Frank Boers

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.

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 ones 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.

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. Hum Brain Mapp, 2012.

Processing of disgusted faces is facilitated by odor primes: A functional MRI study

Facilitation of emotional face recognition is an established phenomenon for audiovisual crossmodal stimulation, but not for other sensory modalities. The present study used a crossmodal priming task to identify brain systems controlling olfactory-visual interactions during emotion processing. BOLD fMRI was acquired for 44 healthy subjects during an emotional face discrimination task preceded by an emotionally valenced odorant. Behavioral performance showed that recognition of disgusted faces was improved by the presentation of an olfactory stimulus irrespective of its emotional valence. No such facilitation was seen for other facial expressions. The neuroimaging data showed a selective default network responsivity to emotional faces which was modulated by odor condition. Among disgust faces, hypoactivations during trials preceded by odorants indicated the presence of priming effects. Consistent with studies investigating the brain systems associated with audiovisual emotional integration, activity modulations in clusters in fusiform gyrus, middle frontal and middle cingulate gyrus corresponded to the observed behavioral facilitation. Our study further shows modulation of signal in the anterior insula during trials combining negatively valenced odor and disgusted faces, suggesting a modality-specific mechanism for integration of the disgust response and olfaction. These results indicate the presence of a central network with modality-specific and -unspecific components modulating emotional face recognition.

Integration of Amplitude and Phase Statistics for Complete Artifact Removal in Independent Components of Neuromagnetic Recordings

In magnetoencephalography (MEG) and electroencephalography (EEG), independent component analysis is widely applied to separate brain signals from artifact components. A number of different methods have been proposed for the automatic or semiautomatic identification of artifact components. Most of the proposed methods are based on amplitude statistics of the decomposed MEG/EEG signal. We present a fully automated approach based on amplitude and phase statistics of decomposed MEG signals for the isolation of biological artifacts such as ocular, muscle, and cardiac artifacts (CAs). The performance of different artifact identification measures was investigated. In particular, we show that phase statistics is a robust and highly sensitive measure to identify strong and weak components that can be attributed to cardiac activity, whereas a combination of different measures is needed for the identification of artifacts caused by ocular and muscle activity. With the introduction of a rejection performance parameter, we are able to quantify the rejection quality for eye blinks and CAs. We demonstrate in a set of MEG data the good performance of the fully automated procedure for the removal of cardiac, ocular, and muscle artifacts. The new approach allows routine application to clinical measurements with small effect on the brain signal.

Early sensory encoding of affective prosody: Neuromagnetic tomography of emotional category changes

In verbal communication, prosodic codes may be phylogenetically older than lexical ones. Little is known, however, about early, automatic encoding of emotional prosody. This study investigated the neuromagnetic analogue of mismatch negativity (MMN) as an index of early stimulus processing of emotional prosody using whole-head magnetoencephalography (MEG). We applied two different paradigms to study MMN; in addition to the traditional oddball paradigm, the so-called optimum design was adapted to emotion detection. In a sequence of randomly changing disyllabic pseudo-words produced by one male speaker in neutral intonation, a traditional oddball design with emotional deviants (10% happy and angry each) and an optimum design with emotional (17% happy and sad each) and nonemotional gender deviants (17% female) elicited the mismatch responses. The emotional category changes demonstrated early responses (<200 ms) at both auditory cortices with larger amplitudes at the right hemisphere. Responses to the nonemotional change from male to female voices emerged later ( approximately 300 ms). Source analysis pointed at bilateral auditory cortex sources without robust contribution from other such as frontal sources. Conceivably, both auditory cortices encode categorical representations of emotional prosodic. Processing of cognitive feature extraction and automatic emotion appraisal may overlap at this level enabling rapid attentional shifts to important social cues.

The temporal dynamics of insula activity to disgust and happy facial expressions: A magnetoencephalography study

The insula has consistently been shown to be involved in processing stimuli that evoke the emotional response of disgust. Recently, its specificity for processing disgust has been challenged and a broader role of the insula in the representation of interoceptive information has been suggested. Studying the temporal dynamics of insula activation during emotional processing can contribute valuable information pertaining to this issue. Few studies have addressed the insulas putative specificity to disgust and the dynamics of its underlying neural processes. In the present study, neuromagnetic responses of 13 subjects performing an emotional continuous performance task (CPT) to faces with disgust, happy, and neutral expressions were obtained. Magnetic field tomography extracted the time course of bilateral insula activities. Right insula activation was stronger to disgust and happy than neutral facial expressions at about 200 ms after stimulus onset. Later only at about 350 ms after stimulus onset the right insula was activated stronger to disgust than happy facial expressions. Thus, the early right insula response reflects activation to emotionally arousing stimuli regardless of valence, and the later right insula response differentiates disgust from happy facial expressions. Behavioral performance but not the insula activity differed between 100 ms and 1000 ms presentation conditions. Present findings support the notion that the insula is involved in the representation of interoceptive information.

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.

High-

We have investigated the microstructural and electron transport properties of 45° step-edge Josephson junctions grown on MgO substrates and used them for the preparation of superconducting quantum interference device (SQUID) magnetometers intended for magnetoencephalography (MEG) measurement systems. The high-Tc SQUID magnetometers also incorporate 16 mm multilayer superconducting flux transformers on the MgO substrates and demonstrate a magnetic field resolution of ~ 4 fT/√Hz at 77 K. Results are illustrated for the detection of auditory evoked magnetic responses of the human cortex and compared between high-Tc SQUIDs and a commercial low-Tc MEG system. Our results demonstrate that MEG systems can be upgraded using high-Tc SQUIDs to make them independent of helium and more user-friendly, saving operating costs and leading to the widespread utilization of MEG systems in clinical practice and at universities.

T_{\rm c}

By attaching arrows to a lines ends, the Müller-Lyer illusion can be used to modulate perceived line length. In the present study, we investigated the dynamics of the brain processes underlying this illusion using magnetoencephalography. Subjects were presented with a horizontal line with arrows attached to its ends. Across trials, the angles formed by the arrows were repeatedly changed such that 2 variants of the Müller-Lyer length illusion were either induced or not. The onset of both variants of the illusion revealed consistent activations in visual areas between 85 and 130 ms after stimulus onset, as well as strong and longer lasting activations along the ventral visual processing stream including inferior occipital, inferior temporal, and fusiform gyrus within the range of 195-220 ms. Subsequent neural activation was observed in the right superior temporal cortex, as well as in the right inferior parietal and the right inferior frontal cortex. The time course and the location of the activations suggest that the mechanisms involved in generating the Müller-Lyer illusion are closely linked to the ones associated with object perception, consistent with theories considering a relevant contribution of higher visual areas to the generation of the Müller-Lyer illusion.