Scientists Watch a Memory Form in a Living Brain

Fraser and his team conditioned the zebra fish to associate a light with being uncomfortably heated in order to induce a memory. The zebra fish learned to swim away from the light. The researchers looked at the pallium before and after the fish learned, and analyzed the changes in location.

The synaptic strengths in the pallium were the same regardless of whether the fish learned anything or not. Fraser said that the fish that learned were replanted in other areas of the pallium.

The visualization of the brain suggests that this method of memory formation may be more significant than researchers realized. Ryan, a neuroscientist at Trinity College Dublin, said that it provides compelling evidence that this could be a major way the brain forms memories.

Everybody has thought about how a brain could be storing memories. I bet all of them are correct.

To reconcile the results of their new study with their initial expectations of memory formation, Fraser, Arnold and their team theorize that the type of memory might direct how the brain chooses to encode it. It's not surprising that you might use strong memories for the fish.

It may not be the best idea to lock in fear-ridden memories. Fraser said that when learning to pronounce someone's name, you probably wouldn't want to take out your brain cells.

Fraser and his team hope that this model will eventually help them examine mechanisms involved in the memories that cause post-traumatic stress disorder, and that it will lead to potential strategies for controlling that condition.

It is possible that the findings have more to do with the age of the zebra fish than with the type of memory formed, said a professor of psychology at the University of Otago in New Zealand who was not part of the study. If the researchers look at adult zebra fish, they might get different results because they are less transparent and have bigger brains.

The paper is a technical tour de force, but it is only a piece of the puzzle of how memories form, and there are still many unanswered questions.

The researchers want to see if the findings can be applied to animals with larger brains and even to mammals, and to see how zebra fish and other animals form memories that are less emotionally laden or traumatic.

Fraser said that everyone has thought that a brain could be storing memories. How does it all work together?