brain does instant replay—in reverse

If you saw your life flash before your eyes, would it run forward or in rewind?

That question may forever go unanswered, but researchers have found in rat brains a kind of instant replay of an event just after it happens—and it plays back in reverse. New Scientist reports:

David Foster and Matthew Wilson at the Massachusetts Institute of Technology in the US exposed four rats to a familiar running track, before exposing them to a new one. The rodents followed each track to eat the food placed at either end.

While the rats ran and then paused after reaching the food, the neurobiologists directly measured the animals’ brain cell activity using carefully placed electrodes....

The recordings revealed that, as the rats ran along each track, the cells in their hippocampus would fire in a particular sequence. But when the animals stopped for food at end of the new track, the same cells would also fire in the opposite order. This reverse-replay did not occur as often when they rested on either end of the familiar track.

The researchers suggest that the reverse signalling etches information into the brains of the rats as part of the learning process.

Maybe something similar helps people try to, say, figure out whether a wide receiver's feet were both in-bounds when he caught the football. Too bad you can't simply do a video instant replay in your head.