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Biomedical subjects

T F Münte

Publications and source records attributed to T F Münte.

At least 73 records · Page 4Linked to original sources
PubMed1997

An electrophysiological analysis of altered cognitive functions in Huntington disease.

BACKGROUND: Neuropsychological deficits are a main feature of Huntington disease (HD) with previous data suggesting involvement of memory functions and visual processing. OBJECTIVE: To increase the knowledge about cognitive malfunction in HD in the domains of visual processing and memory by the use of modern electrophysiological techniques (event-related potentials [ERPs]). DESIGN: A case-control design was used. Three ERP paradigms were used; a parallel visual search paradigm allowed for the simultaneous processing of a multi-element visual array in search of a target stimulus, while a serial search paradigm with varied numbers of distractor items necessitated a serial one by one scanning of the arrays. The third experiment was a word-recognition memory task. SETTING: The measurements were obtained in a neurophysiological laboratory of a university hospital. PATIENTS AND CONTROLS: Nine patients with HD and 9 control subjects matched for age, sex, and education were studied. MAIN OUTCOME MEASURES: Components of averaged ERPs were quantified by latency and amplitude measures and subjected to statistical analysis. Behavioral measures (search time, hit rate, and recognition accuracy) were assessed as well. RESULTS: The early visual components showed a significant latency shift (delay of about 50 milliseconds) in HD. In the search paradigms the P3 components differentiating target and standard stimuli were virtually absent in HD as was the ERP effect indexing word recognition. This was accompanied by a marked delay in search times and lower hit rates in the search tasks and a grossly reduced recognition accuracy in the memory task. CONCLUSIONS: The results suggest marked impairments of patients with HD in early visual sensory processing (early components). Deficits in visual search might be attributed to an impairment to deploy attentional resources across the visual field and/or an inability to control eye movements. The ERPs in the memory task differed grossly from similar data obtained by others in patients with Alzheimer disease, suggesting a different neural basis for the amnesia in HD.

Adult↗
PubMed1997

Blood flow velocity changes in the middle cerebral artery induced by processing of hierarchical visual stimuli.

Transcranial Doppler ultrasound was used to measure mean flow velocities in both middle cerebral arteries while 16 young subjects performed a visual task involving the processing of hierarchically structured stimuli. Specifically, large (global) letters composed of smaller (local) letters were presented, with the subjects' task being to attend either to the local or to the global level and press a button whenever a target on the designated level occurred. Each run was comprised of a 35-sec period of passive stimulation, followed by 65 sec of active task. A highly significant increase of blood flow was detected upon initiation of the active task, which was clearly present after ca. 4 sec. The flow velocity reached a maximum after 20 sec and remained stable for the remainder of the active condition. No hemispheric differences with respect to global or local conditions were observed.

Adult↗
PubMed1997

Event-related brain potentials to unfamiliar faces in explicit and implicit memory tasks.

The purpose of this study was to investigate electrophysiological correlates related to the recognition of repeated faces in the intact human by means of event-related brain potentials (ERPs). A group of young healthy adults performed a continuous face recognition task, in which 240 unfamiliar faces were flashed upon a computer screen with 80 of the faces being repetitions. The subjects had to classify faces as previously seen and previously unseen faces. The concomitantly recorded ERPs from 19 scalp sites revealed a more positive going waveform for the correctly classified repeated faces beginning at about 280 ms (old/new effect). The same subjects performed a similar task with visually presented concrete nouns as stimuli. The old/new effect in this task showed a similar distribution, amplitude and onset latency. It is thus concluded that the old/new effect is not specific to the materials to be memorized. In contrast, the old/new effect in an implicit face repetition experiment (with the detection of famous persons being the task) showed a different distribution. It is argued that the differential distribution might reflect the different requirements of the two tasks (explicit vs. implicit task). Recent interpretations of the old/new effects are discussed.

Adult↗
PubMed1997

Relation of neuropsychological and magnetic resonance findings in amyotrophic lateral sclerosis: evidence for subgroups.

The relationship between neuropsychological impairments and changes in cranial MR images was investigated in a group of 74 consecutive patients with the sporadic form of amyotrophic lateral sclerosis (ALS). Neuropsychological tests included measures of frontal lobe function, memory, intelligence, and attention. Compared with a control group, a significant impairment of the ALS group emerged for the areas of visual attention, inhibition of response alternatives, visual memory, and word generation. These neuropsychological impairments did not show a relation to clinical status of the patients. Likewise, MR parameters derived by computer assisted planimetric analysis showed a ventricular enlargement and parenchymal atrophy in the ALS group compared with age-matched controls. When ALS patients were assigned to two subgroups differing on the basis of the neuropsychological tests by cluster-analysis the cluster with the significant impairment also showed a pronounced change for the MR-parameters while the subgroup showed essentially normal neuropsychological performance. This pattern suggests that subgroups of ALS with differential impairment of neuropsychological functions can be defined.

Adult↗
PubMed1997

How the brain processes complex words: an event-related potential study of German verb inflections.

Event-related brain potentials (ERPs) were recorded as German-speaking subjects read verbs in correct and incorrect participle forms. The critical words were presented in three different versions to three different groups of subjects, as part of a simple sentence, in a word list, and embedded in a story; for each version separate ERPs were recorded. Three types of verbs were investigated, regulars, irregulars and nonce verbs. We compared correct regular and irregular participles with incorrect ones; the latter had -(e)n on verbs that actually take -t participles (* getanz-en), or -(e)t on verbs that require -(e)n (* gelad-et). For the nonce verbs, we compared participles with the unexpected -(e)n ending with the expected -t participle forms. The ERP responses were very consistent across the three versions of the experiment: (i) incorrect irregular participles (* gelad-et) elicited a left frontotemporal negativity; (ii) incorrect regulars (* getanz-en) produced no differences to the correct ones; (iii) nonce verbs were associated with an N400 component but did not show a difference between expected and unexpected endings. We will interpret these findings with respect to psycholinguistic models of morphological processing and argue that the brain processes regularly inflected words differently from irregularly inflected ones, the latter by accessing full-form entries stored in memory and the former by a computational process that decomposes complex words into stems and affixes.

Adult↗
PubMed1996

Human evoked potentials to long duration vibratory stimuli: role of muscle afferents.

Tonic vibratory stimuli of 1000 ms duration and different frequencies were delivered to muscles of the forearms of young human subjects. Evoked potentials (EPs) were recorded from 29 scalp channels and revealed phasic highly lateralised and focally distributed EPs during the first 100 ms of the recording epoch that could be adequately modelled with a single point dipole source located in the vicinity of the central sulcus contralateral to the stimulated arm. A later negativity with an onset of about 400 ms and a duration of about 800 ms was found to be symmetrically distributed over fronto-central regions. This negativity is interpreted in terms of cortical activation beyond the primary sensory fields and could be related to the kinaesthetic phenomena experienced during muscle vibration.

Adult↗
PubMed1996

Transcranial Doppler assessment of cerebral blood flow velocity during visual spatial selective attention in humans.

Blood flow velocities of the posterior cerebral arteries were obtained while healthy subjects were engaged in a visual spatial attention task. Experimental runs consisted of series of stimuli comprised of four elements (two left and two right of a central fixation point) presented briefly in blue against a purple screen. After a period of passive viewing a left or right pointing arrow indicated the visual half-field to be attended by the subjects in order to detect identical symbols on the attended side. Relative to the passive viewing condition a marked increase of flow was seen in both posterior cerebral arteries during the attention period. No differential increase of flow as a function of attended field was detected. These results are discussed in comparison with recent positron-emission tomography (PET) and electrophysiological data obtained with the same task.

Adult↗
PubMed1996

Hierarchical visual stimuli: electrophysiological evidence for separate left hemispheric global and local processing mechanisms in humans.

Using reaction time measurements it has been shown that the neural processing of hierarchically composed visual stimuli may be mediated by partly distinctive mechanisms of global and local features analysis. Patients with focal left hemisphere brain lesions showed an impairment of local and patients with right hemisphere lesions of global stimulus perception. Our experiment was designed to extend the investigations of global/local feature analysis using the event-related brain potential (ERP) technique in healthy subjects. Thirteen subjects viewed a series of hierarchically composed non-linguistic stimuli in a divided attention condition in order to detect target stimuli which could be present at both local and global feature level, ERP analysis showed a posterior negative component (Ne) to be the correlate of early global/local information processing. When local targets were presented there was an effect of the global (non-target) level (termed 'distractor level') upon the onset of Ne but not vice versa. This supports the view of separate cortical mechanisms of global/local feature analysis. At odds with the previous patient data was the finding that both global and local level information was predominantly processed from the left hemisphere.

Adult↗
PubMed1996

Mental representations of morphologically complex words: an event-related potential study with adult humans.

Event related brain potentials (ERPs) were recorded from 13 subjects while performing a lexical decision task. Regular and irregular German principles were presented twice (identical repetition) or were primed by their related infinitives (morphological repetition). Regular participles primed by their infinitives displayed ERP waveforms similar to those evoked by identical repetitions, namely a large positivity with an onset latency of about 200 ms. Irregular participles, by contrast, showed no reliable morphological repetition effects. The results are discussed in terms of the controversy between approaches proposing a single representational mechanism for regular and irregular inflection and the "dual mechanism' account that suggests an associative memory for the storage of irregulars and a rule-based symbolic processor for generating regular forms.

Adolescent↗
PubMed1996

Developmental dyslexia: passive visual stimulation provides no evidence for a magnocellular processing defect.

Livingstone et al. [Livingstone, M. S., Rosen, G. D., Drislane, F. W. and Galaburda, A. M. Physiological and anatomical evidence for a magnocellular defect in developmental dyslexia. Proceedings of the National Academy of Science U.S.A. 88, 7943-7947, 1991] presented evidence for a defect of the magnocellular visual processing stream in developmental dyslexia. We attempted to replicate this effect using transient and steady-state VEPs to checkerboard reversal stimuli in a group of adult developmental dyslexics. Several different reversal rates and contract levels were utilized. No differences were found between the dyslexic and control groups for the low-contrast, rapidly reversing patterns, nor for any combination of stimulus rate or contrast that was tested. Thus, these findings do not support a magnocellular processing deficit in developmental dyslexia.

Adult↗
PubMed1996

Mononeuropathia multiplex and idiopathic intracranial hypertension.

A young obese woman with menstrual irregularities presented with bilateral papilledema, abducens nerve paresis, visual obscurations and severe headache. Neuroimaging studies were normal but CSF opening pressure was elevated. The diagnosis of idiopathic intracranial hypertension was made. Insertion of a shunt quickly alleviated the symptoms. A few weeks later the patient developed a left femoral nerve paresis and an ulnar nerve paresis on the right. Electrodiagnostic tests confirmed the diagnosis of mononeuropathia multiplex. Bone marrow histology showed a vasculitis. We hypothesize that the vasculitis is underlying both, idiopathic intracranial hypertension and mononeuropathia multiplex.

Adult↗
PubMed1996

Effects of alprazolam and bromazepam on visual search and verbal recognition memory in humans: a study with event-related brain potentials.

The effects of two benzodiazepines (alprazolam and bromazepam) on performance and event-related brain potentials (ERPs) in visual search and verbal recognition memory paradigms were tested in a placebo-controlled double-blind paradigm employing 12 young healthy subjects. Both drugs exerted similar effects on performance and electrophysiological measures. Reaction times and hit rates were adversely affected in both paradigms. The ERP pattern in the visual search experiment suggested an impairment in selective attention (reduction of N1 component) and of automatic feature registration (posterior N2 reduction). In the world recognition experiment a dramatic reduction of the N400 component was seen under benzodiazepines. This is interpreted as reflecting an impaired ability to perform context integration processes.

Adult↗
PubMed1995

Brain potential correlates of number errors in the Turkish language.

Event-related potentials (ERPs) were recorded from 16 native speakers of Turkish while they watched Turkish sentences flashed upon the screen of a videomonitor. The sentences were three words long and contained a verb at the terminal position that was manipulated (1) to have either the correct or the incorrect number with regard to the subject of the sentence, and (2) to be semantically appropriate, inappropriate or to be a pseudoverb. The ERPs from 19 scalp channels revealed a more positive waveform at the left-fronto-temporal site with an onset latency of about 200 ms for the verbs having the wrong number regardless of the semantic appropriateness of the word, while at right fronto-temporal sites a more negative waveform was observed for plural words only. This number incongruency ERP-effect in Turkish is clearly at odds with findings from other languages.

Adult↗
PubMed1995

Brain potentials in developmental dyslexia: differential effects of word frequency in human subjects.

The differences of word processing between a group of adult developmental dyslexics and control subjects were examined with the event-related potential (ERP) technique. In particular, the effects of word frequency and word recognition were assessed. The subjects viewed a series of frequently and infrequently used words, most of which were repeated after some intervening items and they discriminated between first and second presentations of the words. It can be shown that in the range from 300 to 550 ms post stimulus the amplitude of the N400 component, an ERP measure of semantic processing, is reduced for high frequency words. This effect is more pronounced in the dyslexic group and the effects of word recognition are also reduced in the dyslexic group for high frequency words. These findings are discussed with respect to current concepts of dyslexia and of semantic processing.

Adult↗
PubMed1995

Cognitive functioning in experimental hypoglycaemia assessed with event-related potentials.

Cognitive effects of experimentally induced hypoglycaemia were investigated by event-related brain potentials (ERPs) in auditory and visual classification tasks. In a cross-over design eight healthy male subjects (age 22-27 years) were studied under control conditions or following administration of 0.15 IU insulin kg-1. The ERPs showed preserved early cortical components, while the N2 component was greatly reduced in both modalities. P3 components did not show an influence of hypoglycemia. These results suggest that the cognitive deficits are due to an impairment of automatic feature extraction from the stimuli.

Adult↗
PubMed1995

Luminance and spatial attention effects on early visual processing.

Event-related potentials (ERPs) were recorded from healthy subjects in response to unilaterally flashed high and low luminance bar stimuli presented randomly to left and right field locations. Their task was to covertly and selectively attend to either the left or right stimulus locations (separate blocks) in order to detect infrequent shorter target bars of either luminance. Independent of attention, higher stimulus luminance resulted in higher ERP amplitudes for the posterior N95 (80-110 ms), occipital P1 (110-140 ms), and parietal N1 (130-180 ms). Brighter stimuli also resulted in shorter peak latency for the occipital N1 component (135-220 ms); this effect was not observed for the N1 components over parietal, central or frontal regions. Significant attention-related amplitude modulations were obtained for the occipital P1, occipital, parietal and central N1, the occipital and parietal P2, and the parietal N2 components; these components were larger to stimuli at the attended location. In contrast to the relatively short latencies of both spatial attention and luminance effects, the first interaction between luminance and spatial attention effects was observed for the P3 component to the target stimuli (350-750 ms). This suggests that interactions of spatial attention and stimulus luminance previously reported for reaction time measures may not reflect the earliest stages of sensory/perceptual processing. Differences in the way in which luminance and attention affected the occipital P1, occipital N1 and parietal N1 components suggest dissociations among these ERPs in the mechanisms of visual and attentional processing they reflect.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Combined spatial and temporal imaging of brain activity during visual selective attention in humans.

Visual-spatial attention is an essential brain function that enables us to select and preferentially process high priority information in the visual fields. Several brain areas have been shown to participate in the control of spatial attention in humans, but little is known about the underlying selection mechanisms. Non-invasive scalp recordings of event-related potentials (e.r.ps) in humans have shown that attended visual stimuli are preferentially selected as early as 80-90 ms after stimulus onset, but current e.r.p. methods do not permit a precise localization of the participating cortical areas. In this study we combined neuroimaging (positron emission tomography) with e.r.p. recording in order to describe both the cortical anatomy and time course of attentional selection processes. Together these methods showed that visual inputs from attended locations receive enhanced processing in the extrastriate cortex (fusiform gyrus) at 80-130 ms after stimulus onset. These findings reinforce early selection models of attention.

Attention↗