We read this very cool paper from Ayelet Sarel, Shaked Palgi, Dan Blum, Johnatan Aljadeff, Liora Las & Nachum Ulanovsky in our lab meeting today.
https://www.nature.com/articles/s41586-022-05112-2 (open access!)
They recorded from two bats flying back and forth in a 135m tunnel. They wirelessly recorded from the hippocampus of one of the bats and recorded the position and ultrasonic vocalizations of the bats. As the bats approach each other, they dramatically increase their vocalizations (presumably to avoid collision).
Hippocampal place cells are modulated by the relative position of the animals in complex ways, and this modulation is very rapid (turns on and off within a few seconds) as the bats approach each other.
I think the paper is quite a beautiful demonstration of how we can use ethological phenomena (like the sudden appearance of a conspecific) to better understand neural dynamics.
That said, I have a substantial concern with the paper. Hopefully, this toot might find its way to the authors - encourage them to join mastodon and reply :)
The authors analyze the neural activity relative to the tunnel , which they call "position" and with respect to the other bat which they call "interbat distance". However, the measure that they call "interbat distance" is not distance. Euclidean distance along a line is defined as +√((x₂-x₁)²). **It is always positive**. The authors _redefined_ distance to be the signed value x₂-x₁. This quantify is the position of x₂ relative to x₁, not the distance.
You might think that I'm being pedantic. Maybe the authors just thought it would be clearer to talk about "position" and "distance" instead of saying "tunnel position" and "position relative to other bat". However, they claim that "hippocampal neurons can rapidly switch their core computation to represent the relevant behavioural variables." If we change their wording to my wording, then what they have shown is that hippocamal neurons can rapidly switch the reference point that is being used to represent their current position, including using a reference point that is moving.
This is still a cool result. But is less novel. There is extensive work examining how hippocampus remaps or "reregisters" place cells when animals have to monitor multiple reference frames. A nice example is from [André Fenton's lab](https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1000403). The authors cite Fenton's work but say that Fenton "reported switching between two position maps, whereas here we found switching from position representation to distance-by-position representation." And that, i think really underscores how their redefinition of distance influenced the way they think about their results.
