TWIS – The Neuroscience of Location and Memory


In the June 2, 2009, episode of This Week in Science, Kirsten and Justin reported on an experiment recently done at Caltech (see Caltech Scientists Reveal How Neuronal Activity is Timed in Brain’s Memory-Making Circuits) showing that in when brains are processing memory and location information through the hippocampus, activation of the neurons travels in waves (rather than all-at-once as previously thought).

The hippocampus consolidates memory information and location information.  Up to this point, our concept of the hippocampus operation was that "place cells" would fire in response to attributes of a place, thought to fire synchronously to report a memory or a location back to the rest of the brain.

An experiment at Caltech was conducted, hooking up electrodes to rats’ brains to watch their hippocampus fire as they made their way through a room.  And it turns out the hippocampus doesn’t activate all at once – it really operates in a step-by-step, wave-like operation.

Kirsten: "The hippocampus has a series of local time-zones just like we have on Earth".

Activation of neurons in the hippocampus doesn’t all happen at once — it’s kind of like a wave. It’ll activate in one area and then spread to the other parts.  Step-by-step activation.

Justin: "What kind of time-frame are we talking here?"
Kirsten: "Oh… very small time frame"
Justin: "I wonder if the time-frame is somehow related to our perception of a moment?"

Hm! It would be interesting to experiment to see whether people who meditate have faster or slower wave-activation in the hippocampus.

Kirsten: "What they’re finding is that what’s encoded is actually a portion of the rats’ trajectory…. so a segment of physical space plus the direction that the rat is moving, so if the rat is moving towards a goal.  …So it’s this trajectory that somehow is being monitored and reported by the hippocampus.  Not so much an "I Am Here", but an "I am going over there" representation.

If true for humans (and we do see a lot of similarities among all mammalian brains), then that means that our perception of present location is always moderated by what’s nearby and (perhaps) our motivations in being anywhere in particular. 

Justin: That is such a Giordano Bruno, Copernicus, sort of way of framing yourself in the universe, as bodies in motion, and their relationship towards each other and away from each other, as opposed to set locations of things intera-  It’s kinda interesting!  that it would be inherent in our brain somewhere.

It’s often noted that you can walk through a place dozens of times and not "notice" a particular painting on a wall, or the gradual death of a tree, or the entrance to a trail that goes away from the top of the mountain you’re climbing.  It’s only when you release yourself from your own expectations of a place, what you’re doing there, and what it’s for, that you are able to take in all these "extraneous" details.

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