Pantomimes are special gestures which rely on working memory

Re-examining the gesture engram hypothesis. New perspectives on apraxia of tool use

In everyday life, we are led to reuse the same tools (e.g., fork, hammer, coffee-maker), raising the question as to whether we have to systematically recreate the idea of the manipulation which is associated with these tools. The gesture engram hypothesis offers a straightforward answer to this issue, by suggesting that activation of gesture engrams provides a processing advantage, avoiding portions of the process from being reconstructed de novo with each experience. At first glance, the gesture engram hypothesis appears very plausible. But, behind this beguiling simplicity lies a set of unresolved difficulties: (1) What is the evidence in favour of the idea that the mere observation of a tool is sufficient to activate the corresponding gesture engram? (2) If tool use can be supported by a direct route between a structural description system and gesture engrams, what is the role of knowledge about tool function? (3) And, more importantly, what does it mean to store knowledge about how to manipulate tools? We begin by outlining some of the main formulations of the gesture engram hypothesis. Then, we address each of these issues in more detail. To anticipate our discussion, the gesture engram hypothesis appears to be clearly unsatisfactory, notably because of its incapacity to offer convincing answers to these different issues. We conclude by arguing that neuropsychology may greatly benefit from adopting the hypothesis that the idea of how to manipulate a tool is recreated de novo with each experience, thus opening interesting perspectives for future research on apraxia.

[Structural and functional neuroimaging of the pathophysiology of apraxia]

A better understanding of the neural bases of apraxia is an important prerequisite to develop new therapeutic strategies for the disabling apraxic deficits after left-hemisphere stroke, like disturbed imitation of gestures, deficient pantomime, and object use deficits. Recently, functional and structural imaging methods allowed deeper insights into the pathophysiology of apraxia: While apraxic object use deficits result from the dysfunction of an extended fronto-parietal network within the left hemisphere, pantomime deficits are caused by impaired functioning of the left inferior frontal cortex. Further apraxia-related, motor cognitive processes (i.e., gesture imitation, integration of temporal and spatial movement information, and intentional movement planning) depend on the integrity of the left parietal cortex. Newly developed functional and structural imaging methods, like dynamic causal modelling (DCM) and diffusion tensor imaging (DTI), promise to further elucidate the pathophysiology of apraxia at the network level.

A systematic review of nursing rehabilitation of stroke patients with aphasia

AIM AND OBJECTIVES

To explore the evidence on rehabilitation of stroke patients with aphasia in relation to nursing care, focusing on the following themes: (1) the identification of aphasia, (2) the effectiveness of speech-language interventions.

BACKGROUND

Patients with poststroke aphasia have higher mortality rates and worse functional outcome than patients without aphasia. Nurses are well aware of aphasia and the associated problems for patients with stroke because they have daily contact with them. The challenge is to provide evidence-based care directed at the aphasia. Although rehabilitation stroke guidelines are available, they do not address the caregiving of nurses to patients with aphasia.

DESIGN

Systematic review.

METHOD

Published studies were reviewed, focusing on identification and treatment of aphasic patients after stroke in terms of the consequences for nursing care. Also, data concerning effective speech-language interventions were extrapolated into nursing practice with respect to the classification of nursing interventions.

RESULTS

Intensive speech-language therapy, which was initiated in the acute stage post stroke, showed the best rehabilitation outcomes. Trained persons other than speech-language therapists provided effective speech-language interventions. Speech-language therapy included several types of intervention that met nursing intervention classifications.

CONCLUSION

The contribution of nursing to the rehabilitation of patients with aphasia is relevant. The use of screening instruments by nurses can increase early detection of aphasia, a precondition for initiating timely speech-language therapy. Collaboration between speech-language therapists and nurses is of the utmost importance for increasing the intensity and functionality of speech-language exercises, which may enhance the quality of treatment.

RELEVANCE TO CLINICAL PRACTICE

The findings of this study can be used to develop nursing rehabilitation guidelines for stroke patients with aphasia. Further research is necessary to explore the feasibility of using such guidelines in clinical nursing practice and to examine the experiences of patients with nursing interventions directed at aphasia.

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.

Rehabilitation of gesture imitation: a case study with fMRI

Acquired disorders of gesture imitation are amenable to treatment, but with poor generalisation toward gestures not included in the training program. We investigated the neural basis of this item-specific recovery in a patient with a slowly progressive posterior cortical atrophy, by means of an fMRI study comparing imitation of rehabilitated and not-rehabilitated gestures. Results suggested that in our patient gesture imitation recruited the mirror system and additional areas relevant to gesture analysis and preparation. Imitation of rehabilitated gestures activated the mirror neuron system, and also left dorsolateral prefrontal cortex and putamen, and the right anterior temporal cortex. This suggests that item-specific recovery was based on interaction of circuitry of imitation with neural systems involved in emotional and motivational processing.

Memory for pantomimed actions versus actions with real objects

A substantial literature indicates that human actions during object use and pantomimed object use are not identical, and can be differentially affected by brain damage such that apraxic patients can be more impaired in performing actions with objects or at pantomiming such actions. A different literature suggests that memory retrieval can involve re-instating or recapitulating some of the same brain activity that occurred during the original event. The current experiment examines memory for pantomimed actions versus those conducted with real objects to determine if accuracy or brain electrical activity differs during the recollection of episodes involving pantomime versus actual object use. Across two sessions, participants were presented with images of studied objects and judged whether each object was studied by (1) performing an action, (2) watching the experimenter perform an action, (3) imagining an action, or (4) the nonmotoric control task of estimating the object's cost. The study phases preceding this source memory test differed across sessions: in one, participants were presented with real objects and estimated its cost or performed, watched, or imagined typical actions with the objects; in the other they viewed images of each object and estimated its cost or performed, imagined, or watched pantomimes of object use. Although source accuracy was the same across sessions, event-related potentials (ERPs) recorded during memory retrieval differed for memory for actions with real objects versus their pantomime equivalents. Retrieval-phase activity did not differ for cost-encoded objects. The real-object/pantomime difference in brain activity was maximal over left frontal and frontocentral cortex, suggesting differential engagement of motor cortex during memory for real actions versus pantomimed actions.

An experimental investigation of the automatic/voluntary dissociation in limb apraxia

The ability of apraxic patients to perform gestures in everyday life is a controversial issue. In this paper, we aimed to evaluate the automatic/voluntary dissociation (AVD) in four patients affected by clinically relevant limb apraxia. For this purpose, we sampled different kinds of gestures belonging to patients' motor repertoire and then assessed their production in a testing session. Our experimental procedure consisted of two steps: in the first phase, we recorded gestures produced by patients in two natural conditions; in the second phase, we assessed production of correctly produced tool-actions, and of spontaneous non tool-actions and meaningless conversational (cohesive and beats) gestures under different modalities. AVD was observed for all types of gestures, albeit to different degree in single patients. The present findings demonstrate that the context provides strong bottom-up cues for the retrieval of motor patterns, while artificial testing conditions impose an additional cognitive load.

Ideomotor apraxia: A review

Ideomotor apraxia (IMA) is a disorder traditionally characterized by deficits in properly performing tool-use pantomimes (e.g., pretending to use a hammer) and communicative gestures (e.g., waving goodbye). These deficits are typically identified with movements made to verbal command or imitation. Questions about this disorder relate to its diagnosis, anatomical correlates, physiological mechanisms involved, and the patients in whom IMA is best characterized. In this review, utilizing information presented at an international workshop, we summarize the present state of knowledge about IMA. We include insights on how to distinguish IMA from the other motor apraxias and confounding disorders. We discuss testing for IMA and the need for more rigorous tests that examine more elements, such as imitation, actual use, task selection, and recognizing proper use. From neurophysiological insights, we propose hypotheses of the necessity of networks in praxis performance. We also point out that more neurophysiological knowledge in humans might lead to a better understanding of how different brain structures may aid in the rehabilitation of praxis. While little is known about exactly how rehabilitation may be pursued, biological evidence warrants the further exploration of this issue.

Processing the spatial configuration of complex actions involves right posterior parietal cortex: An fMRI study with clinical implications

The left hemispheric dominance for complex motor behavior is undisputed. Clinical observations of complex motor deficits in patients with right hemispheric lesions, however, suggest an additional contribution of the right hemisphere to higher motor control. We assessed, using functional MRI (fMRI), which brain regions are implicated in processing the spatial aspects of complex, object-related actions. Using a blocked, factorial design, 17 healthy volunteers were asked to detect either spatial or sequential errors (factor ERROR) in complex activities of daily living, presented as video sequences with the appropriate object(s) or as pantomimes (factor STIMULUS). Observing complex actions (irrespective of stimulus type) activated a bilateral frontoparietal network. Observing actions with objects (relative to pantomimes) differentially increased neural activity in the fusiform gyrus and inferior occipital cortex bilaterally. Observing pantomimes, i.e., the same actions but without any object, differentially activated right prefrontal cortex, anterior cingulate cortex, the precuneus, and left cerebellum. The left cingulate cortex was differentially activated when subjects assessed the sequencing of actions. By contrast, assessing the spatial configuration of complex actions differentially increased neural activity in right posterior parietal cortex. A significant interaction of ERROR and STIMULUS was revealed for the right inferior parietal cortex only. These findings suggest a specific role of the right hemisphere, especially of right posterior parietal cortex, in processing spatial aspects of complex actions and thus provide a physiological basis for the observed apraxic motor deficits in patients with right hemispheric damage.

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.

Posterior parietal negativity preceding self-paced praxis movements

Studies of movement-related cortical potentials (MRCPs) for simple movements have shown a slowly rising negativity (Bereitschaftspotential, or BP) about 2 s prior to movement onset, centered in the bilateral sensorimotor area. However, complex movements may elicit a different temporal and spatial distribution of this pre-movement activity. In this study, 64-channel electroencephalography (EEG) was recorded while normal volunteers were asked to perform a simple thumb adduction once every 10--15 s for three 10--15 min blocks. Following this, they were asked to make tool-use movements (hammer, scissor, and screwdriver pantomime) in the same manner. Surface electromyography (EMG) was recorded on the thumb adductor and forearm flexor. MRCP was analyzed for the beginning part of the epoch (from 3.5 s to 1.5 s before EMG onset, with 0.5 s time bins) for differences in the amplitude and spatial distribution of the BP. Significant differences were seen from 3.0 s to 2.0 s before EMG onset, where the amplitude was greater for the more complex movements. On average, negativity began at 3.0 s before onset for praxis movements, and only 1.7 s before onset for thumb adduction. Additionally, the negativity seen for the complex movements had a distribution beginning over the left hemisphere posterior parietal area, whereas, thumb adduction movements had a more anterior distribution, over the bilateral sensorimotor area. The posterior parietal negativity (PPN) suggests that early parietal activity is essential for tool-use movements and is not a part of preparing simple movements.

Temporal activation pattern of parietal and premotor areas related to praxis movements

OBJECTIVE

We sought to determine the cortical physiology underlying praxis movements in normal subjects using electroencephalography (EEG).

METHODS

Eight normal subjects were instructed to perform six types of self-paced tool-use pantomime and communicative gesture movements with the right hand. We recorded 64-channel EEG using a linked ear reference and electromyogram (EMG) from right thumb and forearm flexors.

RESULTS

Data revealed early slow wave components of the movement-related cortical potential (MRCP) beginning over the left parietal area about 3s before movement onset, similarly for both movement types. At movement onset, maximal amplitude was present over central and bilateral sensorimotor areas. Event-related desynchronization (ERD) in the beta band was seen over the left parietal and sensorimotor cortices during preparation, later spreading to the homologous area of the right hemisphere. Alpha ERD was mainly in the left sensorimotor cortex about 1.5s before movement onset. Beta ERD in mesial frontal areas was greater during preparation for tool use compared to communicative gesture movements. Mesial frontal beta event-related synchronization (ERS) developed more rapidly after communicative gestures than tool-use.

CONCLUSIONS

The dynamics of parietal and frontal activities indicates the timing of these areas in the production of praxis. The posterior parietal cortex contributes to the early slow wave negativity of the MRCP.

SIGNIFICANCE

Planning self-paced praxis movements begins as early as 3s before movement in the left parietal area and subsequently engages frontal cortical regions.

Synchronization of parietal and premotor areas during preparation and execution of praxis hand movements

OBJECTIVE

We sought to determine temporal patterns of functional connectivity between the parietal, premotor, and motor cortices during preparation and execution of praxis hand movements.

METHODS

Normal subjects were instructed to perform six transitive (tool use) and intransitive (communicative gesture) self-paced pantomimes with the right hand while recording 64-channel electroencephalography (EEG) and electromyography (EMG) from right thumb and forearm flexors. Focusing on corticocortical coherence, we explored the time-course of synchronously active parietal and premotor circuits involved in these motor tasks. Trials were marked for EMG onset and averaged across subjects to determine changes in coherence relative to baseline between parietal, premotor, and motor areas.

RESULTS

Coherence of homologous electrode pairs was similar when comparing transitive and intransitive movements. During preparation, beta band (18-22 Hz) coherence was maximal between electrodes over the left parietal lobe and left premotor electrodes. Additionally during preparation, the premotor area showed high coherence to the motor hand area and the parietal cortex. Electrodes over the supplementary motor area also showed coherence to the motor and parietal, but not the premotor area. Before and during execution, a second peak of high coherence increase was present in each area that demonstrated coherence increases during preparation. There was no coherence increase between parietal and motor areas. Coherence rapidly diminished 1.5-2.0 s after movement onset.

CONCLUSIONS

Patterns of increased corticocortical coupling within a parietal, premotor, and motor network are present during preparation and execution of praxis movements.

SIGNIFICANCE

This study adds to evidence that parietofrontal networks may be critical for integrating preparatory and motor-related activity for praxis movements.

Apraxia

In this review, we present a summary of some of the most pertinent new research on aspects of apraxia. Rather than attempt a review of all neurologic syndromes that have been identified as forms of apraxia, such as buccofacial, truncal, apraxia of eye opening, and apraxia of speech, we focus on current literature and trends in the study of limb apraxia. Although the classic empirical approach to the study of apraxia has been through systematic neuropsychologic assessment of various aspects of the syndrome, questions remain regarding the exact neural substrate that forms the foundation of the praxis system. More recent work using sophisticated neuroimaging methods has yielded a wealth of new data that contributes significantly to our understanding of the neuroanatomic correlates of this complex disorder. In addition, the results of recent sophisticated neuropsychologic studies have suggested modifications to classic cognitive models of apraxia. A discussion of current work and directions for future research are also provided.