Space as a framework for representing mental contents in the brain

Jordana Cepelewicz, The Brain Maps Out Ideas and Memories Like Spaces, Quanta Magazine, January 14, 2019. Opening paragraphs:

We humans have always experienced an odd — and oddly deep — connection between the mental worlds and physical worlds we inhabit, especially when it comes to memory. We’re good at remembering landmarks and settings, and if we give our memories a location for context, hanging on to them becomes easier. To remember long speeches, ancient Greek and Roman orators imagined wandering through “memory palaces” full of reminders. Modern memory contest champions still use that technique to “place” long lists of numbers, names and other pieces of information.

As the philosopher Immanuel Kant put it, the concept of space serves as the organizing principle by which we perceive and interpret the world, even in abstract ways. “Our language is riddled with spatial metaphors for reasoning, and for memory in general,” said Kim Stachenfeld, a neuroscientist at the British artificial intelligence company DeepMind.

In the past few decades, research has shown that for at least two of our faculties, memory and navigation, those metaphors may have a physical basis in the brain. A small seahorse-shaped structure, the hippocampus, is essential to both those functions, and evidence has started to suggest that the same coding scheme — a grid-based form of representation — may underlie them. Recent insights have prompted some researchers to propose that this same coding scheme can help us navigate other kinds of information, including sights, sounds and abstract concepts. The most ambitious suggestions even venture that these grid codes could be the key to understanding how the brain processes all details of general knowledge, perception and memory.

And so on and so forth:

This kind of grid network, or code, constructs a more intrinsic sense of space than the place cells do. While place cells provide a good means of navigating where there are landmarks and other meaningful locations to provide spatial information, grid cells provide a good means of navigating in the absence of such external cues. In fact, researchers think that grid cells are responsible for what’s known as path integration, the process by which a person can keep track of where she is in space — how far she has traveled from some starting point, and in which direction — while, say, blindfolded.

“The idea is that the grid code could therefore be some sort of metric or coordinate system,” said Jacob Bellmund, a cognitive neuroscientist affiliated with the Max Planck Institute in Leipzig and the Kavli Institute for Systems Neuroscience in Norway. “You can basically measure distances with this kind of code.” Moreover, because of how it works, that coding scheme can uniquely and efficiently represent a lot of information.

And not just that: Since the grid network is based on relative relations, it could, at least in theory, represent not only a lot of information but a lot of different types of information, too. “What the grid cell captures is the dynamic instantiation of the most stable solution of physics,” said György Buzsáki, a neuroscientist at New York University’s School of Medicine: “the hexagon.” Perhaps nature arrived at just such a solution to enable the brain to represent, using grid cells, any structured relationship, from maps of word meanings to maps of future plans.

Still further on:

Some researchers are making even bolder claims. Jeff Hawkins, the founder of the machine intelligence company Numenta, leads a team that’s working on applying the grid code not just to explain the memory-related functions of the hippocampal region but to understand the entire neocortex — and with it, to explain all of cognition, and how we model every aspect of the world around us. According to his “thousand brains theory of intelligence,” he said, “the cortex is not just processing sensory input alone, but rather processing and applying it to a location.” When he first thought of the idea, and how grid cells might be facilitating it, he added, “I jumped out of my chair, I was so excited.”

Here's a Hawkins article:

Jeff Hawkins*, Marcus Lewis, Mirko Klukas, Scott Purdy and Subutai Ahmad, A Framework for Intelligence and Cortical Function Based on Grid Cells in the Neocortex, Front. Neural Circuits, 11 January 2019 | https://doi.org/10.3389/fncir.2018.00121.

How the neocortex works is a mystery. In this paper we propose a novel framework for understanding its function. Grid cells are neurons in the entorhinal cortex that represent the location of an animal in its environment. Recent evidence suggests that grid cell-like neurons may also be present in the neocortex. We propose that grid cells exist throughout the neocortex, in every region and in every cortical column. They define a location-based framework for how the neocortex functions. Whereas grid cells in the entorhinal cortex represent the location of one thing, the body relative to its environment, we propose that cortical grid cells simultaneously represent the location of many things. Cortical columns in somatosensory cortex track the location of tactile features relative to the object being touched and cortical columns in visual cortex track the location of visual features relative to the object being viewed. We propose that mechanisms in the entorhinal cortex and hippocampus that evolved for learning the structure of environments are now used by the neocortex to learn the structure of objects. Having a representation of location in each cortical column suggests mechanisms for how the neocortex represents object compositionality and object behaviors. It leads to the hypothesis that every part of the neocortex learns complete models of objects and that there are many models of each object distributed throughout the neocortex. The similarity of circuitry observed in all cortical regions is strong evidence that even high-level cognitive tasks are learned and represented in a location-based framework.