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The Evolution of Awareness

The Neurology of Awareness and Self: Part One
by Dr. Rick Hanson

The Evolution of Awareness

Part One: The Evolution of Awareness

To determine by what modes or actions light produceth in our minds the phantasm of colour is not so easie. – Isaac Newton


Since the term consciousness has a rich history in philosophy and theology that give it many associations which can complicate making sense of it – and associations that are not meant by us here – we will generally stay with the more biologically grounded term, awareness.

And we will situate the biology of awareness in an evolutionary context. The reason is that the neurological architecture of awareness in the human brain is built on a series of layers – like floors in a building – that have been laid down during billions of years of evolution on this planet, and especially during the last 650 million years of multi-celled animal evolution.

Awareness in the Animal Kingdom

Understanding how awareness is constructed in our own brains means understanding our kinship – layer by layer – with other members of the animal kingdom.

You may have heard of the zen koan, “Does a dog have Buddha-nature?” Well, here’s a less profound one, but one that is answerable within science today: “Does a dog have ‘awareness-nature’?”

Let’s try to answer that question from the ground up, moving from very simple life forms to mammals and primates.

In the study of animals, “aware” is usually considered a transitive verb, in the sense of “aware of _______ .” So, the operational definition of “aware of” is essentially “perceives.” And how can you tell if the animal perceives something? Typically, by an adaptive response to the stimulus.

In the world of microbes, a one-celled amoeba will receive chemical signals from smaller microbes that trigger an engulfing response by the amoeba. In an operational sense, the amoeba perceived the other microbe and responded adaptively, and was thus “aware” in a limited sense of the other microbe. We don’t think of this as true awareness yet, but it does establish the basement, as it were, of the most elemental enabling of perception and adaptive responses.

Then, moving up the evolutionary ladder, let’s consider a worm or a spider. These relatively large creatures have rudimentary nervous systems, in which something marvelous is occurring, a radical breakthrough in evolution: information is being represented in neuronal tissues.

That capacity for representation is a state change, and it opens up a whole world of possibilities.

For one, the representations – the information – of perceptions and responses can be stored to guide the organism’s future behavior . . . and now we have the beginnings of memory and expectations.

Second, the organism can represent its representations . . . and represent its representations of its representations . . . and so on. As we will see, this architecture of second-order, and third- and fourth-, etc. order representations creates the capacity for representing past and present experiences together in a kind of global workspace in the brain.

The worm perceives dryness in the soil and moves away from it, the spider feels the trembling in its web and moves toward its source: each creature is perceiving and responding adaptively, and is, therefore, in increasingly complex ways, aware.

In the same general way, a frog is aware of the movement of the fly it zaps with its tongue. The shark is aware of even just a few molecules of blood in the water. The squirrel is aware of the shadow of the hawk overhead, and the hawk is aware of the squirrel in the tree.

Closer to home, if your dog hears the familiar can opener and smells that lovely glop and comes running over to eat, we’d say that the dog was aware of the food, right? He perceived it and responded to it. That’s awareness in a nutshell.

Further, dogs seem able to be aware of some of the internal states of their human companions. For example, look over at the can opener in the morning, and your dog will follow your gaze and start getting excited since he infers your intention to get his breakfast; or look over at the leash and he’ll jump and down thinking he’s about to go for a walk.

Recent studies of chimpanzees and other primate species have shown the same thing: for example, those animals will infer that an experimenter intentionally used his elbow to open a food compartment only if his hands were clearly available but not used.

Similarities and Differences

The neurology that supports our six senses – through which we perceive and are aware of the external world, plus the interoceptive sense that registers internal states – is not categorically different from the neurology that supports the six senses in other primates, and in most other mammals, and even in many vertebrates, including birds, reptiles, and fish.

Similarly, the neurology that supports the representation of the internal states of mind – the emotions and intentions – of other members of our species has the same foundational circuitry as other highly social animals, especially other primates.

Therefore, our awareness of the environment, of the internal state of the body, and of the feelings and desires of others – enabled and constrained by the neurology we have been discussing – is probably not categorically different from the awareness of the world of many other animals, particularly the ones that are nearest to us in the tree of evolution.

Where humans do differ from other animals, in terms of awareness, is in at least four areas:
  • The contents of awareness (e.g., language, concepts).
  • The ability to be aware of awareness, both in the moment and in the review of the memory of past moments of awareness.
  • The ability to deliberately control and direct awareness.
  • The textures and complexities of the experiencing subject that is aware; the human personality, or psyche, or self is obviously much more complex than the self – if that term is even usable – of other animals.

Nonetheless, to put it bluntly, we appear to be aware in many of the same fundamental ways that other animals – especially “higher” ones – are aware.

Recognizing this similarity can both demystify some aspects of consciousness – err, awareness – and draw us further into an ethical sense of connection with other living beings besides those of our own species.

Neurology of Core Consciousness

So in that context – and in kinship with our furry friends (and perhaps those as well who are feathered or scaly) – let’s consider the neuroanatomy of awareness, or what is called more formally, or technically, the apparent neural correlates of consciousness.

The simplest, barest awareness of the external environment and the internal state of the body seems rooted in the activities of neural structures resting at the crossroads between the brain stem and the more modern “neocortex.” These include the thalamus, the insula, and the same structures deep in the brain stem.

This awareness is sometimes called “core consciousness,” a term used by Antonio Damasio in his book, The Feeling of What Happens.

Technically, Damasio’s quite interesting theory is that “Level One” sensors register the state of some aspect of the organism, let’s say the amount of heat on the skin.

Level Two sensors register changes in the state of Level One sensors, providing a moving picture of what is happening to the organism, such as it is getting hotter on the skin.

And Level Three sensors register changes in Level Two sensors: When the rate or direction of those are “out of range” and therefore “alarming” in an operational sense, those sensors signal other parts of the brain, which then initiate responses, such as pulling the hand back from the stove.

In Damasio’s proposal, it is at Level-Three sensing that awareness – that core consciousness – begins. In other words, the most basic form of awareness involves the ongoing representation of the equilibrium and the disequilibrium of the body.

Interestingly, the neurological regions that handle core consciousness are particularly involved with interoception, the sensing of the internal state of the body.

For example, strokes in the frontal lobes or in the verbal centers of the temporal lobes, or in the sensory-motor regions of the parietal lobes, may all disrupt or impair autobiographical consciousness while leaving core consciousness intact. But strokes or other forms of brain damage to those interoceptive regions can shut off consciousness altogether and put the individual into a vegetative state.

Why is interoception so primary to awareness, to consciousness?

It is not as if ancient organisms in the wild – swimming around, let’s say, in the primordial seas 500 million years ago – could afford to be unaware of their external environment.

It’s speculation to be sure, but we think that interoception came first since the very first multi-celled animals had very primitive external sensors. But they sure needed to know if they were hungry or thirsty or tired, or getting too hot or too cold.

In the neural architecture of awareness, internal sensing is foundational, and everything got build up from there. By the way, this link between sensing the internal state of the body and the deep layers of awareness can aid contemplative practice, because interoception draws one down into core consciousness.

So, what are the qualities of core consciousness?

Core consciousness is bare, endlessly engaged in the present, unable to project into the future or consider the past, and without much sense of self or personal history.

It lacks language – or more exactly – its language is the vocabulary and syntax of the most evolutionarily ancient and fundamental elements of our experience: sensation, emotional shadings, primal desires.

This bare awareness is like – in the Zen metaphor – the surface of a still pond upon which the shadows of geese fall.

Individuals forced into a state of nothing but core consciousness – they are typically through injury or a transient neurological condition – are aware, but quite impaired in terms of being able to direct their life or interact with others or be known to themselves in meaningful ways.

The Neurology of “Core Consciousness”

  • The most basic awareness of stimuli depends on the structures of the brain stem and limbic system.
  • Level 1 sensors receive stimuli.
  • Level 2 sensors register changes in Level 1.
  • Level 3 represents signals from Level 2: the first awareness of the equilibrium of the body.
  • These three levels rely heavily on neural circuits handling interoception, the internal sensing of the state of the organism.
  • Core consciousness is simple, in the present, with little sense of self or personal history.
  • Core consciousness alone may feel peaceful, but without the capacity for “autobiographical consciousness,” a person is seriously impaired.

Autobiographical Consciousness

Now, upon this architecture of core consciousness are built more elaborated neurological networks that reach into the cingulate gyrus and the frontal and temporal lobes.

The theory is that those circuits are the basis for more complex forms of “autobiographical consciousness.” In that mode of awareness, there is more access to all the records and subtleties of the psyche, and more opportunity to evaluate and direct the course of one’s life.

You have probably had the experience of being aware, at a deep level, of the simultaneous self-referencing verbal processes of rumination. In the brain, that is likely core consciousness systems receiving inputs from autobiographical consciousness systems. Or, to paraphrase Carl Jung and put a deeper spin on this, “The [capital S] Self is that subject to which the ego is an object.”

In reality, like so much about the brain, there is probably a continuum of contributors to consciousness, rather than just two types – core and autobiographical – but Damasio’s work is a great start.

And to extend this humbling recognition, let’s be clear: we have outlined a general description of the major structures in the brain that seem to be required for awareness. But the actual details of how an image of a red light is produced in the brain, let alone the subjective experience of the color, are far, far from clear. That is what has been called “the hard problem in consciousness,” and it is far from solved in any detail.

© Rick Hanson, Ph.D., 2007


This is Part One of a six-part series.

Introduction- The Neurology of Awareness and Self: Introduction

Part Two- The Neurology of Awareness and Self: Part Two

Part Two Continued- Non-Dual Perspectives on Awareness

Part Three- Taking the Body for a Walk

Part Four- The Neurology of “Self”

Part Five- The Evolutionary Origins of Self

Part Six- Transcending the Self

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