A brain magnetic resonance.
Image: NIH

When pushing In a small region of the brain linked to consciousness, scientists caused anesthetized monkeys to suddenly wake up and become alert. This fascinating result provides new clues about the brain and how it produces conscious awareness, ideas that could lead to therapies for patients trapped in a coma.

The brain remains the most mysterious organ in the human body. In recent decades, neuroscientists have torn apart the various regions and networks of the brain to better understand how they contribute to normal cognitive function, but great questions remain about consciousness and what parts of the brain can be described as the neuronal correlates of consciousness. (NCC): that is, the specific regions of the brain that allow us to experience the smell of burnt toast, the redness of a blooming rose or the richness of our inner thoughts.

New investigation published today in Neuron takes us a little but important One step closer to the answer.

When experimenting with macaque monkeys, researchers at the University of Wisconsin-Madison They have discovered new evidence that affirms the central lateral thalamus as an NCC. T stimulantyour little brain region which is located deep in the anterior brain, it caused anesthetized monkeys to suddenly wake up and be alert, although anesthetic medications were still administered. Neuroscientists had previously linked the central lateral thalamus as an NCC, but this latest research adds more credibility to the claim.

The location of the thalamus in the human brain.
Image: Life science databases (LSDB

“This study is significant,” Earl Miller, a professor of neuroscience at the Department of Brain and Cognitive Sciences at the Massachusetts Institute of Technology, said in an email to Gizmodo. “Consciousness theories have suggested that the central lateral thalamus plays a key role in keeping the cortex‘ awake. This study provides important evidence supporting that theory. “

In addition, the document “gives us new knowledge about circuits and brain dynamics that produce awareness,” wrote Miller, who was not involved in the new research.. “Thousands of people receive general anesthesia every year. Knowing how to make people unconscious is an important step in making anesthesia safer. “

Michelle Redinbaugh, the first author of the new study and a graduate student at the University of Wisconsin-MadisonHe said the main objective of the experiment was to locate the NCCs in the brain.

“Achieving this goal will allow us to better understand the mechanisms of general anesthesia and the impacts of brain trauma, [and also] go to clinical interventions to improve the lives of patients suffering from disorders of consciousness, such as coma, “he said. He told Gizmodo.

To that end, Redinbaugh, along with lead author Yuri Saalmann and his colleagues, devised an experiment with the intention of inducing awareness in anesthetized subjects. To do so, they designed a stimulation method that mimicked the way in which brain cells act in the central lateral thalamus during the waking state. Using electrode assemblies, the scientists were able to record the brain activity of multiple areas of the brain, which allowed them to control the consciousness in the macaques while they were awake, sleeping and under anesthesia.

During the experiment, the scientists tried to stimulate several parts of the deep brain, but none got the same response as the central lateral thalamus, which emerged as a kind of point of consciousness in the brain. Stimulation of this region of the brain to 50 hertz while the monkeys were under anesthesia made them wake up. When this happened, the primates behaved just like when they were awake. One time the stimulation went out, the macaques returned to a unconscious state.

A critical aspect of the experiment was to correctly evaluate vigil on the two monkeys used in the experiment, called Monkey R and Monkey W.

“We modeled our evaluation of wakefulness in monkeys in clinical measures that are used to evaluate patients in a coma or patients undergoing anesthesia,” Redinbaugh told Gizmodo. “Essentially, we were looking for increases in behaviors that you would normally see in an animal or human who woke up from anesthesia.”

These measures included things like monkeys opening their eyes, making determined deals, moving their faces and showing responsiveness to touch, Redinbaugh explained. The scientists also monitored their EEG responses to common and unusual sounds, “which can distinguish the consciousness of unconscious subjects,” he added.

In terms of the ethics involved, “The Institutional Committee for Animal Care and Use of the University of Wisconsin-Madison approved all procedures, which were in accordance with the Guide of the National Institutes of Health for the Care and Use of Laboratory Animals,” the authors wrote in the document.

During the experiments, for example, a clinical anesthesiologist should come forward to make sure that the monkeys “received the same level of care as human patients in the hospital,” Redinbaugh said, and the animals were monitored during and after the experiments to ” ensure your health and well-being, “among other measures, said.

That said, the scientists used a dozen ceramic skull and dental acrylic screws to “fix head implants” in monkeys, among other severely invasive measures required for the experiment, some of which were designed to immobilize the heads of the monkeys during EEG readings. It can be argued that, despite the measures taken, the animals suffered during this experiment and that monkeys should never be used for experiments like this.

Whatever that in mind, the new research could result in effective new therapies to treat consciousness disorders, improved deep brain stimulation as a surgical technique, and best Anesthesia medications What’s more, thThe findings could lead us closer to understanding consciousness itself.

Jaan Aru, a neuroscientist at Humboldt University in Berlin, said researchers in the 1990s began to think that the thalamus was important for consciousness, a belief based on the fact that the thalamus is in a central position for the control. and that can change how other regions of the brain process information. However, since the 2000s, neuroscientists have focused primarily on the cortex to find the mechanisms of consciousness, he said.

“This study returns the thalamus to the image”, Aru, whoHe is not affiliated with the new study, he told Gizmodo. “I hope that many studies will be carried out that will try to better understand the role of the thalamus not only in the state of consciousness, but also in the processes of perception.”

Looking to the future, Redinbaugh said that, since Your team now has a method to finely manipulate consciousness, they can test predictions of the main theories of consciousness, “which differ with respect to areas of the brain that are most important to consciousness.” They also plan to stimulate a wider range of areas in the thalamus. and determine which frequencies are most effective in influencing awareness.

“This would pave the way for a similar stimulation paradigm to be used in the clinic,” Redinbaugh said.


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