Biomedical subjects

B Desgranges

Publications and source records attributed to B Desgranges.

11 recordsLinked to original sources

PubMed1998

Effects of healthy aging on the regional cerebral metabolic rate of glucose assessed with statistical parametric mapping.

The aging process is thought to result in changes in synaptic activity reflecting both functional and structural cell derangement. However, previous PET reports on age-related changes in resting brain glucose utilization (CMRglc) have been discrepant, presumably because of methodological as well as subject screening differences. In contrast to other studies, which used a region of interest approach, the objective of the present work was to determine, by means of the SPM software, the changes in regional CMRglc as a function of age in 24 optimally healthy, unmedicated volunteers of ages from 20 to 67 years. Global CMRglc showed a significant decline with age (approximately 6% per decade, P < 0.05), which concerned all the voxels studied save for most of the occipital cortex and part of the cerebellum. The most significant effects (P < 0.001) concerned the association neocortex in perisylvian temporoparietal and anterior temporal areas, the insula, the inferior and posterior-lateral frontal regions, the anterior cingulate cortex, the head of caudate nucleus, and the anterior thalamus, in a bilateral and essentially symmetrical fashion. The high posterior parietal cortex was not sampled in this study. This distribution of changes in CMRglc with age may differ from that seen in Alzheimer' disease, where the earliest metabolic reduction has been shown to affect the posterior cingulate cortex.

Adult↗

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 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

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↗

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

[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

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↗

PubMed1994

Right frontal cortex hypometabolism in transient global amnesia. A PET study.

A 60-year-old lady with previous hypertension was studied with PET in the acute (early recovery) phase of an otherwise typical episode of transient global amnesia (TGA). Follow-up over > 1 year was uneventful, and delayed CT scans and MRI showed no brain damage. No medical cause was disclosed despite extensive work-up. The PET study revealed a matched reduction in cerebral blood flow and oxygen consumption over the entire lateral frontal cortex on the right side, with an associated, less significant reduction in ipsilateral thalamic and lentiform nucleus metabolism, but sparing the hippocampal area. These changes, which had resolved at a repeat PET study 3 months later, suggest right prefrontal metabolic depression, possibly secondary to thalamic dysfunction, as the underlying mechanism for TGA in this case, consistent with the emerging involvement of the prefrontal cortex in strategies or control of memory traces retrieval. Thus, in analogy with permanent amnesia, TGA may be a core syndrome with several possible foci of dysfunction along the neuronal networks that subserve explicit memory. In the future, combined PET neuropsychological assessment in the acute stage of TGA may prove useful in defining distinct neuropsychological-topographical subtypes of this intriguing clinical entity.

Amnesia↗