Escape versus exploratory activity: An interpretation of rats' behaviour in the open field and a light-dark...

To test the assumption that dark preference in rats can serve as a measure of emotionality, dark preference was compared with ambulation and defacation in the open field. One group of 80-days-old male rats was handled for seven days; another group remained undisturbed. All animals were tested on each of five successive days in both a light-dark preference situation and an open field. Handled rats ambulated more in the field and stayed less time in the dark than non-handled ones. Significant negative correlations were found for the different days between open field ambulation and dark preference. Correlations between dark preference and open field defacation were positive except on day one. From the first to the second trial dark preference increased in both groups while open field ambulation decreased. The results were considered to support the hypothesis of dark preference as a measure of emotionality. In a second study an investigation was made as to whether high initial activity in a new situation is brought about by exploration or by an escape tendency. Again one group of male albino rats was handled. During testing, half of the handled and half of the non-handled rats had the chance of escaping from the open field into the adjacent home cage. From there the animals had the possibility of re-entering the field. The second half of each group had to stay in the field. These latter animals showed a remarkable decrease in ambulation from the first to the second trial. Rats which had access to their home cages seldom re-entered the field in the first trial. In later trials, however, ambulation in the field increased. Non-handled rats needed more trials before they started investigating the field. It was concluded that this result gives more support to an explanation of initial activity in terms of escape behaviour.