Social and non-social open field behaviour of rats under light and noise stimulation

In two experiments, male rats were observed in pairs under different environmental stimulations in an open field. In Experiment 1, white noise of 85 dB(A) reduced social activities and increased defecation compared to 75 dB(A) and 65 dB(A). In Experiment 2, the illumination of the open field was varied in addition to a variation of the noise intensity. Again, 85 dB(A) as compared to 50 dB(A) reduced social activities and increased defecation, but also led to changes in non-social behaviours such as sniffing, grooming, and rearing. In contrast, 400 lx did not differ substantially in its effects from 40 lx in any of the observed behavioural categories. Altogether, the behaviour pattern under 85 dB(A) white noise cannot satisfactorily be explained only by increased anxiety of fear. Alternative explanations are discussed.