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M Bach

Publications and source records attributed to M Bach.

At least 55 records · Page 3Linked to original sources
PubMed1999

Impairment in preattentive visual processing in patients with Parkinson's disease.

We explored the possibility of whether preattentive visual processing is impaired in Parkinson's disease. With this aim, visual discrimination thresholds for orientation texture stimuli were determined in two separate measurement sessions in 16 patients with idiopathic Parkinson's disease. The results were compared with those of 16 control subjects age-matched and 16 young healthy volunteers. Discrimination thresholds were measured in a four-alternative spatial forced-choice paradigm, in which subjects judged the location of a target embedded in a background of distractors. Four different stimulus configurations were employed: (i) a group of vertical targets among horizontal distractors ('vertical line targets'); (ii) targets with varying levels of orientation difference on a background of spatially filtered vertically oriented noise ('Gaussian filtered noise'); (iii) one 'L' among 43 '+' signs ('texton'), all of which assess preattentive visual processing; and (iv) control condition, of one 'L' among 43 'T' distractors ('non-texton' search target), which reflects attentive visual processing. In two of the preattentive tasks (filtered noise and texton), patients with Parkinson's disease required significantly greater orientation differences and longer stimulus durations, respectively. In contrast, their performance in the vertical line target and non-texton search target was comparable to that of the matched control subjects. These differences were more pronounced in the first compared with the second session. Duration of illness and age within the patient group correlated significantly with test performance. In all conditions tested, the young control subjects performed significantly better than the more elderly control group, further indicating an effect of age on this form of visual processing. The results suggest that, in addition to the well documented impairment in retinal processing, idiopathic Parkinson's disease is associated with a deficit in preattentive cortical visual processing.

Adult↗
PubMed1998

Natural trans-splicing in carnitine octanoyltransferase pre-mRNAs in rat liver.

Carnitine octanoyltransferase (COT) transports medium-chain fatty acids through the peroxisome. During isolation of a COT clone from a rat liver library, a cDNA in which exon 2 was repeated, was characterized. Reverse transcription-PCR amplifications of total RNAs from rat liver showed a three-band pattern. Sequencing of the fragments revealed that, in addition to the canonical exon organization, previously reported [Choi, S. J. et al. (1995) Biochim. Biophys. Acta 1264, 215-222], there were two other forms in which exon 2 or exons 2 and 3 were repeated. The possibility of this exonic repetition in the COT gene was ruled out by genomic Southern blot. To study the gene expression, we analyzed RNA transcripts by Northern blot after RNase H digestion of total RNA. Three different transcripts were observed. Splicing experiments also were carried out in vitro with different constructs that contain exon 2 plus the 5' or the 3' adjacent intron sequences. Our results indicate that accurate joining of two exons 2 occurs by a trans-splicing mechanism, confirming the potential of these structures for this process in nature. The trans-splicing can be explained by the presence of three exon-enhancer sequences in exon 2. Analysis by Western blot of the COT proteins by using specific antibodies showed that two proteins corresponding to the expected Mr are present in rat peroxisomes. This is the first time that a natural trans-splicing reaction has been demonstrated in mammalian cells.

Animals↗
PubMed1998

Transient molecular visualization of ocular dominance columns (ODCs) in normal adult marmosets despite the desegregated termination of the retino-geniculo-cortical pathways.

The activity-dependent immediate early gene protein Krox-24, expressed in the neocortex at high basal levels, decreases rapidly upon neuronal deactivation (Chaudhuri et al. [1995] Vis. Neurosci. 12:35-50). In infant marmosets, as in most primates, the geniculo-cortical terminations segregate into eye-specific anatomical ocular dominance columns (ODCs), which disappear, however, during adolescence (Spatz [1989] Brain Res. 488:376-380), resulting in balanced inputs from the two eyes (Sengpiel et al. [1996] Vis. Neurosci. 13:145-160). Nevertheless, we found, in adult marmosets, 24 hours after monocular retinal activity blockade by tetrodotoxin, distinct alternating compartments of potentiated and depressed Krox-24-like immunoreactivity (Krox-IR) in layer IV of area 17. This pattern of Krox-IR disappeared at 10 days of retinal silencing, but was still present at this survival time in stains for cytochrome oxidase or NADPH-diaphorase. After 20 days of retinal silencing, the pattern was not demonstrable with any of the three stains. We term these compartments physiological ODCs, in contrast to the anatomical ODCs of most primates. If the anatomical ODCs of infant marmosets disappear by collateral sprouting into the inappropriate ODCs, then the collateral geniculo-cortical synapses might differ slightly in their properties from the original ones. We silenced the sets of original and collateral synapses of the one ocularity. This apparently transiently initiated, at the synapses driven by the intact eye, two different complex processes leading to molecular potentiation at the original synapses and to molecular depression at the collateral synapses.

Age Factors↗
PubMed1998

Biologic variability of prostate-specific antigen and its usefulness as a marker for prostate cancer: effects of finasteride. Finasteride PSA Study Group.

OBJECTIVES: The effects of finasteride on prostate-specific antigen (PSA) variability and usefulness in prostate cancer detection were examined. METHODS: Percent change and crossover of PSA levels between the low (1.0 to 3.9 ng/mL) and high (4.0 to 10.0 ng/mL) ranges were evaluated in 72 men with benign prostatic hyperplasia (BPH) and 77 men with both BPH and prostate cancer (PCa) treated with finasteride or placebo for 6 months. Patients with PCa were studied as a model for evaluating the effects on PSA levels in patients with BPH and latent PCa. As recommended on the product label, PSA levels for finasteride-treated patients were doubled for interpretation. RESULTS: In patients with BPH, most placebo- and finasteride-treated patients with low PSA levels at baseline had subsequent PSA levels below 4.0 ng/mL throughout the study. Among patients with high baseline PSA levels, only 1 of 17 finasteride-treated patients, compared with 8 of 13 placebo-treated patients, crossed into the low range. In the BPH/PCa study, most placebo-treated patients maintained PSA levels in the same range (15 of 19 less than 4.0 ng/mL; 14 of 16 greater than 4.0 ng/mL). Almost one third of finasteride-treated patients with low PSA levels at baseline crossed into the high range (8 of 22), whereas most patients with high PSA levels at baseline were not masked with treatment, with PSA levels remaining high (12 of 15). CONCLUSIONS: PSA levels cross between the low and high PSA ranges in both finasteride- and placebo-treated patients with BPH and those with both BPH and PCa. Doubling the PSA levels in finasteride-treated patients allows appropriate interpretation of PSA values and does not mask the detection of PCa.

Adult↗
PubMed1998

Percutaneous penetration enhancement and its quantification.

True penetration enhancing effects resulting from structural alterations of the barrier stratum corneum manifest themselves in an increase of the drug diffusion coefficient DB and/or of the drug solubility in the barrier csB. The quantification of enhancing effects on drug penetration is possible either by the direct determination of the drug fluxes or by an indirect determination through the measurement of the pharmacodynamic response. In both cases the thermodynamic drug activity has to be considered. In the case of pharmacodynamic measurements, enhancing effects may be determined from the horizontal distance of activity-response lines obtained without and with enhancer, respectively, i.e. the quotient of the drug concentrations that induce the same effect. The activity-standardized bioavailability factors fa obtained from the horizontal distances correspond to the enhancer-induced relative changes in the permeabilities PB, or more exactly in the product DB X csB. On the other hand, the vertical distance between the activity-response lines, i.e. the differences in the drug response after application of preparations with equal (even maximum) thermodynamic drug activities may be used to quantify penetration enhancing effects.

Administration, Topical↗
PubMed1998

Guidelines for calibration of stimulus and recording parameters used in clinical electrophysiology of vision. Calibration Standard Committee of the International Society for Clinical Electrophysiology of Vision (ISCEV).

In order to perform a technically adequate clinical electrophysiological procedure it is necessary to calibrate the stimulating and recording equipment. Published standards for the electroretinogram (ERG), electro-oculogram (EOG), visual evoked potential (VEP), and guidelines for the Pattern ERG (PERG) specify stimulus and recording parameters. Yet, most commercial instruments do not provide the means for calibration of these parameters. The goal of this document is to provide guidelines for proper calibration of stimulus and recording equipment. The need for such guidelines is clear on both clinical and scientific grounds. Stimulus and amplifier characteristics have substantial effects on the peak latency and amplitude measurements that are commonly used in clinical electrophysiology. Many review articles on clinical electrophysiology emphasize the need for establishing norms for each laboratory as a function of age and gender rather than relying on published norms. However, if stimulus and recording parameters are not calibrated periodically, then these norms may actually be misleading due to changes in stimulus or recording conditions induced by aging of equipment or inadvertent change in settings. This document is divided into two major sections. The first is concerned with calibration of the visual stimulus. It begins with background technical information on the physics of light and its measurement. This is followed by protocols for measurement of the luminous intensity of flash stimuli and the mean luminance, contrast, and visual angle of pattern stimuli. The second section is concerned with calibration of electrophysiologic recording systems. It begins with a description of the characteristics of bioelectrical signals and their measurement. This is followed by protocols for measurement of electrode impedance and amplifier calibration. Although this document was prepared as guidelines for clinical electrophysiological testing, it should be noted that the techniques described are more generally applicable to studies which are dependent upon accurate measurement of luminance or electrophysiological signals.

Electrooculography↗
PubMed1998

[Determining visual acuity using European normal values: scientific principles and possibilities for automatic measurement].

PSYCHOMETRIC FUNCTION: According to the European standard EN ISO 8596 the Landolt-C in 8 different orientations has to be used to measure visual acuity. With decreasing size of the Landolt-C the hit rate declines from 100% to the chance level of 12.5%. This gradual transition is described by the "psychometric function". The steepest point of the psychometric function is in the middle between 100 and 12.5, i.e., at 56.25%. This point of the psychometric function (approximated by 5 of 8 Landolt-Cs) has been selected as the threshold for visual acuity, because it is there that the visual acuity is influenced least by (incidental) fluctuations. The subject has to answer by forced choice; a response like "I cannot detect anything" is not acceptable. "NORMAL" VISUAL ACUITY: Cannot be assigned to a certain value, like 1.0 or 6/6. With the standard test procedure, visually healthy, young subjects achieve a visual acuity of about 2.0 or 12/6, while in senior subjects 0.5 (3/6) may be "normal". AVERAGING VISUAL ACUITY: Logarithmic, not arithmetic, scaling of visual acuity approximates the perceptual metric. Consequently, visual acuity values may not be averaged arithmetically. Instead, three steps are required: all values have to be converted to logarithms, then averaged, and finally the average can be reconverted. Geometric averaging is equivalent. "MINIMUM ANGLE OF RESOLUTION" NOT NECESSARY: MAR is the reciprocal of visual acuity. In many studies, clinical outcome has been assessed using log(MAR). Though statistically correct, this term is unnecessary, as log(acuity) has identical statistical properties. Furthermore, log(MAR) is contra-intuitive as its value becomes smaller when vision improves. COMPUTER-ASSISTED INSTRUMENTATION: Facilitates complying with the EN ISO 8596. For instance, the Freiburg Visual Acuity Test relieves the examiner from observing whether 5 responses have been correct, and that not more than 8 tests are given per level.

Europe↗
PubMed1998

[Fixation disparity with the Pola pointing test: not representative for eye position under natural viewing conditions].

BACKGROUND: According to certain findings obtained with the Zeiss Polatest, H.J. Haase defined a "Fixation Disparity Type One". In this diagnosis, the "Zeigertest" is particularly important. The Zeigertest consists of a central ring presented to both eyes for fixation, a vertical clock hand presented to the right eye and two markings at the six and twelve o'clock positions presented to the left eye. All parts are surrounded by a binocularly visible frame. Subjects with a "Fixation Disparity Type One" see a misalignment between the clock hand and the peripheral markings. We investigated (1) whether the perceived misalignment correlated with an objective deviation of the eyes from orthovergence and (2) whether subjects with a "Fixation Disparity Type One" had a deviation of the eyes from orthovergence when looking at a natural, i.e., fully fusionable object. SUBJECTS AND METHODS: Out of 303 medical students, 10 subjects with a "Fixation Disparity Type One" were selected and asked to indicate the perceived alignment or misalignment in the Zeigertest with a laser pointer. Two subjects without fixation disparity served as controls. The position of both eyes was recorded using the search coil technique. One of the 10 subjects with "Fixation Disparity Type One" had to be excluded due to excessive blinking. Experiment 1: In the beginning all parts of the Zeigertest were presented to both eyes (natural viewing condition). Then, the object for one of the eyes was switched off leaving the frame as the only fusional stimulus. The outcome variable was a refixation movement of the other eye. This experiment is similar to the unilateral cover test. Experiment 2: In the beginning all parts of the Zeigertest were presented to both eyes (natural viewing condition). Then, the original Zeigertest was switched on (clock hand presented only to the right eye, peripheral markings only to the left eye). The outcome variable was a change of vergence. RESULTS: Experiment 1: A significant refixation movement did not occur in any of the subjects. Experiment 2. In all 9 subjects with "Fixation Disparity Type One" the vergence changed significantly between 2.4 and 14.9 arcmin. The change of vergence correlated significantly with the angle of the perceived misalignment between clock hand and peripheral markings. CONCLUSION: A fixation disparity ascertained at the Zeigertest does not indicate a fixation disparity under natural viewing conditions.

Adult↗
PubMed1998

Memantine is neuroprotective in a rat model of pressure-induced retinal ischemia.

PURPOSE: To quantify vitreous amino acid concentrations in pressure-induced retinal ischemia and to evaluate the neuroprotective effect of memantine, a N-methyl-D-aspartate (NMDA) antagonist, administered before and at two time intervals after ischemia. METHODS: Retinal ischemia was induced in 10 rats by elevating the intraocular pressure to 120 mm Hg. The concentrations of the amino acids of vitreous samples were measured by high-pressure liquid chromatography. In another series of 56 rats, ischemia was induced in a similar fashion. Fifteen rats received 20 mg/kg x day memantine by a subcutaneous osmotic pump starting 2 days before ischemia, 13 rats received 10 mg/kg memantine intraperitoneally (ip) 0.5 and 4.5 hours after reperfusion, 13 rats received 10 mg/kg memantine ip 3.5 and 7.5 hours after reperfusion, and 15 rats received the vehicle alone. Ischemic damage was histologically quantified 14 days after ischemia. RESULTS: Compared with the nonischemic fellow eyes, there was an elevation (P < 0.05) in the mean vitreous concentration of glutamate (223%+/-41%) and glycine (428%+/-92%). The percentage of surviving neurons in the ganglion cell layer was 33%+/-3% in the controls, 61%+/-5% (P < 0.001) when memantine was infused subcutaneously before ischemia, 52%+/-5% (P < 0.05) when memantine was injected ip 0.5 and 4.5 hours after ischemia, and 48%+/-5% (P > 0.05) when injected ip 3.5 and 7.5 hours after ischemia. CONCLUSIONS: Retinal ischemia increased vitreous concentrations of glutamate and glycine. Both amino acids were agonists at the NMDA receptor. The NMDA receptor antagonist memantine reduced ganglion cell loss when given systemically before or within 30 minutes of retinal ischemia.

Animals↗
PubMed1997

Uses and misinterpretations of genetics in psychology.

An analysis is made of the frequently posed question in psychology of relative contribution of genotypes and environments to phenotypic variation. The illogic of the question, the inappropriateness of the methodology, the inadequacy of the data, and the misleading implications of assertions of proportionality as seen through a sampling of introductory psychology textbooks and referenced publications are outlined. To ask the question of proportionality (of the relative contribution of genotypes and environments in human populations) requires the questioner to make two major erroneous assumptions. The first error is to grant validity to heritability estimates for humans. The second is to conceptualize the genotype as having a range of potential outcomes. An examination is made of these false assumptions.

Data Interpretation, Statistical↗
PubMed1997

[Reproducibility of the pattern electroretinogram].

The pattern ERG (PERG) is used as an indicator of retinal ganglion cell function. Up to now, reports on the reproducibility of the PERG have been contradictory. We investigated the reproducibility under the conditions of the forthcoming ISCEV guidelines for the PERG. We simultaneously recorded the PERG and VEP in 42 eyes of 21 subjects to phase-reversing checkerboard stimuli with DTL electrodes. Both transient (2 rps) and steady-state (16 rps) stimulation was employed. The check sizes were 0.4 degree, 0.8 degree and 16 degrees, the mean luminance 45 cd/m2, the contrast 98%, and the field size 32 degrees x 27 degrees. Measurements were repeated at the same time of day after 1 week. In addition, we compared two different electrode positions in 16 eyes: (1) across the cornea along the lower lid; and deep in the conjunctival sac. With position (1) the amplitudes were found to be higher by 20% than (2). We calculated the coefficient of variation (CV) of amplitude as a measure of reproducibility. CV was 7 +/- 1% for the steady-state PERG, 9 +/- 1% for the transient PERG, 12 +/- 2% for the steady-state VEP and 14 +/- 3% for the transient VEP. For the latency of the PERG, the intersession CV was found to be 1.5%. Amplitude reproducibility was somewhat higher under steady-state as compared to transient stimulation; we attribute this to the high noise rejection of the Fourier analysis. Altogether, the amplitude reproducibility of the PERG is somewhat higher than that of the VEP.

Adult↗
PubMed1997

Shift of equiluminance in congenital color vision deficiencies: pattern-ERG, VEP and psychophysical findings.

We compared electrophysiological responses [pattern-ERG (PERG) and VEP] and psychophysical measures to color stimuli to separate different forms of anomalous color vision. PERG and VEP were recorded from seven normals and 14 subjects with congenital color vision deficiencies. Stimuli were color checkerboards with 0.5 deg check size, phase reversing at 34 rev/sec. The luminances of the red and green parts were varied in opposite direction from 0 to 30 cd/m2, while the hue of individual squares and space-averaged luminance were held constant. This allowed for one equiluminance condition where flicker appeared fused. In the seven normals, the subjective equiluminance was reached at a luminance ratio red/(red + green) = 0.50-0.53. At that point, the PERG amplitude was moderately, and the VEP amplitude sharply reduced. In 14 color anomalous subjects both the PERG and VEP were sharply reduced at equiluminance. These dips were shifted compared to normals and the dip position corresponded to the predicted luminance ratios obtained by calculations from L- and M-cone activation using the Smith-Pokorny transformation. As we found a close correlation of the VEP-dip position and the anomalous quotient, these electrophysiological measures may allow objective assessment of color vision deficiencies.

Adult↗
PubMed1997

Contrast dependency of motion-onset and pattern-reversal VEPs: interaction of stimulus type, recording site and response component.

We compared the contrast dependency (from 0.4 to 98%) of the visual evoked potential (VEP) to motion onset and to pattern reversal at an occipital and lateral recording site using sinewave grating stimuli of 0.9 c/deg, drifting at 4.9 deg/sec. Two differing VEP components were identified: a positive component, peaking at around 130 msec, dominating the occipital derivation, enhanced in pattern-reversal stimulation, a high-threshold, late-saturating contrast response characteristic with a half-amplitude contrast above 7%; and a negative component at around 180 msec, dominating the lateral derivation, enhanced in motion-onset stimulation, exhibiting a low-threshold, saturating contrast characteristic with a half-amplitude contrast below 4%. The results suggest: (1) The negative component (N180) represents motion mechanisms, located more laterally, while the positive component (P100-P130) represents form-processing mechanisms, located near the V1/V2 areas. (2) A pattern-reversal stimulus triggers both form-processing and motion mechanisms that can be discriminated by latency. In an occipital derivation, the clinical reversal VEP P100 will be little contaminated by motion responses.

Adult↗
PubMed1997

Similar electrophysiological correlates of texture segregation induced by luminance, orientation, motion and stereo.

Certain local features induce preattentive texture segregation. Recently, components in the visual evoked potential (VEP) associated with preattentive texture segregation (tsVEPs) have been demonstrated. To assess the similarity and dissimilarity of visual processing across visual dimensions, we compared VEPs and tsVEPs in texture segregation by luminance, orientation, motion and stereo disparity. We found tsVEPs across these four visual dimensions to be remarkably similar when compared to the "low-level" VEPs. The tsVEPs were always negative; their implicit time, peak latency and amplitude were (in msec/msec/microV): 91/234/-5.7, luminance; 84/257/-3.9, orientation; 80/295/-8.3, motion; and 95/310/-5.0 for stereo. The cross-correlation function, as a quantitative measure for similarity, on average was higher for the tsVEPs by a factor of 4.2 as compared to the low-level VEPs (P < 0.0001). The results suggest (1) that the tsVEPs represent activity of neural mechanisms that have generalised to some degree across visual dimensions; and (2) that these hypothetical generalisation mechanisms might exist already in the primary visual cortex.

Evoked Potentials, Visual↗
PubMed1997

Biologic variability of prostate-specific antigen and its usefulness as a marker for prostate cancer: effects of finasteride. The Finasteride PSA Study Group.

OBJECTIVES: The effects of finasteride on prostate-specific antigen (PSA) variability and usefulness in prostate cancer detection were examined. METHODS: Percent change and crossover of PSA levels between the low (1.0 to 3.9 ng/mL) and high (4.0 to 10.0 ng/mL) ranges were evaluated in 72 men with benign prostatic hyperplasia (BPH) and 77 men with both BPH and prostate cancer (PCa) treated with finasteride or placebo for 6 months. Patients with PCa were studied as a model for evaluating the effects on PSA levels in patients with BPH and latent PCa. As recommended on the product label, PSA levels for finasteride-treated patients were doubled for interpretation. RESULTS: In patients with BPH, most placebo- and finasteride-treated patients with low PSA levels at baseline had subsequent PSA levels below 4.0 ng/mL throughout the study. Among patients with high baseline PSA levels, only 1 of 17 finasteride-treated patients compared with 8 of 13 placebo-treated patients crossed into the low range. In the BPH/PCa study, most placebo-treated patients maintained PSA levels in the same range (15 of 19 less than 4.0 ng/mL; 14 of 16 greater than 4.0 ng/mL). Almost one third of finasteride-treated patients with low PSA levels at baseline crossed into the high range (8 of 22), whereas most patients with high PSA levels at baseline were not masked with treatment, with PSA levels remaining high (12 of 15). CONCLUSIONS: PSA levels cross between the low and high PSA ranges in both finasteride- and placebo-treated patients with BPH and those with both BPH and PCa. Doubling the PSA levels in finasteride-treated patients allows appropriate interpretation of PSA values and does not mask the detection of PCa.

Adult↗
PubMed1997

A case of localized retinal damage in thallium poisoning.

PURPOSE: To determine the cause of visual impairment and to document the late eye disturbances in a case of thallium poisoning. PATIENT: A 44-year-old woman presented with a history of repeated attacks of complete alopecia over a period of several months, diffuse pain in both legs, transient gastrointestinal disturbances, abasia with a progressive paraparesis, paresthesia in the fingertips, and polyneuropathy. She complained of slowly progressive visual deterioration in both eyes which began about six months after the first attack of alopecia. The optic discs showed distinct signs of temporal atrophy together with a deep temporal excavation. The Goldmann perimetry revealed an absolute central scotoma. Traces of thallium were found in the urine and in the serum. The district attorney later discovered that her husband had been trying to poison her with thallium. METHODS: The clinical and electrophysiological examinations included visual evoked potentials (VEP) and electroretinography (flash ERG, multifocal ERG and pattern ERG). RESULTS: The VEP showed a reduction in amplitude and a prolonged latency indicating a conduction block. The pattern ERG was initially normal. At a follow-up examination 6 years later, a slight amplitude reduction in the pattern ERG was found. The multifocal ERG showed a diminished amplitude in the center of the retina (up to +/- 10 degrees visual angle). CONCLUSIONS: The electrophysiological investigations in our patient--who had an optic atrophy--indicated a conduction block of the retinal nerve fibers (VEP) and an additional lesion at or before the retinal bipolar cells (multifocal ERG), localized in the central +/- 10 degrees. These findings suggest that thallium poisoning can lead to a combined lesion of the retinal nerve fibers and the neural retina.

Adult↗