On the connection between imagination and memory

Reading Time: 2 minutes

Here’s a sweet little link between the nature of imagination and memory as evidenced in the brain of a rat considering which way to go next in a maze, the activity of whose cortex is being measured live by in-vivo recordings. It’s from some seminal work done by Adam Johnson and A David Redish more than a decade ago.

The gif here shows the position of the rat in a maze that is described by the ‘place cells’ in its own cortex, which were themselves previously mapped as it had made its way through the space. Place cells light up when you’re at a particular point in space, firing independently of anything you’re looking at. The map, in somewhat meta fashion, is derived from measuring directly from the rat’s brain: its memory for the space has come to map the space.

The gif illustrates the moment the creature reaches a T-junction and considers what to do next. The shite circle marks the actual position of the rat. You can see its ‘memory’ for places to right and left lighting up as it considers which path to go down. It’s actively exploring its memory, in an imaginative fashion. It’s a very relatable graphic, extremely thought provoking to consider.

It reminds me of a quote from an engaging article about the recent Carlsen / Caruana world championship Chess bout in which it was said that “Caruana’s brain scurried back and forth through innumerable tunnels of calculation looking for ways to fight back”. This is intuitively phenomenologically what we do when we consider different possibilities, and it’s (as ever) nice to have that conviction that the fresh boots of a easily referenced information gives one.

Some interesting things to wonder about, that I haven’t quite grokked:

  • What happens the first time the creature is in a space and is wondering which way to go next? The memory’s not quite there yet, so how would the explorations work? (perhaps, because experience runs deep into perception, there isn’t a case that isn’t undergirded by some degree of memory, however novel).
  • What is the purpose of the exploration of memory/imagination? Presumably, to fish out some extra information (presumably connected to or part of the memory) to marry with current goals. Cf the Caruana quote. This would make this somehow similar to attention.
  • But if we don’t allow ourselves to talk about “fishing out” (which is lazy and dualistic) then what causal effect on the system as a whole is the
  • And of course, are there a hundred analogues of this in other forms of decision making, in other areas of the brain, with related dynamics and logic?

The research, btw, to derive this result was quite remarkable: requiring disambiguating where the rat was looking from what it was thinking. The places it is exploring in its imagination/memory are distinct from the places it is looking. This is a live read from its memory/imagination as it explores what should happen next.

Adam Johnson, the driving force behind the research sadly died shortly afterwards and much too young of cancer. This is a moving document put together by his colleagues in his lifetime that captures something of his intellect and character and the high regard in which he was held by his colleagues.

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