It's only been in the last few years that things like mental pictures and memories as signals in our brain have become accessible, measurable, and even recordable. An article in Nature this week reveals how memories are actually quantized into little sub-second chunks, and the researchers did it by 'teleporting' rats.
"Quantized" means that there's a single unit of memory that you can't chop up into smaller bits of memory. As it turns out, a quantum of memory (in addition to being the title of the next Bond movie) is about 125 milliseconds worth, which is the minimum amount of time that your brain needs to access and load a memory into your consciousness.
To deduce this number, researchers at the Norwegian University of Science and Technology resorted to teleporting rats. Now, try not to be too disappointed, but the rats were not actually teleported from one place to another. Instead, the whole thing was faked using sets of lights that made the rats think that they were being instantaneously moved between different rooms. The rats were trained to associate detailed patterns of light and shadow with specific places, and as the researchers flipped a light switch to jump between these patterns, the rats were fooled into thinking that they'd changed places.
By watching the patterns of activity in the rat's brain as it was rapidly "teleported" between different rooms, the researchers were then able to see how quickly the spatial memory for each room could be loaded and accessed as the rat tried to figure out where it was. So, the researchers would flip the lights around a bit and stop at one pattern, and the rat's brain would get confused and start rapidly paging between different maps, trying to find a match. It could do this at a maximum speed of eight maps per second, suggesting that (for rats, anyway) the minimum unit of spacial memory is equivalent to an eighth of a second.
The researchers suggest that this same process happens in humans, too. Whenever you get confused about something, or are trying to remember some detail but just end up with a jumble of memories, it's in fact not a jumble at all: really, your brain is just loading and unloading a bunch of entirely separate memories very quickly, looking for the right one. So next time you can't remember the name of that guy who was in that movie that was out last year that you never saw but heard was decent, just cut your brain some slack, 'cause it's flipping through every actor you've ever heard of at a rate of 125 milliseconds each and sooner or later it'll hit on the right one.