Summary: Researchers are investigating the effect of anesthesia on brain function.
Source: DPZ
“When we’re awake, our brain can be thought of as a full-on football stadium,” explains Nikoloz Sirmpilatze, a scientist with the Functional Imaging Unit and lead author of the study.
“Our active neurons are like tens of thousands of spectators, all speaking at the same time. But under anesthesia, neuronal activity is synchronized. You can measure this activity using EEG in uniform waves, as if all the spectators in the stadium were singing the same song.
“In deep anesthesia, this song is repeatedly interrupted by periods of silence. This is called burst suppression. The deeper the anesthesia, the phases of uniform activity, the shorter the bursts, and the longer the periodically repeated inactive phases, the so-called suppression.”
This phenomenon is caused by many different anesthetics, some of which differ in their mechanism of action. And blast suppression can also be detected in comatose patients. However, it is unknown whether this is a protective response of the brain or a symptom of dysfunction.
It is also unclear where suppression of brain burst occurs and which brain regions are involved, as localization is not possible with EEG alone.
To answer this question, Nikoloz Sirmpilatze and his research team used fMRI imaging. The method makes the blood flow changes in the brain visible.
Increased activity of neurons in a particular area of the brain leads to an increase in metabolism, followed by increased blood and oxygen supply at that location, ultimately visible in the fMRI image.
In the first part of the study, the researchers set up a system to evaluate fMRI data in a standardized way in humans, monkeys, and rodents using the same method.
To do this, they used simultaneously measured EEG and fMRI data from anesthetized patients, generated in a previous study at the Technical University of Munich.
“We first looked at whether the burst suppression detected in the EEG was also visible in the fMRI data and showed a particular pattern,” says Nikoloz Sirmpilatze.
“Based on this, we developed a new algorithm that allows detection of blast suppression events in experimental animals using fMRI without additional EEG measurement.”
The researchers then performed fMRI measurements on anesthetized long-tailed macaques, marmosets, and rats. In all animals, they were able to detect and precisely localize blast suppression as a function of anesthetic concentration.
The spatial distribution of burst suppression indicated that certain sensory areas, such as the visual cortex, were excluded from it, in both humans and monkey species.
In contrast, in rats, the entire cerebral cortex was affected by blast suppression.
“At the moment we can only speculate about the causes,” says Nikoloz Sirmpilatze, who was awarded the German Primate Center’s 2021 Doctoral Thesis Award for his work.
“Primates orient themselves mainly through their sense of sight. Therefore, the visual cortex is a highly specialized region that is separated from other brain areas by specific cell types and structures. This is not the case in rats. Future work will ultimately need to understand why fMRI blast suppression cannot be detected there.” “We’re going to investigate exactly what happens in these areas during anaesthesia.”
Susann Boretius, head of the Functional Imaging Unit and senior author of the study, adds: “The study not only raises the question of the extent to which rodents are suitable models for many areas of human brain research, particularly when it comes to anesthesia, but also the evolution of results in neuroscience and neural networks in general. It has many meanings for him.”
About this neuroscience research news
Writer: Susanne Diederich
Source: DPZ
Communication: Susanne Diederich – DPZ
Picture: Image credited to Nikoloz Sirmpilatze
Original research: Open Access.
“Spatial signatures of anesthesia-induced blast suppression differ between primates and rodents.Nikoloz Sirmpilatze et al. e-life
Abstract
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Spatial signatures of anesthesia-induced blast suppression differ between primates and rodents.
During deep anesthesia, the brain’s electroencephalographic (EEG) signal alternates between bursts of activity and periods of relative silence (suppressions). The origin and distribution of blast-suppression in the brain is still a matter of debate.
In this study, we used functional magnetic resonance imaging (fMRI) to map brain areas involved in anesthesia-induced blast suppression in four mammalian species: humans, long-tailed macaques, common marmosets, and rats.
At first, we identified fMRI signatures of burst suppression in human EEG-fMRI data. Applying this method to animal fMRI datasets, we found distinct burst suppression signatures in all species.
The blast suppression maps revealed a marked difference between species: in rats, the entire neocortex was engaged in blast suppression, whereas in primates most sensory areas—predominantly the primary visual cortex—were excluded.
We anticipate that the identified species-specific fMRI signatures and whole brain maps will guide future targeted studies investigating cellular and molecular burst suppression mechanisms in unconscious states.