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Immobility detection

When using Forced swim test and Tail suspension test mode the way that immobility is detected, and the settings that go with it, are different - you'll find the details here.

Introduction

ANY-maze can automatically detect periods when the animal is immobile and include analysis of mobility / immobility in test results.

You can specify whether you want it to do this using the options in the Immobility detection element of the Protocol.

Determining when an animal is immobile

Contrary to expectations, determining when an animal is immobile isn't very obvious. For example, if an animal is walking along, stops for 10 seconds and then starts walking again then you'd probably say it was immobile for 10 seconds. But what if it stopped for 1 second? OK, maybe you'd still say it was immobile, but what if stopped for 1/4 of a second - you'd probably say that it never really stopped. So the first issue is how long it has to stop for before you consider it to be immobile.

A second issue is related to what immobile actually means. For example, if an animal lies down and goes to sleep then you'd probably say it's immobile, but what if it sits in one place and scratches itself. It's not changing location but it's definitely moving, so is it immobile or not?

These two issues are addressed in ANY-maze by allowing you to choose how you want mobility/immobility to be defined.

Defining immobility

There are two aspects to defining immobility; firstly, you need to decide how motionless the animal has to be in order to be considered immobile. For example, does it have to be completely immobile, perhaps asleep, or does it simply have to remain in the same place (even if it's moving its body, for example scratching or moving its tail). You specify this level of immobility by defining the immobility sensitivity on a scale from 50 to 100. In fact, these values are just the percentage of the animal which has to remain in the same place for the animal to be considered immobile. So 100% means the animal must be absolutely immobile, while 50% means that it can actually move quite a lot (grooming, stretching, etc.) and still be considered immobile. In general, a value of around 70% is a good level for most situations.

The second aspect to defining immobility is to specify how long the animal must remain in an immobile state before you want ANY-maze to actually consider it to be immobile. For example, setting 2 seconds will mean that the animal can be technically immobile for say 1 second, without ANY-maze actually counting it as immobile.

The exact values you use for both the immobility sensitivity and the immobile time will largely depend on why you're interested in immobility. For example, you might want to use immobility to end a test if the animal is continuously immobile for 5 minutes, e.g. it's gone to sleep. In this case, you'd probably want to use quite a high immobility sensitivity, as any movement (such as grooming) would suggest that the animal is still awake, and you could also choose quite a high immobile time, say 5 seconds, as you'd only actually stop the test if the animal remains immobile for 5 minutes.

On the other hand, if you want to know how often the animal stops moving around in an open field, then you might use a low value for the immobility sensitivity and a time value of perhaps 2 seconds. In other words, if the animal stops changing its location (even if it continues to move its body) for a period of 2 seconds or more, then you'd say it's immobile.

The actual time value you enter can be expressed in milliseconds, seconds, or minutes by using units of ms, s and min respectively; if you don't enter any units, then seconds will be assumed. You can also enter decimal values, for example '1.5s'. The minimum value you can enter is 200ms and the maximum is 1 minute.

The difference between mobility and activity

As well as mobility, ANY-maze can also analyse activity. In this sense, mobility is determined by the movement of the animal around the apparatus - when it's moving, it's mobile (subject to the conditions described above) whereas activity is determined by whether the animal is doing something. For example, if the animal is feeding then it probably won't be mobile (i.e. it'll be staying in the same place) but you would probably still consider that it's active - i.e. it is doing something. Effectively, then, mobility is one form of activity, but not the only one.

You will actually be able to choose whether other behaviours, such as feeding, should count as an activity when you add them to the protocol - see An introduction to using keys to score behaviours for more details.

Mobility and hidden zones

When the animal is in a hidden zone (i.e. you can't see it), ANY-maze will consider that it's mobile. This may seem odd, but essentially any decision as to whether the animal is mobile or not is arbitrary, as we can't actually know.

This means that results such as 'total time mobile' will include the period that the animal was in the hidden zone. If this doesn't suit your needs, then you can simply use a calculation to deduct the time in the hidden zone from the time mobile.

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ANY-maze help topic T0358