Introduction

The problem with LTP is that it is deceptively simple-looking. Buzz a slice and get a lasting change, what could be simpler? It looks for all the world like you had simply flipped a biochemical "light switch" and turned on LTP. We now know the error of this mindset: we now know that LTP is immensely complex as both a physiologic and biochemical phenomenon. In this chapter, we continue our discussion of LTP physiology, highlighting a few of the complexities that LTP exhibits at the physiologic level. This will help us transition to our discussion of LTP biochemistry in the next section, where things are going to start to get really hairy.

I find it ironic that there was an influx of stellar scientists into the LTP field in the late

1980s and early 1990s, when there was a general sense that LTP would be solved in 5 years or so and that everybody had better hurry in order to be the first. Although nobody ever came right out and said it, I'm sure that more than a few people thought there was a Nobel Prize ripe for the taking. It turned out that LTP was more complicated than most of us imagined, and it seemed like the more we learned, the worse it got. The quick answer was not there to be had, and these days the general mindset in some quarters is to question if the molecular complexity of LTP might not in fact be overwhelming.

From one perspective, this complexity in itself suggests the physiologic relevance of LTP—such an immensely complicated biochemical process is very unlikely to pop up as an experimental artifact. One imagines that a great deal of selection pressure over time is necessary for the evolution of the subtleties and complexities manifest in the biochemistry of LTP. By inference, this also suggests that LTP is doing something very important but also complicated in the behaving animal, such as subserving learning and memory. Thus, one can make the argument that the molecular complexity of LTP is inferential evidence of its involvement in memory in the animal, or at least some evolutionarily important process that has been rigorously selected for over great distances of evolutionary time.

We might call this the "blind watchmaker" argument for a role for LTP in memory formation. Dr. Richard Dawkins has written a book entitled The Blind Watchmaker— one theme of which is that the presence of biological complexity implies functional importance from an evolutionary perspective (1). While Dr. Dawkins was discussing this concept in the context of creationism versus Darwinism, the argument might also, in my opinion, be applied to LTP and memory formation.

In this chapter I will highlight a few of the interesting complexities of LTP. We will expand upon the basics of LTP presented in the last chapter by discussing in more detail some specific attributes of LTP induction and expression that go beyond the fundamental activity-dependence of LTP that we have already covered. In this chapter, we also will touch on many areas that are current topics of investigation, some of which are unresolved, controversial, or speculative. For our purposes here, I will for the most part limit the discussion to complexities that can be observed or demonstrated using physiologic techniques.

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