Biomedical subjects

F Eustache

Publications and source records attributed to F Eustache.

At least 19 recordsLinked to original sources

PubMed2006

Do school-age children remember or know the personal past?

The aim of this study was to examine developmental differences in autobiographical memory using a novel test that assesses its semantic and episodic subcomponents. Forty-two children aged 7-13 years were asked to recall semantic information and episodic events from three different time periods (current school year, last school year, and previous school years). For the recalls of all events, sense of remembering or sense of just knowing was measured via the Remember/Know paradigm. Age-related differences were observed for episodic autobiographical memory whereas semantic autobiographical memory was characterized by a relative developmental invariance. The increase with age was also found in the number of "Remember" responses and their justification in terms of the actual contextual information retrieved-factual, spatial, and, more especially, temporal details. These findings highlight developmental differences between the episodic and semantic subcomponents of autobiographical memory and support the view that mental 'time travel' through subjective time, which allows one to re-experience the past through self-awareness, is the last feature of autobiographical memory to become fully operational.

Adolescent↗

PubMed2006

[Alzheimer's disease and human memory].

Memory disorders observed in Alzheimer's disease gave rise, from the eighties, to a detailed analysis into the framework of cognitive neuropsychology which aimed at describing the deficits of very specific processes. Beyond their clinical interest, these studies contributed to the modelisation of human memory thanks to the characterization of different memory systems and their relationships. The first part of this paper gives an overview of the memory deficits in Alzheimer's disease and insists on particular cognitive phenomena. Hence, several examples are developed in the domains of semantic memory (such as hyperpriming and hypopriming effects) and autobiographical memory. Recent results highlight the existence of severe autobiographical amnesia observed in all neurodegenerative diseases, though with contrasting profiles: Ribot's gradient in Alzheimer's disease (showing that remote memories are better preserved than recent ones), reverse gradient in semantic dementia and no clear gradient in the frontal variant of frontotemporal dementia. The second part of this article presents advances in cognitive neuroscience searching to disclose the cerebral substrates of these cognitive deficits in Alzheimer's disease. The studies using functional imaging techniques are the most informative regarding this problematic. While showing the dysfunctions of an extended network, they emphasize the selectivity of cerebral damages that are at the root of very specific cognitive dysfunctions, coming close in that way to the conceptions of cognitive neuropsychology. These neuroimaging studies unravel the existence of compensatory mechanisms, which until recently were clearly missing in the literature on neurodegenerative diseases. These different researches lead to a wide conception of human memory, not just limited to simple instrumental processes (encoding, storage, retrieval), but necessarily covering models of identity and continuity of the subject, which interact in a dynamic way with eminently changing memory representations.

Alzheimer Disease↗

PubMed2006

[Brain profile of hypometabolism in early Alzheimer's disease: relationships with cognitive deficits and atrophy].

While accurate and early prediction of patients that will develop Alzheimer's disease (AD) in the near future is urgently needed, the amnestic Mild Cognitive Impairment (MCI) state is of particular interest since it most conveniently represents the pre-dementia stage of AD. Consistently, the profile of brain functional alteration constantly evidenced in resting-state SPECT and PET studies is similar to that observed in mild AD, mainly involving the posterior cingulate and temporo-parietal regions. While the former is a characteristic feature of MCI, since it is present in each patient at this stage, the latter seems specifically associated with the future conversion to AD. Moreover, right temporo-parietal hypometabolism has been found to be the best predictor of subsequent global cognitive decline, over and above neuropsychological and MRI volumetric measurements. This review also presents a discussion on the relationships between the brain profile of hypometabolism on the one hand, and cognitive impairment as well as cerebral structural alterations on the other. Thus, firstly, while functional impairment in the posterior cingulate region seems to be associated with deficits in retrieval of episodic memories in MCI, the relationship between right temporo-parietal hypometabolism and cognitive impairment is still obscure. However, several arguments point to its relation with visuo-spatial deficits, which are often associated with future conversion to AD. Secondly, the discordance between brain areas of major functional changes, and those of highest structural alterations, leads to some relevant questions about the relations between both pathological manifestations and their underlying mechanisms. More specifically, additional hypometabolism-inducing factors could occur in areas of highest hypometabolism compared to atrophy, i.e. mainly in posterior associative cortical regions, leading to genuine functional perturbation in early AD before the development of real atrophy and perhaps of disease as well. By contrast, the hippocampus is the main site of atrophy while its functional alteration is still debated, suggesting that compensation/protective mechanisms probably specifically occur in this structure to maintain a high level of metabolism relative to its structural alteration.

Alzheimer Disease↗

PubMed2006

Long-term memory following transient global amnesia: an investigation of episodic and semantic memory.

BACKGROUND: Several studies noted persistence of memory impairment following an episode of transient global amnesia (TGA) with standard tests. AIM: To specify long-term memory impairments in a group of patients selected with stringent criteria. METHODS: Both retrograde and anterograde memory were investigated in 32 patients 13-67 months after a TGA episode with original tasks encompassing retrograde semantic memory (academic, public and personal knowledge), retrograde episodic memory (autobiographical events) and anterograde episodic memory. RESULTS: Patients had preserved academic and public knowledge. Pathological scores were obtained in personal verbal fluency for the two most recent periods, and patients produced less autobiographical events than controls. However, when they were provided time to detail, memories were as episodic as in controls regardless of their remoteness. Anterograde episodic tasks revealed a mild but significant impairment of the capacity of re-living the condition of encoding, i.e. the moment at which words were presented. CONCLUSIONS: Patients who have suffered from an episode of TGA manifest deficits of memory focused on the retrieval of both recent semantic information and episodic memories and especially the capacity of re-living. These deficits may not result from a deterioration of memory per se but rather from difficulties in accessing memories.

Aged↗

PubMed2005

Using voxel-based morphometry to map the structural changes associated with rapid conversion in MCI: a longitudinal MRI study.

Capturing the dynamics of gray matter (GM) atrophy in relation to the conversion from mild cognitive impairment (MCI) to clinically probable Alzheimer's disease (AD) would be of considerable interest. In this prospective study we have used a novel longitudinal voxel-based method to map the progression of GM loss in MCI patients over time and compared converters to non-converters. Eighteen amnestic MCI patients were followed-up for a predefined fixed period of 18 months and conversion was judged according to NINCDS-ADRDA criteria for probable AD. Each patient underwent a high-resolution T1-weighted volume MRI scan both at entry in the study and 18 months later. We used an optimal VBM protocol to compare baseline imaging data of converters to those of non-converters. Moreover, to map GM loss from baseline to follow-up assessment, we used a modified voxel-based morphometry (VBM) procedure specially designed for longitudinal studies. At the end of the follow-up period, seven patients had converted to probable AD. Areas of lower baseline GM value in converters mainly included the hippocampus, parahippocampal cortex, and lingual and fusiform gyri. Regions of significant GM loss over the 18-month follow-up period common to both converters and non-converters included the temporal neocortex, parahippocampal cortex, orbitofrontal and inferior parietal areas, and the left thalamus. However, there was significantly greater GM loss in converters relative to non-converters in the hippocampal area, inferior and middle temporal gyrus, posterior cingulate, and precuneus. This accelerated atrophy may result from both neurofibrillary tangles accumulation and parallel pathological processes such as functional alteration in the posterior cingulate. The ability to longitudinally assess GM changes in MCI offers new perspectives to better understand the pathological processes underlying AD and to monitor the effects of treatment on brain structure.

Aged↗

PubMed2004

Are volunteers delivering semen samples in fertility studies a biased population?

BACKGROUND: It is not known to what extent the results of epidemiological studies on male fertility and semen quality based on voluntary participation in the general population are relevant. METHODS: In a study on the reproductive health of male partners of pregnant women, information was obtained from a group of men agreeing to collect a semen sample and to complete a questionnaire (group A), a group only completing the questionnaire (group B) and from men refusing to participate altogether (group C). RESULTS: The participation rate (group A) was 15.8% for 1409 men approached. Ages and socio-professional status were similar in the three groups. Time to pregnancy (TTP) was not significantly different in groups A and B, although there appeared to be an insignificantly higher proportion of couples taking longer than 12 months to conceive in group A than in group B. A history of urogenital disease appeared to be more frequent in groups A and B than in the general population. However, comparable semen characteristics were found for men with or without a history of urogenital disease. Pregnancy outcomes were similar in the three groups. CONCLUSIONS: The present study does not suggest major selection bias, although the social and reproductive histories of these men may prompt them to participate. Such factors need to be accounted for in similar studies.

Adult↗

PubMed2004

[Brain substrates of episodic memory disorders in Alzheimer's disease].

Resting state PET measurement is useful to unravel brain regions whose dysfunction is responsible for impairment of episodic memory in Alzheimer's disease. First, the consistent hypometabolism of posterior cingulate cortex, temporo-parietal cortex and frontal cortex contrasts with the frequent lack of hippocampal hypometabolism, although it is first to be concerned by neurofibrillary tangles. Several hypotheses are proposed to explain this paradoxical result. Second, the correlative approach (correlations between memory performances and metabolic values on a voxel basis) shows that dysfunction of the hippocampal region is responsible for the earliest deficits of episodic memory, and then suggests the recruitment of neocortical temporal areas normally involved in semantic memory, perhaps as a form of a compensatory mechanism. When applied to the study of Mild Cognitive Impairment, this approach is also very fruitful.

Alzheimer Disease↗

PubMed2004

[At the boundary between normal aging and Alzheimer disease].

Accurately predicting the development of probable Alzheimer's disease (AD) early in the course of the disease would have major implications. Hence, the pre-dementia stage of AD has become a major topic of current research. Amnestic 'mild cognitive impairment' (MCI) has recently emerged as the most convenient avenue to address this Issue, since most of MCI patients will progress to AD, at a rate of 10% to 15% per Year, suggesting that MCI represents the clinical manifestation of incipient AD (Petersen et al., 2001). However, all MCI patients would probably not convert to AD, at least in the near future, so that the Issue of prospective longitudinal studies is to detect specific indices of rapid conversion. In this paper, we focus on longitudinal studies using either neuropsychology, or morphological or functional neuroimaging to find predictive markers allowing to distinguish those MCI patients that rapidly convert to AD from those that do not develop the disease during the follow-up period. Whereas functional neuroimaging, and more specifically FDG-PET, seems particularly accurate to predict AD, the combination of multiple approaches is likely to be a promising avenue.

Aging↗

PubMed2004

The dynamic time course of memory recovery in transient global amnesia.

AIMS: To investigate the dynamic time course of transient global amnesia (TGA)--that is, the process of recovery and the interindividual variability--by testing four patients during the day of TGA itself (on three occasions) and at follow up (on two occasions). METHODS: A specially designed protocol focusing on semantic (both conceptual and autobiographical knowledge) and episodic (both anterograde and retrograde components) memory. RESULTS: Every patient showed marked impairment of both anterograde and retrograde episodic memory during the acute phase, with a relative preservation of personal and conceptual semantic knowledge. During the following phase, the authors observed similarities and differences among the patients' patterns of recovery. In general, retrograde amnesia recovered before the anterograde amnesia and anterograde episodic memory was recovered gradually in every case. In contrast, shrinkage of retrograde amnesia was more heterogeneous. In two of the patients, this shrinkage followed a chronological gradient and the most remote events were recovered first. In the two other patients, it depended more on the strength of the trace, and there was no temporal gradient. For the latter, an executive deficit could account for difficulties in accessing both conceptual knowledge and autobiographical memories. CONCLUSIONS: This profile of recovery suggests a "neocortical to medial temporal" process in every case, and the possibility of an additional frontal dysfunction in some cases. Hence, the acute phase seems to be characterised by a common episodic impairment. This variability between subjects appears in the recovery phase with two different patterns of impairment.

Aged↗

PubMed2003

Mild cognitive impairment: Can FDG-PET predict who is to rapidly convert to Alzheimer's disease?

Patients with mild cognitive impairment (MCI) were assessed, and a metabolic profile associated with conversion to AD at 18-month follow-up was sought. As compared with nonconverters (n = 10), converters (n = 7) had lower fluorodeoxyglucose uptake in the right temporoparietal cortex (p = 0.02, corrected for cluster size), without individual overlap. Awaiting replication in an independent sample, these findings suggest that among patients with MCI, fluorodeoxyglucose PET may accurately identify rapid converters.

Alzheimer Disease↗

PubMed2003

Inter-individual variability in the morphological assessment of human sperm: effect of the level of experience and the use of standard methods.

BACKGROUND: The assessment of human sperm morphology is not devoid of methodological problems, making comparison among laboratories difficult. The main goal of this study was to assess how the experience and compliance to the recommended procedures can modulate it. METHODS: Sixty-two technicians and biologists of varying degrees of andrological experience classified the same 100 sperm in a blind study from images captured on a video microscope and projected onto a screen. David's morphology classification which distinguishes normal and abnormal sperm and calculates a Multiple Anomalies Index (MAI) was used. These sperm were also classified by two trained and experienced biologists using videotaped images to provide reference values. RESULTS: The inter-participant coefficient of variation was 40% for normal sperm, lower for five defects and, 12% for MAI. Experienced participants had the closest results to the reference values. Moreover, participants not routinely using the recommended methodologies, regardless of their experience level, consistently showed marked differences compared with the reference values. CONCLUSIONS: The present data confirm the wide variability in the assessment of normal sperm and show a lower variability for several anomalies and MAI. They underscore the role that experience plays and the importance of following the recommended methodologies for relevant and comparable results.

Clinical Competence↗

PubMed2002

Transient global amnesia: concomitant episodic memory and positron emission tomography assessment in two additional patients.

Transient global amnesia (TGA) is characterized by a profound but transient deficit of episodic memory. The study of cerebral blood flow and oxygen metabolism with positron emission tomography (PET) provides relevant pathophysiologic data, but only three patients have been reported so far and in only one was concomitant neuropsychological testing performed. We report here the concomitant neuropsychological and PET assessment of two additional patients. Episodic disturbance was characterized by a storage disturbance for one case and an incapacity to learn episodic associations in the other, illustrating cognitive heterogeneity despite similar neurological presentation. PET findings disclosed mild but significant changes in the amygdala (right or left) and left posterior hippocampus, which could account for both the storage disturbance and the inability to associate episodic components. The PET findings also argued in favor of a vascular disturbance accompanying TGA.

Aged↗

PubMed2002

Discrimination between Alzheimer dementia and controls by automated analysis of multicenter FDG PET.

A new diagnostic indicator of FDG PET scan abnormality, based on age-adjusted t statistics and an automated voxel-based procedure, is presented and validated in a large data set comprising 110 normal controls and 395 patients with probable Alzheimer's disease (AD) that were studied in eight participating centers. The effect of differences in spatial resolution of PET scanners was minimized effectively by filtering and masking. In controls FDG uptake declined significantly with age in anterior cingulate and frontolateral perisylvian cortex. In patients with probable AD decline of FDG uptake in posterior cingulate, temporoparietal, and prefrontal association cortex was related to dementia severity. These effects were clearly distinct from age effects in controls, suggesting that the disease process of AD is not related to normal aging. Women with probable AD had significantly more frontal metabolic impairment than men. The new indicator of metabolic abnormality in AD-related regions provided 93% sensitivity and specificity for distinction of mild to moderate probable AD from normals, and 84% sensitivity at 93% specificity for detection of very mild probable AD (defined by Mini Mental Score 24 or better). All regions related to AD severity were already affected in very mild AD, suggesting that all vulnerable areas are affected to a similar degree already at disease onset. Ventromedial frontal cortex was also abnormal. In conclusion, automated analysis of multicenter FDG PET is feasible, provides insights into AD pathophysiology, and can be used potentially as a sensitive biomarker for early AD diagnosis.

Aged↗

PubMed2002

Time to pregnancy and semen parameters: a cross-sectional study among fertile couples from four European cities.

BACKGROUND: In fertile populations, little is known about the association between semen parameters and time to pregnancy (TTP). METHODS: Pregnant women from Copenhagen, Edinburgh, Paris and Turku who conceived without medical intervention were asked for their TTP (942 couples), and their partners provided a semen sample. The proportion of morphologically normal sperm and the multiple anomalies index (MAI, ratio of the total number of anomalies to the number of abnormal sperm) were centrally estimated. We estimated rate ratios for the occurrence of a pregnancy by a discrete survival model, adjusted for sexual activity and female factors affecting fecundity. RESULTS: Increasing sperm concentration influenced TTP up to 55 x 10(6)/ml. The proportion of morphologically normal sperm influenced TTP up to 39% according to David's criteria, and this association held among the subjects with a sperm concentration >55 x 10(6)/ml. For strict criteria, the threshold value was 19% normal sperm. An increase of 0.5 in MAI was associated with an adjusted rate ratio for the occurrence of a pregnancy of 0.68 (95% confidence interval: 0.54-0.85). CONCLUSIONS: These results highlight the importance of sperm morphology parameters and indicate that the effect of proportion of normal sperm on TTP may be independent of sperm concentration.

Cross-Sectional Studies↗

PubMed2001

Semantic acquisition without memories: evidence from transient global amnesia.

Transient global amnesia (TGA), characterised by a profound anterograde amnesia, is a model of interest to study the acquisition of novel meanings independent of episodic functioning. Three patients were tested during a TGA attack, two in the early recovery phase and the third during the acute phase of TGA, with a semantic priming task involving a restructuring process of conceptual knowledge. During TGA, all patients demonstrated priming effects. Results obtained the day after the episode with the same task showed that these effects persisted at least one day. Episodic memory seems not to be critical for the formation of novel connections among unrelated semantic representations, in accordance with Tulving's model of memory, i.e. episodic memory is not necessary for the acquisition of semantic information.

Acute Disease↗

PubMed2001

Visual priming within and across symbolic format using a tachistoscopic picture identification task: a PET study.

The present work was aimed at characterizing picture priming effects from two complementary behavioral and functional neuroimaging (positron emission tomography, PET) studies. In two experiments, we used the same line drawings of common living/nonliving objects in a tachistoscopic identification task to contrast two forms of priming. In the within-format priming condition (picture-picture), subjects were instructed to perform a perceptual encoding task in the study phase, whereas in the cross-format priming condition (word-picture), they were instructed to perform a semantic encoding task. In Experiment 1, we showed significant priming effects in both priming conditions. However, the magnitude of priming effects in the same-format/perceptual encoding condition was higher than that in the different-format/semantic encoding condition, while the recognition performance did not differ between the two conditions. This finding supports the existence of two forms of priming that may be subserved by different systems. Consistent with these behavioral findings, the PET data for Experiment 2 revealed distinct priming-related patterns of regional cerebral blood flow (rCBF) decreases for the two priming conditions when primed items were compared to unprimed items. The same-format priming condition involved reductions in cerebral activity particularly in the right extrastriate cortex and left cerebellum, while the different-format priming condition was associated with rCBF decreases in the left inferior temporo-occipital cortex, left frontal regions, and the right cerebellum. These results suggest that the extrastriate cortex may subserve general aspects of perceptual priming, independent of the kind of stimuli, and that the right part of this cortex could underlie the same-format-specific system for pictures. These data also support the idea that the cross-format/semantic encoding priming for pictures represents a form of lexico-semantic priming subserved by a semantic neural network extending from left temporo-occipital cortex to left frontal regions. These results reinforce the distinction between perceptual and conceptual priming for pictures, indicating that different cerebral processes and systems are implicated in these two forms of picture priming.

Adult↗

PubMed2001

Contributions of frontal and medial temporal regions to verbal episodic memory: a PET study.

Using PET, subtraction and correlation analysis were jointly employed to determine the specific and complementary contributions of frontal and medial temporal regions to verbal episodic encoding and retrieval processes. Subtraction analysis highlighted prefrontal rCBF increases which were predominantly left-sided during intentional encoding and exclusively right-sided during retrieval, the latter being moreover associated with bilateral precuneus activation. However, significant correlation between rCBF values obtained during intentional encoding and performance scores obtained during retrieval concerned, among other regions, the left parahippocampal gyrus, which indicated that the higher the neuronal activity in this medial temporal region during encoding, the better the retrieval performance.

Adult↗

PubMed2001

Entorhinal cortex disruption causes memory deficit in early Alzheimer's disease as shown by PET.

Voxel-based mapping of the correlations between cognitive scores and resting-state brain glucose utilization measured by PET has recently emerged as a novel way to reveal in living patients with Alzheimer's disease (AD) the neural systems whose disruption underlies particular neuropsychological, especially mnemonic, deficits. We have now applied this approach using a novel cognitive paradigm designed to selectively assess verbal episodic memory, and show that in early AD disruption of the left entorhinal cortex underlies this memory deficit, consistent with post mortem data showing that this brain area is affected earliest and most severely by tau pathology in AD.

Aged↗