Behavioral Neuroscientists,
I am currently attempting behavioral testing in the Open Field. After plenty of testing, I have been wondering about what is the optimal size of the "center zone" vs "outer zone" in relationship to the size of the box itself?
Any input would be appreciated.
Thanks,
Danny
Are you using mice or rats? Also, what are the dimensions of your box? Are you using an automated tracking system (e.g. ANY-maze) or manual tracking using video recording? If the latter, I would suggest taking half the distance of the boxes width and use that as the square Central Zone. Take half that distance for Peripheral Zones. For example, a box 30cm wide would have a 15cm x 15cm central zone and a 7.5cm peripheral zone on all four sides. This ratio can be adjusted to have a larger central zone as the box becomes smaller, but also depends on species (e.g. mouse or rat). The length of the animal's body, particularly rats, can accidentally ping central timing when using automated systems.
The center area should be half the size (area) of the arena. Otherwise you'll have to correct for the different sizes.
You should divide the area of the box into 16 squares, the inner 4 squares will be the Central Zone. Your box could be 40 cm × 50 cm × 50 cm, where 40 cm is the height of the box.
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@Nandor: the problem with your proportions is that the probability of a random agent finding itself near the walls is 3 times larger than the probability of being in the center just because of spatial constrains. One would like to characterize center avoidance as a measure of anxiety in the baseline condition as fairly as possible so to not reduce any effect you might see from a possible manipulation.
Daniel, as Jacob referred, it is important to know if you are working with mice or rats,if you use software for analysis, and if so, you must consider either the center of body of the animal or the whole body area... Evrything should be optimized for your particular experimental conditions to avoid false results.
As a general rule, the size of the open field arena will influence the size of the central area: what you want to measure is thigmotaxy - the behavior of walking next to the wall, avoiding the central area - and the non-thigmotactic behavior - walking away from the walls. So, for rats, I would consider a corridor of ca. 20 cm width next to the wall to determine the peripheral area, and the rest is the central area. Why would the thigmotactic behavior depend on the size of the apparatus, right? (lighting conditions, height of the wall, animals strain and age, etc. might influence this values a bit)
I used to have a 1 m x 1m apparatus for Wistar adult male rats, with 20 cm width corridors: that leaves 36% for the central area. A smaller central area (10%) yielded too much variability, and a larger area would have the animals´ bodies incorrectly spill into the central area, especially when assessing risk. It was optimized with ANY-maze software, using the center of the body as the reference for the animal's position.
I hope that helps! Good luck!
In any 16 square open-field, the central 4 squares constitute the center zone, while a square mapped out of their adjoining sides makes the central square.
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