THE HIPPOCAMPUS – BRAIN’S GPS

Honey, turn left up there at the stoplight.


Are you sure?

Of course I’m sure. We’re almost there. Turn left and then turn right a couple of stoplights afterwards.

Okay, but it just seems to be taking us off track.

I know, to you it would because you think everything’s a straight line. But it’s not because in this case a straight line would take us right into the river. That’s why we have to take a left and then a right. We’ll be back on the straight road soon enough.

Well, okay, you’re usually right about these things. Just as long as we get to Susan and David’s before nightfall…

And that, my friends, is the scenario, according to Hugo Spiers and his team from the Institute of Behavioural Neuroscience at University College London, of how the hippocampus which is the hub of the brain’s navigation system gets you from Point A to Point B.

It’s long been known that the hippocampus, a structure of the brain located in the medial temporal lobe, is responsible for spacial navigation and memory. In the past, some researchers have thought that it encodes the distance to the goal as the crow flies, the Euclidean straight line while others have thought that it maps distance along the paths you can take to reach that goal while sussing out diversions around obstacles. Spiers and his team wanted to investigate whether the hippocampus might actually do both types of mappings.

In a study which was reported on at the annual meeting of the Society for Neuroscience in Washington earlier this month, Spiers gathered 24 volunteers and gave them maps of London’s Soho district to study. Having no former knowledge of the area, the participants were then taken on a two-hour guided tour of the district. The next day they had their brains scanned while watching a high definition first-person film of the areas they had visited. The researchers paused the film at certain times and asked the participants to tell which direction they should take to get to a particular location.

When Spiers and his team analyzed the data they discovered that the hippocampus actually encodes both types of maps. For instance, when the participants were going to their destination the anterior or front end of the hippocampus was activated. It became less so the closer they got to the goal. At turning points, however, when the participants were asked to make a choice as to what direction to take, the researchers observed that the posterior or back end of the hippocampus became more active, especially when the participants were getting closer to the destination. This is the first time that such a model was observed. In the past it was believed that the hippocampus did one or the other. But to see that it actually does both and flips between the two in a conversational way is news indeed.


It is also interesting to note that for the back seat drivers, those who were asked to watch the movies without navigating, the scans showed that the GPS system of the hippocampus stayed silent. This suggests that it is not an automatic process but one that functions when a person is actively trying to navigate.

Next on the agenda for scientists is to investigate how the brain determines direction. We would assume it is more complex than holding a finger up in the air.


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