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Biomedical subjects

B Pillon

Publications and source records attributed to B Pillon.

At least 55 records · Page 3Linked to original sources
PubMed1998

Spatio-temporal working memory and frontal lesions in man.

The delayed-response paradigm is thought to be a marker of the activity of the dorsolateral convexity of primates' prefrontal cortex, as this procedure requires the activation of working memory processes. Although the role of the dorsolateral prefrontal cortex (DLPC) in working memory seems to be well established, much remains to be understood about the processes this structure actually controls: encoding domain-specific information, its retention in short-term memory, its monitoring in working memory, or its selection and retrieval when a specific response program is required. To clarify the role of the DLPC in delayed-response tasks in humans, a set of sequencing paradigms was designed which incorporates the dissociation of (1) spatial and temporal parameters, (2) recall and recognition processes, and (3) the presence or absence of a delay. Performance of a group of patients with DLPC lesions (n = 8) was compared to that of age-matched normal subjects (n = 8). To verify the specificity of the results obtained for the DLPC lesioned patients, the performance of patients with a temporal lobotomy was also studied (n = 10). A significant effect of the delay was observed only in patients with DLPC lesions, affecting both their spatial and spatio-temporal recall, whereas their spatio-temporal recognition was normal. These findings suggest that the DLPC plays a role in the retrieval of visuospatial information for guiding a response program.

Brain Injuries↗
PubMed1998

Is impaired memory for spatial location in Parkinson's disease domain specific or dependent on 'strategic' processes?

Spatial memory has been found to be impaired in Parkinson's disease (PD). To determine the nature of the deficit, we compared the performance of'standard' levodopa-treated patients with PD to that of matched control subjects in different situations: (i) spatial versus verbal conditional associative learning; (ii) 'global' versus 'local' contextual encoding; (iii) pattern span and related supraspan learning. The relationship between dopaminergic depletion, which characterizes the disease, and the impaired memory processes was investigated by comparing the performance of 'de novo' not yet treated PD patients to that of matched control subjects. Both groups of PD patients were impaired in all situations requiring strategic processes, shared a decreased pattern span and had a normal visuospatial learning once the pattern span was taken into account. All these results suggest that the memory deficit for spatial location observed in PD results mainly from a disturbance of strategic processes and from decreased attentional resources, which may be due, at least in part, to the dopaminergic depletion and related striatofrontal dysfunction.

Aged↗
PubMed1998

Are cognitive changes the first symptoms of Huntington's disease? A study of gene carriers.

BACKGROUND: Huntington's disease is a neurodegenerative disorder due to an excessive number of CAG repeats in the IT15 gene on chromosome 4. The first symptoms are typically choreic movements or psychiatric disorders, whereas global cognitive decline generally becomes obvious later. This study was aimed at detecting early subtle cognitive deficits in asymptomatic gene carriers. METHODS: As part of the testing procedure for predictive diagnosis of Huntington's disease, 91 asymptomatic at risk candidates had a neuropsychological examination, evaluating global efficiency, attention, memory (Wechsler memory scale and California verbal learning test), and executive functions. RESULTS: The groups of carriers (n=42) and non-carriers (n=49) differed only on a few memory variables. When we considered the group of gene carriers as a whole, significant correlations emerged between the number of CAG repeats and (a) performance on several tests of executive functions, and (b) performance on the hard pairs associates of the Wechsler memory scale. Further analysis of performance on this memory subtest led to the division of the group of carriers into two subgroups, without any overlap. The performance of subjects without cognitive deficits (n=32) was similar to that of non-carriers on all tests. The subjects with cognitive deficits (n=10) differed from both carriers without cognitive deficits and non-carriers over a wide array of variables measuring executive functions and memory. Moreover, qualitative aspects of the performance of carriers with cognitive deficits in the California verbal learning test closely resembled those of patients diagnosed as having Huntington's disease. CONCLUSION: This suggests that these subjects already have Huntington's disease, despite a total lack of motor and psychiatric signs. An ongoing follow up study is testing the prediction that they will develop the full range of symptoms of the disease earlier than carriers without cognitive deficits.

Adolescent↗
PubMed1998

Clinicometabolic dissociation of cognitive functions and social behavior in frontal lobe lesions.

OBJECTIVE/BACKGROUND: Case studies suggest a dissociation between cognitive functions that have been impaired after damage to the dorsolateral prefrontal cortex and social skills disturbed when the ventromedial prefrontal areas are affected. Because this dissociation had not been confirmed in a clinical setting, clinicometabolic correlations were sought in 13 patients with various lesions of the prefrontal cortex. DESIGN/METHODS: The clinical assessment included extensive testing of executive functions and evaluation of behavioral abnormalities based on an informant questionnaire. Regional cerebral glucose metabolism (rCMRGlu) was measured with [l8F] fluorodeoxyglucose ([18F] FDG) and 31-slide high-resolution PET. RESULTS: Executive-function test performance was significantly correlated with rCMRGlu in the dorsolateral prefrontal cortex (Brodmann's areas 8, 9, 45, 46, and 47) and anterior cingulate cortex (Brodmann's areas 24 and 32). Behavioral scores were significantly correlated with rCMRGlu in the frontopolar (Brodmann's area 10) and orbitofrontal cortex (Brodmann's areas 11, 12, 13, and 14). CONCLUSION: These results show that impaired executive functions and serial skill deficits are associated with distinct metabolic patterns in patients with frontal lobe pathology. In agreement with activation studies in normal subjects, our data suggest the existence of a modular organization of the frontal cortex in humans, as previously reported in nonhuman primates.

Adult↗
PubMed1997

Cognitive deficits in Parkinson's disease.

Neuropsychological investigations of patients with Parkinson's disease have shown specific impairments even in the early stages of the disease, which include deficit of behavioural regulation in sorting or planning tasks, defective use of memory stores, and impaired manipulation of internal representation of visuospatial stimuli. These deficits, reported in a disease which predominantly involves subcortical structures, have drawn attention to a potential role of the basal ganglia in cognitive processes. Given the modulatory role of the basal ganglia, these disorders might result from more fundamental deficits concerning the allocation of attentional resources, the temporal organization of behaviour, the maintenance of representations in working memory or the self-elaboration of internal strategies, all of which resemble dysfunctions of processes that are commonly considered to be controlled by the frontal lobes. This suggests a functional continuity or complementarity between the basal ganglia and association areas of the prefrontal cortex. The recent description in primates of segregated loops that interconnect discrete regions of the caudate nucleus to the dorsolateral and orbitofrontal regions of the prefrontal cortex via the thalamus may give some support to this hypothesis. Alternatively, degeneration of the ascending cholinergic and catecholaminergic neuronal systems may contribute, at least in part, to the occurrence of this frontal-lobe-like symptomatology associated with Parkinson's disease.

Aging↗
PubMed1997

Memory for spatial location in 'de novo' parkinsonian patients.

A deficit in memory for spatial location was recently reported in typical non-demented parkinsonian patients ('standard'). Is this deficit related to dopamine depletion? Such an association would reinforce the suggestion that striato-frontal neuronal circuits are implicated in memory for item-specific spatial coordinates. To answer this question, we compared the performance of 10 recently diagnosed and not yet treated parkinsonian patients ('de novo'), in which the neurobiochemical deficit is considered to involve mainly the nigrostriatal dopaminergic system, to that of 14 controls matched for age, global cognitive efficiency and mood, on a visuospatial learning test. The task required little motor or constructive functions and was designed to allow control of encoding and comparison of free recall, cued recall and recognition. Compared to controls, 'de novo' patients displayed a lower performance in memory for visuospatial location of pictures, contrasting with relative preservation of verbal memory, perceptive visuospatial and executive functions. These results confirm the sensitivity of visuospatial memory even at an early stage of Parkinson's disease and suggest the implication of the nigrostriatal dopaminergic system, and associated striato-frontal neuronal circuits, in executive processes needed for spatial location learning.

Analysis of Variance↗
PubMed1996

The mental representation of hand movements after parietal cortex damage.

Recent neuroimagery findings showed that the patterns of cerebral activation during the mental rehearsal of a motor act are similar to those produced by its actual execution. This concurs with the notion that part of the distributed neural activity taking place during movement involves internal simulations, but it is not yet clear what specific contribution the different brain areas involved bring to this process. Here, patients with lesions restricted to the parietal cortex were found to be impaired selectively at predicting, through mental imagery, the time necessary to perform differentiated finger movements and visually guided pointing gestures, in comparison to normal individuals and to a patient with damage to the primary motor area. These results suggest that the parietal cortex is important for the ability to generate mental movement representations.

Adult↗
PubMed1996

Cognitive deficits in non-Alzheimer's degenerative diseases.

Although observed in various brain disorders, dementia is particularly frequent in neurodegenerative diseases. Alzheimer's disease is characterized by the association of progressive amnesia with either instrumental (aphasia, apraxia, agnosia) or behavioral (apathy, indifference, anosognosia) disorders, depending upon the location of the underlying neuronal lesions. By contrast, memory, linguistic, praxic, visuo-spatial or comportemental impairments are dissociated in more focal "lobar" atrophies, while planning and retrieval deficits predominate in movement disorders with dementia. Alzheimer's and non-Alzheimer's neurodegenerative diseases can therefore be distinguished insofar as the severity and location of the associated neuronal lesions differ. Dementia may be observed in various brain diseases, either vascular, metabolic, demyelinating, traumatic, infectious, inflammatory, neoplastic or hydrocephalus (Chui, 1989). It is particularly frequent in neurodegenerative diseases. The recent clinical description of focal lobar atrophies (Weintraub and Mesulam, 1993) and the analysis of cognitive impairment observed in diseases with movement disorders (Cummings and Benson, 1984) have changed the conception of dementia, that may no more be defined as a global deterioration of higher cortical functions. The relative specificity of the cognitive picture of each disease depends on the location of the underlying neuronal lesions. Together with other tools, such as the neurological examination or the functional imagery, the neuropsychological exam may contribute to characterize the clinical picture of a patient with non-Alzheimer's degenerative disease and therefore to determine a clinical diagnosis, that remains probable till the neuropathological confrontation.

Alzheimer Disease↗
PubMed1996

Memory for spatial location is affected in Parkinson's disease.

Are the striato-frontal neuronal circuits implicated in learning of item-specific spatial coordinates? To answer this question, we compared the performance of 20 patients with Parkinson's disease to that of 14 controls matched for age, global cognitive efficiency and mood, on a visuo-spatial learning task with little involvement of motor and constructive functions, allowing control of encoding and comparison of free recall, cued recall and recognition. Compared to controls, patients showed a severe memory impairment for visuo-spatial location of pictures, contrasting with relative preservation of verbal memory, and mild difficulties in perceptive visuo-spatial and executive functions. These results implicate striato-frontal neuronal circuits in memory for spatial location.

Aged↗
PubMed1996

Delayed response tasks in basal ganglia lesions in man: further evidence for a striato-frontal cooperation in behavioural adaptation.

To determine the respective contribution of the subcortical structures and the prefrontal cortex in behavioural adaptation, we applied the delayed response paradigm, considered as a functional marker of the dorsolateral region of the prefrontal cortex, to patients with striatal dysfunction: Parkinson's disease (n = 27), progressive supranuclear palsy (n = 20); to patients with prefrontal lesions (n = 10) and to normal control subjects (n = 24). The performance of each group was compared in four experiments: a delayed response task in which the correct answer was previously indicated by an explicit cue (externally guided task); delayed alternation and non-alternation tasks coupled with a delayed reversal task in which the patient had to discover the rule by himself in the absence of explicit cues (internally driven tasks). All groups of patients showed a short-term spatial representational memory deficit in the externally guided situation. Patients with striatal dysfunction showed difficulties in re-engaging attention on a new programme and in maintaining it. However, they did not express the spontaneous tendency to alternate nor the severe difficulties in disengaging from a previous pattern of response demonstrated by patients with prefrontal lesions. These results validate the concept of a striato-frontal functional system in humans and suggest the existence of two different levels of behavioural organization: elaboration of new programmes of behaviour in association with inhibition of previously established ones, that might be under frontal lobe control: maintenance of the new programme until the action has been accomplished and automatization for a routine utilization, that might be under control of the striatum.

Adaptation, Psychological↗
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

Diagnosis of "sporadic" Huntington's disease.

The diagnosis of Huntington's disease (HD) in patients with progressive chorea and mental impairment, but without similarly affected relatives, remains uncertain and impedes genetic counseling. Twenty patients with suspected HD, but with no family history of the disease underwent molecular analysis of the CAG repeat in the IT15 gene for HD. Eighteen patients displayed the HD expanded allele and two had CAG repeats in the normal range. Neuropsychological tests could be performed in 12 of the 20 patients. Of these 10 with the expanded allele presented the deficits typical of HD, but not the two patients without the HD mutation. This study shows that a neuropsychological pattern is specific to patients with the expanded CAG and that most isolated patients with suspected HD are in fact affected.

Adult↗
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↗