Do All Animals Dream?
Every mammal goes through regular cyclic "state-changes" during sleep. By state I mean where the overall allocation of resources in your brain are currently being employed. While sleeping, warm-blooded animals go back and forth between highly-synchronous EEG wave-form periods and lower-frequency, choppier EEG signals that resemble waking-thought (except for in certain areas, including the primary visual cortex). It seems that dreaming is very-much connected to REM-Sleep (at least in humans), if not depending on it completely. But what about dolphins, porpoises, and whales - the mammalian order Cetacea? Dolphins and other cetaceans live in an environment incredibly different from where land-lubbers dwell. So, do dolphins go through REM-Sleep, and do dolphins dream?
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Non-Mammalian Sleep The issue with living in the ocean is that – even though there's still day and night, at least in the upper ocean – there are not many places to hide. To nest. To sleep safely. This is especially true for larger sea creatures. Some animals of the wet can bury themselves in the sand or change their color and camouflage into the seabed. Some fish are small and can catch a break inside sea gardens. But for the biggins, you can imagine how sleep must be a compartmentalized thing within the brain, only covering some operations but leaving others available to maintain a vigilance in an open, winner-takes-all, all-you-can-eat fish fest. There has been little research into actual brain-wave correlations with fish when it comes to sleep stages, but aquarium employees have observed apparent sleep at night for many species. Sleep patterns probably change drastically in fish during spawning and migratory seasons.
Lizards, with a relatively simple central nervous system, like fish, go through EEG changes while asleep but do not demonstrate wave-forms indicative of REM periods. Birds, however, have Non-REM and REM-Sleep like mammals, a trait common to most warm-blooded animals. Birds that nest in safe locations can enter deeper sleep than species left more exposed. There is argument about whether birds actually sleep during long, migration flights. But it is known that birds sleep one cerebral hemisphere at a time. Only half of the brain enters into sleep, so the other side can remain aware of the external world. |
Mammalian Sleep Sleep length per day is very variable between mammal species, and this can even be the case between closely related species – the environment dictates effective behavior. Herbivores tend to sleep the least – they are in a drowsy state most of the day, just eating grass or leaves. Omnivores are in the middle and carnivores require the most sleep. Carnivores usually have more "sophisticated" brains and these brains have to be re-processed with more sleep. Individual circumstances also affect mammalian sleep cycles. Captivity can result in an animal having little to do – it just sleeps all day. For instance, we have a dog, and he seems to sleep for about 23 hours a day if we don't take him for a hike or run. But wolves are not particularly long sleepers. Sloths in captivity can sleep for 16-hours per day, but in the wild sleep less than ten. Mammals born nearly fully-developed exhibit less REM-sleep than immature-at-birth mammals. Horses – able to trot around as soon as popping out – sleep under 3-hours a day. Cats sleep for over 12-hours a day; lions for 13-1/2 hours. This parallels the theme of newborns sleeping predominantly in a Rem-state, probably fostering lots of neural change. Humans get an atypically low amount of sleep for omnivores, especially when considering how much brain processing we do. Maybe working 12-hour days and sleeping for 6 isn't ideal?
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Aquatic-Mammalian Sleep Aquatic mammals had to develop drastically different sleeping methods from land mammals. Like birds, water-mammals sleep uni-hemispehrically. Like other uni-hemisphere sleepers, dolphins "rest" with one eye opened, one closed. Dolphins, whales, and seals keep one hemisphere of the brain awake and aware of the environment. Seals, able to leave the water and spend lengths of time sun-bathing, have almost no REM-sleep when in the water but on land have REM-periods resembling land mammals – surprisingly with no REM-rebound for recovery purposes after all that REM-sleep-deprivation. Except for one exception (a single 1969 study reported a pilot whale was in REM for 6-minutes.), it seems that whales and dolphins do not have REM-sleep. Even when measured continuously for 4-weeks, bottlenose dolphins showed no clear evidence of REM. This makes sense: If REM-sleep causes muscle-atonia and prevents the body from moving around, how would an animal keep swimming? May be that REM-Sleep is just very hard to detect in cetaceans. It was believed for a long time that monotremes – like the platypus and echidna – did not go through cycles of REM. Turned out that even though these guys don't exhibit EEG changes characteristic of REM-sleep, wave-bursts thought to underlie REM do occur in their brain-stems; in fact, the platypus has more of this REM-related activity than any other mammal. Could be that dolphins and whales go through REM periods too, and we haven't been looking in the right places.
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Dolphin Intelligence
Cetacea are brainy. Sperm whales have the largest brain mass of any animal – over 17 pounds! Human brains are about 3 pounds. But cetaceans don't only have big brains – their brains are large in comparison to body size as well. The bottlenose dolphin has a meat-computer weighing about a half-pound more than humans. When comparing brain-size to overall body-mass as a ratio, some sea-mammals – belugas, narwhals, porpoises, dolphins – are only one-upped by humans. Dolphin brains are highly convoluted; like human brains the 3-D folding -- with its valleys and peaks -- allows for greater surface area than a flat, 2-D structure would. But elephants, after humans, have the "thickest" cortex (number of cortical layers), number of cortical neurons and synaptic connections.
It's not easy, or really fair, to compare brain structure across mammals that have to function in such different environments. Intelligence is, in part, defined by an organism's ability to adapt to its situation. The needs of living in the ocean are so alien to what living on solid Earth requires. Dolphins can swim like sharks, use sonar like bats, give birth and raise their young like, I don't know, dogs and cats. Dolphins and other cetaceans play and explore and are seemingly self-aware. They enjoy interacting with humans. But they don't have hands and feet. So we have different types of intelligence. The ketamine injecting, sensory-deprivation-tank inventing, awesome yet crazy Scientist (capital S) – John Lilly – worked extensively with dolphins and felt sure that they were at least as "smart" as we are, but there is a communication gap between us. He spent years trying to bridge that gap. It's still there. This doesn't stop many people from feeling that dolphins, whales, and their relatives are on par with humans when it comes to overall "conscious intelligence." They may or may not dream, but they seem to be very awake. There is a movement to end the keeping of dolphins in aquariums, with people stating this is akin to slavery. Cetaceans are hunted for food in parts of the world and many are victims of getting caught up in nets and hooks intended for fish. These issues need to be addressed, and although it's a shame I have to end this article on a sad note, the continued survival and well-being of these intelligent animals is part of the human-responsibility, and the concern is urgent. |