Neurons’ Sugar Coating is Essential For Long-Term Memories

Source: University of Oslo

Summary: In a new study, researchers showed that long-lived extracellular matrix molecules called perineuronal nets are essential for distant memories and removal of the nets disrupts distant but not decent memories.

Perineuronal nets (PNNs) are specialized extracellular matrix structures that wrap around certain neurons and are responsible for synaptic stabilization in the adult brain. The nets are made up of sugar-coated proteins, forming a rigid structure that contains holes where connections to other neurons are kept in place. When new memories are formed, the connections between neurons change. How the brain is able to store memories over long periods of time has been a persistent mystery to neuroscientists. Researchers from the Centre for Integrative Neuroplasticity (CINPLA) at the University of Oslo, in a new study, showed that long-lived extracellular matrix molecules called perineuronal nets are essential for distant memories and removal of the nets disrupts distant but not decent memories. The research findings were published in the journal Proceedings of the National Academy of Sciences.

Extracellular matrix structures that wrap neurons

The image shows a perineuronal net (green) surrounding a neuron Credit: Kristian K. Lensjø/Oslo University

The research team performed a classical conditioning experiment to test memory function, where rats learn to associate a light blink with an unpleasant event. This type of learning creates a robust and long-lasting memory. After learning, the rats were divided into 2 groups – one where the perineuronal nets were left intact and one where they were removed in a small area, the secondary visual cortex (an area involved in memory storage). A month later, when the rats were asked to recall the memory, the results were astonishing – the group without the nets did not remember anything. The experiments show that perineuronal nets are essential for long-term memories because without them, the memory is lost. In a follow-up experiment where the memory was tested only a few days after learning, the team found that the memory was intact and that the disappearing effect was specific to old memories.

Marianne Fyhn, the leader of the CINPLA project, explained, “If we can increase our understanding of how memories are processed over months and years in the healthy brain, we can start to untangle what goes wrong when they are eventually lost in detrimental diseases like Alzheimer’s and dementia. The surprising finding that extracellular molecules are involved in these processes also suggests potential novel drug targets.”

More Information: Elise Holter Thompson et al, “Removal of perineuronal nets disrupts recall of a remote fear memory”, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1713530115 

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