Alleviation of forgetting in preweanling rats

Abstract

Three experiments tested the learning and retention of neonatal rats (7, 9, and 12 days of age) with a nondirectional active avoidance task, using a vibrotactile conditioned stimulus. The hypothesis was that the substantial deficit of these animals in 24-hr retention is due, at least in part, to a deficiency in memory retrieval. In Experiment I, a reactivation treatment was found to alleviate the forgetting over the 24-hr period for 12-day olds although having somewhat lesser effect for animals 9 days of age. The reactivation treatment seemed ineffective for rats 7 days of age. Experiments II and III confirmed the reliability of the reactivation effects with 9- and 12-day olds, while adding further control conditions and providing new information concerning the ontogenesis of latent inhibition.

Facilitation and impairment of conditioning in the preweanling rat after prior exposure to the conditioned stimulus

“…Although all levels of preexposure to the CS seemed detrimental to the conditioningof 18-day-olds, intermediate levels had either no effect or a facilitating effect on the conditioning of the lo-day-olds. A similar pattern had been reported by Spear and Smith (1978) in testing instrumental conditioning with a quite differentCS and with different ages: prior exposure to the CS tended to facilitate conditioning in younger preweanlings but tended to impair it or have no effect in older preweanlings.…”

“…This factor appears also to have been ruled out, however. Spear and Smith (1978), testing preweanlings on active avoidance learning and retention, found facilitation with brief prior exposure to a vibrotactile stimulus in 9-day-old rats, but not in slightly older rats. Channell and Hall (1981), testing adult rats, also observed facilitation with a short preexposure period (1 h), and latent inhibition following longer (50-h) stimulus exposure.…”

“…Misanin, Guanowsky, and Riccio (1983) and Misanin, Blatt, and Hinderliter (1985) completed ontogenetic investigations of latent inhibition involving gustatory stimuli, but the youngest animals they tested were previously weaned 19-day-olds. Rudy and Cheatle (1979) and Spear and Smith (1978) are the only investigators who have reported effects of brief preexposure on learning in preweanling rats. Rudy and Cheatle (1979) found an impairment in odor-illness conditioning due to CS preexposure in 2-and 8-day-old pups, whereas Spear and Smith (1978) reported both facilitation (in 9-day-old rats) and attenuation (in 12-dayold rats) of avoidance behavior as a function of brief preexposure to the to-be-conditioned vibrotactile stimulus that they employed as the CS.…”

The effect of the home cage environment on retention of an active avoidance response in previsual rats

“…There was no evidence of retention 30 min after training. That the retention deficit in previsual rats is due to the inaccessibility, rather than the unavailability, of the memory for the AR is indicated in the work of Spear and Smith (1978). These investigators were able to get 24-h retention of an active AR in 9-and 12-dayold rats if the rats' memories were reactivated during the retention interval.…”

“…Spear and Smith (1978), for example, found no 24-h retention in 7-12-day-old rats whose memories were not reactivated during the retention interval. Similarly, Goldman and Tobach (1967), who were the first to examine retention of avoidance behavior in previsual rats, provide no convincing evidence of 24-h retention.…”