Dissecting novel object exploration: a fully automated homecage-based novel object recognition test

Abstract

The novel object recognition test is a frequently used memory test in rodents. Due to its ethological nature, cross-species relevance, and specificity to testing hippocampal and parahippocampal function, it has been widely applied in basic and translational research. However, its implementation proves challenging due to multiple uncontrolled factors. Here, we describe a fully automated homecage-based novel object recognition test for assessing long-term object memory in mice. We present an empirically guided computational model to show the robustness of this approach despite ambiguity in defining exploratory behaviours. We show that mice preferentially explored novel compared to familiar objects after 24-hour and 7-day retention periods, starting to discern them while still a distance away. The findings were replicated across two facilities. Furthermore, the ability to recognise the novel object depends on the mouses prior interactions with the replaced object after 24 hours, but not after 7 days. Finally, we showed that external factors may introduce undesired exploration biases, which can be addressed using relative instead of absolute discrimination measures. The fully automated homecage-based object recognition test will improve standardisation, rigour, and reproducibility, as well as expand our understanding of the factors influencing object exploratory behaviours and object memory. MotivationRecognition of objects as novel or familiar is an important cognitive memory function with cross-species relevance. Extensive work has provided a good understanding of the brain regions involved. Despite the apparent simplicity of novel object recognition (NOR) tests, they remain challenging due to their sensitivity to various uncontrolled experimental factors and differences in study design. Here, we report a fully automated standardised NOR test carried out in a mouses homecage, which minimises previously reported variability in NOR tests. HighlightsO_LIFully automated novel object recognition test for assessing long-term object memory in the mouses homecage C_LIO_LIA robust analysis pipeline described C_LIO_LITest replicated in two facilities with comparable results C_LIO_LIAn empirically guided computational model pointing to the robustness of this approach introduced C_LIO_LIMajor factors affecting the ability to discriminate novel from familiar objects, including object exploration bias, are described C_LI