Autonomic Nervous System

The autonomic nervous system (ANS) both regulates and monitors the body, mostly outside consciousness. As Antonio Damasio describes extensively in his books, these two functions form the substrate of emotional functioning. Eighty percent of autonomic nervous fibers are afferent, that is they bring information to the brain. The 'headquarters' of the ANS is the hypothalamus, which communicates extensively with the limbic or emotional areas of the brain. Unlike the voluntary motor system, the autonomic nervous system has synapses outside the brain and spinal cord. This ensures that a broader range of inputs is influential in its functioning.

The autonomic nervous system traditionally has been described with a "bipolar model'. In this model, which matches the table below, the parasympathetic part 'controls' rest and restoration, and the sympathetic part controls action. Ideally they oppose and balance each other for health. Neither is good or bad. This model may explain the maintenance of vital functions for daily functioning and survival, but it does not explain the emotional or motivational aspects of the ANS.

The Polyvagal Model

A much more nuanced model, at least for human affairs, is the polyvagal model, developed by Stephen Porges, which describes three layers of autonomic functioning, arranged hierarchically rather than in opposition.

The top layer is the ventrovagal, which can also be described as the Social Engagement System. It is constituted from fast myelinated vagal fibers that interconnect the ear, the eye muscles, the mouth, the throat and voicebox and the heart. This is the most 'social' and most adaptive system for dealing with the presence of another person or a novel situation. The vagal fibers that go to the facial muscles are called, the special efferent system, and are often overlooked in thinking about the autonomic system. The facial muscles then constitute an interesting system that overall has both voluntary and involuntary control. Some parts of the face such as the cheeks and lips are useable freely by voluntary control, while the orbicularis oculi around the eyes is essentially vagally run. That is why it has been noted that a smile around the mouth may be faked, but a smile around the eyes is inevitably true.

The Social Engagement System both requires a felt sensation of safety to be active, and helps provide such a sensation of safety. Poor eye contact and a flat facial expression are common signs that the Social Engagement System is not active.

When the ventro-vagal system is in a state of disuse, or is inadequate for the challenge, the sympathetic or action system takes over as the driver of behavior and feeling. This is less social and biased toward action not 'inter'-action. The sympathetic system has at least three aspects: 1) a baseline tone that is necessary to sustain life as a human, 2) the capacity to adjust the body to increased purposeful physical activity, and 3) an emergency system, fight or flight' that involves the adrenal system as well.

The baseline sympathetic tone for instance is what insures that blood pressure will be adequate. If the demands for energy output increase, it is possible for the ventral-vagal system to lessen, and the baseline sympathetic tone has more effect, but without involving the adrenals. This means that the effect can be reversed instantly, which is very important in social situations. This use of the interplay of vento-vagal tone and baseline sympathetic tone has been termed 'the vagal brake'.

The most known aspect of the sympathetic system is the ability to provide a sudden massive burst of stimulation, both directly and with the aid of the adrenal system. This provides not only the ability to 'do something' but psychologically, provides a strong sense of urgency to do something. This has been termed 'fight or flight' Though this is 'meant' to be a rare, emergency system, in many people it is chronic. When functioning in this state, a person perceives neutral faces and neutral voices as hostile, and responds defensively very quickly. In a shark attack or fire etc.., this state is very useful. In a social situation it is maladaptive, and makes social relations chaotic and unrewarding.

If as so often happens in modern life, 'flight or fight' is triggered without an objective life or death emergency, it is still a good idea to perform safe moderate physical activity away from the stimulus, because being stimulated this way and not moving has consequences of sympathetic shift, or dorsal shift.

When a person is trapped, or cannot act effectively, the third or 'bottom' layer of the autonomic system is activated, the dorsal vagal, which is constituted from slower unmyelinated fibers to the heart, bronchi, and visceral organs below the diaphragm. The dorsal vagal is like a sudden emergency brake. The person freezes, or 'plays' dead. Speech is limited, eye-contact impossible, motion absent. When the physiology is in freeze, the psychology is mostly in dissociation.

Orienting Response

When there is a change in the environment, human and higher animals have a very basic response, the orienting reflex. The individual stops what it is doing and“turns its head (with eyes ears and nose to the source of stimulation. There is also pupillary dilation, a drop in skin resistance and a momentary drop in heart rate. What is very important, is that this is a take off point for further autonomic response, which can be dorsal vagal, sympathetic, or ventral vagal. That is it can be freeze, flight, fight, or making friends. In complex social environments, what constitutes 'sufficient' novelty to benefit from orienting reflex is not a fixed issue. Concentration inhibits the orienting reflex severely. In ADHD, the reflex seems insufficiently inhibited. We live in a society where novelty is deliberately manipulated constantly. Disordered or excessive orienting seems to be another aspect of autonomic dysfunction.

Defense Ladders

The polyvagal system constitutes a neuro-endocrine defense ladder. Commonly, in psychology, defenses are arranged along an ego-defense ladder, with more 'mature' defenses being encouraged because they allow more interpersonal flexibility. It can be thought that neuro-endocrine defenses preserving the biological integrity of the body and ego defenses preserving the coherence of the ego. However, they are inter-related. 'Higher' ego defenses are based on higher neuro-endocrine defenses. That is why bodywork is often necessary for significant change in interpersonal functioning.

Other Implications

Functioning takes on its flavor from which of the three autonomic states is predominant at the time. However there are two 'states' that seem to be characterized by an increase in both ventral vagal and sympathetic level. These states are play and sexual activity.

There is also a two-layered neuroplexus in the intestinal wall. It has as many neurons as the spinal cord and produces the same neurotransmitters and hormones as the brain. Clearly, this, along with the solar plexus, seems to be the 'belly-brain' that many healing and wellness traditions have intuitively described. This is the source of 'gut feeling.'

Post Traumatic Stress Disorder seems to be a cycling between the fight-or-flight system (sympathetic) and the freeze system (dorsal vagal). The social engagement system falls into disuse. The person continues to try to engage socially but not effectively, because the social engagement system is not available. This happens even if a person had effective social engagement earlier in life, because social skills are not cognitive skills but rather body skills. A stalemate between the freeze system and the fight-or-flight system may superficially appear as a 'well-regulated' state but is actually a state of limited contact.

The table below reflects the cruder, faster-slower, two part oppositional model still in use for most medical explanations. As described above, it is not that useful for explaining emotions or relationships, but is included for it's memory value.

Oppositional Model of Sympathetic and Parasympathetic
Organ System Sympathetic Reaction (Anxiety) Parasympathetic Reaction (Pleasure)
Iris of Eye
Dilation of Pupils Constriction of Pupils
Tear Glands
Inhibition, "dry eyes" Stimulation, "glowing eyes"
Salivary Glands
Inhibition, "dry mouth" Stimulation, "mouth watering"
Sweat Glands
Stimulation, "skin wet, clammy" Inhibition, Dry Skin
Peripheral Blood Vessels
Constriction, Pallor, Cool Skin Dilation, Flushed Warm Skin
Piloereector Muscles
Hair Bristles, "goose flesh" Smooth Skin
Bronchial Muscles
Dilation. Relaxation Constriction, Tension
Heart Muscle
Excitation, Accelerated Pulse Inhibition, Slowing Pulse
Digestive System
Inhibition of Peristalsis Stimulation of Peristalsis
Stimulation of Secretion Inhibition of Secretion
Urinary Bladder
Inhibition of Expulsion Stimulation of Expulsion
Bladder Sphincter
Sphincter Closes, Inhibition Sphincter Relaxes, Urination
Male Genital Penis
Flaccidity, Withdrawal Enlargement, Erection
Male Genital Scrotum
Excites, Tightens Inhibits, Relaxed
Female Genital
Constriction, Dryness Expansion., Moist