Biomedical subjects

Oliver Gruber

Publications and source records attributed to Oliver Gruber.

5 recordsLinked to original sources

PubMed2006

Oddball and incongruity effects during Stroop task performance: a comparative fMRI study on selective attention.

The aim of this fMRI study was to investigate and compare the neural mechanisms of selective attention during two different operationalizations of competition between task-relevant and task-irrelevant information: Stroop-incongruity and oddballs. For this purpose, we employed a Stroop-like oddball task in which subjects responded to the font size of presented word stimuli. Stroop-incongruity was created by (response-)incongruent word information while oddballs comprised low-frequency events in a task-irrelevant, unattended dimension. Thereby, in order to elucidate the influence of processing domain from which competition emanates, oddball conditions were created in two different attribute dimensions, color and word meaning. Either oddball condition was expected to evoke an orienting response, which participants would have to override in order to maintain adequate performance. Incongruent Stroop trials were expected to produce Stroop-interference so that subjects would have to override the predominant tendency to read and respond to word meaning. All competition conditions exhibited significantly prolonged reaction times compared to control trials, demonstrating that our experimental manipulation was indeed effective. fMRI data analyses delineated two discriminative components of competition: one component mainly related to motor preparation and another, primarily attentional component. Regarding the first, Stroop-interference increased activation mainly in regions implicated in motor control or response preparation. Regarding the second, Word-oddballs increased activation in a frontoparietal "attention network". Furthermore, Word-oddballs and Color-oddballs exhibited striking activation overlap mainly in prefrontal regions but also in posterior processing areas. Here, the data emphasized a prominent role of posterior lateral PFC in implementing top-down attentional control.

Adult↗

PubMed2006

Articulatory rehearsal in verbal working memory: a possible neurocognitive endophenotype that differentiates between schizophrenia and schizoaffective disorder.

Recent fMRI studies have identified brain systems underlying different components of working memory in healthy individuals. The aim of this study was to compare the functional integrity of these neural networks in terms of behavioural performance in patients with schizophrenia, schizoaffective disorder and healthy controls. In order to detect specific working memory deficits based on dysfunctions of underlying brain circuits we used the same verbal and visuospatial Sternberg item-recognition tasks as in previous neuroimaging studies. Clinical and performance data from matched groups consisting of 14 subjects each were statistically analyzed. Schizophrenic patients exhibited pronounced impairments of both verbal and visuospatial working memory, whereas verbal working memory performance was preserved in schizoaffective patients. The findings provide first evidence that dysfunction of a brain system subserving articulatory rehearsal could represent a biological marker which differentiates between schizophrenia and schizoaffective disorder.

Adult↗

PubMed2003

The functional neuroanatomy of human working memory revisited. Evidence from 3-T fMRI studies using classical domain-specific interference tasks.

In the present event-related functional magnetic resonance imaging study, the neural implementation of human working memory was reinvestigated using a factorial design with verbal and visuospatial item-recognition tasks each performed under single-task conditions, under articulatory suppression, and under visuospatial suppression. This approach allowed to differentiate between brain systems subserving domain-specific working memory processes and possible neural correlates of more "central" executive or storage functions. The results of this study indicate (1) a domain-specific functional-neuroanatomical organization of verbal and visuospatial working memory, (2) a dual architecture of verbal working memory in contrast to a unitary macroscopic architecture of visuospatial working memory, (3) possible neural correlates for a domain-unspecific "episodic buffer" in contrast to a failure to find brain areas attributable to a "central executive," and (4) competition for neuronal processing resources as the causal principle for the occurrence of domain-specific interference in working memory.

Acoustic Stimulation↗

PubMedDate not supplied

Executive control emerging from dynamic interactions between brain systems mediating language, working memory and attentional processes.

In this theoretical paper, we review findings from a series of recent behavioral and functional neuroimaging studies of working memory and executive control which provide evidence for the following theses: 1. Working memory in humans is represented by two brain systems which differ from each other with respect to their functional-neuroanatomical organization and probably also with respect to their evolutionary origin. 2. One of these brain systems relies on prefronto-parietal and prefronto-temporal cortical networks that presumably also mediate attentional selection by the top-down modulation of domain-specific sensory association areas towards behaviorally relevant information. 3. The other system is implemented by mainly left-hemispheric premotor and parietal brain regions which to a greater part also underlie language functions and which may also be involved in the retrieval and maintenance of verbal goal representations during advance preparation for task switches. 4. Context-sensitive behavioral adaptation is supported by a complementary mechanism for the detection of conflicts and for the triggering of cognitive control processes that relies on parts of the medial frontal cortex. Based on these empirical results reported in the literature we propose a neurocognitive model of executive control according to which the human ability to flexibly adapt to changing behavioral requirements, i.e. executive control, depends on dynamic and context-sensitive interactions between these brain systems.

Attention↗

PubMedDate not supplied

Diffuse axonal injury associated with chronic traumatic brain injury: evidence from T2*-weighted gradient-echo imaging at 3 T.

BACKGROUND AND PURPOSE: Diffuse axonal injury is frequently accompanied by tissue tear hemorrhages. We examined whether high field strength T2*-weighted gradient-echo imaging performed during the chronic stage of traumatic brain injury may have advantages in the evaluation of diffuse axonal injury as compared with T1- and T2-weighted MR imaging. METHODS: Prospective MR imaging of 66 patients (age range, 17-57 years) was performed using a 3-T system 3 to 292 months (median, 23.5 months) after traumatic brain injury. T1-, T2-, T2*-hypointense and T2-hyperintense foci of 1- to 15-mm diameter were registered in 10 brain regions by two readers separately. Foci that appeared hypointense both on the T1- and T2- and/or on the T2*-weighted images were defined as traumatic microbleeds. RESULTS: For 46 (69.7%) of the patients, T2*-weighted gradient-echo imaging revealed traumatic microbleeds. Hyperintense foci were observed on the T2-weighted images of only 15 (22.7%) patients. T2*-weighted imaging showed significantly more traumatic microbleeds (P =.000) than did T1- and T2-weighted imaging. Interobserver agreement was strong (kappa = 0.79, tau = 0.749, P =.000). For 14 (21.2%) of the patients, T2*-weighted gradient-echo imaging revealed traumatic microbleeds in the corpus callosum, whereas for only two (3%), hyperintense callosal lesions were seen on the T2-weighted images. Although a significant correlation existed between the total amount and callosal appearance of traumatic microbleeds and Glasgow Coma Scale scores (P =.000), no correlation existed with extended Glasgow Outcome Scale scores. CONCLUSION: T2*-weighted gradient-echo imaging at high field strength is a useful tool for the evaluation of diffuse axonal injury during the chronic stage of traumatic brain injury. Diffuse axonal injury-related brain lesions are mainly hemorrhagic. The relevance of diffuse axonal injury for long-term clinical outcome is uncertain.

Adolescent↗