ABSTRACT
With the “gentle handling” technique, also called “hand deprivation” or “novel objects exposure,” the subjects-mainly rats and mice, but also rabbits [e.g.,
(1,2)], cats (3) and dogs [e.g., (4,5)]—receive tactile, olfactory, or visual stimulation whenever they enter the forbidden state [rapid-eye-movement (REM) or non-REM (NREM) sleep] as detected by polygraphic recording or behavioral observation. Stimuli may be complex, e.g., novel objects introduced in the cage. This method requires constant monitoring and a score of dedicated investigators. In one study in which sleep deprivation was enforced in rats for 3 hr at the beginning of the light period [animals were kept in 12:12 light/dark (LD) schedule], the number of required stimuli (tactile and/or acoustic stimuli lasting 1-2 sec) was 23 ± 11 [mean ± standard deviation (SD), n = 5 animals], 44 ± 13, and 75 ± 34 in the first, second, and third hour, respectively (Cirelli, unpublished data, 2003). The method is completely effective only for a few hours. For instance, in a study in which TSD was enforced in rats for 6 hr during either the dark or the light phase, NREM sleep represented only 0.5% of total recording time during the deprivation period (6). However, in another study in rats in which TSD continued for the entire dark period (12 hr), short NREM sleep episodes that could not be avoided accounted for about 4% of total recording time (7). REM sleep, by contrast, was completely suppressed in these two studies. In a study in cats in which TSD was enforced for 24 hr it was noted that short mild stimuli such as noise or displacement of the cage were only effective for the first few hours and then failed to prevent the appearance of spindles after the fifth hour. At the end of the experiment, strong and even painful stimuli were presented every 20-30 sec, yet spindle activity accounted for at least 3% of the total recording time (8). One study used gentle handling for up to 15 days, but rats were often immersed in shallow water to maintain wakefulness (9). In that study, the estimated sleep time per day during the deprivation was 3-5% of total recording time and did not change from the second to the last day of deprivation. Similarly, sleep pressure as measured by change in sleep latency increased progressively during the first 3 days but then stabilized for the rest of the experiment.
