- In recent decades, a flurry of research has helped to shed light on the cognitive experience of nonhuman animals. The results have often closed perceived gaps between human and nonhuman intelligence, while hinting at rich inner worlds and an array sensory abilities that can be peculiar – and perhaps often impossible – for us to fathom.
- But what, if anything, can be gleaned about how nonhuman animals might dream?
- In this video from the interview series Closer to Truth, the US author and psychologist Deirdre Barrett contextualises what we know about the rapid eye movements and brain structures of other mammals with high cognitive capacities – including cetaceans like whales and dolphins, and other primates – to detail the fascinating ways in which their dreamworlds might differ from our own.
- There's rather too much of Robert Kuhn in this video - he makes too many suggestions as to what is the case in his interlocutor's area of expertise.
- Is there a step-function or a continuity between the consciousness of humans versus other animals?
- Can the study of dreaming help with this differentiation?
- Yes - REM sleep (during which dreaming occurs) happens in almost all mammals but not in almost all non-mammals.
- Humans are unique - but so are cockroaches. The question is whether we're off at the end of some continuum. Dreams would support differences NOT on that continuum.
- But the similarity of REM sleep is more similar to ours with the larger-brained mammals. Similar patterns / cycles to ours. Primates are the ones with enhanced prefrontal cortex which is shut down during dreaming.
- While mostly linear in mammals, cetaceans buck the trend. They have larger and more complex brains than ours. Kuhn queries 'more complex'. They miss out on some of ours but have 'extras' in social areas that we don't understand.
- Some large-brained mammals are better at some things than we are: chimpanzees tracking numbers that disappeared off the screen considerably better than college students.
- For the above, see
→ Snopes - Chimpanzee Rapidly Memorizes, Locates Numbers on a Screen, and
→ YouTube: BBC - Chimp vs Human! | Memory Test | BBC Earth
- Snopes suggests that chimpanzees do not do better than humans on this short-term memory test when practice is equal, but BBC doesn't agree. The BBC researcher - and this video - suggest that chimps do chimp-things better than we do, and vice versa, but that some chimp-things are cognitive abilities that are particularly useful for them.
- Back to cetaceans - they have little REM sleep because they sleep with one hemisphere at a time, with a more limited repertoire of activities when one hemisphere sleeps. For humans, having one hemisphere completely active while the other is completely comatose would be unusual and hard to imagine. Their solution to breathing while sleeping, though seals don't do it that way.
- Note that in "Walker (Matthew P.) - Why We Sleep: The New Science of Sleep and Dreams", the explanation for 'no REM sleep in cetaceans' is that REM sleep requires the motor cortex to shut down to stop dreams being acted out. In aquatic mammals, this might lead to them drowning.
- No REM sleep would result in a completely different sleep experience.
- In primates, while they can't report the phenomenology of their dreams, similar areas of the visual cortex are active.
- Kuhn: a major difference between us and other mammals is language, which doesn't feature much in our dreams, which may thereby be less distinctive.
- Response: primates are most similar to us in the pre-frontal cortex, which is what damps down the most in dreaming. But we can't know the details of activation in the visual cortex because of the 'reporting' issue. So, it's just an extrapolation to claim that other animals have the visual imagery activated in their dreams. Also it's harder to compare with animals with other preferred sensory modalities (echo-location, smell, ..), easier with visual specialists.
- We don't remember most of our dreams because the mechanism that transfers from short- to long-term memory is shut off and activates only as we wake up. But the biochemistry of that would have to be only a tiny bit different either to have no dream recall or to have complete dream recall. So, it's easy to imagine that other species have one or the other of those, and therefore a completely different experience.
- This sounded a bit speculative, and didn't take into account what dreaming might be for, and whether remembering dreams would be advantageous or not.
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