Surprising Neurons React to Unexpected Situations

Summary: New research reveals chandelier cells, a mysterious type of brain cell, become active during unexpected events. These cells play a crucial role in signaling and adaptation when the brain encounters unexpected changes, a fundamental aspect of learning.

The study used a novel mouse model to observe and understand the behavior of chandelier cells in response to various stimuli. Key findings include the cells’ sensitivity to unexpectedness, their habituation, and the structural changes they induce in synapses on other brain cells.

Key Facts:

  1. Chandelier cells are a unique type of inhibitory brain cell found in small numbers in the cortex.
  2. They respond strongly to unexpected and surprising stimuli, showcasing their role in learning.
  3. Chandelier cells exhibit plasticity, adapting their activity and forming structural changes in synaptic connections.

Source: KNAW

New research from the Netherlands Institute for Neuroscience shows that chandelier cells, a specific type of brain cell, become active during unexpected situations. “Researchers have been wondering about the functionality of these cells for a long time”.

You’re cycling to work through the city and suddenly you see a new building somewhere. On the first day that is very surprising. On day 2 this diminishes somewhat, and after a week you no longer notice it at all.

This is a neuron.
Together, they investigated a special type of brain cell found in small numbers in the cortex: the chandelier cell. In contrast to other inhibitory brain cells, they only inhibit one spot of other cells, but there is remarkably little known about why and when. Credit: Neuroscience News

The same thing happens the other way around: when a building that was always there suddenly disappeared, you 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 lab joined forces with his colleagues from the Kole lab and Roelfsema lab. Together, they investigated a special type of brain cell found in small numbers in the cortex: the chandelier cell. In contrast to other inhibitory brain cells, they only inhibit one spot of other cells, but there is remarkably little known about why and when.

New mouse model

Koen Seignette: “We already knew quite a lot about the function of most types of inhibitory brain cells, but chandelier cells were a mystery. This is because they are not clearly marked genetically, and so could not be properly examined.

“We have now obtained a mouse model in which the chandelier cells are fluorescently labeled. This allows us to image them live and determine when they are active. That offers new opportunities.”

“As a first step, we looked at what chandelier 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 had the mice walk in a virtual tunnel. When the mouse ran, the tunnel moved, and when it stopped, so did the tunnel.

“Using this setup, we could create an unexpected situation by stopping the tunnel while the mouse was still running. It was during these events that the chandelier cells started firing like crazy.”

Plasticity

Christiaan Levelt: “We see that the type of stimulus does not actually matter that much, 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.

“At first the cells react strongly, but after repeated exposure the activity becomes weaker. This shows that the cells are able to adapt, which is a concept known as plasticity. This plasticity also occurs at a structural anatomical level: we can literally see changes in the synapses chandelier cells form on other brain cells.”

“What makes this study important is that this is the first really comprehensive study of chandelier cells in the visual cortex. We have not only determined what they respond to, but also which brain cells they form connections with, and what their influence is on other brain cells. This has never been looked at 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 it really surprises you. If the prediction is incorrect, that’s where you can find the information. You need plasticity to update your insights, and these cells could play a role in that.”

Why are chandelier cells so special?

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

It was thought that chandelier cells could exert strong control over pyramidal cells by blocking the action potential. Surprisingly, the current research shows that this effect is actually very weak, which contradicts previously drawn conclusions.

About this neuroscience research news

Author: Eline Feenstra
Source: KNAW
Contact: Eline Feenstra – KNAW
Image: The image is credited to Neuroscience News

Original Research: Open access.
Experience shapes chandelier cell function and structure in the visual cortex” by Koen Seignette et al. eLife


Abstract

Experience shapes chandelier cell function and structure in the visual cortex

Detailed characterization of interneuron types in primary visual cortex (V1) has greatly contributed to understanding visual perception, yet the role of chandelier cells (ChCs) in visual processing remains poorly characterized.

Using viral tracing we found that V1 ChCs predominantly receive monosynaptic input from local layer 5 pyramidal cells and higher-order cortical regions.

Two-photon calcium imaging and convolutional neural network modeling revealed that ChCs are visually responsive but weakly selective for stimulus content. In mice running in a virtual tunnel, ChCs respond strongly to events known to elicit arousal, including locomotion and visuomotor mismatch.

Repeated exposure of the mice to the virtual tunnel was accompanied by reduced visual responses of ChCs and structural plasticity of ChC boutons and axon initial segment length. Finally, ChCs only weakly inhibited pyramidal cells.

These findings suggest that ChCs provide an arousal-related signal to layer 2/3 pyramidal cells that may modulate their activity and/or gate plasticity of their axon initial segments during behaviorally relevant events.

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