how complex does an animal’s brain have to be in order for it to need sleep?

Question: how complex does an animal's brain have to be in order for it to need sleep?
- Keywords:
  brain,
  complex,
  sleep
Asked by jessc to Jo, Kevin, Louise, Valeria on 20 Jun 2012.
- Joanna Cruden answered on 20 Jun 2012:
  
  Our brains are the most complex so I would say it was more down to where they live, for example fish have a deep period of rest rather than sleep but don’t have very complex brains
- Valeria Senigaglia answered on 20 Jun 2012:
  
  Quite complex. The meaning of sleep as in humans, is to stored informations in the memory. To restore physical energy resting period are sufficient but you need to sleep to make your brain remember properly
- Kevin Mahon answered on 20 Jun 2012:
  
  Sleep as we defined it in humans is also noted in most mammals but also puzzingly in many birds. It’s difficult for us to say what the cut off point for complexity is for this – we know for example that even though reptiles ‘sleep’ (even with REM) their brains don’t go through the activity that Valeria mentioned.
  
  So a reasonable guess would be ‘some where between a bird and a reptile’ but it’s not for us to say exactly at the moment!

Question: how complex does an animal's brain have to be in order for it to need sleep?