Effects of intensity and spacing of prior stimulation on later emotional behavior.

Abstract

410 Wistar rats were subjected to 22 different early-treatment conditions and tested in an open field at 70 days. When the different treatments were ranked, a U-shaped relationship was found between amount of early stimulation and later emotionality. Ss [subjects] receiving stimulation spaced throughout early development were less emotional than Ss receiving the same treatment massed in a short period of time. No "critical-period" effects were found. Apparent contradictions in previous early-experience studies appear to be due to the spacing of stimulation and to the different types of control group used for comparison.