And how can we tell what they're dreaming? Researchers want to reveal the secrets of animal dreams by measuring the brainwaves of rats.
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00:00 Do animals dream?
00:06 They can't tell us about their dreams, of course, but that hasn't stopped curious scientists
00:11 from looking for answers.
00:14 In 2001, researchers at Boston's MIT measured the brainwaves of lab rats, first in the maze
00:21 searching for food, and again while they were asleep.
00:28 The results showed that during sleep, the same brain areas were active as during the
00:33 search for food.
00:34 The rats were mentally retracing their journey through the maze, processing what they'd learned
00:40 during the day.
00:43 Sleep studies have also been done on zebra finches.
00:46 While sleeping, they internally chirped the melody of their songs, the same songs they'd
00:51 sung during the day.
00:54 Researchers concluded that these birds do in fact dream of singing.
00:58 In humans, the sleep phase most closely associated with dreaming is REM, or rapid eye movement.
01:05 As the name suggests, this sleep phase is characterized by quick, uncontrolled eye movements.
01:12 People who are awakened during REM sleep can often recall their previous dream in detail.
01:21 REM sleep can be observed in almost all mammals.
01:25 And when our pets twitch, growl, bark, or meow, it's very likely they're reliving moments
01:31 of their day in their dreams.
01:37 But dream sleep hasn't just been seen in mammals.
01:40 These cuttlefish twitch their eyes and tentacles during sleep, and can even reflexively change
01:46 color.
01:49 Sleep phases similar to REM have now also been identified in reptiles.
01:53 For the researchers, an indication that different sleep phases must have already been developed
01:58 in prehistoric times.
02:01 And what about insects or spiders?
02:03 A recent study found that jumping spiders can twitch in their sleep, similar to other
02:08 animals during REM sleep, evidence that even they have dreams.
02:18 (dramatic music)