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Biomedical subjects

M M Müller

Publications and source records attributed to M M Müller.

At least 55 records · Page 3Linked to original sources
PubMed2000

[High freuquency oscillatory activity in the human brain].

Synchronized neural activity in animal visual cortex in the frequency range above 20 Hz, the gamma band, has been proposed as a signature of temporal feature binding. More and more research in humans by means of noninvasive electrophysiological recordings was stimulated by these studies. Here, research on evoked and induced gamma band activity in human EEG and MEG mainly in the auditory and visual modality is reviewed and their role in perceptual processes, feature integration and language processing is discussed. In addition, research on the attentional modulation of gamma band activity is reviewed. In contrast to evoked gamma band activity, which occurs right after stimulus onset, induced gamma band activity can be recorded with a latency of 200 to 400 ms and a frequency range of 30 to 95 Hz. Cumulative consistent experimental evidence allows us to conclude that gamma band activity in the human cortex is related to neuronal information processing and cognitive functions, e.g. memory processes. The findings are discussed in the light of different functional theories of induced gamma band activity.

Cerebral Cortex↗
PubMed1999

Human gamma band activity and perception of a gestalt.

Neuronal oscillations in the gamma band (above 30 Hz) have been proposed to be a possible mechanism for the visual representation of objects. The present study examined the topography of gamma band spectral power and event-related potentials in human EEG associated with perceptual switching effected by rotating ambiguous (bistable) figures. Eleven healthy human subjects were presented two rotating bistable figures: first, a face figure that allowed perception of a sad or happy face depending on orientation and therefore caused a perceptual switch at defined points in time when rotated, and, second, a modified version of the Rubin vase, allowing perception as a vase or two faces whereby the switch was orientation-independent. Nonrotating figures served as further control stimuli. EEG was recorded using a high-density array with 128 electrodes. We found a negative event-related potential associated with the switching of the sad-happy figure, which was most pronounced at central prefrontal sites. Gamma band activity (GBA) was enhanced at occipital electrode sites in the rotating bistable figures compared with the standing stimuli, being maximal at vertical stimulus orientations that allowed an easy recognition of the sad and happy face or the vase-faces, respectively. At anterior electrodes, GBA showed a complementary pattern, being maximal when stimuli were oriented horizontally. The findings support the notion that formation of a visual percept may involve oscillations in a distributed neuronal assembly.

Adult↗
PubMed1999

[Point-of-care-testing--the intensive care laboratory].

After successful centralization of laboratory analyses since more than 30 years, advances in biosensors, microprocessors, measurement of undiluted whole blood and miniaturization of laboratory analyzers are leading nowadays more and more to a re-decentralization in the laboratory medicine. Point-of-care-testing (POCT), which is defined as any laboratory test performed outside central or decentralized laboratories, is becoming more and more popular. The theoretical advantages of POCT are faster turn-around-times (TAT), more rapid medical decisions, avoidance of sample identification and sample transport problems and the need of only small specimen volumes. These advantages are frequently mentioned, but are not associated with a clear clinical benefit. The disadvantages of POCT such as incorrect handling and/or maintenance of the analyzers by nontrained clinical staff, inadequate or even absent calibrations and/or quality controls, lack of cost-effectiveness because of an increased number of analyzers and more expensive reagents, insufficient documentation and difficult comparability of the obtained POCT-results with routine laboratory results, are strongly evident. According to the authors' opinion the decision for the establishing of POCT has only to be made in a close co-operation between physicians and laboratorians in order to vouch for necessity and high quality of the analyses. Taking the local situation into consideration (24-h-central laboratory, etc.) the spectrum of parameters measured by means of POCT should be rigorously restricted to the vital functions. Such analytes should be: hemoglobin or hematocrit, activated whole blood clotting time, blood gases, sodium, potassium, ionized calcium, glucose, creatinine, ammonia and lactate.

Clinical Laboratory Techniques↗
PubMed1999

Health care system and laboratory medicine in Austria: present status and future perspectives.

In the recent past, the role of laboratory medicine has changed from merely supplier of analytical data to supplier of results together with clinical interpretation. In addition, the role of medical laboratories as important partners of health care management by providing data for management functions and decisions is rapidly growing. The article has the purpose of giving an overview of Austria's population, the governmental system and Austrian health politics in context with European health care. The existing health care system with its historical development, to-date status and recent changes due to socio-economic pressure are outlined. Special emphasis is given to the present situation of medical laboratories in Austria. Furthermore, hospital management strategies and some adjustment processes in the authors' clinical-medical laboratory to alleviate the ongoing economic pressure are described. As far as possible, an attempt of forecasting future scenarios is made.

Austria↗
PubMed1999

Processing of affective pictures modulates right-hemispheric gamma band EEG activity.

The present study was designed to test differential hemispheric activation induced by emotional stimuli in the gamma band range (30-90 Hz). Subjects viewed slides with differing emotional content (from the International Affective Picture System). A significant valence by hemisphere interaction emerged in the gamma band from 30-50 Hz. Other bands, including alpha and beta, did not show such an interaction. Previous hypotheses suggested that the left hemisphere is more involved in positive affective processing as compared to the right hemisphere, while the latter dominates during negative emotions. Contrary to this expectation, the 30-50 Hz band showed relatively more power for negative valence over the left temporal region as compared to the right and a laterality shift towards the right hemisphere for positive valence. In addition, emotional processing enhanced gamma band power at right frontal electrodes regardless of the particular valence as compared to processing neutral pictures. The extended distribution of specific activity in the gamma band may be the signature of cell assemblies with members in limbic, temporal and frontal neocortical structures that differ in spatial distribution depending on the particular type of emotional processing.

Adult↗
PubMed1999

Selective visual-spatial attention alters induced gamma band responses in the human EEG.

OBJECTIVES: The present study was designed to investigate the attentional modulation of gamma band responses in a visual spatial attention task using a 128-channel-EEG-montage. METHODS: Colored rectangles were presented on a screen. After 500 ms an arrow indicated whether subjects had to shift their attention to the left or right half of the screen to detect target stimuli. During the task, either the attended half of the screen rotated horizontally while the unattended part remained motionless, or vice versa. RESULTS: When subjects attended the rotating stimulus, we found significantly higher power in a specific gamma band from 35-51 Hz on parieto-occipital electrode sites contralateral to the stimulation side. In addition, after the onset of the arrow which indicated what side subjects should direct their attention to, the 35-51 Hz response shifted from a broad posterior distribution to an increase of power at parieto-occipital sites contralateral to the to-be-attended side. Furthermore, the rotating stimulus elicited higher gamma band power as compared to the standing stimulus at electrode locations, which may be related to the activity of underlying cortical structures specialized for motion processing. CONCLUSIONS: The present results replicate important parts of previous findings of enhanced gamma power when a moving stimulus was attended.

Adult↗
PubMed1999

Evaluation of the EMIT Mycophenolic Acid Assay from Dade Behring.

The Emit Mycophenolic Acid Assay, a new homogeneous enzyme immunoassay for the quantitative analysis of mycophenolic acid (MPA) in human plasma, was evaluated and compared to a high-performance liquid chromatography (HPLC) method. Coefficients of variation (CV) of the within-run imprecision (n = 10) varied from 2.5% to 4.4% and from 1.3% to 4.9% for the Emit and the HPLC, respectively. The CV's of between-day imprecision (n = 10) ranged from 7.9% to 10.8% for the Emit and from 4.7% to 12.1% for the HPLC. Mean recoveries were 95.6% and 100.1% for Emit and HPLC, respectively. Serial dilution of a patient pool demonstrated a linear relationship between expected (x) and measured (y) concentrations: Emit, y = 0.998x + 0.086; HPLC, y = 1.006x - 0.016. The detection limit and the lower limit of quantification were 0.087 mg/L and 0.20 mg/L for Emit. The detection limit for HPLC was 0.08 mg/L using a signal-to-noise ratio of three. Sample stability under various storage conditions was satisfactory, although storage at -20 degrees C is recommended for storage longer than one day. No cross-reactivity from the major metabolite mycophenolic acid glucuronide (MPAG) was found. A correlation study on 261 patient samples yielded the following regression equation (bivariate Deming procedure): Emit = 1.012HPLC + 0.244, r = 0.970.

Adult↗
PubMed1999

A simple HPLC method for monitoring mycophenolic acid and its glucuronidated metabolite in transplant recipients.

Mycophenolic acid (MPA) is nowadays in broad clinical use as a substitute for azathioprine. An immunoassay for MPA recently received approval for clinical applications. The high performance liquid chromatography (HPLC) assay for measuring MPA and its glucuronide conjugate (MPAG) we describe here is not only rapid and simple but also extremely sensitive at plasma levels obtained during standard immunosuppressive regimens. The determination of MPAG is possible without any change of the chromatographic conditions (detection wavelength of 214 nm, mobile phase: acetonitrile and 50 mmol/l o-phosphoric acid (50:50, V/V), run time: 15 min). The required equipment is a standard HPLC system including a simple UV-detector. Sample volume of 400 microl is required for both determinations. Detection limit is 0.25 micromol/l for MPA and 5 micromol/l for MPAG. Linearity is excellent for serial dilutions (0.5-25 micromol/l for MPA, 25-500 micromol/l for MPAG) and high accuracies favour the method described. More than 2000 plasma samples tested for MPA in patients after heart transplantation within one year and more than 500 samples for MPAG underline the clinical applicability of this assay.

Blood Chemical Analysis↗
PubMed1998

Noninvasive monitoring using serum amyloid A and serum neopterin in cardiac transplantation.

The monitoring of allograft function for cardiac transplant patients still relies on endomyocardial routine biopsies. We investigated the diagnostic value of noninvasive monitoring using the parameters serum amyloid A protein and serum neopterin. The circulating levels of the acute phase reactant, amyloid A protein, and the macrophage product, neopterin, were measured serially in 13 patients after cardiac transplantation. The mean period of observation was 240 days. Nine acute cardiac allograft rejections, five cases of viral infection and eight cases of bacterial infection occurred. The levels of serum amyloid A protein and serum neopterin remained low (x = 6.0 mg/dL and 12.6 nmol/L, respectively) during the periods of stable graft function. In contrast, both parameters were significantly elevated (p < 0.01) during the rejection episodes (x = 12.7 mg/dL and 38.0 nmol/L for serum amyloid A protein and serum neopterin, respectively). For a reliable differentiation between rejection and stable graft function, serum amyloid A protein had a diagnostic accuracy of 84% (with a cut-off level of 10 mg/dL) and serum neopterin had one of 75% (with a cut-off level of 23 nmol/L). However, significant increases in the circulating levels of serum amyloid A protein and serum neopterin were also observed during bacterial (x = 14.9 and 88 nmol/L, respectively) and viral (x = 6.2 mg/dL and 44 nmol/L, respectively) infections. The detection of immunological complications after cardiac transplantation using serial measurements of serum amyloid A protein and serum neopterin is possible. These parameters can be used to help in judging both the need and the optimal timing for the otherwise frequent endomyocardial biopsies.

Antilymphocyte Serum↗
PubMed1998

Perceptual correlates of changes in cortical representation of fingers in blind multifinger Braille readers.

The mature mammalian nervous system alters its functional organization in a use-dependent manner. Enhanced stimulation of a body part enlarges its cortical representational zones and may change its topographic order. Little is known about the perceptual and behavioral relevance of these plastic alterations in cortical organization. We used blind Braille readers who use several fingers on each hand and who do so for many hours each day as a model to investigate this issue. Magnetic source imaging indicated that the cortical somatosensory representation of the fingers was frequently topographically disordered in these subjects; in addition, they frequently misperceived which of these fingers was being touched by a light tactile stimulus. In contrast, neither the disordered representation nor mislocalizations were observed in sighted controls. Blind non-teacher Braille readers who used only one finger for reading were not significantly different from the sighted controls. Thus, use-dependent cortical reorganization can be associated with functionally relevant changes in the perceptual and behavioral capacities of the individual.

Adult↗
PubMed1998

Effects of spatial selective attention on the steady-state visual evoked potential in the 20-28 Hz range.

Steady-state visual evoked potentials (SSVEPs) were recorded from the scalp of subjects who attended to a flickering LED display in one visual field while ignoring a similar display (flickering at a different frequency) in the opposite visual field. The flicker frequencies were 20.8 Hz in the left-field display and 27.8 Hz in the right-field display. The SSVEP to the flicker in either field was enhanced in amplitude when attention was directed to its location. The scalp distribution of this SSVEP enhancement was narrowly focused over the posterior scalp contralateral to the visual field of stimulation. A source analysis using Variable Resolution Electromagnetic Tomography (VARETA) indicated that the source current densities for the SSVEP attention effect had a focal origin in the contralateral parieto-occipital cortex.

Adolescent↗
PubMed1998

The time course of cortical facilitation during cued shifts of spatial attention.

Adaptive behavior requires the rapid switching of attention among potentially relevant stimuli that appear in the environment. The present study used an electrophysiological approach to continuously measure the time course of visual pathway facilitation in human subjects as attention was shifted from one location to another. Steady-state visual evoked potentials (SSVEPs) were recorded to rapidly flickering lights at attended and unattended locations, and variations in SSVEP amplitude over time were calculated after a cue to shift attention. The build-up of cortical facilitation reflected in SSVEP amplitude was found to bear a close temporal relationship with the emergence of accurate target discriminations at the newly attended location.

Attention↗