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Biomedical subjects

Thomas Elbert

Publications and source records attributed to Thomas Elbert.

17 recordsLinked to original sources
PubMed2003

Source distribution of neuromagnetic slow-wave activity in schizophrenic patients--effects of activation.

When slow waves in the EEG delta and theta frequency range appear in the waking state, they may indicate pathological conditions including psychopathology. The generators of focal slow waves can be mapped using magnetic source imaging. The resulting brain maps may possibly characterize dysfunctional brain areas. The present study examined the stability of the density and distribution of MEG slow waves during three conditions-rest, mental arithmetic and imagery-in 30 schizophrenic patients and 17 healthy controls. Schizophrenic patients displayed a higher density of delta and theta generators primarily in temporal and parietal areas. The group difference was not affected by the particular conditions. The focal concentration of delta and theta slow waves did not differ between patients with and without neuroleptic medication, whereas the prominence of theta dipoles in the temporal area correlated with neuroleptic dosage. The relative amount of temporal slow waves was correlated with the negative symptoms score (PANSS-N) suggesting that temporal dysfunction may be related to negative symptomatology.Results suggest that the distribution of slow-wave activity, measured in a standardized setting, might add diagnostic information about brain abnormalities in schizophrenia.

Adult↗
PubMed2003

Effective behavioral treatment of focal hand dystonia in musicians alters somatosensory cortical organization.

New perspectives in neurorehabilitation suggest that behavioral treatments of movement disorders may modify the functional organization of central somatosensory neural networks. On the basis of the assumption that use-dependent reorganization in these networks contributes to the fundamental abnormalities seen in focal dystonia, we treated 10 affected musicians and measured the concomitant somatosensory changes by using whole-head magnetoencephalography. We found that effective treatment, using the method of sensory motor retuning, leads to alterations in the functional organization of the somatosensory cortex. Specifically, before treatment, somatosensory relationships of the individual fingers differ between the affected and unaffected hands, whereas after treatment, finger representations contralateral to the dystonic side become more similar to the less-affected side. Further, somatosensory finger representations are ordered more according to homuncular principles after treatment. In addition, the observed physiologic changes correlated with behavioral data. These results confirm that plastic changes in parallel with emergent neurological dysfunction may be reversed by context-specific, intensive training-based remediation.

Behavior Therapy↗
PubMed2003

Altered hemispheric asymmetry of auditory N100m in adults with developmental dyslexia.

The current study aimed at determining whether the deviance of hemispheric asymmetry in the auditory cortex of children with dyslexia is also evident in dyslexic adults. Ten adult dyslexic subjects and 10 normally literate controls were presented with the syllable [ba:] while event-related brain activity was recorded from both hemispheres using whole-head magnetoencephalography. In control subjects, the auditory N100m source was found to be asymmetrical with a more anterior localization in the right than in the left perisylvian cortex (difference = 0.78 cm). The N100 m dipoles in dyslexic adults did not exhibit the same interhemispheric asymmetry (difference = -0.06 cm). The results indicate that reduced hemispheric laterality of perisylvian regions in dyslexia persists into adulthood.

Adult↗
PubMed2003

Blind Braille readers mislocate tactile stimuli.

In a previous experiment, we observed that blind Braille readers produce errors when asked to identify on which finger of one hand a light tactile stimulus had occurred. With the present study, we aimed to specify the characteristics of this perceptual error in blind and sighted participants. The experiment confirmed that blind Braille readers mislocalised tactile stimuli more often than sighted controls, and that the localisation errors occurred significantly more often at the right reading hand than at the non-reading hand. Most importantly, we discovered that the reading fingers showed the smallest error frequency, but the highest rate of stimulus attribution. The dissociation of perceiving and locating tactile stimuli in the blind suggests altered tactile information processing. Neuroplasticity, changes in tactile attention mechanisms as well as the idea that blind persons may employ different strategies for tactile exploration and object localisation are discussed as possible explanations for the results obtained.

Adult↗
PubMed2003

Cortical representation of vowels reflects acoustic dissimilarity determined by formant frequencies.

We studied neuromagnetic correlates of the processing of German vowels [a], [e] and [i]. The aim was (i) to show an influence of acoustic/phonetic features on timing and mapping of the N100 m component and (ii) to demonstrate the retest reliability of these parameters. To assess the spatial configuration of the N100 m generators, Euclidean distances between vowel sources were computed. Latency, amplitude, and source locations of the N100 m component differed between vowels. The acoustically most dissimilar vowels [a] and [i] showed more distant source locations than the more similar vowels [e] and [i]. This pattern of results was reliably found in a second experimental session after at least 5 days. The results suggest the preservation of spectral dissimilarities as mapped in a F(1)-F(2) vowel space in a cortical representation.

Adult↗
PubMed2003

Altered hemispheric asymmetry of auditory P100m in dyslexia.

In various studies, deviances of hemispheric laterality in the organization of the perisylvian region in dyslexia have been suggested. Although associated with impaired language functioning, the clinical significance of atypical cerebral lateralization remains unclear. The present study examined interhemispheric source differences of magnetic responses to the German synthetic syllable [ba:] in the auditory cortex of 14 dyslexic children and 12 normally literate controls aged 8-15 years. In all subjects, two main deflections, P100m and N260m, were evident in the responses over each hemisphere. While in the control group the right P100m dipole was located more anterior than the corresponding dipole of the left hemisphere, the dyslexic group displayed a rather symmetrical source configuration between the hemispheres. This symmetry reflected a deviance in the right perisylvian region for the dyslexic subjects' P100m, which was generated approximately 1 cm more posterior than the response in controls. The deviation was also obvious relative to the source location of the later component, N260m, which did not systematically differ between the participant groups. Our results suggest that the altered hemispheric asymmetry reflects an atypical organization of the right hemisphere in children and adolescents with dyslexia.

Acoustic Stimulation↗
PubMed2003

Semantic categorization in the human brain: spatiotemporal dynamics revealed by magnetoencephalography.

We examined the cortical representation of semantic categorization using magnetic source imaging in a task that revealed both dissociations among superordinate categories and associations among different base-level concepts within these categories. Around 200 ms after stimulus onset, the spatiotemporal correlation of brain activity elicited by base-level concepts was greater within than across superordinate categories in the right temporal lobe. Unsupervised clustering of data showed similar categorization between 210 and 450 ms mainly in the left hemisphere. This pattern suggests that well-defined semantic categories are represented in spatially distinct, macroscopically separable neural networks, independent of physical stimulus properties. In contrast, a broader, task-required categorization (natural/man-made) was not evident in our data. The perceptual dynamics of the categorization process is initially evident in the extrastriate areas of the right hemisphere; this activation is followed by higher-level activity along the ventral processing stream, implicating primarily the left temporal lobe.

Adult↗
PubMed2002

Expansion of the tonotopic area in the auditory cortex of the blind.

A part of the core area of the auditory cortex was examined in nine blind and 10 sighted individuals by magnetic source imaging and was found to be enlarged by a factor of 1.8 in the blind compared with the sighted humans. Moreover, the latency of the N1m component of the auditory-evoked magnetic response was significantly decreased in the blind. The development of use-dependent cortical reorganization may be a consequence of the absence of visual input in combination with enhanced auditory activity generated by the long-term concentration by blind individuals on nonvisual cues to interact appropriately with the environment. It is consistent with and well suited to mediate the demonstrated increased ability of the blind to accurately localize acoustic sources in peripheral auditory fields and to decode speech.

Acoustic Stimulation↗
PubMed2002

Focal temporoparietal slow activity in Alzheimer's disease revealed by magnetoencephalography.

BACKGROUND: Patients suffering from Alzheimer's disease exhibit more activity in the conventional electroencephalographic delta and theta bands. This activity concurs with atrophy and reduced metabolic and perfusion rates, particularly in temporoparietal structures. METHODS: Whole-head magnetoencephalographic recordings were obtained from 15 patients diagnosed with Alzheimer's disease and 19 healthy control subjects during a resting condition. The generators of focal magnetic slow waves were located employing a single moving dipole model. RESULTS: Dipole density in the delta and theta bands was enhanced in the Alzheimer's disease group compared with healthy control subjects. Slow-wave activity differed significantly between groups in temporoparietal regions of both hemispheres. Right temporoparietal slow-wave activity covaried with cognitive performance, whereas left temporal delta activity varied with a functional status scale. CONCLUSIONS: Our results support the predominant role of the temporoparietal areas in the diagnosis of Alzheimer's disease. Magnetoencephalography and the source analysis of focal slow activity in particular provide interesting and potentially clinically useful tools to assess functional modifications of patients' brain and to evaluate its relationship with the cognitive status.

Aged↗
PubMed2002

Dissociation in human prefrontal cortex of affective influences on working memory-related activity.

Although neural activity associated with emotion is becoming better understood, the influence of affective parameters on brain activity reflecting cognitive functioning in humans remains poorly characterized. We examined affective influences on working memory (WM) and tested the hypotheses that (i) dorsolateral prefrontal cortex (DLPFC) activity reflecting WM is influenced by the emotion-evoking qualities of task-relevant stimuli, but only when brought "on-line" by task demands, and (ii) DLPFC and orbitofrontal cortex (OFC) activities are inversely related as a function of emotional valence. Participants performed two tasks while event-related functional MRI measured brain activity; one task required active maintenance of stimulus representations in WM, and the other task required target detection responses with no demand for WM. Stimuli were standardized emotional (pleasant and unpleasant) and neutral pictures. Emotional stimuli differentially influenced DPFC and OFC activity during WM; DLPFC was influenced by emotional valence, enhanced by pleasant and reduced by unpleasant, compared to neutral stimuli, only when task conditions required WM. OFC was valence-sensitive during both tasks, greater to arousing than neutral stimuli when WM demand was low and in inverse relationship to DLPFC with high WM demand. Further, DLPFC and OFC activities are inversely related with respect to emotional valence during the WM task. The results are consistent with the hypothesis that the intrinsic valence of task-relevant stimuli maintained in WM modulates DLPFC activity but only when the DLPFC is required for task demands. Findings suggest a conceptualization of DLPFC and its involvement in WM that takes into account a role for affective parameters.

Adult↗
PubMed2002

Functional organization of primary somatosensory cortex depends on the focus of attention.

We used magnetic source imaging in human subjects to reveal within-subject variations of the homuncular hand representation within the primary somatosensory cortex modulated by attention. In one condition subjects were trained to detect sequential leftward or rightward stimulus motion across the fingers of the left hand ("hand" condition) and in a different condition to detect stimulus motion at a specific finger on this hand ("finger" condition). Afferent input was controlled by applying exactly the same stimulus pattern to the digits in the two tasks. Segregation of the somatotopic hand representation (an increase in the distance between the representations of digits 2 and 5) was observed, commencing with the onset of practice, in the finger relative to the hand condition. Subsequent training in the hand and finger conditions with feedback for correctness did not modify segregation, indicating that segregation was a task effect and not a training effect. These findings indicate that the hand representation within the primary somatosensory cortex is not statically fixed but is dynamically modulated by top-down mechanisms to support task requirements. A greater capacity for modulation of the functional cortical organization was positively correlated with superior learning and task performance.

Adult↗
PubMed2002

High resolution EEG indicators of pain responses in relation to hypnotic susceptibility and suggestion.

In this report we use a dense array (129 electrodes) EEG procedure to examine the effects of hypnotic susceptibility and hypnotic suggestions on electrocortical and self-report measures of painful stimuli. Self-report and event-related potential measures of six high and six low hypnotic susceptible individuals in response to pain were examined during an initial baseline condition and following a standard hypnotic induction under suggestions to either increase (hyperalgesia) or decrease (hypoalgesia) the painful stimulation. Our results show that high and low hypnotically susceptible individuals: (1) show few self-report or psychophysiological differences in response to baseline pain stimuli; (2) report differential pain experiences depending on hypnotic suggestions and (3) display differential psychophysiological indicators following an hypnotic induction with a suggestion of hypoalgesia. Overall, the findings suggest that hypnotic suggestions with high susceptible individuals modulate the later components of the evoked potential in a global manner and point up the importance of using both high and low hypnotically susceptible individuals preceding and following an hypnotic induction.

Adult↗
PubMed2002

Large-scale neural correlates of affective picture processing.

Hemodynamic and electrophysiological studies indicate differential brain response to emotionally arousing, compared to neutral, pictures. The time course and source distribution of electrocortical potentials in response to emotional stimuli, using a high-density electrode (129-sensor) array were examined here. Event-related potentials (ERPs) were recorded while participants viewed pleasant, neutral, and unpleasant pictures. ERP voltages were examined in six time intervals, roughly corresponding to P1, N1, early P3, late P3 and a slow wave window. Differential activity was found for emotional, compared to neutral, pictures at both of the P3 intervals, as well as enhancement of later posterior positivity. Source space projection was performed using a minimum norm procedure that estimates the source currents generating the extracranially measured electrical gradient. Sources of slow wave modulation were located in occipital and posterior parietal cortex, with a right-hemispheric dominance.

Adult↗
PubMed2002

New treatments in neurorehabilitation founded on basic research.

Recent discoveries about how the central nervous system responds to injury and how patients reacquire lost behaviours by training have yielded promising new therapies for neurorehabilitation. Until recently, this field had been largely static, but the current melding of basic behavioural science with neuroscience promises entirely new approaches to improving behavioural, perceptual and cognitive capabilities after neurological damage. Studies of phenomena such as cortical reorganization after a lesion, central nervous system repair, and the substantial enhancement of extremity use and linguistic function by behavioural therapy, support this emerging view. The ongoing changes in rehabilitation strategies might well amount to an impending paradigm shift in this field.

Animals↗
PubMed2002

Sensory motor retuning: a behavioral treatment for focal hand dystonia of pianists and guitarists.

OBJECTIVE: To evaluate the long-term effectiveness of sensory motor retuning (SMR), a new treatment for focal hand dystonia in musicians. DESIGN: Prospective case series with an (adventitious) comparison group with 3- to 25-month follow-up in piano and guitar and 0- to 4-month follow-up in flute and oboe players. SETTING: General community in Germany. PARTICIPANTS: Eleven professional musicians. INTERVENTION: Immobilization by splints of 1 or more digits other than the focal dystonic finger. This finger carried out repetitive exercises in coordination with 1 or more of the other digits for 1(1/2) to 2(1/2) hours a day for 8 consecutive days under therapist supervision. The subjects then were instructed to continue practice for 1 hour daily for 1 year. MAIN OUTCOME MEASURES: Spectral analysis of the output of a dexterity-displacement device that continuously recorded digital displacement during finger movements and a dystonia evaluation scale on which patients rated how well they had just performed dystonic movement sequences and repertoire passages. RESULTS: The 3 wind players (adventitious placebo controls) did not improve substantially. However, each pianist and guitarist showed marked and significant improvement in spontaneous repertoire performance without the splint. The first subject is now 25 months posttreatment. CONCLUSIONS: Results suggest that SMR is of value for the treatment of focal hand dystonia in pianists and guitarists.

Adult↗
PubMed2002

Longer versus shorter daily constraint-induced movement therapy of chronic hemiparesis: an exploratory study.

OBJECTIVE: To evaluate and compare the effects of 3-hour versus 6-hour daily training sessions in constraint-induced movement therapy (CIMT). DESIGN: Intervention study, 2-group randomized trial; baseline, pretreatment, and posttreatment measures; 1-month follow-up (weekly measures). SETTING: University department of psychology in Germany. PARTICIPANTS: A convenience sample of 15 adults with chronic hemiparesis (13 stroke, 2 traumatic brain injury). INTERVENTION: CIMT (14 consecutive days; constraint of unaffected hand for a target of 90% of waking hours) with either 6 hours (6h/d group, n=7) or 3 hours (3h/d group, n=8) of shaping training with the affected hand per day. MAIN OUTCOME MEASURES: The Motor Activity Log and Wolf Motor Function Test. RESULTS: Significant improvements in motor function in the laboratory and increased use of the affected hand in the real-world environment were found in both groups. The beneficial effects were significantly greater in the 6h/d group than in the 3h/d group. CONCLUSION: The 3-hour CIMT training schedule significantly improved motor function in chronic hemiparesis, but it was less effective than the 6-hour training schedule.

Adult↗