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Measures

The chaining annulus

Right distance from the wall, no idea where the platform is.

By the watermaze.org editors · Updated

Some animals solve the water maze without really solving it. They learn how far the platform is from the wall, then swim round and round at that distance until they bump into it. Latency drops, path length drops, and on those numbers alone the animal looks like it's learning the map. It isn't. This is chaining, and the chaining annulus is how you catch it.

What chaining is

In chaining, the animal circles at a fixed distance from the wall, typically matching the platform's distance from the wall. It's an egocentric, non-spatial strategy that doesn't rely on the room cues. It is often linked to procedural learning systems such as the dorsolateral striatum, rather than the hippocampus. HVS Image describes it as a refinement of pool circling: the animal learns to circle at the right distance between the centre and the wall, so it bumps into the platform.

What the annulus is

The chaining annulus is a ring-shaped (doughnut) zone covering every point in the pool at the platform's distance from the wall. The open-source Pathfinder software defines it as a zone "centered on the goal" that "spans all areas of the maze at a fixed distance from the maze wall", with a width you choose (Cooke and colleagues, 2020). An animal that is chaining keeps its track inside that ring as it goes round.

It's different from the circular zones that split the pool into rings for occupancy, and from the small counters around the platform. The annulus isn't about how close the animal got to the platform. It's about whether it stayed at the platform's distance from the wall while travelling round the pool.

How it's measured

Time in the ring alone isn't enough, because a focused searcher near the platform would also spend time in it. What matters is how far round the pool the animal travelled while inside the ring. HVS Image 2027 (Insight and Strategy levels) reports:

  • Total angular span in the chaining annulus: how many degrees round the pool the animal covered while in the ring.
  • Angular span of the largest episode: the longest single sweep round the ring.
  • Circling: the number of complete circles, clockwise and counter-clockwise. HVS Image counts complete loops that enclose the pool centre; doubling back doesn't change the count.

At the Strategy level, chaining is also identified automatically as a behaviour, with its total qualifying angular span in degrees.

Reading it

  • Learning trials: chaining may mean learning is still at an early stage, or that a procedural strategy is in use. Tracking circling and chaining across days shows whether animals move from non-spatial to spatial strategies, or never make that switch.
  • Probe trials after full training: chaining typically means spatial learning is impaired or absent, for example in Alzheimer's disease models or after hippocampal or entorhinal lesions. Chaining animals keep swimming at the same radius. Target quadrant time is usually near chance, and any platform crossings are incidental.
  • Your set-up: chaining can also mean the room lacks strong spatial cues. If spatial learning is what you're studying, that's a signal to improve the cues.

The useful part is the distinction it gives you. A chaining animal is applying a structured, deliberate strategy, which is different from an animal swimming randomly or disengaged. Those point to different explanations, so it's worth telling them apart.

Other measures help cross-check. Sequential quadrant visits in the quadrant entries list can suggest chaining, and consistent but indirect heading angles may too. See search strategies for where chaining fits among the others.

Quick answers

Is the chaining annulus the same as the "annulus" around the platform? No. Some papers use "annulus" for a zone around the platform position. The chaining annulus is a ring around the whole pool at the platform's distance from the wall.

How wide should it be? There's no single standard. In Pathfinder it's a parameter you set; published studies report their own value (one 5xFAD mouse study used 200 mm in a 1100 mm pool). Report the width you used.

Why does chaining fool latency? Because circling at the right distance reliably finds the platform. The animal gets faster without knowing where the platform is.

Sources

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