What Is Open Field Testing?

Researchers have long been using rodents to test hypotheses related to general mammalian behaviors. In fact, just about all human clinical trials are preceded by animal models like mouse or rat trials, largely because these rodents serve as excellent anatomical, physiological, and genetic analogs. Rodents also make perfect research subjects thanks to their small size, short life cycles, and abundant genetic resources.

Rodent behavioral trials can be used to study everything from anxiety and fear conditioning to locomotor activity and behavior, but only if researchers have access to the right products and systems. While mazes, treadmills, rotarods, and other products may be necessary for some types of rodent behavioral research, anxiety and fear conditioning researchers rely heavily on open field behavior testing.

Open Field Testing?

Open field testing involves the development of simple sensorimotor tests to determine activity levels and exploration habits in rodents. While the particulars of each test vary depending on what is being studied, the general setup is always the same. It features an open arena, typically marked with a grid, with walls to prevent escape. Researchers generally mark the center of the field with a different color to make it easier to differentiate since that is where the rodents generally begin the test.

Until recently, researchers had to make all of their observations in person or with the help of an analog overhead camera. Now, though, open field testing usually involves more modern apparatus equipped with video cameras or infrared beams and associated software programs that can automate assessments.

Rodent Behavioral Patterns Measured In Open Field Tests

Every experimental design is slightly different. However, there are some widely accepted behavioral patterns that can be observed and used to support or disprove hypotheses based on previous research. The most common of them include:

Line Crossings

Line crossings measure the frequency with which a rodent subject crosses the open field’s grid lines with all four paws. This measure of locomotor activity can also be divided into line crossings near the wall vs. in the center of the arena.

Center Square Behaviors

Center square entries refer to the frequency with which subjects enter the colored center square with all four of their paws. Researchers also use the duration of time spent in the center square as a parameter for some behavioral tests.

Rearing Frequency

Rearing behavior, in which a rodent stands on its hind legs and lifts its forepaws without support, is generally accepted by behavioral scientists to be a direct measure of anxiety. Measurements of rearing frequency versus time spent with forepaws at rest against the enclosure’s walls, which has a different set of underlying neural mechanisms, are thus often one of the most important measurements taken during open field testing.

Stretching Postures

Rodents sometimes stretch their bodies out to elongate their heads and shoulders for brief periods before retracting to their original position. If test subjects perform this behavior with high frequency, it’s generally thought to indicate high levels of anxiety.

Defecation And Urination

Some researchers believe that rodent models increase rates of defecation when they are anxious, but this stance remains controversial. There is a general consensus that both urination and defecation rates are indicators of emotionality. However, not all scientists believe that changes in those rates can be assumed to indicate anxiety, in particular.

Applications For Open Field Testing In Rodent Behavioral Research

The applications for open field testing in rodent model research are almost infinite. Anxiety like behavior research receives the majority of the attention from the general scientific community. However, there are also many other behavioral patterns related to general locomotion that can be measured using open field testing. Some researchers study rodent behavior as a simple indicator with limited explanatory power, while others use open field tests to study its functional roles. 

Why Researchers Do Open Field Testing

Anxiety and fear conditioning experiments currently constitute the majority of rodent open field tests. However, some researchers also use this experimental design to assess memory by evaluating subjects’ abilities to recognize objects or stimuli introduced into the arena or to perform novel object recognition tests.

Types Of Equipment Used For Open Field Testing

The primary piece of equipment used for open field testing is an enclosed arena, typically made from plexiglass. A good system will be equipped with an infrared grid for easier recording and analysis of the subjects’ movements and should be easily integrated with other essential research products. The SuperFlex Open Field from Omnitech Electronics, Inc. is a perfect example in that it allows behavioral researchers to study both simple behaviors and their functional roles.

When studying complex behavioral patterns, the housing in which the rodent subjects are reared must also be carefully controlled. Early life conditions, including parental care, single vs social cages, and the presence or absence of environmental enrichment, can all affect behavior later in life. Ordering custom home cage frames and racks is the best way to avoid unnecessary variables and ensure that every subject is reared in the same environment.

Tips For More Effective Open Field Testing

Despite the prevalence of open field testing in behavioral science, there is still a lack of reliability and validity across laboratories. Researchers can help to alleviate these issues by creating more effective and reproducible open field tests. To accomplish this goal, experts recommend:

• Creating more sophisticated testing and result analyses for tests designed to increase understanding of the biological functions of behavior, which should be done in more ethological settings.
• Ensuring that all of the rodents are reared in the same conditions and that those conditions are carefully noted in the experimental design.
• Allow animals to express themselves fully by offering multiple stimuli and possible responses.
• Ensuring that test subjects become familiar with the arena before testing for behaviors of interest.
• Including a sufficient number of subjects in each experimental group.

The Importance Of Good Experimental Design

When designing an open field test, researchers must focus on carefully defined control variables if they want to create reproducible experimental designs. In modern times, they must also be able to gather sufficient data for a complete analysis, often using AI-assisted software programs. The right experimental design always begins with high-quality equipment, so don’t cut corners.