New brain mechanism prioritizes surprises

Sensory prediction errors and brain circuit cooperation.

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Researchers have found how the brain‘s neocortex and thalamus work together to detect when things don’t match expectations. They discovered that unexpected sensory information is highlighted to correct these “prediction errors.”

This study, published in Nature, improves our understanding of brain processing and may provide clues about autism and schizophrenia. It involved studying mice in virtual reality to explore these brain mechanisms.

Professor Sonja Hofer explained that our brains constantly predict what will happen and what our actions will lead to. Different brain areas activate strongly when predictions are wrong, helping us learn and adjust our expectations. Little is known about the brain circuits that handle these prediction errors despite their importance.

Employing an innovative approach, researchers immersed mice in a virtual reality corridor and tasked them with navigating to a reward. Then, the researchers manipulated the mice’s visual experiences, introducing unexpected images.

Using two-photon calcium imaging, they monitored neural activity in the primary visual cortex, the brain region responsible for processing visual information from the eyes.

Dr. Shohei Furutachi explained that previous theories suggested prediction error signals show how actual visual input differs from what was expected. However, the study found that the brain enhances responses from neurons that react strongly to unexpected visual input. This selective amplification makes unexpected events stand out more.

To explore this, researchers used optogenetics to activate or deactivate specific neurons. They identified two key groups: VIP-expressing inhibitory neurons in the visual cortex and the pulvinar, a thalamic region connected to the visual cortex. They discovered that these two groups interact in unexpected ways.

Dr. Furutachi explained that while neuroscience often studies one brain region at a time, his background in molecular biology led him to explore how different brain pathways work together. He found that VIP neurons and the pulvinar interact closely.

When VIP neurons are off, the pulvinar suppresses activity in the neocortex. When VIP neurons are on, the pulvinar boosts sensory responses in the neocortex. This cooperation helps create sensory prediction error signals in the visual cortex.

The team plans to investigate how and where the brain compares predictions with actual sensory input to compute prediction errors and how these errors influence learning. They also aim to see how their findings might help understand autism and schizophrenia.

Dr. Furutachi said, “They are now testing their discovery in animal models of autism and schizophrenia to explore the neural circuits involved in these disorders.”

Journal reference :

  1. Furutachi, S., Franklin, A.D., Aldea, A.M. et al. Cooperative thalamocortical circuit mechanism for sensory prediction errors. Nature. DOI: 10.1038/s41586-024-07851-w.
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