Developmental Psychobiology

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.

These experiments indicate that by Day 15 after birth, the processes that mediate a number of taste‐controlled behaviors in the rat are functional. These include the sensory processes necessary to detect and respond reflexively to sucrose, the event‐learning processes that reduce the rat's neophobic reaction to sucrose, and the integrative‐learning processes that enable it to learn an aversion to sucrose when paired with lithium toxicosis, even when these events are separated by 1 hr. These capacities, however, did not emerge simultaneously. Those necessary to detect and respond reflexively to sucrose emerged prior to those that contribute to the learned control of taste‐guided behaviors. It is argued that these age‐related dissociations in behavioral capacities reflect a caudal‐to‐rostral maturational sequence of components of the ascending gustatory system that are thought to underlie these capacities.

The influence of LiCl preexposure on odor‐aversion conditioning produced by an odor‐LiCl pairing was studied in rats 7–31 days old. LiCl preexposure interfered with the acquisition of the odor aversion in both young and old pups. The time course of this effect depended, however, on the age of the pups. It lasted much longer (over 24 hr) if pups 8–17 days old were preexposed to LiCl than if the pups were preexposed when 30 days old (less 12 hr). Alternative interpretations of these data were discussed, and it was suggested that the age‐dependent differences in the time course of the LiCl preexposed effect may be determined in part by age‐related differences in the rat's excretory processes that clear lithium from the circulatory system.

Five experiments assessed the change in preference for an ambient odor after a brief period of exposure to that odor. Three minutes of exposure to a novel odor consistently increased subsequent preference for that odor. This effect occurred in preweanling rats 10 and 15 days of age even though, relative to the nest, the conditions of exposure were probably aversive tactually and thermally. There was relatively little variation in this effect between the ages of 10 Days postnatal and adulthood and over exposure durations ranging between 3 and 81 min. Substantial retention of this exposure effect was found for the 10‐day‐old rat, with no decline in induced preference over a 24‐hr period. The effect was unchanged by brief familiarization with the testing situation, but was eliminated by prior aversive experience with the testing situation. These results have implications for the design and interpretation of experiments that test learning and memory of odors, and emphazise generally the facility of the developing rat for processing olfactory information.

Two experiments examined in 5‐ and 10‐day‐old rat pups the impact of alcohol olfactory aversions upon subsequent alcohol intake. In Experiment 1 it was observed that at both ages, animals given a single pairing of alcohol odor and LiCl subsequently consumed less alcohol than those in any of 4 control conditions (alcohol odor unpaired with LiCl, alcohol odor exposure, lemon odor paired with LiCl, and untreated animals). In Experiment 2, pups of both age groups were given LiCl following exposure to alcohol odor, the infusion of an alcohol solution or both stimuli simultaneously. Rats given explicitly unpaired presentations of the different conditioned stimuli and internal malaise served as controls. It was observed that equivalent aversions to alcohol ingestion were expressed whether the infants had experienced the alcohol odor, the alcohol infusion, or both, paired with toxicosis. These experiments extend the ontogenetic spectrum of circumstances in which olfactory experiences affect subsequent ethanol ingestion and also may indicate an early nondifferentiated processing of odorant and gustatory cues arising from an ethanol stimulus.

Hybridization to unique DNA by RNA from brain or liver of rats given varying degrees of experience was investigated. RNA from brain of environmentally enriched rats hybridized to more unique DNA than did brain RNA from nonenriched controls. No significant differences were observed with liver RNA. This provides preliminary evidence for an increased transcription of the unique sequences of DNA in the enriched animals. The technique used has great promise for the investigation of experientially‐induced alterations in gene expression.

In this introductory article, we summarize the evidence from humans and animal models on the shaping of postnatal visual development by focused binocular input. When balanced input is missing during a sensitive period, deficits emerge, including seemingly permanent impairments in visual acuity that are labeled amblyopia. Rodent models have identified neurochemical changes that control the onset of such sensitive periods and molecular and structural brakes that lead to the diminution of the plasticity thereafter. Both animal and human studies of amblyopia have recently identified exciting ways to remediate vision in adulthood that bear some similarity to the interventions that have proved successful in promoting recovery from stroke. © 2012 Wiley Periodicals, Inc. Dev Psychobiol 54:224‐238, 2012.

Psychophysical studies of children deprived of early visual experience by dense cataracts indicate that there are multiple sensitive periods during which experience can influence visual development. We note three sensitive periods within acuity, each with different developmental time courses: the period of visually‐driven normal development, the sensitive period for damage, and the sensitive period for recovery. Moreover, there are different sensitive periods for different aspects of vision. Relative to the period of visually driven normal development, the sensitive period for damage is surprisingly long for acuity, peripheral vision, and asymmetry of optokinetic nystagmus, but surprisingly short for global motion. A comparison of results from unilaterally versus bilaterally deprived children provides insights into the complex nature of interactions between the eyes during normal visual development. © 2005 Wiley Periodicals, Inc. Dev Psychobiol 46: 163–183, 2005.

The general relationship between age and investigatory behavior in mammals, and perhaps other taxa, is probably an inverted U‐shaped function, but is said to be a negative correlation in bovines. In Observation Set 1,5 developmental levels of domestic cattle were compared in their responsiveness to a novel stimulus in the form of a person lying on the ground. The age group‐behavior relationship approximated an inverted U. In Observation Set II, 3 developmental levels were compared and the animals' responses to a ball and to the reclined figure of a person were studied. Qualitatively, the cattle reacted similarly to both the inanimate and the human objects; again, the relationship between age and investigatory tendencies appeared to be an inverted U‐shaped function for both stimuli.