A groundbreaking study by researchers at Massachusetts General Hospital and Boston Children’s Hospital has mapped a brain network crucial to human consciousness. Using advanced high-resolution imaging, the team discovered previously unexplored pathways connecting various regions of the brain, forming what they call the “default ascending arousal network” (DAAN). This network plays a central role in maintaining wakefulness and integrating wakefulness and consciousness in the resting human brain.
The results were published in Scientific translational medicine.
Understanding human consciousness, particularly its disturbances in conditions such as coma, vegetative states, and minimally conscious states, has been a long-standing challenge. Consciousness consists of two main elements: arousal, which is the state of awareness, and consciousness, which involves the content of consciousness. These components can be dissociated, as seen in patients who exhibit a state of wakefulness without consciousness, such as those in a vegetative state.
The researchers aimed to fill knowledge gaps about the subcortical pathways that contribute to arousal and how these integrate with cortical pathways related to consciousness. In doing so, they hoped to provide clinicians with better tools to detect, predict and facilitate recovery of consciousness in patients with severe brain injuries.
The study data comes from ex vivo brain samples (postmortem) from three neurologically normal individuals and in vivo (live) 7 Tesla MRI of 84 healthy controls, from the Human Connectome project. The ex vivo brain samples provided a detailed anatomical map, while the in vivo data verified the functional connectivity of these anatomical pathways.
One of the main findings of the study was the identification of 18 nodes within the DAAN that are interconnected via specific projection pathways. These pathways facilitate communication between the brainstem and higher brain regions, thereby forming a structural basis for maintaining wakefulness.
The ventral tegmental area (VTA), in particular, has emerged as an important hub within this network, showing extensive connectivity with the cortical default mode network (DMN), involved in self-awareness and consciousness. other higher cognitive functions. This suggests that dopaminergic pathways in the VTA are essential for modulating arousal and integrating it with consciousness, thereby providing a neuroanatomical basis for the conscious state.
“Our goal was to map a human brain network critical to consciousness and provide clinicians with better tools to detect, predict and promote recovery of consciousness in patients with severe brain injury,” explained lead author Brian Edlow , co-director of the study. of Mass General Neuroscience, Associate Director of the Center for Neurotechnology and Neurorecovery (CNTR) at Mass General, Associate Professor of Neurology at Harvard Medical School, and Chen Institute MGH Fellow 2023-2028.
Edlow continued: “Our connectivity results suggest that stimulation of dopamine pathways in the ventral tegmental area has the potential to help patients recover from coma, as this central node is connected to many brain regions that are essential to consciousness.
Lead author Hannah Kinney, professor emeritus at Boston Children’s Hospital and Harvard Medical School, added that “the human brain connections we identified can be used as a road map to better understand a wide range of associated neurological disorders.” to altered consciousness, from coma to convulsions, to sudden infant death syndrome (SIDS).
While the study offers groundbreaking insights, it also has limitations. The small sample size of three ex vivo brain samples means that further research with larger samples is needed to confirm these results. Additionally, the imaging resolution of the study, although high, is still not sufficient to accurately map individual axons. The results should therefore be considered inferential rather than definitive.
The study, “Multimodal MRI Reveals Brainstem Connections That Support Arousal in Human Consciousness,” was authored by Brian L. Edlow, Mark Olchanyi, Holly J. Freeman, Jian Li, Chiara Maffei, Samuel B. Snider, Lilla Zöllei, J. Eugenio. Iglesias, Jean Augustinack, Yelena G. Bodien, Robin L. Haynes, Douglas N. Greve, Bram R. Diamond, Allison Stevens, Joseph T. Giacino, Christophe Destrieux, Andre van der Kouwe, Emery N. Brown, Rebecca D. Folkerth , Bruce Fischl and Hannah C. Kinney.
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