The effects of trauma on feedback processing: an MEG study

The cognitive impact of psychological trauma can manifest as a range of post-traumatic stress symptoms that are often attributed to impairments in learning from positive and negative outcomes, aka reinforcement learning. Research on the impact of trauma on reinforcement learning has mainly been inconclusive. This study aimed to circumscribe the impact of psychological trauma on reinforcement learning in the context of neural response in time and frequency domains. Two groups of participants were tested - those who had experienced psychological trauma and a control group who had not - while they performed a probabilistic classification task that dissociates learning from positive and negative feedback during a magnetoencephalography (MEG) examination. While the exposure to trauma did not exhibit any effects on learning accuracy or response time for positive or negative feedback, MEG cortical activity was modulated in response to positive feedback. In particular, the medial and lateral orbitofrontal cortices (mOFC and lOFC) exhibited increased activity, while the insular and supramarginal cortices showed decreased activity during positive feedback presentation. Furthermore, when receiving negative feedback, the trauma group displayed higher activity in the medial portion of the superior frontal cortex. The timing of these activity changes occurred between 160 and 600 ms post feedback presentation. Analysis of the time-frequency domain revealed heightened activity in theta and alpha frequency bands (4-10 Hz) in the lOFC in the trauma group. Moreover, dividing the two groups according to their learning performance, the activity for the non-learner subgroup was found to be lower in lOFC and higher in the supramarginal cortex. These differences were found in the trauma group only. The results highlight the localization and neural dynamics of feedback processing that could be affected by exposure to psychological trauma. This approach and associated findings provide a novel framework for understanding the cognitive correlates of psychological trauma in relation to neural dynamics in the space, time, and frequency domains. Subsequent work will focus on the stratification of cognitive and neural correlates as a function of various symptoms of psychological trauma. Clinically, the study findings and approach open the possibility for neuromodulation interventions that synchronize cognitive and psychological constructs for individualized treatment.

GABAA receptor availability relates to emotion-induced BOLD responses in the medial prefrontal cortex: simultaneous fMRI/PET with [11C]flumazenil

Introduction

The fMRI BOLD response to emotional stimuli highlighting the role of the medial prefrontal cortex (MPFC) has been thoroughly investigated. Recently, the relationship between emotion processing and GABA levels has been studied using MPFC proton magnetic resonance spectroscopy (1H-MRS). However, the role of GABAA receptors in the MPFC during emotion processing remains unexplored.

Methods

Using [11C]flumazenil PET, we investigated the relationship between the binding potential of GABAA receptors and emotion processing as measured using simultaneous fMRI BOLD. We hypothesized a correlation between the percent signal change in the BOLD signal and the binding potential of GABAA receptors in the MPFC. In a combined simultaneous fMRI and [11C]flumazenil-PET study, we analyzed the data from 15 healthy subjects using visual emotional stimuli. Our task comprised two types of emotional processing: passive viewing and appraisal. Following the administration of a bolus plus infusion protocol, PET and fMRI data were simultaneously acquired in a hybrid 3 T MR-BrainPET.

Results

We found a differential correlation of BOLD percent signal change with [11C]flumazenil binding potential in the MPFC. Specifically, [11C]flumazenil binding potential in the ventromedial prefrontal cortex (vMPFC) correlated with passive viewing of emotionally valenced pictures. In contrast, the [11C]flumazenil binding potential and the BOLD signal induced by picture appraisal did show a correlation in the paracingulate gyrus.

Conclusion

Our data deliver first evidence for a relationship between MPFC GABAA receptors and emotion processing in the same region. Moreover, we observed that GABAA receptors appear to play different roles in emotion processing in the vMPFC (passive viewing) and paracingulate gyrus (appraisal).

Revealing Whole-Brain Causality Networks During Guided Visual Searching

In our daily lives, we use eye movements to actively sample visual information from our environment ("active vision"). However, little is known about how the underlying mechanisms are affected by goal-directed behavior. In a study of 31 participants, magnetoencephalography was combined with eye-tracking technology to investigate how interregional interactions in the brain change when engaged in two distinct forms of active vision: freely viewing natural images or performing a guided visual search. Regions of interest with significant fixation-related evoked activity (FRA) were identified with spatiotemporal cluster permutation testing. Using generalized partial directed coherence, we show that, in response to fixation onset, a bilateral cluster consisting of four regions (posterior insula, transverse temporal gyri, superior temporal gyrus, and supramarginal gyrus) formed a highly connected network during free viewing. A comparable network also emerged in the right hemisphere during the search task, with the right supramarginal gyrus acting as a central node for information exchange. The results suggest that all four regions are vital to visual processing and guiding attention. Furthermore, the right supramarginal gyrus was the only region where activity during fixations on the search target was significantly negatively correlated with search response times. Based on our findings, we hypothesize that, following a fixation, the right supramarginal gyrus supplies the right supplementary eye field (SEF) with new information to update the priority map guiding the eye movements during the search task.

Conflict processing networks: A directional analysis of stimulus-response compatibilities using MEG

The suppression of distracting information in order to focus on an actual cognitive goal is a key feature of executive functions. The use of brain imaging methods to investigate the underlying neurobiological brain activations that occur during conflict processing have demonstrated a strong involvement of the fronto-parietal attention network (FPAN). Surprisingly, the directional interconnections, their time courses and activations at different frequency bands remain to be elucidated, and thus, this constitutes the focus of this study. The shared information flow between brain areas of the FPAN is provided for frequency bands ranging from the theta to the lower gamma band (4–40 Hz). We employed an adaptation of the Simon task utilizing Magnetoencephalography (MEG). Granger causality was applied to investigate interconnections between the active brain regions, as well as their directionality. Following stimulus onset, the middle frontal precentral cortex and superior parietal cortex were significantly activated during conflict processing in a time window of between 300 to 600ms. Important differences in causality were found across frequency bands between processing of conflicting stimuli in the left as compared to the right visual hemifield. The exchange of information from and to the FPAN was most prominent in the beta band. Moreover, the anterior cingulate cortex and the anterior insula represented key areas for conflict monitoring, either by receiving input from other areas of the FPAN or by generating output themselves. This indicates that the salience network is at least partly involved in processing conflict information. The present study provides detailed insights into the underlying neural mechanisms of the FPAN, especially regarding its temporal characteristics and directional interconnections.

mGluR5 receptor availability is associated with lower levels of negative symptoms and better cognition in male patients with chronic schizophrenia

Consistent findings postulate disturbed glutamatergic function (more specifically a hypofunction of the ionotropic NMDA receptors) as an important pathophysiologic mechanism in schizophrenia. However, the role of the metabotropic glutamatergic receptors type 5 (mGluR5) in this disease remains unclear. In this study, we investigated their significance (using [¹¹C]ABP688) for psychopathology and cognition in male patients with chronic schizophrenia and healthy controls. In the patient group, lower mGluR5 binding potential (BP_ND) values in the left temporal cortex and caudate were associated with higher general symptom levels (negative and depressive symptoms), lower levels of global functioning and worse cognitive performance. At the same time, in both groups, mGluR5 BP_ND were significantly lower in smokers (F_[27,1] = 15.500; p = .001), but without significant differences between the groups. Our findings provide support for the concept that the impaired function of mGluR5 underlies the symptoms of schizophrenia. They further supply a new perspective on the complex relationship between tobacco addiction and schizophrenia by identifying glutamatergic neurotransmission—in particularly mGluR5—as a possible connection to a shared vulnerability.

Alternative headphones for patient noise protection and communication in PET-MR studies of the brain

Introduction

Due to the high noise emission generated by the gradients in magnetic resonance imaging (MRI), an efficient method of noise protection is mandatory. In addition to providing hearing protection, appropriate headphone systems also serve to facilitate communication between the operator and the patient. However, in combined PET-MR devices, use of common pneumatic headphones, as delivered by the manufacturer, is problematic due to the potential generation of attenuation artefacts in the PET measurement. Furthermore, modern multichannel head coils rarely provide space for conventional headphones. This work presents an alternative system, which aims to address these limitations while still being appropriate for both patient noise protection and communication in PET-MR.

Material and methods

As an alternative to the standard headphones supplied with the PET-MR (3T MR-BrainPET, Siemens), the possibility of using earphones built out of commercially available earplugs has been investigated. The air channel (E-A-RLink) of the earplug is connected to the tubes of the original headphones. The attenuation characteristics of the conventional headphones and of the modified earphones were measured using a dedicated PET system with a ⁶⁸Ge transmission source. For this purpose, the headphones, and then the earphones, were attached to a non-radioactive head phantom. To investigate the influence of the different phones on PET emission images, measurements of the head phantom, filled with ¹⁸F solution, were performed in the PET-MR. A measurement of the head phantom without headphones or earphones was used as a reference.

Results

The linear attenuation coefficient of the headphones was 0.11 cm^-1 and that of the head phantom 0.10 cm^-1. The earphones were not identifiable in the transmission image. The emission image showed an activity underestimation of 10% near the headphones, compared to the reference image, whereas the earphones did not affect the image. Communication with the patient via the earphones was successful, and the noise protection—as confirmed by investigated subjects—was satisfying.

Conclusion

The presented earphones, which can be connected to the existing patient communication system, are a preferable alternative to the conventional headphones, as, in contrast to the use of headphones, qualitative and quantitative errors in the PET images can be avoided. Patient acceptance of the earphones was high, despite the increase in preparation time before the PET-MR study.

Association between Cortical GABA and Loudness Dependence of Auditory Evoked Potentials (LDAEP) in Humans

Loudness dependence of auditory evoked potentials (LDAEP) is a widely used EEG-based biomarker for central serotonergic activity. Serotonin has been shown to be associated with different psychiatric disorders such as depression and schizophrenia. Despite its clinical significance, the underlying neurochemical mechanism of this promising marker is not fully understood, and further research is needed to improve its validity. Other neurotransmitters might have a significant impact on this measure. Thus, we assessed the inhibitory action through individual GABA/H20 concentrations and GABA/glutamate ratios by means of magnetic resonance spectroscopy at 3T in healthy subjects. The measurements were assessed in the primary auditory cortex to investigate the association with the LDAEP, whose generators are mainly in the primary auditory cortex. For the first time, this study examines the link between GABAergic neurotransmission and LDAEP, and the data preliminary show that GABA may not contribute to the generation of EEG-based LDAEP.

Examining incidental vocabulary acquisition from captioned video

Previous comparisons of vocabulary uptake from captioned and uncaptioned audio-visual materials have almost consistently furnished evidence in favour of captioned materials. However, it is possible that many such comparative studies gave an advantage to the captioned input conditions by virtue of their use of written word prompts in the tests. The present study therefore examines whether aurally presented test prompts yield equally compelling evidence for the superiority of captioned over uncaptioned video. Intermediate EFL learners watched a ten-minute TED Talks video either with or without captions and were subsequently given a word recognition and a word meaning test, with half of the test prompts presented in print and the other half presented aurally. While the results of the word recognition test were inconclusive, the word meaning test yielded significantly better scores by the group that watched the captioned video. However, this was due entirely to their superior scores on the printed word prompts, not the aural ones. This suggests that evaluations of the benefits of captions for vocabulary acquisitions should take input-modality – test-modality congruency into account.

Integrating modality-specific expectancies for the deployment of spatial attention

The deployment of spatial attention is highly sensitive to stimulus predictability. Despite evidence for strong crossmodal links in spatial attentional systems, it remains to be elucidated how concurrent but divergent predictions for targets in different sensory modalities are integrated. In a series of behavioral studies, we investigated the processing of modality-specific expectancies using a multimodal cueing paradigm in which auditory cues predicted the location of visual or tactile targets with modality-specific cue predictability. The cue predictability for visual and tactile targets was manipulated independently. A Bayesian ideal observer model with a weighting factor was applied to trial-wise individual response speed to investigate how the two probabilistic contexts are integrated. Results showed that the degree of integration depended on the level of predictability and on the divergence of the modality-specific probabilistic contexts (Experiments 1–2). However, when the two probabilistic contexts were matched in their level of predictability and were highly divergent (Experiment 3), higher separate processing was favored, especially when visual targets were processed. These findings suggest that modality-specific predictions are flexibly integrated according to their reliability, supporting the hypothesis of separate modality-specific attentional systems that are however linked to guarantee an efficient deployment of spatial attention across the senses.

Dissociated Crossed Speech Areas in a Tumour Patient

In the past, the eloquent areas could be deliberately localised by the invasive Wada test. The very rare cases of dissociated crossed speech areas were accidentally found based on the clinical symptomatology. Today functional magnetic resonance imaging (fMRI)-based imaging can be employed to non-invasively localise the eloquent areas in brain tumour patients for therapy planning. A 41-year-old, left-handed man with a low-grade glioma in the left frontal operculum extending to the insular cortex, tension headaches, and anomic aphasia over 5 months underwent a pre-operative speech area localisation fMRI measurement, which revealed the evidence of the transhemispheric disposition, where the dominant Wernicke speech area is located on the left and the Broca's area is strongly lateralised to the right hemisphere. The outcome of the Wada test and the intraoperative cortico-subcortical stimulation mapping were congruent with this finding. After tumour removal, language area function was fully preserved. Upon the occurrence of brain tumours with a risk of impaired speech function, the rare dissociate crossed speech areas disposition may gain a clinically relevant meaning by allowing for more extended tumour removal. Hence, for its identification, diagnostics which take into account both brain hemispheres, such as fMRI, are recommended.

Methods for pulse artefact reduction: experiences with EEG data recorded at 9.4 T static magnetic field

BACKGROUND

The feasibility of recording electroencephalography (EEG) at ultra-high static magnetic fields up to 9.4 T was recently demonstrated and is expected to be incorporated into functional magnetic resonance imaging (fMRI) studies at 9.4 T. Correction of the pulse artefact (PA) is a significant challenge since its amplitude is proportional to the strength of the magnetic field in which EEG is recorded.

NEW METHOD

We conducted a study in which different PA correction methods were applied to EEG data recorded inside a 9.4 T scanner in order to retrieve visual P100 and auditory P300 evoked potentials. We explored different PA reduction methods, including the optimal basis set (OBS) method as well as objective and subjective component rejection using independent component analysis (ICA).

RESULTS

ICA followed by objective rejection of components is optimal for retrieving visual P100 and auditory P300 from EEG data recorded inside the scanner.

COMPARISON WITH EXISTING METHODS

Previous studies suggest that OBS or OBS followed by ICA are optimal for retrieving evoked potentials at 3T. In our EEG data recorded at 9.4 T OBS performed alone was not fully optimal for the identification of evoked potentials. OBS followed by ICA was partially effective.

CONCLUSIONS

In this study ICA has been shown to be an important tool for correcting the PA in EEG data recorded at 9.4 T, particularly when automated rejection of components is performed.

The default mode network and EEG regional spectral power: a simultaneous fMRI-EEG study

Electroencephalography (EEG) frequencies have been linked to specific functions as an “electrophysiological signature” of a function. A combination of oscillatory rhythms has also been described for specific functions, with or without predominance of one specific frequency-band. In a simultaneous fMRI-EEG study at 3 T we studied the relationship between the default mode network (DMN) and the power of EEG frequency bands. As a methodological approach, we applied Multivariate Exploratory Linear Optimized Decomposition into Independent Components (MELODIC) and dual regression analysis for fMRI resting state data. EEG power for the alpha, beta, delta and theta-bands were extracted from the structures forming the DMN in a region-of-interest approach by applying Low Resolution Electromagnetic Tomography (LORETA). A strong link between the spontaneous BOLD response of the left parahippocampal gyrus and the delta-band extracted from the anterior cingulate cortex was found. A positive correlation between the beta-1 frequency power extracted from the posterior cingulate cortex (PCC) and the spontaneous BOLD response of the right supplementary motor cortex was also established. The beta-2 frequency power extracted from the PCC and the precuneus showed a positive correlation with the BOLD response of the right frontal cortex. Our results support the notion of beta-band activity governing the “status quo” in cognitive and motor setup. The highly significant correlation found between the delta power within the DMN and the parahippocampal gyrus is in line with the association of delta frequencies with memory processes. We assumed “ongoing activity” during “resting state” in bringing events from the past to the mind, in which the parahippocampal gyrus is a relevant structure. Our data demonstrate that spontaneous BOLD fluctuations within the DMN are associated with different EEG-bands and strengthen the conclusion that this network is characterized by a specific electrophysiological signature created by combination of different brain rhythms subserving different putative functions.

Modality-specific perceptual expectations selectively modulate baseline activity in auditory, somatosensory, and visual cortices

Valid expectations are known to improve target detection, but the preparatory attentional mechanisms underlying this perceptual facilitation remain an open issue. Using functional magnetic resonance imaging, we show here that expecting auditory, tactile, or visual targets, in the absence of stimulation, selectively increased baseline activity in corresponding sensory cortices and decreased activity in irrelevant ones. Regardless of sensory modality, expectancy activated bilateral premotor and posterior parietal areas, supplementary motor area as well as right anterior insula and right middle frontal gyrus. The bilateral putamen was sensitive to the modality specificity of expectations during the unexpected omission of targets. Thus, across modalities, detection improvement arising from selectively directing attention to a sensory modality appears mediated through transient changes in pretarget activity. This flexible advance modulation of baseline activity in sensory cortices resolves ambiguities among previous studies unable to discriminate modality-specific preparatory activity from attentional modulation of stimulus processing. Our results agree with predictive-coding models, which suggest that these expectancy-related changes reflect top-down biases--presumably originating from the observed supramodal frontoparietal network--that modulate signal-detection sensitivity by differentially modifying background activity (i.e., noise level) in different input channels. The putamen appears to code omission-related Bayesian "surprise" that depends on the specificity of predictions.

Staying responsive to the world: modality-specific and -nonspecific contributions to speeded auditory, tactile, and visual stimulus detection

Sustained responsiveness to external stimulation is fundamental to many time-critical interactions with the outside world. We used functional magnetic resonance imaging during speeded stimulus detection to identify convergent and divergent neural correlates of maintaining the readiness to respond to auditory, tactile, and visual stimuli. In addition, using a multimodal condition, we investigated the effect of making stimulus modality unpredictable. Relative to sensorimotor control tasks, all three unimodal detection tasks elicited stronger activity in the right temporo-parietal junction, inferior frontal cortex, anterior insula, dorsal premotor cortex, and anterior cingulate cortex as well as bilateral mid-cingulum, midbrain, brainstem, and medial cerebellum. The multimodal detection condition additionally activated left dorsal premotor cortex and bilateral precuneus. Modality-specific modulations were confined to respective sensory areas: we found activity increases in relevant, and decreases in irrelevant sensory cortices. Our findings corroborate the modality independence of a predominantly right-lateralized core network for maintaining an alert (i.e., highly responsive) state and extend previous results to the somatosensory modality. Monitoring multiple sensory channels appears to induce additional processing, possibly related to stimulus-driven shifts of intermodal attention. The results further suggest that directing attention to a given sensory modality selectively enhances and suppresses sensory processing-even in simple detection tasks, which do not require inter- or intra-modal selection.

Cognitive versus automatic mechanisms of mood induction differentially activate left and right amygdala

The amygdala plays a key role in emotional processing. The specific contribution of the amygdala during the experience of one's own emotion, however, remains controversial and requires clarification. There is a long-standing debate on hemispheric lateralization of emotional processes, yet few studies to date directly investigated differential activation patterns for the left and right amygdala. Limited evidence supports right amygdala involvement in automatic processes of emotion and left amygdala involvement in conscious and cognitively controlled emotion processing. The present study investigated differential contributions of the left and right amygdala to cognitive and automatic mechanisms of mood induction. Using functional magnetic resonance imaging (fMRI), we examined hemispheric amygdala responses during two mood induction paradigms: a purely visual method presenting face stimuli and an audiovisual method using faces and music. Amygdala responses in 30 subjects (16 females) showed differences in lateralization patterns depending on the processing mode. The left amygdala exhibited comparable activation levels for both methods. The right amygdala, in contrast, showed increased activity only for the audiovisual condition and this activity was increasing over time. The left amygdala showed augmented activity with higher intensity ratings of negative emotional valence. These results support a left-lateralized cognitive and intentional control of mood and a right-sided more automatic induction of emotion that relies less on explicit reflection processes. The modulation of the left amygdala responses by subjective experience may reflect individual differences in the cognitive effort used to induce the mood. Thus, the central role of the amygdala may not be restricted to the perception of emotion in others but also extend into processes involved in regulation of mood.

Multisensory integration of emotionally valenced olfactory-visual information in patients with schizophrenia and healthy controls

BACKGROUND

Patients with schizophrenia frequently have deficits in social cognition, and difficulties in the discrimination of emotional facial expressions have been discussed as an important contributing factor. We investigated whether this impairment is aggravated by difficulties relating the observed facial expression to contextual information, as is often provided by emotionally valenced crossmodal stimulation.

METHODS

We investigated the effects of odorant primes on the accuracy and speed of emotional face recognition. Healthy controls and patients with schizophrenia were exposed to 2-second odorant stimuli: vanillin (pleasant), ambient air (neutral) and hydrogen sulfide (unpleasant). The odours were followed by an emotional face recognition task, in which participants determined if a face showed happiness, disgust or neutral affect.

RESULTS

Controls showed improved performance in the categorization of disgusted faces after all types of odour stimulation irrespective of the emotional valence. However, in controls, the response time for happy faces was slower after presentation of any odour. Schizophrenia patients showed an attenuated effect of olfactory priming on disgust recognition, which resulted in the increased performance differences between the groups. This effect was particularly strong for the unpleasant odour.

LIMITATIONS

The study design did not allow us to fully differentiate between the effects of perceived odour intensity and valence. A possible contribution of cognitive deficits on the observed effects should be investigated in future studies.

CONCLUSION

Our results provide novel evidence for a special connection between the presentation of odorant cues and the accuracy of recognition of disgusted faces in healthy controls. This recognition advantage is disturbed in patients with schizophrenia and appears to contribute to the observed deficit in emotional face recognition.

An automatic procedure for the analysis of electric and magnetic mismatch negativity based on anatomical brain mapping

Data processing techniques in electroencephalography (EEG) and magnetoencephalography (MEG) need user interactions. However, particularly in clinical applications, fast and objective data processing is important. Here we present an observer-independent method for EEG and MEG analysis of mismatch negativity (MMN) that allows reliable estimation of source activity based on objective anatomical references. The procedure integrates several steps including artifact rejection, source estimation and statistical analysis. It enables the evaluation of source activity in a fully automatic and unsupervised manner. To test its feasibility we obtained EEG and MEG responses in an auditory oddball paradigm in 12 healthy volunteers. The automatized method of EEG and MEG data analysis estimated source activity. The automatically detected MMN was closely comparable with the results obtained by a user-controlled method based on the dipole fitting. The presented workflow can be performed easily, rapidly, and reliably. This development may open new fields in research and clinical applications of source-based EEG and MEG.

A new toolbox for combining magnetoencephalographic source analysis and cytoarchitectonic probabilistic data for anatomical classification of dynamic brain activity

Size and location of activated cortical areas are often identified in relation to their surrounding macro-anatomical landmarks such as gyri and sulci. The sulcal pattern, however, is highly variable. In addition, many cortical areas are not linked to well defined landmarks, which in turn do not have a fixed relationship to functional and cytoarchitectonic boundaries. Therefore, it is difficult to unambiguously attribute localized neuronal activity to the corresponding cortical areas in the living human brain. Here we present new methods that are implemented in a toolbox for the objective anatomical identification of neuromagnetic activity with respect to cortical areas. The toolbox enables the platform independent integration of many types of source analysis obtained from magnetoencephalography (MEG) together with probabilistic cytoarchitectonic maps obtained in postmortem brains. The probability maps provide information about the relative frequency of a given cortical area being located at a given position in the brain. In the new software, the neuromagnetic data are analyzed with respect to cytoarchitectonic maps that have been transformed to the individual subject brain space. A number of measures define the degree of overlap between and distance from the activated areas and the corresponding cytoarchitectonic maps. The implemented algorithms enable the investigator to quantify how much of the reconstructed current density can be attributed to distinct cortical areas. Dynamic correspondence patterns between the millisecond-resolved MEG data and the static cytoarchitectonic maps are obtained. We show examples for auditory and visual activation patterns. However, size and location of the postmortem brain areas as well as the inverse method applied to the neuromagnetic data bias the anatomical classification. Therefore, the adaptation to the respective application and a combination of the objective quantities are discussed.

Neural mechanism underlying impaired visual judgement in the dysmetabolic brain: an fMRI study

An altered brain metabolism in the parietal and prefrontal regions of the cerebral cortex as well as cognitive alterations have been found in patients suffering from hepatic encephalopathy. The neural mechanisms underlying these metabolically induced cognitive alterations, however, are not known. Since patients with liver cirrhosis without clinically overt encephalopathy already show an impaired performance in a flicker light test, the aim of this study was to analyze the normal and pathologically impaired neural mechanisms of these patients using functional magnetic resonance imaging (fMRI). Nine subjects at the early stage of encephalopathy [nonmanifest hepatic encephalopathy (nmHE)] and ten controls underwent scanning, while they indicated the apparent transition from a steady light to the onset of a flicker light, that is, the critical flicker frequency (CFF). Judgement-related blood oxygenation level-dependent (BOLD) activation was decreased in nmHE compared to controls in the right inferior parietal cortex (IPL). Furthermore, the analysis of psychophysiologic interaction suggests impaired neural interaction in patients with nmHE, especially between the IPL and the parietooccipital cortex (Poc), the intraparietal sulcus, the anterior cingulate cortex (ACC), the right prefrontal cortex (PFC), the medial temporal lobe, and the extrastriate cortex V5. In contrast, nonmanifest patients revealed an enhanced coupling between IPL and the postcentral cortex. Our findings provide evidence of an early-impaired and compensatory neural mechanism during visual judgement already in the earliest stages of hepatic encephalopathy and suggest an aberrant coupling between cerebral regions in the dysmetabolic brain.

Synchronization tomography: a method for three-dimensional localization of phase synchronized neuronal populations in the human brain using magnetoencephalography

We present a noninvasive technique which allows the anatomical localization of phase synchronized neuronal populations in the human brain with magnetoencephalography. We study phase synchronization between the reconstructed current source density (CSD) of different brain areas as well as between the CSD and muscular activity. We asked four subjects to tap their fingers in synchrony with a rhythmic tone, and to continue tapping at the same rate after the tone was switched off. The phase synchronization behavior of brain areas relevant for movement coordination, inner voice, and time estimation changes drastically when the transition to internal pacing occurs, while their averaged amplitudes remain unchanged. Information of this kind cannot be derived with standard neuroimaging techniques like functional magnetic resonance imaging or positron emission tomography.

Synthesis and antiviral activity of 7-O-(omega-substituted)-alkyl-3-O-methylquercetin derivatives

3',4'-Di-O-benzyl-3-O-methylquercetin (2), the precursor in the synthesis of an important antivirally active flavone 3-O-methylquercetin (1), was regioselectively alkylated at the 7-OH position by a series of 1,omega-dihaloalkanes and omega-bromoalkanols. Dimerization of the flavone had to be avoided by applying strict reaction conditions. Subsequent debenzylation was carried out by catalytic transfer hydrogenolysis, affording quantitatively the 7-O-(omega-haloalkyl)-3-O-methylquercetin (11-14) and 7-O-(omega-hydroxyalkyl)-3-O-methylquercetin derivatives (15, 16). All compounds were tested for their antiviral activity against poliomyelitis- and HIV-viruses.