Janna Helfrich, Yale School of Medicine - What Happens to Your Brain Under Anesthesia? It's Not Quite Sleep, Not Quite a Coma

What happens to your brain under anesthesia?

Janna Helfrich, assistant professor at the Department of Anesthesiology at Yale University, says it’s not quite what we expected.

Faculty Bio:

Janna D. Helfrich is an Assistant Professor at the Department of Anesthesiology at Yale University. She has completed her residency training in anesthesiology at the University Medical Center Tuebingen, Germany. In addition to her clinical training, she did a postdoc in neuroscience at the University of California at Berkeley, USA. In her research, she studies the neurophysiological underpinnings of physiological, artificial, and pathophysiological forms of unconsciousness, such as sleep, anesthesia, or coma, and their impact on higher cognition. Dr. Helfrich uses a variety of methods to study the brain, including scalp and intracranial EEG in humans as well as cross-species approaches. She is deeply dedicated to teaching anesthesiologists and advancing their understanding of EEG, thereby enhancing the safety and efficacy of anesthetic practices through education and research.

Transcript:

Every year, millions of people undergo surgery under general anesthesia. The drugs work — patients become unresponsive, have no memory, and feel no pain. But despite decades of use, we still don’t fully understand what anesthesia actually does to the brain. Is it like sleep? Is it like a coma? Or something else entirely?Working with teams at UC Berkeley, the University of Alabama at Birmingham, and the University of Oslo in Norway, we recorded electrical brain activity from the scalp — using a technique called electroencephalography, or EEG — in patients under propofol anesthesia, healthy volunteers during sleep, and patients in a coma in the intensive care unit. We then created detailed “fingerprints” of brain activity across dozens of frequency ranges and time points, and compared them to each other.What we found was striking. The anesthetized brain isn’t simply one thing — it borrows features from multiple states at once. Its slow, low-frequency activity most closely resembles a coma. The characteristic alpha waves — generated by deep brain circuits about ten times per second — look like the sleep spindles seen in deep sleep. And perhaps most surprisingly, certain high-frequency patterns actually mirror rapid eye movement sleep, the stage in which vivid dreams occur.In other words, general anesthesia is a mosaic of brain states — part coma, part sleep, with its own unique signatures o