Open Field

Documentation

Open Field Test (OFT) is a simple apparatus used in the assessment of locomotion, exploration, and anxiety. The open field task explores the innate responses of the subject to open spaces apart from their explorative drive. Thigmotaxis is often seen in animals such as rats and mice. This behavior of avoiding brightly lit open spaces is believed to be an evolutionary adaptive behavior that can be observed in many species. The Open-Field test exploits this fear in species to evaluate the different aspects of anxiety-related behaviors. Animals with a decreased level of anxiety are more likely to explore the central area of the open arena than animals with high levels of anxiety. Animals with high levels of anxiety will display reduced locomotion and exploration, with a preference to stay close to the walls of the open field arena. However, despite the fear, animals have also been known to explore threatening stimulus as part of their exploratory drive.

The apparatus was developed in the early 1930’s by Calvin S. Hall to observe rat behavior in an open arena (Hall & Ballechey 1932). Hall and Ballachey’s experiment used a square arena that was marked into a grid. The experiment involved the observation of the rats to food stimulus placed within a barrier in the center of the arena. This experiment allowed observation of the influence of a positive stimulus on thigmotaxic behaviors of the rats and their emotionality. Though the apparatus is useful in the assessment of anxiety and explorative behaviors, it is debated that the task does not provide a specific measure of anxiety. To overcome these shortcomings, the 3-D Open Field apparatus can be used to allow a more precise measure of anxiety and fear-related behaviors.

The Open Field Test is usually used alongside other mazes that measure anxiety, such as the Elevated Plus Maze, Elevated Zero Maze, and Elevated Y-Maze (see also T-Maze), following anxiolytic and anxiogenic drug treatments. The Ziggurat task is a variation of the Open Field apparatus that uses ziggurats in the open space to create a complex environment. Another task that uses a similar apparatus to the Open-Field task is the Novel Object Recognition task used to evaluate the subject’s responses to novel objects.

The Open Field apparatus has a simple construct. Usually, a square arena that is surrounded by high walls to prevent escaping is used, though circular arenas are also used. These walls can be transparent to allow the subject to view any visual stimuli placed around or can be opaque to limit observation to behaviors in response to brightly lit open spaces. The floors are often marked with square grid crossings, and the center of the arena is marked with a square. In addition, the apparatus can have additions and modifications to test different behaviors and responses.

Origin

The first use of an Open-Field was described in Hall and Ballechey’s 1932 paper, “A study of the rat’s behavior in a field: a contribution to method in comparative psychology.” In their experiment, they utilized a 7 x 7-foot walled arena that had been marked into 49 square grids. In the center, a cylinder wire mesh covering 25 squares was placed to contain a food reward. When the animals were introduced into the arena from a start point, it was observed that the presence of food reward resulted in animals circling the wire-mesh barrier more than when no food reward was present. A similar set-up was once again used by Hall in his 1934 experiment to highlight “the importance of needs or drives and emotionality as factors determining adjustment or maladjustment” (Hall, 1934a). In the same year, Hall published a paper aimed at validating the correlation between the defecation and urination and the individual emotionality of the rats in an open-field task (Hall, 1934b). Although, it has been argued that a measure of defecation or urination simply measures timidity in a controlled environment.

Hall’s experiment for determining the relationship between emotional behavior and the speed of ambulatory activity in an open-field task suggested that emotional rats tended to be less active than their non-emotional counterparts (Hall, 1936). This behavior was further observed by Hall in the “The inheritance of emotionality” paper published in 1938. In the experiment, it was observed that males were more likely to be emotional than the females and the quality of emotionality was inheritable as evident from the higher defecation and urination rates of the progeny of most emotional males and females compared with the progeny of least emotional males and females (Hall, 1938).

Development

Since its initial use as a test for emotionality by Hall, the Open-Field task has seen different modifications and adaptations and a wider range of applications. In 1945, Anderson utilized the open-field task to assess timidity and role of gender in timidity in normal and gonadectomized rats. The results of the investigation showed that the females were less timid than their male counterparts and that gonadectomy before puberty did not affect the sex difference in timidity,

Stern (1957) evaluated the effect of frontal area lesions on the behavioral performances of male albino rats in an open-field task. The author found that the subjects with frontal lesions showed similar and long-lasting behavioral changes in the open field as animals subjected to a series of electroconvulsive seizures (ECS). Subjects showed an increase in emotionality and changes in behavior was more gradual than in the ECS animals.

The effect of aging on the open-field behavior was evaluated by Werboff and Havelena in their 1962 paper. Their test assessed the performances of both sexes of Sprague-Dawley at ages 90, 180, 360, and 540 days. The evaluation of age and gender-based performance in the open-field concluded that activity and emotionality declined with increasing age and that the females exhibited higher activity and emotionality scores than the males.

Levine et al. evaluated the relationship between open-field behavior and changes in adrenal corticoid in male Purdue-Wistar rats. The animals were grouped into two groups based on if they had been handled in infancy or not. The animals were tested on the open-field for 4 days in their adulthood and were immediately killed at the termination of the test. As expected animals that were handled in their infancy were more active in the open-field task, defecated less on all days of testing and had lesser corticosterone response throughout the testing period.

Recent Developments

Itoh et al. investigated the behavioral effects of neuromedin B (NMB) and neuromedin C (NMC) in an open-field task using male Wistar rats. Subjects were intracerebroventricularly (ICV) administered either 5 μl peptide or saline and tested at 1 and 30 minutes after administration in the open-field. At both evaluation points a decrease in the duration of locomotion, the distance moved, and rearing behavior was observed with an increase in excessive grooming and violent scratching. However, the pronounced behavioral changes after 30 minutes was only observed in NMC administered rats.

Brotto’s et al. experiment assessed the effect of chronic melatonin administration and sex differences in forced-swim test and open-field task. Results from both the test showed that females displayed higher activity than the males. Melatonin administration led to decreased activity in the forced-swim test while increasing ambulatory behavior in the open-field task for both genders. The