High-field mid-infrared pulses derived from frequency domain optical parametric amplification.

We present a novel, to the best of our knowledge, approach for scaling the peak power of mid-infrared laser pulses with few-cycle duration and carrier-to-envelope phase stabilization. Using frequency domain optical parametric amplification (FOPA), selective amplification is performed on two spectral slices of broadband pulses centered at 1.8 µm wavelength. In addition to amplification, the Fourier plane is used for specific pulse shaping to control both the relative polarization and the phase/delay between the two spectral slices of the input pulses. At the output of the FOPA, intrapulse difference frequency generation provides carrier-envelope phase stabilized two-cycle pulses centered at 9.5 µm wavelength with 25.5 µJ pulse energy. The control of the carrier-envelope phase is demonstrated through the dependence of high-harmonic generation in solids. This architecture is perfectly adapted to be scaled in the future to high average and high peak powers using picosecond ytterbium laser technologies.

[French adaptation of the Hopkins Verbal Learning Test]. / Adaptation française du <>.

INTRODUCTION: A number of tests are currently used in clinical and research settings for the assessment of patients with memory deficits. Among them, the Hopkins Verbal Learning Test (HVLT) is particularly appropriate for the longitudinal follow-up of patients with memory disorders because it exists in six parallel forms, and therefore avoids the risk of learning effect at retest. Since a test with these characteristics is not available in French, we decided to adapt a French version of the HVLT. METHODS: 180 normal subjects participated in the study. Their mean age was 41 years (SD=11), and they had had on average 12 years of schooling (SD=3). The subjects were randomly divided into 6 groups of 30 subjects. One of the six forms of the French version of the HVLT was administered orally to each group of subjects. Each form consisted of a list of 12 words belonging to 3 different semantic categories. For the construction of the French version of the HVLT, we adopted the same procedure as used in the original version of the test taking into account the French lexical and semantic characteristics of the items. In the first part of the test, the list was administered three times to the subjects. Following each administration, subjects were asked for an immediate free recall. Twenty minutes later, used for intercurrent tasks, subjects were asked for a delayed free recall, which was immediately followed by a recognition memory task. In this task, subjects listened to a list of 24 words, 12 belonging to the studied list and 12 were distractors; the subjects were asked to recognize the 12 studied words. RESULTS: The subjects' performance was equivalent in the six forms of the test, except for the immediate recall of Form 3 (which was excluded from the test). No significant difference emerged in free recall, delayed free recall, and recognition across the five remaining forms of the test. CONCLUSION: Our study provides a useful tool for the longitudinal evaluation of patients with memory impairment and may become the test of reference in European longitudinal clinical trials. The French adaptation of the HVLT represents only a first step, because it needs to be standardized, in order to provide norms, and validated, in order to provide values of sensitivity and specificity.

Right-side neglect in Alzheimer's disease.

Unilateral neglect--the inability to pay attention to events occurring on one side of space--usually occurs for left-side events after focal right-hemisphere damage. We report a 73-year-old woman with probable AD and no evidence of focal brain lesions who showed signs of right-side neglect and extinction. Neglect was more severe after 1 year. Neuroimaging techniques demonstrated an asymmetry of cortical involvement, with cortical atrophy and hypoperfusion predominant in the left posterior regions. Unilateral neglect should be assessed systematically in AD.

Retest effects and cognitive decline in longitudinal follow-up of patients with early HD.

OBJECTIVE: To assess the natural progression of cognitive impairment in Huntington's disease (HD) and to reveal factors that may mask this progression. BACKGROUND: Although numerous cross-sectional studies reported cognitive deterioration at different stages of the disease, progressive cognitive deterioration has been, up to now, difficult to demonstrate in neuropsychological longitudinal studies. METHODS: The authors assessed 22 patients in early stages of HD at yearly intervals for 2 to 4 years (average, 31.2 +/- 10 months), using a comprehensive neuropsychological battery based on the Core Assessment Program for Intracerebral Transplantation in Huntington's Disease (CAPIT-HD). RESULTS: The authors observed a significant decline in different cognitive functions over time: these involved primarily attention and executive functions but also involved language comprehension, and visuospatial immediate memory. Episodic memory impairment that was already present at the time of enrollment did not show significant decline. The authors found a significant retest effect at the second assessment in many tasks. CONCLUSION: Many attention and executive tasks adequately assess the progression of the disease at an early stage. For other functions, the overlapping of retest effects and disease progression may confuse the results. High interindividual and intraindividual variability seem to be hallmarks of the disease.

The influence of semantic encoding on recognition memory in Alzheimer's disease.

Within the framework of the distinction between episodic and semantic memory, it has been argued that these two memory systems are organised in a hierarchical way. The hierarchical hypothesis assumes that episodic memory is a specific subsystem of semantic memory and therefore implies that episodic memory cannot exist without semantic memory. If this hypothesis is correct, it should be expected that patients with impaired semantic memory also have impaired episodic memory. In the present study, two experiments investigated the influence of semantic encoding on recognition memory performance in a population of 20 patients with Alzheimer's disease and 18 normal controls. Both experiments assessed recognition memory for semantically-related items. In Experiment 2, but not in Experiment 1, subjects were explicitly instructed to make a semantic association between the items. Alzheimer's disease patients were impaired, compared to the normal controls, on the recognition memory performance of both experiments. The ability to make a semantic association between two items was significantly and positively correlated with the subjects' performance on the recognition tasks. A further analysis showed that patients who were impaired on the semantic association task did significantly worse on the recognition task of Experiment 2 than normal controls and patients who were unimpaired on the semantic association task. These findings are discussed in the context of memory deficits in Alzheimer's disease, and are interpreted as supporting the view that episodic memory for an item is affected by the level of semantic awareness of that same item.

Anosognosia, intrusions and 'frontal' functions in Alzheimer's disease and depression.

The relationship between anosognosia of memory deficit, intrusions and 'frontal' functions was investigated in 12 Alzheimer (DAT) patients, 12 depressed patients and 24 normal controls. DAT and depressed patients could not be dissociated according to the proportion of intrusion they produced in memory tasks. However, regardless of their clinical diagnosis, patients with anosognosia produced significantly more intrusions than patients without anosognosia, and anosognosia of memory deficit was positively and strongly correlated to the tendency to produce intrusions. By contrast, there was no correlation between intrusions, anosognosia and patients' performance on frontal tasks except for Verbal Fluency. Whereas anosognosia of memory deficit seems indispensable for intrusions, frontal dysfunction must not be considered a necessary condition for intrusions or anosognosia.

The influence of semantic and perceptual encoding on recognition memory in Alzheimer's disease.

Previous results from a population of patients with Alzheimer's disease (Dalla Barba and Goldblum, 1996) demonstrated that the ability of patients to make a semantic association between two items was significantly and positively correlated to their performance on a yes/no recognition task for the same items and that patients who were impaired on the semantic task did significantly worse on the recognition task than patients who were unimpaired on the semantic task. These findings gave support to a hierarchical model of organization of human memory in which episodic memory depends on the integrity of semantic memory. The present study further investigates the relationship between semantic memory deficits and episodic recognition memory in 15 patients with Alzheimer's disease and 15 controls, as a function of their semantic and perceptual encoding abilities and of their cognitive impairment in other domains. The results confirmed the previous findings and showed that, although patients heavily relied on perceptual analysis, this type of encoding did not enhance their recognition memory. Correlations analyses showed that some patients who were not impaired in the semantic association, but with particularly low scores on a verbal fluency task presented with a pattern, in recognition memory tasks, that suggests a possible early involvement of frontal lobes in this subgroup of patients.

Multiple-domain dissociation between impaired visual perception and preserved mental imagery in a patient with bilateral extrastriate lesions.

A brain-damaged patient is described whose pattern of performance provides insight into both the functional mechanisms and the neural structures involved in visual mental imagery. The patient became severely agnosic, alexic, achromatopsic and prosopagnosic following bilateral brain lesions in the temporo-occipital cortex. However, her mental imagery for the same visual entities that she could not perceive was perfectly preserved. This clear-cut dissociation held across all the major domains of high-level vision: object recognition, reading, colour and face processing. Our findings, together with other reports on domain-specific dissociations and functional brain imaging studies, provide evidence to support the view that visual perception and visual mental imagery are subserved by independent functional mechanisms, which do not share the same cortical implementation. In particular, our results suggest that mental imagery abilities need not be mediated by early visual cortices.

Different patterns of confabulation.

In this study we investigated the amnesic-confabulatory condition of two patients, M.B. and S.D., exhibiting different patterns of confabulation. Neuropsychological examination showed in M.B. a normal intellectual efficiency and a selective deficit of episodic memory, whereas S.D. was impaired in tests of intellectual efficiency, episodic memory, semantic knowledge and frontal functions. The relation of confabulation to retrieval conditions and the degree of impairment of the semantic memory system was investigated with a set of questions involving the retrieval of various kinds of information. In M.B. confabulation was restricted to episodic memory tasks, whereas in S.D. it also affected the retrieval of semantic information. S.D.'s confabulatory reports were 'semantically anomalous', whereas the semantic structure of M.B.'s confabulations was appropriate. Further investigation using the encoding specificity paradigm showed an interaction of encoding/retrieval conditions in M.B. but not in S.D. This pattern of results is discussed in terms of a different level of disruption of processes that normally monitor the retrieval of information. It is further argued that the confabulation content must be considered in terms of its semantic structure and relies on the level of integrity of semantic knowledge.

Confabulation in a patient with fronto-temporal dementia and a patient with Alzheimer's disease.

This paper describes two patients, O.I. and B.Y., with a confabulatory syndrome. O.I. was diagnosed with probable fronto-temporal dementia, whereas B.Y. met the criteria for probable Alzheimer's disease. O.I., but not B.Y., was impaired on tests of frontal/executive functions, and performed better than B.Y. on clinical tests of memory. Both patients confabulated in episodic/autobiographical memory tasks and in personal future planning tasks. B.Y. confabulated also in a semantic memory task. It is argued that the pattern of confabulation and the cognitive profile shown by the two patients is explained better by the hypothesis proposed by Dalla Barba and co-workers (Dalla Barba et al., 1997b) than by current theories of confabulation.

Autobiographical memory loss and confabulation in Korsakoff's syndrome: a case report.

A patient with Korsakoff's syndrome is presented, who showed a selective loss of Autobiographical Memory along with a preserved Semantic Memory. Confabulations were a prominent feature. They only involved Autobiographical Memory and were persistent in time and consistent in content. The implications of these findings for understanding the nature of Autobiographical Memory impairment are discussed.

Cortical networks implicated in semantic and episodic memory: common or unique?

While previous functional neuroimaging studies have shown that semantic and episodic memory tasks activate different cortical regions, they never compared regional cerebral blood flow (rCBF) patterns associated with semantic and episodic memory within the same experimental design. In this study, we used H2(15)O PET to study subjects in the course of semantic and episodic memory tasks. rCBF was measured in 9 normal volunteers during a resting baseline condition and two cognitive tasks. In the semantic categorisation task subjects heard a list of concrete words and had to respond to words belonging to the "animals" or "food" category. In the episodic recognition task subjects heard a list of concrete words, half "old", i.e. belonging to the list of the semantic categorisation task, and half "new", i.e. presented for the first time. Subjects had to respond to the "old" words. Both tasks were compared to a resting condition. Statistical analysis was performed with Statistical Parametric Mapping (SPM). Compared to the resting condition, the semantic tasks, activated the superior temporal gyri bilaterally, the left frontal cortex, and right premotor cortex. The episodic tasks activated the left superior temporal gyrus, the frontal cortex bilaterally, and the right inferior parietal cortex. Compared to the episodic memory tasks, the semantic memory tasks activated the superior temporal/insular cortex bilaterally and the right premotor cortex. Compared to the semantic memory tasks, the episodic memory tasks activated the right frontal cortex. These results suggest that cortical networks implicated in semantic and episodic memory show both common and unique regions, with the right prefrontal cortex being the neural correlate specific of episodic remembering.

Temporal gradient in confabulation.

We report on a patient, PL, who developed an amnesic confabulatory syndrome following heart arrest. PL's confabulation occurred both in episodic and semantic memory tasks. In a task in which she was asked to identify photographs of people and events highly familiar to her, a temporal gradient on her performance emerged. Confabulation was massive for the recognition of photographs from the eighties and decreased consistently for the recognition of photographs representing people and events from earlier decades. Correct responses, in contrast, were distributed according to an opposite pattern. Correct recognition was very high for photographs from the fifties but consistently decreased for photographs from the following decades. These results are discussed in terms of the co-occurrence and interaction of preserved awareness of the personal past and impaired ability to access less stable memories. These results also suggest that memories are not stored randomly but according to a temporal criterion that presumably reflects the relative strength and stability of stored episodic memories.

An unusual case of perseveration sparing body-related tasks.

A patient who, following left occipital and posterior callosal lesion, showed a massive pattern of perseveration with sparing of body related tasks is described. It is thought that such dissociation would reflect independence of body related tasks at the level of internal representation.

Remembering and knowing the past: a case study of isolated retrograde amnesia.

We describe a patient, RM, who suddenly became amnesic for premorbid autobiographic events in the absence of any known precipitating event. Learning abilities as well as semantic knowledge were normal. Knowledge of famous facts and persons was good, although not perfect. Whether RM suffered from organic or psychogenic isolated retrograde amnesia (IRA) could not be established on the basis of available clinical and neuropsychological elements. Regardless of its aetiology, RM's case respects the boundaries between semantic and episodic memory and so gives further support to the distinction between these two memory systems.

G.B. Vico, precursor of cognitive neuropsychology? The first reported case of noun-verb dissociation following brain damage.

The first case of selective impairment in retrieving verbs in comparison to nouns, following brain damage, was reported in 1744 by the Neapolitan philosopher G. B. Vico. He considered such observation experimental evidence of the correctness of his theory on mental organization of language, thus anticipating the methods of cognitive neuropsychology.

[Neuropsychological aspects of Alzheimer's disease]. / La neuropsychologie de la maladie d'Alzheimer.

This analysis is centered on the study of cognitive disorders in Alzheimer's Disease (AD), mainly for major neuropsychological functions. We insist on the heterogeneity of the clinical picture especially in the early stages of the illness, when deficits of episodic memory and executive functions are prevalent. We consider that studying early stages of the illness is necessary to delineate the diagnostic signs, to validate the new therapeutic experiments, to predict stages of decline.

Unawareness of memory impairment and behavioral abnormalities in patients with Alzheimer's disease: relation to professional health care burden.

OBJECTIVES: The present study investigates the impact of unawareness of deficit (anosognosia) in patients with Alzheimer's disease upon professional health care burden. DESIGN: Cross-sectional study with a consecutive clinical sample from an Alzheimer day-care hospital in France. SUBJECTS: 65 patients with probable AD, aged from 75 to 94 years old, consecutively admitted at the Alzheimer Day Hospital to complete a program of cognitive stimulation and psychosocial rehabilitation. MEASUREMENTS: Each patient was submitted to a standardized evaluation including clinical investigation, cerebral imagery, and neuropsychological assessment. Anosognosia of memory deficit and anosognosia of behavioral disturbances were measured as the "discrepancy scores" between patients' self-reports and family member ratings of patient memory performance and behavioral disturbances. Professional health care burden was assessed with the Professional Health Care Dementia Burden Index (PCDBI; maximal score: 12), designed for this study. Multiple linear regressions were used to examine the correlations between the PCDBI and the severity of anosognosia. RESULTS: The findings showed a significant positive correlation between the PCDBI and both anosognosia of memory impairment and behavioral abnormalities (both p at least less than 0.05). However, there was no significant correlation between the severity of the burden and the severity of cognitive decline or functional impairment (both p at least>0.05). CONCLUSION: Anosognosia in Alzheimer disease patients has a negative impact upon the professional caregivers' burden over and above the cognitive deficit and the functional impairments.

Recognition memory and recollective experience in Alzheimer's disease.

The phenomenal experience that accompanies the recognition of a previously presented stimulus seems to take at least two distinct forms. Recognition can occur when the stimulus evokes some specific experience in which the stimulus was previously involved, or, alternatively, when the stimulus gives rise only to feeling of familiarity without any recollective experience. These two kinds of conscious awareness can be measured in laboratory conditions by "remember" and "know" responses. A "remember" response indicates that recognising the stimulus brings back to mind some conscious recollection of its prior occurrence, whereas a "know" response indicates that recognising the stimulus is not accompanied by any conscious recollection of its prior occurrence. In the experiments reported here the relationship between recognition memory and conscious experience in Alzheimer's disease (AD) patients was investigated. The purpose of the experiments was to compare "remember" measures of conscious awareness in free recognition and forced-choice recognition memory for words and unfamiliar faces. The point of the experiments was to see whether AD patients' performance might be associated with a decrease in the relative incidence of "remember" responses as compared to normal controls (NC), and whether there was an effect of experimental material (words versus faces) on recognition performance and on recollective experience. In both experiments AD patients produced significantly fewer correct responses and fewer "remember" responses for correctly recognised items than NC. By contrast AD patients produced the same proportion of "know" responses to target items as compared to NC in all recognition conditions, with the exception of forced-choice recognition of faces where they gave more "know" responses to target faces than NC. These results are consistent with the assumption that recognition memory may entail two processes, only one of which gives rise to conscious recollection, and they suggest that an impairment of conscious recollection is responsible for the poor performance of AD patients in recognition memory. Implications of these findings for current theories of retrieval are discussed.