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Michael Erb

Publications and source records attributed to Michael Erb.

At least 37 records · Page 2Linked to original sources
PubMed2005

Overt sentence production in event-related fMRI.

The use of syntactic structures on a sentence level is a unique human ability. Functional imaging studies have usually investigated syntax comprehension. However, language production may be performed by different neuronal resources. We have investigated syntax generation on a sentence level with functional magnetic resonance imaging (fMRI). BOLD contrast was measured while subjects articulated utterances aloud. In the active condition 'sentence generation' (SG), subjects had to produce subject verb object (SVO) sentences (e.g. "The child throws the ball") according to syntactically incomplete stimuli (e.g. "throw ball child") presented visually. In the control condition 'word reading' (WR), subjects had to read identical stimuli without completing the syntactic structure, while in a second control condition 'sentence reading' (SR), subjects had to read complete sentences. The semantic meaning of all expressions was obvious despite the syntactically incomplete structure in conditions SG and WR. In both contrasts, SG minus WR and SG minus SR, activation was mainly present in the left inferior frontal (BA 44/45) and medial frontal (BA 6) gyri, the superior parietal lobule (BA 7) and the right insula (BA 13). A region of interest analysis revealed significantly stronger left-dominant activation in BA 45 compared to BA 44. Our data illustrates the crucial involvement of the left BA 45 in syntactic encoding and is in line with more recent imaging and brain lesion data on syntax processing on a sentence level, emphasizing the involvement of a distributed left and right hemispheric network in syntax generation.

Adult↗
PubMed2005

[Segmentation of the white matter in the brain based on MR-DTI fiber directions].

MR diffusion tensor imaging (DTI) allows the visualization of location and course of brain fiber bundles. To obtain these results, however, special evaluation techniques are necessary in addition to image acquisition and reconstruction. These include first the calculation of a preferential diffusional direction of water molecules in each voxel and then the tracking of brain fibers or segmentation of regions with similar fiber directions. In both cases, the procedures available thus far require the interactive definition of seed points. In this paper, we propose a method to segment voxel groups of connected data points without the need of setting seed points. This method is based first on the identification of all voxels of a brain volume with a sufficiently unique preferential diffusional direction and with interconnection. For each selected voxel, neighboring voxels are then identified that have a small deviation from the chosen preferential direction and can therefore be grouped with this point. Finally, the largest partial volumes determined in this way are marked and color-coded to present them as three-dimensional structures. The present method resulting in a largely automatic subdivision of the white matter in the brain in a number of bilateral partial volumes.

Brain↗
PubMed2005

Cortical activation during cholinesterase-inhibitor treatment in Alzheimer disease: preliminary findings from a pharmaco-fMRI study.

OBJECTIVE: Cholinesterase inhibitors improve cognitive functioning in Alzheimer disease (AD). The authors studied, with functional magnetic resonance imaging (fMRI), the neural mechanism by which this cholinergic enhancement improves memory encoding in AD over longer time periods. METHODS: Brain activation was measured in 10 patients with AD and 10 healthy elderly comparison subjects with fMRI while they were encoding novel faces. Patients were scanned again after a 10-week open treatment with the cholinesterase-inhibitor donepezil. RESULTS: Neuropsychologically-tested memory performance improved during the treatment phase in the patients. During the encoding of novel faces, elderly comparison subjects showed more activation in the right fusiform gyrus than the group of AD patients. After a 10-week treatment with donepezil, the fusiform gyrus was also activated in patients, similar to the comparison group. CONCLUSIONS: The right fusiform gyrus is associated with the processing of faces. Cholinergic enhancement augments selective attention by increased selectivity of perceptual responses in patients with AD. This mechanism may contribute to a more efficient processing of the attended stimulus and thus be a mechanism underlying clinical improvement of cognitive functioning. These promising preliminary findings need to be confirmed in a larger, controlled trial in which both fMRI and attention measures serve as outcomes.

Aged↗
PubMed2004

Processing of a simple aversive conditioned stimulus in a divided visual field paradigm: an fMRI study.

A left visual hemifield advantage for the processing of negative facial expressions has been demonstrated in a variety of studies. We tested whether the same effect is found for a neutral facial expression that had acquired a negative meaning through pairing with an aversive event. Startle reflex amplitudes, skin-conductance responses (SCR), and two verbal measures of affect (negative valence and arousal) were significantly increased after pairing, but no stimulation side by pairing interaction was observed. Functional magnetic resonance imaging (fMRI) revealed a significant increase of BOLD (blood oxygen level dependent) activity in the medial prefrontal cortex (MPFC), and the right frontal opercular region (RFOP). MPFC activity was correlated with psychophysiological and verbal emotional responses across subjects and, like these responses, was independent of the stimulation side. In contrast, RFOP activity was significantly stronger during left than during right hemifield stimulation but did not correlate with psychophysiological or verbal measures of negative affect. These results suggest that emotional responses to an aversive conditioned expressively neutral face are similar in both visual hemifields. MPFC activity seems to be closely linked to the strength of these responses.

Adult↗
PubMed2004

The raft-associated protein MAL is required for maintenance of proper axon--glia interactions in the central nervous system.

The myelin and lymphocyte protein (MAL) is a tetraspan raft-associated proteolipid predominantly expressed by oligodendrocytes and Schwann cells. We show that genetic ablation of mal resulted in cytoplasmic inclusions within compact myelin, paranodal loops that are everted away from the axon, and disorganized transverse bands at the paranode--axon interface in the adult central nervous system. These structural changes were accompanied by a marked reduction of contactin-associated protein/paranodin, neurofascin 155 (NF155), and the potassium channel Kv1.2, whereas nodal clusters of sodium channels were unaltered. Initial formation of paranodal regions appeared normal, but abnormalities became detectable when MAL started to be expressed. Biochemical analysis revealed reduced myelin-associated glycoprotein, myelin basic protein, and NF155 protein levels in myelin and myelin-derived rafts. Our results demonstrate a critical role for MAL in the maintenance of central nervous system paranodes, likely by controlling the trafficking and/or sorting of NF155 and other membrane components in oligodendrocytes.

Animals↗
PubMed2004

Parietal somatosensory association cortex mediates affective blindsight.

To investigate the neural substrates underlying emotional feelings in the absence of a conscious stimulus percept, we presented a visual stimulus in the blind field of partially cortically blind patients and measured cortical activity (by functional magnetic resonance imaging, fMRI) before and after the stimulus had been paired with an aversive event. After pairing, self-reported negative emotional valence and blood oxygen level-dependent (BOLD) responses in somatosensory association areas were enhanced, whereby somatosensory activity predicted highly corresponding reported feelings and startle reflex amplitudes across subjects. Our data provide direct evidence that cortical activity representing physical emotional states governs emotional feelings.

Affective Symptoms↗
PubMed2004

Improvement and decline in tactile discrimination behavior after cortical plasticity induced by passive tactile coactivation.

Perceptual learning can be induced by passive tactile coactivation without attention or reinforcement. We used functional MRI (fMRI) and psychophysics to investigate in detail the specificity of this type of learning for different tactile discrimination tasks and the underlying cortical reorganization. We found that a few hours of Hebbian coactivation evoked a significant increase of primary (SI) and secondary (SII) somatosensory cortical areas representing the stimulated body parts. The amount of plastic changes was strongly correlated with improvement in spatial discrimination performance. However, in the same subjects, frequency discrimination was impaired after coactivation, indicating that even maladaptive processes can be induced by intense passive sensory stimulation.

Adult↗
PubMed2004

Brain activity underlying emotional valence and arousal: a response-related fMRI study.

Emotional behavior is organized along two psychophysiologic dimensions: (1) valence, varying from negative to positive, and (2) arousal, varying from low to high. Behavioral responses along these dimensions are assumed to be mediated by different brain circuits. We recorded startle reflex modulation and skin conductance responses in healthy volunteers during functional magnetic resonance imaging (fMRI) while they viewed a set of emotional pictures and took verbal ratings of the emotional valence and arousal of each picture after scanning. Response-related multiple correlation analysis revealed differential brain activity in five brain regions. Startle reflex changes, associated with the valence of a stimulus, correlated with activity in the amygdala, while verbal reports of negative emotional valence varied with insular activity. Peripheral physiologic and verbal responses along the arousal dimension varied with thalamic and frontomedial activity. Peripheral physiologic responses along both dimensions correlated with activity in somatosensory association areas in the anterior parietal cortex. In the valence dimension, activity in the left anterior parietal cortex was associated with highly correlating peripheral physiologic and verbal responses, suggesting that verbal reports of emotional valence might depend partly on brain circuits representing peripheral physiologic changes. Our data provide direct evidence for a functional segregation of brain structures underlying peripheral physiologic responses and verbal ratings along the emotional dimensions of valence and arousal.

Adult↗
PubMed2004

Initial experience with miniature axial flow ventricular assist devices for postcardiotomy heart failure.

BACKGROUND: The recently introduced Impella Recover (Impella CardioSystems AG, Aachen, Germany) microaxial flow left and right ventricular assist devices (LVAD/RVAD) were evaluated as they provide circulatory support in the setting of postcardiotomy heart failure refractory to high-dose inotropic and intra-aortic balloon pump (IABP) support. METHODS: Between May 2002 and November 2002, the Recover LVAD was implanted in six patients (64 +/- 11 years) with acute left heart failure following coronary artery bypass procedures. Preoperative left ventricular (LV) ejection fraction was compromised (28% +/- 12%, 12% to 45%). Three patients presented with unstable circulation or cardiogenic shock following acute myocardial infarction, with a predicted mortality rate of 44% +/- 11% (EuroSCORE). Intraoperatively, severe heart failure was present with a more than 70% mortality rate predicted by the IABP score. The Recover RVAD and LVAD were combined to provide biventricular assist device (BVAD) support in one case of post-transplant graft failure. RESULTS: The Recover LVAD delivered blood flows of up to 5 L/min. A moderate degree of hemolysis and a reduction in platelet count were noted. Four patients were weaned from the LVAD after 169 +/- 34 hours, two of whom remain long-term survivors. Full recovery of graft function allowed weaning of the patient from BVAD support after six days. CONCLUSIONS: The initial experience with the Impella Recover VADs proved the new systems to be advantageous regarding the ease of implantation and device removal, low anticoagulation requirements, and advanced weaning features. In cases of severe heart failure, survival was improved by using LVADs when compared to that predicted by solely continuing IABP and drug support.

Aged↗
PubMed2004

Neural correlates of metaphor processing.

Metaphoric language is used to express meaning that is otherwise difficult to conceptualize elegantly. Beyond semantic analysis, understanding the figurative meaning of a metaphor requires mental linkage of different category domains normally not related to each other. We investigated processing of metaphoric sentences using event-related functional magnetic resonance imaging (fMRI). Stimuli consisted of 60 novel short German sentence pairs with either metaphoric or literal meaning. The pairs differed only in their last one to three words and were matched for syntax structure, word frequency, connotation and tense. Fifteen healthy subjects (six female, nine male, 19-51 years) read these sentences silently and judged by pressing one of two buttons whether they had a positive or negative connotation. Reading metaphors in contrast to literal sentences revealed signal changes in the left lateral inferior frontal (BA 45/47), inferior temporal (BA 20) and posterior middle/inferior temporal (BA 37) gyri. The activation in the left inferior frontal gyrus may reflect semantic inferencing processes during the understanding of a metaphor. This is in line with the results from other functional imaging studies showing an involvement of the left inferior frontal gyrus in integrating word and sentence meanings. Previous results of a right hemispheric involvement in metaphor processing might reflect understanding of complex sentences.

Adult↗
PubMed2004

Response-related fMRI of veridical and false recognition of words.

OBJECTIVES: Studies on the relation between local cerebral activation and retrieval success usually compared high and low performance conditions, and thus showed performance-related activation of different brain areas. Only a few studies directly compared signal intensities of different response categories during retrieval. During verbal recognition, we recently observed increased parieto-occipital activation related to false alarms. The present study intends to replicate and extend this observation by investigating common and differential activation by veridical and false recognition. METHODS: Fifteen healthy volunteers performed a verbal recognition paradigm using 160 learned target and 160 new distractor words. The subjects had to indicate whether they had learned the word before or not. Echo-planar MRI of blood-oxygen-level-dependent signal changes was performed during this recognition task. Words were classified post hoc according to the subjects' responses, i.e. hits, false alarms, correct rejections and misses. Response-related fMRI-analysis was used to compare activation associated with the subjects' recognition success, i.e. signal intensities related to the presentation of words were compared by the above-mentioned four response types. RESULTS: During recognition, all word categories showed increased bilateral activation of the inferior frontal gyrus, the inferior temporal gyrus, the occipital lobe and the brainstem in comparison with the control condition. Hits and false alarms activated several areas including the left medial and lateral parieto-occipital cortex in comparison with subjectively unknown items, i.e. correct rejections and misses. Hits showed more pronounced activation in the medial, false alarms in the lateral parts of the left parieto-occipital cortex. CONCLUSIONS: Veridical and false recognition show common as well as different areas of cerebral activation in the left parieto-occipital lobe: increased activation of the medial parietal cortex by hits may correspond to true recognition, increased activation of the parieto-occipital cortex by false alarms may correspond to familiarity decisions. Further studies are needed to investigate the reasons for false decisions in healthy subjects and patients with memory problems.

Adult↗
PubMed2004

To act or not to act. Neural correlates of executive control of learned motor behavior.

Successful behavior requires contextual modulation of learned "programs", that is, the retrieval or nonretrieval (inhibition) of behavioral elements depending on situative context. Here we report neural correlates of these elementary aspects of behavior as identified with functional magnetic resonance imaging (fMRI). Inhibition of a "ready-to-go" behavioral program was represented in the brain by reduction of net synaptic activity in the cerebro-cerebellar pathway. The metabolic correlate of inhibition was a multifocal (premotor, primary sensorimotor, superior parietal, cingulate cortex, and cerebellum) decrease of the blood oxygenation level-dependent (BOLD) signal to below the resting state (negative BOLD) with a concomitant decrease of motor cortical excitability. The reverse was true for retrieval. We propose that contextual modulation of learned behavioral programs depends on an interplay of focal increases and decreases of neural activity and that the inhibitory changes are reflected by negative BOLD responses in an extended cerebro-cerebellar network of sensorimotor structures.

Adult↗
PubMed2004

[Calculation of proton spectra of pure brain tissue types by multiple voxel measurements and image segmentation].

In localized in vivo proton NMR spectroscopy (1H MRS) of the human brain, it often cannot be avoided that the selected volume of interest (voxel) includes both gray matter (GM) and white matter (WM). Since the spectra of GM and WM differ, in general, the acquired spectrum represents a mixed spectrum that depends on the tissue composition inside the voxel. This study describes a method that enables the determination of pure GM spectra and pure WM spectra from mixed spectra. The pure tissue spectra are calculated from measured spectra acquired from several voxels with different mixed tissue compositions. For this purpose, the tissue composition in the voxels must be known. It is determined by segmentation of an additionally acquired 3D image data set with higher spatial resolution. In volunteer examinations, measurements were performed in different regions of the cerebrum, cerebellum, and thalamus. In all examined brain regions, particularly in the cerebellum, clear differences were found between the spectra of WM and GM. The detected differences in the spectra of WM and GM indicate that the tissue composition in the voxel has to be considered in patient studies, in order to distinguish pathological alterations in the spectra from the effects of tissue composition.

Brain↗
PubMed2004

Is there a role of visual cortex in spatial hearing?

The integration of auditory and visual spatial information is an important prerequisite for accurate orientation in the environment. However, while visual spatial information is based on retinal coordinates, the auditory system receives information on sound location in relation to the head. Thus, any deviation of the eyes from a central position results in a divergence between the retinal visual and the head-centred auditory coordinates. It has been suggested that this divergence is compensated for by a neural coordinate transformation, using a signal of eye-in-head position. Using functional magnetic resonance imaging, we investigated which cortical areas of the human brain participate in such auditory-visual coordinate transformations. Sounds were produced with different interaural level differences, leading to left, right or central intracranial percepts, while subjects directed their gaze to visual targets presented to the left, to the right or straight ahead. When gaze was to the left or right, we found the primary visual cortex (V1/V2) activated in both hemispheres. The occipital activation did not occur with sound lateralization per se, but was found exclusively in combination with eccentric eye positions. This result suggests a relation of neural processing in the visual cortex and the transformation of auditory spatial coordinates responsible for maintaining the perceptual alignment of audition and vision with changes in gaze direction.

Acoustic Stimulation↗
PubMed2003

Brain areas activated in fMRI during self-regulation of slow cortical potentials (SCPs).

In humans, surface-negative slow cortical potentials (SCPs) originating in the apical dendritic layers of the neocortex reflect synchronized depolarization of large groups of neuronal assemblies. They are recorded during states of behavioural or cognitive preparation and during motivational states of apprehension and fear. Surface positive SCPs are thought to indicate reduction of cortical excitation of the underlying neural networks and appear during behavioural inhibition and motivational inertia (e.g. satiety). SCPs at the cortical surface constitute summated population activity of local field potentials (LFPs). SCPs and LFPs may share identical neural substrates. In this study the relationship between negative and positive SCPs and changes in the BOLD signal of the fMRI were examined in ten subjects who were trained to successfully self-regulate their SCPs. FMRI revealed that the generation of negativity (increased cortical excitation) was accompanied by widespread activation in central, pre-frontal, and parietal brain regions as well as the basal ganglia. Positivity (decreased cortical excitation) was associated with widespread deactivations in several cortical sites as well as some activation, primarily in frontal and parietal structures as well as insula and putamen. Regression analyses revealed that cortical positivity was predicted with high accuracy by pallidum and putamen activation and supplementary motor area (SMA) and motor cortex deactivation, while differentiation between cortical negativity and positivity was revealed primarily in parahippocampal regions. These data suggest that negative and positive electrocortical potential shifts in the EEG are related to distinct differences in cerebral activation detected by fMRI and support animal studies showing parallel activations in fMRI and neuroelectric recordings.

Adult↗
PubMed2003

Brain regions sensitive to the face inversion effect: a functional magnetic resonance imaging study in humans.

Perception of upright faces relies on configural processing. Therefore recognition of inverted, compared to upright faces is impaired. In a functional magnetic resonance imaging experiment we investigated the neural correlate of a face inversion task. Thirteen healthy subjects were presented with a equal number of upright and inverted faces alternating with a low level baseline with an upright and inverted picture of an abstract symbol. Brain activation was calculated for upright minus inverted faces. For this differential contrast, we found a signal change in the right superior temporal sulcus and right insula. Configural properties are processed in a network comprising right superior temporal and insular cortex.

Adult↗
PubMed2003

Why are smiles contagious? An fMRI study of the interaction between perception of facial affect and facial movements.

In human communication there is often a close relationship between the perception of an emotionally expressive face and the facial response of the viewer himself. Whereas perception and generation of facial expressions have been studied separately with functional imaging methods, no studies exist on their interaction. We combined the presentation of emotionally expressive faces with the instruction to react with facial movements predetermined and assigned. fMRI was used in an event related design to examine healthy subjects while they regarded happy, sad, or neutral faces and were instructed to simultaneously move the corners of their mouths either (a). upwards or (b). downwards, or (c). to refrain from movement. The subjects' facial movements were recorded with an MR-compatible video camera. Movement latencies were shortened in congruent situations (e.g. the presentation of a happy face and combined with upward movements) and delayed in non-congruent situations. Dissonant more than congruent stimuli activated the inferior prefrontal cortex and the somatomotor cortex bilaterally. The congruent condition, in particular when seeing a happy face, activated the medial basotemporal lobes (hippocampus, amygdala, parahippocampal region). We hypothesize that this region facilitates congruent facial movements when an emotionally expressive face is perceived and that it is part of a system for non-volitional emotional facial movements.

Adult↗