Why do dolphins sleep with half their brain?

The dolphin sleeps with half its brain and one of its eyes shut at a time to keep a watch on approaching predators and other dolphins. After two hours or so, they shut the other eye and the other half of the brain, so both eyes and brain hemispheres get their due rest.

Dolphins have binocular vision (with their eyes sitting on opposite sides of their head), so the researchers trained one of the dolphins to recognized two shapes, either three horizontal red bars or one vertical green bar. They trained Say with her right eye first.

The scientists thought that because half of the dolphin’s brain would be asleep during testing, Say would only recognize the shapes with the eye connected to the conscious half of her brain. But she gave them a surprise: She trained her left eye on the shapes, even though that eye had not seen the shapes before.

Ridgway said this must mean that information is transferred between the two hemispheres of the brain.

The dolphins proved just as sharp with their eyes as they were with their ears: After 120 hours, they still saw the shapes.

 

Picture Credit : Google