How the Human Brain Evolved to Harness Abstract Thought

Summary: In other primate species, the brain areas that comprise the default mode network involve two systems that are not strongly connected to each other. The regions, one responsible for cognitive tasks and the other for the suppression of external events, appear to be only recently linked by evolution. This linkage may have facilitated the capacity for abstract thought that lead to the rapid evolution of human cognitive abilities.

Source: Vanderbilt

The human brain is organized in functional networks—connected brain regions that communicate with each other through dedicated pathways. That is how we perceive our senses, how the body moves, how we are able to remember the past and plan for the future.

The “default mode” network is the part of our connected brain that is responsible for abstract and self-directed thought. When we process external sensory information, the default mode network turns off, and when there is less going on outside our bodies it turns on.

Whether the same default mode network is found in mammals similar to humans has not been firmly answered; different studies have yielded different conclusions.

In an international collaboration across seven laboratories, in five institutions, across three countries and led by Christos Constantinidis, professor of biomedical engineering, neuroscience and ophthalmology, and Clément Garin, postdoctoral fellow in the Constantinidis lab, researchers compared data from humans and non-hominoid primates (macaques, marmosets and mouse lemurs) to more definitively answer this question.

“Surprisingly, our results showed that in all species other than humans, the brain areas that comprise the default mode network involve two systems not strongly connected with each other,” Constantinidis said.

“These regions, one responsible for suppression of external events and one for more cognitive tasks, appear to be linked only recently in evolution. It is this linkage that may have facilitated the capacity for abstract thought that led to the rapid evolution of human cognitive abilities.”

This shows brain scans of different monkeys
Evolutionary tree of the default mode network in four primate species. Credit: Clément Garin

The unexpected finding changes the way we think about brain networks. Atypical patterns of connectivity between brain areas are signatures of neurodevelopmental disorders and mental illnesses.

These conditions are a significant health and societal issue that affects individuals’ ability to healthily function in society.

Understanding how unusual patterns of brain connectivity emerge could lead to better diagnosis and treatment of these conditions, Garin said.

Next steps of this research will focus on how brain networks normally mature in childhood and adolescence and what goes wrong in mental illnesses, many of which emerge in early adulthood, Constantinidis said.

About this evolutionary neuroscience research news

Author: Press Office
Source: Vanderbilt
Contact: Press Office – Vanderbilt
Image: The image is credited to Clément Garin

Original Research: Open access.
An evolutionary gap in primate default mode network organization” by Christos Constantinidis et al. Cell Reports


An evolutionary gap in primate default mode network organization


  • Resting-state fMRI reveals DMN structure across four primate species
  • Two distinct networks in non-hominoid primates included homolog areas of the human DMN
  • The mPFC cluster is poorly connected to the PCC cluster in non-hominoid primates
  • Functional atlases available for each species


The human default mode network (DMN) is engaged at rest and in cognitive states such as self-directed thoughts. Interconnected homologous cortical areas in primates constitute a network considered as the equivalent.

Here, based on a cross-species comparison of the DMN between humans and non-hominoid primates (macaques, marmosets, and mouse lemurs), we report major dissimilarities in connectivity profiles.

Most importantly, the medial prefrontal cortex (mPFC) of non-hominoid primates is poorly engaged with the posterior cingulate cortex (PCC), though strong correlated activity between the human PCC and the mPFC is a key feature of the human DMN. Instead, a fronto-temporal resting-state network involving the mPFC was detected consistently across non-hominoid primate species.

These common functional features shared between non-hominoid primates but not with humans suggest a substantial gap in the organization of the primate’s DMN and its associated cognitive functions.

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  1. It’s becoming clear that with all the brain and consciousness theories out there, the proof will be in the pudding. By this I mean, can any particular theory be used to create a human adult level conscious machine. My bet is on the late Gerald Edelman’s Extended Theory of Neuronal Group Selection. The lead group in robotics based on this theory is the Neurorobotics Lab at UC at Irvine. Dr. Edelman distinguished between primary consciousness, which came first in evolution, and that humans share with other conscious animals, and higher order consciousness, which came to only humans with the acquisition of language. A machine with primary consciousness will probably have to come first.

    The thing I find special about the TNGS is the Darwin series of automata created at the Neurosciences Institute by Dr. Edelman and his colleagues in the 1990’s and 2000’s. These machines perform in the real world, not in a restricted simulated world, and display convincing physical behavior indicative of higher psychological functions necessary for consciousness, such as perceptual categorization, memory, and learning. They are based on realistic models of the parts of the biological brain that the theory claims subserve these functions. The extended TNGS allows for the emergence of consciousness based only on further evolutionary development of the brain areas responsible for these functions, in a parsimonious way. No other research I’ve encountered is anywhere near as convincing.

    I post because on almost every video and article about the brain and consciousness that I encounter, the attitude seems to be that we still know next to nothing about how the brain and consciousness work; that there’s lots of data but no unifying theory. I believe the extended TNGS is that theory. My motivation is to keep that theory in front of the public. And obviously, I consider it the route to a truly conscious machine, primary and higher-order.

    My advice to people who want to create a conscious machine is to seriously ground themselves in the extended TNGS and the Darwin automata first, and proceed from there, by applying to Jeff Krichmar’s lab at UC Irvine, possibly. Dr. Edelman’s roadmap to a conscious machine is at

  2. Bunk. Evolution can’t make a cell let alone the brain of a human. Nor to mention the thinking of a human brain.

  3. I find it rather entertaining your slanting research in judging me I use cognitive logical thinking over emotions hands down I’m very functional I do not fall under mental illness because I have narrowed out bi polar behaviors I’ve got 2 naturally in me and they work together if not afflicted I’m not a drug addict I’m in recovery stay resident going back to work soon I’ve only been out on medical leave because of jjs condition….

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