Since the start of the project, we have built and tested the experimental setups to perform our experiments, including highly controlled behaviour assays, in-vivo brain recordings in behaving animals, and precise expression of viral tools in selected brain areas. This allowed us to make several important advances:
We started by systematically evaluating the number of experimental sessions we can perform in a mouse without losing its responses to visual threat stimuli, and found that more than 4-5 sessions leads to permanent habituation. These are crucial data for all behaviour experiments of this project.
Applying these insights, we discovered astonishing effects of time and light on behaviour with three main findings: First, the main modulator of escape behaviour is ambient light. Second, the circadian clock only affects behaviour if it mismatches the light conditions (e.g. daylight at night), leading to weaker behaviour whenever there is a mismatch. Third, light history plays an important role and can either counteract or enhance the mismatch effect. If 2-3 of these aspects mismatch, it can have detrimental effects on innate behaviours. Ongoing tests using tools that allow us to specifically inhibit or activate selected neuronal circuits, suggest that direct connections from the “master clock” of the brain to the brain nuclei that mediate innate behaviours are responsible for time-specific reactions to danger. In the meantime, we have prepared everything to start experiments with Rhabdomys pumilio, a diurnal close relative of mice. It will be exciting to see if diurnal species react the same or in an opposite way to changes in time and light.
Furthermore, we have built on preliminary data on how ecological niches affect behaviour and found that two sister-species of Peromyscus (North American deer mice), originating from very different habitats, react differently to approaching danger. Animals that live in vegetated areas with many hiding spots tend to escape from approaching danger, while those that live in empty sand dunes tend to freeze. We could pinpoint the source of these differences to a specific brain nucleus that induces escaping behaviour in one species, but not in the other. Such drastic remodeling in an evolutionary speaking short time has been very surprising. This reinforces additional questions that we have planned to address, such as how similar the brain circuits that mediate essential behaviours are across species.
Finally, we have started experiments to dive deeper into a mechanistic understanding of how time, light and ecological changes precisely impact neural circuits, and how the resulting changes in behaviour are encoded.
