Fifteen-day-old rats made random choices in a T-maze, while adult levels of alternation (approximately 70%) were noted among 30-day-olds, Also, younger pups were insensitive to a lengthening of the intertrial interval, unlike older animals whose rate of alternation decreased when a l-h delay was interposed between arm entries, These findings are consistent with the hypothesis that hippocampal development is a factor in the ontogeny of postweaning locomotion. The unsystematic pattern of goal-arm selections among 15-day-olds suggests that ontongenetic variation in the utilization of stimuli may underlie developmental shifts in spontaneous alternation, Altman, Brunner, and Bayer (1973) have suggested that the 2-or 3-week-old domestic rat is behaviorally similar to the hippocampectornized adult of the species. Further, maturation rates of cells at the dentate gyrus and the development of cholinergic control over behavior are consistent with this brain-development hypothesis (Campbell, Lytle, & Fibiger, 1969;Douglas, 1972).This particular behavioral syndrome, typical of the young rat, includes: (a) elevated and persistent motor activity (Bronstein, Neiman, Wolkoff, & Levine, 1974;Campbell et al, 1969;Feigley, Parsons, Hamilton, & Spear, 1972), (b) considerable difficulty in the acquisition of a passive-avoidance task to a footshock US (e.g., Ricco & Marazzo, 1972), (c) impaired position-habit reversal (Harley & Moody, 1973), and (d) low levels of spontaneous alternation (Douglas, Peterson, & Douglas, 1973;Kirkby, 1967). The present paper describes attempts to replicate and to further understand the age-related differences in spontaneous alternation. EXPERIMENT IThe first experiment is a longitudinal investigation of alternation in the rat. MethodSubjects. Twenty-three male and 14 female rat pups served as Ss. These were derived from four Sprague-Dawley albino litters (9 or 10 pups/dam) born in the Brooklyn College laboratories. The animals were individually marked and housed with their mothers in plastic litter cages. Twenty-two days after parturition, the maternal females were removed from their offspring with all pups left behind in the litter boxes. When the young were 31 days old, they were rehoused, 2 to a cage (same-sex pairs), except for a few individually caged Ss, Purina Lab Chow and water were always available, and the colony was heated to about 74°F. The vivarium was brightly lighted from 8 a.m. to 2 a.m. daily, and Ss were run during the light part of the cycle, always at about the same time of day.Apparatus. One bottomless plywood T-rnaze, painted flat black, was the apparatus. The maze was 6.40 cm high and initially had a width of 6.35 em, but was widened to 10.80 cm throughout after the Ss were 31 days old. This enlargement was needed in order to accommodate the pups' growth. The apparatus was covered with clear Plexiglas, and three guillotine doors of white plastic divided the maze stem into a startbox and runway (each 20.32 cm long) and goal arms (each 28.85 em long). A 15-Wincandescent bulb, shaded ...

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