Biomedical subjects

Anja Ischebeck

Publications and source records attributed to Anja Ischebeck.

16 recordsLinked to original sources

PubMed2007

Neural substrates for episodic encoding and recognition of unfamiliar faces.

Functional MRI was used to investigate brain activation in healthy volunteers during encoding of unfamiliar faces as well as during correct recognition of newly learned faces (CR) compared to correct identification of distractor faces (CF), missed alarms (not recognizing previously presented faces, MA), and false alarms (incorrectly recognizing newly presented faces, FA). Encoding was associated with frontal, occipital/fusiform, thalamic, and cerebellar activation. CR produced activation in frontal and cerebellar regions, whereas CF activated frontal and occipitotemporal regions as well as the thalamus. In contrast, MA was associated with frontal and thalamic activation, and FA with frontal activation. The CR minus CF comparison showed left lateral prefrontal and parietal activation, while no suprathreshold positive signal changes were detected when subtracting the other conditions (CR minus MA, CR minus FA, and vice versa). These results support the view that the successful episodic retrieval of newly learned faces is based on a dorsal visual stream mechanism.

Adult↗

PubMed2006

The neural regions sustaining episodic encoding and recognition of objects.

In this functional MRI experiment, encoding of objects was associated with activation in left ventrolateral prefrontal/insular and right dorsolateral prefrontal and fusiform regions as well as in the left putamen. By contrast, correct recognition of previously learned objects (R judgments) produced activation in left superior frontal, bilateral inferior frontal, and right cerebellar regions, whereas correct rejection of distractor objects (N judgments) was associated with activation in bilateral prefrontal and anterior cingulate cortices, in right parietal and cerebellar regions, in the left putamen, and in the right caudate nucleus. The R minus N comparison showed activation in the left lateral prefrontal cortex and in bilateral cingulate cortices and precunei, while the N minus R comparison did not reveal any positive signal change. These results support the view that similar regions of the frontal lobe are involved in episodic encoding and retrieval processes, and that the successful episodic retrieval of newly learned objects is mainly based on a frontoparietal network.

Adult↗

PubMed2006

Neural correlates of transmeatal cochlear laser (TCL) stimulation in healthy human subjects.

Transmeatal cochlear laser (TCL) treatment has recently been proposed as a therapeutic procedure for cochlear dysfunction such as chronic cochlear tinnitus or sensorineural hearing loss. The aim of this study was to investigate whether TLC has any influence on the central nervous system using functional MRI with healthy young adults. The laser stimulation device was placed on the tympanic membrane of both ears. A laser stimulation run and a placebo run were performed in random order. The participants were unable to differentiate between verum and placebo stimulation. In the comparison of verum to placebo runs, we observed significant activations within the left superior frontal gyrus, the right middle and medial frontal gyrus, the right superior parietal lobule, the left superior occipital gyrus, the precuneus and cuneus bilaterally, the right anterior and the left and right middle and posterior cingulate gyrus and the left thalamus. This network of brain areas corresponds well to results from previous PET studies of patients with tinnitus. Though TCL seems to have a clinically measurable effect on the central nervous system the neurophysiological mechanism leading to the observed activated neuronal network remains unknown.

Adolescent↗

PubMed2006

Sex differences in brain activation patterns during processing of positively and negatively valenced emotional words.

BACKGROUND: Previous studies have suggested that men and women process emotional stimuli differently. In this study, we used event-related functional magnetic resonance imaging (fMRI) to investigate gender differences in regional cerebral activity during the perception of positive or negative emotions. METHOD: The experiment comprised two emotional conditions (positively/negatively valenced words) during which fMRI data were acquired. RESULTS: Thirty-eight healthy volunteers (19 males, 19 females) were investigated. A direct comparison of brain activation between men and women revealed differential activation in the right putamen, the right superior temporal gyrus, and the left supramarginal gyrus during processing of positively valenced words versus non-words for women versus men. By contrast, during processing of negatively valenced words versus non-words, relatively greater activation was seen in the left perirhinal cortex and hippocampus for women versus men, and in the right supramarginal gyrus for men versus women. CONCLUSIONS: Our findings suggest gender-related neural responses to emotional stimuli and could contribute to the understanding of mechanisms underlying the gender disparity of neuropsychiatric diseases such as mood disorders.

Adult↗

PubMed2006

Neural correlates of verbal semantic memory in patients with temporal lobe epilepsy.

Functional imaging data suggest that the core network engaged in verbal semantic memory (SM) processing encompasses frontal and temporal lobe structures, with a strong left lateralization in normal right handers. The impact of long term temporal lobe epilepsy (TLE) on this network has only partly been elucidated. We studied verbal SM in 50 patients with chronic, intractable TLE (left TLE=26, right TLE=24) and 35 right handed normal controls using a verbal fMRI semantic decision paradigm. All patients had language lateralized to the left hemisphere, as verified by the intracarotid amobarbital procedure. Within and between group analyses showed remarkable, group-specific activation profiles. The control group activated frontal and temporal areas bilaterally, with a strong left predominance. Left TLE patients showed a shift of activations of left frontal and medial temporal areas to homologous regions in the right hemisphere. Furthermore, left TLE subjects utilized subcortical structures such as the thalamus and putamen to accomplish the verbal SM task. Contrastively, the activation pattern of right TLE patients resembled that of normal controls, but exhibited "hypofrontality" with a shift from frontal to posterior regions in the temporal, parietal and occipital lobe. Our results show that chronic epileptic activity originating from temporal seizure foci is associated with an alteration of neural circuits which support semantic language processing and that side of seizure focus has a specific impact on the resulting activation network. These findings presumably result from morphological changes and from functional reorganization which are both inherent to chronic TLE.

Adult↗

PubMed2006

Gender differences in regional cerebral activity during the perception of emotion: a functional MRI study.

Whether men activate different brain regions during various emotions compared to women or whether gender differences exist in transient emotional states has been the subject of only few studies. We used event-related functional magnetic resonance imaging (fMRI) to investigate gender differences during the perception of positive or negative emotions. The experiment comprised two emotional conditions (pleasant/unpleasant visual stimuli) during which fMRI data were acquired. Altogether, 38 healthy volunteers (19 males, 19 females) were investigated. When subtracting the activation values of men from those of women, suprathreshold positive signal changes were detected in the right posterior cingulate, the left putamen and the left cerebellum during positive mood induction, and in bilateral superior temporal gyri and cerebellar vermis during negative mood induction. The subtraction of activation values of women from those of men yielded no significant differences. Our findings suggest gender-related neural responses to emotional stimuli and could contribute to the understanding of mechanisms underlying gender-related vulnerability of the prevalence and severity of neuropsychiatric disorders.

Adult↗

PubMed2006

Neural correlates of the number-size interference task in children.

In this functional magnetic resonance imaging study, 17 children were asked to make numerical and physical magnitude classifications while ignoring the other stimulus dimension (number-size interference task). Digit pairs were either incongruent (3 8) or neutral (3 8). Generally, numerical magnitude interferes with font size (congruity effect). Moreover, relative to numerically adjacent digits far ones yield quicker responses (distance effect). Behaviourally, robust distance and congruity effects were observed in both tasks. Imaging baseline contrasts revealed activations in frontal, parietal, occipital and cerebellar areas bilaterally. Different from results usually reported for adults, smaller distances activated frontal, but not (intra-)parietal areas in children. Congruity effects became significant only in physical comparisons. Thus, even with comparable behavioural performance, cerebral activation patterns may differ substantially between children and adults.

Brain Mapping↗

PubMed2006

Isolated numerical skills in posterior cortical atrophy--an fMRI study.

Posterior cortical atrophy (PCA) is characterized by bilateral parieto-occipito-temporal atrophy and hypometabolism. Neuropsychological impairments include complex visual disturbances, alexia, agraphia, finger agnosia, right-left disorientation and dyscalculia. A recent case study reported severe numerical deficits with some selectively preserved numerical skills in a patient affected by PCA [Delazer, M., Karner, E., Zamarian, L., Donnemiller, E., & Benke, T. (2006). Number processing in posterior cortical atrophy--a neuropsycholgical case study. Neuropsychologia]. In a functional magnetic resonance imaging (fMRI) study brain activation patterns related to these selectively preserved numerical skills were analyzed. Recitation of multiplication tables and counting forward were contrasted to word recitation in a block design. Contrasts between experimental conditions and control condition yielded significant activation of inferior and medial temporal structures. Since numerical processing is generally associated with parietal activation, it was hypothesized that preserved brain structures would compensate for the functional deficits.

Acoustic Stimulation↗

PubMed2006

How specifically do we learn? Imaging the learning of multiplication and subtraction.

The present functional magnetic resonance imaging (fMRI) study investigates modifications of brain activation patterns related to the training of two different arithmetic operations, multiplication and subtraction. Healthy young adults were trained in five sessions to answer multiplication and subtraction problems. In the following fMRI session, trained and new untrained problems closely matched for difficulty were presented in blocked order. Contrasts between untrained and trained operations showed stronger activation of inferior frontal and parietal regions, especially along the banks of the intraparietal sulcus. The reverse contrasts, trained minus untrained operations, yielded significantly higher activation in the left angular gyrus for multiplication but no significantly activated area for subtraction. This suggests that training leads to a reduction of general purpose processes, such as working memory and executive control in both operations, indicated by the decrease of activation in inferior frontal areas. For multiplication, however, the increase of activation in the left angular gyrus indicates a switching of cognitive processes. Trained subtraction therefore seems to lead to faster and more efficient strategies, while trained multiplication showed a shift from quantity-based processing (supported by the areas along the intraparietal sulci) to more automatic retrieval (supported by the left angular gyrus). The same training method caused changes in brain activation patterns that depended on the given operation. The effects of learning on the brain therefore seem not only to depend on the method of learning but also on its content.

Adult↗

PubMed2005

Human brain structures related to plantar vibrotactile stimulation: a functional magnetic resonance imaging study.

The purpose of this study was to investigate the sensorimotor cortex response to plantar vibrotactile stimulation using a newly developed MRI compatible vibration device. Ten healthy subjects (20-45 years) were investigated. Vibrotactile stimulation of the sole of the foot with a frequency of 50 Hz and a displacement of 1 mm was performed during fMRI (echo-planar imaging sequence at 1.5 T) using an MRI compatible moving magnet actuator that is able to produce vibration frequencies between 0 and 100 Hz and displacement amplitudes between 0 and 4 mm. The fMRI measurement during vibrotactile stimulation of the right foot revealed brain activation contralaterally within the primary sensorimotor cortex, bilaterally within the secondary somatosensory cortex, bilaterally within the superior temporal, inferior parietal, and posterior insular region, bilaterally within the anterior and posterior cingular gyrus, bilaterally within the thalamus and caudate nucleus, contralaterally within the lentiform nucleus, and bilaterally within the anterior and posterior cerebellar lobe. The advantages of the new MRI compatible vibration device include effective transmission of the stimulus and controlled vibration amplitudes, frequencies, and intensities. The results indicate that plantar vibration can be a suitable paradigm to observe activation within the sensorimotor network in fMRI. Furthermore, the method may be used to determine the optimal responsiveness of the individual sensorimotor network.

Adult↗

PubMed2005

Laser acupuncture induced specific cerebral cortical and subcortical activations in humans.

As recent studies demonstrated, acupuncture can elicit activity in specific brain areas. This study aims to explore further the central effect using laser acupuncture. We investigated the cerebral effects of laser acupuncture at both acupoints GB43 with functional magnetic resonance imaging (fMRI). As a control condition the laser was mounted at the same acupoints but without application of laser stimulation. The group results showed significant brain activations within the thalamus, nucleus subthalamicus, nucleus ruber, the brainstem, and the Brodmann areas 40 and 22 for the acupuncture condition. No significant brain activations were observed within the placebo condition. The activations we observed were laser acupuncture-specific and predominantly ipsilateral. This supports the assumption that acupuncture is mediated by meridians, since meridians do not cross to the other side. Furthermore, we could show that laser acupuncture allows one to design a pure placebo condition.

Acupuncture Points↗

PubMed2005

Neural correlates of distance and congruity effects in a numerical Stroop task: an event-related fMRI study.

This study aimed at investigating the neural correlates of a number-size congruity task. Using an event-related fMRI design, we presented one-digit number pairs to 17 participants in a number-size interference task that required subjects to focus on one stimulus property (e.g., numerical size) and to ignore the other (physical size). In different blocks, participants were asked to decide which digit of a digit pair was numerically larger (numerical comparison task) or physically larger (physical comparison task). Stimuli were classified into three categories: (a) congruent: physical and numerical comparison leads to the same response; (b) incongruent: physical and numerical comparison leads to different responses; (c) neutral: the stimuli differ only with regard to the task-relevant stimulus property. Behavioral results reflect robust distance effects (quicker reaction times for long distances relative to short ones) and size congruity effects (longer reaction times for incongruent relative to congruent stimuli) in both tasks. Imaging results reveal that-compared to congruent trials-incongruent trials led to a stronger activation in the dorsolateral prefrontal cortex and the anterior cingulate cortex, areas associated with attentional control. The distance effect (neutral condition only) led to a stronger activation in bilateral parietal areas including the intraparietal sulcus (IPS).

Adult↗

PubMed2004

Reading in a regular orthography: an FMRI study investigating the role of visual familiarity.

In order to separate the cognitive processes associated with phonological encoding and the use of a visual word form lexicon in reading, it is desirable to compare the processing of words presented in a visually familiar form with words in a visually unfamiliar form. Japanese Kana orthography offers this possibility. Two phonologically equivalent but visually dissimilar syllabaries allow the writing of, for example, foreign loanwords in two ways, only one of which is visually familiar. Familiarly written words, unfamiliarly written words, and pseudowords were presented in both Kana syllabaries (yielding six conditions in total) to participants during an fMRI measurement with a silent articulation task (Experiment 1) and a phonological lexical decision task (Experiment 2) using an event-related design. Consistent over two experimental tasks, the three different stimulus types (familiar, unfamiliar, and pseudoword) were found to activate selectively different brain regions previously associated with phonological encoding and word retrieval or meaning. Compatible with the predictions of the dual-route model for reading, pseudowords and visually unfamiliar words, which have to be read using phonological assembly, caused an increase in brain activity in left inferior frontal regions (BA 44/47), as compared to visually familiar words. Visually familiar and unfamiliar words were found to activate a range of areas associated with lexico-semantic processing more strongly than pseudowords, such as the left and right temporo-parietal region (BA 39/40), a region in the left middle/inferior temporal gyrus (BA 20/21), and the posterior cingulate (BA 31).

Adolescent↗

PubMed2003

On the relative speed account of number-size interference in comparative judgments of numerals.

Humans show systematic congruency effects due to irrelevant variations of the numerical value or the physical size of digits in judgments about either of these 2 attributes alone. According to influential models (e.g., J. Tzelgov, J. Meyer, & A. Henik, 1992), these effects are characterized by genuine asymmetries of size and number processing not accounted for by simple relative speed considerations, whereas some recent work (e.g., A. Pansky & D. Algom, 1999) partly challenges this view. This article presents 2 qualitative gradient-based predictions made by relative speed models and a diffusion-based implementation of the relative speed view to quantitatively account for response times and error rates in comparative judgments of digits. The results of 2 experiments using a completely task-symmetric design are in accord with these detailed predictions; they are also consistent with the view that both number and size are converted into magnitude representations of similar structure.

Adolescent↗

PubMed2003

Differences between digit naming and number word reading in a flanker task.

Numbers can be represented as number words or as digits, but are the two notations processed differently? Two experiments in which a flanker paradigm with a naming task was used were conducted, with digits and number words as targets and flankers. Reaction times were shortest when the flanker denoted the same numerical value as the target. The numerical distance between the target and a numerically different flanker modulated reaction times in all conditions, except for number word targets with digit flankers. The direction of this effect--targets were named faster when the flanker was numerically close than when it was far--indicates that the numerical magnitude representations of numbers are associatively connected. When the target and the flanker were presented in the same format, no difference was observed in the distance effects for the two formats. This indicates that number words activate the abstract representation of their numerical value in a way that is very similar to that for digits.

Adolescent↗

PubMed2001

On the Interpretation of Response Time vs Onset Asynchrony Functions: Application to Dual-Task and Precue-Utilization Paradigms.

The central bottleneck model of dual-task performance (H. Pashler and J. C. Johnston, 1998, Quarterly Journal of Experimental Psychology, 46A, 51-82) and the serial processing model of precue utilization (R. Gottsdanker, 1992, Acta Psychologica, 79, 21-43) are based on a common formal structure: They both represent response time as RT(tau)=max(X-tau, Y)+Z, where X, Y, Z denote the duration of certain processing stages specified by the models and tau denotes the onset asynchrony (SOA) between two stimuli. We consider this model within a stochastic framework in which the stage durations are random variables following an arbitrary joint distribution and derive properties of the function relating E[RT(tau)] to SOA. We present a distribution-free result which relates the slope of this function to the distribution of the random durations of the assumed processing stages. Our results allow for a direct, model-based interpretation of data from related experiments; specifically, they show how the slope of the SOA-function depends on experimental factors which selectively influence individual processing stages. We explain the implications of our results for models of dual-task performance and precue utilization and illustrate their application to data obtained by M. C. Smith (1969, Acta Psychologica, 30, 220-231) and R. Gottsdanker (1992, loc. cit.) Copyright 2001 Academic Press.

Journal Article↗