The Case of the Vanishing Synapses

Watson came in, wordlessly dropped a new folder, and left again. Her most elegant form of panic.

On the cover it read: “Brain fog after infection – MRI unremarkable.” Ah. The classic. When the MRI shows nothing, people start using their imagination against the patient. I opened the file.

The Situation

• Patient: early 30s.
  
• First infection: barely any symptoms.
• Second infection: focus gone, word-finding like a badly shelved library, fatigue with royal stubbornness.
  
  
• And the MRI? Unremarkable. Of course.
• An MRI is like a tourist in London: it sees Big Ben, takes a photo, and claims it “gets the city.”
  

Crime Scene: The Hippocampus

When people say “memory,” they usually mean they can’t find their keys. When I say “memory,” I mean structures, synapses, signalling pathways and the eternal question of who, in biology, decided to put “safety” above “function” again.

In the hippocampus, the brain’s archive, something was missing, without looking dramatic: synapses.

Synapses are the contact points between nerve cells. Or, in normal-person language: tiny little bridges where information jumps across. Without them, thinking becomes… slow. Sticky. Foggy. 🌫️
When synapses disappear, it’s rarely romantic. It’s more like accounting: minus here, minus there, and suddenly the balance is empty.

The Usual Suspects ️

London loves false suspects. Medicine does too.

• Stress.
• Sleep.
  
• “Maybe it’s psychological.”
  
• “Maybe you should drink more.” (Water, not wine—though both get recommended with surprising confidence. 
  

Lovely ideas. Completely useless for explaining why everything escalated after the second infection.
The truth is usually unimpressive—until you understand it.

The Real Mechanism: An Alarm System with a Grudge

There’s an agent team in the brain that’s usually very helpful: microglia. You can call them the “rubbish collectors.” Or “caretakers.” Or, if you’re honest: “the ones who sometimes clean a bit too enthusiastically." 

Microglia tidy up when something looks damaged or suspicious. And during inflammation they get signal flares from the immune world.

One of those signal flares is a messenger that sounds like a Wi-Fi password: interferon gamma (IFN-γ). When it shows up, it’s like someone shouting “FIRE!” in a museum because a visitor breathed too loudly. 

And here’s the part many people don’t see coming:
During the first infection, it’s not only the immune system that wakes up. Neurons can “learn” too, not with thoughts, but with wiring diagrams.

Epigenetics, Briefly and Slightly Mean

DNA is a cookbook. Recipes are genes. Epigenetics is the sticky notes and highlighters:

• “Make this recipe often!” ✅
  
• “Never make this one!” ❌
  
• “Make this one immediately if danger!” 🚨
  

The letters in the cookbook don’t change. But which pages are constantly kept open? That can change.

After the first infection, the brain can basically slap on sticky notes: “Next time, react faster.” That’s logical, biology likes survival.

The problem: next time it may react too fast, too strongly, and calls in microglia who then don’t just look for viral leftovers, but start treating synapses as “suspicious.”
The result isn’t a bang. It’s a vacuum cleaner drama: quieter, but effective .

Reconstruction of the Crime

• First infection: the brain experiences inflammation → an epigenetic “priming” develops.
  

• Second infection: the alarm response switches on faster and harder.
  

  IFN-γ rises: immune alarm inside the brain.
  

• Microglia clean up: too much zeal, not enough finesse.
  

• Synapse loss: thinking gets tougher, memory foggier, everyday life heavier. 
  

And then the MRI strolls in, nods politely, and says: “Looks fine.” Thanks for nothing. 

Conclusion

The patient isn’t imagining it. She isn’t “just stressed.” And she certainly isn’t “simply sensitive.” She’s experiencing a biological effect: a brain that remembers inflammation and overreacts the second time.

WatsOn will translate that into kinder words. I, however, prefer the truth: London doesn’t forget. And sometimes the brain doesn’t either. I took a sip of tea, pulled a face, and wrote the case summary into my notebook:
“Culprit: epigenetic alarm readiness. Accomplice: microglia. Victim: synapses.” And at the very bottom, in small print for my eyes only: “Humans regularly underestimate how grudging biology can be.”

Yours truely

Sherlock MS