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Biomedical subjects

T F Münte

Publications and source records attributed to T F Münte.

16 recordsLinked to original sources
PubMed1992

Parallel and serial visual search after closed head injury: electrophysiological evidence for perceptual dysfunctions.

Event-related potentials (ERPs) were recorded from closed head injury (CHI) patients at least 2 years postinjury and from controls in order to assess their parallel and serial processing abilities during visual search. In Experiment 1, stimuli consisted of arrays of eight triangles; half of the arrays contained a target item. In the "feature-present" condition, the target item was a triangle with an additional horizontal line that could be detected automatically and in parallel, while in the "feature-absent" condition all items except for the target triangle had an additional horizontal line, thus requiring a serial search. In Experiment 2, stimuli consisted of eight solid bars (50%), seven solid bars and a vertical open bar (25%), and seven solid bars and a horizontal open bar (25%): the array containing the horizontal bar served as a target. By recording ERPs to the arrays containing vertical open bars, which were similar to the target items, parallel processing of "pop-out" stimuli could be studied in the absence of any overt response. ERP data were compared with the results of neuropsychological and neuroimaging (MRI, CAT) examination. Patient exhibited a decreased behavioral performance both in the parallel and in the serial processing mode. Furthermore, abnormalities of early and intermediate ERP components (P1, N1, P2, N2) were found, whereas the late component (P3) was less affected by CHI. The results were interpreted as an index of CHI-induced dysfunctions in perceptual processes such as simple feature registration and early target discrimination. It was suggested that these dysfunctions contribute to impairments of parallel as well as serial processes in visual search.

Adult↗
PubMed1992

Computer-aided EMG-analysis in patients with neurogenic lesions.

A new system for computer aided EMG-analysis was tested in 3 groups of patients with neurogenic lesions (ALS, ulnar nerve lesions, diabetic polyneuropathy). The system entails automatic segmentation and parametrization of the single MUAP as well as the automatic classification of the MUAP into motor units. Emphasis was placed on its practicability in an everyday clinical setting. All patient groups differed significantly from normal groups in most of the computed parameters of the motor units. Moreover, on the basis of the computer-aided analysis of the MUAP up to 90% of individual patients in the ALS and ulnar nerve lesion groups and up to 40% in the diabetic polyneuropathy group, who did not have any pathological spontaneous activity or paris, could be classified as pathological. It is concluded, that computer-aided EMG-analysis has become a practical tool for routine use in the clinical laboratory simplifying early diagnosis of subtle EMG-changes, and aiding the less experienced examiner.

Action Potentials↗
PubMed1992

[Computer-assisted analysis of the electromyogram for routine clinical use].

A computerized EMG analysis system implemented on an MS-DOS computer was developed explicitly for clinical routine usage. It incorporates analysis of interference pattern as well as of motor unit action potentials (MUAPs). Key features of MUAP analysis are the automatic segmentation and parameterization of the EMG signal and the automatic assignment of MUAPs to motor units. Determination of muscle activity is based on threshold detection of the signal's first derivative, leading to the definition of a MUAPs central component. Its parameters (length, amplitude, maximal steepness, area between curve and base-line, area between first derivative and base-line, number of turns etc.) are used when comparing MUAPs. The automatic assignment of MUAPs to motor units was implemented as an iterative procedure. MUAPs are compared to a reference MUAP and eventually assigned to it if their parameters are sufficiently similar. For such a group of MUAPs the most representative MUAP is determined which is then used as new reference MUAP in the next iteration step. Most important for clinical routine usage are simple handling, speed and the clearly arranged presentation of results. The system allows for interactive modification of MUAP assignment as well as start and end points of every MUAP. Analysis results may be displayed on the screen and printed, giving the user a quick impression of the muscle under study. Thus this method meets basic requirements for computer assisted decision making in differential diagnosis.

Action Potentials↗
PubMed1992

Thyroid hormones influence perceptual processing in a visual search paradigm.

The mechanisms that mediate the effects of thyroid hormones on higher cognitive processes are not well understood. In the present experiments, event-related potentials (ERPs) and behavioral measurements were recorded in a visual search paradigm where a target item had to be detected in a number of distractor items. 10 healthy subjects were given a daily dose 300 micrograms thyroxine (T4) p.o. and recordings were made before and after 3 weeks of treatment. All subjects developed hyperthyroidism with a completely suppressed TSH (1.6 +/- 0.5 mU/l vs. non detectable), a significant increase in T3 (1.5 +/- 0.2 vs. 1.9 +/- 0.2 ng/ml). T4 (6.6 +/- 1.6 micrograms/dl vs 11.9 +/- 2.7 micrograms/dl) and sex-hormone binding globulin (2.9 +/- 1.1 vs. 3.8 +/- 1.3 micrograms/ml; all p less than 0.0005). Compared to the control group (n = 15), thyroid hormones improved controlled serial visual processing, as indexed by changes of the late positive ERP component and target detection hit rate (in both cases p less than 0.01), whereas parallel detection of salient features remained unchanged. The data suggest a differential impact of thyroid hormones on visual information processing.

Arousal↗
PubMed1991

[Activation of the semantic memory by subliminal word stimuli? An analysis using event-related potentials].

There is a hotly debated question as to whether the meaning of a word can be assessed in the lexicon before conscious identification of this word is possible. Some authors have reported shorter lexical decision times for words, which had been preceded by primes, that had been masked below threshold. This effect was taken as evidence for an automatic activation of the lexicon by the unidentified prime. We report an ERP study using the N400 potential and lexical decision time as an index for associative activation of the lexicon. In a condition with supra-threshold primes the typical acceleration of lexical decision time and reduction of N400 amplitude was found for semantically related target words. In the sub-threshold condition, however, no evidence was found for priming in RT and ERP data. This pilot data, as well as previous RT studies, question the findings gathered on sub-threshold priming. No dissociation between RT and ERP parameters was found in the present study.

Adult↗
PubMed1991

[Experience with computer-assisted EMG analysis: reference values for four muscles].

The characteristics of a newly developed computerized EMG-analysis system are lined out. The analysis steps include segmentation and parametrization of digitized EMG segments followed by automatic classification of single potentials into motor units. Comparison of parameters is used rather than a template matching algorithm for classification. For each motor unit a set of parameters can be computed in addition to duration and amplitude. Normative data are given for four muscles. 60 normal volunteers (50% female, 50% below age 50) were recorded from for each muscle. The recording conditions required to move the electrode until a motor unit could be recorded with its individual maximum. Furthermore, it was attempted to attain the maximum discharge rate of a particular motor unit. A highly significant correlation of the amplitude of the motor unit potentials with age was found for all four muscles. For the duration of the potentials a correlation with age was found only for the M. ext. digitorum brevis. Significant sex differences were found for nearly all parameters and all muscles. Pairwise comparisons of the muscles revealed significant differences of all muscles. The analysis showed, that a muscle can be regarded pathological if more than two of a total of seven recorded motor units show pathological parameters.

Age Factors↗
PubMed1990

Familial migraine coma: a case study.

A family suffering from a rare malignant type of migraine is described. The syndrome is characterized by episodes of coma with meningitic signs and fever and pareses as well as persistent cerebellar signs. Coma attacks last up to several days and can be precipitated by minor head trauma, vigorous work and angiography. From a study of this family and the literature, it is concluded that this syndrome has to be included in the differential diagnosis of coma and that angiography should be avoided in the patients.

Adult↗
PubMed1990

[Event-related brain potentials reflect semantic and syntactic errors during language processing].

Event-related potentials were recorded in a sentence reading paradigm. Sentences were either terminated by a semantically and grammatically appropriate word (word from a different grammatical class syntactic error), a semantically inappropriate word (semantic error) or a semantically appropriate word with a wrong case inflection (morphosyntactic error). For all three types of errors the event-related potential was characterized by a negativity in the 250-600 ms range (N400). The possible implications of these findings for models of sentence processing are discussed. It is concluded that the results strongly support interactive models of sentence processing.

Adult↗
PubMed1990

[Event-related potentials and memory capacity: 1. A comparison of intentional and incidental learning modes].

Event-related brain potentials were recorded from healthy young adults during two paradigms calling for recall and recognition of previously presented words. In the first part of the study incidental learning was employed, i.e. the subject was unaware that he participated in a memory test and engaged in a semantic task instead. ERPs from the encoding phase were averaged according to whether a word was 1. subsequently recalled, 2. recognized or 3. neither recalled nor recognized. The intentional paradigm was identical in all respects except for the instructions to remember as many words as possible for subsequent memory testing. No semantic task was employed during intentional encoding. Both paradigms yielded significantly higher positivities for words which were later recalled.

Adult↗
PubMed1990

[Event-related potentials and memory capacity: 2. Recognition of words].

The second part of this study deals with the behavioral und event-related potential (ERP) findings from the recognition phase of incidental and intentional learning paradigms. Correctly recognized old items were characterized by a significantly more positive ERP in the 400 to 800 ms range when compared to correctly identified new items. Furthermore old words, which had previously been remembered in a free recall test were associated with a more positive ERP when compared to both, correctly recognized and nonrecognized old words. This effect also had an earlier onset latency. The findings are considered in the context of recent results from continuous recognition memory and repetition priming studies. It is concluded that in the present paradigm ERP differences due to recognition can be attributed to unspecific phenomena.

Adult↗
PubMed1989

Post-irradiation lesions of the caudal roots.

The article reports on 3 patients suffering from muscular atrophy after radiotherapy of the para-aortal lymph nodes for malignant testicular tumor without any sensory, bladder, or bowel disturbances. By neurophysiological examination, a lesion of the lumbal plexus and the peripheral nerves of the lower extremities were excluded. On EMG-examination there were no giant motor unit potentials, as they can be found in anterior horn cell lesions. Though there were no sensory deficits, a distinct prolongation of latencies and reduction of amplitudes could be found for lumbar dermatomal somatosensory evoked potentials (SSEP) and those after stimulation of some peripheral nerves of the lower extremities.

Adult↗
PubMed1989

Event-related potentials and visual spatial attention: influence of a cholinergic drug.

The effects of two dosages (200 mg, 600 mg, placebo) of a cholinergic nootropic (WEB 1881 FU) were investigated in a visual spatial attention task. Event-related brain potentials (ERPs) were used as a physiological measure of attention as they have previously been shown to be sensitive to allocation of attention to points in space. The typical enhancement of several peaks of the visual ERP due to attention was found in the present experiment. No systematic effect of the medication was revealed, suggesting that the effects of WEB 1881 FU do not extend to early perceptual processes.

Adult↗
PubMed1989

[Event related brain potentials and signal detection: decision confidence and signal probability].

This paper is concerned with the relation of two components of the late positive complex, P300 and slow wave, to parameters of signal detection theory. In the first experiment, basically a replication of Squires et al., signal probability was 50% and a six point rating scale was used for subjects' answers. Whereas for the P300 the well known relation to subjective confidence (and thus to response criteria) was confirmed, a similar relation could not be found for the slow wave. In the second experiment the local signal probability was varied from 25% to 75% on a trial to trial basis. Under these conditions neither the P300 nor the slow wave exhibited a relation to signal-probability, whilst the relation to decision-confidence was preserved.

Adult↗
PubMed1988

Effects of a cholinergic nootropic (WEB 1881 FU) on event-related potentials recorded in incidental and intentional memory tasks.

In a double-blind placebo-controlled randomized study the influence of a cholinergic nootropic (WEB 1881 FU) on event-related brain potentials (ERPs) related to memory performance was investigated. Two different encoding modes were imposed on the subjects, who had to memorize word lists. No significant drug effects were obtained on memory performance and the ERP-concomitant of encoding, the Dm, while ERP effects related to memory were clearly present. However, the two dosages of the drug significantly influenced the overall amplitude of the late cognitive ERP components, suggesting its effect on cognitive processes.

Adult↗
PubMed1986

Use of endogenous event-related potentials (ERP) in the evaluation of psychotropic substances: towards an ERP profile of drug effects.

Although endogenous event-related potentials (ERPs) have been successfully used in psychology, they have largely been neglected in the study of psychotropic substances. In the present paper an overview is given of the diversified concepts of ERP research and useful adaptations of these approaches to psychopharmacological questions are shown. In particular, the influence of drugs on the various stages of information processing and the description of individual differences in drug reactions seem suitable for the use of endogenous ERPs. Other possible uses of ERPs in psychopharmacological research are briefly discussed and the problems of the technique are pointed out. It is concluded that future research should aim at the recording of 'ERP profiles' of a drug, monitoring pharmacological effects on the different levels of cognitive functions by a set of selected paradigms.

Brain↗