performance relative to the baseline results. The oscillatory entrainment of neural activity between components of the frontoparietal mirror network is considered to alter imitation performance by modulating neural information relating to the goals of actions in the frontal cortex and the means of observed actions in the parietal cortex. To the best of our knowledge, this is the first study that reveals that the rhythmic communication between components of the frontoparietal mirror network has a functional role in imitation.

A Role for the Action Observation Network in Apraxia After Stroke.

Limb apraxia is a syndrome often observed after stroke that affects the ability to perform skilled actions despite intact elementary motor and sensory systems. In a large cohort of unselected stroke patients with lesions to the left, right, and bilateral hemispheres, we used voxel-based lesion-symptom mapping (VLSM) on clinical CT head images to identify the neuroanatomical correlates of the impairment of performance in three tasks investigating praxis skills in patient populations. These included a meaningless gesture imitation task, a gesture production task involving pantomiming transitive and intransitive gestures, and a gesture recognition task involving recognition of these same categories of gestures. Neocortical lesions associated with poor performance in these tasks were all in the left hemisphere. They involved the pre-striate and medial temporal cortices, the superior temporal sulcus, inferior parietal area PGi, the superior longitudinal fasciculus underlying the primary motor cortex, and the uncinate fasciculus, subserving connections between temporal and frontal regions. No significant lesions were identified when language deficits, as indicated via a picture naming task, were controlled for. The implication of the superior temporal sulcus and the anatomically connected prestriate and inferior parietal regions challenges traditional models of the disorder. The network identified has been implicated in studies of action observation, which might share cognitive functions sub-serving praxis and language skills.

Imitation of meaningless gestures in normal aging

ABSTRACT While imitation of meaningless gestures is a gold standard in the assessment of apraxia in patients with either stroke or neurodegenerative diseases, little is known about potential age-related effects on this measure. A significant body of literature has indicated that different mechanisms (i.e., executive functioning, visuospatial skills, sensory integration, body knowledge, categorical apprehension) may underlie the performance depending on imitation conditions (i.e., finger/hand, uni-/bimanual, symmetric/asymmetric, crossed/uncrossed configurations). However, neither the effects of these conditions on performance, nor the contribution of the abovementioned mechanisms to imitation have been explored in normal aging. The aim of the present study was to fill this gap. To do so, healthy adults (n = 103) aged 50 to 89 were asked to imitate 45 meaningless gestures. The authors controlled for general cognitive function, motor function, visual-spatial skills, executive function, sensory integration, body knowledge, and mechanical problem-solving skills. The results showed that asymmetry, body-midline crossing and, to a lesser extent, bimanual activity added an additional layer of difficulty to imitation tasks. After controlling for motor speed and cognitive function, age had an effect on imitation skills after 70 years old. This may reflect a decline in body knowledge, sensory integration, and executive functions. In contrast, the visuospatial and mechanical problem-solving hypotheses were ruled out. An additional motor simulation hypothesis is proposed. These findings may prove useful for clinicians working in memory clinics by providing insights on how to interpret imitation deficits. Lower performance after 70 years old should not be considered abnormal in a systematic manner.

Neural correlates of differential finger gesture imitation deficits in left hemisphere stroke.

Behavioural studies in apraxic patients revealed dissociations between the processing of meaningful (MF) and meaningless (ML) gestures. Consequently, the existence of two differential neural mechanisms for the imitation of either gesture type has been postulated. While the indirect (semantic) route exclusively enables the imitation of MF gestures, the direct route can be used for the imitation of any gesture type, irrespective of meaning, and thus especially for ML gestures. Concerning neural correlates, it is debated which of the visuo-motor streams (i.e., the ventral steam, the ventro-dorsal stream, or the dorso-dorsal stream) supports the postulated indirect and direct imitation routes.To probe the hypotheses that regions of the dorso-dorsal stream are involved differentially in the imitation of ML gestures and that regions of the ventro-dorsal stream are involved differentially in the imitation of MF gestures, we analysed behavioural (imitation of MF and ML finger gestures) and lesion data of 293 patients with a left hemisphere (LH) stroke.Confirming previous work, the current sample of LH stroke patients imitated MF finger gestures better than ML finger gestures. The analysis using voxel-based lesion symptom mapping (VLSM) revealed that LH damage to dorso-dorsal stream areas was associated with an impaired imitation of ML finger gestures, whereas damage to ventro-dorsal regions was associated with a deficient imitation of MF finger gestures.Accordingly, the analyses of the imitation of visually uniform and thus highly comparable MF and ML finger gestures support the dual-route model for gesture imitation at the behavioural and lesion level in a substantial patient sample. Furthermore, the data show that the direct route for ML finger gesture imitation depends on the dorso-dorsal visuo-motor stream while the indirect route for MF finger gesture imitation is related to regions of the ventro-dorsal visuo-motor stream.

279 Apraxia and the temporal lobe in action: a role for biological motion

Limb apraxia is a syndrome that affects the ability to perform skilful actions, despite intact elementary motor and sensory systems. Using voxel-based lesion symptom mapping in a large cohort of 387 stroke patients we determined the neuroanatomy of three tasks traditionally used to study praxis skills in patient populations: these included a meaningless gesture imitation task, a gesture production task involving pantomime of transitive and intransitive gestures and a gesture recognition task, involving recognition of these same categories of gestures. Lesions associated with reduced performance in these tasks involved an integrated network previously described in biological motion, with input areas comprising left pre-striate and occipital regions, left superior temporal sulcus and motor output areas comprising left premotor area, left striatum and the white matter underlying the left primary motor cortex. This study confirms a role for the left hemisphere in limb apraxia and supports the hypothesis it is a white matter disconnection syndrome, whilst shedding new light into the nature of the behavioural deficits described in the disorder comprising parts of an integrated network of brain areas described in biological motion.

Networks involved in motor cognition : Physiology and pathophysiology of apraxia

Apraxia is an umbrella term for different disorders of higher motor abilities that are not explained by elementary sensorimotor deficits (e. g. paresis or ataxia). Characteristic features of apraxia that are easy to recognize in clinical practice are difficulties in pantomimed or actual use of tools as well as in imitation of meaningless gestures. Apraxia is bilateral, explaining the cognitive motor disorders and occurs frequently (but not exclusively) after left hemispheric lesions, as well as in neurodegenerative diseases, such as corticobasal syndrome and Alzheimer's disease. Apraxic deficits can seriously impair activities of daily living, which is why the appropriate diagnosis is of great relevance. At the functional anatomical level, different cognitive motor skills rely on at least partly different brain networks, namely, aventral processing pathway for semantic components, such as tool-action associations, aventro-dorsal pathway for sensorimotor representations of learnt motor acts, as well as adorso-dorsal pathway for on-line motor control and, probably, imitation of meaningless gestures. While these networks partially overlap with language-relevant regions, more clear cut dissociations are found between apraxia deficits and disorders of spatial attention. In addition to behavioral interventions, noninvasive neuromodulation approaches, as well as human-computer interface assistance systems are agrowing focus of interest for the treatment of apraxia.

Bimanual Gesture Imitation in Alzheimer's Disease.

Unimanual gesture production or imitation has often been studied in Alzheimer's disease (AD) during apraxia testing. In the present study, it was hypothesized that bimanual motor tasks may be a sensitive method to detect impairments of motor cognition in AD due to increased demands on the cognitive system. We investigated bimanual, meaningless gesture imitation in 45 AD outpatients, 38 subjects with mild cognitive impairment (MCI), and 50 normal controls (NC) attending a memory clinic. Participants performed neuropsychological background testing and three tasks: the Interlocking Finger Test (ILF), Imitation of Alternating Hand Movements (AHM), and Bimanual Rhythm Tapping (BRT). The tasks were short and easy to administer. Inter-rater reliability was high across all three tests. AD patients performed significantly poorer than NC and MCI participants; a deficit to imitate bimanual gestures was rarely found in MCI and NC participants. Sensitivity to detect AD ranged from 0.5 and 0.7, specificity beyond 0.9. ROC analyses revealed good diagnostic accuracy (0.77 to 0.92). Impairment to imitate bimanual gestures was mainly predicted by diagnosis and disease severity. Our findings suggest that an impairment to imitate bimanual, meaningless gestures is a valid disease marker of mild to moderate AD and can easily be assessed in memory clinic settings. Based on our preliminary findings, it appears to be a separate impairment which can be distinguished from other cognitive deficits.

EP 1. Brain activity after acute left hemispheric stroke in imitation and tool associated actions

Background Apraxia, a disorder of higher motor control, frequently leads to impaired tool use or imitation capacities due to left hemispheric lesions. However, despite similar lesion size or location, patients present with different apraxic deficits thus different early reorganization mechanism may be assumed. To understand the impaired praxis network after stroke on a functional level, we correlated behavioral performance in imitation and tool use tasks with activation patterns in fMRI of 47 acute left-hemispheric stroke patients. Methods A cohort of 47 acute stroke patients (mean age 63.5 years ± SD 13.6; 13 female) with first ever embolic stroke in the left arteria cerebri media territory were tested for deficits in imitation of meaningless hand and finger postures and tool associated actions (pantomime of tool use, imitation of tool use, actual tool use). Testing was performed mean 4.8 days ± SD 2.9 post stroke. FMRI was acquired during presentation of video sequences of tool-associated actions viewed from a first-person perspective. Voxel wise linear regression analyses for task scores only and with lesion volume as covariate as well as group differences for categorized behavioral performance (deficit vs. no deficit) were calculated to analyze activity associated with behavioral performance in tool use and meaningless imitation. Analyses were performed using GLMflex. Results are presented on a p Results Intact imitation of meaningless postures was associated with activation in the left middle occipital gyrus as well as in the left superior temporal lobe in linear regression analyses and categorical group differences (deficit vs. no deficit). Tool associated tasks correlated with activation in the left supramarginal gyrus and superior temporal lobe without occipital activation. For group differences in pantomime of tool use (deficit vs. no deficit) an additional activation for patients with low behavioral performance could be found in the posterior middle temporal gyrus. Conclusion For intact imitation of meaningless postures and tool associated actions, specific left hemispheric activation patterns in the acute phase after stroke could be determined. These areas are commonly associated to the left hemispheric praxis network. While intact imitation of meaningless gestures seems to rely on intact left middle occipital gyrus for visual analysis of the presented movement tool associated actions rather seem to rely on integrity of the supramarginal gyrus, known to store movement engrams. Patients with deficits in pantomime of tool use additionally show activation of posterior middle temporal gyrus for semantic movement information. These mechanisms possibly can be interpreted as early compensatory effort.

Structural brain correlates of defective gesture performance in schizophrenia

IntroductionThe neural correlates of impaired performance of gestures are currently unclear. Lesion studies showed variable involvement of the ventro-dorsal stream particularly left inferior frontal gyrus (IFG) in gesture performance on command. However, findings cannot be easily generalized as lesions may be biased by the architecture of vascular supply and involve brain areas beyond the critical region. The neuropsychiatric syndrome of schizophrenia shares apraxic-like errors and altered brain structure without macroanatomic lesions. Schizophrenia may therefore qualify as a model disorder to test neural correlates of gesture impairments. MethodsWe included 45 schizophrenia patients and 44 healthy controls in the study to investigate the structural brain correlates of defective gesturing in schizophrenia using voxel based morphometry. Gestures were tested in two domains: meaningful gestures (transitive and intransitive) on verbal command and imitation of meaningless gestures. Cut-off scores were used to separate patients with deficits, patients without deficits and controls. Group differences in gray matter (GM) volume were explored in an ANCOVA. ResultsPatients performed poorer than controls in each gesture category (p < .001). Patients with deficits in producing meaningful gestures on command had reduced GM predominantly in left IFG, with additional involvement of right insula and anterior cingulate cortex. Patients with deficits differed from patients without deficits in right insula, inferior parietal lobe (IPL) and superior temporal gyrus. ConclusionsImpaired performance of meaningful gestures on command was linked to volume loss predominantly in the praxis network in schizophrenia. Thus, the behavioral similarities between apraxia and schizophrenia are paralleled by structural alterations. However, few associations between behavioral impairment and structural brain alterations appear specific to schizophrenia.

Brain activity underlying tool-related and imitative skills after major left hemisphere stroke.

Apraxia is a debilitating cognitive motor disorder that frequently occurs after left hemisphere stroke and affects tool-associated and imitative skills. However, the severity of the apraxic deficits varies even across patients with similar lesions. This variability raises the question whether regions outside the left hemisphere network typically associated with cognitive motor tasks in healthy subjects are of additional functional relevance. To investigate this hypothesis, we explored regions where functional magnetic resonance imaging activity is associated with better cognitive motor performance in patients with left hemisphere ischaemic stroke. Thirty-six patients with chronic (>6 months) large left hemisphere infarcts (age ± standard deviation, 60 ± 12 years, 29 male) and 29 control subjects (age ± standard deviation, 72 ± 7, 15 male) were first assessed behaviourally outside the scanner with tests for actual tool use, pantomime and imitation of tool-use gestures, as well as for meaningless gesture imitation. Second, functional magnetic resonance imaging activity was registered during the passive observation of videos showing tool-associated actions. Voxel-wise linear regression analyses were used to identify areas where behavioural performance was correlated with functional magnetic resonance imaging activity. Furthermore, lesions were delineated on the magnetic resonance imaging scans for voxel-based lesion-symptom mapping. The analyses revealed two sets of regions where functional magnetic resonance imaging activity was associated with better performance in the clinical tasks. First, activity in left hemisphere areas thought to mediate cognitive motor functions in healthy individuals (i.e. activity within the putative 'healthy' network) was correlated with better scores. Within this network, tool-associated tasks were mainly related to activity in supramarginal gyrus and ventral premotor cortex, while meaningless gesture imitation depended more on the anterior intraparietal sulcus and superior parietal lobule. Second, repeating the regression analyses with total left hemisphere lesion volume as additional covariate demonstrated that tool-related skills were further supported by right premotor, right inferior frontal and left anterior temporal areas, while meaningless gesture imitation was also driven by the left dorso-lateral prefrontal cortex. In summary, tool-related and imitative skills in left hemisphere stroke patients depend on the activation of spared left hemisphere regions that support these abilities in healthy individuals. In addition, cognitive motor functions rely on the activation of ipsi- and contralesional areas that are situated outside this 'healthy' network. This activity may explain why some patients perform surprisingly well despite large left brain lesions, while others are severely impaired.

Imitation and matching of meaningless gestures: distinct involvement from motor and visual imagery.

The aim of the present study was to understand the underlying cognitive processes of imitation and matching of meaningless gestures. Neuropsychological evidence obtained in brain damaged patients, has shown that distinct cognitive processes supported imitation and matching of meaningless gestures. Left-brain damaged (LBD) patients failed to imitate while right-brain damaged (RBD) patients failed to match meaningless gestures. Moreover, other studies with brain damaged patients showed that LBD patients were impaired in motor imagery while RBD patients were impaired in visual imagery. Thus, we hypothesize that imitation of meaningless gestures might rely on motor imagery, whereas matching of meaningless gestures might be based on visual imagery. In a first experiment, using a correlational design, we demonstrated that posture imitation relies on motor imagery but not on visual imagery (Experiment 1a) and that posture matching relies on visual imagery but not on motor imagery (Experiment 1b). In a second experiment, by manipulating directly the body posture of the participants, we demonstrated that such manipulation evokes a difference only in imitation task but not in matching task. In conclusion, the present study provides direct evidence that the way we imitate or we have to compare postures depends on motor imagery or visual imagery, respectively. Our results are discussed in the light of recent findings about underlying mechanisms of meaningful and meaningless gestures.

Deficits in Limb Praxis in Patients With Obsessive-Compulsive Disorder.

There is recent evidence of deficits in praxis in patients with primary dystonia. Obsessive-compulsive disorder (OCD) has been linked to disorders of higher-order motor function, such as dystonia. However, no clear mechanism underlying such a relationship has been found. This pilot study aimed to identify whether patients with OCD might also show deficits in praxis. Patients with OCD were compared with healthy volunteers on a meaningless gesture imitation task. Patients showed significantly lower scores in this task. Further studies are needed to elucidate the nature of patients' deficits in praxis. This might reveal similar mechanisms underlying OCD and some types of movement disorders.