What does "The brain has its own language for testing the structure and consistency of the world." refer to? The late Dr. Carl Sagan is famous for many different contributions to both scientific research and science education.

One memorable line is discussed in Are we really star-stuff from the interior of collapsing stars?

In the video Carl Sagan - 'A Glorious Dawn' ft Stephen Hawking (Symphony of Science) at about 01:30 Dr. Sagan can be heard to say:


  “But the brain does much more than just recollect it inter-compares, it synthesizes, it analyzes, it generates abstractions. The simplest thought like the concept of the number one has an elaborate logical underpinning. The brain has its own language for testing the structure and consistency of the world.”


This quote can also be found in goodreads and in the script of Season 1, Episode 11 of the TV show Cosmos circa 1980.

What might Dr. Sagan be referring to in the sentence "The brain has its own language for testing the structure and consistency of the world."?

Question: Is this hypothetical "language" a way that information is exchanged between different parts of the brain? Is this concept part of some well known theory of brain function at the time? How is this viewed now, nearly forty years later?



A longer quote (from the episode) for context:


  The brain is a very big place in a very small space. Most of the books in the brain are up here in the cerebral cortex. Down there, in the basement of the brain are the functions that our ancestors mainly depended on for survival: Aggression, child rearing, sex the willingness to follow leaders blindly. Lots of things that we can still recognize in our lives today.
  
  Of the higher brain functions some of them, like reading, writing, speaking seem to be located in particular places in the cerebral cortex.
  
  On the other hand, each memory seems to be stored in many separate locales in the brain. Old memories are in lots of places. Here is one of my earliest memories.
  
  
    (POURS LIQUID) MOTHER: That's a good boy.
    Lunch is almost ready.
    (CLICKS ON RADIO) (MUSIC PLAYS) 
  
  
  That was a long time ago. But its imprint has not faded in the library of this brain. But the brain does much more than just recollect. It inter-compares. It synthesizes. It analyzes. It generates abstractions. The simplest thought, like the concept of the number one has an elaborate, logical underpinning.
  
  The brain has its own language for testing the world's structure and consistency. But we never see the machinery of logical analysis only the conclusions. There is so much more that we must figure out than the genes can know. That's why the brain library has 10,000 times more information in it than the gene library. Our passion for learning is the tool for our survival. And unlike the musty bindings of our gene library in which hardly a word changes in a century the brain library is made of loose-leaf books.
  
  We're constantly adding new pages and new volumes. Emotions and ritual behavior patterns are built very deeply into us. They're part of our humanity. But they're not characteristically human. 
  
  Many other animals have feelings. What distinguishes our species is thought. The cerebral cortex is, in a way, a liberation. We need no longer be trapped in the genetically inherited behavior patterns of lizards and baboons: Territoriality and aggression and dominance hierarchies. We are, each of us largely responsible for what gets put into our brains for what, as adults, we wind up caring for and knowing about.
  
  No longer at the mercy of the reptile brain we can change ourselves.
  
  Think of the possibilities.
Dr. Sagan is referring to the brain's ability to produce models of the world in order to test predictions. 

In terms of psychology contemporary with Carl Sagan, he may have been referring to, in part, the theory of schemas. This is a general representation of a thing or idea that is used in classifying or identifying the thing or idea. In developmental psychology, the idea of Jean Piaget's schema might appear as a young child identifying all four-legged animals as "doggies." As the child grows, they will begin to differentiate, and for example, know horse vs. dog (but might classify a zebra as a horse). 

The "language" of the brain seems to be an emergent property of neuronal firing. When a neuron elicits an action potential, it produces a voltage pulse that (usually) travels down the axon. Neurons can stimulate each other when synapses are triggered by an action potential of the pre-synaptic neuron. This is a simplified explanation: there are also graded synapses that aren't action potential-triggered.

Dr. Sagan might also have been thinking of the 1981 Nobel Prize-winning research by Hubel, Wiesel, and Sperry, whose mid-twentieth century research demonstrates how receptive fields for retinal neurons map onto the visual cortex. Retinotopic maps show how the brain putatively represents visual stimuli in the cortex.

In the early 1990s, researchers began investigating the "neural code" in earnest. A rate code is the idea that information is carried in the particular firing rate of a neuron, that is, the mean number of action potentials per second. A temporal code is when information is contained in the timing of spikes, not just the mean firing rate. Charles Frye has a great explanation with citations.

Symbolic processing in the brain is an active field of research. The problem can be approached from top-down neuropsychological assays, or from down-up electrophysiology. There is little doubt that symbolic processing is performed by neurons working in concert, though the exact mechanisms for all but the crudest processes are unknown. 

Here are some examples: Theoretical models [1, 2] have shown how layers of neurons with different properties can be used to filter or transform data. In addition, high-level models have demonstrated possible methods by which cognitive units comprised of one or more neurons can determine the solution to symbolic problems [3]. In addition, electrophysiological assays show how cells in the cortex of mammals "record" and represent physical data for use in navigation [4].



[1] Gjorgjieva, Julijana &amp; Drion, Guillaume &amp; Marder, Eve. (2016). Computational Implications of Biophysical Diversity and Multiple Timescales in Neurons and Synapses for Circuit Performance. Current Opinion in Neurobiology. 37. 44-52. 10.1016/j.conb.2015.12.008. 

[2] Shankar, K. H., and Howard, M. W. (2012). A scale-invariant internal representation of time, Neural Computation, 24, 134–193.

[3] Hasselmo ME, Stern CE (2018) A network model of behavioural performance in a rule learning task. Phil. Trans. R. Soc. B 373 : 20170275. PMCID: PMC5832697. PDF

[4] Hinman JR, Dannenberg H, Alexander A, Hasselmo ME. (2018) Neural mechanisms of navigation involving interactions of cortical and subcortical structures. J. Neurophysiol. 119(6):2007-2029. PDF