Erratic Sleep Behaviour

Hi I am the primary carer for my brother who has a learning disability since birth.  He is 64 and has a very erratic sleep pattern.  His mind seems to go into overdrive when he gets into bed and constantly talks to himself and it would appear others most of the night.  He is completely exhausted throughout the day and can become abusive because he is so tired.  His doctor did put him on some medication to help him fall asleep.  But it only lasts for about an hour or so then he is back to the constant talking, singing and even whistling all night long.  Any advice would be greatly appreciated.  Thank you