What does the hippocampus do at night while we sleep? Small testicles?
- Olav Bouman
- May 22
- 4 min read
In a TED presentation, renowned sleep researcher Matt Walker caused astonished murmurs among the audience when he claimed that poor sleep could lead to smaller testicles. Yes, you read that right. A bold claim – and Walker couldn't resist citing a relevant study. Is that true? Well, that's for urologists and statistical experts to decide. For us, the much more intriguing question is: What does poor sleep really do to our bodies – and especially to our brains?
Sleep is not a break – but a high-performance program
Many people think of sleep as a kind of rest mode, in which the body shuts down and the brain takes a break. Quite the opposite is true: While we sleep, a fascinating program runs in our brains—one that determines who we are , what we can do , and what we remember .
At the center of this nighttime miracle: the hippocampus – a small, seahorse-shaped structure deep within our brain. It is, in a sense, the conductor of our memory orchestra.
Short-term memory: The everyday notepad
Let's start with short-term memory. Imagine it like a small notepad that your brain fills with all sorts of information during the day: the name of your new colleague, the password for the hotel Wi-Fi, the location where you parked your car (hopefully). But this notepad is ephemeral—it gets erased regularly.
To prevent important information from being lost, it must be transferred to a more robust archive: long-term memory . And this is where our friend, the hippocampus, comes into play.
The hippocampus as a transfer manager
The hippocampus acts like a busy data manager: It decides which information can be moved from the notepad to the long-term archive – and which disappears into digital nirvana.
This process is called memory consolidation —a cumbersome term for a highly complex process. It involves stabilizing neuronal activity patterns and storing them permanently. And this process occurs—you guessed it— primarily during sleep .
Why sleep is so crucial
During the day, the hippocampus is very busy: It absorbs information, connects it, and evaluates it. But it's only during sleep , particularly during deep sleep and REM sleep phases, that it has the necessary rest to consolidate key memories through repetition. You can imagine this like practicing a piece of music—with repetition, the melodies become more secure and the rhythm more stable.
Scientists call this "long-lasting potentiation" —a process in which synapses (the connections between nerve cells) are strengthened so that information is better retained. The better the sleep, the more stable the memory.
REM, deep sleep and neuronal night shifts
There are two phases of sleep that play a key role:
Deep sleep (also called non-REM sleep): This is where the first major storage activity takes place. The brain sorts, filters, and decides what is "archive-worthy."
REM sleep (Rapid Eye Movement): During this phase, experiences are emotionally colored and linked to existing memories. REM sleep helps us relate the new to the old—an essential step for learning and understanding.
Not only the hippocampus works
Of course, the hippocampus doesn't operate alone. It works closely with other brain regions—especially the prefrontal cortex , which is responsible for planning, problem-solving, and logical thinking. One could say that the hippocampus pre-sorts the information, and the prefrontal cortex later organizes it into meaningful order.
But the hippocampus remains the star of this nightly show. Without it, much of what we learn during the day would simply fizzle out – like fog in the sunshine.
What happens when you lack sleep?
If we sleep too little or poorly, this finely tuned system gets out of sync. The hippocampus can't properly complete its nightly sorting and storage work—with the result that we have less concentration the next day, remember less, and feel mentally "foggy."
In the long term, chronic sleep deprivation can even cause structural changes in the brain – and possibly, some studies suggest, increase the risk of neurodegenerative diseases such as Alzheimer's.
A good reason to go to bed early
Who would have thought that healthy sleep is so much more than just rest? It's memory training , emotional sorting , and creative connection —all without conscious effort.
Our hippocampus is a patient helper that helps us understand the world and learn from our experiences every day. We just need to give it a good night's sleep.
Conclusion: Sleep is memory care
The hippocampus is crucial for the conversion of short-term to long-term memory.
Information is consolidated and stored especially during sleep.
Deep sleep and REM sleep are essential for good memory performance.
Lack of sleep disrupts these processes and impairs memory.
If you want to be smart, you should do one thing above all: sleep well .
PS: And what about the testicles?
Whether they actually decrease with sleep deprivation is something we'll leave to medical associations to decide. One thing is certain: if you want to do something good for your brain and body, the best place to start is in the bedroom. With plenty of rest, fresh air—and perhaps without a smartphone under your pillow.
The video on sleep and testicles
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