Dyspraxia in a patient with corticobasal degeneration: the role of visual and tactile inputs to action

The social cognitive dimension of pantomime

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

Pantomime of tool use: looking beyond apraxia

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

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The challenge of apraxia: Toward an operational definition?

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

Language impairment in progressive supranuclear palsy and corticobasal syndrome

Although commonly known as movement disorders, progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS) may present with changes in speech and language alongside or even before motor symptoms. The differential diagnosis of these two disorders can be challenging, especially in the early stages. Here we review their impact on speech and language. We discuss the neurobiological and clinical-phenomenological overlap of PSP and CBS with each other, and with other disorders including non-fluent agrammatic primary progressive aphasia and primary progressive apraxia of speech. Because language impairment is often an early and persistent problem in CBS and PSP, there is a need for improved methods for language screening in primary and secondary care, and more detailed language assessments in tertiary healthcare settings. Improved language assessment may aid differential diagnosis as well as inform clinical management decisions.

Anosognosia for limb and bucco-facial apraxia as inferred from the recognition of gestural errors

Anosognosia is a multifaceted syndrome characterized by a lack of awareness of motor, cognitive, or emotional deficits. While most studies have focused on basic motor disorders such as hemiplegia, only recently, the issue of whether anosognosia also concerns higher-order motor disorders like apraxia has been addressed. Here, we explore the existence of a specific form of anosognosia for apraxia in forty patients with uni-hemispheric vascular lesions. The patients were requested to imitate actions involving upper limb or bucco-facial body parts and then judge their performance. Successively, they were also asked to observe video recordings of the same actions performed by themselves or by other patients and judge the accuracy of the displayed actions. The comparison of participants versus examiner judgement and between error recognition of others' versus self's actions was considered as an index of awareness deficit for the online and offline conditions, respectively. Evidence was found that awareness deficits occurred both immediately after action execution (online anosognosia) and in the video recording task (offline anosognosia). Moreover, bucco-facial and limb apraxic patients were specifically unaware of their errors in bucco-facial and limb actions, respectively, indicating for the first time a topographical organization of the syndrome. Our approach allowed us to distinguish awareness deficits from more general disorders in error recognition; indeed, anosognosic patients were able to identify errors when the same action was executed by another patient but not when the video showed their own actions. Finally, we provide evidence that anosognosia for apraxia might be associated with frontal cortical and subcortical networks.

A progressive breakdown of the body in space

A 74 year-old woman (MD), free of previous neurological history, presented with difficulty in handling cutlery, clothes, writing with what was initially described as an atypical apraxia in acts related to space. Initial neurological evaluation revealed mixed, asymmetric pyramidal, and extrapyramidal semiology. Νeuropsychological testing revealed dressing and constructional deficits, ideomotor apraxia and signs of executive dysfunction in absence of memory, language, and visual perception pathology. The final diagnosis was that of a corticobasal degeneration, where the rare occurrence of a progressively emerging syndrome of self-management loss within peripersonal space is observed.

Creating Affording Situations: Coaching through Animate Objects

We explore the ways in which animate objects can be used to cue actions as part of coaching in Activities of Daily Living (ADL). In this case, changing the appearance or behavior of a physical object is intended to cue actions which are appropriate for a given context. The context is defined by the intention of the users, the state of the objects and the tasks for which these objects can be used. We present initial design prototypes and simple user trials which explore the impact of different cues on activity. It is shown that raising the handle of a jug, for example, not only cues the act of picking up the jug but also encourages use of the hand adjacent to the handle; that combinations of lights (on the objects) and auditory cues influence activity through reducing uncertainty; and that cueing can challenge pre-learned action sequences. We interpret these results in terms of the idea that the animate objects can be used to create affording situations, and discuss implications of this work to support relearning of ADL following brain damage or injury, such as might arise following a stroke.

The role of the motor system in action naming in patients with neurodegenerative extrapyramidal syndromes

Previous studies of patients with brain damage have suggested a close relationship between aphasia and movement disorders. Neurodegenerative extrapyramidal syndromes associated with cognitive impairment provide an interesting model for studying the neural substrates of cognitive and motor symptoms. In this review, we focused on studies investigating language production abilities in patients with Parkinson's disease (PD), Corticobasal Syndrome (CBS) and Progressive Supranuclear Palsy (PSP). According to some reports, these patients exhibit a reduction in performance in both action and object naming or verb production compared to healthy individuals. Furthermore, a disproportional impairment of action naming compared to object naming was systematically observed in patients with these disorders. The study of these clinical conditions offers the unique opportunity to examine the close link between linguistic features and motor characteristics of action. This particular pattern of language impairment may contribute to the debate on embodiment theory and on the involvement of the basal ganglia in language and in integrating language and movement. From a translational perspective, we suggest that language ability assessments are useful in the clinical work-up, along with neuropsychological and motor evaluations. Specific protocols should be developed in the near future to better characterize language deficits and to permit an early cognitive diagnosis. Moreover, the link between language deficits and motor impairment opens a new issue for treatment approaches. Treatment of one of these two symptoms may ameliorate the other, and treating both may produce a greater improvement in patients' global clinical conditions.

Persistent sparing of action conceptual processing in spite of increasing disorders of action production: A case against motor embodiment of action concepts

In this study, we addressed the issue of whether the brain sensorimotor circuitry that controls action production is causally involved in representing and processing action-related concepts. We examined the three-year pattern of evolution of brain atrophy, action production disorders, and action-related concept processing in a patient (J.R.) diagnosed with corticobasal degeneration. During the period of investigation, J.R. presented with increasing action production disorders resulting from increasing bilateral atrophy in cortical and subcortical regions involved in the sensorimotor control of actions (notably, the superior parietal cortex, the primary motor and premotor cortex, the inferior frontal gyrus, and the basal ganglia). In contrast, the patient's performance in processing action-related concepts remained intact during the same period. This finding indicated that action concept processing hinges on cognitive and neural resources that are mostly distinct from those underlying the sensorimotor control of actions.

The Representation of Objects in Apraxia: From Action Execution to Error Awareness

Apraxia is a well-known syndrome characterized by the sufferer's inability to perform routine gestures. In an attempt to understand the syndrome better, various different theories have been developed and a number of classifications of different subtypes have been proposed. In this article review, we will address these theories with a specific focus on how the use of objects helps us to better understand upper limb apraxia. With this aim, we will consider transitive vs. intransitive action dissociation as well as less frequent types of apraxia involving objects, i.e., constructive apraxia and magnetic apraxia. Pantomime and the imitation of objects in use are also considered with a view to dissociating the various different components involved in upper limb apraxia. Finally, we discuss the evidence relating to action recognition and awareness of errors in the execution of actions. Various different components concerning the use of objects emerge from our analysis and the results show that knowledge of an object and sensory-motor representations are supported by other functions such as spatial and body representations, executive functions and monitoring systems.

Progression of limb apraxia in corticobasal syndrome: neuropychological and functional neuroimaging report of a case series

The current study described the progression of limb apraxia in seven corticobasal syndrome patients through a comprehensive battery, including both gesture production tasks and conceptual tool/action knowledge tasks. The examination of the behavioral and neuroimaging (SPECT) data revealed two patient subgroups. One group consisted of patients with preserved conceptual tool/action knowledge, relatively mild gesture production and neuropsychological deficits with few significantly hypoperfused regions of interest. The other group consisted of those whose conceptual tool/action knowledge and general cognition eventually deteriorated and who were quite severely affected in their gesture production performance. These patients were characterized by bilateral hypoperfusion in parietal regions and in one case bilateral anterior cingulate regions.

Limb apraxia in neurodegenerative disorders

SUMMARY Apraxia is a cognitive-motor disorder affecting gestural communication and tool use, and is seen in various neurodegenerative disorders. Apraxia is a major feature of the corticobasal syndrome associated with nonlevodopa-responsive, typically asymmetric parkinsonism. Mild apraxia may also be seen in Parkinson’s disease, at least in later stages of the disease. Furthermore, patients with Alzheimer’s disease or posterior cortical atrophy are prone to develop apraxia during their disease course. However, apraxia may be difficult to dissect from other motor (e.g., dystonia and bradykinesia in corticobasal syndrome) or cognitive (e.g., dysexecutive or semantic memory deficits in Alzheimer’s disease) dysfunction. Therefore, the ecological significance of apraxia in neurodegenerative disorders may not always be obvious. Although treatment protocols for apraxia have been developed in stroke, there is little information on the management of apraxia in neurodegenerative disorders. Owing to their progressive nature, benefits from therapeutic interventions are certainly limited, although some capacity of motor learning may be preserved, at least in earlier disease stages. In advanced cases, management of apraxia should focus on compensatory measures, for instance, on adapting the patient’s environment to their needs, particularly when related to safety and comfort.

The benefits and protective effects of behavioural treatment for dysgraphia in a case of primary progressive aphasia

BACKGROUND: Spoken and written language difficulties are the predominant symptoms in the progressive neurodegenerative disease referred to as primary progressive aphasia (PPA). There has been very little research on the effectiveness of intervention on spoken language impairments in this context and none directed specifically at progressive written language impairment. AIMS: To examine the effectiveness of behavioural intervention for dysgraphia in a case of primary progressive aphasia. METHODS #ENTITYSTARTX00026; PROCEDURES: We carried out a longitudinal single-case study that allowed us to examine the effectiveness of a non-intensive spell-study-spell intervention procedure. We did so by comparing performance on four sets of words: trained, repeated, homework, and control words at five evaluations: baseline, during intervention, after the intervention, and at 6- and 12-month follow-up. OUTCOMES #ENTITYSTARTX00026; RESULTS: We find that: (1) at the end of the intervention, Trained words show a small but statistically significant improvement relative to baseline and an advantage in accuracy over Control, Homework, and Repeated word sets. (2) All word sets exhibited a decline in accuracy from the end of treatment to the 6-month follow-up evaluation, consistent with the degenerative nature of the illness. Nonetheless, accuracy on Trained words continued to be superior to that of Control words and not statistically different from pre-intervention baseline levels. (3) Repeated testing and practice at home yielded modest numerical advantages relative to Control words; but these differences were, for many comparisons, not statistically significant. (4) At 12 months post-intervention, all words sets had significantly declined relative to pre-intervention baselines and performance on the four sets was comparable. CONCLUSIONS: This investigation documents-for the first time-that behavioural intervention can provide both immediate and short-term benefits for dysgraphia in the context of primary progressive aphasia.

Update on apraxia

Apraxia is classically defined as difficulty performing learned, skilled gestures. In this review, we describe the range of motor impairments classified as apraxia, focusing on ideomotor limb apraxia. We present several prominent models of praxis to explain the variety of difficulties seen in patients with apraxia. We also discuss the large-scale frontal-parietal-basal ganglia network thought to underlie praxis. In this context, we highlight the common occurrence of limb apraxia in corticobasal degeneration, a neurodegenerative condition characterized by frontal, parietal, and basal ganglia disease.

Longitudinal assessment of language and memory impairments in pathologically confirmed cortico-basal ganglionic degeneration

We report a longitudinal case study (patient EP) of histologically confirmed cortico-basal ganglionic degeneration (CBD) who presented with non-fluent progressive aphasia (NFPA). While NFPA has been documented in clinical descriptions of other reports of CBD, details are often limited and the majority of studies are cross-sectional in nature. The present study conducted detailed longitudinal assessment with EP over a period of two years that revealed substantial impairments of episodic memory, semantic memory, naming and particular aspects of reading and spelling. Our investigations identify key features of EP's pattern of impairment that warrant further examination with other cases of CBD. In particular, testing of EP's nonword reading and spelling found that both were impaired and declined over time. In addition, verbal recognition deteriorated faster than non-verbal recognition through the course of the disease. Our review of the literature suggests that poor nonword reading and spelling may be consistent features of CBD, but more studies are needed to confirm this suggestion, and to determine whether they warrant inclusion in profiling CBD.

Retrieval by a patient with apraxia of sensorimotor information from visually presented objects

Motor representations are reported to be implicitly evoked when one observes manipulatable objects (action potentiation). The relationship was examined between action potentiation and pantomime deficit in apraxia. Participants responded to line drawings of manipulatable objects with either the left or right hand, according to the color of the stimulus. In normal participants (N= 10, four women, six men, M age = 28.5 yr., SD = 5.6), responses were faster when the orientation of the stimulus was compatible with the response-hand grasp. However, the apraxic patient did not exhibit this compatibility effect. On a control task in which a nonobject (circle) was presented, all participants exhibited the compatibility effect. These results indicated that the apraxic patient was impaired in evoking motor representation associated with objects. Thus, in some cases, apraxic disorders may be attributable to a deficit in retrieving object-specific information for manipulation.

Treatment of dementia in parkinsonian syndromes with cholinesterase inhibitors

In Parkinsonian syndromes behavioural symptoms and dementia can be even more debilitating than motor symptoms and are an important predictor for nursing home placement and mortality. Neuropathologically, dementia seems to be primarily related to cortical changes rather than to subcortical alterations. Concerning neurotransmitter systems, the cholinergic system has been proposed to play a key role in cognitive disturbances. Based on studies with patients with Alzheimer disease, the application of cholinesterase inhibitors is vividly discussed also for dementia associated with parkinsonian syndromes. This review focuses on the specific symptoms of dementia in different parkinsonian syndromes and critically questions the effect of cholinergic treatment on cognitive functions in patients with extrapyramidal syndromes and dementia. There is evidence that medication with some cholinesterase inhibitors can enhance cognition as well as activities of daily living in dementia with Parkinson's disease and seems to reduce behavioural disturbances in both dementia with Parkinson's disease and dementia with Lewy bodies. The effect of treatment with cholinesterase inhibitors in progressive supranuclear palsy and corticobasal degeneration warrants carefully designed studies including a sufficient number of patients and symptom-adopted dementia scales.

The syndrome of progressive posterior cortical dysfunction: A multiple case study and review

Dementia presenting with prominent higher order visual symptoms may be observed in a range of neurodegenerative conditions and is often challenging to diagnose.

OBJECTIVES

To describe cases of progressive dementia presenting with prominent visual cortical symptoms.

METHODS

We conducted a retrospective search of cases of progressive dementia with predominant visual symptoms, seen at our dementia unit from 1996 to 2006.

RESULTS

Twelve patients (5 men, 7 women) were identified, with ages ranging from 49 to 67 years. At the first examination, the duration of the symptoms ranged from one to ten years and the Mini-Mental State Examination scores from 7 to 27. Eleven patients presented with predominant visuospatial symptoms (partial or complete Balint syndrome) and one with visuoperceptive impairment. Other reported manifestations were: constructional apraxia in 11 patients, partial or complete Gerstmann syndrome in ten, ideomotor apraxia in nine, hemineglect or extinction in four patients, alien hand phenomenon in three, and prosopagnosia in one patient. Memory loss was reported by ten patients, but was not the main complaint in any of these cases. Insight was relatively preserved in five patients even after a long period following the onset of symptoms. Six patients developed parkinsonism during evolution. Clinical diagnoses were possible or probable AD in seven patients, cortico-basal degeneration in four, and dementia with Lewy body in one.

CONCLUSIONS

Clinicians should consider this condition especially in presenile patients with slowly progressive higher-order visual symptoms. Although described in association with different conditions, it may also occur in Alzheimer disease.

The deficit for the word-class “verb” in corticobasal degeneration: Linguistic expression of the movement disorder?

We describe five patients with corticobasal degeneration who had apraxia with an ideational component and reduced action/verb naming ability. Patients also had difficulty in a series of tasks devised to explore the conceptual representation of actions associated with manipulable objects, such as action recognition, action miming and pantomime recognition; however, their ability to name manipulable objects was comparatively preserved. According to the current interpretation of ideational apraxia [De Renzi, E., & Lucchelli, F. (1988). Ideational apraxia. Brain, 111, 1173-1185] we considered the patients' apraxic disorder as the motor expression of decay of the action representation and we hypothesized that this may also have contributed to the action-naming deficit. The results are discussed within a "multimodal model" of semantic memory in which the concept of action is seen as the product of the integration between sensorial and motor attributes. We suggest that corticobasal degeneration might offer a unique opportunity to validate this model because it is typically characterized by a frontoparietal damage [Gibb, W. R., Luthert, P. J., & Marsden, C. D. (1989). Corticobasal degeneration. Brain, 1, 1171-1192] that prevents integration of sensory and motor information. We conclude that the selective impairment of action/verb should also be studied from the point of view of a movement disorder and not only in terms of a lexical-semantic deficit.

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.

Clinical characteristics of corticobasal syndrome amongst Chinese in Taiwan

This study reviewed the clinical characteristics of nine patients, the female-to-male ratio being 2 (6/3), with corticobasal syndrome (CBS) from 2001 to 2006. The mean age of onset was 60.33+/-5.20 years. The most popular symptom was rigidity (100%), followed by bradykinesia (88.89%), apraxia (88.89%) and dystonia (66.67%). The common presentations in neuropsychological assessment included frontal dysfunction (88.89%), disorientation (66.67%), memory impairments (66.67%) and visuospecial defects (66.67%). Single proton emission-computed tomography (CT) showed hypoperfusion at contralateral basal ganglia, thalamic, parietal or temporal region in eight of nine patients. This investigation suggests that functional neuroimages and neuropsychological tests are useful tools for the diagnosis of CBS.

Quantifier comprehension in corticobasal degeneration

In this study, we investigated patients with focal neurodegenerative diseases to examine a formal linguistic distinction between classes of generalized quantifiers, like "some X" and "less than half of X." Our model of quantifier comprehension proposes that number knowledge is required to understand both first-order and higher-order quantifiers. The present results demonstrate that corticobasal degeneration (CBD) patients, who have number knowledge impairments but little evidence for a deficit understanding other aspects of language, are impaired in their comprehension of quantifiers relative to healthy seniors, Alzheimer's disease (AD) and frontotemporal dementia (FTD) patients [F(3,77)=4.98; p<.005]. Moreover, our model attempts to honor a distinction in complexity between classes of quantifiers such that working memory is required to comprehend higher-order quantifiers. Our results support this distinction by demonstrating that FTD and AD patients, who have working memory limitations, have greater difficulty understanding higher-order quantifiers relative to first-order quantifiers [F(1,77)=124.29; p<.001]. An important implication of these findings is that the meaning of generalized quantifiers appears to involve two dissociable components, number knowledge and working memory, which are supported by distinct brain regions.

Spatial and kinematic features of apraxic movement depend on the mode of execution

Knowledge about the dependency of apraxic movements on the mode of execution may enhance the understanding of apraxia and of the cerebral representation of actions. We examined a common tool-use action in nine patients with left hemisphere damage and apraxia. Arm movements during the use of a handsaw were measured and tested in three different modes of execution: pantomime, pantomime with a bar shaped like the handle of the saw, and actual sawing. Analysis concentrated on spatial and kinematic features of the wrist trajectories during these repetitive movements. In healthy control subjects, both pantomime conditions differed from actual use mainly by larger amplitudes during miming. Apraxic patients executed large proportions of their pantomiming movements in an incorrect direction away from the appropriate anteroposterior direction, while other movement features were normal. The availability of the handle-like bar did not improve performance. During actual use, movement direction was constraint by mechanical demands. In this condition patients moved with moderately decreased velocity. However, this deficit was not related to the errors in movement direction characteristic of pantomiming. These data suggest that pantomiming and actual execution of an action are dictated by different external requirements and constraints, pantomiming serves to convey information, while actual use has to obey the mechanical demands of the task. Due to these differences, spatial and kinematic movement features in healthy subjects vary between the modes of execution, movements are differently vulnerable to apraxia, and deficits in patients may dissociate.

Posterior cortical atrophy: a review of the literature

The past three decades have seen an accumulation of reports of neurodegenerative disease with disruption to visual processing. Disorders of both visuospatial processing and visual recognition have been described, though the former predominate. But the conundrum of posterior cortical atrophy (PCA) is that while the clinical presentation is relatively homogeneous, the nosological status remains something of a puzzle. Many cases coming to pathology have had Alzheimer's Disease (AD) but in a different distribution from that seen in typical AD (tAD). Patients with non-specific subcortical gliosis and, more occasionally, Creutzfeldt Jacob disease, neither of which have an obvious affinity with PCA, have also been described. On the other hand, no case of PCA has been reported with the pathology of either corticobasal degeneration or dementia with Lewy Bodies, both of which do commonly present with prominent parietal symptomatology.

Corticobasal degeneration as a cognitive disorder

The presence of cognitive impairment in corticobasal degeneration (CBD) is now widely recognised. Our review of the literature reveals that, although the pattern and severity of neuropsychological impairments can be highly variable across patients, several general trends can be identified. The most characteristic impairments are limb apraxia (usually ideomotor), constructional and visuospatial difficulties, acalculia, frontal dysfunction, and nonfluent aphasia. The limb apraxia is associated with deficits in drawing, copying, and handwriting, but there is emerging evidence that the problems with handwriting are not due exclusively to the apraxia. The findings with respect to episodic memory are more variable, but when there is impairment in this area, it tends to be milder than that seen in Alzheimer's disease. Semantic memory functioning appears relatively preserved but has been poorly studied. Problems with speech are common, and may be due to dysarthria or buccofacial apraxia. Aphasia, although initially considered rare, is in fact a common accompaniment of CBD, may be the presenting feature, and is typically nonfluent in type. More systematic investigation of the clinical and neuropathological overlap between progressive nonfluent aphasia (generally considered to be a form of frontotemporal dementia) and CBD is needed.

Alien hand phenomena: a review with the addition of six personal cases

This is a comprehensive literature review of the motor abnormalities that have come to be included under the designation of Alien Hand Phenomena (AHP). Some of the disorders are dyspractic in nature - intermanual conflict, mirror movements, interference etc., while others - groping, grasping with inability to release, utilization etc. are frontal lobe reflexes. AHP are mainly associated with two pathological processes: 1) Infarction or hemorrhage in the territory of the anterior cerebral arteries; and 2) Corticobasal degeneration. Included in the review is a description of AHP in six personal cases of corticobasal degeneration. The summary includes a short discussion of the possible anatomy of 'free will' based on AHP.