Rat (Rattus norvegicus) defensive behavior in total darkness: risk-assessment function of defensive burying.

Although rats (Rattus norvegicus) spend much of their lives in the darkness of burrows, defensive behavior in the dark has rarely been studied. We compared rats' reactions to aversive stimuli in dark and lighted 2-alley, burrowlike environments. Experiment 1 assessed reactions to an unsignaled airblast; Experiment 2 assessed neophobic reactions to an unfamiliar steel ball. Half of the rats were tested in light and half, in total darkness. In both experiments rats directed defensive burying and stretched approach toward the aversive stimulus. Darkness increased airblast-induced burying behavior but not burying behavior toward the unfamiliar object; it had no effect on stretched-approach behavior in either experiment. Because the location and nature of the aversive stimulus was ambiguous in Experiment 1 but not in Experiment 2, these results support the hypothesis that risk assessment is one function of defensive-burying behavior.