Currently, little is known about the origin or neurobiology of sleeping disorders. Recent research has revealed that sleepwalking, night terrors, and sexsomnia may be due to an underlying pattern of brain activity shared by dolphins and aquatic seabirds.
The coexistence of awake-like and sleep-like activity patterns may be normal for the developing brain and may recapitulate a pattern of brain activity shared with other vertebrates.
A similar coexistence of awake-like and sleep-like patterns of brain activity occurs in sea-going birds and aquatic mammals, such as dolphins. This well-known pattern of brain activity allows these animals to continue swimming, flying, or monitoring for predators. The only difference is that in the bird and dolphin brains the activity gradient is lateralized to one hemisphere at a time while in humans the disordered sleeping brain has an anterior-to-posterior gradient of activity during non-rapid eye movement sleep. It is possible that the peculiar features of these human sleep disorders are revealing hidden secrets about how the human brain evolved.
