The open field test is a common experiment used in scientific research to evaluate behavior in mice. It provides a way for scientists to observe how animals react to a new and potentially stressful environment. This method allows for the study of general movement, exploration, and anxiety-like responses.
What is an Open Field Test?
The open field test is an experiment designed to assess locomotor activity and emotionality in rodents. The test leverages the conflict in a mouse’s instincts: the drive to explore a new space against the fear of being in an open, unprotected area. This internal conflict elicits a range of measurable behaviors that can be analyzed.
The apparatus is a simple, enclosed arena, typically square or circular, with high walls to prevent escape. The floor is often made of a non-porous material and may be divided into a grid of squares or tracked by infrared beams. The environment is uniformly lit, which mice find aversive, enhancing the anxiety-like component of the test.
How the Test is Conducted with Mice
The procedure for conducting an open field test is standardized for consistency. A single mouse is gently placed into the arena, often in the center or along one of the walls, and is allowed to move freely for a set period. Test sessions last between 5 and 30 minutes, though some can extend up to an hour.
Data collection is often automated using video cameras and specialized tracking software. This technology monitors the mouse’s position, speed, and movements, and can automatically calculate distance traveled and time spent in different zones. Between each trial, the arena is cleaned with a 70% ethanol solution to remove any olfactory cues that could influence the behavior of the next mouse.
Key Mouse Behaviors Observed
Researchers quantify several behaviors to build a comprehensive profile. General locomotor activity is assessed by recording the total distance the mouse travels and its average speed. Exploratory patterns offer deeper insights, measuring the time spent in the center of the arena versus near the walls, a tendency known as thigmotaxis. Other specific actions are also recorded:
- Rearing, standing on the hind legs to scan the environment, is noted as an exploratory or risk-assessment behavior.
- Self-grooming behaviors, like face washing or fur licking, are timed as they can indicate stress responses.
- The number of fecal boli and urination events are counted, as these physiological responses are associated with emotionality.
- The number of times the mouse enters the center zone is also counted.
What the Results Reveal About Mice
Interpreting these behaviors allows scientists to draw conclusions about a mouse’s internal state. A mouse that spends most of its time near the walls and rarely enters the center is interpreted as having a higher level of anxiety, as the center is perceived as more threatening. Conversely, a higher total distance traveled and more frequent entries into the center zone can indicate lower anxiety and a more exploratory nature. Extremely high levels of activity could point to hyperactivity, while reduced movement may indicate sedation or sickness.
Changes in specific actions also provide information. An increase in grooming or defecation can be correlated with heightened stress, and the frequency of rearing relates to exploratory drive. By analyzing these behavioral patterns, researchers can assess the effects of genetic modifications, medications, or environmental conditions on mouse behavior.