Tie a knot in DNA to remember. DNA methylation may be part of the machinery our brains use to store information.

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SYDNEY: Long-term memories have their roots in a process called DNA methylation, according to U.S. researchers. This is the same process that allows cells to specialise during embryonic development.

By uncovering the role of DNA methylation in the formation of new memories, the researchers argue that they have revealed a "crucial step" in the mysterious process by which our brain stores memories.

The find may also lend new insights into the causes of brain disorders like schizophrenia, wrote the team in the U.S. journal Neuron.

Throughout our lives, every cell in our body produces thousands of different proteins from instructions encoded in our genes. But the need for a specific protein may occur only in certain cell types, so our bodies turn unwanted genes off through processes such as methylation. Methylation inactivates genes by attaching small molecules called methyl groups to DNA, which act like a kind of clamp, preventing the proteins that that DNA encodes from being produced.

Methylation plays a crucial role in embryonic development by turning certain cellular functions off and allowing generalist cells to specialise into neurons, muscle cells, and other types present in an adult body. However, studies have revealed that, for resaons unknown until now, some methylation continues in adulthood, particularly in the brain. Defects in this continuing methylation have been linked to schizophrenia and some forms of mental retardation.

With this in mind, neurobiologists Courtney Miller and J. David Sweatt of the University of Alabama in Birmingham, designed experiments to test whether the methylation as a role memory formation in rats, whose nervous system closely resembles that of humans.

The pair created fearful memories in the rats by giving them mild electric shocks whenever they were in a specific training chamber. They then gave drugs to some of those rats that inhibit DNA methylation.

The pair found that rats in the group who had not received the drug would freeze in fear when placed in the chamber, but those who had received the drug did not react. Further tests showed that the level of methylation directly controlled the activity of a pair of genes known to suppress or promote memory formation.

This is evidence that DNA methylation could be a crucial step in the chain of events that forms long-term memories, Sweatt told Cosmos Online.

The researchers have only studied rats, but the same mechanism could be working in humans, they say.

Gavan McNally, a psychologist at the University of New South Wales in Sydney, was not involved in the study, but was impressed by its discoveries. "The surprising finding is the quite rapid changes in the DNA methylation that are occurring … [The changes] appear to be absolutely critical for memory formation," he said.

The study suggests that methylation may be behind memory storage in the hippocampus, said McNally, and that this fits with what we know about that part of the brain.

The hippocampus is "generally thought to be important for memory formation and memory storage, but not permanently … it's only a transient storage site important for enabling other parts of the brain to store them more permanently," he said.

Beyond memory research, the researchers suggest that their findings may have implications for treating cancer, autism, and schizophrenia – all of which are caused in part by malfunctions in mechanisms like methylation.