Study reveals engagement of different cortical networks while humans are unconscious

States of unconsciousness, such as those that occur during sleep or under the effect of anesthesia, have been the subject of countless neuroscience studies. Although this work has identified certain brain regions that are active and inactive when humans are unconscious, the precise contribution of each of these regions to consciousness remains largely unclear.

Researchers at Massachusetts General Hospital recently conducted a study aimed at better understanding the activity of different regions of the cortex, the outer layer of the mammalian brain, during different states of unconsciousness, namely sleep and general anesthesia. Their article, published in Neuronidentifies distinct cortical networks that are engaged during different states of unconsciousness.

“We have always wanted to better understand how neuronal activity in the brain gives rise to consciousness,” Dr. Rina Zelmann, lead researcher of the study, told Medical Xpress. “This is a huge and difficult question to answer. In this project, we started with seemingly simple questions, such as: what happens in the human brain when we are unconscious? And what happens in the human brain when we are unconscious? when we can’t be woken up?”

Dr. Zelmann, Dr. Cash and their colleagues have been recording and studying activity inside the brain for several years, using brain stimulation techniques. Their recent study on states of unconsciousness focuses on sleep versus general anesthesia induced by the drug propofol.

“We realized we were in a unique position to study these difficult questions in a limited way by comparing the human brain’s response to stimulation in different conscious and unconscious states,” said Dr. Zelmann. “For this project, we brought together an extraordinary group of neurologists, engineers, electrophysiologists, neurosurgeons and anesthesiologists.”

The researchers carried out their study on patients diagnosed with epilepsy and who had electrodes implanted in the brain as part of their medical treatment. By recording brain activity inside the brain, these electrodes help doctors monitor and treat epileptic seizures. Dr. Zelmann, Dr. Cash and their colleagues asked these patients if they wanted to participate in their study.

“We used short pulses of electrical stimulation (0.2 ms duration) delivered one by one to different regions of the brain while recording brain activity from all other regions (i.e. where found the clinical electrodes),” explained Dr. Zelmann.

“As these patients stay in the hospital for 1-2 weeks while their brain activity is recorded 24/7, in an effort to understand their seizures, we could perform this protocol while they were awake , asleep and under general anesthesia just before the procedure.” The electrodes were removed in the operating room. We then compared the responses with different mathematical techniques to understand the difference in response to stimulation in terms of complexity of responses, how the brain network was involved, and consistency of responses. ”

To effectively characterize the involvement of different cortical networks during sleep versus general anesthesia, the researchers compared what happened in participants’ brains during unconscious states to what happened when they were awake in the same environment.

Interestingly, Dr. Zelmann and colleagues found that, compared to when they were awake, during sleep the brain was uniformly affected in all patients, exhibiting simpler, reduced brain connections, as well as greater high variability in recorded activity.

“All measures were more pronounced during propofol-induced anesthesia, but brain involvement was not uniform; changes in prefrontal regions were particularly prominent,” said Dr. Zelmann.

“This indicates that during different forms of unconsciousness, distinct parts of the brain are involved in different ways. Our results in turn imply that the transition from unconscious to conscious may use different mechanisms depending on the nature of the unconscious state.”

Overall, this recent study unveils some of the differences in cortical network activity when humans are unconscious (i.e., during sleep) and when they are in an unconscious state from which they cannot be awakened (i.e. when under the effect of propofol). induced general anesthesia).

In the future, these findings could pave the way for new studies further exploring the contribution of the identified brain regions to unconscious states and to our general understanding of consciousness. In the meantime, Dr. Zelmann and her colleagues plan to continue their research in this area.

“The fact that the human brain responds differently to a single pulse of stimulation in different states of consciousness also has implications for therapeutic neuromodulation, which is used to help control seizures and, increasingly, psychiatric problems,” added Dr. Zelmann.

“Stimulation is usually adjusted during periods of wakefulness, but perhaps we should think more about how it changes the brain during sleep, because they are not the same. We now plan to continue this line of research exciting, increasing our understanding of how the human brain responds to stimulation in different states.

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