Do all animals dream?

And how can we tell what they're dreaming? Researchers want to reveal the secrets of animal dreams by measuring the brainwaves of rats.

Transcript

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)