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Biomedical subjects

P Fries

Publications and source records attributed to P Fries.

17 recordsLinked to original sources
PubMed2002

Pathophysiological changes after traumatic brain injury: comparison of two experimental animal models by means of MRI.

In an experimental study MRI was used to compare the pathophysiological changes of brain tissue after lateral fluid percussion injury (FPI) versus cold injury (CI) as models of traumatic brain injury (TBI). Two groups of Sprague-Dawley rats (n=23) were subjected to mild FPI, respectively, CI localized over the right parietal cortex. MRI was performed at different time points including T1w, T2w and T1w-CE (Gd-DTPA 0.2 mmol/kg BW) sequences as well as perfusion-weighted imaging with calculation of regional cerebral blood volume (rCBV) and regional cerebral blood flow (rCBF). T2w and T1w-CE images showed hyperintense areas in the traumatised cortex demonstrating brain edema and blood-brain barrier (BBB)-breakdown increasing up to 12 h. Perfusion-weighted imaging demonstrated a significant decrease of rCBV and rCBF in the ipsilateral cortex of CI animals compared with the contralateral hemisphere. In contrast, rats of the FPI group showed only slight differences in rCBF and rCBV comparing the left and right cortex. The results of our study confirm that both mild FPI and CI produced focal brain edema with concomitant breakdown of the BBB as a model of TBI. Since differences regarding perfusion are much more pronounced in CI our results suggest that, this model more likely seems to reflect pathophysiological changes of brain ischemia, whereas FPI seems to be better suited to model the pathophysiological characteristics of TBI.

Animals↗
PubMed2001

Modulation of oscillatory neuronal synchronization by selective visual attention.

In crowded visual scenes, attention is needed to select relevant stimuli. To study the underlying mechanisms, we recorded neurons in cortical area V4 while macaque monkeys attended to behaviorally relevant stimuli and ignored distracters. Neurons activated by the attended stimulus showed increased gamma-frequency (35 to 90 hertz) synchronization but reduced low-frequency (<17 hertz) synchronization compared with neurons at nearby V4 sites activated by distracters. Because postsynaptic integration times are short, these localized changes in synchronization may serve to amplify behaviorally relevant signals in the cortex.

Action Potentials↗
PubMed2001

Conditions of perceptual selection and suppression during interocular rivalry in strabismic and normal cats.

Presenting the two eyes with incongruent stimuli leads to the phenomenon of interocular rivalry. At any given time, one of the stimuli is perceptually suppressed in order to avoid double vision. In squinting subjects, rivalry occurs permanently also for congruent stimuli because of developmental rearrangement of cortical circuitry. In this study, we have investigated the dynamics and stimulus dependence of rivalry in six esotropic, four exotropic and three non-strabismic cats. As an indicator for perception, we used optokinetic nystagmus that was induced by moving gratings. The esotropic cats were tested for their visual acuity by means of a jumping stand procedure. The results show that one eye can dominate perception even if both eyes have equal visual acuity and are presented with stimuli of equal contrast. Strong eye dominance asymmetry was found in all but one of the tested cats. Notably, all three of the normal cats showed a clear asymmetry in perceptual selection. Measurements with varying contrast and velocity of the stimuli revealed that the influence of these parameters on perceptual selection was independent of the presence of strabismus. In all cats, the time during which a given eye dominated perception increased with the contrast and decreases with the velocity of the stimulus presented to this eye.

Animals↗
PubMed2001

Dynamic predictions: oscillations and synchrony in top-down processing.

Classical theories of sensory processing view the brain as a passive, stimulus-driven device. By contrast, more recent approaches emphasize the constructive nature of perception, viewing it as an active and highly selective process. Indeed, there is ample evidence that the processing of stimuli is controlled by top-down influences that strongly shape the intrinsic dynamics of thalamocortical networks and constantly create predictions about forthcoming sensory events. We discuss recent experiments indicating that such predictions might be embodied in the temporal structure of both stimulus-evoked and ongoing activity, and that synchronous oscillations are particularly important in this process. Coherence among subthreshold membrane potential fluctuations could be exploited to express selective functional relationships during states of expectancy or attention, and these dynamic patterns could allow the grouping and selection of distributed neuronal responses for further processing.

Animals↗
PubMed2001

Rapid feature selective neuronal synchronization through correlated latency shifting.

Spontaneous brain activity could affect processing if it were structured. We show that neuron pairs in cat primary visual cortex exhibited correlated fluctuations in response latency, particularly when they had overlapping receptive fields or similar orientation preferences. Correlations occurred within and across hemispheres, but only when local field potentials (LFPs) oscillated in the gamma-frequency range (40-70 Hz). In this range, LFP fluctuations preceding response onset predicted response latencies; negative (positive) LFPs were associated with early (late) responses. Oscillations below 10 Hz caused covariations in response amplitude, but exhibited no columnar selectivity or coordinating effect on latencies. Thus, during high gamma activity, spontaneous activity exhibits distinct, column-specific correlation patterns. Consequently, cortical cells undergo coherent fluctuations in excitability that enhance temporal coherence of responses to contours that are spatially contiguous or have similar orientation. Because synchronized responses are more likely than dispersed responses to undergo rapid and joint processing, spontaneous activity may be important in early visual processes.

Action Potentials↗
PubMed1999

Temporal binding, binocular rivalry, and consciousness.

Cognitive functions like perception, memory, language, or consciousness are based on highly parallel and distributed information processing by the brain. One of the major unresolved questions is how information can be integrated and how coherent representational states can be established in the distributed neuronal systems subserving these functions. It has been suggested that this so-called "binding problem" may be solved in the temporal domain. The hypothesis is that synchronization of neuronal discharges can serve for the integration of distributed neurons into cell assemblies and that this process may underlie the selection of perceptually and behaviorally relevant information. As we intend to show here, this temporal binding hypothesis has implications for the search of the neural correlate of consciousness. We review experimental results, mainly obtained in the visual system, which support the notion of temporal binding. In particular, we discuss recent experiments on the neural mechanisms of binocular rivalry which suggest that appropriate synchronization among cortical neurons may be one of the necessary conditions for the buildup of perceptual states and awareness of sensory stimuli.

Arousal↗
PubMed1997

Synchronization of oscillatory responses in visual cortex correlates with perception in interocular rivalry.

In subjects suffering from early onset strabismus, signals conveyed by the two eyes are not perceived simultaneously but in alternation. We exploited this phenomenon of interocular suppression to investigate the neuronal correlate of binocular rivalry in primary visual cortex of awake strabismic cats. Monocularly presented stimuli that were readily perceived by the animal evoked synchronized discharges with an oscillatory patterning in the gamma-frequency range. Upon dichoptic stimulation, neurons responding to the stimulus that continued to be perceived increased the synchronicity and the regularity of their oscillatory patterning while the reverse was true for neurons responding to the stimulus that was no longer perceived. These differential changes were not associated with modifications of discharge rate, suggesting that at early stages of visual processing the degree of synchronicity rather than the amplitude of responses determines which signals are perceived and control behavioral responses.

Animals↗
PubMed1997

Role of the temporal domain for response selection and perceptual binding.

Most cognitive functions are based on highly parallel and distributed information processing by the brain. A paradigmatic example is provided by the vertebrate visual system where numerous cortical areas have been described which analyse different types of visual information. At present, it is unclear how information can be integrated and how coherent representational states can be established in such distributed systems. We suggest that this so-called 'binding problem' may be solved in the temporal domain. The hypothesis is that synchronization of neuronal discharges can serve for the integration of distributed neurons into cell assemblies and that this process may underlie the selection of perceptually and behaviourally relevant information. We review experimental results, mainly obtained in the visual system, which support this temporal binding hypothesis.

Animals↗
PubMed1994

[The value of thallium myocardial scintigraphy (single photon emission computerized tomography, SPECT) for diagnosis of ischemia after myocardial infarct].

BACKGROUND: Patients with prior myocardial infarction and additional stenosis in noninfarct-related coronary artery have a high risk of reinfarction. Angina pectoris and exercise electrocardiography have a low sensitivity und specificity in detection of such coronary artery stenosis. We assessed the diagnostic value of tomographic thallium scintigraphy for detection of ischemia in myocardium not supplied by the infarct-related coronary artery. PATIENTS AND METHOD: In 77 patients with prior myocardial infarction (59 patients with acute infarction, 18 patients with chronic infarction) sensitivity and specificity of angina pectoris, exercise electrocardiography and tomographic thallium scintigraphy was determined. Coronary arteriography was the gold standard method. The predictive value of tomographic thallium scintigraphy was assessed by serial testing. RESULTS: Tomographic thallium scintigraphy detected 40 of 51 patients with significant stenosis in noninfarct-related coronary artery (sensitivity: 78%; positive predictive value: 83%). In 18 of 26 patients with no additional significant stenosis tomographic thallium scintigraphy did not show ischemia at a distance (specificity: 69%; negative predictive value: 62%). In sequential testing tomographic thallium scintigraphy did not give any additional diagnostic information in patients with angina pectoris. In patients without angina pectoris exercise electrocardiography had a high positive predictive value (90%), tomographic thallium scintigraphy did not yield a higher positive result. Only in patients without angina pectoris and negative exercise electrocardiographic findings tomographic thallium scintigraphy was helpful: 16 of these patients had an additional coronary artery stenosis and were detected by tomographic thallium scintigraphy only (positive predictive value: 75%); in 13 of 17 patients without an additional coronary artery stenosis thallium scintigrams were negative (negative predictive value: 76%). CONCLUSION: The presence of significant coronary artery stenosis in noninfarct-related vessels can be predicted by serial noninvasive testing. Tomographic thallium scintigraphy has its place in postinfarction patients without angina and with negative exercise electrocardiographic findings.

Adult↗
PubMed1993

Optic nerve sheath decompression for visual loss in patients with acquired immunodeficiency syndrome and cryptococcal meningitis with papilledema.

Visual dysfunction developing in association with acquired immunodeficiency syndrome (AIDS) can be multifactorial. Two patients with this syndrome and cryptococcal meningitis had papilledema and visual loss. Both were treated by optic nerve sheath fenestration. One patient had bilateral nonsimultaneous optic nerve sheath fenestrations; visual function improved in one eye. The other patient had bilateral visual improvement after a unilateral optic nerve sheath fenestration. Cryptococcal organisms were present in the dural sheath specimens of both patients despite ongoing therapy with antifungal medication. Postoperative orbital infectious complications did not occur. Autopsy examination of one patient showed that the sites of fenestration were patent. Medical treatment of cryptococcal meningitis associated with AIDS has a guarded prognosis. Optic nerve sheath fenestration offers a treatment alternative for papilledema and visual loss that occur with cryptococcal meningitis.

AIDS-Related Opportunistic Infections↗
PubMed1985

[Duhring's dermatitis herpetiformis].

We report on a 56-year-old man suffering from chronic itching, papulovesicular, polymorph dermatosis. Clinical aspects, diagnostics, as well as therapeutic procedure in dermatitis herpetiformis are discussed.

Dapsone↗
PubMed1985

[Climate therapy of psoriasis: critical evaluation].

As with many chronic, recurrent skin diseases, psoriasis in all its forms is within the domain of dermatological climatotherapy. However, this is only successful in genuinely stimulating climates, such as in the North Sea islands or in particularly high alpine regions (over 1500 m) under correct topographical conditions. If dermatological climatotherapy is to retain its justifiably good name, care must be taken not to misuse this important therapeutic means (unsuitable climates), or it may be discredited due to insufficient conditions and thus poor results.

Altitude↗
PubMed1977

[Modification of relative amount of free amino acids in the stratum corneum of human epidermis by special factors of the environment. I. The influence of UV-irradiation (author's transl)].

By repeated uv-irradiation the quantity of all free amino acids (per surface unit) in human horny layer increase considerably. 4 different groups of substances are found by taking the relative values in mole per cent. 1. No difference for urea, threonine, serine, glutamine, tyrosine and ammonia. 2. Decrease of about 20 p.c. for glutaminic acid, citrulline, arginine, histidine. 3. Increase of about 20 p.c. for urocanic acid, aspartic acid, proline, glycine, valine, isoleucine. 4. The rest of amino acids increase about 30--50 p.c.

Amino Acids↗