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Biomedical subjects

J Hennig

Publications and source records attributed to J Hennig.

At least 91 records · Page 5Linked to original sources
PubMed1999

Visual processing in infants and children studied using functional MRI.

We studied the development of visual processing in 58 children, ranging from 1 d to 12 y of age (median age 29 mo), using functional magnetic resonance imaging. All but nine children had either been sedated using chloral hydrate (n = 12) or pentobarbital (n = 28). Nine children were studied under a full halothane/ N2O:O2 anesthesia. In the first postnatal month, 30% of the neonates showed a positive blood oxygenation level-dependent (BOLD) contrast signal, whereas, for infants between the ages of 1 mo and 1 y, 27% did so. Thirty-one percent of children between 1 and 6 y of age and 71% of children aged 6 y and above showed a positive BOLD contrast signal change to our visual stimulation paradigm. Besides the usual positive BOLD contrast signal change, we also noted that a large portion of the children measured displayed a negative BOLD contrast signal change. This negative BOLD contrast signal change was observed in 30% of children up to 1 mo of age, in 27% between 1 mo and 1 y of age, in 47% between 1 and 6 y of age, and in 14% of children 6 y and older. In the children in which we observed a negative correlating BOLD contrast signal change, the locus was more anterior and more lateral than the positive BOLD contrast signal, placing it in the secondary visual cortical area. The results indicate that when using functional magnetic resonance imaging on children, the primary visual cortical area does not respond functionally in the same manner as that of the adult until 1.5 y of age. This supports earlier clinical and electrophysiologic findings that different cortical mechanisms seem to contribute to visual perception at different times postnatally.

Adult↗
PubMed1998

The processing of first- and second-order motion in human visual cortex assessed by functional magnetic resonance imaging (fMRI).

We have examined the activity levels produced in various areas of the human occipital cortex in response to various motion stimuli using functional magnetic resonance imaging (fMRI) methods. In addition to standard luminance-defined (first-order) motion, three types of second-order motion were used. The areas examined were the motion area V5 (MT) and the following areas that were delineated using retinotopic mapping procedures: V1, V2, V3, VP, V3A, and a new area that we refer to as V3B. Area V5 is strongly activated by second-order as well as by first-order motion. This activation is highly motion-specific. Areas V1 and V2 give good responses to all motion stimuli, but the activity seems to be related primarily to the local spatial and temporal structure in the image rather than to motion processing. Area V3 and its ventral counterpart VP also respond well to all our stimuli and show a slightly greater degree of motion specificity than do V1 and V2. Unlike V1 and V2, the response in V3 and VP is significantly greater for second-order motion than for first-order motion. This trend is evident, but less marked, in V3A and V3B and absent in V5. The results are consistent with the hypothesis that first-order motion sensitivity arises in V1, that second-order motion is first represented explicitly in V3 and VP, and that V5 (and perhaps also V3A and V3B) is involved in further processing of motion information, including the integration of motion signals of the two types.

Brain Mapping↗
PubMed1998

Ethylene-insensitive tobacco lacks nonhost resistance against soil-borne fungi.

Enhanced ethylene production is an early response of plants to pathogen attack and has been associated with both resistance and susceptibility to disease. Tobacco plants were transformed with the mutant etr1-1 gene from Arabidopsis, conferring dominant ethylene insensitivity. Besides lacking known ethylene responses, these transformants (Tetr) did not slow growth when contacting neighboring plants, hardly expressed defense-related basic pathogenesis-related proteins, and developed spontaneous stem browning. Whereas hypersensitive resistance to tobacco mosaic virus was unimpaired, Tetr plants had lost nonhost resistance against normally nonpathogenic soil-borne fungi.

Journal Article↗
PubMed1998

Improvement of spatial resolution of keyhole effect images.

An algorithm is proposed which improves the spatial resolution of difference or effect images acquired with a keyhole sampling strategy. This new reconstruction algorithm uses a priori information about sharp structures in the observed signal changes from a high resolution reference scan. The potential of this algorithm even being able to deal with noisy effect images is illustrated by application to functional MRI data.

Algorithms↗
PubMed1998

Functional imaging by I0- and T2*-parameter mapping using multi-image EPI.

A new functional imaging method has been developed and used to measure T2*- and initial intensity (I0)-parameter maps of multiple slices during activation of the cortex with high temporal resolution. Multiple echo-planar images (EPIs) are read out after a single excitation of the spin system, leading to several images with increasing effective echo times. Changes induced by primary visual stimulation in T2* and I0 were measured in eight subjects. Although stimulation-induced increases in I0 only occurred at short repetition times, T2* increased from 57.3 to 60.9 ms on average. The method combines the high stability of a single shot EPI experiment with the high information content of a multiecho acquisition. In addition, stimulation-induced changes in inflow can be easily separated from true blood oxygenation level dependent (BOLD) signal changes.

Arousal↗
PubMed1998

Reduced circular field-of-view imaging.

A rapid dynamic imaging technique based on polar k-space sampling is presented. A gain in temporal resolution is achieved by angular undersampling. A detailed analysis of the point spread function of angular undersampled polar imaging reveals a reduced diameter of the corresponding circular field of view. Under the assumption that dynamic changes are restricted to a local circular field of view, angular undersampled dynamic imaging allows the recording of rapid changes at high temporal and spatial resolution. The theoretical and experimental details of the technique are presented.

Artifacts↗
PubMed1998

Personality related effects of nicotine, mode of application, and expectancies on performance, emotional states, and desire for smoking.

Three separate factors relevant to nicotine effects have been investigated in this experiment in combination: the experimentally induced expectation about receiving a sham or a nicotine cigarette, the mode of application of nicotine by a tablet, by a cigarette or not at all, while the belief of receiving the nicotine via smoking was held constant in each condition (by nicotine or sham smoking), and the personality factors of extraversion or neuroticism, respectively. Ninety-six healthy female student smokers were tested in a 2 x 3 x 2 factorial group comparison design with respect to critical flicker fusion and reaction time performance as well as to self-ratings on emotional and cortical arousal and ratings on desire for further cigarettes (satisfaction from smoking a single cigarette containing either 0.8 mg nicotine or a sham cigarette). In each case, a tablet containing either nicotine or placebo was administered together with the cigarette. The results showed that performance is sensitive to interaction effects of instruction and mode of application. The instruction of sham or nicotine assignment when applied with a congruent treatment (sham with a sham cigarette, or nicotine with a nicotine cigarette) both increased performance, while groups with discordant information showed worse performance. The administration of nicotine by tablets or by smoking differs considerably, nicotine cigarettes causing a stronger increase in emotional arousal, tablets rather a decrease or no effect, while the true placebo condition increases arousal due to deprivation effects. This leads to an enhancement of the nicotine effect with real smoking and to reactive increase of effort when sham smoking. The instruction affects alertness, the nicotine illusion leading to a lower reduction in subjective reports of alertness and concentration than that observed with the sham instruction. Neurotic subjects become more anxious and tense with nicotine cigarettes than stable subjects. This effect is less pronounced or even reversed with tablets. No interactions with instructions are observed with neuroticism. Extraverts tend to show a decrease in performance but an increase in alertness with the instruction of receiving nicotine as opposed to the sham expectation, whereas introverts behave the opposite way. Subjective ratings on arousal seem to follow the law of transmarginal inhibition, with extraverts being pushed from low arousal to high and introverts vice versa by the mere expectation.

Adult↗
PubMed1998

The fibromyalgia syndrome as a manifestation of neuroticism?

After elucidating the components and theory of neuroticism (N) as well as of psychosomatic complaints and their relationships to personality dimensions and to psychosomatic diseases, comparisons are performed between patients suffering from fibromyalgia syndrome (FMS) or related pain diseases with healthy subjects scoring high on personality dimensions related to neuroticism. FMS and pain patients score high on depression, anxiety, and experience of stress although questionnaire scores on depression are higher in subjects not exhibiting somatic features of the disease. High subjective pain sensitivity and low thresholds for pain perception are also common features in high N subjects and FMS patients. On the endocrinological level cortisol responses to challenge tests with CRH as well as prolactin responses to TRH are higher in FMS patients than in high N healthy subjects indicating an endocrinological difference. A common feature, however, is the lack of adaptability in the two groups, since neurotics are in particular characterized by a low capacity to shift their behavior from one state to the other (waking-sleeping, working-relaxing), to re-adapt to baseline levels after endocrinological or physiological stress responses, or to adjust to conditions of shift work. This is reflected by chronobiological disturbances in FMS patients and could also explain their maintainance of pain perception, because they are incapable of correcting conditioned pain-producing muscle tension.

Adaptation, Psychological↗
PubMed1998

A comparison between electric source localisation and fMRI during somatosensory stimulation.

The present study investigates the electric source localisation of somatosensory evoked potentials (SEPs) using high-resolution EEG (61 scalp electrodes) considering the individual brain morphology as obtained from magnetic resonance images (MRI). A comparison with the activation maps in fMRI under the same somatosensory stimulation paradigm was done. The somatosensory evoked potentials (SEPs) to electrical stimulation of the right median nerve were collected from the scalp of 8 healthy right-handed subjects. The source reconstruction for the 20 ms SEP component was performed by using a single moving dipole model as a source model and a spherical three-shell model as a head model. In 6 of the subjects fMRI was performed using the same electric stimulation of the right median nerve. The source location of the 20 ms SEP component was found to be within the postcentral gyrus. The fMRI activation maps were also located in the postcentral gyrus when using the same somatosensory stimulation paradigm. The appropriateness of using high-resolution EEG and fMRI in the functional localisation of the primary somatosensory cortex is discussed.

Adult↗
PubMed1998

Absolute metabolite quantification by in vivo NMR spectroscopy: II. A multicentre trial of protocols for in vivo localised proton studies of human brain.

We have performed a multicentre trial to assess the performance of three techniques for absolute quantification of cerebral metabolites using in vivo proton nuclear magnetic resonance (NMR). The techniques included were 1) an internal water standard method, 2) an external standard method based on phantom replacement, and 3) a more sophisticated method incorporating elements of both the internal and external standard approaches, together with compartmental analysis of brain water. Only the internal water standard technique could be readily implemented at all participating sites and gave acceptable precision and interlaboratory reproducibility. This method was insensitive to many of the experimental factors affecting the performance of the alternative techniques, including effects related to loading, standing waves and B1 inhomogeneities; and practical issues of phantom positioning, user expertise and examination duration. However, the internal water standard method assumes a value for the concentration of NMR-visible water within the spectroscopic volume of interest. In general, it is necessary to modify this assumed concentration on the basis of the grey matter, white matter and cerebrospinal fluid (CSF) content of the volume, and the NMR-visible water content of the grey and white matter fractions. Combining data from 11 sites, the concentrations of the principal NMR-visible metabolites in the brains of healthy subjects (age range 20-35 years) determined using the internal water standard method were (mean+/-SD): [NAA]=10.0+/-3.4 mM (n=53), [tCho]=1.9+/-1.0 mM (n=51), [Cr + PCr]=6.5+/-3.7 mM (n=51). Evidence of system instability and other sources of error at some participating sites reinforces the need for rigorous quality assurance in quantitative spectroscopy.

Adult↗
PubMed1998

[Clinical uses of proton magnetic resonance spectroscopy of the brain].

In spite of all the scientific advances of the past few years, proton magnetic resonance spectroscopy of the brain has not attained the status of a routine examination technique with clinically accepted indications. The method should be considered as an additional option to MR imaging for inherited and acquired encephalopathic changes as well as, in future, for localization diagnosis of epilepsies. A proton magnetic resonance spectroscopic investigation without a prior intensive clinical and imaging investigation is not useful. Above all, factors influencing metabolite distribution such as for example, serum osmolality must be known. Methodological prerequisites for the clinical application of proton resonance spectroscopy are, first of all, a high stability of the chosen technique as well as a sufficiently certain quantification of metabolites and the availability of a reference group. The use of short echo times is necessary for the quantification of glutamine and the osmolyte myo-inositol. Indications for individual cases in which clinical investigations and MR topography cannot provide sufficient certainty and spectroscopy can furnish additional information are, in addition to uses in neuropediatrics, the suspicion of Alzheimer's dementia, HIV encephalopathy in early manifestations, and unclarified depressions of consciousness accompanying liver cirrhosis.

AIDS Dementia Complex↗
PubMed1998

Personality correlates of +/- pindolol induced decreases in prolactin.

The present study was conducted to investigate if personality traits can be usefully related to serotonergic vs. dopaminergic action of the 5-HT1a-antagonist +/- pindolol. Forty healthy male volunteers (aged between 20 and 30 years) were randomly assigned to a placebo or a +/- pindolol (30 mg, oral dose) group in a double blind trial. Blood samples were drawn and analyzed for PRL concentrations. In addition, the subjects completed questionnaires on personality. The results indicated that +/- pindolol decreases PRL concentrations depending on personality. While subjects high on impulsivity and related traits (aggression and disinhibition) show lower PRL decreases, well-being and personality traits frequently related to dopaminergic activity were not correlated with changes in PRL. Since reduced (blunted) PRL-responses after 5-HT challenge tests have been reported for impulsives, the present results favor the involvement of primarily serotonergic and probably only secondarily dopaminergic control of +/- pindolol induced PRL decreases.

Adrenergic beta-Antagonists↗
PubMed1998

Changes in cortisol secretion during shiftwork: implications for tolerance to shiftwork?

The present study was conducted to determine the size of changes and the time point of those changes in biological rhythms during night-shift and whether they are associated with tolerance to shiftwork. The adrenal hormone cortisol has frequently been investigated in the field of shiftwork since it follows a pronounced circadian variation and has been demonstrated to be affected by night-work. However, studies are restricted with respect to sample size, number of measurements or duration of sampling periods. Therefore, a sample of 24 night-shift workers was investigated in a cardiac emergency unit for seven nights. Saliva samples were collected frequently for determination of cortisol. A total of 28 cortisol measurements in each subject were made in order to decide whether the circadian rhythm changed, and if so at which time point. A clear reversal of circadian function could be observed for the total group (mean cortisol concentrations) after the fifth night. However, inspection of individual patterns revealed that six out of 24 subjects did not change in circadian function. These subjects exhibited lower durations of and less consistency in recovery sleep across the following days after night-work. With respect to personality dimensions a pattern associated with neuroticism can be observed in subjects without appropriate changes in cortisol rhythm. However, owing to the small sample size of non-adapters these results are preliminary and should be replicated with larger samples. The overall relationship between neuroticism and low adaptability has been discussed.

Adaptation, Physiological↗
PubMed1998

[Recent developments and applications of MRI sequence technique. I: turbo spin echo, HASTE, turbo inversion recovery, turbo gradient echo, turbo gradient spin sequences].

Goal of this two-part report is to provide clinical MRI radiologists with a guide to the world of new and clinically available MRI pulse sequences. Discussed are the principles of rapid scan techniques like multiple spin-echo imaging, multiple gradient echo imaging, echo planar imaging, diffusion and perfusion imaging, and future perspectives (review article).

Echo-Planar Imaging↗
PubMed1997

Molecular mechanism of regulation of the pyruvate dehydrogenase complex from E. coli.

The pyruvate dehydrogenase multienzyme complex from E. coli shows a sigmoidal dependency of the reaction rate on the substrate concentration when product formation is followed in the presence of physiological concentrations of the cofactor thiamin diphosphate. To elucidate the molecular mechanism of this regulation, the influence of the substrate pyruvate on the coenzyme-protein interaction has been investigated using several coenzyme analogues. The observed binding constants of all coenzymatically active analogues are increased in the presence of the substrate pyruvate, whereas those of all coenzymatically inactive analogues are not altered in the presence of pyruvate. This points to an increased binding affinity of a reaction-intermediate-coenzyme complex to the protein. Since cofactor binding and dissociation at physiological concentrations of thiamin diphosphate are slow compared to the catalytic reaction, a slow transition to the active state of the enzyme occurs. After lowering the pyruvate concentration, the opposite effect, a dissociation of the thiamin diphosphate from the enzyme is observed. This slow substrate dependent enhancement of cofactor binding enables efficient regulation of the pyruvate dehydrogenase complex by its substrate pyruvate.

Coenzymes↗
PubMed1997

1H-magnetic resonance spectroscopy in obsessive-compulsive disorder: evidence for neuronal loss in the cingulate gyrus and the right striatum.

We compared 12 patients with obsessive-compulsive disorder (OCD) and six control subjects by 1H-magnetic resonance spectroscopy. Significantly lower relative N-acetyl-aspartate (NAA) levels were found in the right striatum of OCD patients, as well as a decrease of anterior cingulate NAA that correlated with severity of illness. Age and sex were correlated to striatal NAA levels.

Adult↗
PubMed1997

Time-resolved projection angiography after bolus injection of contrast agent.

A method for MR angiography after bolus injection of a normal dose (0.1 mmol/kg) of contrast agent is presented. Projection angiograms are acquired with a non-slice selective Snapshot FLASH sequence with a time resolution of 1 s per image or better. Typically 40 to 60 images are acquired consecutively after bolus injection of a contrast agent. The signal from vessels can be separated from background by postprocessing based on the observed temporal evolution of the signal intensities during bolus passage. The subsecond projection MR-DSA is a reliable and robust technique to produce high resolution anatomical images of the vascular system avoiding the necessity of exact timing of the contrast agent bolus. It also supplies functional information about the hemodynamics in the observed region including perfusion.

Contrast Media↗