Biomedical subjects

B M Wieringa

Publications and source records attributed to B M Wieringa.

25 records · Page 2Linked to original sources

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.

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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.

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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.

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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.

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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.

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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.

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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.

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