A Mass General researcher discusses anesthesia and our new ability to understand the brain’s “music” by tracking brainwaves in the operating room.

If you’ve ever been put under anesthesia, chances are you don’t remember a thing about your operation – and you’d rather not. But the question of how anesthesia works has been a mystery ever since ether was first used in the operating room, at Massachusetts General Hospital, nearly two centuries ago.

Now, Patrick Purdon, PhD, of Massachusetts General and Harvard, says news insights into the brain under anesthesia could lead to better care in the operating room and beyond. He explains — partly in song.

These insights into how anesthesia works are also helping us understand sleep disorders, Alzheimer’s disease, and even child development.

This may not be comforting to hear, but when you’re under general anesthesia, your doctors are basically flying blind. They don’t know exactly how your brain is responding to the anesthesia, and so they don’t know exactly how much to give you. And the stakes couldn’t be higher: too little anesthesia, and you might be aware during your operation! But too much, and it raises your risk for delirium and mental impairment after the operation.

But it doesn’t have to be this way. We have new tools, and new insights into how anesthesia affects brain activity, so that, with just a few electrodes on your scalp to record your brainwaves, we can monitor how different areas of your brain are working, and that can help us give you the right drug dosage.

Anesthesia and Music

To understand what happens under anesthesia, think of your brain as a complex machine, like an orchestra that needs precise timing and coordination among its various parts. Now, imagine that we’re listening to its electrical activity in one area. In musical terms, we might hear, “Fly me to the moon, and let me play among the stars …”

What our new ways of monitoring the brain show is that when we give anesthesia, the music changes — it’s more like, “Fly … moon … live … stars …”

What we now understand is that anesthetic drugs are altering the timing of brain circuits: Their effect is so powerful that the activity of neurons is periodically silenced, disrupting brain function.

My song was also monotone — just one note. See, that was a clue: We’ve also found that under anesthesia, your brainwaves become limited to just a few frequencies. And it turns out that the specific notes depend on which drugs you’re given.

Tracking Your Brainwaves

Some drugs, like ketamine, produce an excited state, and the brain plays predominantly high notes, like “Flight of the Bumblebee.”

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Other drugs produce a more mellow sedated state, and there’s pretty much just, “one note … intermittently … one note … one note … intermittently.” As children grow, and as adults age, the sound quality of these notes change, too.

Our new ability to understand the brain’s “music” by tracking your brainwaves in the operating room can take the guesswork out of figuring out how much anesthetic to give you, making it more personalized and precise.

So if, for example, I know your brain should be sounding like this (“One Note Samba”) and instead it’s playing multiple notes (“Scrapple From The Apple”), I know you need more anesthesia. And if there are long periods of silence, I know you need less.

Most anesthesiologists aren’t doing this yet, but it’s easily done with a little training and some small improvements to existing technology. These insights into how anesthesia works are also helping us understand sleep disorders, Alzheimer’s disease, and even child development.

So we’re making progress — even when you’re out cold.

To learn more about how you can support anesthesia research at Mass General, please contact us.

This article first appeared on WBUR’s CommonHealth blog at commonhealth.wbur.org

Patrick Purdon, PhD

Patrick Purdon, PhD, of the Massachusetts General Hospital Department of Anesthesia, Critical Care and Pain Medicine, develops and applies novel methods in neuroimaging and biomedical signal processing to study the systems neuroscience of general anesthesia and other altered states of consciousness. Dr. Purdon is the first incumbent of the Nathaniel Sims, MD Endowed Chair in Anesthesia Innovation and Bioengineering.

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