Differential effects of background noise of various intensities on neuronal activation associated with arousal and stress response in a maze task

Background noise (BGN) can affect performance of various tasks as a function of its intensity. Such effects may involve modulation of arousal level during task performance, though the neural mechanisms responsible for the intensity-dependence of effects of BGN are still unclear in detail. We examined the effects of BGN (white noise) of various intensities (control, < 40 dB without BGN; 70 dB; 100 dB) during maze task on neuronal activity related to arousal and stress responses using c-Fos immunohistochemistry in rats. Performance (number of errors, time to goal, and number of rearings) during the maze task under 70 dB-BGN, but not 100 dB-BGN, was improved compared with the control condition. In addition, 70 dB-BGN increased c-Fos expression in brain areas responsible for arousal, including mesopontine tegmentum, basal forebrain (BF), locus coeruleus (LC), and cortex, whereas 100 dB-BGN markedly activated neurons in stress-related nuclei, such as the hypothalamic paraventricular nucleus, central nucleus and basolateral nucleus of the amygdala, as well as BF cholinergic neurons, LC neurons, and cortex. These findings suggest that BGN during maze task can induce differential neuronal activation depending on the intensity of BGN in the brain areas relating to arousal and stress responses, which might be involved in maze performance.