Odor valence linearly modulates attractiveness, but not age assessment, of invariant facial features in a memory-based rating task.

Scented cosmetic products are used across cultures as a way to favorably influence one's appearance. While crossmodal effects of odor valence on perceived attractiveness of facial features have been demonstrated experimentally, it is unknown whether they represent a phenomenon specific to affective processing. In this experiment, we presented odors in the context of a face battery with systematic feature manipulations during a speeded response task. Modulatory effects of linear increases of odor valence were investigated by juxtaposing subsequent memory-based ratings tasks--one predominantly affective (attractiveness) and a second, cognitive (age). The linear modulation pattern observed for attractiveness was consistent with additive effects of face and odor appraisal. Effects of odor valence on age perception were not linearly modulated and may be the result of cognitive interference. Affective and cognitive processing of faces thus appear to differ in their susceptibility to modulation by odors, likely as a result of privileged access of olfactory stimuli to affective brain networks. These results are critically discussed with respect to potential biases introduced by the preceding speeded response task.

Effect of hydration on the tactile and thermal sensitivity of the lip.

The vermilion lip is a body site particularly susceptible to water loss. Therefore, the role of hydration in tactile perception at the lip was investigated. A series of measures of tactile performance and response were obtained from 22 female subjects, namely: (1) the subjective assessment of lip feel, (2) tactile sensitivity, (3) spatial acuity, (4) thermal sensitivity, and (5) the subjective assessment of thermal stimulation. These measures were obtained from lips in their natural (untreated) state, and lips that had been treated using a hydrating preparation. The preparation altered the subjective feel of the lips consistent with the treatment increasing lip hydration and compliance. Hydrated lips showed greater sensitivity to light touch, and there was a trend toward the lip's thermal sensitivity being altered consistent with the lip treatment having a physical cooling effect. Spatial acuity was unaltered by the state of lip hydration. The sensitivity changes on hydration were proposed to have mechanical basis.

The development and validation of sensory and emotional scales of touch perception.

No comprehensive language exists that describes the experience of touch. Three experiments were conducted to take steps toward establishing a touch lexicon. In Experiment I, 49 participants rated how well 262 adjectives described sensory, emotional and evaluative aspects of touch. In Experiment II, participants rated pairwise dissimilarities of the most descriptive words of the set. Multidimensional scaling (MDS) solutions representing semantic-perceptual spaces underlying the words resulted in a touch perception task (TPT) consisting of 26 'sensory' attributes (e.g., bumpiness) and 14 'emotional' attributes (e.g., pleasurable). In Experiment III, 40 participants used the TPT to rate unseen textured materials that were moved actively or received passively against the index fingerpad, volar forearm, and two underarm sites. MDS confirmed similar semantic-perceptual structures in Experiments II and III. Factor analysis of Experiment III data decomposed the sensory attribute ratings into factors labeled Roughness, Slip, Pile and Firmness, and the emotional attribute ratings into Comfort and Arousal factors. Factor scores varied among materials and sites. Greater intensity of sensory and emotional responses were reported when participants passively, as opposed to actively, received stimuli. The sensitivity of the TPT in identifying body site and mode of touch-related perceptual differences affirms the validity and utility of this novel linguistic/perceptual tool.

Sensory and affective judgments of skin during inter- and intrapersonal touch.

Here we report two experiments that investigated the tactile perception of one's own skin (intrapersonal touch) versus the skin of other individuals (interpersonal touch). In the first experiment, thirteen female participants rated, along four perceptual attributes, the skin of their own palm and volar forearm, then that of several of the other participants. Ratings were made using visual analogue scales for perceived smoothness, softness, stickiness, and pleasantness. One's own skin was rated less pleasant than the skin of others. For both intra- and interpersonal touch, the forearm skin was rated smoother, softer, less sticky and more pleasant than the palmar skin. In the second experiment, ten pairs of female participants rated each other's palm and volar forearm skin, with the skin of the touched individual being assessed before and after the application of skin emollients that alter skin feel. As in the first experiment, the untreated skin of others was rated more pleasant than the participants' own skin, and the forearm versus palm differences were replicated. However, the emollient had generally larger effects on self-assessments than the assessments of others, and the site effect showed greater positive sensory and pleasantness increases for palm versus volar forearm. The disparate results of the two experiments suggest that attention, influenced by the ecological importance of the stimulus, is more important to assessment of touched skin than ownership of the skin or the contribution to self-touch made by the additional receptors in the passively touched skin. In both experiments, the pleasantness of touched skin was associated with the skin's perceived smoothness and softness, with weak trends toward negative associations with its perceived stickiness, consistent with prior research using inanimate surfaces (e.g., textiles and sandpapers).

Activation of neurons in trigeminal caudalis by noxious oral acidic or salt stimuli is not reduced by amiloride.

We investigated the possible role of amiloride-sensitive ion channels of the ENaC/DEGenerin superfamily in the activation of trigeminal nociceptive neurons elicited by noxious chemical stimulation of the oral mucosa using two methodologies, single-unit recording and c-fos immunohistochemistry. In pentobarbital-anesthetized rats, single-unit recordings were made from neurons in superficial laminae of dorsomedial trigeminal subnucleus caudalis (Vc) that responded to noxious thermal and chemical stimuli applied to the dorsal tongue. Successive application of each of three chemicals (250 mM pentanoic acid, n=6 units; 250 mM citric acid, n=8; 5 M NaCl, n=6) evoked responses that were not affected following topical application of amiloride (1 mM). In separate experiments, pentobarbital-anesthetized rats received one of the following stimuli delivered to the dorsal tongue: 250 mM pentanoic acid (n=6); 1 mM amiloride followed by 250 mM pentanoic (N=6); 5 M NaCl (n=5); or 1 mM amiloride followed by 5 M NaCl (n=5). Two hours later they were perfused with 4% paraformaldehyde and the brain stems processed for c-fos immunoreactivity. Both pentanoic acid and 5 M NaCl evoked similar numbers and patterns of fos-like immunoreactivity (FLI) in dorsomedial Vc and other brain stem regions, with no significant difference in counts of FLI in animals pretreated with amiloride. These results suggest that amiloride-sensitive Na(+) channels are not essential in mediating the activation of intraoral trigeminal nociceptors.

C-fos induction in rat superficial dorsal horn following cutaneous application of noxious chemical or mechanical stimuli.

The method of c-fos immunodetection was used to map the distributions of neurons in the lumbar spinal dorsal horn that were activated following intracutaneous (i.c.) microinjection, or iontophoretic application, of different irritant chemicals to the lateral hindpaw of rats. Microinjections (1 microl) of histamine, serotonin (5-HT), nicotine, capsaicin, or formalin each elicited similar distributions of Fos-like immunoreactivity (FLI) in laminae I-II of the ipsilateral superficial dorsal horn, with little or no FLI in deeper laminae or contralaterally. In laminae I and II, FLI cell counts were significantly higher following i.c. histamine, 5-HT, capsaicin, formalin, and noxious pinch, compared to i.c. saline controls. Capsaicin-evoked FLI was dose-dependent. Multivariate analysis of variance revealed no significant difference in spatial distributions of FLI induced by any of the chemical or pinch stimuli. Iontophoretic application of histamine, 5-HT, or nicotine also elicited similar distributions of FLI in the superficial dorsal horn, and cell counts of FLI were significantly higher compared to controls receiving iontophoretic vehicle (methyl cellulose). These results indicate either that individual laminae I-II neurons are activated by each of the irritant chemicals, or that neurons selectively responsive to a given irritant are comingled without any apparent laminar segregation.

Sensitization of trigeminal caudalis neuronal responses to intraoral acid and salt stimuli and desensitization by nicotine.

In human studies, repeated intraoral application of strong acidic or salt stimuli induces irritation that progressively increases across trials (sensitization), whereas irritation elicited by nicotine progressively decreases (desensitization). We investigated whether nociceptive neurons in trigeminal subnucleus caudalis (Vc) exhibit increasing or decreasing patterns of firing to the intraoral application of these irritants. In rats anesthetized with halothane and thiopental, single-unit recordings were made from nociceptive neurons in superficial layers of dorsomedial Vc that responded to mechanical and noxious thermal and chemical stimulation of the tongue. NaCl (5M), citric acid (300 mM), pentanoic acid (300 mM) or nicotine (600 mM) were separately delivered to the tongue by constant flow (0.32 ml/min) for 15 or 25 min. NaCl, citric acid and pentanoic acid each elicited a progressive, significant increase in Vc neuronal firing over the initial 10 min to a plateau level that was maintained for the stimulus duration. Nicotine induced a significant increase in firing rate of Vc neurons within 6 min, followed by a decline back to the baseline level over the ensuing 10 min. Following a rest period, reapplication of nicotine no longer activated Vc neurons, indicative of self-desensitization. We additionally tested for nicotine cross-desensitization to acid. After recording the responses of Vc neurons to pentanoic acid and noxious heat, nicotine was then applied for 15 min. Post-nicotine responses to pentanoic acid were markedly reduced (to 13% of control), indicative of cross-desensitization; responses to noxious heat were also reduced to a lesser degree (to 71% of control). The progressive increase in Vc neuronal firing elicited by NaCl and acid, and the decline in firing after initial nicotinic excitation, resemble psychophysical patterns of sensitization and desensitization, respectively, and support the involvement of Vc neurons in the signaling of oral irritant sensations.