The path efficiency ratio, also known as path ratio or path efficiency, can be used in Morris Water Maze experiments to assess how directly a subject navigates toward the platform. It allows fair comparison of navigational performance across trials with different spatial configurations.

Unlike latency and path length, path ratio is:

• Not affected by the distance between the start point and the platform position.
• Ideal for comparing navigational performance across:
  • spatial learning trials with moving start points;
  • reversal learning trials with moving platform positions;
  • experiments carried out with different pool sizes (e.g. in different laboratories).

The path ratio is the value of the actual path length divided by the shortest possible (ideal or direct) path between the start point and the platform or target location. A perfectly direct swim would have a ratio of 1. Higher values indicate less efficient paths, with more meandering, looping, or wall-following behavior: the higher the value, the less efficient the path.

Comparing across trials with different start positions

When the platform is fixed but the start point varies (as in spatial memory tests), path length and latency will vary according to the varying distance between the start point and platform location. In contrast, the path ratio gives a consistent measure of navigational efficiency. For example, subjects that have learned the spatial location of the platform well will take direct routes regardless of the start point, keeping the path efficiency ratio high.

Comparing across trials with different platform positions

When the platform moves to a new location (as in reversal trials), the distance from each start point to the platform changes. This makes raw path length misleading when trying to compare performance across trials. A longer path length could simply reflect a greater start-to-goal distance.

Path efficiency ratio solves this by normalizing the actual path length against the ideal path from the current start point to the current platform location. This allows you to compare spatial accuracy fairly, allowing accurate assessment of cognitive flexibility.

Comparing across different pool sizes

Equally good performance has greater latency and path length in a larger pool than it does in a smaller pool, but the ideal path length (directly from the start point to the platform) increases proportionally. The path efficiency ratio is therefore consistent when the subjects’ navigational quality is the same.

So if you want to be able to compare results from your current experiments with those you do in future, when your pool may have been replaced with one larger or smaller or you may have moved to a different lab, or if you want to collaborate with other labs whose set up is different, you can with HVS Image: path ratio will allow you to make direct comparison of spatial accuracy across different setups.

In the HVS Image system, path efficiency is calculated automatically and can be viewed across individual trials or entire experiments, by checking one box. Once the box is checked, path ratio will be included in all individual and batch analysis, ready for your results export.