Georg Goldenberg

The meaning of meaningless gestures: a study of visuo-imitative apraxia.

In two patients with damage to the inferior portion of the left angular gyrus severely defective imitation of meaningless gestures contrasted with preserved performance of meaningful gestures to verbal command and with preserved imitation of meaningful gestures. In one patient the imitation deficit was restricted to the imitation of hand positions while imitation of finger configurations was normal. In both patients replication of the hand positions on a mannikin was as defective as imitation on themselves. This pattern of preserved and impaired performances is incompatible with two-stage models of apraxia which posit that defective imitation stems from damage to an executional stage of gesture production. Interruption of a direct route from perception to execution of action could account for the dissociation between defective imitation of meaningless and preserved performance of meaningful gestures. We propose that functioning of this route requires the integrity of general knowledge about the structure of the human body.

The neural basis of tool use

Misuse of tools and objects by patients with left brain damage is generally recognized as a manifestation of apraxia, caused by parietal lobe damage. The use of tools and objects can, however, be subdivided in several components. The purpose of our study was to find out which of these are dependent on parietal lobe function. Thirty-eight patients with left brain damage and aphasia were examined using tests to assess the retrieval of functional knowledge from semantic memory (Functional Associations), mechanical problem solving (Novel Tools) and use of everyday tools and objects (Common Tools). Voxel-wise analysis of magnetic resonance images revealed two regions where lesions had a significant impact on the test results. One extended rostrally from the central region and ventrally through the middle frontal cortex to the dorsal margin of the inferior frontal gyrus. The other reached dorsally and caudally from the supramarginal gyrus, through the inferior, to superior parietal lobe. Whereas the frontal lesions had an adverse influence on all experimental tests as well as on the subtests of the Aachen Aphasia test, parietal lesions impaired Novel and Common Tools, but did not have an adverse effect on the Functional Associates. An association between Functional Associations and temporal lesions became apparent when patients with only a selective deficit in the test were considered, but did not show up in the whole group analysis. The parietal influence was as strong for the selection as for the use of either novel or common tools, although choice of appropriate manual configuration and movements was more important for use than for selection. We conclude that the contribution of the parietal lobe to tool use concerns general principles of tool use rather than knowledge about the prototypical use of common tools and objects, and the comprehension of mechanical interactions of the tool with other tools, recipients or material rather than the selection of grip formation and manual movements.

Defective imitation of gestures in patients with damage in the left or right hemispheres.

OBJECTIVES--Defective imitation of meaningless gestures has repeatedly been demonstrated in patients with apraxia and has been interpreted as being due to a deficit of motor execution. There is, however, controversy as to whether some impairment of imitation also occurs in patients with right brain damage. The aim was to compare defective imitation in patients with left and right brain damage and to explore whether there are qualitative differences between them. METHODS--Imitation was examined in 80 patients with left brain damage (LBD) and aphasia, 40 patients with right brain damage (RBD), and 60 controls for three types of gestures:hand positions, finger configurations, and combined gestures which required a defined hand position as well as a defined configuration of the fingers. RESULTS--Regardless of whether imitation of hand positions and finger configurations were tested each on their own or together, they showed differential susceptibility to RBD and LBD. Whereas imitation of finger configurations was about equally impaired in RBD and LBD, defective imitation of hand positions occurred almost exclusively in patients with LBD, and whereas controls as well as patients with RBD committed less errors with hand positions than with finger configurations, the reverse was the case in patients with LBD. CONCLUSIONS--The pattern of results goes against a deficit of motor execution as being the cause of defective imitation in patients with LBD, as it is difficult to see why such a deficit should affect proximal movements necessary for reaching hand positions more than differential finger movements. An alternative explanation would be that in patients with LBD errors are due to defective mediation by knowledge about the human body whereas in patients with RBD they stem from faulty visuospatial analysis of the demonstrated gesture.

It takes the whole brain to make a cup of coffee: The neuropsychology of naturalistic actions involving technical devices.

Left hemisphere dominance has been established for use of single familiar tools and tool/object pairs, but everyday action in natural environment frequently affords multi-step actions with more or less novel technical devices. One purpose of our study was to find out whether left hemisphere dominance extends to such naturalistic action. Another aim was to analyze the cognitive components contributing to success or failure. Patients with LBD and aphasia, patients with RBD, and healthy controls were examined on experimental tests assessing retrieval of functional knowledge from semantic memory, inference of function from structure, and solution of mechanical and non-mechanical multi-step problems, and were confronted with two naturalistic tasks involving technical devices: preparing coffee with a drip coffee maker and fixing a cassette recorder. Both patient groups were about equally impaired on both naturalistic actions. Analysis of the experimental tests and their correlations to naturalistic actions suggested that different cognitive deficits caused failure in both patient groups, and that in LBD patients there were also different causes for failure on both naturalistic actions. The main difficulty of RBD patients seemed to reside in the demand to keep track of multi-step actions. In aphasic LBD patients difficulties with making coffee but not the cassette recorder were correlated with aphasia and defective retrieval of functional knowledge from semantic memory, whereas the cassette recorder correlated more strongly with a test probing solution of multi-step mechanical problems. Inference of function from structure which had been shown to be important for use of single familiar tools or tool/objects pairs [Goldenberg, G., Hagmann, S. (1998). AT Tool use and mechanical problem solving in apraxia. Neuropsychologia, 36, 581-589] appeared to play only a subordinate role for naturalistic actions involving technical devices.

Imitating gestures and manipulating a mannikin—The representation of the human body in ideomotor apraxia

Imitation of meaningless gestures was examined in patients with left brain damage (LBD), right brain damage (RBD) and controls. In addition to imitation on the own body, patients were asked to replicate the gestures on a life-sized mannikin. Manual dexterity was assessed by manipulation of beads, and general visuospatial abilities by block-design. LBD patients who displayed apraxia when imitating gestures on their own bodies scored dramatically worse than any other group when imitation was assessed on the mannikin. By contrast, on block-design and manipulation of beads patients with RBD were inferior not only to LBD patients without apraxia but also to apractic patients. Analysis of CT scans revealed that apraxia occurred with frontal, parietal and deep lesions, and that the impairment on the manipulation of the mannikin was present regardless of lesion site. The results support the contention that the basic deficit underlying impaired imitation of meaningless gestures in apraxia is to be sought at a conceptual level. Possibly, patients with apraxia are not able to evoke and represent conceptual knowledge about the human body which is necessary for performing the apparently simple task of imitating gestures.

Cortical Correlates of Gesture Processing: Clues to the Cerebral Mechanisms Underlying Apraxia during the Imitation of Meaningless Gestures

The clinical test of imitation of meaningless gestures is highly sensitive in revealing limb apraxia after dominant left brain damage. To relate lesion locations in apraxic patients to functional brain activation and to reveal the neuronal network subserving gesture representation, repeated H2(15O)-PET measurements were made in seven healthy subjects during a gesture discrimination task. Observing paired images of either meaningless hand or meaningless finger gestures, subjects had to indicate whether they were identical or different. As a control condition subjects simply had to indicate whether two portrayed persons were identical or not. Brain activity during the discrimination of hand gestures was strongly lateralized to the left hemisphere, a prominent peak activation being localized within the inferior parietal cortex (BA40). The discrimination of finger gestures induced a more symmetrical activation and rCBF peaks in the right intraparietal sulcus and in medial visual association areas (BA18/19). Two additional foci of prominent rCBF increase were found. One focus was located at the left lateral occipitotemporal junction (BA 19/37) and was related to both tasks; the other in the pre-SMA was particularly related to hand gestures. The pattern of task-dependent activation corresponds closely to the predictions made from the clinical findings, and underlines the left brain dominance for meaningless hand gestures and the critical involvement of the parietal cortex. The lateral visual association areas appear to support first stages of gesture representation, and the parietal cortex is part of the dorsal action stream. Finger gestures may require in addition precise visual analysis and spatial attention enabled by occipital and right intraparietal activity. Pre-SMA activity during the perception of hand gestures may reflect engagement of a network that is intimately related to gesture execution.

Left inferior parietal dominance in gesture imitation : an fMRI study

The inability to imitate gestures is an essential feature of apraxia. However, discrepancies exist between clinical studies in apraxic patients and neuroimaging findings on imitation. We therefore aimed to investigate: (1) which areas are recruited during imitation under conditions similar to clinical tests for apraxic deficits; (2) whether there are common lateralized areas subserving imitation irrespective of the acting limb side; and also (3) whether there are differences between hand and finger gestures. We used fMRI in 12 healthy, right handed subjects to investigate the imitation of four types of variable gestures that were presented by video clips (16 different finger and 16 different hand gestures with either the right or the left arm). The respective control conditions consisted of stereotyped gestures (only two gestures presented in pseudorandom order). Subtraction analysis of each type of gesture imitation (variable>stereotyped) revealed a bilateral activation pattern including the inferior parietal cortex Brodmann Area (BA 40), the superior parietal cortex, the inferior frontal cortex (opercular region), the prefrontal motor cortex, the lateral occipito-temporal junction, and the cerebellum. These results were supported by statistical conjunction of all four subtraction analyses and by the common analysis of all four types of gesture imitation. The direct comparison of the right and left hemispheric activation revealed a lateralization to the left only of the inferior parietal cortex. Comparisons between different types of gesture imitation yielded no significant results. In conclusion, gesture imitation recruits bilateral fronto-parietal regions, with significant lateralization of only one area, namely the left inferior parietal cortex. These in vivo data indicate left inferior parietal dominance for gesture imitation in right handers, confirming lesion-based theories of apraxia.

Matching and imitation of hand and finger posturesin patients with damage in the left or right hemispheres

To disentangle perceptual, conceptual and motor aspects of imitation of gestures, reproduction of meaningless postures of either the hand or the fingers was examined in two conditions. In the matching test a target gesture had to be identified among an array of four gestures performed by different persons and seen under different angles of views. For imitation, the same gestures had to be imitated. Thirty-five patients with LBD, 21 patients with RBD, and 17 healthy controls were examined. LBD patients had more difficulties with imitation than with matching while RBD patients had more difficulties with matching than with imitation. Regardless of whether imitation or matching was tested, LBD patients made more errors with hand than with finger postures whereas RBD patients made more errors with finger than with hand postures. This constellation of results is compatible with the assumption that errors are caused by faulty visuoperceptual processing in RBD, and by defective conceptual mediation in LBD. Defective motor execution does not appear to be a significant source of imitation errors in either group.

Defective pantomime of object use in left brain damage: apraxia or asymbolia?

Disturbance of pantomime of object use in patients with left brain damage (LBD) and aphasia has been firmly established but its nature remains controversial. It may be due to an inability to perform movements from memory without external support by objects (apraxia) or to an inability to produce signs referring to absent objects and actions (asymbolia). The need to perform movements without external support is shared with imitation of gestures, and the demand to designate absent objects with drawing from memory. Both of these tasks have been found to be impaired in LBD. We examined pantomime of object use, drawing objects from memory, imitation of meaningless gestures, and aphasia in 40 patients with LBD and aphasia and compared them to healthy controls and to patients with right brain damage (RBD). Whereas drawing showed comparable sensitivity to LBD and RBD, pantomime was distinctly more disturbed in LBD than in RBD patients. Pantomime was worse than drawing in LBD but better than drawing in RBD. In the LBD group scores on pantomime showed significant correlations of very similar strength to drawing, imitation, and all language tests. Multidimensional scaling of the correlational structure placed pantomime in an intermediate position between verbal and non-verbal tests. We conclude that neither apraxia nor asymbolia can satisfactorily explain our results. It seems as if pantomime of object use taps a central aspect of left hemisphere function which is compromised by any LBD. We propose that this may be the ability to select and combine distinctive features of objects and actions.

Apraxia and Beyond: Life and Work of Hugo Liepmann

Nearly 100 years after their publication Hugo Liepmanns ideas are still influential for todays neuropsychology. This influence is, however, restricted to a small, albeit central, portion of his work. Cognizance of their wider biographical and scientific context may help to bring about a deeper understanding of their significance. This paper provides a comprehensive review of Liepmanns life and work. In the first part of this paper I try to give an impression of his life, his personality and his style as a clinician and as a scientific writer. The second part is a review of his ideas on cerebral localization of psychological function, and the third an account of his writings on apraxia. Finally, I briefly consider Liepmanns legacy and argue that the less well known parts of his writings are at least as topical today as are his famous papers on apraxia.