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Biomedical subjects

W K Strik

Publications and source records attributed to W K Strik.

At least 37 records · Page 2Linked to original sources
PubMed1998

Prefrontal hypooxygenation during language processing assessed with near-infrared spectroscopy.

Near-infrared spectroscopy (NIRS) is a noninvasive optical method which allows in vivo measurements of relative concentrations of oxygenated (O2Hb) and desoxygenated hemoglobin (HHb). It has been successfully applied to assess the blood oxygenation changes during cerebral ischemia in man. An interesting application of NIRS is the investigation of regional cerebral blood oxygenation during physiological brain functions. In the present study, left and right anterior prefrontal brain areas of 10 healthy subjects were investigated with 2-channel NIRS during language processing (reading aloud). Nonverbal visual perception (picture observation) was performed as a control condition. Compared to the respective baseline conditions, a significant HHb increase and an O2Hb decrease as a trend were found during language processing but not during the nonverbal perceptual task, and no hemispheric differences were found. The metabolic activation patterns differed significantly between the tasks indicating the changes due to the language-related efforts but not to visual perception. Based on previous findings of metabolic brain imaging studies the results are best explained as a complementary phenomenon consisting in relative anterior prefrontal hypoperfusion due to a blood volume redistribution which favors language-related temporal areas.

Adult↗
PubMed1997

Decreased EEG microstate duration and anteriorisation of the brain electrical fields in mild and moderate dementia of the Alzheimer type.

Spatially oriented segmentation allows researchers to break down the continuous stream of the ongoing EEG into microstates with stable topography of the brain electrical landscapes. The resulting microstates were shown to be related to conscious mental experience as well as to psychiatric disorders typically associated with thought disorders. In the present study, the microstates of the resting EEG of patients presenting with mild or moderate probable dementia of the Alzheimer type (DAT) were investigated. A significant anteriorisation of the centers of gravity of the microstate fields, an increase of the microstates' optimal window size and a reduced duration of sustained microstates were found. These differences were statistically more robust than the typical changes in the frequency domain (diffuse slowing) and were significantly correlated with the cognitive decline. The adaptive spatial segmentation into microstates is discussed as a method to extract meaningful EEG parameters for the early diagnosis and staging of Alzheimer's disease.

Aged↗
PubMed1997

Right frontal activation during the continuous performance test assessed with near-infrared spectroscopy in healthy subjects.

Near-infrared spectroscopy (NIRS) is a non-invasive optical technique which has been successfully used to register substantial cerebral ischemia. There are indications that NIRS is sensible enough to detect also small metabolic changes during the performance of cognitive tasks. In the present study, two-channel NIRS of left and right anterior frontal brain areas was applied to investigate brain oxygenation of 10 healthy subjects carrying out the continuous performance test (CPT). Significant differences between the left and right hemisphere were found. These consisted of different changes in deoxyhaemoglobin (HHB), but not in oxyhaemoglobin (O2HB) in right frontal brain areas compared to baseline during the test. Despite of some methodological restrictions, the findings suggest that the sensitivity of the NIRS-method is sufficient to detect brain oxygenation changes during cognitive activation. Furthermore, the results support the view that execution of the CPT is associated with prevalently right frontal activation.

Adult↗
PubMed1997

Auditory P300 topography and neuropsychological test performance: evidence for left hemispheric dysfunction in schizophrenia.

Asymmetrical topography of the auditory P300 with reduced left hemispheric amplitudes and, consequently, a right-lateralized peak of the P300 electrical field has been repeatedly reported in schizophrenia. This was interpreted as an indication of reduced left-hemispheric activity during the simple cognitive P300 task. Since generator locations calculated from the surface potentials are ambiguous, further evidence is required to support this conclusion. In the present study, 13 stabilized DSM-III-R schizophrenic patients were studied with an auditory P300 paradigm and neuropsychological methods sensitive to functional brain asymmetries. The tests included the verbal paired associates test (Goldstein et al 1988, Cortex 24:41-52) and the nonspatial conditional associative learning test (Petrides 1985, Neuropsychologia 23:601-614). A significant correlation was found between right-sided lateralization of the P300 maximal positivity and neuropsychological evidence for left hemispheric temporal- hippocampal dysfunction. Attentional performance was correlated with P300 amplitudes. The results of this study provide further evidence that right-sided lateralization of the P300 peaks results from dysfunction of left-hemispheric neuronal generators.

Acoustic Stimulation↗
PubMed1997

EEG-microstates in mild memory impairment and Alzheimer's disease: possible association with disturbed information processing.

The only available functional neuroimaging methods reaching the time resolution of human information processing are EEG and MEG. Since spectral analysis implies analysis of longer time epochs, the high temporal resolution of EEG is partly lost. By dividing the EEG in the time-domain into segments of similar spatial distribution on the scalp (microstates) it has been possible to assess patterns of neuronal activity representing the information process currently performed by the brain. In the present study alterations of EEG microstates in subjective (n = 31) and objective (n = 38) memory impairment as well as in probable Alzheimer disease (DAT: n = 64) compared to healthy controls (n = 21) were investigated. The main findings were reduced segment durations and a more anterior center of gravity of the microstate topography in DAT. With more pronounced cognitive dysfunction larger window sizes were found. Shorter microstates and larger windows reflect more rapidly changing spatial activation patterns, and are interpreted as an impaired capability to establish stable brain states necessary for normal brain function. The anteriorization of the microstates is consistent with results in the frequency domain and may reflect neuropathological changes in DAT.

Aged↗
PubMed1997

A robust assessment of the NoGo-anteriorisation of P300 microstates in a cued Continuous Performance Test.

The Continuous Performance Test (CPT) is successfully applied in clinical routine to evaluate attentional performance. The aim of the present study was to investigate the features of the ERPs related to the conditions of a cued CPT, in particular the Go- and the NoGo-condition demanding either the execution or the inhibition of a prepared motor response. For that purpose, 21-channel-ERPs of ten healthy subjects elicited by the Go, NoGo, primer and distractor cues were analyzed with reference-independent methods. The P300 microstates were identified by means of a data-driven segmentation of the ERPs based on the individual peaks of the Global Field Power (GFP). The topographical assessment of the P300 fields yielded an extraordinarily robust result consisting of a more anterior location of the positive centroid in the NoGo compared to the Go condition in every single subject. In conclusion, this result is an impressive validation of the applied reference-independent spatial analysis which reveals the rapid changes of the brain electrical field configurations related to the execution/inhibition paradigm within the cued CPT. Because of the stability of the NoGo anteriorisation we propose to use this parameter as a topographical standard index, analogous to the amplitude effect between oddball targets and nontargets which defines the classical P300.

Adult↗
PubMed1997

A comparison of qEEG and HMPAO-SPECT in relation to the clinical severity of Alzheimer's disease.

Electroencephalographical studies have disclosed correlations between topographical features of Fast Fourier Transformation maps and the severity of Alzheimer's disease (DAT). The object of the present study was to explore the relations of HMPAO-SPECT and quantitative EEG (qEEG) with the severity of dementia. Twenty-three patients were included in the study. Spectral and topographical EEG parameters were compared with global and regional cerebral blood flow, and with psychometric measures of clinical severity. None of the regions of interest of the SPECT scans were significantly correlated with clinical severity. Low values in delta- and theta bands, however, were related to high scores on the Mini-Mental-State examination (P < 0.01), whereas the Syndrome-Kurz test correlated inversely with the power values in the alpha and beta band. The global decrease in cerebral blood flow (CBF) was associated with a shift on the topographical alpha-centroids in the posterior direction (P < 0.01). In previous studies correlations between CBF and clinical severity were weak, indicating a high interindividual variance, or interactions with concomitant vascular lesions. Whereas SPECT is a well-established tool for the diagnosis of dementia, the present study indicates qEEG as a potential marker for the staging of the cognitive decline in DAT.

Aged↗
PubMed1997

[The psychiatric illness of Vincent van Gogh].

Vincent van Gogh's illness has been the object of much speculation. Explanations as disparate as acute intermittent porphyria, epilepsy and schizophrenia have been proposed. Many of the diagnostic hypotheses, however, are based on partial or incomplete consideration of the biography and of the reports of his subjective experience in his letters to his brother. Karl Leonhard showed, in a detailed analysis of Vincent's biography, that both the course and symptoms of the disorder were consistent with the diagnosis of a cycloid psychosis (anxiety-elation psychosis). In the present paper, the diagnostic judgement of Leonhard is described and discussed in the light of independent research on van Gogh's letters, his works and biography. The bibliographical sources were investigated for information consistent with a cycloid psychosis, but also for information that might contradict this hypothesis. The course and symptoms of the disorder are presented as comprehensively and systematically as possible and are documented with the respective citations. Furthermore, the most important diagnoses proposed in the literature are critically discussed. Based on this investigation, it was possible to show that only the diagnosis of a cycloid psychosis allowed us to connect all the available information to a typical psychiatric syndrome.

Famous Persons↗
PubMed1997

[Reversible neuropsychiatric side effects of lithium with normal serum levels. A case report].

Lithium therapy in patients with manic depressive disorder occasionally causes neuropsychiatric side effects even at therapeutic serum levels. Those lithium-induced symptoms can be polymorphous and may be hard to differentiate from other disorders and from other drugs' side effects. We report the case of a 56-year-old woman with manic-depressive illness, who developed neuropsychiatric side effects from lithium prophylaxis at therapeutic serum levels. The symptoms included disorientation, aphasia, ideatoric apraxia, parkinsonism, restlessness and severe sleep disorder. In contrast to previous reports, the casual role lithium was underscored by symptom increase after lithium re-exposure at therapeutic serum levels. The patient recovered completely after cessation of the lithium prophylaxis.

Antimanic Agents↗
PubMed1997

Neurophysiological correlates of mental imagery in different sensory modalities.

Mental Imagery is supposed to be a basic phenomenon of conscious mental operations, which is exerted in any sensory modality. The aim of the present study was to investigate neurophysiological correlates of mental imagery in the visual, the acoustic and tactile modality. For that purpose, word lists were created based on their power to evoke mental imagery in these modalities. Nine young healthy volunteers were included. Words were presented on a computer screen with 3-s intervals. Evoked electrical activity was recorded simultaneously with a 21-channel system. After inspection for artifacts and off-line averaging, further analysis was performed in a time range of 250-450 ms, corresponding to the P300 component. Within this range, six topographically stable segments were found. A repeated measures ANOVA was significant for the left-right directions of the positive and of the negative centroid, but not for the anterior-posterior directions. The posterior centroid was most right-located in the visual sensory modality and most left-located for tactile imagery; in the acoustic modality it had a midline-position. These differences in centroid locations during mental imagery in different sensory modalities can be explained by the underlying activity of different neural generator ensembles, possibly involving modality specific primary cortical areas.

Adult↗
PubMed1997

Loss of functional hemispheric asymmetry in Alzheimer's dementia assessed with near-infrared spectroscopy.

In a total of 10 patients with dementia of the Alzheimer-type (DAT) and in 10 healthy controls near-infrared spectroscopy (NIRS), a new non-invasive optical method, was used to measure the changes of concentrations of oxy- (O2HB) and deoxyhemoglobin (HHB) in left and right hemispheric prefrontal brain tissue areas during performance of the Verbal Fluency Test (VFT). On a neuropsychological level, the healthy subjects performed better in the VFT than patients with DAT. Statistical analysis of the relative concentrations of O2HB and HHB measured with NIRS during performance of the VFT revealed a significant interaction of the hemispheric effects with the diagnosis. A possible interpretation of this finding is that a good performance in the VFT relies on a predominantly left hemispheric activation observed in controls, whereas a low number of correct responses is associated with a loss of this asymmetric activation in patients with DAT. Although both, patients and controls, performed better in the category version of the VFT, the metabolic effects of this task were significantly less pronounced than in the letter version. This indicates that different energy demands, according to the type of access to the memory stores, may be interpreted as the result of a less energy-demanding access to categorically stored information and adds further evidence to the view that memory departments in humans are organized according to categorical principles.

Adult↗
PubMed1997

Specific P300 features in patients with cycloid psychosis.

In previous studies, low amplitudes and asymmetrical topography with right-sided peaks of the P300-evoked response have been repeatedly described in schizophrenic patients. A sample consisting of 18 patients with cycloid psychosis fulfilling the criteria of Perris and Brockington and 18 controls was investigated with a standard auditory odd-ball paradigm and multichannel evoked potential recordings. Patients had normal P300 topographies and latencies but significantly higher amplitudes than the controls. Higher than normal P300 amplitudes have not been described in any other psychiatric disorder until now, and indicate an enhanced level of arousal. Future studies are expected to shed light on the question of whether high P300 amplitudes are transitory sequelae of the acute psychotic episode or a trait of cycloid psychosis.

Adult↗
PubMed1997

Correlations of topographical EEG features with clinical severity in mild and moderate dementia of Alzheimer type.

Quantitative electroencephalography (qEEG) and the Folstein Mini Mental State examination (MMSE) were obtained from 31 patients affected by probable dementia of Alzheimer's type (DAT). qEEG data were examined both by spectral analysis (Fast Fourier Transformation) and by single frequency band topographical centroid, and compared with those of 24 healthy subjects of the same age group. DAT patients were found to have higher absolute power in the slow (delta and theta) frequency bands. Quantitative topographical assessment showed significantly more anteriorly located centers of gravity for the alpha and beta activity. Only alpha anteriorization was correlated with the degree of cognitive impairment as measured by the global deterioration scale and MMSE. It is concluded that quantitative topographical assessment was successful for the statistical handling of the EEG power maps, and to identify a potential parameter for the functional staging of the disease.

Aged↗
PubMed1996

The predictive value of P300-amplitudes in the course of schizophrenic disorders.

Auditory P300-amplitudes have been found to be correlated with the social functioning and with the impairment in daily life by negative symptoms in cross-sectional studies. In this prospective longitudinal study, the correlation of auditory P300-amplitudes registrated at the index examination was investigated with the clinical outcome after an average of 2.4 years. Based on previous studies, only schizophrenic patients who were in a stabilized residual state were included in the study. Reference-independent P300-parameters of the index examination were correlated with axis V of DSM-III-R (GAF), with the Brief Psychiatric Rating Scale (BPRS) and with the Scale for Assessment of Negative Symptoms (SANS) assessed at the follow-up examination. The correlation of index P300-amplitude with social functioning at follow-up was significant. No correlations of index P300 with the current symptomatology at follow-up, as expressed by BPRS and SANS was found, however. The results indicate a predictive value of the P300-amplitude on the clinical outcome in terms of social functioning of schizophrenic patients.

Acoustic Stimulation↗
PubMed1996

Event-related potential P300 microstate topography during visual one- and two-dimensional tasks in chronic schizophrenics.

Reports on left-lateralized abnormalities of component P300 of event-related brain potentials (ERP) in schizophrenics typically did not vary task difficulties. We collected 16-channel ERP in 13 chronic, medicated schizophrenics (25 +/- 4.9 years) and 13 matched controls in a visual P300 paradigm with targets defined by one or two stimulus dimensions (C1: color; C2: color and tilt); subjects key-pressed to targets. The mean target-ERP map landscapes were assessed numerically by the locations of the positive and negative map-area centroids. The centroids time-space trajectories were searched for the P300 microstate landscape defined by the positive centroid posterior of the negative centroid. At P300 microstate centre latencies in C1, patients' maps tended to a right shift of the positive centroid (p < 0.10); in C2 the anterior centroid was more posterior (p < 0.07) and the posterior (positive) centroid more anterior (p < 0.03), but without left-right difference. Duration of P300 microstate in C2 was shorter in patients (232 vs 347 ms; p < 0.03) and the latency of maximal strength of P300 microstate increased significantly in patients (C1: 459 vs 376 ms; C2: 585 vs 525 ms). In summary only the one-dimensional task C1 supported left-sided abnormalities; the two-dimensional task C2 produced abnormal P300 microstate map landscapes in schizophrenics, but no abnormal lateralization. Thus, information processing involved clearly aberrant neural populations in schizophrenics, different when processing one and two stimulus dimensions. The lack of lateralization in the two-dimensional task supported the view that left-temporal abnormality in schizophrenics is only one of several task-dependent aberrations.

Adolescent↗
PubMed1996

Specific P300 features in patients with cycloid psychosis.

In previous studies, low amplitudes and asymmetrical topography with right-sided peaks of the P300-evoked response have been repeatedly described in schizophrenic patients. A total of 18 patients with cycloid psychosis fulfilling the criteria of Perris and Brockington and 18 controls were investigated with a standard auditory odd-ball paradigm and multichannel-evoked potential recordings. Patients had normal P300 topographies and latencies but significantly higher amplitudes than controls. Higher than normal P300 amplitudes have not been described in any other psychiatric disorder until now, and indicate an enhanced level of arousal. Future studies are expected to shed light on the question of whether high P300 amplitudes are transitory sequelae of the acute psychotic episode or a trait of cycloid psychosis.

Adult↗
PubMed1996

[Acute organic psychosis after malaria tropica].

Neuropsychiatric complications in the course of plasmodium falciparum infection are usually summarized as cerebral malaria. Heterogeneous clinical symptoms, different courses and inconstant parasitemia, however, suggest different pathogenic mechanisms. We report a case of an acute symptomatic psychosis occurring two weeks after successful therapy of a primary manifestation of plasmodium falciparum infection. The diagnosis of meningoencephalitis was based on lymphocytic pleocytosis of cerebrospinal fluid and hyperintense lesions in cranial magnetic resonance imaging. Due to the lack of plasmodium falciparum parasitemia and of serological evidence of viral infection a final diagnosis was not possible. Considering the pertinent literature, an immune-mediated complication of plasmodium falciparum infection (acute disseminated encephalomyelitis, ADEM) appears to be more probable than a direct viral or plasmodium CNS infection. We propose to reverse the term cerebral malaria for the cases with direct pathogenic influence of plasmodium falciparum, and to distinguish it from cases with possible immune-mediated pathogenesis.

Adult↗