4- An Updated Map

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Essay 3 reviewed the triune brain model, and expanded it to include the reticular system and cerebellum.  All five systems deserve equal emphasis in an overview brain map.

This essay addresses a widely recognized shortcoming of the triune model:  its view of emotion.  With new evidence, the need to update that view has become obvious.

The idea of the limbic system as the “emotional brain,” outlined in Essay 3, has given way to an expanded brain map of emotion.  In this more recent view, the limbic system underlies just one level of emotion, primarily the social emotions.   But positive and negative emotion is programmed on all brain levels.  From ancient core to modern cortex, human nature is organized around this positive-negative emotional duality.

This basic duality is the defining feature of emotion (see Notes).   Positive and negative emotions shape all our experience and behavior —

“Nature has placed mankind under the governance of two sovereign masters, pain and pleasure. It is for them alone to point out what we ought to do, as well as to determine what we shall do.”

– Jeremy Bentham, English philosopher, 1789

So here’s a basic principle of brain function:  Positive and negative emotion is programmed in the reticular system, brainstem, limbic system, and cerebral cortex.  The cerebellum adds a third force  –  a neutral balancing  force  –  to positive and negative processing at each level.  Here’s a brief overview  —

Core Consciousness Medial View of Brain


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The Reticular System

As noted in Essay 1, reticular neurons are organized more loosely than the well-defined pathways of other brain systems.  Most form diffuse, interwoven networks which are said to “grade almost imperceptibly from one to another.”

However, those reticular networks connected with the cerebellum are described as “separate and distinct from the major reticular formation.”  Another scientist put it this way:  “the first and most obvious division of reticular [networks] is between those that are related to the cerebellum and those that are not.”

Again, microscopic inspection of the core shows those networks connected with the cerebellum are easily distinguished from other reticular networks.  This anatomical division underlies basic functional differences.    Those networks projecting to the cerebellum are essential for its (non-emotional) balance functions.  The rest of the core contains many intermingled positive and negative networks.

These networks form the brain’s emotional core.  They activate other positive and negative programs throughout the brain.  Here are the “reward and punishment centers”  —  experimental stimulation in certain networks causes intense pleasure, in others intense pain or discomfort.  Reticular networks underlie core pleasures and pains, our deepest positive and negative emotions.  More on that shortly.

The Brainstem

Specific (non-reticular) brainstem pathways and systems evolved from the reticular core. They control our basic animal instincts, which are largely programmed in positive and negative emotional patterns.

Positive drives involve physical pleasures and approach behaviors.  They include eating, drinking, sexual drives, and other needs or desires for sensory gratification.


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Negative drives are pain-avoidance programs.  They include flight-or-fight, escape or attack responses to painful, unpleasant, or threatening stimuli.

Most brainstem programs reflect this positive-negative duality.  Sensory processing is largely organized around pleasure and pain perception.  Motor processing is largely organized around approach and avoidance behaviors.  Visceral control systems are similarly organized in two major divisions (see Notes), also reflecting that basic emotional duality.

Newer emotion systems are built on those brainstem patterns.  Limbic and cortical levels elaborate the brainstem’s instinct programs, adding new emotional dimensions, while maintaining the basic positive and negative patterns.

The Limbic System

The limbic system is now recognized as one major level of emotional processing.  It’s particularly important in positive and negative social emotions, as described in Essay 3.

On the positive side, we have caring, sharing, playing, helping, and belonging.  We share these complex pleasure-approach emotions with other mammals.

On the negative side, we have social aggression and anxiety, associated with power/status competition and the pain of separation/loss.  We also share these emotions with other mammals.

Our cerebral cortex further elaborates social emotions into more complex, uniquely human versions.  But the basic mammalian programs are still in our limbic systems.


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The Cerebral Cortex

Now what’s this about thinking being emotional?   It may be hard to believe that the intellect is basically emotional.  Western philosophical traditions have long separated thinking and emotion, and this view remains deeply ingrained.  Likewise, the traditional view of the brain, outlined in previous essays, separates the limbic “emotional brain” from cognitive functions of the cortex.

But in recent decades that view has shifted.  It’s now clear that emotion is an integral part of thinking, and of cerebrocortical functions in general.

“As the brain evolved, it did not leave emotion…in the lower reaches of the brain but carried [it] into the evolving neural structures, each level adding new dimensions and broadening the original scope in subtle ways.  If you wish to see emotion in full flower it is to man that you must turn…Emotion plays a role in the highest level of human intellectual achievement.”

– Neurophysiologist C. Van Toller

The part of the cerebral cortex most directly involved in emotion is the prefrontal cortex.

In most mammals, prefrontal areas make up less than 5% of the cortex (and most mammals don’t have much cortex).  In chimps it’s 17%, and in humans 29% of the cerebral cortex is prefrontal cortex.

Its evolution, there at the front of the brain, caused the sloping brows of our ancestors to bulge into the high foreheads of Homo sapiens.  More than any other brain region (except the new cerebellum, which evolved with it), prefrontal cortex distinguishes us from other animals.

In recent years some basic principles have emerged regarding prefrontal functions.  This region is mainly involved in emotion, and it drives the rest of the cortex.  Our thinking is shaped and directed by positive and negative emotion of prefrontal cortex.


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Prefrontal cortex provides a new, uniquely human level of emotion.  It expands the simpler emotions programmed on brainstem and limbic levels, broadens their scope, and adds new positive and negative dimensions.

“In fact, the higher up the evolutionary scale an animal is, the more emotion it can display. Human beings are the most emotional creatures of all.”

– Neurophysiologists F. Bloom and A. Lazerson

And prefrontal emotions drive the rest of the cortex.  They

“control the active state of the cortex…[They] determine the direction of human activity and [give it] an elective and purposive character.”

– Neuropsychologist A. R. Luria

These uniquely human emotions drive your imagination and intellect.  They shape your perception, calculation, planning, and decision-making.  Prefrontal emotions – positive and negative – direct your thinking.

So we have all kinds of pleasant and unpleasant thoughts.  We wish for good things and worry about bad things.  We idealize and we criticize.  We cling to some ideas and block others from awareness.  We approach positive goals, avoid or attack negative problems, with our thinking as well as our action.

“This basic principle of approach-avoidance…persists through all levels of behavior, including the most complex patterns of human beings.”

– Neuropsychiatrist Robert Heath

The cerebral cortex, driven by its prefrontal areas, is very much involved with emotion.

So we have positive and negative emotion at reticular, brainstem, limbic, and cortical levels.  But at each level we also have a third, emotionally neutral, balance force  –


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The Cerebellum

The cerebellum contains over half of the brain’s neurons, is interconnected with all other systems, and has strong influences throughout the brain.  It balances, coordinates, and integrates processing patterns  –  including positive and negative patterns  –  on all brain levels.

But as noted in Essay 2, we’re still not clear on just how the cerebellum  modulates our minds.  Its psychological influences remain largely matters of speculation.  What does “mental balance” or “personality integration” actually mean at each brain level?  Just how does this neutral stabilizing force, interacting with positive and negative emotion, play out in our lives?

On the brainstem level, there’s not much need to speculate.  We know the cerebellum coordinates all kinds of approach and avoidance behaviors, integrating body movements as it maintains body balance.  It modulates sensory processing, including pleasure-pain perception, and promotes sensory integration.  It has similar stabilizing effects on positive and negative visceral programs.

On the limbic level, the cerebellum modulates our social emotions.  It promotes social-emotional balance, and the word that best describes that balance is probably respect.  Sometimes confused with positive (love, admiration) or negative (fear, submission) emotions, respect actually is neither.  It is balanced regard for others and/or oneself.  With respect, all kinds of positive and negative feelings are integrated into stable self-esteem and relationship patterns.

On the cortical level, the cerebellum is widely assumed to “coordinate cognitive functions.”  That probably includes a major role in reason, or logical thinking.  Indeed, reason is balanced, coordinated, and integrated thinking.  The cerebellum may bring objective balance to positive and negative emotional thinking.  It may bring realism to optimism and pessimism, practical planning to wishful thinking and worrying.

In the reticular system, we have positive and negative core networks, central to all emotion systems.  The cerebellum modulates those networks, stabilizing core emotions.  (Speculating further) it modulates our deepest pleasures and pains  –  existential joy and angst, inner light and darkness, undifferentiated goodness and badness in our cores.  The cerebellum brings equanimity to them all.  It helps smooth all kinds of positive and negative turmoil in our souls.  With spiritual growth, this inner balance deepens and strengthens, as core awareness becomes more stable and integrated into the personality.

NOTES

Page 1 – “Emotion” is notoriously difficult to define.  One researcher listed almost 100 different definitions proposed by various experts during the 1900’s.  The only consistent agreement among them was that emotions are positive or negative.  Today this positive-negative duality is central to our understanding of emotion, even if we still don’t have a good consensus definition.

Page 3 – Visceral regulation occurs primarily in the brainstem. The parasympathetic system, associated with pleasure-approach drives, prepares internal organs for eating (increased salivation, hunger sensations), sex (erection, physical attraction), and other instinctual needs/desires. The sympathetic system prepares the body for fight or flight (increased respiration and heart rate, release of adrenaline) in response to pain, threats, and other negative stimuli.  Parasympathetic-sympathetic interactions, like all positive-negative interactions, are very complex. The cerebellum modulates them, promoting autonomic balance and visceral stability.

Page 5 – Prefrontal cortex drives the rest of the cortex.  This basic drive energy comes, of course, from the core  –  reticular projections to prefrontal cortex are particularly strong.

Page 6 – “Balance” is, like emotion, difficult to define.  There are all kinds of balances throughout nature and at all levels of brain function.  It’s certainly not just a cerebellar function.  The same can be said of “integration” and similar terms.  But in these essays they refer to the cerebellum’s global or superordinate balancing and integrating functions.

REFERENCES

  • Bentham, Jeremy. The Principles of Morals and Legislation, 1789.
  • Bloom, Floyd and Lazerson, Arlyne. Brain, Mind, and Behavior. W.H. Freeman, New York, 1988.
  • Heath, Robert. The Neural Substrate for Emotion. In Emotion: Theory, Research, and Experience. Ed R. Plutchik and H. Kellerman. Academic Press, New York, 1986.
  • Luria, Alexander. The Frontal Lobes and the Regulation of Behavior. In Psychophysiology of the Frontal Lobes. Ed K. Pribram and A. Luria.   Academic Press, New York, 1973.
  • Mountcastle, Vernon. Medical Physiology. C.V. Mosby, St. Louis, 1968.
  • Noback, Charles. The Human Nervous System. McGraw-Hill, New York, 1967.
  • Van Toller, C. The Nervous Body: An Introduction to the Autonomic Nervous System and Behavior. John Wiley and Sons, New York, 1979.