Introduction

Our brains are composed of more than 170 billion cells, about half of which are called neurons - the information processing cells that communicate via electrical and chemical signals. The other half are called glial cells, which provide several supportive cellular functions, including helping to maintain homeostasis. If that sounds like a whole lot of cells, it is! Although the brain is only about 2% of body's mass, it consumes roughly 20% of the body's total energy at rest, reflecting an extraordinary concentration of metabolic investment in this information processing center.

To grasp all that we're about to dive into, it's important to have at least a basic understanding of how our neurons "wire and fire" with one another. When groups of neurons repeatedly activate together, they can strengthen their connections, forming a neural circuit. Multiple interacting neural circuits create broader neural networks, which underlie complex functions like perception, memory, and decision-making. Neurons connect across synapses - specialized junctions where the axon terminal of one neuron meets the dendrite, soma, or axon of another. A synapse includes the presynaptic terminal, the tiny gap called the synaptic cleft, and the postsynaptic membrane (see Figure I.1). Signals travel electrically within a neuron and chemically across most synapses via neurotransmitters (though some synapses are purely electrical). The average adult human brain has between 100 and 500 trillion synaptic connections (depending on whom you ask), which produce hundreds of trillions of synaptic events every minute.

Figure I.1 Synapse.

These magnitudes, and the resulting, interdependent mental, emotional, and physiological outputs, are impossible to conceptualize or to understand even for sophisticated neuroscientists. In fact, the most respected neurobiologists still don't have a full grasp of how this incredible enigma works. In this sense, our internal universe is probably as mysterious and complex as the external universe. It is one of the last frontiers on earth, perhaps as enigmatic as the deep seas, of which only about 5 percent have been explored. In my opinion, the ocean depths, the cosmos, and the brain should all be considered on the same plain when it comes to mystery and, ideally, awe.

There are three main functions of your brain: coordination, regulation, and prediction. To put it succinctly, your brain's core functions are to coordinate your body's organs and biochemical processes in order to regulate their metabolic output to best meet the demands that it predicts the body will need in each situation. I have laid these out in a particular order, beginning with what we might call bottom-up functionality, pointing to coordination as the bottom of the funnel: the most unconscious and, thus, most uncontrollable component of your brain's functions. There's nothing much we can or should do to interrupt the brain's ability to coordinate the rest of the body and its processes.

So, let's discuss instead the middle of the funnel: regulation. Neurobiologists and psychologists use the term regulation to refer to the activity of the nervous system. This could be conscious, goal-directed activity (e.g., how we can deliberately regulate our system) or nonconscious activity (e.g., how the brain regulates the body). The term regulation on its own often refers to a state of homeostatic balance, wherein the brain is attempting to coordinate the body's various elements in a way that brings them back to a manageable baseline. So, when the nervous system is responding to the demands of the immediate environment-whether those demands require little metabolic outlay or a hefty level of metabolic resources-if it responds adequately and appropriately, the system can be said to be regulated.

When particular systems or networks are more active, we call those systems upregulated, and when systems are less active or blunted, we call those downregulated. The sympathetic nervous system, a branch of the autonomic or unconscious system, is the network of neural circuits that facilitate physiological mobilization, activating energy expenditure and arousal states that prepare the organism for action. Hence, when we are excited, our sympathetic nervous system can be said to be upregulated. When we calm back down, it becomes downregulated. Simultaneously, our parasympathetic system-the network associated with restoration, relaxation, and recovery-become upregulated, sort of like the opposite end of a see-saw.

In cases where there seems to be a mismatch of up- or downregulation of the nervous systems' or its subsystems' components, leading to some disruption of normal or healthy function, we call this dysregulation. In other words, if the system is not responding adequately or appropriately to the immediate demands of the situation, likely because of faulty or inapplicable predictions, the system can be said to be dysregulated.

The regulation function of the brain is what I'm calling middle of the funnel, suggesting that we are somewhat aware of and have some, albeit limited, control over its functionality. For example, when we are anxious for no good reason-presumably a state of dysregulation-we can and often do become aware of the feeling of anxiety. Perhaps we notice our heart beating faster, our stomach feeling butterflies, our chest tightening, or any number of sensations indicating an upregulation of the sympathetic nervous system. And if there is no obvious need for such a metabolic output, we label it as anxiety, since it is obviously not responding to the demands of the immediate environment but rather some imagined or predicted future. In dysregulation of this sort, we might take steps to regulate the system by slowing and deepening our breathing and consciously relaxing the body, thereby hoping to upregulate the parasympathetic system and downregulate the sympathetic system. We don't have total control over our regulation at this level, but we do have some, and with practice we can get better at regulating our autonomic system.

Many of us are motivated to learn more about the nervous system because we feel dysregulated. That is, we feel chronically anxious or depressed or nervous about some particular circumstances or, in many cases, about seemingly nothing at all, pointing to the largely nonconscious nature of regulation. If you're reading this book, perhaps you're acutely aware of your own dysregulation as a result of internal, interpersonal, or intergroup conflict you are personally experiencing or witnessing. So, you may be looking for ways to change it. Perhaps interacting with a coworker or a family member, or even the thought of being around them, elevates your heart rate or stirs the butterflies in your stomach (and not in a good way). So, you're looking for ways to alter the dynamic in order to stop feeling so stressed or dysregulated around that person. Well then, let's move into the top of the brain function funnel: prediction.

The model I'm presenting, with regard to the brain's functionality, suggests that the brain predicts the metabolic resources the body will need to meet the demands of the immediate to long-term situations. This model stems from the most widely accepted conception of brain functionality at the time of this writing, which blends a top-down and bottom-up framework, where incoming sensory information (from the bottom) is checked against predictive processing (from the top). These processes then cause up- and/or downregulation of various components of the nervous system, all of which are managed through nonconscious biochemical coordination. Unlike the middle and bottom portions of the funnel, however, we can become more acutely aware of and, thus, have more control over prediction-the top of the funnel.

To be clear, much of what our brains are predicting is either totally nonconscious (i.e., purely physiological) or hidden within the subconscious (i.e., beneath conscious awareness). We might be acutely aware of the stress or anxiety we feel in a situation or we might not be, but we are often unaware of exactly what the brain is predicting might happen or why it's making such a prediction.

With some reflective work, however, we can uncover a great deal of what lies beneath the surface of awareness to learn what exactly our brains are predicting (and even why they're predicting such things, though it's unclear how much the why matters for purposes of changing predictive patterns). Once we become aware of predictions that cause components of the autonomic nervous system to up-, down-, and dysregulate, we can take conscious steps to interrupt the patterns if desired. We might tell ourselves new predictive messages, such as "it's going to be okay" or "I can handle this," which can help calm the nervous system from this top-down approach. However, there is an even more important aspect to this business of interrupting neural patterns and predictions that cause dysregulation: memory.

Inherent in the brain's future-focused prediction function is a past-focused memory function. In fact, it stands to reason that the entire reason the brain remembers and learns from past experiences is to appropriately position resources to meet the demands of the predicted future. In order to accurately predict and carry out its main functions, therefore, the brain pulls from past experience. It's the only way the brain...