Human Brain Mapping
January 24, 2008
Lucina Q. Uddin, A.M. Clare Kelly, Bharat B. Biswal et al.
1,198 citations
The default mode network (DMN), which is most active when the mind is at rest, is often treated as a single system, but its two main hubs—the ventromedial prefrontal cortex (vmPFC) and the posterior cingulate cortex (PCC)—interact with different task-focused brain networks. Using resting-state fMRI and a seed correlation approach, activity in vmPFC negatively predicted activity in networks for visual spatial and temporal attention, while activity in PCC negatively predicted activity in motor control circuits. Granger causality analyses indicated that vmPFC and PCC exert greater influence on their anticorrelated networks than the reverse, suggesting these DMN nodes may directly modulate task-positive networks. The DMN is thus more heterogeneous than commonly appreciated.
Human Brain Mapping
July 3, 2014
Enzo Tagliazucchi, Robin Carhart‐Harris, Robert Leech et al.
423 citations
Psilocybin, the active compound in magic mushrooms, increases the variability and range of brain activity and connectivity. Using fMRI, fifteen healthy volunteers were scanned before, during, and after receiving psilocybin or a placebo. Psilocybin raised the variability of blood-oxygen-level-dependent signals in the hippocampi and anterior cingulate cortex. Changes in the spectral behavior of brain signals were limited to higher-order networks, including the default mode, executive control, and dorsal attention networks. The brain also explored a wider repertoire of connectivity states after psilocybin than under control conditions. These findings help explain the unconstrained, hyper-associative quality of consciousness in the psychedelic state.
Human Brain Mapping
May 22, 2015
Alexander V. Lebedev, Martin Lövdén, Gidon Rosenthal et al.
347 citations
Psilocybin, the active compound in magic mushrooms, produces ego-dissolution—a feeling that the self is disintegrating or that the boundary between self and world is dissolving—similar to ego-disturbances seen in schizophrenia. In a placebo-controlled study of 15 healthy volunteers, functional MRI scans showed that psilocybin-induced ego-dissolution was linked to decreased connectivity between the medial temporal lobe and high-level cortical regions, disintegration of the salience network, and reduced communication between brain hemispheres. Individuals with lower diversity of executive network nodes at baseline were more likely to experience ego-dissolution. These findings suggest that maintaining a coherent sense of self depends on normal functioning of these brain systems.
Human Brain Mapping
September 16, 2011
Dráulio Barros de Araújo, Sidarta Ribeiro, Guillermo Cecchi et al.
241 citations
Ayahuasca, a hallucinogenic brew containing serotonergic agonists and reuptake inhibitors, triggers vivid visual imagery during ceremonies. Using functional magnetic resonance imaging while participants performed a closed-eyes imagery task, the brew produced a robust increase in activation across occipital, temporal, and frontal brain areas. In the primary visual area, activation levels matched those of natural image viewing with eyes open. This effect correlated with individual perceptual changes measured by psychiatric scales. Activity in areas BA30 and BA37, linked to episodic memory and contextual associations, was also potentiated. Modulation of BA10, involved in prospective imagination and working memory, was detected. The findings suggest Ayahuasca seeings arise from an extensive network for vision, memory, and intention, lending a sense of reality to inner experiences.
Human Brain Mapping
October 14, 2016
Samantha Cunningham, Dardo Tomasi, Nora D. Volkow
221 citations
The precuneus and thalamus show strong structural and functional connections to each other and to the default mode network (DMN). Using diffusion tensor imaging and resting-state functional connectivity in 37 healthy adults, structural connectivity was greatest between the precuneus and thalamus, and connection fractional anisotropy increased with age. The precuneus also connected structurally to the hippocampus and middle prefrontal cortex but minimally to the angular gyrus and midcingulate cortex. Functionally, the precuneus connected most strongly with the angular gyrus.
Human Brain Mapping
August 27, 2001
Edi Frei, Alex Gamma, Roberto D. Pascual‐marqui et al.
175 citations
A single dose of MDMA (1.7 mg/kg) in 16 healthy, MDMA-naïve volunteers produced widespread decreases in slow and medium frequency brain activity and increases in fast frequency activity in the anterior temporal and posterior orbital cortex, as measured by scalp EEG and low resolution brain electromagnetic tomography (LORETA). These changes were accompanied by heightened mood, emotional arousal, and increased extraversion. The EEG pattern suggests that serotonin, noradrenaline, and, to a lesser degree, dopamine contribute to MDMA's effects on brain activity and possibly mood and behavior, indicating modulation of limbic orbitofrontal and anterotemporal structures involved in emotional processes.
Human Brain Mapping
October 4, 2018
Annemarie Wolff, Daniel A. di Giovanni, Javier Gómez‐Pilar et al.
135 citations
Private self-consciousness—the tendency to focus on one's inner thoughts and feelings—is linked to specific temporal patterns in the brain's resting state activity. In an EEG study, higher scores on the Private dimension of the Self-Consciousness Scale correlated with three measures of resting state activity: a steeper power-law exponent (PLE), a longer auto-correlation window (ACW), and a stronger modulation index (MI). These temporal features reflect how self-related information is temporally nested, continuous, and integrated in spontaneous brain activity. Source localization further linked Private self-consciousness to activity in cortical midline structures, including the perigenual anterior cingulate cortex and posterior cingulate cortex. A machine learning algorithm could accurately classify individuals as having high or low Private self-consciousness based on these spatiotemporal measures.
Human Brain Mapping
February 10, 2009
Alexandre R. Franco, Aaron Pritchard, Vince D. Calhoun et al.
129 citations
Near perfect agreement was found between human raters selecting the default mode network (DMN) component from resting-state fMRI data, but agreement between human raters and an automated template-matching method was only moderate. The automated method's performance improved significantly when a weighted combination of anterior and posterior cingulate nodes was used. The study involved 42 healthy controls and compared interrater and intermethod reliability for identifying DMN activation, highlighting the need for careful template design in automated component selection.
Human Brain Mapping
May 7, 2019
Michiel van Elk, M. Andrea Arciniegas Gomez, Wietske van der Zwaag et al.
122 citations
Watching awe-inspiring videos reduces activity in brain regions linked to self-focused thinking, such as the frontal pole, angular gyrus, and posterior cingulate cortex, which are part of the default mode network. In contrast, regions of the fronto-parietal network, including the supramarginal gyrus, medial frontal gyrus, and insula, become more active when people analytically count perspective changes while viewing awe videos. These findings suggest that awe diminishes self-referential processing, consistent with participants reporting feeling their self was smaller.
Human Brain Mapping
January 1, 1995
Karl Friston, Giulio Tononi, Olaf Sporns et al.
114 citations
Neuronal interactions in the brain balance two opposing organizational principles: functional segregation, where specialized cortical areas exhibit relatively high entropy (unpredictable dynamics), and functional integration, where distributed influence across areas produces lower entropy overall. A measure of complexity is highest when small brain regions have high entropy on average relative to the whole system's entropy, equivalent to the average mutual information between small regions and the rest of the system. Applied to nonlinear simulations and fMRI data during photic stimulation, complexity peaked between high-dimensional chaotic behavior and low-dimensional orderly behavior—between asynchronous oscillations and global synchrony—confirming the hypothesis.
Human Brain Mapping
July 1, 2013
Zirui Huang, Rui Dai, Xuehai Wu et al.
104 citations
Patients with disorders of consciousness (DOC) show reduced brain activity in midline regions (anterior and posterior cingulate cortex) during self-referential thinking tasks compared to healthy individuals. The degree of signal reduction in the perigenual anterior cingulate cortex predicts their level of consciousness. These same midline regions also display abnormal resting-state functional connectivity and low-frequency fluctuations. The findings link self-referential processing, resting-state brain activity, and consciousness, suggesting that neural abnormalities in these areas contribute to DOC.
Human Brain Mapping
July 22, 2020
Ivar R. Kolvoort, Soren Wainio‐Theberge, Annemarie Wolff et al.
92 citations
The self integrates information across time, but how this psychological temporal integration relates to neuronal temporal integration is unclear. In a modified self-matching task with temporal delays, participants showed a self-prioritization effect—greater accuracy for self-related stimuli—across all delay conditions, indicating stronger temporal integration of self-related information. Resting-state EEG measures of scale-free dynamics (power law exponent and autocorrelation window) indexed neuronal temporal integration. Higher neuronal integration was associated with a stronger increase in the self-prioritization effect over longer delays. Temporal integration on the neuronal level appears to serve as a template for psychological-level self-integration, suggesting it acts as a common currency linking neuronal and psychological aspects of self.
Human Brain Mapping
February 25, 2016
Milan Scheidegger, A Henning, Martin Walter et al.
78 citations
Ketamine, an NMDA receptor antagonist, reduced neural reactivity in the bilateral amygdalo-hippocampal complex during emotional stimulation in 23 healthy subjects. Reduced amygdala reactivity to negative pictures correlated with resting-state connectivity to the pregenual anterior cingulate cortex. The intensity of psychedelic alterations of consciousness during ketamine infusion predicted the reduction in neural responsivity to negative but not to positive or neutral stimuli. These findings suggest that modulation of glutamate-responsive circuits, associated with a shift in emotional bias and reduced amygdalo-hippocampal reactivity, may represent an early mechanism to restore disrupted neurobehavioral homeostasis in major depressive disorder.
Human Brain Mapping
May 8, 2008
Melanie Boly, Christophe Phillips, Evelyne Balteau et al.
73 citations
Variability in how people perceive the same sensory stimulus from one moment to the next may stem from ongoing fluctuations in baseline brain activity. This review examines evidence that activity levels in sensory brain areas before a stimulus predict whether that stimulus will be consciously perceived. The findings are discussed in the context of recent discoveries about the structure of spontaneous BOLD signal fluctuations in the awake human brain, and possible sources of these baseline fluctuations are considered.
Human Brain Mapping
March 19, 2021
Andrea I. Luppi, Daniel Golkowski, Andreas Ranft et al.
72 citations
The human brain alternates between states of high integration and segregation, which are thought to support consciousness. Using dynamic functional connectivity and graph theory on resting-state fMRI data from healthy volunteers, the authors show that the integrated state is especially vulnerable to the anaesthetic sevoflurane. At higher doses (3% vol and burst-suppression), anaesthesia reduces the complexity and small-world character of integrated brain states and disrupts the temporal balance between integration and segregation. These effects reverse upon recovery, linking them to consciousness. Reduced anticorrelations between the default mode and executive control networks also reconfigure dynamically depending on the brain's integration state. The breakdown of the integrated sub-state may serve as a generalisable biomarker of loss and recovery of consciousness.
Human Brain Mapping
September 18, 2019
Norman Zacharias, Francesco Musso, Felix Müller et al.
70 citations
Resting-state brain activity is not steady but dynamic, with vigilance fluctuations playing a key role. In a randomized, double-blind, placebo-controlled crossover study of 24 healthy young adults, subanesthetic S-ketamine decreased functional connectivity in the medial prefrontal cortex and increased connectivity in intraparietal cortices, measured with simultaneous EEG-fMRI. Ketamine also shifted EEG power toward slow (delta, theta) and fast (gamma) frequencies. Frontal connectivity negatively related to EEG gamma and theta activity, while parietal connectivity positively related to delta power. These results indicate a direct link between ketamine-induced connectivity changes and reduced vigilance, offering potential surrogate endpoints for understanding ketamine's antidepressant effects.
Human Brain Mapping
January 28, 2018
Jianfeng Zhang, Zirui Huang, Yali Chen et al.
70 citations
During anesthetic-induced unconsciousness, two temporal features of brain activity—long-range temporal correlations (measured by power-law exponent) and temporal variability (measured by standard deviation)—both decrease globally across the brain compared to wakefulness. The spatial relationship between these two features becomes altered, or 'decoupled,' primarily due to changes in the spatial pattern of long-range temporal correlations rather than temporal variability. This suggests that the topographical organization of long-range temporal correlations is crucial for maintaining optimal neural dynamics during normal consciousness, supporting the temporo-spatial theory of consciousness.
Human Brain Mapping
November 6, 2013
Patrícia Bado, Annerose Engel, Ricardo de Oliveira‐souza et al.
49 citations
Mind-wandering, which occupies much of daily life, often involves autobiographical recall and self-reflection. Brain imaging shows that a set of regions called the default mode network (DMN) is active during such spontaneous thought, but the roles of different cognitive components within the DMN were unclear. Using fMRI, researchers compared brain activity during emotional autobiographical memory recall, neutral memory recall, and resting wakefulness, with a subtraction task as a control. Both emotional recall and resting state activated shared DMN regions compared to the control.
Human Brain Mapping
August 21, 2020
Lukasz Smigielski, Michael Kometer, Milan Scheidegger et al.
42 citations
A placebo-controlled, double-blind experiment with 17 participants found that psilocybin, a serotonin receptor agonist, alters self-perception by disrupting the brain's ability to distinguish between self- and other-related stimuli. Participants performed a verbal self-monitoring task while brain activity was recorded. Psilocybin reduced accuracy in identifying whether auditory feedback was their own voice or another's, and it eliminated the typical difference in electrical brain patterns (P300) between self and other stimuli. This effect was linked to changes in the anterior cingulate and insular cortex. The strength of this brain change correlated with feelings of unity and altered meaning. The findings suggest that serotonin signaling modulates how the brain processes self-referential information, offering insight into self-disturbances in mental health conditions.
Human Brain Mapping
April 9, 2021
Obada Al Zoubi, Masaya Misaki, Jerzy Bodurka et al.
39 citations
A single 90-minute session of Floatation-REST, which minimizes sensory input, reduces resting-state functional connectivity within and between posterior hubs of the default-mode network and somatomotor cortices extending into the posterior insula. A control condition of resting in a zero-gravity chair produced a similar pattern of reduced connectivity. The findings suggest that reducing nervous system stimulation is reflected by decreased connectivity in brain networks that construct and map the sense of self.
Human Brain Mapping
July 29, 2022
Hang Zhang, Shiyou Yang, Yang Qiao et al.
27 citations
Spontaneous low-frequency fluctuations in sustained attention, which cause cognitive and behavioral lapses, originate in the default-mode network (DMN). Analysis of two independent fMRI and behavior datasets shows that neural fluctuations in the DMN mediate behavioral reaction-time fluctuations during sustained attention. The DMN's increased amplitude of fluctuation correlates with behavioral fluctuation specifically in the 0.01-0.1 Hz frequency range, not at lower or higher frequencies. This pattern appears during both auditory and visual sustained attention and replicates across datasets. These findings reveal the DMN as a neural source of attention fluctuation, extending the former view that the DMN is simply deactivated during cognitive tasks.
Human Brain Mapping
October 21, 2019
Bhim M. Adhikari, Juergen Dukart, Joerg F. Hipp et al.
24 citations
Ketamine, given at subanesthetic doses to healthy volunteers, produces psychosis-like symptoms and reduces functional connectivity in the salience network, auditory network, and default mode network (DMN). Midazolam, a sedative, only reduces DMN connectivity. The pattern of connectivity deficits caused by ketamine positively correlates with the pattern seen in schizophrenia, whereas midazolam's effects do not. After subtracting midazolam's effects, the remaining ketamine-specific disconnectivity pattern still correlates with schizophrenia deficits. This suggests that ketamine's psychosis-like effects have a brain functional basis that overlaps with schizophrenia-related connectivity disruptions.
Human Brain Mapping
January 30, 2023
B. Taraku, R. Woods, Michael Boucher et al.
23 citations
In treatment-resistant depression, four intravenous ketamine infusions (0.5 mg/kg) given over 2–3 days led to significant improvements in depression and anhedonia scores. Brain scans revealed decreased neurite density in occipitotemporal white matter pathways after treatment. Greater reductions in anhedonia correlated with decreased neurite density in the left internal capsule and left superior longitudinal fasciculus. No significant changes were seen in other white matter measures. The neurite orientation dispersion and density imaging model may detect ketamine-induced white matter changes more sensitively than standard diffusion tensor imaging.
Human Brain Mapping
December 6, 2019
Anna Forsyth, Rebecca McMillan, Doug Campbell et al.
19 citations
The validity of fMRI functional connectivity as a drug biomarker was tested by comparing seven preprocessing pipelines and by simultaneously measuring EEG and fMRI in a placebo-controlled, three-way crossover study with ketamine and midazolam. Independent components analysis (ICA)-denoising produced stronger reductions in connectivity after ketamine and weaker increases after midazolam than pipelines using physiological noise modelling or averaged signals from cerebrospinal fluid or white matter. This indicates that pipeline decisions should match a drug's unique noise structure; when unknown, extensive ICA denoising may sacrifice some signal but increase confidence in remaining results. No significant relationship was found between changes in electrophysiological and hemodynamic correlation structures, cautioning against cross-modal comparisons of pharmacologically-modulated functional connectivity.
Human Brain Mapping
January 11, 2019
Dea Siggaard Stenbæk, Sara Kristiansen, Daniel Burmester et al.
11 citations
Trait Openness, a personality dimension linked to curiosity and creativity, is not related to the availability of serotonin 2A receptors in the neocortex. In 159 healthy individuals, no significant association was found between receptor binding—measured with two different PET tracers—and scores on the NEO Personality Inventory-Revised. Sex did not influence the result. Although psilocybin, a serotonin 2A receptor agonist, can increase Openness, the receptor's baseline availability does not explain natural variation in this trait.