On the Your Amazing Brain page, you met the mid-prefrontal cortex (the MPFC), which we described as "the captain of the ship." Now it’s time to meet the rest of the mind-body "crew" – the other parts of the brain and nervous system that help run the mind-body ship.
Although it’s one organ, scientists sometimes talk about the brain as if it were made up of three parts, which we’ll be referring to here as the instinctive brain, the emotional brain, and the thinking brain.
The brain stays in constant communication with the rest of the body with the help of the autonomic nervous system. And since the nervous system extends from our head to our feet, you could say that, in a way, the brain is distributed throughout the whole body.
In fact, in recent years, scientists have discovered that the heart, too, has a "brain" of its own which collaborates closely with the head brain, and plays an integral role in enabling us to live from a core of calm, ease, and well-being. Many now consider the system of nerves in and around the heart to be our fourth brain.
The main job of the instinctive brain is to assure our physical survival. It works tirelessly behind the scenes, tending to the involuntary functions of our body that keep us alive. Without our needing to consciously participate, it makes sure that we keep breathing, it regulates our blood pressure, produces feelings of hunger, and manages many other vital functions.
When it’s working in harmony with the other members of the crew, the instinctive brain keeps our body in a state of balance – energized and relaxed. But when we feel threatened, it instinctively tries to protect us through a series of physiological changes called “the fight or flight response.” We’ll describe this in more detail on the Stress Page.
The main job of the emotional brain is to help us move beyond mere physical survival. It adds emotional richness to our lives by giving us the capacity to connect emotionally to others and form enduring emotional bonds.
That means we don’t have to be stuck in repetitive behaviors and emotional reactions that no longer serve us – we are potentially free to choose new, more appropriate ways of responding to the people and situations in our lives.
The heart contains neurons that very closely resemble those of the head brain, and makes decisions of its own that are independent of the head brain. For this reason the heart is considered to be a separate brain. It has its own kind of non-verbal, intuitive intelligence, which can guide us to make wise decisions and act in ways that are naturally more loving and compassionate.
The autonomic nervous system (ANS) keeps the body, the “head brain” and the “heart brain” in constant communication with each other. It carries information about what’s happening in the body and the heart up to the brain. And it carries messages from the brain down to the heart and the body, advising them what to do in any given situation.
The ANS is made up of two parts – the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The SNS functions like the gas pedal of a car – it revs the body up to prepare us for action. The PNS functions like the brakes, slowing our heart rate and other functions down so that our body can replenish and repair itself.
When the MPFC is in charge, it keeps the instinctive brain, the emotional brain, and the thinking brain working in harmony. As a result, the brain is sending clear messages to the SNS and the PNS, their activity is well-balanced, and the body thrives.
However, when the captain is less skillful, he’s not as able to manage the crew, and they tend to get into conflict with each other. When the crew is in conflict, it sends conflicting messages to the ANS, which is kind of like having your foot on the gas pedal and brake at the same time. We experience that as stress and it results in wear and tear on the body.
Hold your hand with your palm facing you. Then cross your thumb over the middle of the palm, and curl your fingers over the thumb. This gives you what Siegel refers to as “a handy model of the brain.”
Imagine this is the brain of a person who is facing you. Your wrist is the top of their spinal cord. The lower part of your palm is the person’s instinctive brain or brainstem. Now lift your fingers to uncover your thumb. The thumb is their emotional brain or limbic system. Now curl your fingers back over the thumb. Your fingers represent their thinking brain or cortex.
The MPFC is represented by the fingernails of your third and fourth fingers. You can see that the MPFC is in close contact with the instinctive, emotional and thinking brains – which is why it is so well-positioned to integrate the whole brain.
The heart brain plays a special role in supporting the MPFC in its work of creating harmony and balance between the various members of the crew. It is central to creating the core experience of calm, contentment, and connection to others. When the MPFC and heart are in tune, you just kind of “know” what to say and how to act in a way that will be best for all concerned. So keep in mind that whenever we refer to the MPFC on this site, we mean the MPFC and heart-brain working as a team to guide the brain and body.