26 August 2008

Failed models, Part 2

Back in the 1960s, there was a lot of research interest in little flatworms, Planaria. They were being used as model organisms in research on learning and memory.

On the face of it, Planaria shared many advantages with other model organisms: it's small, easy to look after, and common. The field had its own journal, The Worm Runner's Digest, (later the Journal of Biological Psychology).

But I suspect you'd be hard pressed to find anyone using Planaria today as a general model organism. Indeed, there's a book titled, Whatever happened to Planaria? So why did Planaria fail as a model organism? I will confess to not having read the book above, but I can see a few reasons.

First, a major finding based on Planaria was... well.. weird. Basically, if you taught one animal something (like running a maze), then killed it and fed the pieces to another animal, it performed better at the task than expected. Much was written about this, and I think the bottom line is that it didn't replicate well. It didn't lead to useful experiments in other species. In some sense, this one claim may have discredited the field.

Second, as a model for learning and memory, Planaria were being studied just at a time when electrophysiology started to make huge progress in understanding the neural basis of learning. And here, Planaria are not convenient: they and their neurons are a bit small for electrophysiology. The sea slug Aplysia, on the other hand, had huge nuerons, and it filled the niche of a simple invertebrate model for studying learning.

Third, I can't help shake the impression that the field was somewhat insular. Maybe this is just an impression I get from The Worm Runner's Digest, at least. I don't know where a lot of other Planaria research at that time was published. This is the downside of having specialty journals on one organism: other people don't read it. If you're going to have a model organism, this is lethal.

To this day, though, The Worm Runner's Digest is justly remembered for its irreverent humour.


Alvarado AS. 2004. Planarians. Current Biology 14(18): R737-R738. http://dx.doi.org/10.1016/j.cub.2004.09.005

Mitman G, Fausto Sterling A. 1992. Whatever happened to Planaria? C.M. Child and the Physiology of Inheritance. Princeton University Press: Princeton.

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