Watching new memories form

Biologically-speaking, new memories are based on changes to synapses – the gaps across which neurons communicate with each other. Now scientists in America say they have found a way to witness these synaptic changes right after they’ve happened, using rats and a fluorescent staining technique.

Gary Lynch, professor of psychiatry and human behaviour at the University of California, Irvine, and colleagues injected rats with fluorescent antibodies that are known to attach themselves to synapses undergoing long term potentiation (LTP) – a key physical substrate of memory formation.

The researchers placed the injected rats in a maze-like environment for 30 minutes on two successive days. The rats’ behaviour on the second day indicated they had remembered their way around from the first day. Crucially, other rats given an injection that blocks LTP didn’t show this learning. After the second day in the maze, some of the rats were killed and a tiny part of their brains from within the hippocampus was viewed under a microscope.

Thanks to the fluorescent staining, and by comparing the brain tissue from the rats who had learned their way around, with tissue from the rats who’d hadn’t, the scientists were able to see the dramatic synaptic changes associated with memory formation. “This is the first time anyone has seen the physical substrate, the ‘face’ of newly encoded memory. We have cleared a hurdle that once seemed insurmountable,” Professor Lynch said.

The researchers believe their technique may pave the way for mapping ‘engrams‘ – physical memory traces – across the brain.

Further reading

The findings are published in the Journal of Neuroscience.