Prefrontal Cortex Dissociation from Amygdala and Personality Types

Eric Lombrozo

Phylogeny

Evolutionarily, it seems that the PFC (prefrontal cortex) region probably grew in size and complexity as a way to deal with inadequacies of the limbic system in successfully tackling new survival and reproductive challenges. The limbic system is more primitive and in many ways less flexible than the cerebral cortex.(1)

I think it is true for all mammals that healthy individuals learn to face threats successfully whereas unhealthy individuals have a tendency to overreact to nonthreats and underreact to real threats.

Experiments have shown that injecting rats with drugs that activate the amygdala strengthens conditioning to stressful stimuli whereas drugs that inactivate the amygdala tend to supress learning - suggesting that the amygdala not only is important in the response to and experience of fear - but to the formation of memories of stressful events as well.(2)

But neutral stimuli are too easily misidentified as threatening stimuli. The amygdala alone is not sufficiently sophisticated to truly work out the nature of the threat and sort out what elements of an experience are threatening and what elements are neutral and benign. So an animal like a rat, which relies much more on the limbic system than a human in making actual decisions, will more readily act out its immediate fears and desires and is thus much more prone to serious error in the assessment of novel threats. This restricts rat behavior significantly - and seems to promote shorter lifespan and higher reproductive rate as a means of coping with errors in learning.

Humans, on the other hand, seem to be faced with quite a different situation - especially in the developed parts of the world where food and water are plentiful, war is remote, and people are much more likely to die from cancer or stroke than from wild animal attacks or machine gun fire. Our amygdalae are too easily oversensitized to stimuli which we consciously and rationally know to be benign. People with phobias can often talk at length about their irrational fears, indicating that the PFC is acutely aware of the fact that the fear is not grounded in any actual threat while the amygdala continues to react to the stimulus in a stressful way.

It seems there are two potential kinds of mechanism that can develop in coping with such phobias:

1. the PFC assists the amygdala in correctly relearning the fear association
2. the PFC learns to compensate by becoming more selective in its sensitivity to amygdala signals as well as more "clever" in its responses to them

It seems that the first mechanism is the healthier and more preferable option - if available. However, if the first mechanism is unavailable, the second one might be used instead. The problem with the second one is that it merely treats the symptoms of poor amygdala learning and not the causes. And it might just lead to the nine Enneagram personality types!(3)

Personality Types

Deeply inspired by the brilliant and groundbreaking work of Peter Savich, I have come to suspect that the key to a detailed and comprehensive neurobiological theory of personality lies in the neural pathways between the amygdala and the PFC. In this monumental work, Savich explains that the nine Enneagram types can be placed into a 3x3 table with the columns denoting which cerebral hemisphere is dominant and the rows denoting which amygdala is dominant for each of the nine Enneagram types. The center column and center row correspond to symmetric activity levels for the PFC and the amygdala respectively.(4) I seek to improve upon this work and continue to pave the way towards a complete neurobiological model that can account for the Enneagram personality types as well as their dynamics, appealing merely to what we presently know about the brain.

I propose the following two-part hypothesis:

1. Both sides of the PFC have defense mechanisms which can block, override, or desensitize the PFC from amygdala signals - and the different types show different tendencies towards dissociation or numbness to different kinds of amygdala signals.

   For instance, a 5 might learn to dissociate both sides of the PFC from the left amygdala signals - and this might cause the left amygdala to become overactive since the PFC doesn't manage to address and fully resolve the amygdala's concerns. However, at this point, the exact mechanism is obviously just a matter of speculation.

2. The degree of dissociation is different for each side of the PFC for different types. This can potentially lead to a competitive dynamic between the two sides of the PFC where one tries to dissociate while the other insists on urgent attention to amygdala concerns - or one side might attempt to actively suppress the other.

   For instance, an 8's right PFC might have a tendency to dissociate more strongly than her left PFC from right amygdala signals. The left PFC might decide to ignore or suppress the right PFC and go attend to the amygdala's concerns alone. This might lead to a measurable asymmetry in PFC activity level in an 8.

Behavior (mood)

Studies have shown a noticeable cortical lateralization in the processing of emotions. The left PFC tends towards optimism in the interpretation of amygdala signals whereas the right PFC tends towards pessimism. In other words, the left PFC tends to seek out opportunities favorable to the individual, ignoring any potential risks; whereas the right PFC tends to seek out ways to eliminate risk, ignoring any potential opportunities.(5)

If we do what Savich has done and associate aggressive behavior with left PFC activity and compliant behavior with right PFC activity, then my hypothesis immediately suggests the following:

1. Right PFC dissociation leads to aggressive behavior
2. Left PFC dissociation leads to compliant behavior
3. Symmetric PFC dissociation leads to withdrawn behavior

I believe this is a significant improvement over Savich's original lateral dominance hypothesis, since it can account for all the dynamic aspects of the Enneagram as well as explain tendencies toward withdrawn behavior.

Fear

Savich has noted that experiments by Jan Gläscher and Ralph Adolphs strongly suggest that the left amygdala is associated with fears which vividly present themselves to our conscious awareness whereas the right amygdala is associated with fears which do not evoke strong conscious awareness.(6)

Savich has called them "aware" and "unaware" fears, respectively.

The Enneagram

Putting together all these elements, we construct the modified Savich table describing each personality type's tendencies to dissociate from amygdala signals:

Each of the links above shows nine health levels for each of the nine Enneagram personality types. These dissociation tendencies are most pronounced at the unhealthy levels and tend to disappear as one moves up to the healthier levels.

References:

1. Dale Purves, George J. Augustine, David Fitzpatrick, Lawrence C. Katz, Anthony-Samuel LaMantia, James O. McNamara and S. Mark Williams (2001)
2. Barbara Ferry, Benno Roozendaal and James L. McGaugh (1999)
3. Don Richard Riso and Russ Hudson (1998-2007)
4. Peter Savich (2005)
5. Richard J. Davidson (2004)
6. Jan Gläscher and Ralph Adolphs (2003)

Eric Lombrozo
San Diego, California
February 21-26, 2007

Copyright © 2007 Eric Lombrozo