Biomedical subjects

F Eustache

Publications and source records attributed to F Eustache.

At least 19 recordsLinked to original sources

PubMed1999

Episodic memory in transient global amnesia: encoding, storage, or retrieval deficit?

OBJECTIVES: To assess episodic memory (especially anterograde amnesia) during the acute phase of transient global amnesia to differentiate an encoding, a storage, or a retrieval deficit. METHODS: In three patients, whose amnestic episode fulfilled all current criteria for transient global amnesia, a neuropsychological protocol was administered which included a word learning task derived from the Grober and Buschke's procedure. RESULTS: In one patient, the results suggested an encoding deficit, and in two others, a storage deficit. CONCLUSIONS: The encoding/storage impairment concerning anterograde amnesia documented in our patients stands in clear contrast with the impairment in retrieval which must underly the retrograde amnesia that also characterises transient global amnesia. This dissociation in turn favours the idea of a functional independence among the cognitive mechanisms that subserve episodic memory.

Aged↗

PubMed1998

Effect of environmental sound familiarity on dynamic neural activation/inhibition patterns: an ERD mapping study.

The aim of this study was to analyze the timing and topography of brain activity in relation to the cognitive processing of different types of auditory information. We specifically investigated the effects of familiarity on environmental sound identification, an issue which has been little studied with respect to cognitive processes, neural substrates, and time course of brain activity. To address this issue, we implemented and applied an electroencephalographic mapping method named event-related desynchronization, which allows one to assess the dynamics of neuronal activity with high temporal resolution (here, 125 ms); we used 19 recording electrodes with standard positioning. We designed an activation paradigm in which healthy subjects were asked to discriminate binaurally heard sounds belonging to one of two distinct categories, "familiar" (i.e., natural environmental sounds) or "unfamiliar" (i.e., altered environmental sounds). The sounds were selected according to strict preexperimental tests so that the former should engage greater semantic, and the latter greater structural, analysis, which we predicted to preferentially implicate left posterior and right brain regions, respectively. During the stimulations, significant desynchronizations (thought to reflect neuronal activations) were recorded over left hemisphere regions for familiar sounds and right temporofrontal regions for unfamiliar sounds, but with only few significant differences between the two sound categories and a common bilateral activation in the frontal regions. However, strongly significant differences between familiar and unfamiliar sounds occurred near the end of and following the stimulations, due to synchronizations (though to reflect deactivations) which appeared over the left posterior regions, as well as the vertex and bilateral frontal cortex, only after unfamiliar sounds. These unexpected synchronizations after the unfamiliar stimuli may reflect an awareness of the unfamiliarity of such sounds, which may have induced an inhibition of semantic and episodic representations because the latter could not be associated with meaningless sounds.

Arousal↗

PubMed1998

The functional neuroanatomy of episodic memory: the role of the frontal lobes, the hippocampal formation, and other areas.

Because it allows direct mapping of synaptic activity during behavior in the normal subject, functional neuroimaging with the activation paradigm, especially positron emission tomography, has recently provided insight into our understanding of the functional neuroanatomy of episodic memory over and above established knowledge from lesional neuropsychology. The most striking application relates to the ability to distinguish the structures implicated in the encoding and the retrieval of episodic information, as these processes are extremely difficult to differentiate with behavioral tasks, either in healthy subjects or in brain-damaged patients. Regarding encoding and retrieval, the results from most studies converge on the involvement of the prefrontal cortex in these processes, with a hemispheric encoding/retrieval asymmetry (HERA) such that the left side is preferentially involved in encoding, and the right in retrieval. However, there are still some questions, for instance, about bilateral activation during retrieval and a possible specialization within the prefrontal cortex. More expected from human and monkey lesional data, the hippocampal formation appears to play a role in both the encoding and the retrieval of episodic information, but the exact conditions which determine hippocampal activation and its fine-grained functional neuroanatomy have yet to be fully elucidated. Other structures are activated during episodic memory tasks, with asymmetric activation that fits the HERA model, such as preferentially left-sided activation of the association temporal and posterior cingulate areas in encoding tasks and preferentially right-sided activation of the association parietal cortex, cerebellum, and posterior cingulate in retrieval tasks. However, this hemispheric asymmetry appears to depend to some extent on the material used. These new data enhance our capacity to comprehend episodic memory deficits in neuropsychology, as well as the neural mechanisms underlying the age-related changes in episodic memory performances.

Brain Mapping↗

PubMed1998

The neural substrates of memory systems impairment in Alzheimer's disease. A PET study of resting brain glucose utilization.

The aim of this study was to determine the neuronal basis for memory impairment in Alzheimer's disease by taking advantage of the clinical and metabolic heterogeneity of this pathology. To this end, 19 patients satisfying the NINCDSADRDA criteria for probably Alzheimer's disease of mild-to-moderate severity underwent a detailed examination of the five memory systems according to Tulving's model, together with a PET measurement of resting regional cerebral glucose utilization (CMRGlc). Compared with controls, the patients as a group showed the expected memory and metabolic profiles of impairment. Correlations (corrected for the effects of ageing) were calculated between memory scores and CMRGlc (normalized by the vermis CMRGlc) using two methods: (i) the classic regions-of-interest method, based on a priori hypotheses and individual coregistered structural MRI; and (ii) the statistical parametric mapping method which allows a systematic voxel-by-voxel analysis, in a more descriptive and exploratory way. Significant correlations were above chance levels and largely consistent between the two methods. They were almost exclusively positive (i.e. in the neurobiologically expected direction) and their distribution showed striking differences according to each memory system. Thus, verbal episodic memory impairment was related to changes in a large neuronal network including not only the limbic structures (mesial temporal cortex, thalamus and cingulate gyrus, with left side predominance) but also the parietotemporal and frontal association cortices of the right hemisphere, possibly on a compensatory basis. Regardless of modality, short-term memory tests were mainly correlated with bilateral activity in posterior association cortex, and also with activity in left prefrontal cortex for the visuospatial span, possibly indicating essentially uniform strategies for the performance of the different tasks. As predicted, semantic memory scores correlated with activity in temporoparietal and frontal association cortices of the left hemisphere, and also with activity in left cingulate cortex. Thus, for episodic, short-term and semantic memory, many findings fit classical neuropsychology, while most of the less expected ones were consistent with recent results from functional neuro-imaging in healthy subjects, notably with the hemispheric encoding/ retrieval asymmetry (HERA) model; only few findings suggested possible reorganization processes and/or recourse to unexpected cognitive strategy. Finally, only negative correlations were found for perceptual priming and procedural memory; although they could arise by chance, some of these unexpected findings give rise to interesting hypotheses about the cognitive relationships between the most and least affected memory systems. This study documents the validity and usefulness of our approach in unravelling the neural substrates of cognitive impairment in brain pathology without focal tissue loss such as that seen in neurodegenerative diseases.

Aged↗

PubMed1998

Preservation of cognitive procedural memory in a case of Korsakoff's syndrome: methodological and theoretical insights.

Using the Tower of Hanoï puzzle, Butters, et al. in 1985 illustrated the difficulties in learning the procedure and questioned the suitability of this task for assessment of the cognitive procedural memory in Korsakoff's syndrome. Our objective, in the light of these criticisms, was to show preservation of cognitive procedure capacities with the Tower of Hanoï for a man (P.F.) who was suffering from alcoholic Korsakoff's syndrome. For this procedural task, some aids helped to compensate in part for the difficulties with declarative memory and with working memory. In this condition, P.F. was able to learn the cognitive procedure. This study suggests that cognitive procedure memory may be preserved in some patients suffering from Korsakoff's syndrome and that this may be shown when a suitable task is used. The result makes it possible to discuss the interaction between declarative and procedural knowledge in the solving of the Tower of Hanoï.

Alcohol Amnestic Disorder↗

PubMed1998

Preservation of the attribute knowledge of concepts in normal aging groups.

The aim of this study was to detect possible alterations in semantic representation during normal aging. Forty young subjects (aged 20 to 30 years) and 40 elderly ones (divided into two groups of 60 to 70 years and 70 to 80 years), all in good health and with high education, completed a test protocol used for assessing semantic knowledge in the study of Alzheimer's disease. The same list of 42 words belonging to three different semantic categories was presented visually three times to the subjects, each time with different instructions: (a) find the words with one letter N (or more) (training task); (b) find the names of animals (test of categorical knowledge); (c) find the words representing something that prick (test of attribute knowledge of concepts). A two-way analysis of variance showed an effect of task (the times taken were significantly longer for the attribute-knowledge test), a group effect (the elderly subjects were slower) and an absence of interaction (the elderly subjects had the same profile as the young group). The results indicate the preservation of the semantic memory in normally aging groups and the usefulness is emphasized in the context of the data given in the literature on Alzheimer's disease.

Adult↗

PubMed1998

[Clinical assessment of dysarthria: presentation and validation of a method].

We adapted in French the Frenchay Dysarthria Assessment (FDA) developed by P. Enderby in 1983. This tool quantitatively evaluates the organs involved in speech and provides a measurement of intelligibility. Productions of normal subjects were analyzed. Reproductibility of data (correlation and interobserver concordance) was high in 18 dysarthric patients. A study performed in 100 dysarthric patients corresponding to 4 types of dysarthria (spastic, ataxic, hypokinetic and mixte) showed that dysarthria resulted from a global impairment of organs implied in speech, rather than one specific organ. The reduction in the intelligibility score was related to organ impairment.

Aged↗

PubMed1998

[Clinical evaluation of memory].

An assessment of memory is relevant in many clinical contexts, but its objectives differ from one situation to another. An initial investigation should make it possible to define these objectives and to formulate hypotheses following the interview with the patient and/or his family and with the help of the overall anamnestic data. The tests proposed would aim at answering the questions according to the particular case of the patient: the supposed disorders, a suggested diagnosis, but also demographic data such as age and educational level. Consequently there is no across-the-board examination of memory and this assessment must be situated in a specific theoretical context. Memory is no longer considered as a single but as a compound function made up of different, relatively independent systems. The examination not only seeks to show the deficits which have a certain significance according to the clinical context, but also aims at bringing out preserved abilities which may contribute to the establishing of the diagnosis and on which rehabilitation and cognitive management may be based. In this article we present several methods of memory assessment with reference to the ideas of Tulving and Schacter, who propose five different memory systems: episodic memory, working memory, semantic memory, perceptive representation system and procedural memory. These assessments are made using standardized tools (tests, questionnaires) and experimental paradigms which have recently emerged in clinical neuropsychology (study of priming effects, of acquisition of skills). One of the present issues is the problem of reconciling the use of standard tools with that of the more sophisticated paradigms drawn up in the light of the most recent theoretical models. Another objective is to relate the findings of these tests to the difficulties the patients have in their everyday lives and so to achieve an ecological understanding of memory disorders.

Humans↗

PubMed1997

The structural components of music perception. A functional anatomical study.

This work explores the cerebral structures involved in the appreciation of music. We studied six young healthy subjects (right handed, French, without musical talent), using a high resolution PET device (CTI 953B) and 15O-labelled water. In three tasks, we studied the effects of selective attention to pitch, timbre and rhythm; a final task studied semantic familiarity with tunes (considered as divided attention for pitch and rhythm). These four tasks were performed on the same material (a tape consisting of 30 randomly arranged sequences of notes). We selected a paradigm, without a reference task, to compare the activations produced by attention to different parameters of the same stimulus. We expected that the activations recorded during each task would differ according to the differences in cognitive operations. We found activations preferentially in the left hemisphere for familiarity, pitch tasks and rhythm, and in the right hemisphere for the timbre task. The familiarity task activated the left inferior frontal gyrus, Brodmann area (BA) 47, and superior temporal gyrus (in its anterior part, BA 22). These activations presumably represent lexico-semantic access to melodic representations. In the pitch task, activations were observed in the left cuneus/precuneus (BA 18/19). These results were unexpected and we interpret them as reflecting a visual mental imagery strategy employed to carry out this task. The rhythm task activated left inferior Broca's area (BA 44/6), with extention into the neighbouring insula, suggesting a role for this cerebral region in the processing of sequential sounds.

Adult↗

PubMed1997

Transient global amnesia: implicit/explicit memory dissociation and PET assessment of brain perfusion and oxygen metabolism in the acute stage.

OBJECTIVES: To assess explicit memory and two components of implicit memory--that is, perceptual-verbal skill learning and lexical-semantic priming effects--as well as resting cerebral blood flow (CBF) and oxygen metabolism (CMRO2) during the acute phase of transient global amnesia. METHODS: In a 59 year old woman, whose amnestic episode fulfilled all current criteria for transient global amnesia, a neuropsychological protocol was administered, including word learning, story recall, categorical fluency, mirror reading, and word stem completion tasks. PET was performed using the (15)O steady state inhalation method, while the patient still exhibited severe anterograde amnesia and was interleaved with the cognitive tests. RESULTS: There was a clear cut dissociation between impaired long term episodic memory and preserved implicit memory for its two components. Categorical fluency was significantly altered, suggesting word retrieval strategy--rather than semantic memory--impairment. The PET study disclosed a reduced CMRO2 with relatively or fully preserved CBF in the left prefrontotemporal cortex and lentiform nucleus, and the reverse pattern over the left occipital cortex. CONCLUSIONS: The PET alterations with patchy CBF-CMRO2 uncoupling would be compatible with a migraine-like phenomenon and indicate that the isolated assessment of perfusion in transient global amnesia may be misleading. The pattern of metabolic depression, with sparing of the hippocampal area, is one among the distinct patterns of brain dysfunction that underlie the (apparently) uniform clinical presentation of transient global amnesia. The finding of a left prefrontal hypometabolism in the face of impaired episodic memory and altered verbal fluency would fit present day concepts from PET activation studies about the role of this area in episodic and semantic memory encoding/retrieval. Likewise, the changes affecting the lenticular nucleus but sparing the caudate would be consistent with the normal performance in perceptual-verbal skill learning. Finally, unaltered lexical-semantic priming effects, despite left temporal cortex hypometabolism, suggest that these processes are subserved by a more distributed neocortical network.

Acute Disease↗

PubMed1997

[Clinical and cognitive study of apraxia in cortico-basal atrophy. A selective disorder of the production system].

The aim of this study was to characterize the different processes underlying apraxic disorders in cortico-basal degeneration. Three patients were submitted to a prospective paradigm elaborated in the theoretical framework proposed by Roy and Square (1985). This cognitive model postulates a two-steps system in the control mechanisms in limb praxis: the conceptual system and the production system. Our results, strictly similar for the three patients, showed a sparing of the conceptual system and an impairment of the production system with a dramatic lack in the control of the temporal and spatial aspects of the gestures. These results suggest a dysfunction of the premotor cortex including the supplementary motor area.

Aged↗

PubMed1996

Agraphia in Alzheimer's disease: an independent lexical impairment.

This study was conducted to delineate the pattern of the writing impairments in 12 patients with Alzheimer type dementia. The patients performed writing tasks involving regular and irregular words and nonwords given by dictation as well as a decision test composed of printed words and pictures requiring phonologic, lexical, and semantic processing. Writing from dictation demonstrated a predominant, but nonisolated, lexical deficit. In order to better evaluate this lexical disorder, the correlation between the dictation writing scores and the decision task scores was analyzed. No significant correlation was found among scores for irregular words, phonologically plausible errors, and scores of the lexical or semantic decision tasks, but there was a significant correlation among scores for the nonwords, nonphonological spelling errors, and scores of the phonologic decision task using printed words. These results would suggest that the "lexical" deficit in agraphia, i.e., difficulty in retrieval or loss of the spelling representations of words, is independent of the lexical or semantic capacities involved in other modalities.

Aged↗

PubMed1996

Memory disorders in Alzheimer's disease and the organization of human memory.

The Squire and Zola-Morgan parallel organization model of the memory and the Tulving hierarchical model were developed mainly through the study of amnesic patients. The predictions of these two models are different, the first being more open to double dissociations and less restrictive than the second. Alzheimer's Disease is characterized by a differential impairment of the memory systems and by an interindividual variability which may take the form of dissociations between preserved and disturbed abilities in some patients. The objective of this study was to use the memory dysfunctions of patients with AD to test the validity of the two models. Analysis of the group data provided an average profile of memory disturbance consistent both with much of the data given in AD literature and with the two models. Using a multiple single-case strategy, we demonstrated several simple dissociations which are for the greater part compatible with the two models. Two of the dissociations underline the limits of the Tulving model, which otherwise accounts for a lot of results. The study supports the relevance of AD for the understanding of the cognitive architecture of the human memory.

Aged↗

PubMed1996

Effect of gastrin-releasing peptide on sperm functions.

Male infertility can be related to defects in motility, capacitation, acrosome reaction, binding and penetration of the zona pellucida. While different in-vitro techniques (such as micromanipulation which is complicated and expensive) are available for the treatment of male infertility, several pharmacological agents have been shown to increase fertilizing capacity under accurate experimental conditions. Gastrin-releasing peptide (GRP, the mammalian homologue of the amphibian skin peptide bombesin) is present in the reproductive tract and expressed by the pregnant ovine endometrium prior to attachment and throughout the pregnancy. A bombesin-like peptide resulting from alternate splicing of the GRP gene in testis has been detected in primates. In this study, we have tested the ability of GRP to enhance human sperm functions such as motility, capacitation, zona binding and acrosome reaction. Analysis of sperm motility was performed with the ATS 20 computer-assisted semen analysis (CASA) system. Zona binding was analysed using intact human unfertilized oocytes and selective labelling of spermatozoa with two fluorochromes. Our results did not show any positive effect of GRP on these parameters under our experimental conditions. However, when GRP at the concentration of 100 nM was added after ionophore treatment, the percentage of reacted cells increased. significantly (P < 0.05) compared with situations where each agent was used alone. This led us to suppose that the role of bombesin in the different stages of fertilization might not exclude other unknown factors.

Acrosome↗

PubMed1996

[Neuro-cognitive models of spelling and Alzheimer disease: mutual clarification].

The neuro-cognitive models developed over the last twenty years have considerably added to the understanding of disorders of spelling and writing resulting from brain lesions. These models differentiate between central processes, damage to which explains linguistic disorders, and peripheral processes, damage to which results in praxia and related disorders. This article analyses studies which have applied these distinctions to disorders observed in Alzheimer's disease. This disease causes unusual pathological situations which show certain types of agraphia rarely seen in the relevant literature, particularly certain peripheral forms. Several studies considered demonstrate the frequency of lexical agraphia in Alzheimer's disease. These lexical disorders of written expression seem to be independent of the lexico-semantic disorders found in other areas of the intellectual processes, Central writing disorders-lexical but also phonological-would appear to be the result of relatively focussed dysfunctionings, the left gyrus angularis and left gyrus supramarginalis respectively, as is suggested in brain metabolism studies. Moreover, certain patients develop peripheral writing disorders which are at present less well known, on a cognitive and neurobiological point of view. Inferences from other pathological contexts reveals that these disorders are often associated with diffuse cerebral lesions. Therefore disorders of written expression in Alzheimer's disease may be the result of two different pathological mechanisms: central disorders arising from localized areas of dysfunctioning at the left temporo-parietal intersection; peripheral disorders linked to the dysfunctioning of a much wider network involving the parietal and frontal regions of both cerebral hemispheres. To account for the diversity of clinical pictures, we suggest a physiopathological hypothesis which could also be used as a therapeutic model in Alzheimer's disease.

Agraphia↗

PubMed1996

[Edouard Claparède and human memory].

The Genevan neurologist and psychologist Edouard Claparède is not well enough known to present-day neuropsychologists However, at the beginning of the century he developed certain modern concepts by introducing the notions of "implicit" and "explicit" into the study of memory. Edouard Claparède applied the saving method in relearning, initiated by Ebbinghaus, in the assessment of abilities retained by patients suffering from Korsakoff's syndrome. He described the two implicit-memory phenomena which are today called "priming effects" and "skill learning". Edouard Claparède also showed the influence of the implicit and explicit memories in recognition. His approach places him in the tradition of the multisystem theories of the memory: he made a distinction between habits and memories and then integrated the idea of familiar knowledge in this architecture of the memory, which is very close to that of Tulving (1985). Moreover, the importance that he gaves to perceptive data in recognition and the self in voluntary recall bring to mind the more recent distinction between data-driven and concept-driven processes in functional theories of memory. This integration of the two approaches, the structural and functional, must place Edouard Claparède among the most important precursors of the theories of human memory.

History, 19th Century↗

PubMed1995

Topographic EEG activations during timbre and pitch discrimination tasks using musical sounds.

Successive auditory stimulation sequences were presented binaurally to 18 young normal volunteers. Five conditions were investigated: two reference tasks, assumed to involve passive listening to couples of musical sounds, and three discrimination tasks, one dealing with pitch, and two with timbre (either with or without the attack). A symmetrical montage of 16 EEG channels was recorded for each subject across the different conditions. Two quantitative parameters of EEG activity were compared among the different sequences within five distinct frequency bands. As compared to a rest (no stimulation) condition, both passive listening conditions led to changes in primary auditory cortex areas. Both discrimination tasks for pitch and timbre led to right hemisphere EEG changes, organized in two poles: an anterior one and a posterior one. After discussing the electrophysiological aspects of this work, these results are interpreted in terms of a network including the right temporal neocortex and the right frontal lobe to maintain the acoustical information in an auditory working memory necessary to carry out the discrimination task.

Adolescent↗

PubMed1995

Healthy aging, memory subsystems and regional cerebral oxygen consumption.

The present study was designed to search for concomitant age-related changes in memory subsystems, defined according to current structural theories, and resting oxygen consumption in selected brain regions. We have investigated a sample of subjects between 20 and 68 years of age and strictly screened for their good health. We applied in the same subjects a battery of neuropsychological tests selected to investigate several memory subsystems, and high-resolution positron imaging with stereotaxic localization to study a purposely limited number of cerebral structures, selected on a priori hypotheses to match the different memory subsystems. Our results showed significant age-related changes in performance on some tests, consistent with the literature, including an increase in semantic memory and a decrease in both working memory (central executive system) and verbal episodic and explicit memory. There was also an age-related linear decrease in global brain oxygen consumption which regionally reached statistical significance for the neocortical areas and the left thalamus. There was a limited number of significant, age-independent correlations between the raw psychometric test scores and resting regional oxidative metabolism. Consistent with our present understanding of the functional anatomy of memory, the Associate Learning scores (verbal episodic and explicit memory) were positively correlated with left hippocampal and thalamic metabolism. The positive relationships found between right hippocampal metabolism and performance in the Associate Learning and the Brown-Peterson tests were less expected but would be consistent with findings from recent PET activation studies. The results from this investigation are discussed in the light of current knowledge concerning the neuropsychology and the neurobiology of both aging and memory.

Adult↗