“The point of the cognitive map is flexibility. It gives animals the ability to plan novel paths within their environment,” said Redish [A. David Redish, University of Minnesota Medical School, USA]. “This replay process may be an animal’s way of learning how the world is interconnected, so it can plan new routes or paths.”
Dr. Redish is talking about studying brain activity in the hippocampus of rats. The hippocampus, a bean-shaped section of the brain in the medial temporal lobe, has long been associated with the memory process, and as a location for ‘replay’ activity. It was thought that’s when the brain replays experienced events in order to consolidate long-term memories. What Dr. Redish along with colleagues at Carnegie Mellon University (Pennsylvania, USA) discovered is that the replay function of the hippocampus is a much more complicated cognitive process. It is an important part of producing the ‘cognitive map’ and is a way the brain organizes experiences so that it can ‘plan novel paths’ – it is part of the decision making process.
The research team used lab rats outfitted with sensors that could pinpoint the firing of specific neurons (brain cells). For example, neurons called place cells fire according to the animal’s current location and contribute to the animal’s internal cognitive map of their environment. This mapping process proved to be the way into understanding the replay process. During replay, the pattern of place neuron activity indicated that the animal was processing information about locations other than where it actually was.
The researchers went on to give the rats specific tasks, say A and B. They found that afterwards the hippocampus would replay the lesser performed of the two tasks. That the rats were most likely to replay tasks performed less often was an indicator that the brain was attempting to get a fix on a broader cognitive map than just things done often or recently. Confirmation of this mental activity was even more pointed; the rats would ‘replay’ connections never physically travelled. For example, if the animal had been in a maze traveling from point A to point B, and from B to C – but never from A to C – it would make the connection A to C in its replay.
These observations led the research team to conclude that hippocampus replay doesn’t just review experiences on the way into long-term memory. It provides an important part of evaluating experiences – often older and less strong experiences – so that a more complete cognitive map can be assembled.
As usually seems to be the case, more research on brain processes reveals them to be more complex than originally thought. The researchers in this study admit that (especially in humans) brain cognition and decision making are poorly understood. There’s something about studying the brain processes by gross location with an EEG or fMRI that is reminiscent of the blind men studying an elephant: It’s not what they can’t see that counts; it’s that their tidbits of insight don’t add up to a whole elephant.