Coding sound direction in noisy environment in the superior colliculus of the rat

The aim of the present study was to evaluate the effect of background noise on the directional sensitivity of neurons in the deep layers of the superior colliculus. Extra-cellular recordings were carried out in anaesthetized adult Long Evans rats. When stimulated in a noisy environment, most of the neurons remained sensitive to sound direction and only a few changed their optimal direction by more than 15 degrees. When stimulated at their optimal direction in the presence of background noise, a majority of neurons did not modify their response rate, whereas a limited proportion of neurons showed either a significant drop or facilitation of their response rate. Moreover, the neurons' receptive fields showed significant tuning modifications in the presence of background noise. In a noisy environment, the larger receptive fields became narrower, whereas the sharply tuned receptive fields got broader.