• The Sense of Place: an Astrobiological Point of View on the 2014 Physiology Nobel Prize

    Okay, stay with me, guys. I’m about to say something you might not like…

    How incredibly fortuitous that the announcement of the Physiology Nobel Prize happened during Mercury Retrograde!

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    Hear me out! This is going to take a minute…

    In case you aren’t familiar with John O’Keefe and his fellow 2014 Physiology Nobel Laureates (and former post-docs) May-Britt and Edvard Moser this trio earned the prize for their discovery of cells in the brain that store and recall location and navigation information.

    Back in the early 1970s John O’Keefe found that their were collections of cells within the hippocampus of rats would be activated in response to a corresponding physical location. O’Keefe called these “place cells”. Anylocation would trigger a unique response in a unique collections of cells related just to that place. Every place the rat had been had a unique set of place cells would be activated in that spot. If the rat was placed in a new location it had never been in, once a minimum of sensory information was recorded, a new unique collection of place cells would be activated that would be forever associated with that location. Place cells form the basis for spatial memory. In the following years place cell activity was found in the hippocampi of many rodents and rabbits, monkeys, humans, even bats. The presence of these cells in early evolutionary branches of the mammal family indicates they are likely to be present in all mammals. These self-location cells have been found in brain structures of fish and reptiles that are analogous to the mammal hippocampus.

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    The Mosers went on to study how the brain responds to a path between known locations – is there any particular activiation of hippocampal cells as an animal goes between known locations that illicits responses in place cells? What they found is that there are cells in another part of the brain – the entorhinal cortex, the part of the brain that connects the hippocampus with the cerebral cortex – that record grid-like patterns in response to paths. These grids form a mental latitude and longitude and the cells fire in an algorthim that connects place cells (discrete locations) to one another. These cells are the basis of our “sense of direction” and once established allow animals to follow mental maps by memory, guided by sensory cues.

    One of the really interesting discoveries the Mosers and O’Keefes made was in what kind of sensory information triggered a “place” or “path” memory – a memory in this case being the literal triggering of either place cells or grid cells. What they found was that if a rat was walked in a circle they could observe a rotation in the activated grid cells that followed the rotation of the visual cues in the environment. They then experimented with rotating the environment around a rat to see if that would produce a response in grid cells. They found that the proximal (near) environment of the rat did not produce a memory response but a change in the distal (farther) environment would. Similarly with place cells – the nearby (proximal) cues were not as important as farther (distal) cues.

    How does this all relate to Mercury in retrograde? Let’s talk about human vision, from the physiological and the evolutionary point of view.

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    Our eyes get a lot of credit they don’t deserve for as being wonderful recorders of three-dimensional information. We are told this is because we are binocular and our two eyes provide depth perception. In actuality though, we don’t really see in 3D but in what Colin Ware (Visual Thinking for Design) refers to as “2.5D”.

    Of the millions of fibers in your eyes that are constantly transmitting information through your optic nerve to your brain only a tiny portion of these fibers are telling your brain anything about distance. The vast majority of these cells are relaying information about the up-down and side-to-side planes of vision. Very little depth information is actually being sensed; hence the 2.5D. Depth cues in the brain actually come from motion not vision. In order to perceive depth, objects must move with respect to viewpoint. The easiest way to get this information is to travel in the environment. So, in order for us to understand depth we must move through space, activating the grid cells in the entorhinal cortex that the Mosers identified.

    So, if we’re not getting depth information from our binocular vision what’s the point of two eyes? According to work by Mark Changizi (The Vision Revolution) two forward-facing eyes give us x-ray vision. That’s right. X-ray vision. You and thousands of other animals have superpowers – but you already knew that right?

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    You know that if you hold your finger in front of your eyes and then concentrate on the distance your finger just disappears – like you are seeing right through it! This ability is a function of having two eyes. Any object smaller than the separation between our eyes can be removed from our vision by the brain. This ability is absolutely essential for any creature moving in a visually cluttered environment. Think about back in the day when our ancestors were creeping through forests – wouldn’t it be a pain to have our field of vision constantly obstructed by every leaf in front of our face when we are trying to avoid predators and pitfalls? Our eyes and brains adapted to essentially remove these obstacles.

    What does this all have to do with Mercury then?

    Our eyes were designed to keep us out of tiger’s mouths and to navigate complex environments but they are pretty bad at reconstructing distal three-dimensional space for us. Think of how ancient man perceived the heavens. They thought of all the stars as a tapestry, a blanket of moving lights thrown over the landscape at night. The sky became a 2-d parade of gods, heroes, battles, love stories.

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    Even our more recent ancestors had no way of really understanding depth, how far away stars were, even when they knew we were in space. We were the center of the universe and the skies moved past us because that is how we see it – with no depth. In fact, the first person to understand that we on Earth were actually not the center of a moving system of bodies, Copernicus, was persecuted for his three-dimensional understanding. When we look up in the sky and see the planet Mercury moving backwards we have no sensory way of knowing why this is happening. Our depth perception isn’t good enough to see that the Mercury is moving towards us faster than Earth is moving in it’s orbit, so the overall effect is that the planet suddenly changes direction, zipping backwards for a while.

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    How could we solve this perceptive problem of understanding our relationship with Mercury? Well, according to the work of O’Keefe and the Mosers we would have to travel to it. We would have to leave our little rock and observe our path to Mercury, encoding entorhinal cortex grid cells along the way. These cells would become our mental map and give us a sense of distance and depth. When we got there Mercury would be a foreign place. We would have no space cells in our hippocampus to tell us where we were. We would rely on our senses to provide cues that would be implanted in our brains as a unique location we would then recognize.

    In this sense, this year’s 2014 Physiology Nobel prize is very deeply connected to the goals of astrobiology. Astrobiology is the search for understanding of the origin and distribution of life in the Universe – where we came from, how far we can go. Through our study of the universe we too, like O’Keefe and the Mosers, are gaining new understanding of our sense of place. Maybe by understanding how the brain locates and directs us the idea of leaving our pale blue home can then become less frightening – after all we are highly adaptive! We have cells in our brain that can be accustomed to a new place so it becomes familiar. And just as important, we also have cells in our brain that will provide us with a map back home.

    H.