It is known that dolphins never sleep in the sense that we do, instead they have one hemisphere of the brain sleeping while the other one is awake. I wonder, do they show observable changes in behavior in regard to this, depending on which hemisphere is active? Do their hemispheres even have a specification similar to ours (logic and emotion)?


1 Answer 1


Sleeping is a biological stage which we presume as a relaxation period but its really a highly functional stage for brain. Most of the memory related processing such as management of working memory and cognitive functions such as decision making, reasoning, and episodic memory are closely related with sleep.

Dolphins never sleep in the sense that we do, CORRECT, because we close our both eyes and enter into a stage of decreased ability to react to a stimuli. But in the case of dolphins they need to breath, so by fully entering into a sleep stage like us is suicidal in their case. Dolphins have a specialised way of dealing with this problem, they do a "unihemispheric slow-wave sleep". They only sleep with one hemisphere of the brain while the other being active, when the right hemisphere is sleeping the left eye is closed and vice-verse, as the right hemisphere controls the left part of the body. The observable change in their behavior is visible from the closed single eye.

Humans and dolphins had a common ancestor that lived 95 million years ago. During the last 50 million years dolphins have been evolving in water and their brain evolution had taken a different route. The neocortex, the outer most layer of brain which is considered as the recent evolved part of brain. The neocortex is actively developing in both humans and dolphins, one of the most striking features among them is that human neocortex is having large thickness and dolphins are having thin one with more folds than ours. The folding in neocortex is a technique to increase its surface area. This substantial difference is due to the evolutionary divergent way both the species took.

Dolphins have a complex echolocation system and binocular eyes, they need to create the visual and sonar image of their surroundings and studies shown that their increased brain size is due to the tremendous volume of data they need to process for these purposes. Also being a social animal their neocortex consists of connections like us but as we both are evolutionary separated for about 95 million years ago most of the brain areas are diversified and evolved.

Dolphins showed that they can understand a symbolic, human-based language, where the words are either whistles or hand gestures. And the dolphins could easily understand that we use different word orders to mean different things. So they understand syntax. The dolphin brain is arranged in a completely different way from ours, and yet they can still understand what we are trying to teach them. Lou Herman also showed that dolphins are right up there with humans and chimpanzees in being able to understand that when we point at something or look at something, we’re meaning “Don’t look at me; look at what I’m looking at.” He’s done all kinds of really fascinating things, and his work has contributed the most to our understanding of what these animals can do.Reference

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    $\begingroup$ "The observable change in their behavior is visible from the closed single eye." Here you have stated that an answer to the question is possible. But other than that sentence, your response does not even attempt answer the question. $\endgroup$
    – Qubei
    Mar 30, 2015 at 20:08
  • $\begingroup$ @Qubei: yes, I wish there was a more descriptive answer, like does their behavior become more logic or emotional, with examples, if possible.. but strangely looks like there are no people who can say anything like that about the subject.. $\endgroup$
    – noncom
    Mar 31, 2015 at 1:11
  • $\begingroup$ @noncom: What do you mean by "does their behavior become more logic or emotional" $\endgroup$ Mar 31, 2015 at 2:53

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