Keeping your brain's symphony in sync
Dr. Brenna Shortal was one of the two lead authors of this publication. Her graduate and undergraduate research focused on understanding the neurological mechanisms of consciousness, and she has published a number of papers on the topic. While she was a student at UPenn, Dr. Shortal was the director of Brains in Briefs, and her passion for science communication led her to pursue a career as a medical writer for Red Nucleus following her graduation in 2021. She hopes to continue working to communicate and advocate for scientific research to broad audiences.
or technically,
Weakly correlated local cortical state switches under anesthesia lead to strongly correlated global states
[See Original Abstract on Pubmed]
Authors of the study: Ethan B Blackwood, Brenna P Shortal, Alex Proekt
The most complicated piece of machinery you will ever encounter is sitting right between your ears: your brain. Our ability to move, sense, and think is thanks to billions of individual neurons that interact in varied and complicated ways. With this level of complexity, it’s miraculous that our brains work at all, let alone as well or as long as they do. Even more impressively, when our brain gets knocked off track, like from a seizure or anesthesia, it can quickly go back to typical patterns of activity. How does such a complex thing keep itself in sync?
Ethan Blackwood is a fifth-year neuroscience graduate student in the lab of Dr. Alex Proekt. Before coming to Penn and as a rotation student with Dr. Proekt, his research focused on how neural oscillations ("brain waves") change over time or with stimulation and what this means for behavior. More recently, he has been zooming in to the individual neuron level and studying how the firing of large groups of neurons changes during learning.
Neuroscience PhD student Ethan Blackwood and Drs. Brenna Shortal and Alex Proekt at the University of Pennsylvania sought to answer this question by studying brain activity in rats under anesthesia. Anesthesia is a useful way to study the coordination of brain activity because it is easy to put animals under anesthesia in the lab and because researchers already know a lot about the patterns of brain activity that occur when people are under anesthesia. The team studied this phenomenon in rats because they were able to directly record the activity of the neurons in the rat’s brain, something that is rarely possible in the human brain.
The team had two ideas about how the brain keeps itself in sync. Their ideas are easiest to understand if we think of the brain as a symphony with your neurons as the musicians. Just like an orchestral piece comes together because the musicians move in sync from one part of the music to the next, so too do the groups of neurons in your brain. The researchers’ first idea about how the brain might keep its symphony together was that there is a conductor who dictates how all the groups of neurons behave. The second possibility was that there is no conductor, but nearby neurons listen to each other so that the whole orchestra stays together.
To distinguish between these two possibilities, the team recorded a kind of brain signal called a local field potential in two parts of the rat brain. They did this by placing electrodes in the rat’s brain and listening to the activity of nearby neurons. This is like listening to a few microphones placed in the cello and violin sections to understand how the whole orchestra works. Each microphone captures sound produced by several nearby musicians, but it can’t capture the whole orchestra’s sound.
The team started by identifying what musical melodies, which they call brain states, each electrode recorded and noting when the nearby neurons switched from one state to the next. By doing this for all the electrodes, they showed that there were only a small number of brain states that the neurons played, and the same states appeared in different rats. The relatively small number of brain states they found is something other neuroscientists have observed, and it’s key to how the brain keeps itself in sync. If every musician in the orchestra played their own tune, it would be hard to make sense of what was going on. However, by moving through different sections of the same piece of music in sync, the instruments create a beautiful piece of music together. The same is true of your brain’s symphony. Rather than coordinating billions of songs, each sung by different neurons, your brain’s symphony sings just a few, transitioning between a small number of brain states over time.
Now that they had their brain recordings, the team could see which of their two proposals about how the neural symphony stays in sync was true. If their first prediction, that there is a conductor that signals when to transition from one state to another, was true, the team expected to see all the groups of neurons transitioning between states at similar times. On the other hand, if their second prediction was true, that the neural symphony stays in sync by listening to nearby neurons, the researchers would expect to see groups of nearby neurons transitioning between themes mostly together, with nearby neurons more likely to move together than neurons that are further apart. When they measured the neurons’ activity, they found that transitions between states measured on different electrodes corresponded only weakly to each other, but that the closer the electrodes were, the more the state transitions were related. This supported their second prediction, that neurons listen to their neighbors to decide when to transition from one state to another.
This is an exciting step toward understanding how the brain coordinates the movements between states that help keep our complex brains in sync. Understanding this process is important because it can help us develop therapies that mimic it for patients whose brain activity can’t always keep up healthy patterns, such as seizure patients. Beyond medical uses, understanding nature’s elegant solution to managing the complexity of brain signaling can teach us how to build computer systems and models that can handle increasingly more complexity to do things like power robots. And if none of these applications excite you, hopefully you can appreciate the wonder of understanding a little more about what makes us tick and how our neural symphonies stay in sync.
About the brief writer: Catrina Hacker
Catrina Hacker is a PhD candidate working in Dr. Nicole Rust’s lab. She is broadly interested in the neural correlates of cognitive processes and is currently studying how we remember what we see. She also co-directs PennNeuroKnow.