Propofol greatly changes and controls the dynamics of the brain rhythm

At the same time, measuring the nerve rhythm and peak value in five regions of the animal brain revealed how propofol induced unconsciousness. Slow rhythm signals can guide anesthesiologists to improve patient care.

The laboratory of the Picower Institute for Learning and Memory at MIT cooperates to conduct a unique in-depth and detailed study on how the commonly used anesthetic propofol causes unconsciousness. The results show that when this drug occupies the brain, a large number of regions coordinate through a very slow rhythm, so as to maintain the slow rhythm of corresponding neural activities. Electrical stimulation of the deeper region, thalamus, restores the normal high-frequency rhythm of the brain and synchronization of activity levels, wakes up the brain, and recovers wake-up.

"There is a folk psychology or default hypothesis that the role of anesthesia is just to 'shut down' the brain," said Earl Miller, professor of neuroscience and co senior author of the study on eLife. "What we have shown is that propofol greatly changes and controls the dynamics of the brain rhythm."

Consciousness functions such as perception and cognition depend on coordinated brain communication, especially between the thalamus and the cerebral surface area (or cortex), with frequencies ranging from 4 to 100 Hz. Studies have shown that propofol seems to reduce the coordination between thalamus and cortex to about 1 hz.

Miller's laboratory is led by Andre Bastos, a postdoctoral fellow, and Jacob Donoghue, a former graduate student, and cooperates with the co senior author, Emery N. Brown, a professor of medical engineering and computational neuroscience, Edward Hood Taplin, and an anesthesiologist at Massachusetts General Hospital. Therefore, this cooperation effectively unifies the expertise of Miller Laboratory in how to coordinate the neural rhythm of the cortex to produce conscious brain functions with the expertise of Brown Laboratory in anesthetic neuroscience and statistical analysis of neural signals.

Brown said that research showing how anesthetics change the brain rhythm can directly improve the safety of patients, because these rhythms can be easily seen on the EEG in the operating room. The main finding of this study is that the rhythm of the cerebral cortex is very slow, which provides a model for directly measuring the time that subjects enter the unconscious state after taking propofol

, the depth of maintaining this state, and the speed of awakening after taking propofol.

"Anesthesiologists can use this method to take better care of patients," Brown said

For a long time, Brown has been studying how the rhythm of human brain is affected under general anesthesia. He used scalp EEG electrodes to measure and analyze the rhythm, and to a certain extent, he also used cortical electrodes of epilepsy patients. Because this new research is conducted on these dynamic animal models, the research team can implant electrodes to directly measure the activity or "peak" and rhythm of many individual neurons in the cerebral cortex and thalamus. As a result, Brown said, the research results significantly deepened and expanded his findings on people.

For example, the neurons they measured chattering at the peak voltage of 7-10 times per second in the awake state usually send out signals only once or less per second in the unconscious state induced by propofol. This obvious deceleration is called "descending state". In conclusion, the scientists measured the rhythm and peak value of five regions at the same time: two in the anterior cortex, two in the posterior cortex, and the thalamus.

"It is convincing that we are getting data that are accurate to the peak level," Brown said "This slow oscillation regulates peak activity in most areas of the cerebral cortex."

Miller said that this study not only explains how propofol produces unconsciousness, but also helps explain the unified experience of consciousness.

"All cerebral cortex must be on the same page to produce consciousness," Miller said "One theory is to synchronize the cortex through the thalamus cortex ring. Propofol may disrupt the normal operation of these cycles through supersynchronization in a long-term decline state. It will damage the communication ability of the cerebral cortex."

For example, through the measurement of different skin layers, the research team found that the high-frequency "gamma" rhythm, which is usually related to new sensory information such as vision and sound, is particularly obvious on the surface. Miller has demonstrated that the lower frequency" α" And" β" Waves tend to regulate the processing of information carried by gamma rhythms, especially in deeper layers.

In addition to the ubiquitous synchronization at very slow frequencies, the research team also noticed other features of unconsciousness in the data. As Brown and others have previously observed in humans, when awake α and β Rhythmic abilities were significantly higher, but after unconsciousness, these rhythmic abilities flipped to a higher level in the anterior region.

The research team further showed that stimulation of the thalamus with high-frequency current pulses (180Hz) could eliminate the effect of propofol.

In the study, the authors wrote: "By increasing the peak rate and decreasing the slow frequency power, stimulation produces a cortical state similar to waking." In all regions, the peak value during stimulation interval increased significantly compared with the baseline before stimulation. "

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