No abstract

Rats were given electrical stimulation to the midbrain reticular formation or to the hippocampus 4 seconds after they received shocks contingent on the animals' bar-press responses. They were retested for memory of the shocks 64 seconds or 24 hours after the shocks. The animals that received stimulation to the midbrain reticular formation showed amnesia at the 64-second retest and memory at the 24-hour retest. In contrast, animals that received stimulation to the hippocampus showed memory at the 64-second retest and amnesia at the 24-hour retest. The data support a dual, parallel-processing model of memory.

Twenty-four hours after the administration of a footshock (FS) followed 4 or 256 sec later by an electroconvulsive shock (ECS), rats exhibited amnesia for the aversive experience. They were then given a "reminder" cue (tone), which was earlier paired as a conditioned stimulus with footshocks. Presentation of the tone resulted in attenuation of the amnestic effect in FS•ECS 256-sec delay group but failed to alter the amnestic effect in FS-ECS 4•sec delay group. Results were interpreted in support of an "incomplete" memory consolidation hypothesis.

Two groups of 12 Long-Evans rats were alternately isolated and crowded. Order of housing and familiarity of the subjects with the test apparatus were also varied systematically. Subjects were deprived of food, trained to bar press, and allowed to compete in pairs for sugar water in a Skinner box. Isolated pairs produced more agonistic and contact behaviors and fewer bar presses than did crowded pairs. Weight was found to increase more rapidly during free feeding when animals were isolated. Familiarity of only 1 isolate with the testing environment led to the display of less aggression than was observed in other isolate conditions.Animal experimental findings seem equivocal regarding the hypothesis that crowding leads to aggression. This uncertainty exists because investigators have employed 2 different manipulations of the independent variable. Studies have been designed to examine the effects of (a) differences in population size and (b) differences between grouped and isolated housing conditions.Two conclusions may be drawn from such studies: (a) Larger groups of animals exhibit more aggression than do smaller groups (Gregor, Smith, Simons, & Parker, 1972); and (b) isolated animals exhibit more aggression than do grouped animals