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Biomedical subjects

B Rockstroh

Publications and source records attributed to B Rockstroh.

At least 19 recordsLinked to original sources
PubMed2000

EEG brain mapping of phonological and semantic tasks in Italian and German languages.

OBJECTIVES: Event-related potential correlates of phonological encoding - as compared with lexical access and semantic categorization - were measured in two studies involving two groups of 14 German and 14 Italian subjects. METHODS: A two stimulus reaction time paradigm was used. Stimulus pairs presented one-by-one with 2 s inter-stimulus intervals (ISI) had to be matched with respect to lexical identity (word-picture) in a word comprehension task or with respect to the phonological representative of objects in a rhyming task. A semantic categorization task was added for the Italian sample. In both studies, the EEG was recorded from 26 scalp electrodes according to the 10-20 system. The slow negative potential during the ISI (CNV) was determined as the electrocortical correlate of preparation for and activation of the specific language-related task. RESULTS: In both samples, phonological encoding (rhyming) evoked a more pronounced CNV over the left- compared with the right-frontal area, while less lateralized central dominance of the CNV was found in the word comprehension task. Semantic categorization was accompanied by the least asymmetry of activity. CONCLUSIONS: Results indicate that the different degree of asymmetry induced by phonological and semantic processing may be determined from the scalp distribution of slow cortical potentials with cross-lingual reliability.

Acoustic Stimulation↗
PubMed1999

Topography of the auditory P300 in schizotypal personality.

BACKGROUND: Research with schizophrenic patients has demonstrated reduced amplitude of the P300b elicited with the auditory "oddball" paradigm, as well as reduced P300a amplitude following "novel" stimuli. The focus of the present study was the investigation of these components in a nonclinical sample of participants with high expressions of the schizotypal personality trait. METHODS: By use of an acoustic oddball task, including the presentation of novel stimuli, the event-related brain potentials of 14 participants with "low" and 13 participants with "high" scores on the German adaptation of the "Schizotypal Personality Questionnaire" were investigated. Current source density (CSD) curves and spline-interpolated CSD maps were generated. Peak amplitudes and latencies of the N100, P200, P300a, and P300b were determined for the CSD data. RESULTS: Results indicate no group differences with respect to N100, P200, and P300a amplitudes and latencies. By contrast, the P300b amplitude was significantly smaller in high- as compared to low-scoring participants. Left-temporal as compared to right-temporal P300b was significantly smaller in high- than in low-schizotypal participants. CONCLUSIONS: Confirming results of other researchers, this present study suggests that a reduced P300b amplitude and an altered P300b topography at temporal sites may be a trait-like "marker" of the schizophrenia spectrum.

Adult↗
PubMed1999

Determining working memory from ERP topography.

Event-related potentials were recorded during a delayed matching-to-sample design from 17 volunteers (5 f) using high-resolution (65 channels) EEG-recordings. In the two-stimulus paradigm, the 500-ms stimulus S1 comprised a visual pattern of two diamonds differing in size, angular rotation and location; in the delay period, Working Memory (WM) load was varied in the following way: a stimulus-free interval of 1 s was followed by a 6-s presentation either of a pattern identical to the S1 (low WM load) or of a pattern differing from S1 (high WM load). The 500-ms stimulus S2 comprised one diamond; the subject's task was to indicate by left- or right-hand (respectively) button press, whether the S2 matched the (a) left- or (b) right-positioned S1-diamond, or (c) did not match at all (NoGo). The topographical distribution of activity in the time intervals (a) following S1-offset, (b) during the WM manipulation interval and (c) prior to S2 were evaluated in the signal (scalp potential) and source (Minimum Norm) space. Following S1-offset the ERP pattern was characterised by negativity over posterior areas, slightly more so over the right hemisphere. In the subsequent 6-s interval high WM load elicited a larger negative slow ERP than low WM load, the negativity increase due to high WM load being larger over frontal than central areas. Source modelling indicated activity in anterior areas under high, and posterior activity under low WM load. Asymmetry of activity, although indicating a shift to left-hemispheric activity under high compared to low WM load, varied considerably between subjects. Results suggest that high-resolution ERP recordings allow to examine cortical activity during WM challenge.

Adolescent↗
PubMed1999

Event-related potential correlates of proactive interference in schizophrenic patients and controls.

Performance and event-related potentials (ERPs) were examined in a proactive interference (PI) task with 15 male schizophrenic patients and 15 matched healthy controls. Within a paired-associate task, 30 pairs of semantically unrelated words (A-B) were presented twice, followed by cued recall, in which the paired-associate B had to be named upon cue A. Subsequently, 50% of the A-words were paired with new words (A-C) and presented in random order together with 15 novel pairings (D-E). Slower responses and poorer recall of C- than of E-words in the final recall indicated PI in both groups. During acquisition, the paired-associates (C/E) evoked larger P3 and positive slow wave in controls than in patients. During recall, cues (A/D) evoked a slow wave with predominating anterior negativity in controls and posterior positivity in patients. The group-specific ERP pattern suggests deviant encoding and retrieval processes in schizophrenic individuals.

Adult↗
PubMed1998

Failure of dominant left-hemispheric activation to right-ear stimulation in schizophrenia.

Schizophrenia is associated with an absence of the lateralizations that typify the human brain. Previous evidence emphasized structural changes, particularly reduced asymmetry in extension and surface of the planum temporale, although gross structural deviations occur only in a minority of patients. The present study describes an absence of lateralization on a robust functional measure that characterized schizophrenia patients: healthy subjects but not schizophrenics displayed a contralateral left-hemispheric dominance of the auditory evoked magnetic field to right-ear auditory stimulation. Absence of contralateral dominance in response to auditory stimuli among schizophrenia patients may indicate a failure to establish unequivocal left-hemispheric dominance of the phonological loop as hypothesized by Crow.

Acoustic Stimulation↗
PubMed1998

Alteration of digital representations in somatosensory cortex in focal hand dystonia.

Focal hand dystonia involves a loss of motor control of one or more digits; it is associated with the repetitive, synchronous movements of the digits made by musicians over periods of many years. Magnetic source imaging revealed that there is a smaller distance (fusion) between the representations of the digits in somatosensory cortex for the affected hand of dystonic musicians than for the hands of non-musician control subjects. The data suggest that use-dependent susceptibility to digital representation fusion in cortex may be involved in the etiology of focal dystonia. A successful therapy for the condition has been developed based on this consideration.

Adult↗
PubMed1998

Dynamical aspects of motor and perceptual processes in schizophrenic patients and healthy controls.

The present study examined the temporal stationarity of the performance of 16 schizophrenic patients and 16 controls matched for age and sex in a bimanual coordination task and a perceptual task. In the motor task, rhythmic finger oscillations (alternating activity of homologue muscle groups) at increasing speed levels resulted in two measures, the preferred oscillation frequency and the critical frequency at which phase transitions (change towards simultaneous activity of homologue muscle groups) occurred. A measure of local dimensional complexity (pointwise D2 or PD2), which is a measure of non-linear dynamics, was determined for the acceleration profiles of the subjects' movements. Schizophrenics exhibited less stable movement dynamics than controls in horizontal finger cycling, indicated by a lower ratio critical/preferred frequency (critical ratio) and by higher means and standard deviations of the pointwise D2. In vertical cycling, the critical ratio did not differentiate between groups, while PD2 means and standard deviations did. Groups also differed specifically in perception of two ambiguous figures (Schroeder stairs and Rubin vase). Schizophrenics showed significantly higher reversal rates for the Rubin vase and a differential perceptive in comparison to controls in the perception of the Schroeder stairs. Measures of perceptual and motor stability were unrelated, which suggests that perceptual and motor processes are not influenced by a common underlying mechanism.

Adult↗
PubMed1998

Monitoring brain activity of human subjects during delayed matching to sample tasks comparing verbal and pictorial stimuli with modal and cross-modal presentation: an event related potential study employing a source reconstruction method.

The time course of the event related potentials evoked within a delayed matching to sample task employing verbal and pictorial stimuli was analyzed with a source reconstruction method (minimum norm method). During signal stimulus presentation pictorial stimuli evoked more activity than verbal stimuli. Activity was particularly prominent in left frontal areas for the match of verbal-verbal stimulus pairs and over right posterior regions for the match of verbal-pictorial stimuli. Anticipation of the to-be-matched stimulus produced more pronounced activity for pictorial stimuli and generally stronger left and frontal activity. Results are discussed referring to a biological model of language processing.

Adult↗
PubMed1998

Perceptual correlates of changes in cortical representation of fingers in blind multifinger Braille readers.

The mature mammalian nervous system alters its functional organization in a use-dependent manner. Enhanced stimulation of a body part enlarges its cortical representational zones and may change its topographic order. Little is known about the perceptual and behavioral relevance of these plastic alterations in cortical organization. We used blind Braille readers who use several fingers on each hand and who do so for many hours each day as a model to investigate this issue. Magnetic source imaging indicated that the cortical somatosensory representation of the fingers was frequently topographically disordered in these subjects; in addition, they frequently misperceived which of these fingers was being touched by a light tactile stimulus. In contrast, neither the disordered representation nor mislocalizations were observed in sighted controls. Blind non-teacher Braille readers who used only one finger for reading were not significantly different from the sighted controls. Thus, use-dependent cortical reorganization can be associated with functionally relevant changes in the perceptual and behavioral capacities of the individual.

Adult↗
PubMed1998

Topography of CNV and PINV in schizotypal personality.

The topography of the postimperative negative variation (PINV) was analyzed in participants with high and low scores on the German version of the Schizotypal Personality Questionnaire. Scalp amplitude and Laplacian maps of the terminal contingent negative variation (tCNV) and PINV and the time course of the PINV were compared between the two groups. CNV and PINV were induced with a delayed matching-to-sample task, in which the pattern of the imperative stimulus was either clearly or ambiguous matched to one of the two diamonds simultaneously presented as a warning stimulus 4.0 s earlier. Electroencephalograms were recorded with a DC amplifier (32 channels). Negativity increased from tCNV to PINV, especially at frontal sites, and the PINV was larger under ambiguous than under clear matching conditions. Low-scoring participants showed a right-sided predominance of the PINV, which was absent in high-scoring participants. These results resemble differences in the topography of the PINV between healthy control participants and those with schizophrenia under identical experimental conditions and suggest functional differences between tCNV and PINV.

Adult↗
PubMed1997

Dynamical aspects of the EEG in different psychopathological states in an interview situation: a pilot study.

Dynamical brain states can be characterized by non-linear measures of EEG. The present study shows that critical transitions, i.e., abrupt changes from one dynamic pattern of neural mass activity to another one, may be detected by abrupt variations in local chaoticity. Using an ambulatory device, EEG was recorded from 10 patients with a schizophrenic and two patients with an affective disorder during a series of 25-min interviews. Dynamical aspects, in particular, phase transitions in the EEG-dynamics of the EEG were characterized by means of a measure that continuously estimates the chaoticity of the EEG signal and is thus related to its predictability. Results indicate simpler dynamics of the EEG time series in paranoid-hallucinatory patients, while at the same time these patients tended to exhibit more abrupt transitions/unit of time between different dynamical EEG states. Such sudden phase transitions in brain activity were significantly enhanced prior to expressions of thought disorders that were detected by the interviewer and an observer in the conversation, compared with time periods during the interview without such symptoms.

Adult↗
PubMed1997

Mapping EEG-potentials on the surface of the brain: a strategy for uncovering cortical sources.

This paper describes a uniform method for calculating the interpolation of scalp EEG potential distribution, the current source density (CSD), the cortical potential distribution (cortical mapping) and the CSD of the cortical potential distribution. It will be shown that interpolation and deblurring methods such as CSD or cortical mapping are not independent of the inverse problem in potential theory. Not only the resolution but also the accuracy of these techniques, especially those of deblurring, depend greatly on the spatial sampling rate (i.e., the number of electrodes). Using examples from simulated and real (64 channels) data it can be shown that the application of more than 100 EEG channels is not only favourable but necessary to guarantee a reasonable accuracy in the calculations of CSD or cortical mapping. Likewise, it can be shown that using more than 250 electrodes does not improve the resolution.

Brain↗
PubMed1997

Input-increase and input-decrease types of cortical reorganization after upper extremity amputation in humans.

A plastic remodeling of regions in somatosensory cortex has previously been observed to occur in separate experimental paradigms in response to loss of somatosensory input and to increase in input. In this study, both types of cortical reorganization have been observed to occur concurrently in the same adult human nervous system as a result of a single intervention. Following upper extremity amputation, magnetic source imaging revealed that tactile stimulation of the lip evoked responses not only in the area of the somatosensory cortex corresponding to the face, but also within the cortical region that would normally correspond to the now absent hand. This "invasion" of the cortical amputation zone was accompanied by a significant increase in the size of the representation of the digits of the intact hand, presumably as a result of an increased importance of sensory stimulation consequent to increased dependence on that hand imposed by the loss of the contralateral extremity.

Adolescent↗
PubMed1997

The postimperative negative variation following ambiguous matching of auditory stimuli.

Previous studies using the delayed-matching-to-sample paradigm with visual stimuli reliably induced a postimperative negative variation (PINV) in both schizophrenic patients and healthy controls. The PINV was found to be: (a) larger in schizophrenic patients than controls; (b) larger under conditions of ambiguous as compared to clear matching conditions; and (c) larger over right-hemispheric, fronto-temporal regions in controls, while a less asymmetrical distribution with a tendency for left-frontal predominance occurred in schizophrenic patients. The present study examined to what extent the development and scalp distribution of the PINV were modality-specific by applying the delayed-matching-to-sample design using auditory stimuli. Furthermore, the neurophysiological state during anticipatory negativity (CNV) and PINV was examined by presenting acoustic probe stimuli (one per trial on 50% of the trials) during baseline, CNV or PINV interval. Event-related slow and probe-evoked potentials were recorded in 13 patients with a chronic schizophrenic disorder (DSM-III-R) and 13 healthy control Ss from 15 electrode sites including midline and two sagittal rows over each hemisphere. Comparable group differences and effects of ambiguity on PINV amplitudes were found for both modalities, visual and auditory. The auditory stimuli produced a fronto-central distribution of the PINV in both groups. The probe-evoked vertexpotential was smaller in patients compared to controls, but exhibited comparable modulation with the largest amplitude during the CNV in both groups. Results suggest modality-non-specific cognitive determinants of the PINV. However, stimulus modality did affect the scalp distribution of the PINV. Probe-evoked responses point to different functional meaning of negativities prior to (CNV) and following (PINV) task-relevant stimuli.

Acoustic Stimulation↗
PubMed1997

[Visually-induced gamma band responses in human EEG- expression of cortical stimulus representation?].

The features of a visual stimulus are processed in different regions of the visual cortex with no direct axonal connections. Therefore, neurons in the distributed processing areas must be connected in some way to form the physiological substrate of the percept. On the basis of theoretical considerations and animal experiments, it has been proposed that synchronization of neuronal oscillatory firing patterns in the gamma band range (above 30 Hz) might be essential in linking the anatomically distant cell assemblies that represent the various features of the stimulus. The present work reports on three experiments in which the functional relevance of induced gamma band responses were investigated in the human EEG. Using an identical stimulation design, as used in animal studies, it was demonstrated that human induced gamma band responses resembled those reported from intracortical recordings from animals. It was further shown that alpha and gamma band activities differed in temporal characteristics as well as in topographical features, indicating the representation of different cortical functional states. In accordance with previous animal and human experimental findings, a complex moving stimulus was related to a suppression of induced gamma band activity as opposed to a standing complex stimulus.

Animals↗