Cerebral Cortex
April 9, 2008
2,227 citations
Resting-state functional connectivity MRI, which measures correlated brain activity while a person lies quietly in a scanner, has been questioned as possibly reflecting noise rather than true neural connections. By combining diffusion tensor imaging tractography with resting-state functional connectivity MRI, this work tested whether the functional correlations correspond to actual structural pathways. Focusing on the default mode network—a set of brain regions involved in memory, including the medial prefrontal cortex, medial temporal lobes, and posterior cingulate/retrosplenial cortex—the analysis found that structural connections matched the functional connectivity maps. Medial temporal lobes connected to retrosplenial cortex, while medial prefrontal cortex connected to posterior cingulate cortex. The results demonstrate that resting-state functional connectivity reflects structural connectivity, and combining methods can deepen understanding of brain networks.
Cerebral Cortex
February 17, 2011
408 citations
As people fall asleep, the brain's default mode network (DMN) and its anticorrelated network (ACN) break down. In 25 healthy participants, functional connectivity between key brain regions—especially the posterior cingulate cortex, parahippocampal gyrus, and medial prefrontal cortex—decreased with deeper non-REM sleep. The loss of synchronization between the posterior and anterior midline nodes of the DMN, and between the DMN and ACN, suggests that preserved corticocortical connectivity is necessary for maintaining internal and external awareness. The posterior cingulate/retrosplenial cortex appears particularly important for regulating consciousness.
Cerebral Cortex
March 7, 2011
Elizabeth C. Mormino, Andre Smiljic, Amynta O. Hayenga et al.
349 citations
Beta-amyloid deposition, a hallmark of Alzheimer's disease, is also common in cognitively normal older adults. Using Pittsburgh compound-B PET imaging, the study found that greater beta-amyloid burden in normal controls is associated with altered functional connectivity within the default mode network during rest. Connectivity decreased in regions critical for episodic memory, including posteromedial cortex, ventral medial prefrontal cortex, and angular gyrus, while increases appeared in dorsal and anterior medial prefrontal and lateral temporal cortices. The decreases align with known vulnerability of memory-related areas in Alzheimer's disease, and the increases may reflect compensatory mechanisms.
Cerebral Cortex
April 24, 2012
Renaud Jardri, Pierre Thomas, Christine Delmaire et al.
180 citations
Hallucinations in psychosis may arise when the brain's default-mode network (DMN) disengages abnormally, similar to its response to real external stimuli. In 20 drug-free adolescents with brief psychotic disorder, multimodal MRI showed that during auditory, visual, and multisensory hallucinations, cortical thickness was reduced and blood oxygen level-dependent signal increased in modality-dependent association sensory cortices, while primary sensory cortex recruitment was not systematic and linked to greater vividness. DMN disengagement coincided with hallucinations, and spatial and temporal instabilities of the DMN correlated with hallucination severity and persisted even without symptoms. This suggests hallucinations emerge from spontaneous DMN withdrawal, offering a model beyond the auditory modality.
Cerebral Cortex
June 21, 2018
173 citations
The default mode network (DMN) is typically thought to support internally focused thought, but a new brain imaging study shows it also activates during certain external task switches. Using fMRI, 24 participants performed a task-switching experiment. The DMN increased activity not only during task switches, replicating prior findings, but also during brief rests and task restarts after rest. These results challenge theories that restrict DMN function to internal or self-directed cognition. The authors propose that the DMN encodes scene, episode, or context by integrating spatial, self-referential, and temporal information. Context representations are strong at rest, but re-reference to context also occurs at major cognitive transitions.
Cerebral Cortex
November 10, 2004
G. Honey, R. Honey, C. O'Loughlin et al.
116 citations
Ketamine, a drug that blocks NMDA receptors, impairs episodic memory. Using fMRI, brain activity was measured in healthy volunteers during memory encoding and retrieval under two intravenous doses of ketamine in a double-blind, placebo-controlled, randomized, within-subjects design. Encoding and retrieval were separated across two study-test cycles to isolate drug effects on each process. Results suggest that ketamine increases left frontal activation when elaborative semantic processing is needed during encoding, and successful encoding on the drug relies on additional incidental non-verbal processing. At retrieval, ketamine appears to impair access to contextual features of studied items. Even when behavior appears normal, ketamine alters recruitment of key brain regions for episodic memory.
Cerebral Cortex
August 8, 2012
André Schmidt, Andreea O. Diaconescu, Michael Kometer et al.
110 citations
Using dynamic causal modeling and Bayesian model selection on data from a double-blind, placebo-controlled, crossover ketamine study, the authors investigated how the NMDA-receptor antagonist ketamine reduces mismatch negativity (MMN) amplitudes. Guided by a predictive coding framework that unifies adaptation and model adjustment theories, they compared models allowing different expressions of neuronal adaptation and synaptic plasticity. Results replicated that both adaptation and short-term plasticity are necessary for MMN generation. Ketamine significantly affected synaptic plasticity but not adaptation, with a selective effect on the forward connection from left primary auditory cortex to superior temporal gyrus. This model-based estimate of ketamine's effect on synaptic plasticity correlated with ratings of ketamine-induced impairments in cognition and control, suggesting a concrete mechanism linking ketamine effects on MMN to drug-induced psychopathology.
Cerebral Cortex
May 14, 2018
Lisa Miller, Iris M. Balodis, Clayton H. Mcclintock et al.
65 citations
People across cultures and throughout history report spiritual experiences that involve a sense of union transcending the ordinary self, but their neural mechanisms are poorly understood. Using an individualized guided-imagery task, the authors compared brain activity during personally meaningful spiritual experiences with that during stressful and neutral-relaxing experiences. During spiritual experiences, the left inferior parietal lobule showed reduced activity compared to neutral-relaxing experiences, suggesting this region contributes to perceptual processing and self-other representations. Compared to stress cues, spiritual cues reduced activity in the medial thalamus and caudate, regions linked to sensory and emotional processing. The findings point to neural mechanisms underlying broadly defined, personally experienced spirituality.
Cerebral Cortex
June 10, 2021
Patricia Duerler, Silvia Brem, Gorka Fraga González et al.
64 citations
Psilocybin reduces brain responses to surprising tactile stimuli, altering the sense of body and self. In a combined EEG-fMRI study, psilocybin decreased activity in frontal regions, visual cortex, and cerebellum during unexpected touch, and reduced mismatch negativity signals at frontal electrodes. These changes were linked to altered body- and self-experience. The findings highlight the role of the 5-HT2A receptor system in processing unexpected bodily sensations and integrating them with self-awareness, which may inform treatments for psychiatric disorders involving distorted body perception.
Cerebral Cortex
July 16, 2013
Fosco Bernasconi, André Schmidt, Thomas Pokorny et al.
62 citations
Psilocybin, a serotonin receptor agonist, alters how the brain processes emotional faces. Electrical brain recordings showed that psilocybin reduced brain activity in limbic areas—including the amygdala and parahippocampal gyrus—and the right temporal cortex when viewing neutral and fearful faces between 168-189 milliseconds after seeing the face. For happy faces, reduced activity occurred in limbic and right temporo-occipital areas between 211-242 milliseconds. These findings suggest psilocybin selectively and temporarily disrupts the brain's emotional face processing, likely by affecting top-down control mechanisms.
Cerebral Cortex
September 12, 2017
Frederick S. Barrett, Katrin H. Preller, Marcus Herdener et al.
52 citations
Classic psychedelic drugs that activate serotonin 2A receptors alter how the brain responds to the changing tonal structure of music. In 25 healthy adults, brain imaging after placebo, LSD, and LSD combined with a serotonin 2A blocker showed that serotonin 2A signaling changes neural activity in regions for basic and higher-level music processing, memory, emotion, and self-referential thought. This signaling appears critical for tracking musical tonality and for the heightened emotionality, connectedness, and meaningfulness people often report after taking psychedelics. The findings clarify the neuropsychopharmacology of music perception and why music can feel profoundly altered during psychedelic experiences.
Cerebral Cortex
September 6, 2018
Gregory M. James, Gregor Gryglewski, Thomas Vanicek et al.
16 citations
The cerebral cortex can be divided into distinct areas based on the density of proteins involved in the serotonin system. Using positron emission tomography in healthy participants, the study quantified serotonin 1A receptors (n = 30), 5-HT2A receptors (n = 22), the serotonin-degrading enzyme monoamine oxidase A (n = 32), and the serotonin transporter (n = 24). Clustering analysis identified five optimal clusters of cortical regions defined by these molecular profiles. These clusters explained the effects of psychotropic drugs acting on serotonin, such as antidepressants and psychedelics, suggesting the method is useful for integrating multimodal imaging data in neuropharmacology and psychiatry.