Repeated failures in reducing rat’s spontaneous alternation through the intertrial disruption of spatial orientation

Abstract

Three experiments examined the contention that an extramaze cue representing relative spatial direction controls rats' spontaneous alternation. Attempts to eliminate this short-term directional memory by horizontally rotating the Ss were without effect. These data, along with other recent findings, cast doubt upon the completeness of Douglas's model of spontaneous alternation.Spontaneous alternation, the tendency to enter opposing arms of a T-maze on successive turns, has been reported in rats for more than half a century (cf. Fowler, 1965). One of the more elaborate, successful, and perhaps the most widely cited of the recent studies of alternation was conducted by Douglas (1966a). In these experiments, alternation was attributed to only two cues. First, there was the relatively weak tendency for an animal to avoid its own odor trail. Second, the rats displayed a strong inclination to use extramaze spatial cues when encountering a T-maze choice point on successive occasions. Furthermore, these two factors were shown to combine additively.The same investigations showed that spatial information would be eliminated and alternation would not exceed chance levels if the rats were shaken horizontally between maze-arm choices. Since vertical tilting of the rats was without significant effect, while middle ear disease was disruptive (Douglas, 1966b), a "vestibular" memory system was postulated as the mechanism mediating alternation in response to extramaze spatial cues.In order to document further the importance of rats' spatial memories in spontaneous alternation, three attempts were made to disrupt the behavior through the horizontal turning of Ss between choices. EXPERIMENT I MethodSUbjects and Apparatus. The Ss were 37 male and female Sprague-Dawley albino rats born in the Brooklyn College colony; these animals were 48 days old at the start of the procedure and had previously experienced both handling and maze adaptation trials (without any food or water reinforcement). Except for an occasional individually housed S, these rats were placed two to a cage (same-sex pairs) on a schedule of ad lib Purina Lab Chow