Making the Limbic System Connection

The hypothesis underlying the Dynamic Neural Retraining System, which was the centerpiece of all my neuroplastic recovery, is that people with multiple chemical sensitivity (MCS), chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME), and fibromyalgia have had a brain injury that results in the limbic system malfunctioning. At first, I didn’t understand or believe this hypothesis, but after a while, it started to make sense to me.

For example, the amygdala processes smell and pheromones, receiving input from the olfactory bulb, as well as being very involved in learning, memory, and emotion. These processes are connected. The amygdala is integral to emotional learning — things we learn that have a strong emotional charge. This fits with the olfactory role, too, because from an evolutionary perspective, smell and fear are intertwined: smell is a key way to tell when danger is around. Prey animals (such as mice) have a pronounced fear response when exposed to the scent of a predator (such as a cat), even if the mouse has never been around a cat. But if the mouse’s amygdala is damaged, it will not show fear when exposed to a predator’s smell that would normally make it scurry away.

People with MCS usually have not just a heightened sense of smell but also a strong physiological response to many smells and to many foods. (I mention foods because smell is a big part of taste and of our digestive processes.) So, if there is a malfunction in a person’s limbic system – the amygdala, hippocampus, and hypothalamus – the parts of the brain most responsible for fight/flight/freeze response, how does this relate to to physical symptoms in the digestive system, immune system, or musculoskeletal system?

Well, what is the physiological response that goes along with the kind of big fear that comes with running for your life (such as you would if you were a mouse that smelled a cat)? The Wiki on the fight/flight/freeze response sums it up:

The adrenal gland is activated almost simultaneously and releases the neurotransmitter epinephrine. The release of chemical messengers results in the production of the hormone cortisol, which increases blood pressure, blood sugar, and suppresses the immune system. The initial response and subsequent reactions are triggered in an effort to create a boost of energy…. Additionally, the circulation of cortisol functions to turn fatty acids into available energy, which prepares muscles throughout the body for response. Catecholamine hormones, such as adrenaline (epinephrine) or noradrenaline (norepinephrine), facilitate immediate physical reactions associated with a preparation for violent muscular action. These include the following:

  • Acceleration of heart and lung action
  • Paling or flushing, or alternating between both
  • Inhibition of stomach and upper-intestinal action to the point where digestion slows down or stops
  • General effect on the sphincters of the body
  • Constriction of blood vessels in many parts of the body
  • Liberation of metabolic energy sources (particularly fat and glycogen) for muscular action
  • Dilation of blood vessels for muscles
  • Inhibition of the lacrimal gland (responsible for tear production) and salivation
  • Dilation of pupil (mydriasis)
  • Relaxation of bladder
  • Inhibition of erection
  • Auditory exclusion (loss of hearing)
  • Tunnel vision (loss of peripheral vision)
  • Disinhibition of spinal reflexes
  • Shaking

A lot of these responses are things I had wrong with me when I was ill. When I was around a fume that caused problems for me (MCS), or when I had a CFS flare, common symptoms for me were red, flushed skin; shortness of breath and asthma; digestive problems; tremors; and frequent urination. And the constant exhaustion and muscle pain and weakness I had could be compared to the physical state one would be in after running a marathon, which is essentially what the flight-or-fight response prepares one to do (“violent muscular action”).

That’s not the whole enchillada, but it’s a taste of some of the things that rang bells with me. When I watched the DNRS program, I realized that it was based on science, which was compelling to me. I still didn’t know if it could really help me get well — that seemed impossible — but I knew people who just had MCS who had gotten better using it, so I thought it was at least worth a try.

Does This Mean that My Illness Was Psychological?

No, this is a misunderstanding of how neuroplasticity works (unless you also view stroke, traumatic brain injury, or chronic pain as psychological). Rick Hanson, PhD, explains neuroplasticity this way in his book, Hardwiring Happiness:

The brain is the organ that learns, so it is designed to be changed by your experiences. It still amazes me but it’s true: Whatever we repeatedly sense and feel and want and think is slowly but surely sculpting neural structure. As you read this, in the five cups of tofu-like tissue inside your head, nested amidst a trillion support cells, 80-100 billion neurons are signaling each other in a network with about half a quadrillion connections called synapses. All this incredibly fast, complex, and dynamic neural activity is continually changing your brain. Active synapses become more sensitive, new synapses start growing within minutes, busy regions get more blood since they need more oxygen and glucose to do their work, and genes inside neurons turn on or off. Meanwhile, less active connections wither away in a process sometimes called neural Darwinism: the survival of the busiest.

All mental activity—sights and sounds, thoughts and feelings, conscious and unconscious processes—is based on underlying neural activity. Much mental and therefore neural activity flows through the brain like ripples on a river, with no lasting effects on its channel. But intense, prolonged, or repeated mental/neural activity—especially if it is conscious—will leave an enduring imprint in neural structure, like a surging current reshaping a riverbed. In the saying in neuroscience: Neurons that fire together, wire together. Mental states become neural traits. Day after day, your mind is building your brain.

This is what scientists call “experience-dependent neuroplasticity,” which is a hot area of research these days. For example, London taxi drivers memorizing the city’s spaghetti snarl of streets have thickened neural layers in their hippocampus, the region that helps make visual-spatial memories; like building a muscle, these drivers worked a part of their brain and grew new tissue there. Moving from the cab to the cushion, mindfulness meditators have increased gray matter—which means a thicker cortex—in three key regions: prefrontal areas behind the forehead that control attention; the insula, which we use for tuning into ourselves and others; and the hippocampus. Your experiences don’t just grow new synapses, remarkable as that is by itself, but also somehow reach down into your genes—into little strips of atoms in the twisted molecules of DNA inside the nuclei of neurons – and change how they operate. For instance, if you routinely practice relaxation, it will increase the activity of genes that calm down stress reactions, making you more resilient.

Neuroscientists often explain the difference between the “mind” and the “brain” as, “the mind is what the brain does.” I think this definition is a little confusing to most people because the brain does a lot of things that have nothing to do with what people think of as “the mind.” Most of the time, when people speak of the “mind,” they’re referring to activities related to consciousness, such as thought, imagination, emotions, dreams, memories, etc.

Yet, most of the brain’s activities are unconscious. These include largely automated actions like regulating cardiac and respiratory function (heart rate and breathing), sleep cycles, hunger/thirst and satiety, and sensory processing, including proprioception (awareness of where your body is in space), the vestibular system (sense of balance), and the more familiar senses of sight, sound, smell, taste, and touch. The brain also regulates the release of neurotransmitters, hormones, and other chemicals (a few are cortisol, adrenaline, oxytocin, vasopressin, and dopamine) which have a huge impact on our minds (moods, feelings), as well as on our physiology.

While it is possible to become aware of some of these processes and bring them under conscious control — this is where stories of yogis who can stop their hearts or put metal rods through their skin without pain come from — that can take decades of intense, exclusively focused attention and is certainly not what most people mean when they talk of the “mind.” So, the brain is constantly performing a huge number of activities that have nothing to do with the mind in the way most of us mean it — with thinking or with who we are as individuals. However, the fascinating thing about neuroplasticity is that we can use the conscious mind (the activity of the brain we have some control over) to change the brain’s unconscious activities and even its structure and anatomy!

This is one way people can recover from traumatic brain injury and stroke. Even if part of the brain is dead, if someone with a brain injury repeatedly focuses on or performs the same physical or mental activities that the dead areas used to perform — even if someone else is moving their arm or leg to perform that action — other areas of the brain will begin to take over performing the activities associated with that use or movement. This is why people say the brain operates by “use it or lose it”; the pathways in the brain that are being used stay strong and active, and pathways that are not in use get recruited for other jobs.

More about my recovery and related topics:

To contact me with comments, questions, or to book a coaching session, please use the form below. Thank you!

To contact me with comments, questions, or to book a coaching session, please use the form below. Thank you!