Spontaneous Alternation Behavior and the Brain

Abstract

One strategy for writing this chapter would have been to prepare an immense list of all studies linking spontaneous alternation behavior to brain lesions or drugs. Our minds thoroughly boggled, we could then have identified a few missing items in the list and agreed that further research was necessary. I believe, however, that even though there are many studies crying out to be done, it is possible to make considerable sense out ofthe staggering amount of evidence already in existence. The results of hundreds of alternation experiments do tell a story-two quite different stories, in fact. And these stories reveal more than why a rat turns right or left in a T maze. The alternating rat is trying to tell us how the brain works, and my intent in writing this chapter is to convey to you what the alternating rat tells me. The most basic way of studying brain function is to destroy a given region or structure and see what happens. Such studies have shown that while SAB is definitely not affected by brain damage in general, there are in fact many brain structures that appear to be involved in alternation. This can be bewildering if one is unaware of the anatomical relationships between these seemingly different structures, which can be assembled into systems on the basis of interconnections. As we shall see, it is possible to align each alternation-related structure with either of two systems, one of which is centered on the hippocampus and the other on the vestibular system. The problem then becomes one of trying to determine what each of these sets contributes to SAB and what each structure contributes to its set. This procedure is facilitated by considering exactly what is involved when a rat alternates in a T maze. First, the animal must be able to apportion its perceptual world into two parts, recognize the difference between them, and remember which one has been most recently visited. Second, the animal must have some motive for avoiding revisits. Call it curiosity. But another motive is also often operative in the T maze, and "fear" is a good name for it. Fear and Perseveration It has been known for almost half a century that fearfulness antagonizes alternation (e.g., Heathers, 1940). Rats often perseverate when placed in a two-choice situation involving danger. They do not alternate when forced to leap into space W. N. Dember et al., Spontaneous Alternation Behavior