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A Gade

Publications and source records attributed to A Gade.

At least 19 recordsLinked to original sources
PubMed2003

New direct reaction: two-proton knockout from neutron-rich nuclei.

The reaction 9Be(28Mg,26Ne+gamma)X has been studied at 82 MeV/nucleon together with two similar cases, 30Mg and 34Si. Strong evidence that the reactions are direct is offered by the parallel-momentum distributions of the reaction residues and by the inclusive cross sections. The pattern of the partial cross sections for 28Mg suggests the presence of correlations. A preliminary theoretical discussion based on eikonal reaction theory and the many-body shell model is presented. The reaction holds great promise for the study of neutron-rich nuclei.

Journal Article↗
PubMed2003

The Danish PET/depression project: cognitive function and regional cerebral blood flow.

OBJECTIVE: To clarify the relationship between cognitive functions and regional cerebral blood flow (rCBF) in a large group of depressed patients compared with healthy controls. METHOD: A set of principal components was extracted from scores of a battery of neuropsychological tests of 40 patients suffering from major depression and 49 healthy controls. The components were correlated by multiple linear regression analyses to selected regions of interest in the brain obtained from positron emission tomography images. RESULTS: In contrast to findings in the healthy controls, cognitive functions in the depressed patients correlated significantly with rCBF in specified regions of interest in only a few instances. CONCLUSION: Our study indicates that disturbed cognitive functions in depression do not relate to specific areas of the brain in the same way as normal cognitive functioning, suggesting that the abnormalities of brain function in major depression may be qualitative, rather than quantitative, in nature.

Adolescent↗
PubMed2002

Chromosome 3 linked frontotemporal dementia (FTD-3).

BACKGROUND: The authors have identified and studied a large kindred in which frontotemporal dementia (FTD) is inherited as an autosomal dominant trait. The trait has been mapped to the pericentromeric region of chromosome 3. METHODS: The authors report on the clinical, neuroimaging, neuropsychological, and pathologic features in this unique pedigree collected during 17 years of study. RESULTS: Twenty-two individuals in three generations have been affected; the age at onset varies between 46 and 65 years. The disease presents with a predominantly frontal lobe syndrome but there is also evidence for temporal and dominant parietal lobe dysfunction. Late in the illness individuals develop a florid motor syndrome with pyramidal and extrapyramidal features. Structural imaging reveals generalized cerebral atrophy; H2 15 O-PET scanning in two individuals relatively early and late in the disease shows a striking global reduction in cerebral blood flow affecting all lobes. On macroscopic pathologic examination, there is generalized cerebral atrophy affecting the frontal lobes preferentially. Microscopically, there is neuronal loss and gliosis without specific histopathologic features. CONCLUSIONS: FTD-3 shares clinical and pathologic features with other forms of FTD and fulfills international consensus criteria for FTD. There is involvement of the parietal lobes clinically, radiologically, and pathologically in FTD-3 in contrast to some forms of FTD. This more diffuse involvement of the cerebral cortex leads to a distinctive, global pattern of reduced blood flow on PET scanning.

Autopsy↗
PubMed2002

The role of action knowledge in the comprehension of artefacts--a PET study.

Activation of the left ventral premotor cortex (PMv) has in previous imaging studies been associated with the processing of visually presented artefacts. It has been suggested that this activation reflects processing of action knowledge and that action knowledge contributes to the comprehension of artefacts. The purpose of the present study was to test whether activation of the left PMv is common for all tasks involving the comprehension of artefacts or whether it is task specific. This was done by comparing performance and regional cerebral blood flow (rCBF) associated with two categorization tasks and two naming tasks divided by category (natural objects vs artefacts). The left PMv (BA 6/44) was more activated by the categorization task for artefacts than by the categorization task for natural objects and the naming task for artefacts. However, the left PMv was not associated with the contrast between the naming task for artefacts and the naming task for natural objects nor with the processing of artefacts in general. If the PMv does mediate action knowledge, these results suggest that action knowledge does not contribute directly to the comprehension of artefacts but may support the categorization of artefacts. The significance of these findings is discussed in relation to category-specific recognition impairments for artefacts.

Adult↗
PubMed2002

Brain activity related to integrative processes in visual object recognition: bottom-up integration and the modulatory influence of stored knowledge.

We report evidence from a PET activation study that the inferior occipital gyri (likely to include area V2) and the posterior parts of the fusiform and inferior temporal gyri are involved in the integration of visual elements into perceptual wholes (single objects). Of these areas, the fusiform and inferior temporal gyri were more activated by tasks with recognizable stimuli than by tasks with unrecognizable stimuli. We propose that the posterior parts of the fusiform and inferior temporal gyri, compared with the inferior occipital gyri, are involved in higher level integration, due to the involvement of re-entrant activation from stored structural knowledge. Evidence in favor of this interpretation comes from the additional finding that activation of the anterior part of the left fusiform gyrus and a more anterior part of the right inferior temporal gyrus, areas previously associated with access to stored structural knowledge, was found with recognizable stimuli, but not with unrecognizable stimuli. This latter finding also indicates: (i) that subjects may not refrain from (automatically) identifying objects even if they only have to attend to the objects' global shape, and (ii) that perceptual and memorial processes can be dissociated on both functional and anatomical grounds. No evidence was obtained for the involvement of the parietal lobes in the integration of single objects.

Adult↗
PubMed2000

Effects of attention on dichotic listening: an 15O-PET study.

The present study investigated the effect of attention on brain activation in a dichotic listening situation. Dichotic listening is a technique to study laterality effects in the auditory sensory modality. Two different stimuli were presented simultaneously, one in each ear. Twelve subjects listened to lists of consonant-vowel syllables, or short musical instrument passages, with the task of detecting a "target" syllable or musical instrument by pressing a button. The target stimulus appeared an equal number of times in the left and right ear. The subjects were instructed to either concentrate on the stimuli presented in both ears, or only on the left or right ear stimulus. Brain activation was measured with 15O-PET, and significant changes in regional normalized counts (rNC) were evaluated using statistical parametric mapping (SPM96) software. Concentrating on either the right or left ear stimulus significantly decreased activity bilaterally in the temporal lobes compared to concentrating on both ear stimuli, at the expense of an increased activation in the right posterior and inferior superior parietal lobe. The CV-syllables activated areas corresponding to the classic language areas of Broca and Wernicke. The musical instrument stimuli mainly activated areas in visual association cortex, cerebellum, and the hippocampus. An interpretation of the findings is that attention has a facilitating effect for auditory processing, causing reduced activation in the primary auditory cortex when attention is explicitly recruited. The observed activations in the parietal lobe during the focused attention conditions could be part of a modality non-specific "attentional network".

Adult↗
PubMed2000

Categorization and category effects in normal object recognition: a PET study.

To investigate the neural correlates of the structural and semantic stages of visual object recognition and to see whether any effects of category could be found at these stages, we compared the rCBF associated with two categorization tasks (subjects decided whether pictures represented artefacts or natural objects), and two object decision tasks (subjects decided whether pictures represented real objects or nonobjects). The categorization tasks differed from each other in that the items presented in the critical scan window were drawn primarily from the category of artefacts in the one task and from the category of natural objects in the other. The same was true for the object decision tasks. The experiment thus comprised a two-by-two factorial design. The factors were Task Type with two levels (object decision vs. categorization) and Category also with two levels (natural objects vs. artefacts). The object decision tasks were associated with activation of areas involved in structural processing (fusiform gyri, right inferior frontal gyrus). In contrast, the categorization tasks were associated with activation of the left inferior temporal gyrus, a structure believed to be involved in semantic processing. In addition, activation of the left premotor cortex was found during the categorization of artefacts compared with both the categorization of natural objects and object decision to artefacts. These findings suggest that the structural and semantic stages are dissociable and that the categorization of artefacts, as opposed to the categorization of natural objects, is based, in part, on action knowledge mediated by the left premotor cortex. However, because artefacts and natural objects often caused activation in the same regions within tasks, processing of these categories is not totally segregated. Rather, the categories differ in their weight on different forms of knowledge in particular tasks.

Adult↗
PubMed1999

Brain activation during dichotic presentations of consonant-vowel and musical instrument stimuli: a 15O-PET study.

Dichotic listening means that two different stimuli are presented at the same time, one in each ear. This technique is frequently used in experimental and clinical studies as a measure of hemispheric specialization. The primary aim of the present study was to record regional changes in the distribution of cerebral blood flow (CBF) with the 15O-PET technique to dichotically presented consonant-vowel (CV) and musical instrument stimuli, in order to test the basic assumption of differential hemispheric involvement when stimuli presented to one ear dominate over stimuli presented in the other ear. All stimuli were 380 ms in duration with a 1000 ms interstimulus interval, and were presented in blocks of either CV-syllable or musical instrument pairs. Twelve normal healthy subjects had to press a button whenever they detected a CV-syllable or a musical instrument target in a stream of CV- and musical instrument distractor stimuli. The targets appeared equally often in the right and left ear channel. The CV-syllable and musical instrument targets activated bilateral areas in the superior temporal gyri. However, there were significant interactions with regard to asymmetry of the magnitude of peak activation in the significant activation clusters. The CV-syllables resulted in greater neural activation in the left temporal lobe while the musical instruments resulted in greater neural activation in the right temporal lobe. Within-subjects correlations between magnitude of dichotic listening and CBF asymmetry were, however, non-significant. The changes in neural activation were closely mimicked by the performance data which showed a right ear superiority in response accuracy for the CV-syllables, and a left ear superiority for the musical instruments. In addition to the temporal lobe activations, there were activation tendencies in the left inferior frontal lobe, right dorsolateral prefrontal cortex, left occipital lobe, and cerebellum.

Adult↗
PubMed1999

Perceptual differentiation and category effects in normal object recognition: a PET study.

The purpose of the present PET study was (i) to investigate the neural correlates of object recognition, i.e. the matching of visual forms to memory, and (ii) to test the hypothesis that this process is more difficult for natural objects than for artefacts. This was done by using object decision tasks where subjects decided whether pictures represented real objects or non-objects. The object decision tasks differed in their difficulty (the degree of perceptual differentiation needed to perform them) and in the category of the real objects used (natural objects versus artefacts). A clear effect of task difficulty was found in both the behavioural and in the PET data. In the PET data, the increase in task difficulty was associated with increased regional cerebral blood flow in the posterior part of the right inferior temporal gyrus and in the anterior part of the right fusiform gyrus. This may be the neural correlate of matching visual forms to memory, and the amount of activation in these regions may correspond to the degree of perceptual differentiation required for recognition to occur. With respect to behaviour, it took significantly longer to make object decisions on natural objects than on artefacts in the difficult object decision tasks. Natural objects also recruited larger parts of the right inferior temporal and anterior fusiform gyri compared with artefacts as task difficulty increased. Differences in the amount of activation in these regions may reflect the greater perceptual differentiation required for recognizing natural objects. These findings are discussed in relation to category-specific impairments after neural damage.

Adult↗
PubMed1995

Regional cerebral blood flow and neuropsychological performance in a Danish family with X-linked bulbo-spinal neuronopathy.

Regional Cerebral Blood Flow (rCBF) measurements and neuropsychological evaluation were performed in 6 patients from a Danish family affected with X-linked Bulbo-Spinal Neuronopathy (XBSN). This inherited form of motor neuron disease (MND) has been shown to affect various functions within the nervous and the endocrine systems. We investigated the possibility that focal or diffuse cortical deficits, already demonstrated in MND, were present in XBSN. The global CBF values of the patients, when compared to age- and sex-matched healthy controls, were found reduced, but no focal rCBF alterations, nor increased regional side-to-side asymmetry were observed. The neuropsychological evaluation showed no cognitive impairments. We conclude that cortical perfusion and cognitive functions are not significantly altered in XBSN.

Adult↗
PubMed1992

Linear versus normalized T scores as standardized neuropsychological test scores.

In this paper we present and discuss standardized T score systems for neuropsychological test data. Both linear and normalized T scores were calculated for 141 normal subjects and a group of 141 patients with diffuse or focal brain damage. Many standard neuropsychological tests have skewed raw score and linear T score distributions, and we argue that normalized T scores have practical advantages because they permit simple descriptions of both patient groups and individual test score distributions. We also argue that skewness can be partially explained by ceiling effects and other test construction artefacts and that skewed raw score distributions do not necessarily reflect skewed distributions of the underlying mental abilities. Consequently, use of normalized T scores seems appropriate in many research and clinical contexts.

Adult↗
PubMed1991

[HIV infection and the development of dementia].

Progressive dementia has been described in AIDS patients as the most significant neurologic complication, related to HIV-1 infection directly rather than to opportunistic infections. As the virus seems to enter brain early in the course of infection, incipient dementia or subclinical cognitive impairment have been assumed to occur in otherwise asymptomatic HIV-1 seropositive individuals. A review of relevant neuropsychological studies indicates that this suspicion receives no support in large well-controlled studies. The natural history of AIDS dementia is still not clearly delineated, but encephalopathy seems to develop only with or after systemic immunosuppression.

AIDS Dementia Complex↗
PubMed1991

A critical note on Lezak's 'best performance method' in clinical neuropsychology.

A fundamental problem in clinical neuropsychology is the estimation of premorbid levels of cognitive functioning. Lezak (1983) described the so-called 'best performance method' of estimating premorbid abilities. Essentially, this method consists in using the highest test scores or the best performance in everyday tasks as the best estimate of premorbid ability. This paper describes three studies of the empirical consequences of using the 'best performance method': The first study demonstrates that application of this method on WAIS subtests leads to a gross overestimation of intelligence as measured by the IQ. The second study corroborates this finding and also shows that overestimation of intelligence leads to systematic errors in the expected performance in neuropsychological tests in normal subjects. Finally, the third study shows that this is also the case in patients with diffuse cerebral atrophy.

Adult↗
PubMed1990

Temporal gradient in the remote memory impairment of amnesic patients with lesions in the basal forebrain.

Recall and recognition of premorbid public events were studied in four groups of subjects. Dementia patients showed equal losses from all time periods compared to normal controls. In contrast, two groups of amnesic patients showed extensive remote memory losses, which were most marked for the last few years prior to onset. The difference between recall and recognition was similar in the groups. The results indicate that the retrograde amnesia associated with aneurysms of the anterior communicating artery cannot be distinguished from that of amnesia with other etiologies. Implications of the finding of a temporal gradient in the retrograde amnesia of non-alcoholic amnesics are discussed.

Adult↗
PubMed1988

"Chronic painter's syndrome". A reanalysis of psychological test data in a group of diagnosed cases, based on comparisons with matched controls.

Twenty solvent-exposed workers, most of them painters, had been diagnosed as cases of toxic encephalopathy in 1978/79. Two years later they were re-examined with an extensive battery of neuropsychological tests. Their performance was unchanged on retesting. We have now compared their test results with those of non-exposed control subjects. Previous impressions of significant intellectual impairment in the solvent-exposed patients could not be confirmed when the influence of age, education, and intelligence was taken into consideration. The present group with presumed toxic encephalopathy is assumed to be representative of other patients who were similarly diagnosed in our department. The presently reanalyzed cases had been diagnosed as brain damaged and reported as such in the literature. Thus, they may have contributed to the formation of the concept of the "chronic painters' syndrome" with dementia.

Adult↗
PubMed1987

High-resolution nuclear magnetic resonance imaging and single photon emission computerized tomography--cerebral blood flow in a case of pure sensory stroke and mild dementia owing to subcortical arteriosclerotic encephalopathy (Binswanger's disease).

Pure sensory stroke (PSS) is typically caused by a lacunar infarct located in the ventral-posterior (VP) thalamic nucleus contralateral to the paresthetic symptoms. The lesion is usually so small that it cannot be seen on computerized tomography (CT), as illustrated by our case. In our moderately hypertensive, 72-year-old patient with PSS, CT scanning and conventional nuclear magnetic resonance imaging (NMRI) scanning using a 7-mm-thick slice on a 1.5 Tesla instrument all failed to visualize the thalamic infarct. Using the high-resolution mode with 2-mm slice thickness it was, however, clearly seen. In addition, NMRI unexpectedly showed diffuse periventricular demyelinization as well as three other lacunar infarcts, i.e., findings characteristic of subcortical arteriosclerotic encephalopathy (SAE). This prompted psychometric testing, which revealed signs of mild (subclinical) dementia, in particular involving visiospatial apraxia; this pointed to decreased function of the right parietal cortex, which was structurally intact on CT and NMRI. Single photon emission computerized tomography by Xenon-133 injection and by hexamethyl-propyleneamine-oxim labeled with Technetium-99m showed asymmetric distribution of cerebral blood flow (CBF), with an 18% lower value in the right parietal cortex compared to the left side; this indicated asymmetric disconnection of the cortex by the SAE. Thus, the tomograms of the functional parameter, CBF, correlated better with the deficits revealed by neuropsychological testing than by CT or NMRI.

Aged↗