SEVERAL RECENT SUHVKYS of the literature (2,3,4,9) reflect the increased emphasis being placed upon study of the relationship between early environment and later behaviour in animals. Learning ability has received particular attention, and several studies have shown that the learning ability of adult animaLs is affected by the quality of their infant environment. More specifically, they indicate that animals raised in "enriched" or "stimulating" environments are superior in adult learning ability to animals raised in "restricted" or "unstimulating" environments.These results were obtained with animals possessing a normal heritage of learning ability; hence there remains the possibility of differential effects for animals of superior or inferior endowment. The present study was designed to explore this possibility. Its specific object was to test for possible differential effects of enriched and restristed early environments on the problem-solving ability of bright and of dull rats.
SUMMARY Initially subconvulsive doses (20 mg/kg I.P.) of pentylenetetrazol (PTZ) were given never more frequently than once every two days to several groups of normal and brain‐lesioned rats. After a few drug administrations myoclonic convulsions began to follow the injections in some of the brain‐lesioned animals. Tonic‐clonic convulsions were observed in some of these animals after further injections. Convulsions occurred with greater frequency in the brain‐damaged subjects but did eventually develop in some animals in the normal groups. For both the lesioned and the normal rats, the increase in sensitivity to the drug appeared to be relatively permanent since it did not diminish when the injections were withheld for even as long as three months. For the brain‐lesioned rats, time of surgery did not prove to be an important variable. The increase in sensitivity to pentylenetetrazol developed just as rapidly in animals started on a series of drug injections one month after surgery as in animals started on PTZ three months after surgery. The present study and other recent work (e.g., Goddard et al. 1969) indicate that repeated stimulation of neural tissue leads to a permanent change in the response to the stimulation, a change which may be reflecting a structural alteration of neurons. RESUME On a donné des doses intiales subconvulsives (20 mg/Kg I.P.) de pentetrazol (PTZ) à raison d'une dose tous les 2 jours à un groupe de rats normaux et à un groupe de rats présentant des lésions cérébrales. Après un certain nombre d'administrations de PTZ, quelques rats ayant des lésions cérébrales ont commencéà présenter des convulsions myocloniques, puis après de nouvelles administrations de PTZ, des crises tonico‐cloniques. Les crises étaient plus nombreuses chez les rats avec lésions cérébrales mais il y avait aussi quelques crises chez les rats normaux. Chez les rats avec des lésions aussi bien que chez les rats normaux, on a observé une hypersensibilité relativement persistante qui a duré jusqu'à 3 mois après l'arrêt des injections de PTZ. Le moment de la lésion cérébrale ne jouait pas un rôle important puisque l'hypersensibilité au PTZ se manifestait avec la même rapidité chez les animaux injectés au PTZ, un mois ou 3 mois après la lésion. Cette étude, ainsi que celle récente de Goddard et al. 1969, indique qu'une stimulation neuronale répétée induit des modifications permanentes dans la réponse aux stimulations, modifications qui peuvent refléter une altération structurale des neurones.
Three groups of rats received electroconvulsive shock (ECS) lO sec .• 2 min .• or 5 hr. after one-trial avoidance training. These Ss as well as additional no-ECS control Ss were tested for retention 25 hr. afterward. Three more groups received one-trial avoidance training followed by a test of retention 10 sec .• 2 min .• or 5 hr. later. Both the ECS gradient effect and the incubation effect were demonstrated. The close relationship between the two functions suggested a new interpretati on of the ECS gradient effect.A nwnber of investigators have demonstrated an electroconvulsive shock (ECS) gradient effect, that is, that the sooner an ECS is administered after training the more the performance on a later test of retention is disrupted. Brady (1952) demonstrated a gradient effect after emotional conditioning which occurred over a period of months. On the other hand, Pinel & Cooper (1966) found a gradient effect after one-trial avoidance training which occurred over a period of hours.This ECS gradient effect has generally been attributed to an underlying consolidation process; however, the findings of Brady (1951) and Pinel & Cooper (1966) that their respective passive avoidance tasks incubated or increased in strength over time intervals similar to those over which they were able to demonstrate gradient effects have suggested another interpretation. Possibly, ECS has a greater disruptive effect when administered shortly after learning because the learned response has not had a chance to incubate, and, therefore, is relatively weak. This present experiment was designed to test this hypothesis by attempting to demonstrate both the ECS gradient effect and incubation effect after one-trial avoidance training. ProcedureSeven groups of 10 experimentally naive, male, black-hooded rats were trained to drink from a spout located just above a large bar which was invariably depressed when Ss drank. Water was not contingent on a bar press but the bar enabled a record of drinking behavior to be kept. On the last pre shock training trial, the median latency, that is, the amount of time it took Ss to depress the bar after being placed in the test box, was 2 sec. On the avoidance training day, all Ss received a 12 rna DC shock (calibration resistance = 100 K) the first time they depressed the bar, and then were immediately removed from the box. Three groups of Ss received an ECS 10 sec., 2 min., or 5 hr. afterward. Convulsions were induced by a 0.3 sec., 50 rna AC current passed via saline-soaked, gauze-covered alligator clips attached to Ss' ears. All Ss were adapted to the ear clips by attaching them briefly after preshock training trials. The three ECS groups plus an additional no-ECS control group were all tested for retention 25 hr. afterward. The other three groups received tests of retention at the same intervals at which the ECS groups were receiving an ECS, that is, 10 sec., 2 min., or 5 hr. after avoidance training. All Ss were deprived of water for 23.5 hr. prior to the last preshock training trial and the postshock t...
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