Dolphins are always awake and sleeping at the same time

One study showed that dolphins may not sleep for many days continuously and remain alert. In fact, only half of their brains were active, while the other half rested.

The performance of the ears and eyes of dolphins does not change after many days of continuous awakening.Photo: wallpaperimg.com.

Because dolphins have to go to the surface to get air periodically and watch out for predators, dolphins cannot rest completely while sleeping like terrestrial mammals. They are forced to remain alert even during sleep.

In humans and many mammals, the senses function poorly after staying up all night. Sam Ridgway, a scientist from the US Navy's Oceanic Animal Program, wants to find out if 24 / 24h alertness reduces the ability of the dolphin to function properly. The team also wants to know why dolphins can awake even when sleeping.

Rigway and colleagues conducted experiments with two dolphins. Whenever there is food, the dolphin will always hear a "beep" sound with a duration of 1.5 seconds. After the dolphins are familiar with the command signal, the expert team plays continuous "beeps" of 0.5 seconds. Under these conditions, the 1.5-second "beep" sound is randomly generated. Sounds with frequencies low enough for dolphins to not feel disturbed when they roam in the tank during the day, and high enough for them to recognize the "beep" 1.5 seconds.

The results showed that, after listening continuously for 5 days, the dolphin pair still recognized the "beep" signaling food with constant accuracy. In the next experiment, the team designed a vision test to see if the dolphin's eyes looked as clear as they were at the beginning. Besides, they continued to check their sound discrimination ability.

The dolphin's eyes lie on opposite sides on the head. So the experts trained one of the two dolphins (Say's name) to recognize two cubes (a green bar horizontally and a red bar vertically). They train Say with his right eye first.

The team thinks that because half of the dolphin's brain sleeps during sleep, Say will only recognize two shapes with the eye corresponding to the part of the brain that works. But the animal surprised them: He recognized the shape with his left eye even though he had never been trained with this eye before.

According to Rigway, that means that information has been transmitted between the two hemispheres of the dolphin. The fast level of the eyes and dolphin ears are similar. After hearing the "beep" sound for 120 hours, they still recognize the shapes. The team analyzed the blood of the dolphin to look for signs that they fell into a state of lack of sleep, but did not detect any signs.