We drank and nodded at each other. --Private detective Philip Marlowe with racketeer Eddie Mars (The Big Sleep by Raymond Chandler, 1939, p. 131)
Gesture. 1. A vertical, up-and-down movement of the head used to show agreement or comprehension while listening. 2. A flexed-forward, lowering motion of the skull, used to emphasize an idea, an assertion, or a key speaking point.
Usage: Rhythmically raised and lowered, the head-nod is an affirmative cue, widely used throughout the world to show understanding, approval, and agreement. Emphatic head-nods while speaking or listening may indicate powerful feelings of conviction, excitement, or superiority, and sometimes even rage.
Anatomy. 1. In the affirmative head-nod, longus capitis, rectus capitis anterior, and longus colli flex our neck and head forward, while splenius (a deep muscle of the back) and trapeziusbend the head and neck backward. 2. In the emphatic head-nod, forced expiration while stressing an important word contracts muscles of the abdominal wall (i.e., the oblique andtransverse muscles, and latissimus dorsi), which depress our lower ribs and bend our backbone and head forward (Salmons 1995:818-19).
Evolution. Paleocircuits for the reptilian head-bobbing display (used aggressively by lizards, e.g., to affirm their presence in Nonverbal World) may underlie the nods we ourselves use to reinforce our words. The reptilian principle of isopraxism may explain why speakers and listeners often nod in synchrony.
RESEARCH REPORTS: 1. Though other types of affirmative head movements have been observed cross-culturally (LaBarre 1947), the affirmative head-nod is well-documented as a nearly universal indication of accord, agreement, and understanding (Darwin 1872; Eibl-Eibesfeldt 1970, 1971; Morris 1994). 2. "Others see it [the head-nod] as an abbreviated form of submissive body-lowering - in other words, as a miniature bow" (Morris 1994:142).
Neuro-notes. That we head-nod in agreement may be due, in part, to trapezius's origin as a "gut reactive" branchiomeric muscle for respiration and feeding (see SPECIAL VISCERAL NERVE). 1. Today, e.g., it assists movements of a baby's head in accepting the breast--a behavior some have used to explain the universality of the head-nod cue (e.g., Morris 1994:142). 2. Moreover, the accessory nerve (cranial XI, which innervates trapezius), has a relationship with the vagus nerve (cranial X, which innervates the larynx in producing "hmm," "uh huh," and other "digestive" vocalizations). Thus, the affirmative head-nod may reflect an agreeable response to food. 3. Regarding the emphatic head-nod, the strong physical emphasis during its downward phase suggests a separate origin from the "yes" nod, which begins with an upward motion.
See also HEAD-SHAKE.