Kenjiro Aoyama

Habituation may contribute to within-session decreases in responding under high-rate schedules of reinforcement

Two experiments tested the hypothesis that habituation contributes to within-session decreases in responding. In Experiment 1, rats’ leverpressing was reinforced under a fixed ratio (FR) 4 schedule throughout the baseline sessions. During the dishabituation sessions, the first 21 min and the last 21 min were FR 4; dishabituating events occurred during the middle 3 min. The dishabituating events altered the manner of reinforcer delivery in four different ways. Response rates increased after all dishabituating events. In Experiment 2, rats responded on several FR and variable ratio (VR) schedules. The ratio requirement varied from 3 to 15. Within-session decreases in responding were steeper during FR schedules than during VR schedules. In addition, response rates were well described as linear functions of cumulative number of food pellets eaten within sessions. These results support the habituation hypothesis but do not rule out the possibility that other satiety variables might contribute simultaneously.

Within-session Response rate in rats decreases as a function of amount eaten

In past studies, within-session changes of rat feeding behavior were always treated as functions of time. This study aimed to describe the within-session decreases of operant response as a function of cumulative amount of food intake. Rats (n = 8) were trained to obtain food pellets by lever-press responses. Session lengths were 45 min. The following results were observed: 1) Response rates during a CRF schedule were well described as a linear function of cumulative amount of food pellets eaten; 2) The linear equation was also accurate in describing the response rates during a semi-VI schedule; and 3) Even if schedules of reinforcement were changed within a single session, response rates in each reinforcement schedule were well described as linear functions of cumulative food intake. Thus, response rates decreased proportionally to the increase in cumulative amount of food intake.

Food Craving and Its Relationship with Restriction and Liking in Japanese Females

Craved foods are thought to be those that are well liked but restricted. However, this claim has not been demonstrated empirically. Japanese female undergraduate students (n = 144) completed a questionnaire measuring their craving for, degree of liking, and frequency of restricting their eating of 47 widely consumed foods. The food with the highest mean craving score was rice. We plotted the craving scores as a function of restriction and liking scores for the 47 foods. The students’ craving scores were strongly correlated with their restriction scores and liking scores. Thus, craved foods are those that are restricted and liked. However, in both scatter plots, rice was an outlier. While it was the most craved food, neither the restriction nor liking score of rice was very high. These findings were consistent with the view that craved foods are generally liked, yet restricted, implying the generation of food related conflicts. Interestingly, the mechanism of craving rice, the main staple in Japan, may differ from other foods.

Tool-use by rats (Rattus norvegicus): tool-choice based on tool features

In the present study, we investigated whether rats (Rattus norvegicus) could be trained to use tools in an experimental setting. In Experiment 1, we investigated whether rats became able to choose appropriate hook-shaped tools to obtain food based on the spatial arrangements of the tool and food, similar to tests conducted in non-human primates and birds. With training, the rats were able to choose the appropriate hooks. In Experiments 2 and 3, we conducted transfer tests with novel tools. The rats had to choose between a functional and non-functional rake-shaped tool in these experiments. In Experiment 2, the tools differed from those of Experiment 1 in terms of shape, color, and texture. In Experiment 3, there was a contradiction between the appearance and the functionality of these tools. The rats could obtain the food with a functional rake with a transparent blade but could not obtain food with a non-functional rake with an opaque soft blade. All rats chose the functional over the non-functional rakes in Experiment 2, but none of the rats chose the functional rake in Experiment 3. Thus, the rats were able to choose the functional rakes only when there was no contradiction between the appearance and functionality of the tools. These results suggest that rats understand the spatial and physical relationships between the tool, food, and self when there was no such contradiction.

Tool manipulation by rats ( Rattus norvegicus ) according to the position of food

Tool-use behaviour has been observed in nonhuman animals in the wild and in experimental settings. In the present study, we investigated whether rats (Rattus norvegicus) could manipulate a tool according to the position of food to obtain the food in an experimental setting. Eight rats were trained to use a rake-shaped tool to obtain food beyond their reach using a step-by-step protocol in the initial training period. Following training, the rake was placed at the centre of the experimental apparatus, and food was placed on either the left or right side of the rake. Rats learned to manipulate the rake to obtain food in situations in which they could not obtain the food just by pulling the rake perpendicularly to themselves. Our findings thus indicate that the rat is a potential animal model to investigate the behavioural and neural mechanisms of tool-use behaviour.