The present study examined open-field behavior in the high- and low-activity mouse strains, ICR, and five inbred strains of mice (BALB/c, C3H/He, CBA/Ca, C57BL/6, and DBA/2). The high- and low-activity strains were characterized as the highest and the lowest in ambulatory activity, respectively. However, they did not differ for defecation. A principal component analysis applied to observational data based on 11 behavioral items revealed four components, which accounted for 64% of the total variance. The strain differences found in component 1 and 2 could be described from four elements (initial values, changes in 1-3min and 4-10min of the test period, and final values). The high-activity strain contrasted with the low-activity strain in component 1, whereas they resembled each other in component 2. The similar pattern of strain differences was also found between BALB and C57BL. Component 2 might be related to a trait independent of “activity” or “emotionality”. Open-field behavior of the high-activity strain was much more similar to that of ICR (a base population of the selection) than the low-activity strain, which indicated that genetic changes had occurred mainly in the low-activity strain.

View full abstract

The present study examined operant conditioning in domestic pigs that were bred under the ordinary feeding scheme of the livestock industry. Two castrated male pigs were shaped to press a lever by successive approximation method with 3.4-g food pellets and 2-s buzzers. Shaping was accomplished within about 40 min and about 90 reinforcements. During acquisition, the number of responses in a 20-min session was increased from about 100 to 200 during 20 sessions of training with continuous reinforcement. During extinction sessions, rapid extinction and minimal spontaneous recovery was observed. In later sessions during the acquisition phase, pigs began to press the lever several times consecutively before consuming rewards in the feeder. In Experiment 2, the consecutive responses were eliminated when only one reinforcer was delivered for a train of responses. This result suggests that the consecutive response is a foraging strategy to save response cost required for shuttling behavior between the lever and the feeder.

View full abstract

A modified Hill maze, which consisted of four selection boxes arranged in a rotating style, was used to investigate rats' serial learning. Four rats were trained to master a three-item series including three distinctive objects presented simultaneously in each selection box. All rats learned to choose the objects in a prescribed order (A-B-C). After rats learned their series reliably, novel spatial arrangements of the item objects were introduced as a test for a response chaining strategy. In spite of these spatial changes of the items, their performance for the novel arrangements was maintained at exactly the same level of accuracy as for the original arrangements. The results suggest that rats learned the three-item series not based on response chaining, and that the modified version of Hill maze is a useful tool to investigate rats' serial learning.

View full abstract