Jacob E. Steiner

Human facial expressions in response to taste and smell stimulation.

Publisher Summary Facial expressions, whether innate or acquired, are one of the richest nonverbal communicational catalogs of man. This chapter shows facial expressions in the experimental part of the discussion and illustrates the three prototypes of facial play described by Darwin as that of “good spirit,” of “contempt,” and of “low spirit or disgust.” Darwin intended to describe facial expressions used by man to reflect his feelings, his mood, and his spirit. The expressions demonstrated in the chapter are by no means acquired; they are present at the date of birth, perhaps even earlier, and are elicitable by different chemical stimuli. The hedonically different meaning of the sweet and the bitter and the hedonically polar value of odors of fresh and good food and that of rotten one, unlock facial expressions identical to those indicating “high and low spirits.” The individual first exposed to typical stimulants of “good” and “bad” food-related chemical cues evaluates these signals at low levels of the central nervous system.

Neonatal facial expressions in response to different qualities and intensities of gustatory stimuli

Facial expressions of 23 neonates were analyzed for specific features following oral stimulation with distilled water, 0.1 and 1.0 M sucrose, 0.15 and 0.25 M urea, and 0.0001 M quinine hydrochloride. Responses were videotaped and later decoded in a double-blind setting. While some features were present for all stimulations, other components were consistently associated with a specific taste quality. Within a quality, increasing the concentration elevated the incidence of features associated with that quality. Estimates of magnitude and hedonic tone conveyed by the total facial response to each stimulus suggested that the face was, within limits, an accurate reflection of stimulus quality and intensity.

DISCUSSION PAPER: INNATE, DISCRIMINATIVE HUMAN FACIAL EXPRESSIONS TO TASTE AND SMELL STIMULATION

In an earlier study’. * we described the “Gustofacial Response.” This is a welldifferentiated motor reaction of the facial muscles to adequate stimulation of the peripheral, gustatory receptors. These reactions are rigidly fixed features, different in their appearance as related to sweet, sour, and bitter stimuli. They are of innate character, and controlled by the neural structures of the brainstem, not necessarily involving structures of the cerebral cortex. We interpreted these reflex-like reactions as stimulus-dependent, innate, communication signals, as part of the human-nonverbal communication repertory, serving the child-mother relationship. This phenomenon became apparent to us while we were observing adult human subjects, testing them by a simple psychophysiological procedures to determine the functional state of their sense of taste.3-6 These adult subjects represented a cross section of the variegated population of Israel, some of them healthy young adults, tested as control subjects. Some others were tested under experimental or pathological conditions. In the majority of our subjects, we observed that suprathreshold stimulation with sweet, sour, and bitter compounds induced typical and differentiated facial expressions to each of these three types of stimuli. The constant appearance of the “grimaces,” the irresistable way in which they appeared, often embarassing even to the subjects themselves, led us to hypothesize that this reaction is more innate than of acquired (learned) character. We verified this hypothesis with 175 neonate infants, among them a group of 75 less than 16 hours of age, tested in the period between birth and the first breast (or bottle) feeding. In addition to this population of normal healthy neonates, we had the opportunity to test four neonates with severe developmental malformation of the central nervous system (anencephalic and hydroanencephalic neonates). Both the normal and the malformed babies tested displayed typical facial expressions to the aforementioned tastants. The reactions can be described as follows: T o the presentation of sweet stimuli, a marked relaxation of the facial muscle, retraction of the mouth angles resembling a “smile” or “satisfaction,” in general accompanied by eager movements of licking and sucking. Presentation of sour stimulation elicited a pursing of the lips, which can be of a steady holding of this position or of a repeated type with a twitching element. Bitter stimulation induced a facial reaction characterized by depression of the mouth angles with a simultaneous or subsequent elevation of the central part of the upper lip, creating an “arch-like” mouth opening. This facial expression resembles “dislike” or

Classical conditioning in newborn humans 2–48 hours of age

Classical conditioning was studied in newborn humans 2–48 hours of age. Infants in the Experimental group received 18, 2-min conditioning trials, each consisting of 10 s of gentle forehead stroking followed immediately by midline intraoral delivery of 0.2 ml 12.5% (0.037 M) sucrose solution via pipette. Sucrose delivery for infants in one control group was delayed following stroking by intervals of 10, 20, or 30 s presented randomly. Infants in the second control group were not stroked but only received sucrose on each trial. Immediately following the 18 sucrose trials, all infants received 9, 1-min extinction trials which consisted exclusively of 10 s of forehead stroking with no other manipulations during the remaining 50 s. All sessions were video-recorded and analyzed at a later date, with special attention paid to head-orienting, sucking, and crying behaviors. Only infants in the Experimental group presented evidence for classical conditioning. Relative to infants in the first control group, they emitted many more head-orient and sucking responses during the 10-s stroking intervals. Moreover, they exhibited a classic extinction function to stroking in sucrose absence. Finally, 7 of 8 Experimental infants cried during extinction, whereas only 1 of 16 Control infants cried. These findings demonstrate the ability of human newborn infants to extract predictability between two related events and that this form of conditioning is strongly affective. Implications for early mother-infant bond development are discussed.

TASTE AND ODOR: REACTIVITY IN DEPRESSIVE DISORDERS, A MULTIDISCIPLINARY APPROACH

Depressive patients often complain about dullness of taste of previously liked food items as well as of persistent bad taste. Taste and smell experience can be reflected by cognitive (psychophysical) indicators and also by reflectory (facial expressive) responses. In the present study 21 depressed, hospitalized patients and 16 control subjects were exposed to food-related gustatory and olfactory stimuli. Psychophysical and videotaped facial reactions were recorded from both groups. Analysis indicated that cognitive estimates of taste hedonics were similar for depressed and control groups; the former responded to sweet taste with a shorter-lasting facial reaction, involving markedly fewer facial features expressing enjoyment, than did controls. Aversive tastes, in contrast, triggered comparable facial expressive features of disgust in both groups. Facial reactions of depressed patients to acceptable and aversive olfactory stimuli were all significantly shorter and more muted than those of controls. Facial reflexes triggered by chemical cues are known to be controlled primarily by brainstem structures. Present findings suggest a possible influence of the profound anhedonia of severe depression on subcortical processes.

Differential behavioral responses to taste stimuli in non-human primates

Gustatory stimuli are known to elicit differential orofacial motor reactions in man. This phenomenon is named gustofacial reflex and has been shown to be elicitable in perinatal neonate human infants. Sweet and bitter stimuli (0·4 m sucrose and 0·0007 m quinine hydrochloride aqueous solutions, respectively) were presented to 12 different species of non-human primates. Some of the animals tested were several weeks of age, others were adolescents or adults. Both types of taste solutions, even in small amounts, were found to serve as potent stimuli to trigger characteristic and differential orofacial and other behavioral responses. Videotaped behavior reactions were presented in a double-blind manner to naive evaluators, who easily classified the behavior patterns along a pleasant-unpleasant continuum and were able to identify the stimuli. Analysis of the videotaped reactions made it possible to present the findings in a semi-quantitative manner. These findings are compared with taste-triggered behavior both in man and in non-primate mammals.

A MULTIDISCIPLINARY APPROACH TO THE EXPRESSION OF PAIN IN PSYCHIC DEPRESSION

The expression of cold pressor pain was measured by recording simultaneously verbal magnitude estimates, heart rates, and facial displays of 16 recently hospitalized depressed patients, and 16 nondepressed adults. Independence of the two groups for the depression factor was verified using the Hamilton Scale for Depression and the 100-mm line self-rating scale. Verbal responses and amount of time the ice bath was tolerated, as well as heart-rate measures, indicated that depressed individuals were significantly more sensitive to the pain stimulus. However, this elevated intolerance to pain was not reflected by marked changes of facial display. Reasons for this discrepancy are discussed. Nondepressed subjects, although clearly able to verbalize intensity of pain, were much less reactive to the pain along all dimensions.

Facial Expression in Response to Smell and Taste Stimuli in Small and Appropriate for Gestational Age Newborns

Small for gestational age newborns can later suffer from eating difficulties and slow growth. Nutritional preferences can be influenced by changes in sensory perception of smell and taste. To determine whether these could be detected at birth, the authors examined the different recognition pattern of smell and taste in small for gestational age newborns compared to appropriate for gestational age controls, as expressed by gusto-facial and naso-facial reflexes. The authors performed video analysis of facial expressions of 10 small for gestational age and 12 control newborns exposed to various tastes and smells. No difference in the facial recognition patterns for taste or smell was demonstrated between small for gestational age and controls, except for perception of distilled water. Newborns show recognizable patterns of facial expression in response to taste and smell stimuli. Perception of taste and smell in small for gestational age newborns is not different from controls, as measured by the method of facial recognition.

Behavior Manifestations Indicative of Hedonics and Intensity in Chemosensory Experience

Adequate stimulation of a sensory system initiates a cascade of neural events. This results in the arousal of a “sensation”, or “feeling”. Stimulating events and their neural sequels occur in the public domain, and therefore are subject to direct measurement. Sensations in contrast, are psychological events, occurring in the private domain, and are therefore not subject to direct measurement.

Differential arousal response to gustatory stimuli in the awake rabbit

ECoG arousal response as elicited by deionized water and by several concentrations of sweet, salty, sour and bitter tasting substances, all applied intraorally, were studied in the awake restrained rabbit. The study was carried out on 17 chronic preparations of adult male animals (2.6 kg average body weight). Water as a stimulant was presented in 60 trials and tastants across qualities and concentrations in 245 trials. Arousal was quantitatively characterized by its duration, frequency increment and amplitude decrement as compared to prestimulus conditions. Arousal induced by tastants was compared to that induced by water. Water and tastants induced arousals differentiable by the parameters measured. Further, most tastants produced a dose-dependent response. Comparison of ECoG and behavioral data clearly indicate that tastants inducing behavioral aversion also produce an arousal which significantly differs from response to water while behavioral preference was found not to show similar correspondence with ECoG data. The possibility of using arousal as an objective indicator for taste aversion is discussed.