Staring at one side of the face increases blood flow on that side of the face

The blushing brain: neural substrates of cheek temperature increase in response to self-observation

Darwin proposed that blushing-the reddening of the face owing to heightened self-awareness-is 'the most human of all expressions'. Yet, relatively little is known about the underlying mechanisms of blushing. Theories diverge on whether it is a rapid, spontaneous emotional response that does not involve reflection upon the self or whether it results from higher-order socio-cognitive processes. Investigating the neural substrates of blushing can shed light on the mental processes underlying blushing and the mechanisms involved in self-awareness. To reveal neural activity associated with blushing, 16-20 year-old participants (n = 40) watched pre-recorded videos of themselves (versus other people as a control condition) singing karaoke in a magnetic resonance imaging scanner. We measured participants' cheek temperature increase-an indicator of blushing-and their brain activity. The results showed that blushing is higher when watching oneself versus others sing. Those who blushed more while watching themselves sing had, on average, higher activation in the cerebellum (lobule V) and the left paracentral lobe and exhibited more time-locked processing of the videos in early visual cortices. These findings show that blushing is associated with the activation of brain areas involved in emotional arousal, suggesting that it may occur independently of higher-order socio-cognitive processes. Our results provide new avenues for future research on self-awareness in infants and non-human animals.

Anticipating noxious stimulation rather than afferent nociceptive input may evoke pupil asymmetry

Unilateral nociceptive stimulation is associated with subtle signs of pupil asymmetry that may reflect lateralized activity in the locus coeruleus. To explore drivers of this pupil asymmetry, electrical stimuli, delivered alone or 200 ms before or after an acoustic startle stimulus, were administered to one ankle under four experimental conditions: with or without a 1.6 s anticipatory period, or while the forearm ipsilateral or contralateral to the electrical stimulus was heated tonically to induce moderate pain (15 healthy participants in each condition). Pupil diameter was measured at the start of each trial, at stimulus delivery, and each second for 5 s after stimulus delivery. At the start of the first trial, the pupil ipsilateral to the side on which electric shocks were later delivered was larger than the contralateral pupil. Both pupils dilated robustly during the anticipatory period and dilated further during single- and dual-stimulus trials. However, pupil asymmetry persisted throughout the experiment. Tonically-applied forearm heat-pain modulated the pupillary response to phasic electrical stimuli, with a slight trend for dilatation to be greater contralateral to the forearm being heated. Together, these findings suggest that focusing anxiously on the expected site of noxious stimulation was associated with dilatation of the ipsilateral pupil whereas phasic nociceptive stimuli and psychological arousal triggered bilateral pupillary dilatation. It was concluded that preparatory cognitive activity rather than phasic afferent nociceptive input is associated with pupillary signs of lateralized activity in the locus coeruleus.

The sensory and affective components of pain differentially shape pupillary dilatation during cold pressor tests

Nociceptive and affective stimuli increase reflex sympathetic outflow to the pupils. To investigate effects of stimulus intensity, unpleasantness and distress on these pupillary reflexes, and to assess their stability, healthy participants immersed their hand in ice-water three times (for 20, 40 and 60 s; or 60, 40 and 20 s; or three times for 60 s) (N = 21 in each condition). Each ice-water immersion was preceded by a 90 s warm water immersion. To evaluate phasic sympathetic influences on pupil diameter, pupillary re-dilatation after 1 s of bright light was assessed during the last 10 s of each immersion. By-and-large, pain ratings and pupil diameter were greater during longer than shorter ice-water immersions, and ice-water immersions facilitated pupillary re-dilatation after the flash stimulus. However, mean pupil diameter during ice- and warm water immersions, minor ipsilateral amplification of the pupillary response, and ratings of pain unpleasantness and distress decreased across the experiment. Together, these findings suggest that nociceptive input increased sympathetic pupillary tone and amplified phasic increases in sympathetic activity after exposure to light. However, tonic sympathetic influences on pupil diameter and lateralization decreased across repeated immersions, possibly as novel or threatening aspects of the experience declined. Pupillary nociceptive and affective reflexes involve the locus coeruleus, an integral component of neural circuits that heighten cortical arousal and regulate pain. As these reflexes appear to reflect different aspects of sensory and affective processing, their combined assessment might increase the sensitivity and specificity of tests of locus coeruleus function in patients with suspected deficits.

Skin Complexion and the Blush

The implications of variation in skin pigmentation for the blush have attracted discussion for centuries. Two long-standing positions are identified. First, the blush has been identified with shame, giving rise to claims that because people with dark skin do not blush they do not have the capacity to experience shame. Second, the meaning of a visible blush can be ambiguous. A review of more recent theorizing and empirical research suggests that people blush whatever their level of pigmentation; the blush tends to be associated with embarrassment rather than shame; it serves both intraindividual and communicative functions. Nevertheless, there has been little systematic investigation into the impact of the relative discernibility of the blush on emotional experience or its functions.

Transdermal optical imaging revealed different spatiotemporal patterns of facial cardiovascular activities

Human cardiovascular activities are important indicators of a variety of physiological and psychological activities in human neuroscience research. The present proof-of-concept study aimed to reveal the spatiotemporal patterns of cardiovascular activities from the dynamic changes in hemoglobin concentrations in the face. We first recorded the dynamics of facial transdermal blood flow using a digital video camera and the Electrocardiography (ECG) signals using an ECG system simultaneously. Then we decomposed the video imaging data extracted from different sub-regions of a face into independent components using group independent component analysis (group ICA). Finally, the ICA components that included cardiovascular activities were identified by correlating their magnitude spectrum to those obtained from the ECG. We found that cardiovascular activities were associated with five independent components reflecting different spatiotemporal dynamics of facial blood flow changes. The strongest strengths of these ICA components were observed in the bilateral forehead, the left chin, and the left cheek, respectively. Our findings suggest that the cardiovascular activities presented different dynamic properties within different facial sub-regions, respectively. More broadly, the present findings point to the potential of the transdermal optical imaging technology as a new neuroscience methodology to study human physiology and psychology, noninvasively and remotely in a contactless manner.

Seeing a Blush on the Visible and Invisible Spectrum: A Functional Thermal Infrared Imaging Study

So far blushing has been examined in the context of a negative rather than a positive reinforcement where visual displays of a blush were based on subjective measures. The current study used infrared imaging to measure thermal patterns of the face while with the use of a video camera quantified on the visible spectrum alterations in skin color related to a compliment. To elicit a blush a three-phase dialog was adopted ending or starting with a compliment on a female sample (N = 22). When the dialog ended with a compliment results showed a linear increase in temperature for the cheek, and forehead whereas for the peri-orbital region a linear decrease was observed. The compliment phase marked the highest temperature on the chin independent of whether or not the experiment started with a compliment contrary to other facial regions, which did not show a significant change when the experiment started with a compliment. Analyses on the visible spectrum showed that skin pigmentation was getting deep red in the compliment condition compared to the serious and social dialog conditions for both the forehead and the cheeks. No significant association was observed between temperature values and erythrocyte displays on the forehead and cheek. Heat is the physiological product of an arousing social scenario, however, preconceived notions about blushing propensity seem to drive erythrocyte displays and not necessarily conscious awareness of somatic sensations.

Regional differences in facial skin blood flow responses to the cold pressor and static handgrip tests

We have previously reported the unique regional responses of facial skin blood flow (SkBF) to oral application of the basic tastes without simultaneous systemic circulatory changes. In the present study, we determined whether a systemic circulatory challenge due to sympathetic activation induces regional differences in facial SkBF by observing the responses in facial SkBF and blood pressure to a 2-min cold pressor test (CPT) and static handgrip exercise (HG) by right hand in 20 healthy subjects. The CPT significantly increased SkBF in the forehead, eyelid, cheek, upper lip and lower lip by 6 ± 2 to 8 ± 2 % (mean ± SEM) as compared to resting baseline, with a significant simultaneous increase (13 ± 2 %) in mean arterial pressure (MAP), whereas it significantly decreased the SkBF in the nose by 5 ± 2 %. The HG significantly increased SkBF in the forehead, cheek and lower lip by 6 ± 3 to 10 ± 3 %, with a significant simultaneous increase in MAP (13 ± 2 %), while it induced no significant change in the other regions. Increases in SkBF were greater in the right than left cheek during CPT. These results demonstrate that a systemic circulatory challenge via sympathetic activation elicits regional differences in the facial SkBF response.

The effect of facial blood flow on ratings of blushing and negative affect during an embarrassing task: preliminary findings

Expecting to blush is a common source of social anxiety, and is associated with heightened perceptions of blushing and embarrassment. To assess whether sensory cues associated with heightened facial blood flow are an additional source of anxiety, the vasodilator niacin (100mg) or placebo was administered double-blind to 33 participants, and facial blood flow was investigated when they sang a children's song. Vasodilatation during singing was greater in the niacin than placebo condition, and niacin-evoked flushing and increases in pulse rate were greater in participants with high than low fear of negative evaluation. Nevertheless, ratings of embarrassment, anxiety, blushing and facial heat were similar in both drug conditions. This dissociation implies that cognitive appraisals or negative affect overrode more subtle physiological cues of blushing during embarrassment. Clarifying how judgments about blushing are made could be crucial for correcting faulty assumptions about blushing in people who are frightened of this response.

Blushing in rosacea sufferers

OBJECTIVE

Rosacea is characterized by extremely sensitive skin and persistent facial flushing, perhaps initiated or exacerbated by frequent or intense blushing. To investigate this, blushing was assessed in rosacea sufferers and controls during embarrassing laboratory tasks.

METHODS

Changes in forehead blood flow were monitored with laser Doppler fluxmetry in 31 rosacea sufferers (12 with severe symptoms and 19 with mild symptoms) and 86 controls while singing, giving an impromptu speech, and listening to recordings of these activities.

RESULTS

Changes in forehead blood flow were similar in rosacea sufferers and controls, and were similar in subgroups with mild and severe rosacea. Even so, rosacea sufferers thought that that they blushed more intensely and were more embarrassed than controls during most of the tasks. Likewise, changes in forehead blood flow were similar in participants with mild and severe rosacea. Nevertheless, ratings of embarrassment and blushing were greater in those with severe than mild symptoms. Within the rosacea group, increases in blood flow while singing were greatest in participants with the highest blushing ratings, whereas increases in blood flow while listening to the speech were greatest in the most embarrassed participants.

CONCLUSIONS

These findings do not support the hypothesis that blushing is abnormal in rosacea but, nevertheless, suggest that rosacea sufferers are more aware of and embarrassed by blushing than controls. This might contribute to social anxiety in rosacea sufferers.

Harnessing color vision for visual oximetry in central cyanosis

Central cyanosis refers to a bluish discoloration of the skin, lips, tongue, nails, and mucous membranes, and is due to poor arterial oxygenation. Although skin color is one of its characteristic properties, it has long been realized that by the time skin color signs become visible, oxygen saturation is dangerously low. Here we investigate the visibility of cyanosis in light of recent discoveries on what color vision evolved for in primates. We elucidate why low arterial oxygenation is visible at all, why it is perceived as blue, and why it can be so difficult to perceive. With a better understanding of the relationship between color vision and blood physiology, we suggest two simple techniques for greatly enhancing the clinician's ability to detect cyanosis and other clinical color changes. The first is called "skin-tone adaptation", wherein sheets, gowns, walls and other materials near a patient have a color close to that of the patient's skin, thereby optimizing a color-normal viewer's ability to sense skin color modulations. The second technique is called "biosensor color tabs", wherein adhesive tabs with a color matching the patient's skin tone are placed in several spots on the skin, and subsequent skin color changes have the effect of making the initially-invisible tabs change color, their hue and saturation indicating the direction and magnitude of the skin color shift.

Continuous wavelet transform of laser-Doppler signals from facial microcirculation reveals vasomotion asymmetry

Facial laser Doppler flux (FLDF) consists of a mean value and complex oscillatory components called vasomotion. Vasomotion can be expressed as spectral amplitudes (SA) after the application of continuous wavelet transform. Vasomotion is influenced by cardiac activity (frequency interval I), respiration (interval II), intrinsic myogenic activity (interval III), neural mechanisms (interval IV) and endothelial mechanisms (intervals V and VI). Asymmetry of FLDF mean value was previously documented and hereby we present homogeneity assessment for FLDF vasomotion. Mean FLDF (p<0.001), total SA (p<0.001) and SA within frequency intervals I-VI were significantly higher in both cheeks compared to forehead. Total SA (p=0.009) and SA within frequency intervals I (p=0.041), II (p=0.005), III (p=0.009), IV (p=0.001) and V (p=0.036) were significantly higher in right than in left forehead. Human face is a heterogeneous microvascular region. Angiographic characteristics of deep horizontal sub-dermal plexus, endothelial and vascular smooth muscle cell heterogeneity, and plasticity of the microvasculature, autonomic asymmetry and facial neuropsychological asymmetry are possible causes of microvascular asymmetry. The origin and significance of microvascular imbalance need to be elucidated further.

Autonomic correlates of social anxiety and embarrassment in shy and non-shy individuals

Social anxiety and embarrassment are closely related constructs, both of which are relevant to the study of shyness. To examine the psychophysiological correlates of anxiety and embarrassment in relation to shyness, we measured autonomic arousal (heart rate, respiratory sinus arrhythmia, skin conductance level, and blushing response) in shy and non-shy female participants while they performed tasks designed to elicit either social anxiety or embarrassment. Results indicated that social anxiety and embarrassment are difficult to disentangle at the autonomic level. Blushing may be an important psychophysiological marker of shyness and social anxiety.

Immersion of the hand in ice water releases adrenergic vasoconstrictor tone in the ipsilateral temple

Immersion of the hand in painfully cold water induces cutaneous vasodilatation in the temples, more so ipsilaterally than contralaterally. To investigate the mechanism of this response, guanethidine or saline was administered by transcutaneous iontophoresis to a recording site in the temple of ten participants before they immersed one of their hands in ice water. Guanethidine displaces noradrenaline from sympathetic nerve terminals and inhibits sympathetic noradrenergic neurotransmission. Therefore, it was hypothesized that guanethidine pre-treatment would block vasodilatation mediated by release of sympathetic vasoconstrictor tone in cutaneous vessels in the temple. During hand immersion, increases in the amplitude of the pulse waveform detected by laser Doppler flowmetry were greater in the ipsilateral than contralateral temple (86% vs. 34% above baseline, p<0.05), and pre-treatment with guanethidine prevented this asymmetric response (ipsilateral response 21% above baseline and contralateral response 32%, difference not significant). Guanethidine also inhibited ipsilateral increases in cutaneous blood flow during hand immersion in responsive participants. These findings suggest that limb pain inhibited ipsilateral adrenergic vasoconstrictor outflow in the temple. Thus, the findings challenge the concept of the sympathetic nervous system as a "mass action" system that discharges in unison to meet environmental demands. Instead, they suggest that the sympathetic nervous system is highly differentiated, with separate control of discrete reflex pathways on each side of the body.

Left-right asymmetry of the facial microvascular control

Facial blood flow and temperature were significantly higher on the right side of the forehead compared to the left. This asymmetry implies that the hemispheric autonomic control of the face differs and could influence the expression of emotion.