Biomedical subjects

Thomas Wolbers

Publications and source records attributed to Thomas Wolbers.

7 recordsLinked to original sources

PubMed2006

The predictive value of white matter organization in posterior parietal cortex for spatial visualization ability.

Humans differ substantially in their ability to imagine spatial transformations of novel stimuli (i.e., mental rotation). Whereas "high-spatial" individuals are able to maintain high-quality representations even after complex mental transformations, "low-spatial" individuals often experience substantial degradation of the initial representation. Even though subdivisions of the posterior parietal cortex are known to instantiate the necessary spatial transformations, a direct demonstration of neuroanatomical differences predicting this behavioral variability is currently missing. Because recent evidence suggests that interindividual differences on the behavioral level might be related to regionally specific white matter organization, we addressed this question using diffusion tensor imaging in combination with well-established psychometric tests. As expected, behavioral results revealed a substantial disparity in mental rotation performance. Most importantly, despite controlling for differences in spatial short-term memory capacity, we observed a tight relationship between mental rotation proficiency and white matter organization near the anterior part of the intraparietal sulcus. Whereas high-level proficiency was paralleled by high fractional anisotropy (FA) values, the opposite pattern was observed in "low spatials". The present results strongly indicate that the efficiency of information transfer between posterior parietal regions involved in the mental transformation process could be one decisive factor in individual spatial visualization proficiency.

Adult↗

PubMed2005

Changes in connectivity profiles as a mechanism for strategic control over interfering subliminal information.

Human behavior can be influenced by information that is not consciously perceived. Recent behavioral and electrophysiological evidence suggests, however, that the processing of subliminal stimuli is not completely beyond an observer's conscious control. The present study aimed to characterize the cortical network that implements strategic control over interfering subliminal information at multiple stages. Fourteen participants underwent functional magnetic resonance imaging (fMRI) scanning while performing a metacontrast masking paradigm. We systematically varied the amount of conflicting versus non-conflicting trials across experimental blocks, and behavioral performance demonstrated strategic effects whenever a high proportion of subliminal prime stimuli induced response competition. A psychophysiological interaction analysis revealed the pre-supplementary motor area (pre-SMA) to exhibit context-dependent covariation with activation in the lateral occipital complex (LOC) and the putamen. The pre-SMA thereby appears to fulfill a superordinate function in the control of processing subliminal information by simultaneously modulating perceptual analysis and motor selection.

Adaptation, Physiological↗

PubMed2005

Implementation of visuospatial cues in response selection.

We used functional magnetic resonance imaging to examine neuronal activity reflecting the dynamic interplay of external and internal guidance of action. Participants performed a choice reaction time task based on spatial visual cues with their right and left middle and index finger. In a given trial, the cue either fully determined the motor response (no-selection) or indicated the number and location of alternative responses (selection). Compared with fully determined responses, the selection among (two to four) alternative responses activated a widespread bilateral parieto-premotor-prefrontal cortical network along with the cerebellum. Within this network, task-related activity patterns allowed to delineate two sets of brain areas. In the anterior part of rostral dorsal premotor cortex (PMd), the rostral cingulate and supplementary motor area and the right dorsolateral prefrontal cortex, the increase in activity was independent of spatially defined restrictions. In contrast, there was an additional increase in activity in the posterior part of rostral PMd, superior parietal lobule and parieto-occipital sulcus bilaterally as well as in the right anterior intraparietal sulcus, when the visuospatial cue imposed specific constraints on response selection. We propose that the latter set of dorsal parieto-frontal areas subserves rapid implementation of spatial information during visually guided response selection.

Adult↗

PubMed2005

Dissociable contributions within the medial temporal lobe to encoding of object-location associations.

The crucial role of the medial temporal lobe (MTL) in episodic memory is well established. Although there is little doubt that its anatomical subregions-the hippocampus, peri-, entorhinal and parahippocampal cortex (PHC)-contribute differentially to mnemonic processes, their specific functions in episodic memory are under debate. Data from animal, human lesion, and neuroimaging studies suggest somewhat contradictory perspectives on this functional specialization: a general participation in declarative memory, an exclusive involvement in associative mnemonic processes, and a specific contribution to spatial memory are reported for the hippocampus, adjacent cortices, and the PHC. A functional lateralization in humans dependent on the verbalizability of the material is also discussed herein. To further elucidate the differential contributions of the various MTL subregions to encoding, we employed an object-location association memory paradigm. The memory for each of the studied associations was tested twice: by the object, and by the location serving as retrieval cue. The memory accuracy in response to both cue types was also assessed parametrically. Brain activity during encoding which leads to different degrees of subsequent memory accuracy under the two retrieval conditions was compared. We found the bilateral posterior PHC to participate in encoding of both the object associated with a location and the location associated with an object. In contrast, activity in an area in the left anterior PHC and the right anterior MTL was only correlated with the memory for the location associated with an object.

Adult↗

PubMed2005

Hippocampus activity differentiates good from poor learners of a novel lexicon.

Language proficiency is a key to academic and workplace success for native and non-native speakers. It is largely unknown, however, why some people pick up languages more easily than others. We used event-related functional magnetic resonance imaging (e-fMRI) to elucidate which brain regions are modulated during the acquisition of a novel lexicon and which of these learning-related activity changes correlated with general semantic language knowledge. Fourteen healthy young subjects learned a novel vocabulary of 45 concrete nouns via an associative learning principle over the course of five blocks during e-fMRI. As a control condition, subjects took part in a structurally identical "No-Learning" condition lacking any learning principle. Overall, increasing vocabulary proficiency was associated with (intercorrelated) modulations of activity within the left hippocampus and the left fusiform gyrus, regions involved in the binding and integration of multimodal stimuli, and with an increasing activation of the left inferior parietal cortex, the presumed neural store of phonological associations. None of these activity changes were observed during the control condition. Furthermore, subjects who showed less suppression of hippocampal activity over learning blocks scored higher on semantic knowledge in their native language and learned the novel vocabulary more efficiently. Our findings indicate that (a) the successful acquisition of a new lexicon depends on correlated amplitude changes between the left hippocampus and neocortical regions and (b) learning-related hippocampus activity is a stable marker of individual differences in the ability to acquire and master vocabularies.

Adult↗

PubMed2005

Dissociable retrosplenial and hippocampal contributions to successful formation of survey representations.

During everyday navigation, humans encounter complex environments predominantly from a first-person perspective. Behavioral evidence suggests that these perceptual experiences can be used not only to acquire route knowledge but also to directly assemble map-like survey representations. Most studies of human navigation focus on the retrieval of previously learned environments, and the neural foundations of integrating sequential views into a coherent representation are not yet fully understood. We therefore used our recently introduced virtual-reality paradigm, which provides accuracy and reaction-time measurements precisely indicating the emergence of survey knowledge, and functional magnetic resonance imaging while participants repeatedly encoded a complex environment from a first-person ground-level perspective. Before the experiment, we gave specific instructions to induce survey learning, which, based on the clear evidence for emerging survey knowledge in the behavioral data from 11 participants, proved successful. Neuroimaging data revealed increasing activation across sessions only in bilateral retrosplenial cortices, thus paralleling behavioral measures of map expertise. In contrast, hippocampal activation did not follow absolute performance but rather reflected the amount of knowledge acquired in a given session. In other words, hippocampal activation was most prominent during the initial learning phase and decayed after performance had approached ceiling level. We therefore conclude that, during navigational learning, retrosplenial areas mainly serve to integrate egocentric spatial information with cues about self-motion, whereas the hippocampus is needed to incorporate new information into an emerging memory representation.

Adult↗

PubMed2004

Neural foundations of emerging route knowledge in complex spatial environments.

Behavioral evidence suggests that spatial knowledge derived from ground-level navigation can consist of both route and survey knowledge. Neuroimaging and lesion studies aiming to identify the neural structures responsible for topographical learning in humans have yielded partially inconsistent results, probably due to the lack of an effective behavioral parameter allowing for a reliable distinction between different representations. Therefore, we employed a novel virtual reality environment that provides accuracy and reaction time measures precisely indicating the emergence of route vs. survey knowledge. Functional magnetic resonance imaging (fMRI) was used to localize brain regions involved in the acquisition of pure route knowledge in the form of associations between consecutive landmark views and the direction of intermediate movements. Participants were scanned during repeated encoding of the complex environment from a first-person, ground-level perspective. Behavioral data revealed emerging route knowledge in 11 out of 14 subjects. Overall comparisons between encoding and control conditions identified activation in medial frontal gyrus, retrosplenial cortex and posterior inferior parietal cortex. Most importantly, only posterior inferior parietal regions showed increasing activation across sessions, thus paralleling behavioral measures of route expertise. Given the established role of the posterior parietal cortex in spatial processing, this area is thought to provide the pivotal spatial link between two landmarks encountered in immediate temporal succession.

Adult↗