A brain imaging study suggests that loss of consciousness is associated with the dysfunction of two neural circuits

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A team of scientists recently aimed to gain a better understanding of consciousness and its pathologies by studying the neural activity of patients with disorders of consciousness and healthy volunteers using brain imaging technology. They identified two critical brain circuits involved in consciousness. The results of the study are published in Mapping the Human Brain.

Conscience is a complex, subjective experience, and its nature and origins are still the subject of much debate among scientists and philosophers. However, in clinical settings, doctors dealing with patients with severe brain injuries and vision disorders must find ways to help their patients, regardless of the exact definition of vision. The authors of the new study sought to better understand the mechanisms behind the pathological loss of consciousness and its recovery, as well as to have reliable ways to assess the condition of patients.

“In recent years, many studies have attempted to objectively assess levels of consciousness using various neuroimaging techniques. Although these studies improved the way we diagnose patients with disorders of consciousness, they did not fully explain how consciousness occurs,” explained study author Jitka Annen, a postdoctoral researcher at the Coma Science Group at the University of Liege.

“With this work, we wanted to characterize how stimulation (or disturbances in ongoing activity) affects the flow of neural activity in different states of reduced consciousness after brain injury. By doing this, insights are gained into how regions receive activity from and transmit activity to other brain regions, or how some subjects can maintain consciousness while others cannot. In short, we tried to better understand the difference between the flow of information in different states of consciousness.”

To achieve these goals, the researchers used neuroimaging methods, particularly functional magnetic resonance imaging (fMRI), to study brain activity in patients with disorders of consciousness and healthy volunteers. They focused on how external disturbances, such as sensory stimuli or artificial stimulation, propagate through the brain in various states of reduced consciousness. By observing these brain dynamics, they aimed to understand how information flows in the brain and how different regions interact with each other during consciousness and altered states of consciousness.

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For the study, they included subjects with disorders of consciousness after severe brain injury (such as those in a minimally conscious state and unresponsive wakefulness syndrome) and healthy control volunteers without neurological problems. They performed behavioral assessments and used glucose PET scans to confirm the diagnosis of disorders in conscious patients. ​​​​The researchers obtained structural and functional MRI data from all participants.

Using the fMRI data, the team studied the propagation of exogenous (spontaneous) and in-silicon (model-based) disturbances in the brains of patients with disorders of consciousness. They estimated direct and causal interactions between brain regions based on resting-state fMRI data and related them to a linear model of activity propagation.

The researchers found that patients with disorders of consciousness had malfunctioning neural circuits in their brains. These circuits failed to communicate and integrate information properly, resulting in a lack of consciousness.

In healthy individuals, they found that specific brain regions were responsible for transmitting and receiving information, which is crucial for conscious perception. However, in patients with unresponsive awakening syndrome (UWS), the brain’s ability to transmit and integrate information was severely impaired. They observed a rapid decline in brain activity and reduced connectivity between brain regions, leading to a lack of conscious perception.

For patients in a minimally conscious state, who had partially regained consciousness, some of these brain functions improved, indicating that certain brain regions were regaining their ability to process and integrate information.

“The brains of patients with a disorder of consciousness have inhibited their ability to respond to events,” Annen told PsyPost. “And when events reach the cortex, their activity does not propagate successfully to other cortical areas for further processing. In healthy volunteers, brain regions are embedded in specialized networks.”

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“Specifically, the posterior part of the brain (back of the brain, receiving sensory information) and thalamus (inner part of the brain functioning as a gateway between the body and the brain) are specialized to integrate the flow of activity in front and temporal (lateral). cortical regions (responsible for various cognitive processes) are specialized to propagate event activity.”

“This functional specialization appears to be lost in unconscious patients. All regions behave the same, and activity is not sustained long enough for the relevant regions to process it. In patients who show minimal consciousness, these symptoms of functional neural processing recover.”

The study also found that the brain’s glucose consumption (measured via PET scans) was directly related to how well it processed six stimuli. In other words, when the brain’s glucose metabolism was higher, it showed a better ability to respond and effectively process information. This suggests that the brain’s ability to process information is closely linked to its overall health.

“Stimulus processing was proportional to the brain’s sugar consumption, a very strong measure of neural integrity,” Annen said. “While this might be expected, it is remarkable to me that the relationship is so direct especially since the glucose consumption data comes from completely different brain scans in the same subjects.”

The study provides important insights into the mechanisms behind consciousness and how they can affect brain injuries. Understanding these processes may help clinicians find better ways to treat and support patients with disorders of consciousness. But as with all research, the study includes some caveats.

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“This work was done within the framework of the Human Brain Project and would not have been possible without Dr. Rajanikant Panda, and our collaborators at Pompeu Fabra University Barcelona (Spain), Ane López-González and Gorka Zamora-López,” she added. with him.

The study was by Rajanikant Panda, Ane López-González, Matthieu Gilson, Olivia Gosseries, Aurore Thibaut, Gianluca Frasso, Benedetta Cecconi, “Brain analysis shows impairment of posterior integration and thalamo-frontotemporal transmission in disorders of consciousness”. , Anira Escrichs, Coma Science Group Collaborators, Gustavo Deco, Steven Laureys, Gorka Zamora-López, and Jitka Annen.

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