Do we have a reptilian brain? At last, a question we can easily answer.

_{Denyse O'Leary

March 15, 2014

Intelligent Design, Naturalism, Neuroscience, News}

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No. “Forget all about the triune model of the brain.”

In her blog on the vagaries of neuroscience, Janet Kwasniak explains,

The reptilian brain is a myth that should not be taken seriously and yet is referred to by many writers and is even seen in educational sites for children. It is the idea that we have three brains: a reptilian one, the paleomammalian one and the mammalian one. The story goes that these were acquired one after another during evolution. The details differ with the writer. But it is all a myth based on an idea from the ’70s of Paul MacLean which he republished in 1990. Over the years in has been popularized by Sagan and Koestler among others.

It would be astonishing if they had not. Such a simple, naturalist answer. And so wrong.

The model presumes that birds and reptiles cannot feel or think, which is a preposterous idea. And early mammals could feel, it was supposed, but not think, again not believable. Birds and many reptiles (perhaps all) have a brain area which does not anatomically resemble the neocortex but which develops from the same part of the embryonic brain and has the same functions as the neocortex. All the descendants of amniotes have essentially the same architecture of brain with the same functions. There are differences in proportions, sizes, connections, fine-scale anatomy but not a gross difference of kind in the brains of land vertebrates.

Indeed, if what the alligator mom feels for the eggs she is protecting aren’t feelings, it’s hard to know what they could be. And people have died assuming that a decades-old gator was really stupid.

Wonder what science would look like, rid of all the junk accumulated through many decades of materialism.

Images

Hat tip: Stephanie West Allen at Brains on Purpose

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Comments

I don't think there is a unconscience in anyone. I think there is just a awareness of self/soul and then using the memory. Animals use the memory more then us because they do little thinking. I also don't agree there are reptiles. There are only kinds and some kinds simply have like attributes for like needs. No reptiles were created by god. No such divisions. Its demanding to see the brain as largely a memory machine. Nothing evolving at all.Robert Byers_{March 16, 2014
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Hi News, I should also point out that birds, like mammals, are warm-blooded, and lead a more active lifestyle than reptiles. One would therefore expect them to possess a more sophisticated level of awareness than reptiles. A final feature of Janet Kwasniak's article which I object to is that it equates "unconscious" with "reflexive." This is a popular lay myth: that if a behavior is not reflexive, it must be conscious. There's no reason why this should be so. Learning can take place in the absence of consciousness: even cockroaches' legs are capable of associative learning, for instance. Sophisticated motor activity need not be conscious, and vice versa. Here's what Professor James D. Rose has to say about the brains of fish, reptiles and mammals in his article, "The Neurobehavioral Nature of Fishes" (Reviews in Fisheries Science, 10(1): 1–38, 2002) at http://www.nal.usda.gov/awic/pubs/Fishwelfare/Rose.pdf . Rose credits mammals with consciousness, but not reptiles or fish. Nevertheless, he allows that fish are capable of sophisticated behavior: "It is important to emphasize that fish brains can have highly complex, unique adaptations due to their diverse evolutionary paths. Consequently, these brains are not merely simpler versions of mammalian (or amphibian or reptilian) brains (Nieuwenhuys et al., 1998b; Butler and Hodos, 1996; Wulliman, 1998). In spite of the diversity and complexity among species, the behaviors of fishes are nonetheless highly stereotyped and invariant for a given species. Such stereotyped species-typical behaviors, however, are not simple or merely reflexive. Species-typical behaviors in vertebrates are known to be controlled by motor patterning mechanisms that are far more complex than reflexes (Ewert, 1987; Fentress, 1987). The basic behaviors involved in reproduction, feeding and drinking, escape or defense, and reactions to noxious stimuli, are controlled by motor patterning mechanisms that are located mainly in the brainstem and spinal cord of mammals (Berntson and Micco, 1976; Rose, 1990) and nonmammalian vertebrates alike (Ewert, 1987; Rose, 2000)." It remains true that brain activity which is confined to the brainstem and spinal cord is not deemed to be conscious. Rose writes: "Diverse, converging lines of evidence have shown that consciousness is a product of an activated state in a broad, distributed expanse of neocortex. Most critical are regions of "association" or homotypical cortex (Laureys et al., 1999, 2000a-c; Mountcastle, 1998), which are not specialized for sensory or motor function and which comprise the vast majority of human neocortex. In fact, activity confined to regions of sensory (heterotypical) cortex is inadequate for consciousness (Koch and Crick, 2000; Lamme and Roelfsema, 2000; Laureys et al., 2000a,b; Libet, 1997; Rees et al., 2000)." While there are increasing signs that birds possess brain structures which are capable of a comparative level of neural sophistication, nothing similar has been observed in the brains of reptiles. As Rose notes: "...[T]he cerebral hemispheres of fishes have a more rudimentary structure that differs substantially from the structure of mammalian neocortex. A simple type of three-layered, "general cortex" is present in the cerebral hemispheres of reptiles, but true neocortex, with its greatly enriched information processing capacity is found only in mammals (Nieuwenhuys, 1998a; Northcutt and Kaas, 1995). Whereas the qualitative differences in cortical structure and function are quite pronounced between reptiles and the simplest mammals, these differences are overshadowed by the large differences in neocortical structure and function found between orders of mammals. The proportion of the mammalian brain that is neocortex varies greatly. Insectivores such as hedgehogs, which are thought to resemble the early mammals, have fairly small amounts of neocortex. Simians have 45.5 times more neocortex for a given body size than primitive insectivores and humans have 145 times more neocortex than the most primitive mammals (Stephan and Andy, 1964). This enlargement of human neocortex is accompanied by greater cortical structural differentiation and functional diversification (Mountcastle, 1998)."vjtorley_{March 16, 2014
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Hi News, Back again. I should add that there seem to be four behaviors which are unique to mammals and birds: (i) a clear-cut distinction between REM sleep that animals undergo during conscious dreams, and slow-wave sleep (SWS) - mammals and birds being the only groups of animals known to unequivocally exhibit both slow-wave sleep and REM sleep; (ii) the ability to simultaneously access and integrate information from multiple sensory channels (as Dennett points out in a 1995 article at http://instruct.westvalley.edu/lafave/dennett_anim_csness.html , snakes cannot do this); (iii) awareness of Piagetian object constancy, which is found in at least some birds – doves, magpies, parrots and ravens (see Butler, Manger, Lindahl and Arhem, "Evolution of the neural basis of consciousness: a bird-mammal comparison", in Bioessays (September 2005), 27(9): 923-36); and (iv) the ability to visually anticipate the trajectory of a moving object (see "Origin and evolution of sleep: Roles of Vision and Endothermy" at https://www.eeb.ucla.edu/Faculty/Kavanau/OriginEvolutionSleep.pdf by Jack Kavanau, in Brain Research Bulletin, 1997, Vol. 42, No. 4, pp. 245–264 – especially p. 255).vjtorley_{March 16, 2014
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Hi News, I'd like to make a few quick comments about the triune brain. The triune brain is seldom defended by neuroscientists these days, for reasons which are summarized reasonably accurately by Wikipedia (see http://en.wikipedia.org/wiki/Triune_brain#Status_of_the_model )although Jaak Panksepp (author of Affective Neuroscience) has defended a refined version of the hypothesis. Panksepp, however, believes that reptiles, birds and mammals all possess a form of consciousness which he terms affective consciousness: unlike Maclean, he thinks reptiles have conscious feelings too. The blog cited in the post refers to the idea "that birds and reptiles cannot feel or think, which is a preposterous idea." I find the author's lumping together of birds and reptiles objectionable on scientific grounds. Behaviorally it's inaccurate: a New Caledonian crow is capable of far more sophisticated behavior than a turtle, say. It's neurologically wrong, too. The Encyclopedia of Neuroscience (2009) has a good article titled "Bird Brain: Evolution" (vol. 2, pp. 209-215) by E. D. Jarvis of Duke University Medical Center, which is available online here: http://jarvislab.net/Publications/Jarvis_2009_Bird_Brain_Evolution.pdf . The article points out that the avian brain has specializations of its own: the avian hyperpallium possesses a unique organization, so far found only in birds (p. 212). A homologue (not analogue) of the mammalian neocortex has now been identified in birds: see http://www.sciencedaily.com/releases/2012/10/121001151953.htm . However, no other animals, apart from birds, are known to possess brain structures which are capable of widely distributed brain activity that is simultaneously diverse, temporally coordinated, and of high informational complexity, as in the neocortex of mammals. These are the neural characteristics associated with consciousness, and by and large, reptiles lack them.vjtorley_{March 16, 2014
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