A new primate study shows that the anesthetic propofol has a dramatic effect on the brain waves that travel through it.
When we are conscious, the brain is dominated by higher frequencies, but under the influence of propofol-based general anesthesia, it seems that very slow-frequency traveling waves are more common.
Waves moving through the cortex shift from traveling in different directions to all pointing the same way. There are small pockets not covered by delta waves that still have somebeta waves.
Earl Miller is a neuroscientist from the Massachusetts Institute of Technology.
Delta waves that have been altered and made more powerful by the anesthetic push away the beta waves that are seen during wakefulness. The deltas are like a bull in a china shop.
The scientists compare the awake brain to a sea rolling with waves of all shapes and sizes, which is then flattened by the arrival of an ocean liner. The effect that propofol has is like waves on an ocean.
The brain activity observed under anesthesia is different from the brain activity observed under sleep. Delta waves are rotating in sleep, perhaps to help consolidate memories.
The findings are based on an analysis of brain scans of two macaque monkeys, and the study is one of the first to track subjects all the way through the process of losing and regaining consciousness.
Being able to see how the waves are changed in the same subjects as they change from being awake to being asleep is important. The analysis of the data was published last year.
We continuously monitored how these waves behaved when the animals were awake, and then how they changed when they lost consciousness, all in the same animals.
This allowed us to explore in real-time how neural pathways that produce the waves were altered.
The brain wave patterns of the monkeys went back to normal after they regained consciousness. That suggests a connection between the activity and the application of propofol.
It is believed that brain waves do a variety of important functions in terms of coordinating brain activity, such as keeping time and seeing the world, for example.
When the brain is anesthetized, there is a loss of consciousness. Different anesthetic drugs can work in different ways on the brain.
The traveling waves generated by propofol help us appreciate that there are many dynamical phenomena that anesthetics create that can contribute to altered arousal states.
It is unreasonable to think that there is a single mechanism of action for all anesthetics.
The research was published in a journal.