Habituation of the EEG arousal response in rats: short- and long-term effects, frequency specificity, and wake--sleep transfer.

Presentation of auditory stimuli over interstimulus intervals (ISIs) of several minutes to sleeping rats produced significant habituation of the electroencephalographic (EEG) arousal response. The arousal response habituated to an asymptote after only two or three stimulus presentations. Little or no spontaneous recovery occurred between sessions separated by 24 or 72 hr. The habituation produced by a single stimulus presentation was retained for at least 24 hr, and orderly habituation was shown with a 24-hr ISI. Approximately 90% retention of habituation was shown 32 days following 10 stimulus presentations, and some degree of retention was shown for as long as 50 days. After habituation had reached a long-term asymptote, 600 stimulus presentations over 2-sec ISIs produced further response decrements, but these decrements recovered completely within a matter of minutes and responsiveness returned to the previously established long-term asymptote. Habituation was shown to be frequency-specific over both 24-hr and 32-day intervals. Habituation produced by stimulus presentations to awake animals transferred to the condition in which stimuli were presented to sleeping animals.