Long-term memories protected by tiny ‘fishnets’ in the brain

The recently-discovered structures look like small fishnets tightly wrapped around neurons, and long-term memories are lost if they are removed.
Perineuronal nets ©Arnst.nikita CC BY-SA-4.0

Researchers from the University of Oslo, Norway, are the first in the world to discover that structures on the outside of neurons play an important role in storing long-term memories.

The recently-discovered structures look like small fishnets tightly wrapped around neurons, and long-term memories are lost if they are removed.

It is widely accepted that the brain creates and stores memories because of physical changes in synapses – the connecting points between neurons. A memory is stored through changes in a whole network of synapses; and the network is specific for each memory.

Researchers from the university have now shown that structures on the outside of neurons are important for long-term memories. They have studied proteoglycans, a type of protein structure that is connected to a large amount of sugar chains. The structure forms a net around neurons in some parts of the brain.

There are small holes in the nets, giving it the ‘fishnet’ appearance, and these holes are there to make room for the synapses, which make up the connections to other neurons. The net therefore ensures the size and placement of the connections that are so important for long-term memories.

Old brains turned young again

The researchers discovered that long-term memories could be captured in the ‘fishnets’ confirming that the structure affects these memories. By using rats, the scientists are researching brains that are fairly similar to humans’, and so new knowledge from the rats’ brains can provide information about how the human brain works.

Marianne Fyhn explains that the perceived ‘holes’ in the net structure is actually where synapses reside, the connections between the cell body and its connected neurons.

Researcher Kristan K. Lensjø added: “Young individuals, both in rodents and humans, are able to learn faster than adults, and the young brain has very few perineuronal nets (fishnets). But at a certain age, as we go from adolescence to adulthood, the nets are formed, probably to stabilise the neurons. The disadvantage is that is becomes more demanding to learn something new.

“Luckily, the brain maintains a certain ability to learn even after the nets are formed. The neurons produce enzymes that are capable of shaping the structure of the perineuronal nets.”

Links to Alzheimer’s disease and schizophrenia

The researchers hope that new knowledge about the brain will increase our understanding of diseases, and over time contribute to new treatments for conditions such as Alzheimer’s and other diseases. The perineuronal nets are also linked to schizophrenia, and the scientists are already looking into this.

The group has, together with collaborators at Oslo University Hospital and others, started a large new project called DigiBrain, which will study the possible causes to the differences in brain oscillations by using electroencephalogram (EEG) measurements in healthy and diseased humans and in animal models. By combining genetics, measurements in humans and animals, and mathematical models they hope to uncover some of the mechanisms underlying the disease.

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