Study shows special brain cells respond to unexpected situations

New research from the Netherlands Institute of Neuroscience shows that candlestick cells, a specific type of brain cell, become active during unexpected situations. Researchers have long wondered about the functionality of these cells.

Imagine you are cycling to work in the city and suddenly see a new building somewhere. The first day is very surprising. On the second day this diminishes somewhat; After a week, you no longer notice it. The same thing happens the other way around: when a building that has always been there suddenly disappears, we are also surprised. But how does your brain signal unexpected changes and which cells are involved?

To learn more about this phenomenon, Koen Seignette from Christiaan Levelt’s laboratory teamed up with his colleagues from the Kole and Roelfsema laboratories. Together, they studied a particular type of brain cell present in small numbers in the cortex: the candlestick cell. Unlike other inhibitory brain cells, they only inhibit other cells at a single point, but little is known about why and when.

New mouse model

Koen Seignette says: “We already knew a lot about the function of most types of inhibitory brain cells, but candlestick cells remained a mystery. Indeed, they are not clearly genetically marked and therefore cannot be examined correctly. We have now obtained a mouse model in which chandelier cells are fluorescently labeled. This allows us to view them live and determine when they are active. This offers new opportunities.

“First, we looked at what the candlestick cells in the visual cortex respond to. What happens to these cells when the mouse starts running or when we present visual stimuli?”

“In one of the experiments, we made the mice walk through a virtual tunnel. When the mouse ran, the tunnel moved, and when it stopped, so did the tunnel. With this setup, we could create a situation unexpectedly by stopping the tunnel. while the mouse was still running. During these events, the chandelier’s cells started shooting like crazy.

Plasticity

Christiaan Levelt says: “We find that the type of stimulus doesn’t really matter, what matters is that it is unexpected and surprising. We also noticed that habituation and change occurs, comparable to the aforementioned example of the new building. , the cells react strongly, but after repeated exposure the activity weakens. »

“This shows that cells are able to adapt, which is a concept known as plasticity. This plasticity also occurs at the structural anatomical level: we can literally see changes in the candlestick synapses formed on other brain cells.”

“What makes this study important is that it is the first truly comprehensive study of candlestick cells in the visual cortex. We have determined what they respond to, which brain cells they connect with, and what influence they have on other brain cells.

“This has never been examined in such detail before. Understanding the role of these inhibitory neurons in the cortex is crucial for many processes, including learning from unexpected circumstances. We all know that you remember things better when they really surprise you. If the “The prediction is incorrect, this is where you can find the information. You need plasticity to update your knowledge, and these cells could play a role in that. “

Why are chandelier cells so special?

Candlestick cells, named for their resemblance to a chandelier, are inhibitory brain cells that focus on the starting point (initial segment of the axon) of electrical signals in pyramidal cells, the most common cells in the cortex.

It was thought that candlestick cells could exert powerful control over pyramidal cells by blocking the action potential. Surprisingly, current research shows that this effect is very small, contradicting conclusions drawn previously.

The research is published in the journal eLife.