Human NREM Sleep Promotes Brain-Wide Vasomotor and Respiratory Pulsations.

The physiological underpinnings of the necessity of sleep remain uncertain. Recent evidence suggests that sleep increases the convection of cerebrospinal fluid (CSF) and promotes the export of interstitial solutes, thus providing a framework to explain why all vertebrate species require sleep. Cardiovascular, respiratory and vasomotor brain pulsations have each been shown to drive CSF flow along perivascular spaces, yet it is unknown how such pulsations may change during sleep in humans. To investigate these pulsation phenomena in relation to sleep, we simultaneously recorded fast fMRI, magnetic resonance encephalography (MREG), and electroencephalography (EEG) signals in a group of healthy volunteers. We quantified sleep-related changes in the signal frequency distributions by spectral entropy analysis and calculated the strength of the physiological (vasomotor, respiratory, and cardiac) brain pulsations by power sum analysis in 15 subjects (age 26.5 ± 4.2 years, 6 females). Finally, we identified spatial similarities between EEG slow oscillation (0.2-2 Hz) power and MREG pulsations. Compared with wakefulness, nonrapid eye movement (NREM) sleep was characterized by reduced spectral entropy and increased brain pulsation intensity. These effects were most pronounced in posterior brain areas for very low-frequency (≤0.1 Hz) vasomotor pulsations but were also evident brain-wide for respiratory pulsations, and to a lesser extent for cardiac brain pulsations. There was increased EEG slow oscillation power in brain regions spatially overlapping with those showing sleep-related MREG pulsation changes. We suggest that reduced spectral entropy and enhanced pulsation intensity are characteristic of NREM sleep. With our findings of increased power of slow oscillation, the present results support the proposition that sleep promotes fluid transport in human brain.SIGNIFICANCE STATEMENT We report that the spectral power of physiological brain pulsation mechanisms driven by vasomotor, respiration, and cardiac rhythms in human brain increase during sleep, extending previous observations of their association with glymphatic brain clearance during sleep in rodents. The magnitudes of increased pulsations follow the rank order of vasomotor greater than respiratory greater than cardiac pulsations, with correspondingly declining spatial extents. Spectral entropy, previously known as vigilance and as an anesthesia metric, decreased during NREM sleep compared with the awake state in very low and respiratory frequencies, indicating reduced signal complexity. An EEG slow oscillation power increase occurring in the early sleep phase (NREM 1-2) spatially overlapped with pulsation changes, indicating reciprocal mechanisms between those measures.

Altered global brain network topology as a trait marker in patients with anorexia nervosa.

BACKGROUND: Resting state functional magnetic resonance imaging studies have identified functional connectivity patterns associated with acute undernutrition in anorexia nervosa (AN), but few have investigated recovered patients. Thus, a trait connectivity profile characteristic of the disorder remains elusive. Using state-of-the-art graph-theoretic methods in acute AN, the authors previously found abnormal global brain network architecture, possibly driven by local network alterations. To disentangle trait from starvation effects, the present study examines network organization in recovered patients. METHODS: Graph-theoretic metrics were used to assess resting-state network properties in a large sample of female patients recovered from AN (recAN, n = 55) compared with pairwise age-matched healthy controls (HC, n = 55). RESULTS: Indicative of an altered global network structure, recAN showed increased assortativity and reduced global clustering as well as small-worldness compared with HC, while no group differences at an intermediate or local network level were evident. However, using support-vector classifier on local metrics, recAN and HC could be separated with an accuracy of 70.4%. CONCLUSIONS: This pattern of results suggests that long-term recovered patients have an aberrant global brain network configuration, similar to acutely underweight patients. While the finding of increased assortativity may represent a trait marker of AN, the remaining findings could be seen as a scar following prolonged undernutrition.

The anterior insula channels prefrontal expectancy signals during affective processing.

Expectancy shapes our perception of impending events. Although such an interplay between cognitive and affective processes is often impaired in mental disorders, it is not well understood how top-down expectancy signals modulate future affect. We therefore track the information flow in the brain during cognitive and affective processing segregated in time using task-specific cross-correlations. Participants in two independent fMRI studies (N1 = 37 & N2 = 55) were instructed to imagine a situation with affective content as indicated by a cue, which was then followed by an emotional picture congruent with expectancy. To correct for intrinsic covariance of brain function, we calculate resting-state cross-correlations analogous to the task. First, using factorial modeling of delta cross-correlations (task-rest) of the first study, we find that the magnitude of expectancy signals in the anterior insula cortex (AIC) modulates the BOLD response to emotional pictures in the anterior cingulate and dorsomedial prefrontal cortex in opposite directions. Second, using hierarchical linear modeling of lagged connectivity, we demonstrate that expectancy signals in the AIC indeed foreshadow this opposing pattern in the prefrontal cortex. Third, we replicate the results in the second study using a higher temporal resolution, showing that our task-specific cross-correlation approach robustly uncovers the dynamics of information flow. We conclude that the AIC arbitrates the recruitment of distinct prefrontal networks during cued picture processing according to triggered expectations. Taken together, our study provides new insights into neuronal pathways channeling cognition and affect within well-defined brain networks. Better understanding of such dynamics could lead to new applications tracking aberrant information processing in mental disorders.

Echoes of Affective Stimulation in Brain connectivity Networks.

Affective experience has effects on subjective feelings, physiological indices, entails immediate activity changes in the brain, and even influences brain networks in a protracted manner. However, it is still unclear, how the functional connectivity (FC) interplay between major intrinsic connectivity networks upon affective stimulation depends on affective valence, and whether this is specific for affective experience, i.e., can be distinguished from cognitive task execution. Our study included fMRI scans during and after affective stimulation with sad and neutral movies and a working memory task complemented with measures of cardiovascular activity and mood. Via parcellation of the brain into default mode network (DMN), central executive network (CEN), and dorsal attention network, and application of network-based statistics, we identified subnetworks associated with changing psychological contexts. Specific effects for affective stimulation with negative valence were both reduced heart rate variability and mood, and upregulated FC of inter-CEN-DMN connections while intra-DMN connections were downregulated. Furthermore, results demonstrated a valence-specific dynamic carry-over effect in nodes of the CEN, which temporarily increased their FC strength after affective stimulation with negative valence and exhibited distinct temporal profiles. The reported effects were clearly distinguishable from those of a cognitive task and further elucidate the trajectory of affective experience.

Evidence for superior neurobiological and behavioral inhibitory control abilities in non-offending as compared to offending pedophiles.

Neurobehavioral models of pedophilia and child sexual offending suggest a pattern of temporal and in particular prefrontal disturbances leading to inappropriate behavioral control and subsequently an increased propensity to sexually offend against children. However, clear empirical evidence for such mechanisms is still missing. Using a go/nogo paradigm in combination with functional magnetic resonance imaging (fMRI) we compared behavioral performance and neural response patterns among three groups of men matched for age and IQ: pedophiles with (N = 40) and without (N = 37) a history of hands-on sexual offences against children as well as healthy non-offending controls (N = 40). As compared to offending pedophiles, non-offending pedophiles exhibited superior inhibitory control as reflected by significantly lower rate of commission errors. Group-by-condition interaction analysis also revealed inhibition-related activation in the left posterior cingulate and the left superior frontal cortex that distinguished between offending and non-offending pedophiles, while no significant differences were found between pedophiles and healthy controls. Both areas showing distinct activation pattern among pedophiles play a critical role in linking neural networks that relate to effective cognitive functioning. Data therefore suggest that heightened inhibition-related recruitment of these areas as well as decreased amount of commission errors is related to better inhibitory control in pedophiles who successfully avoid committing hands-on sexual offences against children. Hum Brain Mapp 38:1092-1104, 2017. © 2016 Wiley Periodicals, Inc.

Preprocessing strategy influences graph-based exploration of altered functional networks in major depression.

Resting-state fMRI studies have gained widespread use in exploratory studies of neuropsychiatric disorders. Graph metrics derived from whole brain functional connectivity studies have been used to reveal disease-related variations in many neuropsychiatric disorders including major depression (MDD). These techniques show promise in developing diagnostics for these often difficult to identify disorders. However, the analysis of resting-state datasets is increasingly beset by a myriad of approaches and methods, each with underlying assumptions. Choosing the most appropriate preprocessing parameters a priori is difficult. Nevertheless, the specific methodological choice influences graph-theoretical network topologies as well as regional metrics. The aim of this study was to systematically compare different preprocessing strategies by evaluating their influence on group differences between healthy participants (HC) and depressive patients. We thus investigated the effects of common preprocessing variants, including global mean-signal regression (GMR), temporal filtering, detrending, and network sparsity on group differences between brain networks of HC and MDD patients measured by global and nodal graph theoretical metrics. Occurrence of group differences in global metrics was absent in the majority of tested preprocessing variants, but in local graph metrics it is sparse, variable, and highly dependent on the combination of preprocessing variant and sparsity threshold. Sparsity thresholds between 16 and 22% were shown to have the greatest potential to reveal differences between HC and MDD patients in global and local network metrics. Our study offers an overview of consequences of methodological decisions and which neurobiological characteristics of MDD they implicate, adding further caution to this rapidly growing field.

Abnormal functional global and local brain connectivity in female patients with anorexia nervosa.

BACKGROUND: Previous resting-state functional connectivity studies in patients with anorexia nervosa used independent component analysis or seed-based connectivity analysis to probe specific brain networks. Instead, modelling the entire brain as a complex network allows determination of graph-theoretical metrics, which describe global and local properties of how brain networks are organized and how they interact. METHODS: To determine differences in network properties between female patients with acute anorexia nervosa and pairwise matched healthy controls, we used resting-state fMRI and computed well-established global and local graph metrics across a range of network densities. RESULTS: Our analyses included 35 patients and 35 controls. We found that the global functional network structure in patients with anorexia nervosa is characterized by increases in both characteristic path length (longer average routes between nodes) and assortativity (more nodes with a similar connectedness link together). Accordingly, we found locally decreased connectivity strength and increased path length in the posterior insula and thalamus. LIMITATIONS: The present results may be limited to the methods applied during preprocessing and network construction. CONCLUSION: We demonstrated anorexia nervosa-related changes in the network configuration for, to our knowledge, the first time using resting-state fMRI and graph-theoretical measures. Our findings revealed an altered global brain network architecture accompanied by local degradations indicating wide-scale disturbance in information flow across brain networks in patients with acute anorexia nervosa. Reduced local network efficiency in the thalamus and posterior insula may reflect a mechanism that helps explain the impaired integration of visuospatial and homeostatic signals in patients with this disorder, which is thought to be linked to abnormal representations of body size and hunger.

State and Training Effects of Mindfulness Meditation on Brain Networks Reflect Neuronal Mechanisms of Its Antidepressant Effect.

The topic of investigating how mindfulness meditation training can have antidepressant effects via plastic changes in both resting state and meditation state brain activity is important in the rapidly emerging field of neuroplasticity. In the present study, we used a longitudinal design investigating resting state fMRI both before and after 40 days of meditation training in 13 novices. After training, we compared differences in network connectivity between rest and meditation using common resting state functional connectivity methods. Interregional methods were paired with local measures such as Regional Homogeneity. As expected, significant differences in functional connectivity both between states (rest versus meditation) and between time points (before versus after training) were observed. During meditation, the internal consistency in the precuneus and the temporoparietal junction increased, while the internal consistency of frontal brain regions decreased. A follow-up analysis of regional connectivity of the dorsal anterior cingulate cortex further revealed reduced connectivity with anterior insula during meditation. After meditation training, reduced resting state functional connectivity between the pregenual anterior cingulate and dorsal medical prefrontal cortex was observed. Most importantly, significantly reduced depression/anxiety scores were observed after training. Hence, these findings suggest that mindfulness meditation might be of therapeutic use by inducing plasticity related network changes altering the neuronal basis of affective disorders such as depression.

Reduced functional connectivity in the thalamo-insular subnetwork in patients with acute anorexia nervosa.

The neural underpinnings of anorexia nervosa (AN) are poorly understood. Results from existing functional brain imaging studies using disorder-relevant food- or body-stimuli have been heterogeneous and may be biased due to varying compliance or strategies of the participants. In this study, resting state functional connectivity imaging was used. To explore the distributed nature and complexity of brain function we characterized network patterns in patients with acute AN. Thirty-five unmedicated female acute AN patients and 35 closely matched healthy female participants underwent resting state functional magnetic resonance imaging. We used a network-based statistic (NBS) approach [Zalesky et al., 2010a] to identify differences between groups by isolating a network of interconnected nodes with a deviant connectivity pattern. Group comparison revealed a subnetwork of connections with decreased connectivity including the amygdala, thalamus, fusiform gyrus, putamen and the posterior insula as the central hub in the patient group. Results were not driven by changes in intranodal or global connectivity. No network could be identified where AN patients had increased coupling. Given the known involvement of the identified thalamo-insular subnetwork in interoception, decreased connectivity in AN patients in these nodes might reflect changes in the propagation of sensations that alert the organism to urgent homeostatic imbalances and pain-processes that are known to be severely disturbed in AN and might explain the striking discrepancy between patient's actual and perceived internal body state.

MEG reveals preference specific increases of sexual-image-evoked responses in paedophilic sexual offenders and healthy controls.

OBJECTIVES: Paedophilic disorder is characterised by sexual attraction towards children. Classification of a counterpart as sexually attractive likely occurs rapidly, and involves both conscious and unconscious attentional and cognitive processes. Magnetoencephalography (MEG) is an imaging method especially well-suited to examine visual and attentional processes triggered by sexual images within the range of milliseconds. METHODS: We investigated brain responses to sexual images depicting adults (frequent) and children (infrequent stimulus) in seventeen paedophilic patients with a history of child sexual offending (P + CSO) and twenty healthy controls (HC) during a passive visual oddball paradigm. Event-related fields (ERF) were measured to extract the magnetic visual mismatch negativity (vMMNm), and how it relates to the processing of different classes of sexual stimuli. RESULTS: P + CSO exhibited significantly longer vMMNm latencies (100-180 ms post-stimulus) than HC. Moreover, P + CSO showed widespread increased amplitudes in response to child images starting from P3a and P3b components and lasting up to 400 ms post-stimulus presentation localised in frontal and temporal brain regions. CONCLUSIONS: This study uncovers the first MEG differences in automatic change detection between P + CSO and HC during the presentation of subliminal sexual images of adults and children, contributing towards a better understanding of the neurobiological processes of P + CSO.

Evaluation of spontaneous regional brain activity in weight-recovered anorexia nervosa.

Whereas research using structural magnetic resonance imaging (sMRI) reports sizable grey matter reductions in patients suffering from acute anorexia nervosa (AN) to be largely reversible already after short-term weight gain, many task-based and resting-state functional connectivity (RSFC) studies suggest persistent brain alterations even after long-term weight rehabilitation. First investigations into spontaneous regional brain activity using voxel-wise resting-state measures found widespread abnormalities in acute AN, but no studies have compared intrinsic brain activity properties in weight-recovered individuals with a history of AN (recAN) with healthy controls (HCs). SMRI and RSFC data were analysed from a sample of 130 female volunteers: 65 recAN and 65 pairwise age-matched HC. Cortical grey matter thickness was assessed using FreeSurfer software. Fractional amplitude of low-frequency fluctuations (fALFFs), mean-square successive difference (MSSD), regional homogeneity (ReHo), voxel-mirrored homotopic connectivity (VHMC), and degree centrality (DC) were calculated. SMRI and RSFC data were analysed from a sample of 130 female volunteers: 65 recAN and 65 pairwise age-matched HCs. Cortical grey matter thickness was assessed using FreeSurfer software. Fractional amplitude of low-frequency fluctuations (fALFF), mean-square successive difference (MSSD), regional homogeneity (ReHo), voxel-mirrored homotopic connectivity (VHMC), and degree centrality (DC) were calculated. Abnormal regional homogeneity found in acute AN seems to normalize in recAN, supporting assumptions of a state rather than a trait marker. Aberrant fALFF values in the cerebellum and the infertior temporal gyrus could possibly hint towards trait factors or a scar (the latter, e.g., from prolonged periods of undernutrition), warranting further longitudinal research.

Dynamic lag analysis reveals atypical brain information flow in autism spectrum disorder.

This study investigated whole-brain dynamic lag pattern variations between neurotypical (NT) individuals and individuals with autism spectrum disorder (ASD) by applying a novel technique called dynamic lag analysis (DLA). The use of 3D magnetic resonance encephalography data with repetition time = 100 msec enables highly accurate analysis of the spread of activity between brain networks. Sixteen resting-state networks (RSNs) with the highest spatial correlation between NT individuals (n = 20) and individuals with ASD (n = 20) were analyzed. The dynamic lag pattern variation between each RSN pair was investigated using DLA, which measures time lag variation between each RSN pair combination and statistically defines how these lag patterns are altered between ASD and NT groups. DLA analyses indicated that 10.8% of the 120 RSN pairs had statistically significant (P-value <0.003) dynamic lag pattern differences that survived correction with surrogate data thresholding. Alterations in lag patterns were concentrated in salience, executive, visual, and default-mode networks, supporting earlier findings of impaired brain connectivity in these regions in ASD. 92.3% and 84.6% of the significant RSN pairs revealed shorter mean and median temporal lags in ASD versus NT, respectively. Taken together, these results suggest that altered lag patterns indicating atypical spread of activity between large-scale functional brain networks may contribute to the ASD phenotype. Autism Res 2020, 13: 244-258. © 2019 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc. LAY SUMMARY: Autism spectrum disorder (ASD) is characterized by atypical neurodevelopment. Using an ultra-fast neuroimaging procedure, we investigated communication across brain regions in adults with ASD compared with neurotypical (NT) individuals. We found that ASD individuals had altered information flow patterns across brain regions. Atypical patterns were concentrated in salience, executive, visual, and default-mode network areas of the brain that have previously been implicated in the pathophysiology of the disorder.

Attachment-specific speech patterns induce dysphoric mood changes in the listener as a function of individual differences in attachment characteristics and psychopathology.

OBJECTIVES: Early childhood experiences influence cognitive-emotional development, with insecure attachment predisposing to potential psychopathologies. We investigated whether narratives containing attachment-specific speech patterns shape listeners' emotional responses and social intentions. DESIGN: First, 149 healthy participants listened to three narratives characteristic for secure, insecure-preoccupied, and insecure-dismissing attachment. Following each narrative, the well-being and interpersonal reactivity as a particular aspect of emotional reactivity of the listener were assessed. Likewise, psychopathological aspects of personality were evaluated. A follow-up study compared 10 psychosomatic patients with a current depressive episode and/or personality disorder with distinct depressive symptoms and 10 age- and gender-matched healthy controls. METHODS: Effects of narratives on listeners' mental state were tested with repeated-measures AN(C)OVA. Mediating effects in the listener (attachment characteristics in the context of personality traits) were explored. Narrative effects were compared between patients and controls. RESULTS: Listening to insecure attachment narratives reduced well-being in controls. Nevertheless, tendency for social interaction was highest following the insecure-preoccupied narrative. Importantly, listeners' individual attachment characteristics mediated the relationship between well-being/interpersonal reactivity following the insecure-preoccupied narrative and levels of psychopathology. Furthermore, compared with healthy participants, patients showed higher emotional reactivity following exposure to the insecure-preoccupied narrative, represented by lower well-being and lower estimation of friendliness towards the narrator. CONCLUSIONS: Exposure to attachment-specific speech patterns can result in dysphoric mood changes. Specifically, the insecure-preoccupied narrative influenced the listeners' emotional state, which was further mediated by the individual attachment patterns and psychopathological personality characteristics. This deepens the understanding of interpersonal processes, especially in psychotherapeutic settings. PRACTITIONER POINTS: In clinical populations, insecure-preoccupied attachment has a high prevalence. In this study, listening to a narrative characteristic of insecure-preoccupied speech patterns resulted in reduced well-being in healthy listeners. Patients with depressive symptoms showed a higher emotional reactivity towards the insecure-preoccupied narrative compared to healthy controls. While working on (childhood) traumata, for example, in group therapy or inpatient settings, therapists should raise awareness to possible mood changes through discourse-conveyed attachment characteristics in listeners as a 'side effect'.

Alterations in Brain Structure and Amplitude of Low-frequency after 8 weeks of Mindfulness Meditation Training in Meditation-Naïve Subjects.

Increasing neuroimaging evidence suggests that mindfulness meditation expertise is related to different functional and structural configurations of the default mode network (DMN), the salience network (SN) and the executive network at rest. However, longitudinal studies observing resting network plasticity effects in brains of novices who started to practice meditation are scarce and generally related to one dimension, such as structural or functional effects. The purpose of this study was to investigate structural and functional brain network changes (e.g. DMN) after 40 days of mindfulness meditation training in novices and set these in the context of potentially altered depression symptomatology and anxiety. We found overlapping structural and functional effects in precuneus, a posterior DMN region, where cortical thickness increased and low-frequency amplitudes (ALFF) decreased, while decreased ALFF in left precuneus/posterior cingulate cortex correlates with the reduction of (CES-D) depression scores. In conclusion, regional overlapping of structural and functional changes in precuneus may capture different components of the complex changes of mindfulness meditation training.

Glutamate in Salience Network Predicts BOLD Response in Default Mode Network During Salience Processing.

BACKGROUND: Brain investigations identified salience network (SN) comprising the dorsal Anterior Cingulate Cortex (dACC) and the Anterior Insula (AI). Magnetic resonance spectroscopy (MRS) studies revealed the link between the glutamate concentration in the ACC and alterations in attentional scope. Hence, we investigated whether glutamate concentration in the dACC modulates brain response during salience processing. METHODS: Twenty-seven healthy subjects (12♀, 15♁) provided both STEAM MRS at 7T measuring glutamate concentrations in the dACC as well as a functional magnetic resonance imaging (fMRI) task to study the influence on content-related salience processing and expectedness. Salience was modulated for both sexual and non-sexual emotional photos in either expected or unexpected situations. Correlation between MRS and task fMRI was investigated by performing regression analyses controlling for age, gender, and gray matter partial volume. RESULTS/CONCLUSION: During picture processing, the extent of deactivation in the Posterior Cingulate Cortex (PCC) was attenuated by two different salience attributions: sexual content and unexpectedness of emotional content. Our results indicate that stimulus inherent salience induces an attenuation of the deactivation in PCC, which is in turn balanced by higher level of glutamate in the dACC.

Diminished fronto-limbic functional connectivity in child sexual offenders.

BACKGROUND: Child sexual abuse and neglect have been related to an increased risk for the development of a wide range of behavioral, psychological, and sexual problems and increased rates of suicidal behavior. Contrary to the large amount of research focusing on the negative mental health consequences of child sexual abuse, very little is known about the characteristics of child sexual offenders and the neuronal underpinnings contributing to child sexual offending. METHODS AND SAMPLE: This study investigates differences in resting state functional connectivity (rs-FC) between non-pedophilic child sexual offenders (N = 20; CSO-P) and matched healthy controls (N = 20; HC) using a seed-based approach. The focus of this investigation of rs-FC in CSO-P was put on prefrontal and limbic regions highly relevant for emotional and behavioral processing. RESULTS: Results revealed a significant reduction of rs-FC between the right centromedial amygdala and the left dorsolateral prefrontal cortex in child sexual offenders compared to controls. CONCLUSION & RECOMMENDATIONS: Given that, in the healthy brain, there is a strong top-down inhibitory control of prefrontal over limbic structures, these results suggest that diminished rs-FC between the amygdala and the dorsolateral prefrontal cortex and may foster sexual deviance and sexual offending. A profound understanding of these concepts should contribute to a better understanding of the occurrence of child sexual offending, as well as further development of more differentiated and effective interventions.

Sampling Rate Effects on Resting State fMRI Metrics.

Low image sampling rates used in resting state functional magnetic resonance imaging (rs-fMRI) may cause aliasing of the cardiorespiratory pulsations over the very low frequency (VLF) BOLD signal fluctuations which reflects to functional connectivity (FC). In this study, we examine the effect of sampling rate on currently used rs-fMRI FC metrics. Ultra-fast fMRI magnetic resonance encephalography (MREG) data, sampled with TR 0.1 s, was downsampled to different subsampled repetition times (sTR, range 0.3-3 s) for comparisons. Echo planar k-space sampling (TR 2.15 s) and interleaved slice collection schemes were also compared against the 3D single shot trajectory at 2.2 s sTR. The quantified connectivity metrics included stationary spatial, time, and frequency domains, as well as dynamic analyses. Time domain methods included analyses of seed-based functional connectivity, regional homogeneity (ReHo), coefficient of variation, and spatial domain group level probabilistic independent component analysis (ICA). In frequency domain analyses, we examined fractional and amplitude of low frequency fluctuations. Aliasing effects were spatially and spectrally analyzed by comparing VLF (0.01-0.1 Hz), respiratory (0.12-0.35 Hz) and cardiac power (0.9-1.3 Hz) FFT maps at different sTRs. Quasi-periodic pattern (QPP) of VLF events were analyzed for effects on dynamic FC methods. The results in conventional time and spatial domain analyses remained virtually unchanged by the different sampling rates. In frequency domain, the aliasing occurred mainly in higher sTR (1-2 s) where cardiac power aliases over respiratory power. The VLF power maps suffered minimally from increasing sTRs. Interleaved data reconstruction induced lower ReHo compared to 3D sampling (p < 0.001). Gradient recalled echo-planar imaging (EPI BOLD) data produced both better and worse metrics. In QPP analyses, the repeatability of the VLF pulse detection becomes linearly reduced with increasing sTR. In conclusion, the conventional resting state metrics (e.g., FC, ICA) were not markedly affected by different TRs (0.1-3 s). However, cardiorespiratory signals showed strongest aliasing in central brain regions in sTR 1-2 s. Pulsatile QPP and other dynamic analyses benefit linearly from short TR scanning.

Dorsal and Ventral Posterior Cingulate Cortex Switch Network Assignment via Changes in Relative Functional Connectivity Strength to Noncanonical Networks.

The posterior cingulate cortex (PCC) is often used as a seed region for probing default-mode network (DMN) connectivity. However, there is evidence for a functional segregation between its dorsal (dPCC) and ventral (vPCC) subregions, which suggests differential involvements of d-/vPCC in regulating cognitive demands. Our paradigm included functional magnetic resonance imaging measures for baseline resting state, affective or cognitive tasks, and post-task resting states. We investigated the effect of task demands on intra-PCC coupling and d-/vPCC network assignment to major intrinsic connectivity networks (ICNs), which was estimated via edge weights of a graph network encompassing DMN, dorsal-attention network, and central-executive network (CEN). Although PCC subregions were functionally coupled during both resting-state conditions and cognitive tasks, they decoupled during affective stimulation. For dPCC, functional connectivity strength (FCS) to CEN was higher than to the other two ICNs; whereas for vPCC, FCS to DMN was the highest. We, hence, defined CEN and DMN as the canonical networks at rest for dPCC and vPCC, respectively. Switching from rest to affective stimulation, however, induced the strongest effects to relative network assignments between non-canonical networks of dPCC and vPCC. Although vPCC showed a durable functional connectivity (FC) to DMN, dPCC played a crucial role during switches of between-network FC depending on cognitive versus affective task requirements. Our results underline that it is crucial for future seed-based FC studies to consider these two subregions separately in terms of seed location and discussion of findings. Finally, our findings highlight the functional importance of connectivity changes toward regions outside the canonical networks.

Breath hold effect on cardiovascular brain pulsations - A multimodal magnetic resonance encephalography study.

Ultra-fast functional magnetic resonance encephalography (MREG) enables separate assessment of cardiovascular, respiratory, and vasomotor waves from brain pulsations without temporal aliasing. We examined effects of breath hold- (BH) related changes on cardiovascular brain pulsations using MREG to study the physiological nature of cerebrovascular reactivity. We used alternating 32 s BH and 88 s resting normoventilation (NV) to change brain pulsations during MREG combined with simultaneously measured respiration, continuous non-invasive blood pressure, and cortical near-infrared spectroscopy (NIRS) in healthy volunteers. Changes in classical resting-state network BOLD-like signal and cortical blood oxygenation were reproduced based on MREG and NIRS signals. Cardiovascular pulsation amplitudes of MREG signal from anterior cerebral artery, oxygenated hemoglobin concentration in frontal cortex, and blood pressure decreased after BH. MREG cardiovascular pulse amplitudes in cortical areas and sagittal sinus increased, while cerebrospinal fluid and white matter remained unchanged. Respiratory centers in the brainstem - hypothalamus - thalamus - amygdala network showed strongest increases in cardiovascular pulsation amplitude. The spatial propagation of averaged cardiovascular impulses altered as a function of successive BH runs. The spread of cardiovascular pulse cycles exhibited a decreasing spatial similarity over time. MREG portrayed spatiotemporally accurate respiratory network activity and cardiovascular pulsation dynamics related to BH challenges at an unpreceded high temporal resolution.