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The complementary structural and functional connectivity maps provide a neuroanatomic basis for integrating arousal and awareness in human consciousness. Credit: Neuroscience News

Key Consciousness Connections Uncovered

Summary: Using neuroimaging, researchers identified a brain network crucial to human consciousness. Using advanced multimodal MRI techniques, the team mapped connections among the brainstem, thalamus, and cortex, forming what they call the “default ascending arousal network,” which is vital for sustaining wakefulness.

Their research not only enhances our understanding of consciousness but also aims to improve clinical outcomes for patients with severe brain injuries by providing new insights for targeted treatments. The findings could revolutionize approaches to various consciousness-related neurological disorders and have already spurred clinical trials aimed at reactivating consciousness in coma patients.

Key Facts:

  1. Advanced Imaging Techniques: The study utilized high-resolution multimodal MRI scans to visualize and map critical brain pathways at submillimeter spatial resolution, revealing connections that sustain human wakefulness.
  2. Functional Integration: Researchers linked the subcortical arousal network with the cortical default mode network, providing a comprehensive map of the networks involved in maintaining consciousness even during rest.
  3. Clinical Applications: The insights gained from this study are being applied in clinical trials, aiming to stimulate specific brain areas to help coma patients recover consciousness, showcasing the study’s direct impact on treatment strategies.

Source: Mass General

In a paper titled, “Multimodal MRI reveals brainstem connections that sustain wakefulness in human consciousness,” published today in Science Translational Medicine, a group of researchers at Massachusetts General Hospital, a founding member of the Mass General Brigham healthcare system, and Boston Children’s Hospital, created a connectivity map of a brain network that they propose is critical to human consciousness.

The study involved high-resolution scans that enabled the researchers to visualize brain connections at submillimeter spatial resolution.  This technical advance allowed them to identify previously unseen pathways connecting the brainstem, thalamus, hypothalamus, basal forebrain, and cerebral cortex. 

Together, these pathways form a “default ascending arousal network” that sustains wakefulness in the resting, conscious human brain.  The concept of a “default” network is based on the idea that specific networks within the brain are most functionally active when the brain is in a resting state of consciousness. In contrast, other networks are more active when the brain is performing goal-directed tasks. 

To investigate the functional properties of this default brain network, the researchers analyzed 7 Tesla resting-state functional MRI data from the Human Connectome Project. 

These analyses revealed functional connections between the subcortical default ascending arousal network and the cortical default mode network that contributes to self-awareness in the resting, conscious brain.

The complementary structural and functional connectivity maps provide a neuroanatomic basis for integrating arousal and awareness in human consciousness.  The researchers released the MRI data, brain mapping methods, and a new Harvard Ascending Arousal Network Atlas, to support future efforts to map the connectivity of human consciousness.

“Our goal was to map a human brain network that is critical to consciousness and to provide clinicians with better tools to detect, predict, and promote recovery of consciousness in patients with severe brain injuries,” explains lead-author Brian Edlow, MD, co-director of Mass General Neuroscience, associate director of the Center for Neurotechnology and Neurorecovery (CNTR) at Mass General, an associate professor of Neurology at Harvard Medical School and a Chen Institute MGH Research Scholar 2023-2028.

Dr. Edlow explains, “Our connectivity results suggest that stimulation of the ventral tegmental area’s dopaminergic pathways has the potential to help patients recover from coma because this hub node is connected to many regions of the brain that are critical to consciousness.”

Senior author Hannah Kinney, MD, Professor Emerita at Boston Children’s Hospital and Harvard Medical School, adds that “the human brain connections that we identified can be used as a roadmap to better understand a broad range of neurological disorders associated with altered consciousness, from coma, to seizures, to sudden infant death syndrome (SIDS).”

The authors are currently conducting clinical trials to stimulate the default ascending arousal network in patients with coma after traumatic brain injury, with the goal of reactivating the network and restoring consciousness. 

Disclosures: Disclosure forms provided by the authors are available with the full text of this article.

Funding: This study was funded in part by the James S. McDonnell Foundation, the National Institutes of Health, the American SIDS Institute, and the Chen Institute MGH Research Scholar Award.

About this consciousness and neuroscience research news

Author: Brandon Chase
Source: Mass General
Contact: Brandon Chase – Mass General
Image: The image is credited to Neuroscience News

Original Research: Closed access.
Multimodal MRI reveals brainstem connections that sustain wakefulness in human consciousness” by Brian Edlow et al. Science Translational Medicine


Multimodal MRI reveals brainstem connections that sustain wakefulness in human consciousness

Consciousness is composed of arousal (i.e., wakefulness) and awareness. Substantial progress has been made in mapping the cortical networks that underlie awareness in the human brain, but knowledge about the subcortical networks that sustain arousal in humans is incomplete.

Here, we aimed to map the connectivity of a proposed subcortical arousal network that sustains wakefulness in the human brain, analogous to the cortical default mode network (DMN) that has been shown to contribute to awareness.

We integrated data from ex vivo diffusion magnetic resonance imaging (MRI) of three human brains, obtained at autopsy from neurologically normal individuals, with immunohistochemical staining of subcortical brain sections.

We identified nodes of the proposed default ascending arousal network (dAAN) in the brainstem, hypothalamus, thalamus, and basal forebrain.

Deterministic and probabilistic tractography analyses of the ex vivo diffusion MRI data revealed projection, association, and commissural pathways linking dAAN nodes with one another and with DMN nodes.

Complementary analyses of in vivo 7-tesla resting-state functional MRI data from the Human Connectome Project identified the dopaminergic ventral tegmental area in the midbrain as a widely connected hub node at the nexus of the subcortical arousal and cortical awareness networks.

Our network-based autopsy methods and connectivity data provide a putative neuroanatomic architecture for the integration of arousal and awareness in human consciousness.

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