The HexMaze: A previous knowledge and schema task for mice

Abstract

New information is rarely learned in isolation, instead most of what we experience can be incorporated into or uses previous knowledge networks in some form. However, most rodent laboratory tasks assume the animal to be naïve with no previous experience influencing the results. Previous knowledge in form of a schema can facilitate knowledge acquisition and accelerate systems consolidation: memories become more rapidly hippocampal independent and instead rely more on the prefrontal cortex. Here, we developed a new spatial navigation task where food locations are learned in a large, gangway maze -the HexMaze. Analysing performance across sessions as well as on specific trials, we can show simple memory effects as well as multiple effects of previous knowledge accelerating both online learning and performance increases over offline periods. Importantly, we are the first to show that schema build-up is dependent on how much time passes, not how often the animal is trained.

Naïve to expert: Considering the role of previous knowledge in memory

“…This was evident by a drop in performance on the first trial of the first session following an update when the goal location changed. However, by the following session, performance improved at the same level for all conditions, showing that one session was enough for the memory update and long-term memory (Alonso et al, 2020).…”

“…Intra-and extra-maze cues (star and hexagon) aid navigation in the maze. (Alonso et al, 2020) developed for mice to identify a pattern over time; however, many other schema prerequisites were not included. In a water maze-based task (Figure 2(b), centre-left), mice had to find a hidden platform below the water surface in a fixed place over four trials in 1 day, but the position of the platform changed slightly from 1 day to the next over nine training days, drawn from a statistically predefined distribution in space.…”

“…In the effort to establish a different task to test for previous knowledge in rodents, the HexMaze was developed (Alonso et al, 2020). It is based on multiple episodes, is adaptable and has the same cognitive load throughout.…”

“…In the first 3 weeks of the build-up, during which the location of the reward stays stable, a gradual increase in the performance was seen in each session, as mice gained experience in navigating the maze. If the goal location changed, performance initially dropped to the same level as when the animal was first introduced to the task, but by the second session following this goal location change, the overall performance was better compared to the second session of the previous goal location (Alonso et al, 2020). However, in this build-up phase, long-term memory (48 h) still took multiple sessions to develop.…”

“…In addition, we found that the build-up phase was not dependent on amount of training, but rather on time, that is, by training mice three times a week versus twice a week. The increase in performance depended on the amount of time that had passed since the beginning of the experiment and not in how many times they were trained per week (Alonso et al, 2020).…”