Rat Neophobia

Wild rats, though highly exploratory, do not always responds to novelty by approach; and even a laboratory rat may freeze, or pause in its movements and groom itself, when faced with something strange. In colloquial terms, we might attribute these responses to fear. Berlyne has written fully on the aversive affects of unfamiliarity. The response to novel stimulation, he suggests, depends on two factors;

1. the initial state of arousal of the animal
2. the arousal value of the stimulus.

These determine whether the reward system or the aversion system of the brain is the more active. His evidence is behavioral, and largely from experiments on laboratory rats. In some experiments he used a Skinner box. Pressing the lever switched on either a light or, briefly, a buzzer. As we know, rats will work even for such meager rewards. The experiments were done in two conditions; in one, the animals were in quite surroundings; in the other, there was continuous noise. In the quite, the light or the buzzer were more effective as reward if they were completely unfamiliar; but in the noisy environment the animals were more ready to work for light or sound if they had already experienced the light or buzzer. The assumption is that the general noise induced such a state of arousal in the animals, that the additional arousal of a novel stimulus tended to be aversive. Further evidence comes from experiments by Berlyne in which a stimulant, amphetamine, was used to increase "arousal"; rats which had received the drug responded at a higher rate when the stimuli were familiar. while control animals, which received only injections of salinc, responded that there is an optimum when the stimuli were novel.