Response to novelty induced by change in size and complexity of familiar objects in Lister-Hooded rats, a follow-up of 2019 study

Abstract

This study examines the relationship between the change in size and change in complexity of well-known/familiarized objects and exploratory activity regulation in rats. In our experiment, the rats were exposed to three types of environmental novelty in a well-familiarized chamber: (1) addition of new tunnels to the chamber, (2) increased size of a familiarized tunnel, and (3) increased complexity of the existing tunnels. The animals responded to the addition of new tunnels with a significant behavioural shift involving increased exploration of the newly installed tunnels. This effect was stable across all three test trials. The rats exposed to a change in size of the familiar object initially reacted with a behavioural shift towards the enlarged tunnel but then re-focused on the unchanged one. There was also a significant increase in the frequency of moving between the zones of the chamber. The experimental group exposed to an increased complexity of familiar objects responded with a pronounced behavioural shift towards the complex tunnel and then slightly intensified their exploration of the unchanged one. A decrease was also observed in the frequency of moving between the zones of the chamber in the first and second test trials. In the effect size analysis, no differences were found in any of the three groups, which suggests that all manipulations had similar impact. The data obtained in this study supports the view that in rats, curiosity is at least two-dimensional: activational and cognitive. The activational aspect of curiosity may be explained by novelty-related arousal processes, while the cognitive processes are activated at longer time intervals in response to more complex stimulation. The validation of this hypothesis requires further research involving manipulations with a recently standardized protocol for measuring free exploration.

Rat’s response to a novelty and increased complexity of the environment resulting from the introduction of movable vs. stationary objects in the free exploration test

“…The results obtained for the Add and MovAdd groups seem to corroborate this assumption. The results of our previous studies [27,28] are also confirmed,…”

“…The results obtained for the Add and MovAdd groups seem to corroborate this assumption. The results of our previous studies [ 27 , 28 ] are also confirmed, which showed that an increase in the complexity of the environment through the addition of tunnels triggers a more intensive exploratory activity in rats.…”

“…In the MovAdd group, the novelty the animals encountered had a higher degree of complexity but also a greater level of uncertainty than in the other groups. These features may have strengthened the rats’ motivation to explore, resulting in less time being also spent in the familiar, unchanged zone of the chamber [ 25 , 27 , 28 ].…”

“…Moreover, complex environments help reduce anxiety and increase the rat’s activity [ 25 ], stimulating novelty-seeking behaviors [ 26 ]. The results of experiments suggest that rats prefer environments where the level of complexity is higher than the level they previously encountered [ 27 , 28 ]. In our previous experiments, environmental complexity was manipulated by increasing the number of elements (addition of tunnels) or decreasing the number of elements (removal of tunnels) in the test environment.…”

“…Our present work is a continuation of a series of studies on the various aspects of environmental novelty in rat behavior regulation [ 27 , 28 ]. This study is aimed at the analysis of the reaction to novelty, understood as a change in environmental properties that involve both change in complexity and controllability (the presence of movable and unmovable objects).…”