A story about what happens in the brain during swimming and a mysterious event at a lake.

Content warnings

• mysterious disappearance
• reckless behavior
• PTSD

The short story

When I swim, it feels like you are still there. The waves are choppy and irregular and the sky over Sicily is already way too dark. I should not be out here still. Most of the locals left the ocean one or two hours ago. I do not care. The dark, salty water crashes over the faded turtle tattoo on my left shoulder. My front crawl is still strong, even after all these years. Left arm, right arm, left arm, forever… - or at least until the pain recedes. I breathe, my head just a little bit over the water’s surface. My feet kick up and down, nice and steady, with minimal force. “No force in the legs, it’s a waste of energy.”, your words echo in the depths of my auditory cortex like so many times before. “Legs are just there to keep you afloat, not to propel you forward, which is what arms are for”. Left arm, right arm, left arm, breathe. My left eye burns badly. I was not careful enough when fitting my swimming goggles and somehow the lukewarm and very salty sea water made its way into my left goggle. I do not care. I swim and for a fraction of a glorious second, it feels like you are still swimming with me.

I smile, a little bit. Just as much as I can still smile after what happened on that day at the lake. “People always leave.”, my daddy used to say when he was still alive, but I had never dreamed in my worst nightmares that you all leave so soon. That day at the lake was supposed to be a good day. The Turbo Turtles were one of Germany’s finest open-water swimming teams and we were sure that we would take the championship this year. We had trained hard. Long, grueling days of ever-repetitive freestyle swimming at the moldy, run-down pool in our hometown. Chlorine is my perfume coach used to say and it was pretty accurate. No matter the weather we jumped in and did our lanes, even on days when no one else showed up at the pool. Even in September, when brown leaves started floating atop the pool’s surface and the water got so cold our lips went blue after the first two lanes.

We had hoped that it all will pay out on that day at the lake, lounged for that trophy, but it came differently. Mere minutes after the referee fired his gun to signal the start of the race, a thick and impenetrable fog covered the lake. Nobody had ever seen anything like it, it was impossible to see more than half a meter in advance. I swam nevertheless, unrelenting like an orca hunting its prey.

When I crossed the finish line, I was the only one that did.

57 of Germany’s most elite open water swimmers were missing and no matter how many police divers search the lake in the days after the race, nothing was ever found. The Turbo Turtles were gone, forever, and so were all other teams. It made the newspaper headlines as far as in New York: “57 elite swimmers missing, German authorities have no explanation”. To this day I sometimes hope that it all was just an elaborate joke and that you all will show up any day now and laugh at me.

In the days after what happened at the lake, I was desperate. I visited many doctors and therapists and learned all that I could about post-traumatic stress disorder, but nothing these well-meaning people tried to help me had any effect on the horrors my hippocampus conjured every night and most of my waking hours.

Strangely enough, the only thing that helped me calm down was the very thing that took you from me: Swimming. Out of curiosity, I participated in a neuroscientific study on swimming I saw advertised at the university cafeteria. When I went to the pool for the study, the researchers explained to me that I was about to participate in a very cutting-edge experiment: Using a new type of measurement device they were to record my brain waves while I was swimming, something that was always thought to be impossible. They fitted a cap with electrodes on my head and gave me a floating device with a smartphone that was used to record the data from the cap. After the recording, the friendly yet professional research assistant explained that, like the ocean, the human brain shows different waveforms. There were delta waves that flooded my brain during deep sleep, theta waves that abounded when I dreamt of my team winning the swimming championship, alpha waves that occurred when I was relaxed, beta waves when I was concentrating on something, and last but not least gamma waves. This type of wave showed up when I paid attention to something or tried to keep something in mind. She further explained that my brain waves during swimming were unusual in that I showed an unusually large fraction of alpha waves, suggesting deep relaxation when I was in the water.

Abruptly, I stop daydreaming about the study and concentrate on swimming again. Left. Right. Left. Breathe. When I finally lift my head over the water again, I realize I am surrounded by an impenetrable fog. I cannot see more than half a meter ahead. There should not be any fog over the ocean this time of the year in Southern Italy, but I feel a strange calmness. It feels almost like … relief. Maybe I will be reunited with my team sooner than I thought. “Turbo Turtles forever!”, I yell, and I feel how the alpha waves get stronger and stronger. My left hand hits the choppy waves, and I race through the ocean like an orca.

This story was originally written in English.

The paper

Klapprott, M., & Debener, S. (2023). Flooding brain waves: Mobile EEG Acquisition During Freestyle Swimming. Poster Presentation at the Psychologie und Gehirn meeting 2023, Tübingen, Germany. https://twitter.com/mBrainTrain/status/1667134065063993345

Klapprott, M., & Debener, S. (2024). Mobile EEG for the study of cognitive-motor interference during swimming?. Frontiers in Human Neuroscience, 18, 1466853. https://doi.org/10.3389/fnhum.2024.1466853

Connection between story and paper

EEG (Electroencephalography) is a widely used technique to assess brain waves. It has traditionally been used largely in laboratory settings, but the recent development of mobile EEG systems has allowed EEG recording in real-life settings, such as driving a car or bungee jumping. Since EEG measures electricity, recordings during swimming are notoriously difficult due to the conductive properties of water. Klapprott & Debener (2023) have shown that it is technically possible, which is an impressive scientific achievement and a major breakthrough in mobile EEG research. In the study cognitive-motor interference was investigated and the focus was on the P300, a so-called event-related potential (ERP), that was recorded during a so-called oddball task. This is a common EEG task in which many common and few rare acoustic stimuli are presented. In the study acoustic stimuli were presented over earphones under a swimming cap. In the story, alpha waves which have been associated with relaxation are measured instead. Why this was not done in the study, the technique used in the study would make it possible to assess these and other brain waves which is an important step forward towards a neuroscience of swimming.

The author

Sebastian Ocklenburg is a book author, blogger, and neuroscientist working with EEG. He also likes to go swimming.