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Biomedical subjects

A Sirigu

Publications and source records attributed to A Sirigu.

31 records · Page 2Linked to original sources
PubMed1996

Selective impairments within episodic memories.

We report the case of a patient (T.R.) who developed a severe and selective amnesia for names and dates associated with events. His amnesia was temporally limited, affecting only the last two to three decades of his life. When recalling an event he was able to evoke both its content and place, while he could not provide any information about people (names or their physical features) and the time (date/period) of its occurrence. His performance on event-memory tests was consistent across the type of material used (personal and public events) or the period of life investigated. These results suggest that knowledge of an episode is specified across multiple representations.

Amnesia↗
PubMed1996

Encoding of sequence and boundaries of scripts following prefrontal lesions.

Script analysis was investigated in patients with lesions in the prefrontal (n = 10) and posterior (n = 8) cortical regions, and in normal subjects (n = 15). The selection and temporal organization of relevant actions belonging to different pre-established sequences were studied in three different situations: (A) script with headers, (B) script with headers and distractors, and (C) scripts without headers. Contrarily to Normals and Posterior patients, Frontal patients committed sequence and boundary errors, and failed to eliminate distractors elements. The analysis of errors suggests two different cognitive modes of representing actions: (1) One using temporal contiguity between actions, that would be mainly under the control of the posterior associative areas; (2) the other, using the goal of the action and its consequences as a binding element between script and context, that would require the intervention of prefrontal cortex.

Adolescent↗
PubMed1995

Congruent unilateral impairments for real and imagined hand movements.

The chronometry of imagined and actual movements was investigated in a patient with a unilateral lesion of the motor cortex. Motor imagery generated highly accurate estimates of motor performance in a variety of situations, reflecting the hypokinesia of the contralesional hand. There were parallel increases in mental and actual movement times from proximal to distal limb segments. Bimanual movements adopted the slower speed of the impaired hand in both conditions. Imagined motor sequences to the beat of a metronome predicted the maximum speed reached in actual performance. Finally, visually guided pointing showed the same target-size effects in the imagery and movement conditions. The results are in agreement with the hypothesis that common cerebral motor representations are activated when imaging and planning voluntary movements.

Aged↗
PubMed1995

A selective impairment of hand posture for object utilization in apraxia.

This study reports the case of an apraxic patient who was impaired in all aspects of gestural behavior following bilateral posterior parietal cortex lesions. The main impairment concerned manual prehension of objects during their utilization. The deficit contrasted with both normal movement trajectories of the arm during execution of such gestures, and with accurate manual prehension in the context of simple reaching movements. Although recognition of gestures and pantomimes made by the examiner was preserved, the patient showed a striking inability to visually discriminate or describe manual prehension associated with object utilization. We thus propose the existence of specialized cortical mechanisms for the representation and activation of the postural schemata of the hand required for complex actions.

Apraxias↗
PubMed1995

Selective impairments in managerial knowledge following pre-frontal cortex damage.

Script generation was investigated in patients with lesions in the prefrontal (n = 9) and posterior (n = 8) cortical regions and in normal subjects (n = 16). Three different activities ranging in degree of familiarity were studied. Frontal patients did not differ from patients with posterior lesion and Normal subjects in the number of actions evoked, mean evocation time, or centrality. Impairments in script information processing were observed only in patients with prefrontal lesions, and for the three types of scripts. Specifically these patients made errors in ordering actions in the correct temporal sequence, failed to close scripts and to remain within the stated boundaries, and made deviant estimates of action importance. The results suggest that pre-frontal cortical lesions provoke a selective impairment in managerial knowledge (Grafman, 1989) that may contribute to difficulties in the formulation and execution of plans.

Adult↗
PubMed1995

What can preservation of autobiographic memory after muscarinic blockade tell us about the scopolamine model of dementia?

Autobiographic memory is reported to be impaired in patients with Alzheimer's disease (AD). To determine if cholinergic blockade fully reproduces the amnestic disorder found in dementia, we evaluated aspects of autobiographic and episodic memory in six healthy elderly controls after both scopolamine and placebo administration compared with untreated age- and education-matched patients with AD. The performance of patients with AD was significantly worse than that of controls after both treatment conditions. Scopolamine impaired episodic but not autobiographic memory. Thus, even though the cholinergic system is severely affected in patients with AD, muscarinic blockade alone does not seem to be a good model of this disorder.

Aged↗
PubMed1995

The neuropsychological pattern of corticobasal degeneration: comparison with progressive supranuclear palsy and Alzheimer's disease.

The pattern of cortical and subcortical neuropathologic lesions in corticobasal degeneration (CBD) should predict a specific cognitive profile in this disease. To characterize this profile and to determine its specificity by comparison with progressive supranuclear palsy (PSP) and senile dementia of the Alzheimer's type (SDAT), we used an extensive neuropsychological battery assessing global efficiency, executive functions, various tests of encoding and retrieval, dynamic motor organization, and upper limb praxis. We compared the performance of patients with CBD (n = 15) with that of controls (n = 19) matched for age and education, and with that of patients with PSP and SDAT (15 in each group), matched for severity of dementia and depression. Patients with CBD showed: (1) a moderate global deterioration; (2) a dysexecutive syndrome similar to that of patients with PSP and more severe than in SDAT; (3) explicit learning deficits, without retention difficulties and easily compensated by using the same semantic cues at encoding and retrieval as in PSP; this was in contrast with SDAT where cued recall and recognition were also impaired; (4) disorders of dynamic motor execution (temporal organization, bimanual coordination, control, and inhibition) similar to those of patients with PSP and not in SDAT; (5) asymmetric praxis disorders (posture imitation, symbolic gesture execution, and object utilization) that were not observed in PSP or SDAT. Patients with CBD show a specific neuropsychological pattern associating a dysexecutive syndrome, likely due to degeneration of the basal ganglia and prefrontal cortex, and asymmetric praxis disorders, which might be related to premotor and parietal lobe lesions. This neuropsychological profile may help to distinguish this condition clinically from other neurodegenerative diseases.

Aged↗
PubMed1992

Saccadic dysmetria in a patient with a right frontoparietal lesion. The importance of corollary discharge for accurate spatial behaviour.

Double-step experiments have demonstrated that retinotopic coding is inadequate to explain the spatial performance of the saccadic system. In such experiments a subject is asked to make two successive saccades to fixate two sequentially flashed targets each of which disappears before the first saccade. Despite the dissonance thus created between the retinal location of the second target and the saccade necessary to acquire it, normal humans and monkeys perform the task perfectly well. Single unit recording in monkeys indicates that neurons in the superior colliculus, frontal eye fields and in parietal cortex generate a spatially accurate signal during the performance of double-step saccades, which is thought to be obtained by combining a retinotopic signal with a signal corollary to the previous saccadic eye movement. We studied saccadic eye movements in a patient with a right fronto-parietal lesion using single- and double-step tasks. Single saccades into the left (contralesional) hemifield had longer latency and were hypometric relative to those into the right (ipsilesional) hemifield. Varying the initial orbital position had no effect on the latency and accuracy of saccades to left and right retinal stimuli. When the patient was asked to do a double-step task with targets flashed first into the right field and then into the left field, she performed well. When she was asked to do the same task with a target flashed first into the left field and then into the right field she made the first saccade correctly but never acquired the second target, even though this required her to make a saccade in the normal direction to a stimulus that appeared in the normal field. Such a deficit therefore cannot be one of retinotopic or spatial coding, nor can it be one of generating a certain direction of saccade. We suggest that the deficit is a failure of corollary discharge, the inability to register the amplitude and direction of a saccade into the contralesional field, and use that information to update the representation of the location of the next saccade target.

Aged↗
PubMed1992

Cognitive planning deficit in patients with cerebellar atrophy.

We compared the performance of 12 patients with cerebellar atrophy (CA) and 12 normal controls matched for age and education on the Tower of Hanoi, a nine-problem task that requires cognitive planning. CA patients performed significantly worse than controls on this task despite no difference in planning and between-move pause times. A reanalysis of the data using just the subgroup of patients with pure cerebellar cortical atrophy (CCA) (N = 9) replicated the above results and also showed that CCA patients had significantly increased planning times compared with controls. Neither age, sex, education level, severity of dementia, word fluency, response time, memory, nor visuomotor procedural learning predicted CA or CCA performance. This deficit in cognitive planning suggests a functional link between the cerebellum, basal ganglia, and the frontal lobe concerning specific cognitive processes. However, the exact role of the cerebellum in cognitive planning remains undetermined.

Adult↗
PubMed1991

Multiple representations contribute to body knowledge processing. Evidence from a case of autotopagnosia.

Body schema disturbances were studied in a 62-yr-old woman with Alzheimer's disease. She was severely impaired in verbal and nonverbal tasks requiring her to localize body parts (on her own body, the examiner's body or a doll's body) even though she correctly named the same parts when pointed at by the examiner. Pointing responses were misdirected mainly to parts contiguous with the target area and, to a lesser extent, to functionally equivalent body parts. We also found that the patient was able to define body part names functionally but not spatially. In another series of tasks, and in contrast to the above results, performances were normal when small objects, attached to the patient's body, served as pointing targets. Furthermore, on subsequent testing she pointed correctly at the remembered position of these objects. The fact that the same point in 'body space' is localized correctly when it corresponds to an external object and erroneously when it corresponds to a body part contradicts the idea of the body schema as a unitary function. Learning the position of objects on the body surface requires access to some form of body-reference system on which this information can be mapped. We argue that such a system can be available in autotopagnosia and is independent from the visuospatial representations of the body structure that are postulated to be damaged or inaccessible in this syndrome. An integrated account of the present results and of those reported by other authors suggests that multiple levels of representation (e.g., sensorimotor, visuospatial, semantic) are involved in the organization of body knowledge.

Agnosia↗
PubMed1991

The role of sensorimotor experience in object recognition. A case of multimodal agnosia.

Object recognition was studied in a 19-yr-old male patient who presented severe multimodal amnesia and agnosia without significant intellectual, linguistic or perceptual deficits. Bilateral temporal lobe lesions involved medial, polar and anterior infero-temporal structures. Although visual recognition was impaired to various extents for all categories of objects, preservation of certain capacities were demonstrated. In particular, the patient was able to determine specifically how to manipulate certain objects, in spite of his incapacity to define their function or their context of utilization. It is argued that object recognition involves different processing modes such that when direct access to representations of an object is impaired, sensorimotor information activated via alternative cortical and subcortical pathways may provide a limited mechanism for recognition.

Adult↗
PubMed1987

Pure topographical disorientation: a definition and anatomical basis.

Four patients showing the syndrome of "topographical disorientation" are reported. Patients became unable to find their way, especially in unfamiliar surroundings, following a single lesion in the territory of the right posterior cerebral artery, as evidenced on CT-scan. Associated disturbances included: left hemianopia, mild face recognition problems, and various degree of impairment in face-learning and visual maze-learning tasks. Language, visuo-perceptive and constructional abilities, object and picture recognition were intact. Memory tests only showed a mild, generally non-significant, impairment of visual memory. As inferred from the lesion located in the 4 patients, this syndrome seems to be strongly related to damage to the right parahippocampal gyrus, a structure that thus appears crucial for specifically storing and/or retrieving visual information necessary to achieve orientation in the locomotor environment.

Adult↗