Ever wonder how the ubiquity of texting will affect our evolution?

Neurophysiologist Stephen Porges, professor of psychiatry at the University of North Carolina, stresses that physiological connectedness is a biological imperative. He proves this by referencing his polyvagal theory which describes the function of the 10th cranial nerve, the vagus.

The vagus is a component of the autonomous nervous system (ANS) which is the system that keeps vital organs like the heart and lungs working. The ANS contributes into the sympathetic and parasympathetic systems which spend and renew physiological resources.

Porges suggests we pay attention to the area around the eyes when talking to someone because “physiology determinology psychology.” If we feel safe when seeing kindness in someone's face, our vagus nerve acts as a “brake” on the heart rate which, without the high vagal tone, would speed out of control. The vagus “inhibits” other behaviors, like talking, which encourages listening.

The vagus nerve arises from two separate nuclei in the brain stem which accommodates older and newer branches. The unmyelinated older branch descends down the back spine and innervates organs below the diaphragm. This vegetative” vagus is common to all vertebrates – including reptiles who freeze when threatened.

The newer myelinated vagal branch descends down the front spine and activates organs above the diaphragm. This “smart” vagus is shared by all mammals. Since mammals are dependent on other mammals to survive, this vagus encourages social engagement.

The 7th cranial nerve controls the face muscles and arises from the same nucleus on the brain stem as the smart vagus. The facial nerve activates the muscles around the eye, including the orbicularis oculi, which registers emotion. Cues we read on another's face track back into the vagus and affect our physiology.

The fight or flight response is part of the new vagus and arises if we do not see a kind face but a flat face; or we do not hear a prosodic voice but a low monotone. The vagus takes the brake off the heart to mobilize either the fight or flight response. If that system fails and our life is threatened, the vegetative vagus asserts itself and we lose consciousness.

Since the smart vagus controls heart and breathing, respiratory sinus arrhythmia (RSA) measures vagal tone. RSA occurs as heart rate speeds up while inhaling and slows down when exhaling. This variable characterizes a healthy heart.

Greater RSA advances the calm physiology of the smart vagus and encourages affiliative behaviors like face-to-face contact, listening, prosody and conforming posture. These features help us detect whether we are safe and, if so, supports optimal learning behaviors.

In summary, the polyvagal theory is hierarchical: the newer myelinated vagus inhibits sympathetic defenses which inhibit unmyelinated immobilization defenses.

Texting interrupts the “neural exercises” of face-to-face communication so necessary to ground our mammalian nervous system. Lack of practice hinders these rules of engagement. Lose the phone. Reach out and touch someone.