The neurons in question were in the hippocampus. This brain region is known to be important for a variety of memory related, but also decision making, functions. (See my earlier posting on hippocampal representation of physical locations forward of actual movement in the rat.) The authors of this study describe this as evidence of encoding of the 'concept of nest'.
Aside: Some researchers have tiresomely mantained that conceptual thinking is distinctively human. It doesn't help that philosophers and psychologists don't use 'concept' univocally, and rarely in the same ways as each other. Appropriate behaviour is going to be reasonably responsive to interesting equivalence classes (predators, escape routes, possible mates, nest materials, etc., etc.) and the cognitive processes relating to these classes is at least necessary for 'conceptual' cognition, even if some might want to demand additional features (like compositionality).Back to the main story: This crowd stuck the tools for ensemble recording into region CA1 of the hippocampus of each of the subject mice, and the exposed the mice to a variety of nests and objects that were in some sense nest-like, but not appropriate (being upside down, far too big, of poor materials, etc.) as well as unusual but suitable nests (like oddly shaped ones). The mice also approached the target objects from different directions. In the luxurious world of the lab-mouse, a nest is a paper or plastic cup about the right size to curl up in (see the images with the supplemental information.)
Their analysis found three categories of interesting activity:
- "Transient-on" cells responded temporarily to, for example, initial encounter with the home nest, but not to a similar circular object (a water cup) or to a nest when upside down. (These cells are associated with activity amounting to "there's a nest!") See the movie below.
- "Persistent-on" cells responded persistently to presence in the home nest, irrespective of direction of original approach. (These cells are associated with activity amounting to "I'm in a nest!")
- "Persistent-off" cells were the opposite of the above, going quiet outside nests. ("I'm not in a nest!")
Additional sub-experiments placed appropriate nests under odd conditions (e.g. being under a glass floor) and found that the 'nest cells' weren't keen on nests that weren't readily useable. This complements the finding that the cells didn't like upside down (otherwise appropriate) nests either.
This is very cool. Encodings like this are efficient resources for other processing, like selecting responses (whether to "poop here" or not), and populating more plainly spatial memory with meaning ("here be a nest"). The Johnson and Redish paper I blogged previously suggests that "here be good stuff" is encoded in some way that indexes to spatial memory, although their main point is to show something about the use of that memory in action selection. It also wasn't obvious in advance that the encoding would be, as it seems to be, primarily functional, although I'd have been surprised if it wasn't.
It would be good to know more about how these encodings are constructed.
I wonder if any of those Heideggereans, prone to letting off clouds of portentous bull about how science can't tell us anything about the real nature of embodied being in the world, or how it is that we come to relate in an immediate way to objects that are appropriate for our purposes, are paying attention. I doubt it, and doubt that they read PNAS.
Lin, L., Chen, G., Kuang, H., Wang, D., Tsien, J.Z. (2007). Neural encoding of the concept of nest in the mouse brain. Proceedings of the National Academy of Sciences, 104(14), 6066-6071. DOI: 10.1073/pnas.0701106104