Biomedical subjects

Bruno Fimm

Publications and source records attributed to Bruno Fimm.

4 recordsLinked to original sources

PubMed2005

A special role for numbers in working memory? An fMRI study.

Although numbers carry averbal semantics (i.e., magnitude), they are often utilized in verbal Working Memory (vWM) tasks. However, vWM is thought to rely on a purely phonological code. Here, we tested the influence of (a) averbal semantics and (b) different tasks on performance in a vWM context by examining stimulus and task-specific variation of activity in the horizontal parts of the intraparietal sulcus (hIPS). The hIPS has previously been shown to subserve magnitude processing modulated by (a) specific stimuli and (b) specific tasks. Two variants of an n-back paradigm (comparison and identity match tasks) utilizing letters and numbers as stimulus material at different levels of vWM load were administered in 16 participants. Behavioral and functional imaging data reveal stimulus-specific modulation of activity in the hIPS suggesting a semantic influence of numbers. In the identity match task, numbers induced additional hIPS activation compared to letters while letters never induced additional hIPS activation when compared to numbers. Letters as compared to numbers only induced additional hIPS activation in the comparison task. These results question the assumption of a purely phonological code in vWM because hIPS activation subserving magnitude processing is modulated by stimulus semantics and task demands.

Adult↗

PubMed2004

Network for auditory intrinsic alertness: a PET study.

Intrinsic alertness designates the internal (cognitive) control of wakefulness and arousal; typical tasks to assess optimal levels of intrinsic alertness are simple reaction time (RT) measurements without preceding warning stimuli. Until now, cerebral networks subserving alertness after visual and somatosensory stimulation have been reported. Studies concerning other intensity aspects of alertness like sustained attention and vigilance, on the other hand, have been performed in the auditory modality, too. In a 15O-butanol PET-activation study in 10 right-handed young healthy male volunteers an intrinsic alertness network was studied for the auditory modality. In contrast with a sensorimotor control condition we found an extended predominantly right-hemisphere network similar to those reported for other sensory modalities including frontal, cingular, inferior parietal, temporal and thalamic structures, when subjects waited for and rapidly responded to a 1000 Hz tone signal by pressing a response key with the right-hand thumb. There were, however, some differences in the topography of the frontal, temporal and thalamic activations between auditory and visual stimulation which are discussed with respect to similar results for auditory vigilance and auditory selective attention tasks reported in the literature.

Acoustic Stimulation↗

PubMed2003

Cerebral activation in abstinent ecstasy (MDMA) users during a working memory task: a functional magnetic resonance imaging (fMRI) study.

The popular recreational drug ecstasy (3,4-methylenedioxymethamphetamine=MDMA and related congeners) is neurotoxic upon central serotonergic systems in animal studies. So far, the most convincing evidence for neurotoxicity-related functional deficits in humans derives from neurocognitive studies demonstrating dose-related long-term learning and memory problems in ecstasy users. In our study we used functional magnetic resonance imaging (fMRI) and a working memory task to investigate cerebral activation in eleven heavy, but currently abstinent MDMA users and two equally sized groups of moderate users and non-users. There were no significant group differences in working memory performance and no differences in cortical activation patterns for a conservative level of significance. However, for a more liberal statistical criterion, both user groups showed stronger activations than controls in right parietal cortex. Furthermore, heavy users had a weaker blood oxygenation level-dependent (BOLD) response than moderate users and controls in frontal and temporal areas. Our results may indicate subtle altered brain functioning associated with prior MDMA use, although alternative interpretations of these group differences must be considered.

Adult↗

PubMed2003

A truly simultaneous combination of functional transcranial Doppler sonography and H(2)(15)O PET adds fundamental new information on differences in cognitive activation between schizophrenics and healthy control subjects.

UNLABELLED: Working memory deficits are a cardinal feature of the pathophysiology of schizophrenia. Lesion studies and functional blood flow-dependent imaging methods with coarse temporal resolution, such as PET and functional MRI (fMRI), tend to paint a fairly static picture of the cortical regions involved. In contrast, functional transcranial Doppler sonography (fTCD) provides a high temporal resolution. Truly simultaneous fTCD-fMRI is not yet possible for technical reasons, but H(2)(15)O PET and fTCD can be used really simultaneously. However, this combination has not yet been used for cognitive activations in schizophrenia. We therefore investigated the extent to which there are both spatial (PET) and temporal changes (fTCD) in the activation patterns of schizophrenic patients. METHODS: Eleven clinically stable chronic schizophrenic, right-handed patients and 10 healthy, right-handed control subjects, matched for age, sex, education, and intelligence quotient, participated in the study. We selected stable chronic schizophrenic patients who could perform a working memory task (N-back task) as well as healthy volunteers to exclude the possibility of imaged artifacts due to poor performance. All subjects were examined with a truly simultaneous fTCD-H(2)(15)O PET combination under cognitive activation. RESULTS: Schizophrenic patients activate a significantly larger cortical volume for adequate task performance (P < 0.05), but with a significantly lower blood flow increase in this volume (P < 0.01), than do control subjects. Furthermore, they cannot significantly increase blood flow velocity during the time course of cognitive activation as control subjects do. There were only significant correlations between neuropsychologic performance and imaging parameters (fTCD changes, PET blood flow changes) in control subjects (all r >or= /0.65/; P < 0.05), but no significant correlations in schizophrenics (all r < /0.3/; P > 0.4). CONCLUSION: We demonstrated that schizophrenic patients exhibit qualitative differences in the spatial and temporal resolution of cognitive processing. All facts could be interpreted as a sign of alternative, less efficient problem-solving strategies in schizophrenia that lead to the working memory deficits observed during the further course of this disease. Truly simultaneous fTCD-PET can be used in neuroscience to add fundamental new information on spatial and temporal cognitive activation behavior to understand the true physiologic nature of the disease-specific differences of mental illnesses that are seen as disorders of the mind arising in the brain.

Adult↗