Biomedical subjects

Axel Mecklinger

Publications and source records attributed to Axel Mecklinger.

5 recordsLinked to original sources

PubMed2003

Cortical activity reduction with stimulus repetition: a whole-head MEG analysis.

Event related field responses to line drawings of novel visual objects were recorded in a simple target detection task using whole-head magnetoencephalography. Brain-current-source-density reconstruction indicated that, relative to initial presentations, immediately repeated nontarget stimuli elicited reduced neural activity in a region of cortex extending from the parietal lobe into the superior frontal lobe in a time window from 250 ms and 450 ms. There are at least two plausible accounts of this neural activity reduction between conditions. It may reflect facilitated stimulus processing due to the existence of a representation of the repeated stimulus or it may reflect differential levels of attentional allocation to initial and repeated stimulus presentations.

Adolescent↗

PubMed2003

ERP correlates of true and false recognition after different retention delays: stimulus- and response-related processes.

Performance and electrophysiological correlates of true and false recognition were examined after short (40 s) and long (80 s) delays. True recognition showed no significant decrease after a long delay, whereas false recognition increased. Early frontal and parietal ERP old/new effects, considered as correlates of familiarity and recollection, were observed across delay for true recognition. No frontal effect occurred in the long delay for false recognition. This absence may arise from weakened memory traces preventing familiarity discrimination for LUREs. Response-related analysis revealed an error-related negativity (ERN) for true and false recognition, assuming that the effect reflects at least partly an internal misrepresentation of the correct response. The larger and topographically different ERNs for false recognition suggest an additional contribution of increased task demands and conditions of high response uncertainty.

Adult↗

PubMed2002

Differential contribution of frontal and temporal cortices to auditory change detection: fMRI and ERP results.

The present study addresses the functional role of the temporal and frontal lobes in auditory change detection. Prior event-related potential (ERP) research suggested that the mismatch negativity (MMN) reflects the involvement of a temporofrontal network subserving auditory change detection processes and the initiation of an involuntary attention switch. In the present study participants were presented with repetitive spectrally rich sounds. Infrequent changes of either small (10% change), medium (30% change), or large (100% change) magnitude were embedded in the stimulus train. ERPs and fMRI measures were obtained in the same subjects in subsequent sessions. Significant hemodynamic activation in the superior temporal gyri (STG) bilaterally and the opercular part of the right inferior frontal gyrus was observed for large and medium deviants only. ERPs showed that small deviants elicited MMN when presented in silence but not when presented with recorded MR background noise, indicating that small deviants were hardly detected under fMRI conditions. The MR signal change in temporal lobe regions was larger for large than for medium deviants. For the right fronto-opercular cortex the opposite pattern was observed. The strength of the temporal activation correlated with the amplitude of the change-related ERP at around 110 ms from stimulus onset while the frontal activation correlated with the change-related ERP at around 150 ms. These results suggest that the right fronto-opercular cortex is part of the neural network generating the MMN. Three alternative explanations of these findings are discussed.

Adult↗

PubMed2002

Separable neuronal circuitries for manipulable and non-manipulable objects in working memory.

Previous work using single-cell recordings in monkeys and neuro-imaging studies in humans has shown that perceiving an object or imaging the action associated with the object recruits the same brain regions in the ventral premotor cortex as performing an action with the object. We used functional magnetic resonance imaging (fMRI) for examining whether similar brain regions are also activated while maintaining information about manipulable objects in working memory. Holding information about manipulable objects in working memory activated the left ventral premotor cortex and the left inferior frontal gyrus (Broca's area). Conversely, non-manipulable objects to be held in working memory co-activated Broca's area and the left angular gyrus. When contrasted directly, manipulable relative to non-manipulable objects activated the left ventral premotor cortex and the anterior intraparietal sulcus, a circuitry that is assumed to mediate the transformation of movement-relevant object properties into hand actions. These results indicate that visual working memory for manipulable objects is based on motor programmes associated with their use. Similar to speech motor programmes in verbal memory tasks, hand motor programmes may allow the maintenance of objects in working memory over short intervals.

Adult↗

PubMed2002

Priming visual face-processing mechanisms: electrophysiological evidence.

Accumulated evidence from electrophysiology and neuroimaging suggests that face perception involves extrastriate visual mechanisms specialized in processing physiognomic features and building a perceptual representation that is categorically distinct and can be identified by face-recognition units. In the present experiment, we recorded event-related brain potentials in order to explore possible contextual influences on the activity of this perceptual mechanism. Subjects werefirst exposed to pairs of small shapes, which did not elicit any face-specific brain activity. The same stimuli, however, elicitedface-specific brain activity after subjects saw them embedded in schematic faces, which probably primed the subjects to interpret the shapes as schematic eyes. No face-specific activity was observed when objects rather than faces were used to form the context. We conclude that the activity of face-specific extrastriate perceptual mechanisms can be modulated by contextual constraints that determine the significance of the visual input.

Adult↗