The shared neural basis of empathy and facial imitation accuracy.

Empathy involves experiencing emotion vicariously, and understanding the reasons for those emotions. It may be served partly by a motor simulation function, and therefore share a neural basis with imitation (as opposed to mimicry), as both involve sensorimotor representations of intentions based on perceptions of others' actions. We recently showed a correlation between imitation accuracy and Empathy Quotient (EQ) using a facial imitation task and hypothesised that this relationship would be mediated by the human mirror neuron system. During functional Magnetic Resonance Imaging (fMRI), 20 adults observed novel 'blends' of facial emotional expressions. According to instruction, they either imitated (i.e. matched) the expressions or executed alternative, pre-prescribed mismatched actions as control. Outside the scanner we replicated the association between imitation accuracy and EQ. During fMRI, activity was greater during mismatch compared to imitation, particularly in the bilateral insula. Activity during imitation correlated with EQ in somatosensory cortex, intraparietal sulcus and premotor cortex. Imitation accuracy correlated with activity in insula and areas serving motor control. Overlapping voxels for the accuracy and EQ correlations occurred in premotor cortex. We suggest that both empathy and facial imitation rely on formation of action plans (or a simulation of others' intentions) in the premotor cortex, in connection with representations of emotional expressions based in the somatosensory cortex. In addition, the insula may play a key role in the social regulation of facial expression.

It is all in the face: carotenoid skin coloration loses attractiveness outside the face.

Recently, the importance of skin colour for facial attractiveness has been recognized. In particular, dietary carotenoid-induced skin colour has been proposed as a signal of health and therefore attractiveness. While perceptual results are highly consistent, it is currently not clear whether carotenoid skin colour is preferred because it poses a cue to current health condition in humans or whether it is simply seen as a more aesthetically pleasing colour, independently of skin-specific signalling properties. Here, we tested this question by comparing attractiveness ratings of faces to corresponding ratings of meaningless scrambled face images matching the colours and contrasts found in the face. We produced sets of face and non-face stimuli with either healthy (high-carotenoid coloration) or unhealthy (low-carotenoid coloration) colour and asked participants for attractiveness ratings. Results showed that, while for faces increased carotenoid coloration significantly improved attractiveness, there was no equivalent effect on perception of scrambled images. These findings are consistent with a specific signalling system of current condition through skin coloration in humans and indicate that preferences are not caused by sensory biases in observers.

Cross-cultural variation in women's preferences for cues to sex- and stress-hormones in the male face.

Women in the UK prefer the faces of men with low levels of the stress hormone cortisol, and the relationship is moderated by the sex hormone testosterone. In a Latvian sample, however, women's preferences were not affected by cortisol, and the interaction with testosterone differed from that of the UK. To further explore cross-cultural variation in preferences for facial cues to sex- and stress-hormones, we tested the preferences of women from 13 countries for facial composites constructed to differ in combinations of the hormones. We found significant relationships between a measure of societal development (the United Nations human development index 2011) and preferences for cues to testosterone in the face, and the interaction between preferences for cues to testosterone and cortisol. We also found a significant relationship between preferences for cues to testosterone and a societal-level measure of parasite stress. We conclude that societal-level ecological factors influence the relative value of traits revealed by combinations of sex- and stress-hormones.

Face structure predicts cooperation: men with wider faces are more generous to their in-group when out-group competition is salient.

Male facial width-to-height ratio appears to correlate with antisocial tendencies, such as aggression, exploitation, cheating, and deception. We present evidence that male facial width-to-height ratio is also associated with a stereotypically male prosocial tendency: to increase cooperation with other in-group members during intergroup competition. We found that men who had wider faces, compared with men who had narrower faces, showed more self-sacrificing cooperation to help their group members when there was competition with another group. We propose that this finding makes sense given the evolutionary functions of social helpfulness and aggression.

Assessment of bruise age on dark-skinned individuals using tristimulus colorimetry.

INTRODUCTION: Studies on the ageing of bruises have been reported on Caucasians or individuals of fair ethnicity. This study focuses on bruise changes in dark-skinned individuals using tristimulus colorimetry for forensic analysis in such individuals. METHODS: Eighteen subjects of South Indian or Sri-Lankan ethnicity were recruited. Subjects were bruised using a vacuum pump and then daily colour measurements were taken of the bruise using a tristimulus colorimeter. The L*a*b* readings were recorded of a control area and of the bruise until it disappeared. Two Caucasians were used for comparison. RESULTS: This study showed that, using colorimetry, bruises on dark-skinned individuals can be measured and analysed even if the bruises are unclear visually. As the bruise is beneath the skin, the colour difference ΔL*, Δa* and Δb* were calculated. All values showed a trend, indicating that the L*a*b* measuring technique is a reliable method to analyse bruises on dark-skinned individuals. Comparisons of Asian subjects and Caucasian subjects were performed. The largest difference was seen in the b* value. Statistical analysis showed that ΔL* colour difference was the most consistent (95% CI -4.05 to -2.49) showing a significant difference between days 1-4 and 5-8. CONCLUSION: Objective assessment of bruises on dark-skinned individuals using the L*a*b* method of measuring gave reproducible results. Furthermore, the study showed that the yellowing of a bruise cannot be seen or measured with a tristimulus colorimeter on dark-skinned individuals due to the pigmentation of the skin. With further studies and more subjects, the age of bruises could potentially be assessed for use in forensic analysis.

Evidence for the stress-linked immunocompetence handicap hypothesis in human male faces.

The stress-linked immunocompetence handicap hypothesis (SL-ICHH) of sexual selection incorporates a role of the stress hormone corticosterone (C; cortisol in humans) in relationships between testosterone (T), immunity and secondary sexual trait expression. In support of this, C has been shown to mediate and moderate relationships between T and immune response and to be inversely related to attractiveness in some avian species. We predicted that female preferences for cues to T in human male faces would be contingent upon co-occurring cortisol levels. In study 1, we tested relationships between T and cortisol and attractiveness, masculinity and health ratings of raw male faces. We found cortisol to be inversely related to attractiveness. In study 2, we tested female preferences for male faces that were parametrically manipulated on the basis of cues to naturally co-occurring levels of T and cortisol across the menstrual cycle. Women preferred cues to low cortisol in general and in the fertile phase of the cycle, and there was an interaction between T and cortisol in general and in the non-fertile phase. Results were consistent with the SL-ICHH but not the original immunocompetence handicap model: females expressed preferences for cues to cortisol but not for cues to T, except in interaction with the stress hormone. Results inform the SL-ICHH by demonstrating female preferences for low cortisol and the nature of its interaction with T in humans, as well as indicating the traits that may be signalled by different combinations of the hormones including immune response, current health and resource acquisition characteristics.

Cues to sex- and stress-hormones in the human male face: functions of glucocorticoids in the immunocompetence handicap hypothesis.

The stress-linked version of the immunocompetence handicap hypothesis has been proposed to account for inconsistencies in relationships between testosterone and immune response. The model has received some support from studies demonstrating roles of stress hormones in relationships between testosterone, immune function and secondary sexual ornamentation. Such work, however, has relied on artificial elevation of testosterone so may not reflect relationships in natural populations. We created human male facial stimuli on the basis of naturally co-occurring levels of salivary testosterone and the stress hormone cortisol. In Study 1 we tested female preferences for male faces with cues to combinations of the hormones across the menstrual cycle, and in Study 2 we tested perceptions of health and dominance in a novel set of facial stimuli. Females preferred cues to low cortisol, a preference that was strongest during the fertile phase of the menstrual cycle. The effects of cortisol on attractiveness and perceived health and dominance were contingent upon level of testosterone: the effects of the stress hormone were reduced when testosterone was high. We propose explanations for our results, including low cortisol as a cue to a heritable component of health, attractiveness as a predictor of low social-evaluative threat (and, therefore, low baseline cortisol) and testosterone as a proxy of male ability to cope efficiently with stressors.

Can we assess the age of bruises? An attempt to develop an objective technique.

AIMS: The aims of this study were (A) to investigate whether the number of years of forensic experience affected the accuracy with which forensic experts (FEs) were able to age bruises and (B) to identify the properties and colours of a bruise that were utilized by FEs in their assessment of bruise age. The study then investigated the possibility of using a more objective technique. It was decided to use readily available digital photography and software to objectively assess changes in bruise colouration and to investigate if this can be used to age bruises. METHODS: Twenty-three FEs were shown 25 photographs of bruises of varying but known ages and asked to estimate the ages. In part two of the study, bruises were inflicted on volunteers using a vacuum pump and photographs taken of the bruise daily from infliction to resolution. The images were analysed using Adobe Photoshop. Red, green and blue (RGB) values were recorded for each bruise and analyses carried out comparing the values over time between subjects and within subjects. RESULTS: This study both enhanced and supported a previous conclusion that visual assessment of photographs is an unreliable method for ageing bruises. Additionally, it found that the degree of forensic experience had no effect on accuracy. It also identified that colour (particularly yellow, red and purple) and intensity of colour were the most commonly used properties of a bruise in the assessment of its age. The RGB method proved to be a reliable technique with which to measure bruise colour, but its validity in the assessment of bruise age was poor. CONCLUSIONS: Visual assessment of bruises is unreliable and the accuracy of ageing was not improved by the degree of forensic experience. The RGB method gave highly reproducible results, but did not accurately assess bruise age. However, results within subjects suggested that there may be individual variation in haemoglobin metabolism.

Valid facial cues to cooperation and trust: male facial width and trustworthiness.

Decisions about whom to trust are biased by stable facial traits such as attractiveness, similarity to kin, and perceived trustworthiness. Research addressing the validity of facial trustworthiness or its basis in facial features is scarce, and the results have been inconsistent. We measured male trustworthiness operationally in trust games in which participants had options to collaborate for mutual financial gain or to exploit for greater personal gain. We also measured facial (bizygomatic) width (scaled for face height) because this is a sexually dimorphic, testosterone-linked trait predictive of male aggression. We found that men with greater facial width were more likely to exploit the trust of others and that other players were less likely to trust male counterparts with wide rather than narrow faces (independent of their attractiveness). Moreover, manipulating this facial-width ratio with computer graphics controlled attributions of trustworthiness, particularly for subordinate female evaluators.

The cutest little baby face: a hormonal link to sensitivity to cuteness in infant faces.

We used computer image manipulation to develop a test of perception of subtle gradations in cuteness between infant faces. We found that young women (19-26 years old) were more sensitive to differences in infant cuteness than were men (19-26 and 53-60 years old). Women aged 45 to 51 years performed at the level of the young women, whereas cuteness sensitivity in women aged 53 to 60 years was not different from that of men (19-26 and 53-60 years old). Because average age at menopause is 51 years in Britain, these findings suggest the possible involvement of reproductive hormones in cuteness sensitivity. Therefore, we compared cuteness discrimination in pre- and postmenopausal women matched for age and in women taking and not taking oral contraceptives (progestogen and estrogen). Premenopausal women and young women taking oral contraceptives (which raise hormone levels artificially) were more sensitive to variations of cuteness than their respective comparison groups. We suggest that cuteness sensitivity is modulated by female reproductive hormones.

Rapid analysis of tetracaine for a tape stripping pharmacokinetic study using short-end capillary electrophoresis.

A rapid and simple short-end (reverse) capillary zone electrophoresis method was developed and validated for the separation and quantification of tetracaine in skin using tape samples. The separation was performed in a 485 mm (400 mm to window) x 50 microm internal diameter fused silica capillary using a background electrolyte of phosphoric acid-Tris pH2.5 at -25 kV. The extraction of tetracaine from tape samples was achieved using methanol diluted to 50% with water before injection. Procaine was the internal standard. The migration times for procaine and tetracaine were 1.25 and 1.36 min, respectively. The limit of quantification for tetracaine was 50 microg, with a signal-to-noise ratio greater than 10. The calibration curve was linear from 50 to 1200 microg with r(2) greater than 0.99. The CV for both within- and between-assay imprecision and the percentage inaccuracy for the quality control samples including lower and upper limits of quantitation were <12.1% and <11%, respectively. The absolute mean recovery of tetracaine was >97%. The accuracy and selectivity of this method allowed the rapid measurement of tetracaine in tape samples obtained from a skin tape stripping study of local anaesthetics in healthy subjects.

Sex-contingent face aftereffects depend on perceptual category rather than structural encoding.

Many studies have used visual adaptation to investigate how recent experience with faces influences perception. While faces similar to those seen during adaptation phases are typically perceived as more 'normal' after adaptation, it is possible to induce aftereffects in one direction for one category (e.g. female) and simultaneously induce aftereffects in the opposite direction for another category (e.g. male). Such aftereffects could reflect 'category-contingent' adaptation of neurons selective for perceptual category (e.g. male or female) or 'structure-contingent' adaptation of lower-level neurons coding the physical characteristics of different face patterns. We compared these explanations by testing for simultaneous opposite after effects following adaptation to (a) two groups of faces from distinct sex categories (male and female) or (b) two groups of faces from the same sex category (female and hyper-female) where the structural differences between the female and hyper-female groups were mathematically identical to those between male and female groups. We were able to induce opposite aftereffects following adaptation between sex categories but not after adaptation within a sex category. These findings indicate the involvement of neurons coding perceptual category in sex-contingent face aftereffects and cannot be explained by neurons coding only the physical aspects of face patterns.

Event-related potentials modulated by the perception of sexual dimorphism: The influence of attractiveness and sex of faces.

Sexual dimorphism has been proposed as one of the facial traits to have evolved through sexual selection and to affect attractiveness perception. Even with numerous studies documenting its effect on attractiveness and mate choice, the neurophysiological correlates of the perception of sexual dimorphism are not yet fully understood. In the present study, event-related potentials (ERPs) were recorded during visualisation of faces that had been previously transformed in shape to appear more masculine or more feminine. The participants' task consisted of judging the attractiveness of half of the total number of faces, and performing a sex discrimination task on the other half. Both early and late potentials were modulated by the sex of faces, whereas the effect of the sexually dimorphic transform was mainly visible in the P2 (positive deflection around 200 ms after stimulus onset), EPN (early posterior negativity) and LPP (late positive potential) components. There was an effect of sexual dimorphism on P2 and EPN amplitudes when female participants visualised male faces, which may indicate that masculinity is particularly attended to when viewing opposite sex members. Also, ERP results seem to support the idea of sex differences in social categorisation decisions regarding faces, although differences were not evident on behavioural results. In general, these findings contribute to a better understanding of how humans perceive sexually dimorphic characteristics in other individuals' faces and how they affect attractiveness judgements.

Intermediate hyperhomocysteinaemia and compound heterozygosity for the common variant c.677C>T and a MTHFR gene mutation.

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme in the regulation of plasma homocysteine levels. MTHFR deficiency, an autosomal recessive disorder, results in homocystinuria and hypomethioninaemia and presents with highly variable symptoms affecting many organs but predominantly the central nervous system. The common polymorphism of the MTHFR gene, c.677C>T, a known risk factor for elevated plasma homocysteine levels, occurs frequently in the caucasian population. In this study we investigated three subjects with moderate hyperhomocysteinaemia (total plasma homocysteine 72 micromol/L in case 1 and 90 micromol/L in case 3, total non-protein-bound homocysteine 144-186 micromol/L in case 2) but different clinical presentation with no symptoms in case 1, muscle weakness at 17 years of age in case 2, and syncopes and cerebral convulsions at 18 years of age in case 3. Each subject was compound heterozygous for the c.677C>T polymorphism and a novel mutation of the MTHFR gene (case 1: c.883G>A [p.D291N]; case 2: c.1552_c.1553delGA [p.E514fsX536]; case 3: c.616C>T [p.P202S]). Moderately decreased fibroblast MTHFR activity was associated with severely reduced affinity for NADPH and increased sensitivity to inhibition by S-adenosylmethionine (AdoMet) in case 2, and with mild FAD responsiveness in case 3. In case 1, fibroblast MTHFR activity was normal but the sensitivity to inhibition by AdoMet was slightly reduced. This study indicates that the sequence alteration c.677C>T combined with severe MTHFR mutations in compound heterozygous state may lead to moderate biochemical and clinical abnormalities exceeding those attributed to the c.677TT genotype and might require in addition to folate substitution further therapy to normalize homocysteine levels.

The 'Ideal Homunculus': decoding neural population signals.

Information processing in the nervous system involves the activity of large populations of neurons. It is possible, however, to interpret the activity of relatively small numbers of cells in terms of meaningful aspects of the environment. 'Bayesian inference' provides a systematic and effective method of combining information from multiple cells to accomplish this. It is not a model of a neural mechanism (neither are alternative methods, such as the population vector approach) but a tool for analysing neural signals. It does not require difficult assumptions about the nature of the dimensions underlying cell selectivity, about the distribution and tuning of cell responses or about the way in which information is transmitted and processed. It can be applied to any parameter of neural activity (for example, firing rate or temporal pattern). In this review, we demonstrate the power of Bayesian analysis using examples of visual responses of neurons in primary visual and temporal cortices. We show that interaction between correlation in mean responses to different stimuli (signal) and correlation in response variability within stimuli (noise) can lead to marked improvement of stimulus discrimination using population responses.

Facial appearance is a cue to oestrogen levels in women.

Although many accounts of facial attractiveness propose that femininity in women's faces indicates high levels of oestrogen, there is little empirical evidence in support of this assumption. Here, we used assays for urinary metabolites of oestrogen (oestrone-3-glucuronide, E1G) and progesterone (pregnanediol-3-glucuronide, P3G) to investigate the relationship between circulating gonadal hormones and ratings of the femininity, attractiveness and apparent health of women's faces. Positive correlations were observed between late follicular oestrogen and ratings of femininity, attractiveness and health. Positive correlations of luteal progesterone and health and attractiveness ratings were marginally significant. Ratings of facial attributions did not relate to hormone levels for women wearing make-up when photographed. There was no effect of sex of rater on the relationships between oestrogen and ratings of facial appearance. These findings demonstrate that female facial appearance holds detectable cues to reproductive health that are considered attractive by other people.

Surface decontamination of surgical instruments: an ongoing dilemma.

The issues of cross-infection and the survival of variant Creutzfeldt Jakob disease (vCJD) on surgical instruments have highlighted the importance of cleanliness of multiple-use surgical instruments. The aim of this study was to assess the levels of total protein contamination on a wide range of surgical instruments as an indication of the effectiveness of routine cleaning and disinfection in hospitals. Anonymized trays of wrapped and autoclaved instruments were supplied to two laboratories for analysis at the stage where they would normally be returned to operating theatres. Instruments were assessed for residual protein and total organic matter. Laboratory A showed that 17% (35/206) of instruments were above a threshold that equated to 200 microg. The worst examples, a McIvor gag, a Draffin rod (child) and a Yankaur sucker, had 1.028, 1.286 and 2.228 mg of extractable protein, respectively. The median (25th, 75th percentiles) amount of protein from instruments from different hospitals assessed in Laboratory B ranged from 8 (3, 30)mug (Hospital C) to 91 (35, 213) mug (Hospital D) (P=0.044). The residual matter washed from instruments varied from 0.62 (0.32, 0.81) mg (Hospital E) to 3.5 (3.5, 4.0) mg (Hospital A) (P=0.0001). In one case, 45 mg of residual organic matter was washed from an instrument (split stem). In conclusion, this study demonstrated that a proportion of instruments at the point of use show levels of protein that could pose a direct cross-infection risk via prion agents and other organic contamination that may reduce the effectiveness of cleaning/disinfection strategies targeted against either prions or traditional infectious agents.

Studies on adenine and adenosine metabolism by intact human erythrocytes using high performance liquid chromatography.

Adenine and adenosine metabolism has been studied in intact human erythrocytes in vitro using high performance liquid chromatography, isotopic labeling and electrophoresis. Their metabolism to nucleotides was controlled by phosphoribose diphosphate synthesis which was phosphate dependent. Adenosine formed hypoxanthine or IMP depending upon Pi concentration, but adenosine kinase and deaminase activities were not affected by P levels. Free [14C]adenine and [14C]hypoxanthine were found in cellular extracts. Rapid interconversions occurred to give a distribution for ATP : ADP : AMP of 10 : 1 : 0.1. Marked decomposition of ATP to ADP and AMP occurred during incubations in plasma and Earle's media in air on nitrogen, but ATP levels remained stable in phosphate buffers and in the presence of oxygen. At physiological Pi (1 mM) adenosine kinase activity grossly exceeded adenine phosphoribosyltransferase activity. The latter was approximately 7 fold that of hypoxanthine phosphoribosyltransferase activity. These differences decreased with increasing Pi levels. No significant increase in corresponding nucleotides was obtained by incubation with high levels (0.5 mM) of adenine, guanine or guanosine at physiological Ii, ATP increased by 10% independently of the substrate employed and significant amounts of IMP and GTP were formed adenosine and guanosine, respectively. The existence of a bound intracellular pool of ATP is suggested.

Are the perceptual biases found in chimeric face processing reflected in eye-movement patterns?

Studies of patients with focal brain lesions and neuroimaging indicate that face processing is predominantly based on right hemisphere function. Additionally, experiments using chimeric faces, where the left and the right-hand side of the face are different, have shown that observers tend to bias their responses toward the information on the left. Here, we monitored eye-movements during a gender identification task using blended face images for both whole and chimeric (half female, half male) faces [Neuropsychologia 35 (1997) 685]. As expected, we found a left perceptual bias: subjects based their gender decision significantly more frequently on the left side of the chimeric faces. Analysis of the first saccade showed a significantly greater number of left fixations independent of perceptual bias presumably reflecting the tendency to first inspect the side of the face better suited to face analysis (left side of face/right hemisphere). On top of this though, there was a relationship between response and fixation pattern. On trials where participants showed a left perceptual bias they produced significantly more left saccades and fixated for longer on the left. In contrast, for trials where participants showed a right perceptual bias there was no reliable difference between the number, or total fixation duration, on the left or the right. These results demonstrate that on a trial-by-trial basis subtle differences in the extent of left or right side scanning are related to the perceptual response of the participant, although an overall initial fixation bias to the left occurs irrespective of response bias.