In the course of examining single unit responses from the cortex of unrestrained and
unanesthetized cats, we have come upon a population of cells that appears to be sensitive to auditory stimuli only if the cat «pays attention» to the sound source.
Type 2 theta is comparatively rare in
unanesthetized rats: it may be seen briefly when an animal is preparing to make a movement but hasn't yet executed it, but has only been reported for extended periods in animals that are in a state of frozen immobility because of the nearby presence of a predator such as a
cat or ferret (Sainsbury et al., 1987).