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Biomedical subjects

G Goldenberg

Publications and source records attributed to G Goldenberg.

At least 37 records · Page 2Linked to original sources
PubMed1997

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.

Aged↗
PubMed1997

Brain/behaviour dissociation on old/new distinction in a patient with amnesic syndrome.

Event-related potentials (ERP) were recorded in a recognition memory task in 5 healthy subjects and an amnesic patient. A list of high-imagery words with low probability in everyday language was presented visually for 200 ms each. A second list, consisting of 50% previously presented ('old') words and 50% 'new' words was presented immediately after the first list. Old/new distinction was determined by the subject's motor response. For each subject single trial analysis of ERPs was performed. In each healthy subjects, correct old/new distinction was associated with significant ERP differences from 500 to 900 ms after stimulus onset. It was, therefore, assumed that task and recording procedures were appropriate for the study of ERPs with recognition memory. The main finding is a dissociation between brain activity and behaviour with old/new distinction in the patient with amnesic syndrome. Frequently, the patient incorrectly classified previously shown words ('old' words) to be presented for the first time ('new'). But ERP showed that brain processing of 'old' words which had incorrectly been classified to be 'new' is different from correctly classified new words. ERP differences were significant between 900 and 1200 ms after stimulus presentation. These data indicate preserved memory functions which are not assessed at the behavioural level in the memory recognition task.

Adult↗
PubMed1997

Speed of motor execution and apraxia.

We used a reaction time paradigm to explore the relationship between motor execution and apraxia. The task required reaching for one to three keys. The instruction was varied by introducing a model of a hand indicating which fingers to use. Whereas patients with right-brain damage were slower than controls regardless of condition, the performance of patients with left-brain damage was only impaired when movements had to be carried out according to the model. Although this indicates a deficit in movement planning, there was no correlation between the impairment of patients with left-brain damage and clinical manifestations of apraxia. It thus remains an open question whether the impairment reflects an aspect of motor dominance of the left hemisphere that is too subtle to be detected by clinical apraxia testing, or whether it is related to task demands outside the domain of motor control. In any case, the results of this study demonstrate the need to control cognitive task demands when exploring motor capabilities of patients with left-brain damage.

Adult↗
PubMed1996

Ideomotor apraxia and cerebral dominance for motor control.

Ideomotor apraxia is a symptom of left hemisphere damage. Patients with ideomotor apraxia commit errors when imitating movements with their left, non-paralyzed hand. This has been taken as evidence for a motor dominance of the left hemisphere. It has been hypothesized that the left hemisphere is dominant for internal preprogramming of skilled movements of either hand. We investigated the kinematics of movement trajectories of imitation of meaningless gestures. Group analysis confirmed that hesitant, feedback-controlled movement prevail in patients with apraxia, but analysis of single cases revealed the existence of kinematically normal movements leading to apractic errors. Enhanced reliance on feedback-control appears to be a compensatory strategy rather than the source of apractic errors. In a second study we explored the alternative hypothesis that patients with apraxia lack a general concept of the human body which is necessary to mediate the translation of a target position seen on the model into a target position on the patient's body. Imitation of movements was examined on oneself and on a mannikin. Patients with apraxia who made errors when imitating on themselves committed errors also when imitating on the mannikin. Taken together, both studies support the view that the source of errors in the imitation of gestures is to be sought at a conceptual level. This casts doubts on the alleged dominance of the left hemisphere for motor control.

Apraxias↗
PubMed1996

Kinematic analysis of movement imitation in apraxia.

Accuracy of the final position and kinematics of movement were analysed during the imitation of meaningless gestures in patients with unilateral brain lesions who performed with the hand ipsilateral to the lesion and in control subjects. Controls imitated the gestures virtually without spatial errors. The kinematics of their movements was characterized by single-peaked and approximately bell-shaped velocity profiles of the transport phase combined with no or only minor corrective movements in the final phase. Patients with right brain damage (RBD) performed as well as control subjects with respect to both spatial accuracy of final hand-positions and kinematic parameters of the movement trajectories. Patients with left brain damage (LBD) committed spatial parapraxias and had a much higher frequency of kinematic abnormalities. However, there was no correlation between kinematic abnormalities and apraxic errors. There were kinematically abnormal movements which reached a correct final position as well as kinematically normal movements leading to apraxic errors. One possible explanation for the combined occurrence of kinematic abnormalities and parapraxias in LBD patients would be that they are independent sequels of left hemisphere lesions. An alternative account is that the associations and dissociations result from an interaction between one common basic deficit and strategies to cope with this deficit. The basic deficit may concern the mental representation of the target position. The LBD patients may react to the absence of an appropriate representation of the target by one of two alternative strategies; they may switch to a strategy of slowed, on-line controlled movements to find the required final position, or they may move their hand smoothly at normal speed to a roughly specified location without taking note of their deficiency. Depending on whether these strategies are successful or not they would lead to the observed associations and dissociations between kinematic abnormalities and spatial parapraxias.

Adult↗
PubMed1996

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.

Adult↗
PubMed1995

Unimanual motor learning impaired by frontomedial and insular lesions in man.

We correlated impaired unimanual motor learning with the lesion site in 53 patients with chronic lesions predominantly of the frontal lobe. The lesions were assessed using computed tomography (CT), then transferred to standard templates of nine slices parallel to the canthomeatal plane and digitized with a raster matrix of 3 mm by 3 mm width. The learning task was to track a moving target on a computer screen with a dot guided by the preferred hand, while the horizontal coupling between hand movement and screen was inverted. The mean tracking error was recorded over eight successive trials of 80s duration. If the mean error of the last three trials was not lower than that of the first three trials, impaired motor learning was assumed. We correlated performance and lesion with a contingency table analysis for each raster element. Impaired motor learning was associated with a lesion within the supplementary motor area and adjacent anterior cingulate, and within the anterior insular region. Our results indicate that these regions are critical for motor learning and functional plasticity in man. Our data support activation patterns obtained with positron emission tomography.

Adolescent↗
PubMed1995

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.

Aged↗
PubMed1995

Imagery without perception--a case study of anosognosia for cortical blindness.

A patient with complete cortical blindness after bilateral posterior cerebral artery infarctions denied her blindness. Her pretended visual experiences could frequently be traced back to synaesthetic translations of acoustic or tactile perceptions into mental visual images. Possibly, the belief to see resulted from a confusion of mental visual images with real percepts. The patient manifested preserved visual imagery also by correct responses to questions concerning the shapes of letters and the shapes and colours of objects. MRI showed an almost complete destruction of primary visual cortex with sparing of only small remainders of cortex at the occipital tip of the left upper calcarine lip. In the literature there are a few cases of denial of blindness with similarly severe damage to primary visual cortex but none with unequivocal evidence of complete destruction of primary visual cortex. We conclude that severe damage to primary visual cortex is compatible with visual imagery but that there is a possibility that islands of visual cortex must be spared to permit the generation of mental visual images.

Blindness↗
PubMed1994

A program for measuring timing and accuracy in a complex motor reaction task.

A program was developed to explore a subject's accuracy and response timing in a reaction-time paradigm, which involves a multiple choice along with a complex response. The program can be run on an IBM-PC or compatible computers. The subject's task is: (1) to react to a stimulus (task) pattern by releasing a go-key (release time); the pattern is displayed on a keyboard as a combination of up to five light-emitting diodes associated with five answer keys; (2) then to press correctly the key combination indicated (response completion time). The keys are located at positions corresponding to finger tips. The response is complete at the moment all keys of the required combination are held down simultaneously, the order in response completion is not important. Responses are classified according to possible errors: whenever a key is pressed that does not belong to the required combination or the full key combination is not held until a (preset) waiting time period, the response is classified as incorrect. Various task patterns representing the required response combination of any subset of the five keys can be designed. Both the left and the right hand can be tested separately. In this way, possible distortions in performance caused, for instance, by apraxia can be analyzed. Basic statistical characteristics of the release times and completion times for correct responses are computed from the data and stored. The program is written in MODULA-2, the output files are in the ASCII format, which enables further processing of the data by standard statistical packages.

Apraxias↗
PubMed1994

Influence of size and site of cerebral lesions on spontaneous recovery of aphasia and on success of language therapy.

Changes in linguistic competence were assessed with the Aachen Aphasia Test in 18 aphasic patients across 8 weeks of spontaneous recovery, 8 weeks of intensive language therapy, and after a follow-up period of 8 weeks without therapy. CT scans were obtained from all patients and were evaluated for size of lesion and for affection of Wernicke's area, adjacent regions of superior and middle temporal gyrus, inferior parietal lesions, and temporobasal lesions. Size of lesion had a negative influence on recovery in all phases. Patients with lesions to temporobasal regions showed less improvement during therapy and less total recovery, but a similar amount of spontaneous recovery than patients without such lesions. Lesions that affected the temporobasal regions were on average larger than those which spared them, but the dissociation between reduced therapy success and unaffected spontaneous recovery became even more conspicuous when the concurrent effect of lesion size was minimized by appropriate selection of patients. Possibly, temporobasal lesions cause a disconnection between the hippocampal formation and perisylvian language areas and hinder explicit learning of linguistic knowledge and compensatory strategies.

Adult↗
PubMed1994

Tactile mental imagery in sighted persons and in patients suffering from peripheral blindness early in life.

Patterns of cortical activity as measured by scalp-recorded event-related slow negative DC potential shifts were recorded in 9 early blind and 23 sighted normals while they imagined the feel of textures with the fingertips of one hand. All sighted subjects reported to have concomitant visual imagery as well. Hence, it was not surprising to observe occipital negative shifts, previously described as a sign of occipital visual cortex involvement in visual mental imagery. Though having never had visual perception, the blind, too, had occipital negativities. Their absolute amplitudes were smaller than in the sighted, not only occipitally but also and more pronounced at other areas, particularly frontally where amplitudes were even positive. On the hypothesis that the smaller overall amplitudes in the blind could obscure topographical differences between groups, the relative distribution of negativity across the scalp was assessed, using normalized data. Such normalized parameters significantly differed between groups, indicating that the occipital potentials of the blind were relatively more negative as related to the other scalp areas, than were the occipital potentials of the sighted as related to the other scalp areas. This occipital finding might indicate a participation of the blind's visually deprived occipital cortex in tactile imagery. Second, parietal DC potentials were maximal over the hemisphere contralateral to the imaging hand, possibly indicating involvement of the contralateral parietal association cortex in tactile imagery. Reasons why this was true only for the sighted, are discussed.

Adolescent↗
PubMed1993

Components of random generation by normal subjects and patients with dysexecutive syndrome.

The study presents a hypothesis on how randomness could be simulated by human subjects. Three sources of deviation from randomness are predicted: (1) the preferred application of overlearned production schemata for producing sequences of digits, (2) a wrong concept of randomness, and (3) the impossibility to monitor for redundancies of higher- than those of first-order. Deviations of random generation of digits produced by healthy subjects, patients with chronic frontal lobe damage, and patients with Parkinson's disease from random sequences produced by a computer program can be explained by the differential influence of these factors. Whereas incorrect concepts of randomness and limits on monitoring capacity distinguished all sequences produced by humans from actual random sequences, persistence on a single production strategy distinguished brain-damaged patients from controls. Random generation of digits appears to be a theoretically transparent and clinically useful test of executive function.

Adult↗
PubMed1993

The neural basis of mental imagery.

Mental visual images can be employed for widely different tasks and they can depict widely different kinds of visual entities. There is evidence that the context and content of mental visual images matter for the determination of their neural basis. Single case studies demonstrate that there are at least five kinds of visual entities whose imagery can be affected independently from each other: shapes of objects, colours of objects, faces, letters and spatial relationships.

Brain↗
PubMed1992

Regional cerebral blood flow patterns related to verification of low- and high-imagery sentences.

Although several SPECT studies have shown left inferior occipital activation with visual imagery, the reliability of this finding remains doubtful. The present study replicated two conditions of a previous SPECT-study exploring rCBF in subjects verifying the correctness of low- and high-imagery sentences. As in the previous study, verification of high-imagery sentences was associated with higher flow rates in the left inferior occipital region and lower flow rates in the right anterior frontal region. By contrast, a bilateral increase of thalamic flow rates with imagery was not replicated, and there was a higher flow rate in the left inferior temporal region with low-imagery sentences which had not been found in the original study.

Adult↗
PubMed1992

Loss of visual imagery and loss of visual knowledge--a case study.

As a sequel of a left posterior cerebral artery infarction a patient had severely defective mental imagery of shapes and colours of objects. Imagery of faces, letters, and topological relationships was preserved. The impairment of imagery of object colours was associated with colour agnosia and colour anomia. For colours, there was no difference between performance on tasks calling for imagery of object colours and tasks affording a distinction between correctly and incorrectly coloured objects. For shapes of objects, imagery appeared to be below the level of the patient's knowledge about the visual appearance of objects as manifested by the ability to identify objects and to distinguish correctly from incorrectly drawn pictures. The apparently selective image generation deficit for shapes of objects could be a sequel of loss of knowledge about visual attributes of objects, if superior performance on shape recognition tasks was afforded by perceptual entry level representation which enable a rapid identification of objects but are inaccessible to introspective consciousness.

Aged↗
PubMed1992

Cerebral correlates of disturbed executive function and memory in survivors of severe closed head injury: a SPECT study.

Thirty six patients in the chronic stage after severe closed head injury were examined with tests of executive function, memory, intelligence, and functional capacities in daily living. Correlations were sought between test results and Tc-99m-HMPAO uptake of frontal, temporal, and thalamic regions assessed by SPECT. Neither the number of significant correlation coefficients between memory tests and regional uptake nor that between temporal uptake and tests exceeded chance. For the remaining tests, correlations to thalamic regions were stronger than those to the frontal regions, and those to right brain regions stronger than those to homologous left brain regions. Relationships of thalamic isotope uptake to neuropsychological performance may reflect the impact of diffuse brain damage and particularly of diffuse axonal injury on mental capacities.

Adult↗