The significance of body part as tool errors in limb apraxia

fNIRS-Based Differences in Cortical Activation during Tool Use, Pantomimed Actions, and Meaningless Actions between Children with and without Autism Spectrum Disorder (ASD)

Children with autism spectrum disorder (ASD) have difficulties with tool use and pantomime actions. The current study utilized functional near-infrared spectroscopy (fNIRS) to examine the neural mechanisms underlying these gestural difficulties. Thirty-one children with and without ASD (age (mean ± SE) = 11.0 ± 0.6) completed a naturalistic peg-hammering task using an actual hammer (hammer condition), pantomiming hammering actions (pantomime condition), and performing meaningless actions with similar joint motions (meaningless condition). Children with ASD exhibited poor praxis performance (praxis error: TD = 17.9 ± 1.7; ASD = 27.0 ± 2.6, p < 0.01), which was significantly correlated with their cortical activation (R = 0.257 to 0.543). Both groups showed left-lateralized activation, but children with ASD demonstrated more bilateral activation during all gestural conditions. Compared to typically developing children, children with ASD showed hyperactivation of the inferior parietal lobe and hypoactivation of the middle/inferior frontal and middle/superior temporal regions. Our findings indicate intact technical reasoning (typical left-IPL activation) but atypical visuospatial and proprioceptive processing (hyperactivation of the right IPL) during tool use in children with ASD. These results have important implications for clinicians and researchers, who should focus on facilitating/reducing the burden of visuospatial and proprioceptive processing in children with ASD. Additionally, fNIRS-related biomarkers could be used for early identification through early object play/tool use and to examine neural effects following gesture-based interventions.

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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Upper Limb Apraxia

PURPOSE OF REVIEW

Limb apraxia is one of the most common and most disabling disorders caused by brain damage. However, apraxia is one of the least recognized disorders associated with cerebral disease. This article discusses the signs and symptoms of, means of testing for, the pathophysiology of, and possible management of upper limb apraxia.

RECENT FINDINGS

Upper limb apraxia has four major forms: ideomotor, limb-kinetic, conceptual, and ideational. Although recent findings are included in this article, a full understanding of these disorders, including the means of testing, their possible pathophysiology, and the diseases that may cause these disorders, requires that some older literature is also discussed.

SUMMARY

This article guides clinicians in testing for and diagnosing the different forms of upper limb apraxia, identifying the underlying diseases that may cause apraxia, managing the different forms of the disorder, and possible forms of rehabilitation.

Gesture errors in left and right hemisphere damaged patients: A behavioural and anatomical study

OBJECTIVE

Erroneous gesture execution is at the core of motor cognition difficulties in apraxia. While a taxonomy of errors may provide important information about the nature of the disorder, classifications are currently often inconsistent. This study aims to identify the error categories which distinguish apraxic from non-apraxic patients.

METHOD

Two groups of mixed (bucco-facial and limb) and bucco-facial apraxic patients suffering from stroke were compared to non-apraxic, left and right hemisphere damaged patients in tasks tapping the ability to perform limb and bucco-facial actions. The errors were analysed and classified into 6 categories relating to content, configuration or movement, spatial or temporal parameters and unrecognisable actions. Furthermore, an anatomical investigation (VLMS) was conducted in the whole group of left hemisphere damaged patients to investigate potential correlates of the various error categories.

RESULTS

Although all the above error typologies may be observed, the most indicative of mixed apraxia is the content-related one in all the typologies of actions (transitive and intransitive), and configuration errors in transitive ones. Configuration and content errors in mouth actions seem to be typical of bucco-facial apraxia. Spatial errors are similar in both apraxic and right brain damaged, non-apraxic patients. A lesion mapping analysis of left-brain damaged patients demonstrates that all but the spatial error category are associated with the fronto-parietal network. Moreover, content errors are also associated with fronto-insular lesions and movement errors with damage to the paracentral territory (precentral and postcentral gyri). Spatial errors are often associated to ventral frontal lesions.

CONCLUSIONS

Bucco-facial and mixed apraxic patients make different types of errors in different types of actions. Not all errors are equally indicative of apraxia. In addition, the various error categories are associated with at least partially different neural correlates.

Gesture deficits and apraxia in schizophrenia

Aberrant performance of skilled action has long been noted in schizophrenia and relatedly, recent reports have demonstrated impaired use, performance, and perception of hand gestures in this group. Still, this deficit is not acknowledged as apraxia, which to the broader medical field, characterizes impairments in skilled actions. Understanding the relationship between apraxia and schizophrenia may shed an invaluable new perspective on disease mechanism, and highlight novel treatment opportunities as well. To examine this potential link, we reviewed the evidence for the types of praxis errors, associated psychopathology, and cerebral correlates of the praxis deficit in schizophrenia. Notably, the review indicated that gesture deficits are severe enough to be considered genuine apraxia in a substantial proportion of patients (about 25%). Further, other potential contributors (e.g., hypokinetic motor abnormalities, cognitive impairment) are indeed associated with gesture deficits in schizophrenia, but do not sufficiently explain the abnormality. Finally, patients with praxis deficits have altered brain structure and function including the left parieto-premotor praxis network and these neural correlates are specific to the praxis deficit. Therefore, we argue that the gestural disorder frequently observed in schizophrenia shares both the clinical and neurophysiological features of true apraxia, as in other neuropsychiatric disorders with impaired higher order motor control, such as Parkinson's disease.

Effect of test instructions: The example of the pantomime production task

The production of pantomime is a sensible task to detect praxis deficits. It is usually assessed by presenting objects visually or by verbal command. Verbal instructions are given either by providing the name of the object (e.g., "Show me how to use a pen") or by requiring the object function (e.g., "Show me how to write"). These modes of testing are used interchangeably. The aim of this study is to investigate whether the different instructions generate different performances. Fifty-one healthy participants (17-89 years old) were assessed on three pantomime production tasks differing for the instruction given: two with verbal instructions (Pantomime by Name and Pantomime by Function) and one with the object visually presented (Pantomime by Object). Results showed that Pantomime by Function produced the poorest performance and the highest frequency of Body Parts as Tool (BPT) errors, suggesting that the way the instructions are given may determine the performance in a task. Nuances in test instructions could result in misleading outcome.

Action performance in children with autism spectrum disorder at preschool age: a pilot study

Objectives: Motor deficits related to imitation have been observed in autism spectrum disorder (ASD) patients. This pilot investigation focused on motor performances, including daily tool-use actions, performing an action in the absence of the tool, and imitating (copying tool-use action presented visually), in eight children with ASD and eight children with typical development (TD), with all of pre-school age (4-6 years). Methods: Motor performances were compared between the children with ASD and TD. Differences between an actual tool-use action and performing a tool-use action without the tool according to verbal instruction were also assessed between the groups. Results: Children with ASD showed impairments in imitating, but their actual tool-use actions and tool-use actions without tools following verbal instruction were not different from those of TD children. The spatial error rate in the tasks was higher in children with ASD. Conclusions: The present study indicates that disturbance in imitating actions appears by the age of 4-6 years in children with ASD, possibly as a characteristic symptom affecting motor performance at pre-school age. Generalized apraxia might follow by the age of 8 years or older.

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.

Unilateral Apraxic Agraphia without Ideomotor Apraxia from a callosal lesion in a patient with Marchiafava-Bignami disease

Apraxic agraphia can be caused by left hemispheric cerebral lesions in the area that contains the spatial representations of the movements required to write, from a lesion in, or connections to, the frontal premotor cortex that converts these spatial representations to motor programs (Exner's area).  A right-handed woman with Marchiafava Bignami disease and lesions of the genu and splenium of her corpus callosum had apraxic agraphia without ideomotor apraxia of her left. A disconnection of Exner's area in the left hemisphere from the right hemisphere's premotor and motor areas may have led to her inability to write with her left hand.

Handling or being the concept: An fMRI study on metonymy representations in coverbal gestures

In "Two heads are better than one," "head" stands for people and focuses the message on the intelligence of people. This is an example of figurative language through metonymy, where substituting a whole entity by one of its parts focuses attention on a specific aspect of the entity. Whereas metaphors, another figurative language device, are substitutions based on similarity, metonymy involves substitutions based on associations. Both are figures of speech but are also expressed in coverbal gestures during multimodal communication. The closest neuropsychological studies of metonymy in gestures have been nonlinguistic tool-use, illustrated by the classic apraxic problem of body-part-as-object (BPO, equivalent to an internal metonymy representation of the tool) vs. pantomimed action (external metonymy representation of the absent object/tool). Combining these research domains with concepts in cognitive linguistic research on gestures, we conducted an fMRI study to investigate metonymy resolution in coverbal gestures. Given the greater difficulty in developmental and apraxia studies, perhaps explained by the more complex semantic inferencing involved for external metonymy than for internal metonymy representations, we hypothesized that external metonymy resolution requires greater processing demands and that the neural resources supporting metonymy resolution would modulate regions involved in semantic processing. We found that there are indeed greater activations for external than for internal metonymy resolution in the temporoparietal junction (TPJ). This area is posterior to the lateral temporal regions recruited by metaphor processing. Effective connectivity analysis confirmed our hypothesis that metonymy resolution modulates areas implicated in semantic processing. We interpret our results in an interdisciplinary view of what metonymy in action can reveal about abstract cognition.

The comprehensibility of pantomimes produced by people with aphasia

BACKGROUND

People with aphasia (PWA) use pantomime, gesture in absence of speech, differently from non-brain-damaged people (NBDP).

AIMS

To evaluate through an exploratory study the comprehensibility of PWA's pantomimes and to find out whether they can compensate for information PWA are unable to convey in speech.

METHODS & PROCEDURES

A total of 273 naïve observers participated in one of two judgement tasks: forced-choice and open-ended questions. These were used to determine the comprehensibility of pantomimes produced to depict objects by PWA as compared with NBDP. Furthermore, we compared the information conveyed in pantomime with the information in speech. We looked into factors influencing pantomime's comprehensibility: individual factors, manner of depiction and information needed to be depicted.

OUTCOME & RESULTS

Although comprehensibility scores for PWA's pantomimes were lower than for those produced by NBDP, all PWA were able to convey information in pantomime that they could not convey in speech. Comprehensibility of pantomimes was predicted by apraxia. The inability to use the right hand related to slightly lower comprehensibility scores. Objects for which individuals depicted its use were best understood.

CONCLUSION & IMPLICATIONS

Our findings highlight the potential benefit of pantomime for clinical practice. Pantomimes, even though sometimes impaired, can convey information that PWA cannot convey in speech. Clinical implications are discussed.

Limb apraxia in aphasic patients

ABSTRACT Limb apraxia is usually associated with left cerebral hemisphere damage, with numerous case studies involving aphasic patients. The aim of this study was to verify the occurrence of limb apraxia in aphasic patients and analyze its nature. This study involved 44 healthy volunteers and 28 aphasic patients matched for age and education. AH participants were assessed using a limb apraxia battery comprising subtests evaluating lexical-semantic aspects related to the comprehension/production of gestures as well as motor movements. Aphasics had worse performances on many tasks related to conceptual components of gestures. The difficulty found on the imitation of dynamic gesture tasks also indicated that there were specific motor difficulties in gesture planning. These results reinforce the importance of conducting limb apraxia assessment in aphasic patients and also highlight pantomime difficulties as a good predictor for semantic disturbances.

Praxis and writing in a right-hander with crossed aphasia

Studies of patients with brain lesions have demonstrated that language and praxis are mediated by dissociable networks. However, language has the capacity to influence the selection of purposeful actions. The abilities to use language and to program purposeful movements are often mediated by networks that have anatomic proximity. With hemispheric injury, the diagnosis of apraxia is often confounded by the specific influence of language impairments on the ability to select and produce transitive gestures. We report a patient who illustrates this confound. This patient is a right-handed man who developed global aphasia and neglect after a right hemispheric stroke. His right hand remained deft, and when asked to produce specific transitive gestures (pantomimes), he often performed normally but did make some body part as object and perseverative errors. However, he did not demonstrate the temporal or spatial errors typical of ideomotor apraxia. He also had a perseverative agraphia. Our patient's left hemisphere praxis system appeared to be intact, and the error types demonstrated during production of transitive gestures cannot be attributed to a degradation of postural and movement (praxis) programs mediated by his left hemisphere. The praxis errors types are most consistent with a deficit in the ability to select the necessary praxis programs. Thus, our patient appeared to have dissociation between language and praxis programs that resulted in body part as object and perseverative errors.

Callosal disconnection and limb-kinetic apraxia

According to Liepmann, patients with limb-kinetic apraxia (LKA) have a loss of upper limb deftness-dexterity. Prior studies have revealed in right-handed patients that, whereas injury of the left hemisphere induces an ipsilesional LKA, injury to the right hemisphere does not induce an ipsilesional LKA. There are at least two possible means by which the left hemisphere may influence the deftness of the left hand, either by callosal connections or by ipsilesional corticospinal projections. The purpose of this study was to learn whether a patient with a focal lesion of the corpus callosum had a callosal disconnection LKA. This 57-year-old right-handed man had a memory impairment, and upon brain imaging, was found to have a septum pellucidum cyst, which was causing mild ventricular obstruction to the occipital and temporal horns. He underwent an endoscopic-assisted fenestration of the septum pellucidum. Postoperative imaging revealed a lesion of the mesial portion of his corpus callosum and an assessment of praxis revealed that he had both a limb-kinetic and ideomotor apraxia of his left but not his right hand. The observation that this man had a callosal disconnection LKA of his left hand suggests that in some people it is the left hemisphere's premotor or motor cortex that enables the right hemisphere's motor system to program deft movements of the left hand.

The dorsal stream contribution to phonological retrieval in object naming

Meaningful speech, as exemplified in object naming, calls on knowledge of the mappings between word meanings and phonological forms. Phonological errors in naming (e.g. GHOST named as 'goath') are commonly seen in persisting post-stroke aphasia and are thought to signal impairment in retrieval of phonological form information. We performed a voxel-based lesion-symptom mapping analysis of 1718 phonological naming errors collected from 106 individuals with diverse profiles of aphasia. Voxels in which lesion status correlated with phonological error rates localized to dorsal stream areas, in keeping with classical and contemporary brain-language models. Within the dorsal stream, the critical voxels were concentrated in premotor cortex, pre- and postcentral gyri and supramarginal gyrus with minimal extension into auditory-related posterior temporal and temporo-parietal cortices. This challenges the popular notion that error-free phonological retrieval requires guidance from sensory traces stored in posterior auditory regions and points instead to sensory-motor processes located further anterior in the dorsal stream. In a separate analysis, we compared the lesion maps for phonological and semantic errors and determined that there was no spatial overlap, demonstrating that the brain segregates phonological and semantic retrieval operations in word production.

Apraxia

Humans need to perform skilled movements to successfully interact with their environment as well as take care of themselves and others. These important skilled purposeful actions are primarily performed by the forelimb, and the loss of these skills is called apraxia. This review describes the means of testing, the pathophysiology, and the clinical characteristics that define five different general forms of forelimb apraxia including: (1) ideational apraxia, an inability to correctly sequence a series of acts leading to a goal; (2) conceptual apraxia, a loss of mechanical tool knowledge; (3) ideomotor apraxia, a loss of the knowledge of how when making transitive and intransitive movements to correctly posture and move the forelimb in space; (4) dissociation apraxia, a modality-specific deficit in eliciting learned skilled acts; and (5) limb-kinetic apraxia, a loss of hand-finger deftness.

The function of the left anterior temporal pole: evidence from acute stroke and infarct volume

The role of the anterior temporal lobes in cognition and language has been much debated in the literature over the last few years. Most prevailing theories argue for an important role of the anterior temporal lobe as a semantic hub or a place for the representation of unique entities such as proper names of peoples and places. Lately, a few studies have investigated the role of the most anterior part of the left anterior temporal lobe, the left temporal pole in particular, and argued that the left anterior temporal pole is the area responsible for mapping meaning on to sound through evidence from tasks such as object naming. However, another recent study indicates that bilateral anterior temporal damage is required to cause a clinically significant semantic impairment. In the present study, we tested these hypotheses by evaluating patients with acute stroke before reorganization of structure–function relationships. We compared a group of 20 patients with acute stroke with anterior temporal pole damage to a group of 28 without anterior temporal pole damage matched for infarct volume. We calculated the average percent error in auditory comprehension and naming tasks as a function of infarct volume using a non-parametric regression method. We found that infarct volume was the only predictive variable in the production of semantic errors in both auditory comprehension and object naming tasks. This finding favours the hypothesis that left unilateral anterior temporal pole lesions, even acutely, are unlikely to cause significant deficits in mapping meaning to sound by themselves, although they contribute to networks underlying both naming and comprehension of objects. Therefore, the anterior temporal lobe may be a semantic hub for object meaning, but its role must be represented bilaterally and perhaps redundantly.

Support for anterior temporal involvement in semantic error production in aphasia: new evidence from VLSM

Semantic errors in aphasia (e.g., naming a horse as "dog") frequently arise from faulty mapping of concepts onto lexical items. A recent study by our group used voxel-based lesion-symptom mapping (VLSM) methods with 64 patients with chronic aphasia to identify voxels that carry an association with semantic errors. The strongest associations were found in the left anterior temporal lobe (L-ATL), in the mid- to anterior MTG region. The absence of findings in Wernicke's area was surprising, as were indications that ATL voxels made an essential contribution to the post-semantic stage of lexical access. In this follow-up study, we sought to validate these results by re-defining semantic errors in a manner that was less theory dependent and more consistent with prior lesion studies. As this change also increased the robustness of the dependent variable, it made it possible to perform additional statistical analyses that further refined the interpretation. The results strengthen the evidence for a causal relationship between ATL damage and lexically-based semantic errors in naming and lend confidence to the conclusion that chronic lesions in Wernicke's area are not causally implicated in semantic error production.

Reviewing the limb apraxia concept: From definition to cognitive neuropsychological models

Apraxia is a disorder of learned skilled movements, in the absence of elementary motor or sensory deficits and general cognitive impairment such as inattention to commands, object-recognition deficits or poor oral comprehension. The first studies on apraxia were performed between the late 19th and early 20th centuries, however controversy remains in praxis literature concerning apraxia types, neuroanatomical and functional correlates, as well as assessment and treatment of apraxia. Thus, a critical review of the literature was conducted searching the literature for evidence contributing to a more detailed description of apraxia and its clinical patterns, physiopathology and clinico-anatomical correlations, as well as apraxia assessment.

Cognitive Approach to the Assessment of Limb Apraxia

A new instrument for the assessment of the different levels of gesture processing, as identified by recent cognitive models of apraxia, is presented. The battery comprises thirteen tasks -- eight assess the production of meaningful gestures both on command and on imitation, four tasks assess the ability to recognize and identify gestures, and one task assesses imitation of meaningless gestures. The battery encompasses a novel test of gesture production on visual command. A total of 60 healthy British volunteers were tested with the entire battery. On the whole, participants made more errors with pantomimes than with other tasks. Their scores served as norms.

Apraxia: a review

Praxic functions are frequently altered following brain lesion, giving rise to apraxia - a complex pattern of impairments that is difficult to assess or interpret. In this chapter, we review the current taxonomies of apraxia and related cognitive and neuropsychological models. We also address the questions of the neuroanatomical correlates of apraxia, the relation between apraxia and aphasia and the analysis of apraxic errors. We provide a possible explanation for the difficulties encountered in investigating apraxia and also several approaches to overcome them, such as systematic investigation and modeling studies. Finally, we argue for a multidisciplinary approach. For example, apraxia should be studied in consideration with and could contribute to other fields such as normal motor control, neuroimaging and neurophysiology.

Left Inferior Parietal Representations for Skilled Hand-Object Interactions: Evidence from Stroke and Corticobasal Degeneration

Patients with ideomotor apraxia (IM) are frequently more impaired in the production and imitation of object-related (transitive) than non-object-related, symbolic (intransitive) gestures, but reasons for this dissociation, and its anatomical underpinnings, remain unclear. Our theoretical model of praxis (Buxbaum, 2001) postulates that left inferior parietal lobe (IPL) gesture representations store information about postures and movements of the body and hand for skillful manipulation of familiar objects; in contrast, bilateral fronto-parietal dynamic calculations provide constantly-updated information about the current position and movement of the body and hand for both familiar and novel, transitive and intransitive movements. This account predicts distinct patterns of IM in patients with left IPL damage versus bilateral fronto-parietal involvement. Consistent with predictions, 16 stroke patients with left IPL damage were more impaired with transitive than intransitive gestures, whereas 4 patients with bilateral fronto-parietal damage due to corticobasal degeneration (CBD) were not [F (1, 18) = 8.5 p < .01]. Additionally, the hand posture component of transitive gestures was the most impaired aspect of gesture in CVA, but tended to be the least impaired aspect of gesture in CBD [F (3, 54) = 5.1, p < .005]. Finally, CVA patients were more impaired with transitive hand postures than meaningless or intransitive hand postures, whereas CBD patients showed the opposite pattern. These data indicate that the left IPL mediates representations of skilled hand-object interactions, as distinct from dynamic coding of the body in space, and suggest that the IPL maps between representations of object identity in the ventral stream and spatial body representations mediated by the dorsal system.

[Apraxia--neuroscience and clinical aspects. A literature synthesis]

Apraxic phenomena occur in various neurological conditions. Selective motion control is viewed as the basic capacity to make fine and precise, isolated or independent face or limb movements. Its deficit can indicate limb-kinetic apraxia if it is not explained by paresis, somatosensory deafferentation, or ataxia. The core deficit in ideomotor apraxia could be deficient movement representations, i.e. the combination of invariant features of intrinsic and extrinsic coding for a given movement, which are most important when movements have to be performed outside their typical context. Ideational apraxia would be defined by a semantic deficit related to action. Frontal apraxia is characterised by an action-sequencing deficit. A detailed model is proposed regarding processes relevant to praxis.

Pantomimes are special gestures which rely on working memory

The case of a patient is reported who presented consistently with overt deficits in producing pantomimes in the absence of any other deficits in producing meaningful gestures. This pattern of spared and impaired abilities is difficult to reconcile with the current layout of cognitive models for praxis. This patient also showed clear impairment in a dual-task paradigm, a test taxing the co-ordination aspect of working memory, though performed normally in a series of other neuropsychological measures assessing language, visuo-spatial functions, reasoning function, and executive function. A specific working memory impairment associated with a deficit of pantomiming in the absence of any other disorders in the production of meaningful gestures suggested a way to modify the model to account for the data. Pantomimes are a particular category of gestures, meaningful, yet novel. We posit that by their very nature they call for the intervention of a mechanism to integrate and synthesise perceptual inputs together with information made available from the action semantics (knowledge about objects and functions) and the output lexicon (stored procedural programmes). This processing stage conceived as a temporary workspace where gesture information is actively manipulated, would generate new motor programmes to carry out pantomimes. The model of gesture production is refined to include this workspace.