This is a clearly written and beautifully illustrated article. My minor edits were mainly in re-spelling "opisthobranch." Congratulations to the authors!
This is an extremely well written, comprehensive, and beautifully illustrated short review. I have only several minor concerns, none of which temper my enthusiasm for the article.
1. The absence of references suggests to me that this is the standard format for Sholarpedia. Of course I think that references would benefit the reader.
2. It’s the nature of a short review, but in several places oversimplification can be misleading. For instance, it is said that “Emanating from each of the pedal ganglia are three pedal nerves (p1, p2, p3), which control locomotor behavior and reflexive foot and body wall movements” These pathways are not well understood (which is made explicit elsewhere in the article), and these kind of statements can lead a reader to believe that more is understood than actually is. As the authors are aware, this “over-selling” has probably been to the detriment of invertebrate research. I don’t think that this concern warrants any revision, but is probably a point worth considering.
3. There is no explicit statement as to how the modifications of the B photoreceptors that accompany associative learning lead to modifications of behavior. This may reflect the author’s acknowledgment that these pathways are not well understood, but nevertheless, at least some noted conjecture may be warranted. Figure 4 is very nice, but it does not illustrate the inhibitory interaction between A and B photoreceptors. Absent this interaction, it would be difficult for the reader to discern from this figure the decrease in locomotion that accompanies the increase in excitability of the B cells following classical conditioning. While this old story is clearly inadequate, it should probably at least be proposed and illustrated.
4. Associative learning in Hermissenda is a form of reflex modification. As such, it may be a precursor to what modern theorists describe as associative learning. It is unlikely to reflect the type of learning that mammals undergo when stimuli are associated. Despite the nominal correspondence between learning processes in Hermissenda and those that have been described for mammals, persons familiar with contemporary learning principles may see this as a glaring problem for any extrapolation between the species.
5. The section on signaling pathways (and accompanying figure) would benefit from a explicit description of the link of the described signaling cascade to the modification of potassium conductance.