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Biomedical subjects

S Johannes

Publications and source records attributed to S Johannes.

At least 37 records · Page 2Linked to original sources
PubMed1999

Evidence for changed recognition of emotionally charged words in patients with Gilles de la Tourette syndrome and obsessive compulsive disorder.

Patients with Gilles de la Tourette syndrome (TS) frequently show obsessions and compulsions. Pathophysiologically, TS has been linked to abnormalities of the basal ganglia and forebrain which are related to emotional processes. Because recordings of event-related potentials (ERPs) have shown that the emotional content of words interacts with the subjects' ability to recognise repeated words we hypothesised that patients who were diagnosed to have TS and obsessive compulsive disorder (OCD) utilised a changed cognitive process for the recognition of emotional words. ERPs were recorded while 12 patients and matched control subjects viewed a series of emotionally neutral, negative, and positive words. These were repeated after some intervening items with the task being to discriminate between new words and repeated words. In both groups, correctly detected repeated words showed a more positive ERP waveform than new words between 350 msec and 550 msec after stimulus presentation. Although we found no group difference of this old-new effect for emotionally neutral words, patients had a smaller effect than control subjects for negative and positive words. This finding is discussed with respect to the literature and is viewed as evidence for changed memory mechanisms for emotionally charged words in patients with TS and OCD.

Journal Article↗
PubMed1999

Abnormalities of visual search behaviour in ALS patients detected with event-related brain potentials.

A number of recent reports have emphasized neuropyschological symptoms in ALS, including frontal functions, memory and attention. We investigated visual search behaviour of ALS in two types of tasks: a simple, relatively effortless parallel search task and a more complex attention-demanding serial search task. Behavioural parameters and cognitive event-related potentials (ERP) from 19 scalp channels were obtained from 13 ALS patients and 13 matched controls during task performance. ALS patients showed the same target detection rates as controls in the parallel task but were significantly impaired in the serial task. Performance was slower in the patients than in the controls. This slowing could be attributed to cognitive rather than motor impairments, by inspection of the latency of the P3 component, which was delayed by 120 ms in the patients. In addition, the ERPs in the serial task showed a grossly reduced P3 amplitude, indicating disturbed stimulus evaluation in the patients under these conditions. Changes of an early attention-sensitive ERP component suggest an attention deficit underlying the disturbances in search behaviour.

Adult↗
PubMed1999

Neurophysiological aspects of synesthetic experience.

Synesthesia is a perceptual condition in which stimulation in one sensory modality elicits a concurrent sensation in another. The authors studied possible electrophysiological correlates of synesthetic experience in 17 subjects claiming to continuously experience chromatic-graphemical synesthesia and a matched control group. Subjects had to respond to one of four numbers and one of six letters by pressing a button. Even-related potentials (ERPs) were recorded from multiple scalp sites. Most synesthetic subjects reported strong synesthetic perceptions during the experiment. The ERPs of both groups showed a distinct P300 component when subjects encountered the assigned target number or letter. Synesthetic subjects had significantly and clearly more positive waveform over frontal and prefrontal scalp regions than control subjects for target and nontarget stimuli. This electrophysiological marker is discussed in terms of cortical inhibition in synesthetic subjects and the role of prefrontal regions in multisensory integration.

Adult↗
PubMed1999

Potency Testing of Swine Erysipelas Vaccines by Serology Results of a Pre-validation Study.

The European Pharmacopoeia (Ph. Eur.) monograph on Swine Erysipelas Vaccine (inactivated) (Ph. Eur., 1997) requires the potency of each batch to be demonstrated in a mouse protection test. In this parallel-line bioassay, mice are challenged with a virulent strain of Erysipelothrix (E.) rhusiopathiae after immunisation with different doses of either the standard preparation or of the test vaccine. More than one hundred animals are necessary for the routine testing of a single batch. In previous studies (Beckmann und Cubetaler, 1994; Rosskopf-Streicher et al., 1998), we have shown that an indirect enzyme-linked immunosorbent assay (ELISA) may be used to quantify the humoral response of mice. This method can replace the challenge model for the purposes of potency testing in the following manner: Ten mice are immunised subcutaneously with 1/10 of the vaccine dose required for pig vaccination. After three weeks, the mice are bled under anaesthesia. Serum samples are pooled and the antibody content is compared to that of a reference serum. In view of animal welfare the advantages of the alternative model are obvious: A highly reduced number of animals and the replacement of challenge exposure. This includes the discontinuation of the control group with a mortality rate of 100%. A pre-validation study was initiated to evaluate the performance of the serological method. Eight laboratories used the test kits to evaluate pooled serum samples from vaccinated mice. Both the reagents and the test protocol were shown to be satisfactory. The intra- and inter-laboratory reproducibility that was achieved indicates that the method is a strong candidate for validation.

Journal Article↗
PubMed1998

Brain potentials in patients with music perception deficits: evidence for an early locus.

Twelve patients with an acute cerebrovascular accident were assigned to a group with music perception deficits (amusia, n = 6) or a group without such deficits (n = 6) on the basis of a new test-battery for music-perception skills. Event-related brain potentials (ERPs) were recorded in an auditory classification task designed to elicit several components; the N1 as a correlate of initial auditory cortical processing, the P3a as an index of automatic attentional orienting, and the P3b as a measure for controlled stimulus evaluation. Patients with amusia showed a significant amplitude decrement for the P3a relative to controls and patients without amusia suggesting an impairment of early stimulus evaluation. P3b was reduced in both patient groups relative to control. These data show that amusia is quite common in unselected stroke patients and suggest deficits of generic rather than music-specific cognitive processes as the underlying cause.

Acoustic Stimulation↗
PubMed1998

Alteration of early components of the visual evoked potential in amyotrophic lateral sclerosis.

Evoked potentials were recorded in three different visual experiments in 14 patients with amyotrophic lateral sclerosis (ALS) and 14 matched control subjects. Control subjects' evoked potentials (EPs) were characterized by an initial positivity in the 90-140 ms range (P1) at the temporo-occipital site. This component was absent from the group average of the ALS patients as well as the individual patients' EPs. As the P1 is known to emanate from inferior occipito-temporal areas, this finding provides electrophysiological evidence for a cortical involvement in ALS including visual areas.

Adult↗
PubMed1998

Brain potentials and syntactic violations revisited: no evidence for specificity of the syntactic positive shift.

One of the current issues in the investigation of language by means of event-related brain potentials (ERPs) is whether there is an ERP effect that can be specifically related to the processing of syntactic information. It has been claimed that a late positivity (P600 or SPS-syntactic positive shift) occurring to syntactic violations or ambiguities qualifies as such an effect. In the present investigation we compared ERPs elicited by morphosyntactic (case inflection errors), semantic, and orthographic (misspelled words) violations in a group of young German subjects. All three types of violations gave rise to late positivities having the characteristics of the previously described P600/SPS. In an earlier time window, however, semantic violations were associated with a centroparietally distributed N400 component, whereas syntactic violations gave rise to a negativity of smaller amplitude that had a frontocentral distribution. In light of the present experiment, the view that the P600/SPS as a whole reflects specific syntactic processes appears to be untenable and an alternative interpretation is proposed. The different distributions of the late positive shifts merit further investigation.

Adult↗
PubMed1998

Differential effects of two motor tasks on ERPs in an auditory classification task: evidence of shared cognitive resources.

The aim of the study was to assess cognitive demands and fatigue during the execution of two different motor tasks. Event-related brain potentials (ERPs) were recorded from 15 healthy subjects while they concurrently performed, (1) one of two motor tasks, and (2) a three stimulus (70% standard tones, 15% target tones, 15% novel stimuli) auditory classification task. Both motor tasks required the externally paced adduction of the right thumb with the force task requiring a precise movement (feedback given) with about 50% of maximum force output (6 s on task, 4 s rest) while the displacement task required the same precise movement with only minimal force requirements. In separate sessions, both tasks were performed for about an hour with the subjects concurrently paying attention to the auditory task with button presses required for the target stimuli. This provided a dual task situation with trade-offs in P3b amplitude as a function of difficulty of the primary (motor) task. The P3b to the auditory target stimuli was reduced during the force session compared to the displacement session, indicating that the force-task placed a higher demand on cognitive resources. No differential effect of fatigue (time on task) could be ascertained over six consecutive parts of the session. The P3a component, a putative correlate of orienting of attention, showed a rapid attenuation over time but, attesting to its automatic nature, no effect of concurrent motor task. ERP components recorded timelocked to the movements showed a marked difference between the two tasks with the displacement task giving rise to higher amplitudes. Moreover, only for the force task an influence of time on task (fatigue) on the MP was found. The dual task methodology is a potentially useful tool to disentangle cognitive and motor components of central fatigue.

Acoustic Stimulation↗
PubMed1998

Brain potentials reveal the timing of face identity and expression judgments.

Event-related brain potentials (ERPs) were recorded from multiple scalp locations from young human subjects while they performed two different face processing tasks. The first task entailed the presentation of pairs of faces in which the second face was either a different view of the first face or a different view of a different face. The subjects had to decide whether or not the two faces depicted the same person. In the second task, pairs of faces (frontal views) were presented with the task of judging whether the expression of the second face matched that of the face. Incongruous faces in the view (identity) matching task gave rise to a negativity peaking at about 350 ms with a frontocentral maximum. This effect was similar to the N400 obtained in linguistic tasks. ERP effects in the expression matching task were much later and had a different distribution. This pattern of results corresponds well with neuropsychological and neuroimaging data suggesting specialized neuronal populations subserving identity and expression analysis but adds a temporal dimension to previous investigations.

Adult↗
PubMed1998

Recognition memory deficits in amyotrophic lateral sclerosis assessed with event-related brain potentials.

OBJECTIVES: Amyotrophic lateral sclerosis (ALS) has been shown to cause neuropsychological deficits. The present investigation sought to delineate memory deficits by recording cognitive event-related potentials (ERPs). SUBJECTS AND METHODS: Eight ALS patients and 8 matched controls were subjected to a 2-phase recognition memory test. During the first phase words were presented consecutively on a video-screen with one-third of the words being repeated. The subject had to press buttons according to whether a word had been repeated or not. During the second phase (delay 1 h) a second list containing 33% old items from phase 1 and 66% new words was shown with an old/new decision required. RESULTS: ALS patients showed less accurate recognition in the second phase. The ERPs of the controls showed a reliable difference between old and new items in both phases. This difference was nearly absent in the patients in both phases. CONCLUSION: The ERP pattern suggests abnormal memory processes in ALS. The results are compared with data from similar experiments in Huntington's and Alzheimer's disease and are interpreted in terms of an encoding deficit in ALS.

Adult↗
PubMed1998

The effects of tetrahydrocannabinol on the recognition of emotionally charged words: an analysis using event-related brain potentials.

The effects of synthetic tetrahydrocannabinol (THC) on event-related brain potentials (ERPs) were assessed in 19 healthy male volunteers while they performed a visual continuous word recognition task. The study used a double-blind cross-over design. Specifically, word lists were manipulated to contain an equal number of emotionally neutral, negative, and positive words. Most words were repeated after several intervening items with the subject's task to classify each word as old (previously seen) or new. Behaviorally, a decrease in recognition rate was observed under THC but no influence of the emotional charge of a word on recognition rate was seen. The ERPs showed a typical difference between old and new words taking the form of an enhanced positivity for old words beginning 250 ms poststimulus. The effects of THC were confined to the positive words, for which an enhancement of the positivity to the old words was seen. This effect was interpreted in terms of a congruity of the drug-induced mood state and the material to be recognized. The dissociation between ERPs and behavioral indices suggested that the former primarily reflect implicit memory processes.

Adult↗
PubMed1997

Human brain potentials to reading syntactic errors in sentences of different complexity.

In order to determine if an event-related brain potential (ERP) effect described for syntactic violations (P600/SPS) varies with the amount of reprocessing entailed by a violation, number incongruencies were presented either within simple declarative or within subordinate clauses. ERPs were recorded while 12 German subjects read the stimulus materials presented word by word on a video monitor. The ERPs showed a P600/SPS effect for all sentence types, which was smallest in amplitude and earliest in latency for simple declarative sentences. This effect therefore qualifies as a metric for the amount and timing of syntactic reprocessing entailed by a syntactic error. In addition, a late frontal negativity (1000-1400 ms range) was found for the simple declarative sentences.

Adult↗
PubMed1997

Brain potentials and time estimation in humans.

Several parameters of the event-related potential (ERP) were assessed while 12 healthy volunteers performed a time production task. Each trial consisted of a series of 20 flashes presented at regular intervals on a videomonitor (interval 768 ms). After these flashes the subjects had to estimate the time it would take for an additional five flashes and to press a button upon the 5th interval. ERPs were recorded from 19 electrodes with three effects being of interest: (1) possible emitted potentials at the times at which flashes had occurred, if the series had continued, (2) the ERP to probe flashes presented during the production period, and (3) the slow potential shift during the estimation period. In addition reaction times were recorded. While ERP effects (1) and (2) were not informative with respect to time estimation processes, the slow potential shift with a frontopolar distribution appears to index time-keeping functions in humans.

Adult↗
PubMed1997

Relation of cerebral blood flow velocity and level of vigilance in humans.

Blood flow velocities in both middle cerebral arteries (MCA) were measured using transcranial Doppler ultrasound (TCD) in healthy subjects engaged in a continuous static visual vigilance task. Stimuli comprised white vertical gratings on a black background with a size of 5 x 5" (non-targets) or 5 x 3.5" (targets). Button presses were required to the rare (8.5%) targets. Over the 30 min session a decrease in hit rate and an increase in reaction time were seen, indicating a decrease in vigilance. These performance changes were paralleled by a decrease in flow velocity in both MCAs. No hemispheric difference was seen. These data suggest a close coupling of performance and blood flow in vigilance tasks. Modulation of cholinergic activity during the vigilance task might be the common underlying mechanism.

Adult↗
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↗