Nov 09 2018

Navigation May Be Fundamental to Thinking

Have you ever been in a semi-familiar location but couldn’t quite place where you were, then suddenly the landmarks line up and you know where you are? This might happen when entering a familiar location from an unusual direction, for example. Also (a seemingly unrelated question), when you visualize abstract ideas, do you arrange them physically. For example, do you visualize time (like days, weeks, months, years), and if so is there a particular physical relationship by which you mentally organize the progress of time?

Scientists from the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) and the Kavli Institute for Systems Neuroscience in Trondheim, Norway have published a paper in which they propose these two mental phenomena are directly related. One of the scientists, Edvard I. Moser, won the 2014 Nobel Prize for some of this work.

For background, researchers discovered that there are a type of neuron called place cells in the hippocampus (specifically area CA1) that store the memory for specific locations. When you are in a familiar location, a unique pattern of place cells will light up. Further, there is a second type of cell called grid neurons, which are arranged in a hexagonal pattern in the nearby entorhinal cortex. These grid cells light up in sequence as you move through your physical space – the physical arrangement of the grid neurons map to the physical arrangement of your environment.

This is an elegant system – your brain basically has a movable grid map, the grid keeps track of your local navigation, while the place cells keep track of where the map is.

This is also not the only example of so-called “somatotopic mapping” in the brain, where the physical location of neurons maps to their function. The other obvious example is the primary visual cortex. There the arrangement of neurons maps to the image itself, like a bitmap built of pixels, with each pixel being a neuron.

This kind of physical mapping is easy to understand, but now here is where the new paper comes in and where things get interesting. The authors propose that we navigate our abstract thoughts using the same neurons as for navigating physical space. They cite a 2016 study in which subjects learned to associate specific symbols with types of birds, and found:

In a subsequent memory test, performed in a brain scanner, volunteers indicated whether various birds were associated with one of the symbols. Interestingly, the entorhinal cortex was activated, in much the same way as it is during navigation, providing a coordinate system for our thoughts.

Therefore, perhaps one of the basic principles of abstract thought is that we develop “cognitive spaces” in which we arrange information, and then can mentally navigate around that information. This hypothesis has the strength of fitting with much of our subjective experience. For example, there is a phenomenon known as embodied cognition – abstract ideas are anchored to physical metaphors. We talk about a “big” idea, or a “deep” thought, someone can be hierarchically “above” someone else, and argument can be “strong”, “weak”, or even “beautiful”. We use physical metaphors about size, physical characteristics, and relationships to represent abstract ideas.

This may also explain the appeal of infographics, where information is represented graphically using physical and spacial relationships.

What the authors are suggesting is that perhaps our brains are wired specifically to do this – that we are literally navigating our abstract thoughts. Perhaps we don’t do this all the time, but this may be the way, or one way, in which we organize information in our brains. I even learned in a formal course to deliberately and consciously do this – to enhance memory by arranging information in a familiar physical space (a memory house or memory palace). This strategy works really well.

This all may reflect a general pattern of the evolution of the vertebrate brain, that it began by mapping simple physical phenomena and relationships, which then became progressively more complex and abstract. That is also how evolution works in general, by refining and expanding what it already has. Once the basic hardwiring of the vertebrate brain was established, that would constrain evolution to some extent. Developing new cognitive abilities would likely come from the existing wiring. In this case modules and networks evolved for navigating physical spaces was adapted to more abstract spaces.

I also can’t help pointing out the deeper lessons from this and similar research. Our brains are just really sophisticated massively parallel processors. They are machines, and thinking is just a process of those machines. The neuroscience paradigm continues to be incredibly successful in reverse engineering how the brain works, down to a reductionist model of neurons firing. There also doesn’t appear to be any theoretical limit to our ability to understand how the brain works, it’s just a matter of doing the research and refining our tools.

This kind of research also strongly supports the meta-experiment regarding the materialist paradigm of cognition. The closer we look, with better and better tools, the more we find that the anatomy and function of the brain directly correlates with measures of cognitive function. The mind is what the brain does. Dualists, those who think there is some ghost in the machine, have shrinking gaps in our knowledge to point to. The physical brain is doing more and more, and the ghost less and less, as our knowledge advances. Similar to the life force, there is simply nothing left for it to do, and it can safely fade into irrelevancy.


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