A model‐based approach to limb apraxia in Alzheimer's disease

Limb apraxia is a neurological deficit characterized by an inability to pantomime and/or imitate gestures, which can result from neurodegenerative disorders such as Alzheimer's disease (AD). The major goal of the study was to describe comprehensively the apraxia deficits observed in AD patients and to relate those deficits to general cognitive status, measures of daily activity, and other neuropsychological measures. Limb apraxia was assessed on a variety of conceptual and gesture production tasks in 30 AD patients. As a group, AD patients were impaired across gesture production tasks: of note was the greater impairment in imitation, as opposed to pantomime, which was especially pronounced when patients were imitating with a delay. Imitation performance was best predicted by measures of visuospatial processing, while imitation with delay was best predicted by measures of working memory. In addition, pantomime in response to pictures of tools was less accurate than Pantomime to Verbal Command and holding the tool during performance did not decrease the participants' impairment, while introducing a verbal cue during imitation increased the severity of deficits. Furthermore, investigation into patterns of deficits clearly demonstrated that the nature of limb apraxia deficits observed in AD can be quite heterogeneous and that dissociations between the conceptual and the production system exist. Finally, we also report on significant correlations between general cognitive status and limb apraxia.     

A Model-Based Approach to Understanding Apraxia in Corticobasal Syndrome

Limb apraxia is a neurological disorder of higher cognitive function characterized by an inability to perform purposeful skilled movements and not attributable to an elementary sensorimotor dysfunction or comprehension difficulty. Corticobasal Syndrome (CBS) is an akinetic rigid syndrome with asymmetric onset and progression with at least one basal ganglia feature (rigidity, limb dystonia or myoclonus) and one cortical feature (limb apraxia, alien hand syndrome or cortical sensory loss). Even though limb apraxia is highly prevalent in CBS (70–80%), very few studies have examined the performance of CBS patients on praxis measures in detail. This review aims to (1) briefly summarize the clinical, neuroanatomical and pathological findings in CBS, (2) briefly outline what limb apraxia is and how it is assessed, (3) to comprehensively review the literature on limb apraxia in CBS to date and (4) to briefly summarize the literature on other forms of apraxia, such as limb-kinetic apraxia and buccofacial apraxia. Overall, the goal of the review is to bring a model-based perspective to the findings available in the literature to date on limb apraxia in CBS.     

Associations and dissociations of transitive and intransitive gestures in left and right hemisphere stroke patients

The study investigated performance on pantomime and imitation of transitive and intransitive gestures in 80 stroke patients, 42 with left (LHD) and 38 with right (RHD) hemisphere damage. Patients were also categorized in two groups based on the time that has elapsed between their stroke and the apraxia assessment: acute–subacute (n = 42) and chronic (n = 38). In addition, patterns of performance in apraxia were examined. We expected that acute–subacute patients would be more impaired than chronic patients and that LHD patients would be more impaired than RHD patients, relative to controls. The hemisphere prediction was confirmed, replicating previous findings. The frequency of apraxia was also higher in all LHD time post-stroke groups. The most common impairment after LHD was impairment in both pantomime and imitation in both transitive and intransitive gestures. Selective deficits in imitation were more frequent after RHD for transitive gestures but for intransitive gestures they were more frequent after LHD. Patients were more impaired on imitation than pantomime, relative to controls. In addition, after looking at both gesture types concurrently, we have described cases of patients who suffered deficits in pantomime of intransitive gestures with preserved performance on transitive gestures. Such cases show that the right hemisphere may be in some cases critical for the successful pantomime of intransitive gestures and the neural networks subserving them may be distinct. Chronic patients were also less impaired than acute–subacute patients, even though the difference did not reach significance. A longitudinal study is needed to examine the recovery patterns in both LHD and RHD patients.     

An update on the Conceptual-Production Systems model of apraxia: evidence from stroke

Limb apraxia is a neurological disorder characterized by an inability to pantomime and/or imitate gestures. It is more commonly observed after left hemisphere damage (LHD), but has also been reported after right hemisphere damage (RHD). The Conceptual-Production Systems model (Roy, 1996) suggests that three systems are involved in the control of purposeful movements: the conceptual, the production and the sensory/perceptual system. Depending on which system is damaged different patterns of apraxia are expressed. To determine the apraxia pattern, pantomime, delayed, and concurrent imitation tasks need to be administered, as well as conceptual tasks assessing one's knowledge of actions. Based on the model, eight patterns of apraxia should emerge. The purpose of this study is to determine whether these patterns are in fact observed in stroke patients and examine their frequency. If the performance of most stroke patients falls into one of the patterns, then we would have strong support for the conceptual-production model. Stroke (34 LHD and 39 RHD) patients and 27 age- and education-matched healthy controls participated in the study. Participants were assessed in four task modalities: pantomime, delayed imitation, concurrent imitation and conceptual knowledge (two tasks were used: tool naming by action and action identification). Patients were categorized as impaired on a task if they scored 2 SD below the mean performance of the controls for gesture production tasks, or below a cut-off score on the conceptual tasks. They were then classified into patterns depending on their performance on the four task modalities. Most patients (86%) fell into one of seven patterns originally predicted from the Conceptual-Production Systems model. The two most common patterns were deficits in pantomime and imitation with preserved gesture recognition and conduction apraxia (selective deficit in imitation). Four new patterns emerged, but mostly single cases of these were found. Overall, the study provides strong support for the Conceptual-Production Systems model.     

Source and destination memory: Two sides of the same coin?

Whereas source memory involves remembering from whom you have heard something, destination memory involves remembering to whom you have told something. Despite its practical relevance, destination memory has been studied little. Recently, two reports suggested that generally destination memory should be poorer than source memory, and that it should be particularly difficult for older people. We tested these predictions by having young and older participants read sentences to two examiners (destination encoding) and listen to sentences read by two examiners (source encoding), under intentional (Experiment 1) or incidental encoding (Experiments 2 and 3). Only in Experiment 3 (in which cognitive demands during destination encoding were increased) was destination memory significantly poorer than source memory. In none of the experiments were older adults inferior to the young on destination or source memory. Destination- and source-memory scores were significantly correlated. Item memory was consistently superior for sentences that had been read out loud (during destination encoding) versus those that had been heard (during source encoding). Destination memory needs not always be poorer than source memory, appears not to be particularly impaired by normal ageing and may depend on similar processes to those supporting source memory.