According to the late physician and neuroscientist Dr Paul D. MacLean, our brain has evolved many times since the evolution. MacLean proposed the basic formulated working of his model in 1960s but in the 1990s in his book “The Triune Brain in Evolution” he went to a great length to explain his model, working and theory. Dr Paul MacLean proposed the name triune because according his logic and theory our forebrain has three structures, reptilian complex, the Phaleomammalian Complex (Limbic System) and Neomammalian Complex (Neocortex). The modern times neuroscientist’s do not believe in his researches have proved this theory, of brain evolution, wrong and most of them don’t link themselves to Dr Paul MacLean’s theory. His work the triune hypothesis got fame and became familiar to the audience through Carl Sargan’s Pulizer prize book The Dragon of Eden in the in the 1977 award winning book competitions.
Dr Paul MacLean named it Reptilian complex also known as r-complex or reptilian brain which was previously known as basal ganglia structures. They basal ganglia structures were introduced through a when the floor of the forebrain were under study by Dr Paul MacLean. Dr Paul MacLean named him the r-complex because the comparative neuroanatomist’s scientist once believed that the forebrain birds or other reptiles have the same brain as human. Dr MacLean believed that this part of the brain is to be held responsible for an uncertain change in mood or the mood swings we face like aggression, dominance or territorial swings. According to his work, this is the oldest part of brain.
Phalemammalian part of brain consist of so many structure and elements such as septum, amygdalae, hypothalamus, hippocampal complex and cingulate cortex. Dr Paul introduced the word limbic first in his work in 1952 to refer to the internally chained structure of the brain. Neuroscientist do not recognize Dr Paul MacLean Limbic system as a major functional system in the brain but they do offer his some grace as they normally link this as the most important contribution to the field. He maintained the idea that the structure of the limbic system arose right at the start of the mammalian evolution also known as Phalemammalian. And this Limbic system is responsible for the motivation and emotion involved in the feeding, reproductive and parental behavior.
This neomammalian complex is made up of a cerebral neocortex, a design found mainly in the chain of higher category mammals such as human beings. Dr Paul MacLean regards this acknowledgement as the most recent step involved in the evolution of mammalian brain. This helps in conferring the language for language, abstraction, planning and perception.
He draws this idea of triune brain hypothesis in the 1960s with the help of work done by some other people. 1980s saw the reviving of this idea in comparative neuroanatomy, due to the availability of a verity of new technique that is useful while sketching the circuitry of an animal brain. Later finding have supported have improvised the forth coming traditional idea upon which MacLean’s researched was based on. Taking an example of Basal Ganglia structure that are taken out from the forebrain structure and Dr’s reptilian complex were shown to take up small chunks of the forebrain of reptiles and birds together called sauropsids. Basal Ganglia are also the part of the modern forebrain in all the vertebrates; they are likely to be linked with the most common evolutionary ancestors of the vertebrates. And that was 500 million years ago when the origin of reptile is found.
Some new discoveries in behavioral study not at all support the ancient views on sauropsids as ritualistic and old, same as in MacLean’s reptile’s concept. Birds have posses the highly sophisticated cognitive abilities for example tool making, and matching some of the traits of African grey parrot region. Limbic structure which were proposed by MacLean arose in early mammals are now shown to exist across a range of modern vertebrates. The paleomammalian feature of parenting is also found in the birds and in some cases fish too. Like Basal Ganglia, evolution of this system might take you to the ancient common vertebrates.
Summing it all, and based on paleontological working, studies strongly show that the neocortex was there in the first ever emerging mammals. All though all the mammals doesn’t have the attributes of neocortex in the true nature but they have the qualities of pallium regions. Some parts of the pallium are assumed to be homologues to the mammalian cortex. Lacking in the grounds of six neocortical layers, birds and reptiles have stronger region in the dorsal pallium. Telencephalon of birds and mammals make neuroanatomical with other telencephalic structure same as made by neocortex. It also provides similar function such as learning and memory decision making, conceptual memory and motor control.
The work on triune model done by Dr Paul MacLean of the mammalian brain is seen as a lot easy organizing by few people in the field of comparative neuroscience. And due to the scale of simplicity it still grabs public attention. On the other hand being simple isn’t all what is required but accuracy too and in technical terms it in accurate explanation for brain activity. It also has a very thin line of truth in whole exploration of approximation that we have to work with. The neocortex is symbolizing pile of brain structure involved in advance cognition which includes planning, modeling and simulation. The limbic brain refers to those brain structures wherever located associated with social and nurturing behavior, mutual reciprocity and the other behaviors and affects that arose during the age of mammals. The reptilian brain refers to those brain structures related to territoriality, ritual behavior and other reptile behaviors. The gigantic explanatory values make this approximation very interesting and is a useful level of complexity for anyone doing research related with brain exploring.