Sleeping habits

[Daly]

Which animal when asleep has half it's brain still active?

[New Forester]

Whales and dolphins. They do not breathe automatically like land mammals -- they must take each breath deliberately. They use the more awake half of their brain to keep breathing while the other half sleeps. They do not (I heard on the radio yesterday) have REM sleep.

[moonunit100]

This is true for dolphins such as the bottle-nosed in which one cerebral hemishpere sleeps for 30-60 mins. while the other stays awake, then the two hemispheres reverse their roles. This allows the dolphin to surface for air periodically. However, the Indus dolphin (found in the Indus river) sleeps for a few seconds at a time over the whole day. It is beleived they have adopted this strategy so they can remain constantly vigilant as the Indus river is full of large debris which could cause them serious injury. A further interesting fact involving the sleep patterns of dolphins is that, along with spiny anteaters, they are the only mammals which do not experience REM sleep.