Gender Differences in Brain Activation During Encoding and Recognition of Male and Female Faces

Asymmetries in event-related potentials part 1: A systematic review of face processing studies

The human brain shows distinct lateralized activation patterns for a range of cognitive processes. One such function, which is thought to be lateralized to the right hemisphere (RH), is human face processing. Its importance for social communication and interaction has led to a plethora of studies investigating face processing in health and disease. Temporally highly resolved methods, like event-related potentials (ERPs), allow for a detailed characterization of different processing stages and their specific lateralization patterns. This systematic review aimed at disentangling some of the contradictory findings regarding the RH specialization in face processing focusing on ERP research in healthy participants. Two databases were searched for studies that investigated left and right electrodes while participants viewed (mostly neutral) facial stimuli. The included studies used a variety of different tasks, which ranged from passive viewing to memorizing faces. The final data selection highlights, that strongest lateralization to the RH was found for the N170, especially for right-handed young male participants. Left-handed, female, and older participants showed less consistent lateralization patterns. Other ERP components like the P1, P2, N2, P3, and the N400 were overall less clearly lateralized. The current review highlights that many of the assumed lateralization patterns are less clear than previously thought and that the variety of stimuli, tasks, and EEG setups used, might contribute to the ambiguous findings.

Sound-encoded faces activate the left fusiform face area in the early blind

Face perception in humans and nonhuman primates is accomplished by a patchwork of specialized cortical regions. How these regions develop has remained controversial. In sighted individuals, facial information is primarily conveyed via the visual modality. Early blind individuals, on the other hand, can recognize shapes using auditory and tactile cues. Here we demonstrate that such individuals can learn to distinguish faces from houses and other shapes by using a sensory substitution device (SSD) presenting schematic faces as sound-encoded stimuli in the auditory modality. Using functional MRI, we then asked whether a face-selective brain region like the fusiform face area (FFA) shows selectivity for faces in the same subjects, and indeed, we found evidence for preferential activation of the left FFA by sound-encoded faces. These results imply that FFA development does not depend on experience with visual faces per se but may instead depend on exposure to the geometry of facial configurations.

Executive function and episodic memory composite scores in older adults: relations with sex, mood, and subjective sleep quality

Executive function and episodic memory processes are particularly vulnerable to aging. We sought to learn the degree to which sex, mood, and subjective sleep quality might be related to executive function and episodic memory composite scores in community-dwelling older adults. We replicated Glisky and colleagues' two-factor (i.e., executive function [N=263] versus episodic memory [N=151]) structure, and found that it did not significantly differ between males and females. Moderation analyses revealed no interactions between sex, mood, and sleep in predicting either composite score. However, females significantly outperformed males on the episodic memory composite, and on all the individual tests comprising it. Ours is the first study to look at sex differences in this battery's factor structure and its potential relations with mood and sleep. Future longitudinal studies in both healthy and clinical populations will help us further probe the possible influence of these variables on executive function and episodic memory in aging.

Hormonal contraception & face processing: Examining face gender, androgenicity & treatment duration

Previous cross-sectional studies observed differences between users and non-users of combined oral contraceptives (COCs) in both the structure and function of the fusiform face area (FFA) related to face processing. For the present study 120 female participants performed high-resolution structural, as well as functional scans at rest, during face encoding and face recognition. Participants were either never-users of COCs (26), current first-time users of androgenic (29) or anti-androgenic COCs (23) or previous users of androgenic (21) or anti-androgenic COCs (21). Results suggest that associations between COC-use and face processing are modulated by androgenicity, but do not persist beyond the duration of COC use. The majority of findings concern the connectivity of the left FFA to the left supramarginal gyrus (SMG), which is a key region in cognitive empathy. While connectivity in anti-androgenic COC users differs from never users irrespective of the duration of COC use already at rest, connectivity in androgenic COC users decreases with longer duration of use during face recognition. Furthermore, longer duration of androgenic COC use was related to reduced identification accuracy, as well as increased connectivity of the left FFA to the right orbitofrontal cortex. Accordingly, the FFA and SMG emerge as promising ROIs for future randomized controlled trials on the effects of COC use on face processing.

How Do Women and Men Look at the Past? Large Scanpath in Women during Autobiographical Retrieval—A Preliminary Study

While research has consistently demonstrated how autobiographical memory triggers visual exploration, prior studies did not investigate gender differences in this domain. We thus compared eye movement between women and men while performing an autobiographical retrieval task. We invited 35 women and 35 men to retrieve autobiographical memories while their gaze was monitored by an eye tracker. We further investigated gender differences in eye movement and autobiographical specificity, that is, the ability to retrieve detailed memories. The analysis demonstrated shorter fixations, larger duration and amplitude of saccades, and higher autobiographical specificity in women than in men. The significant gender differences in eye movement disappeared after controlling for autobiographical specificity. When retrieving autobiographical memory, female participants generated a large scan with short fixation and high saccade amplitude, while male participants increased their fixation duration and showed poorer gaze scan. The large saccades in women during autobiographical retrieval may constitute an exploratory gaze behavior enabling better autobiographical memory functioning, which is reflected by the larger number of autobiographical details retrieved compared to men.

Gender effects on the controllability of hemispheric white matter networks

Male and female adults exhibited significant group differences in brain white matter (WM) asymmetry and WM network controllability. However, gender differences in controllability of hemispheric WM networks between males and females remain to be determined. Based on 1 principal atlas and 1 replication atlas, this work characterized the average controllability (AC) and modal controllability (MC) of hemispheric WM network based on 1 principal dataset and 2 replication datasets. All results showed that males had higher AC of left hemispheric networks than females. And significant hemispheric asymmetry was revealed in regional AC and MC. Furthermore, significant gender differences in the AC asymmetry were mainly found in regions lie in the frontoparietal network, and the MC asymmetry was found in regions involving auditory and emotion process. Finally, we found significant associations between regional controllability and cognitive features. Taken together, this work could provide a novel perspective for understanding gender differences in hemispheric WM asymmetry and cognitive function between males and females.

It's time for sex in cognitive neuroscience

In a discussion paper published in the special issue of Cognitive Neuroscience, Sex Differences in the Brain, we investigated whether certain experimental parameters contributed to findings in functional magnetic resonance imaging studies of sex differences during long-term memory. Experimental parameters included: the number of participants, stimulus type(s), whether or not performance was matched, whether or not sex differences were reported, the type of between-subject statistical test used, and the contrast(s) employed. None of these parameters determined whether or not differences were observed, as all included studies reported sex differences. We also conducted a meta-analysis to determine if there were any brain regions consistently activated to a greater degree in either sex. The meta-analysis identified sex differences (male > female) in the lateral prefrontal cortex, visual processing regions, parahippocampal cortex, and the cerebellum. We received eight commentaries in response to that paper. Commentaries called for an expanded discussion on various topics including the influence of sex hormones, the role of gender (and other social factors), the pros and cons of equating behavioral performance between the sexes, and interpreting group differences in patterns of brain activity. There were some common statistical assumptions discussed in the commentaries regarding the 'file drawer' issue (i.e., the lack of reporting of null results) and effect size. The current paper provides further discussion of the various topics brought up in the commentaries and addresses some statistical misconceptions in the field. Overall, the commentaries echoed a resounding call to include sex as a factor in cognitive neuroscience studies.

High confidence spatial long-term memories produce greater cortical activity in males than females

Many functional resonance imaging (fMRI) studies have reported sex differences during long-term memory. The present fMRI investigation aimed to identify whether sex differences exist during high- versus low-confidence accurate spatial memories. During the study phase, abstract shapes were presented to the left or right of fixation. During the test phase, each shape was presented at fixation and participants made an old-"left" or old-"right" judgment followed by an "unsure" or "sure" response. The conjunction of female high- versus low-confidence spatial memory and male high- versus low-confidence spatial memory identified common activity in visual processing regions and parietal cortex, which suggests amplification of activity in some of the regions commonly associated with long-term memory yields high confidence. The contrast of female high- versus low-confidence spatial memory and male high- versus low-confidence spatial memory did not produce any significant activity. However, the reverse contrast produced greater male than female activity in the lateral prefrontal cortex, parietal cortex, sensorimotor cortex, and visual processing regions. An independent region-of-interest (ROI) analysis (ROIs were identified by contrasting hits versus misses) produced complementary results in the lateral prefrontal cortex. Greater lateral prefrontal cortex activity suggests a higher degree of subjective confidence in males than females, greater parietal cortex and visual processing activity suggests more vivid visualization in males than females, and greater activity in sensorimotor cortex indicates that males have a more reactive processing style than females. More broadly, the present and previous functional sex differences argue against the practice of collapsing across sex in cognitive neuroscience studies.

Singles and Faces: High Recognition for Female Faces in Single Males

A substantial body of research has assessed the effect of gender on face recognition; however, little is known about the effect of relationship status on face recognition. In this study, we assessed for the first time how relationship status impacts face recognition by asking 62 male and female participants to decide whether they had previously encountered faces of males and females. Participants were also asked to fill a socio-demographic variables questionnaire which included, among other information, question about their relationship status (i.e., single vs. in a relationship). A significant effect of relationship status on face recognition was observed only in males; namely, single males demonstrated higher face recognition than males in relationships, whereas similar face recognition was observed in single and in-relationship females. More specifically, single males demonstrated higher recognition for female than for male faces, whereas no differences were observed in single females, males in relationships, or in females in relationship. Single males seem to be motivated by mating opportunity and, thus, unlike single females or males and females in relationships, devote high attentional resources to processing faces of the opposite gender.  

An ecological measure of rapid and automatic face-sex categorization

Sex categorization is essential for mate choice and social interactions in many animal species. In humans, sex categorization is readily performed from the face. However, clear neural markers of face-sex categorization, i.e., common responses to widely variable individuals from one sex, have not been identified so far in humans. To isolate a direct signature of rapid and automatic face-sex categorization generalized across a wide range of variable exemplars, we recorded scalp electroencephalogram (EEG) from 32 participants (16 females) while they were exposed to variable natural face images from one sex alternating at a rapid rate of 6 Hz (i.e., 6 images per second). Images from the other sex were inserted every 6th stimulus (i.e., at a 1-Hz rate). A robust categorization response to both sex contrasts emerged at 1 Hz and harmonics in the EEG frequency spectrum over the occipito-temporal cortex of most participants. The response was larger for female faces presented among male faces than the reverse, suggesting that the two sex categories are not equally homogenous. This asymmetrical response pattern disappeared for upside-down faces, ruling out the contribution of low-level physical variability across images. Overall, these observations demonstrate that sex categorization occurs automatically after a single glance at natural face images and can be objectively isolated and quantified in the human brain within a few minutes.

Hemisphere and Gender Differences in the Rich-Club Organization of Structural Networks

Structural and functional differences in brain hemispheric asymmetry have been well documented between female and male adults. However, potential differences in the connectivity patterns of the rich-club organization of hemispheric structural networks in females and males remain to be determined. In this study, diffusion tensor imaging was used to construct hemispheric structural networks in healthy subjects, and graph theoretical analysis approaches were applied to quantify hemisphere and gender differences in rich-club organization. The results showed that rich-club organization was consistently observed in both hemispheres of female and male adults. Moreover, a reduced level of connectivity was found in the left hemisphere. Notably, rightward asymmetries were mainly observed in feeder and local connections among one hub region and peripheral regions, many of which are implicated in visual processing and spatial attention functions. Additionally, significant gender differences were revealed in the rich-club, feeder, and local connections in rich-club organization. These gender-related hub and peripheral regions are involved in emotional, sensory, and cognitive control functions. The topological changes in rich-club organization provide novel insight into the hemisphere and gender effects on white matter connections and underlie a potential network mechanism of hemisphere- and gender-based differences in visual processing, spatial attention and cognitive control.

Emotion recognition associated with polymorphism in oxytocinergic pathway gene ARNT2

The ability to correctly understand the emotional expression of another person is essential for social relationships and appears to be a partly inherited trait. The neuropeptides oxytocin and vasopressin have been shown to influence this ability as well as face processing in humans. Here, recognition of the emotional content of faces and voices, separately and combined, was investigated in 492 subjects, genotyped for 25 single nucleotide polymorphisms (SNPs) in eight genes encoding proteins important for oxytocin and vasopressin neurotransmission. The SNP rs4778599 in the gene encoding aryl hydrocarbon receptor nuclear translocator 2 (ARNT2), a transcription factor that participates in the development of hypothalamic oxytocin and vasopressin neurons, showed an association that survived correction for multiple testing with emotion recognition of audio-visual stimuli in women (n = 309). This study demonstrates evidence for an association that further expands previous findings of oxytocin and vasopressin involvement in emotion recognition.

Investigating the Influence of Biological Sex on the Behavioral and Neural Basis of Face Recognition

There is interest in understanding the influence of biological factors, like sex, on the organization of brain function. We investigated the influence of biological sex on the behavioral and neural basis of face recognition in healthy, young adults. In behavior, there were no sex differences on the male Cambridge Face Memory Test (CFMT)+ or the female CFMT+ (that we created) and no own-gender bias (OGB) in either group. We evaluated the functional topography of ventral stream organization by measuring the magnitude and functional neural size of 16 individually defined face-, two object-, and two place-related regions bilaterally. There were no sex differences in any of these measures of neural function in any of the regions of interest (ROIs) or in group level comparisons. These findings reveal that men and women have similar category-selective topographic organization in the ventral visual pathway. Next, in a separate task, we measured activation within the 16 face-processing ROIs specifically during recognition of target male and female faces. There were no sex differences in the magnitude of the neural responses in any face-processing region. Furthermore, there was no OGB in the neural responses of either the male or female participants. Our findings suggest that face recognition behavior, including the OGB, is not inherently sexually dimorphic. Face recognition is an essential skill for navigating human social interactions, which is reflected equally in the behavior and neural architecture of men and women.

The characteristics of social categorization based on the unidimensional variation of gender versus age

The present study explored the characteristics of social categorization based on the unidimensional variation of gender or age using the Garner's Selective Attention Paradigm. The task of the experiment was to judge whether there was a mole on a person's face, and the results showed that young participants' response times were slower when the age or gender of the face stimuli varied, demonstrating that young people, rather than older people, can activate both an age category and a gender category automatically. Meanwhile, all participants' responses to the old faces were slower than that to the young faces. Females reacted faster than males, demonstrating that females tend to have an advantage for face processing.

Of Kith and Kin: Perceptual Enrichment, Expectancy, and Reciprocity in Face Perception

Race powerfully affects perceivers' responses to faces, promoting biases in attention, classification, and memory. To account for these diverse effects, we propose a model that integrates social cognitive work with two prominent accounts of visual processing: perceptual learning and predictive coding. Our argument is that differential experience with a racial ingroup promotes both (a) perceptual enrichment, including richer, more well-integrated visual representations of ingroup relative to outgroup faces, and (b) expectancies that ingroup faces are normative, which influence subsequent visual processing. By allowing for "top-down" expectancy-based processes, this model accounts for both experience- and non-experience-based influences, such as motivation, context, and task instructions. Fundamentally, we suggest that we treat race as an important psychological dimension because it structures our social environment, which in turn structures mental representation.

Faces on Her and His Mind: Female and Likable

Faces are a valuable source of non-verbal information for daily life social interaction. Mounting evidence points to gender specificity in face perception. Here we search for the factors that can potentially trigger gender differences in tuning to faces. By using a set of Face-n-Food images slightly bordering on the Giuseppe Arcimboldo style, we examine: (i) whether face resemblance is linked to gender specific face impression, and, if so, whether this association is perceiver gender specific; and (ii) whether images most resembling a face are also most likable for female and male perceivers. First, in a spontaneous recognition task, participants were shown a set of Face-n-Food images in a predetermined order from the least to most resembling a face. Then in a two-alternative forced-choice (2AFC) task, participants judged whether each face appeared for them (i) either female or male (Exp. 1); or (ii) either likable or unlikable (Exp. 2). Remarkably, face resemblance is closely connected to gender specific impressions: images more resembling a face elicit also more female-face responses. This link is not perceiver gender specific as it occurs for both females and males. Moreover, face resemblance is positively linked to face likability, but this holds true only for female perceivers. The findings shed light on gender specificity in tuning to faces, and help to clarify abnormalities of the social brain in neurodevelopmental, psychiatric and psychosomatic disorders.

Neural correlates of autobiographical memory retrieval in children and adults

Autobiographical memory (AM) is a critically important form of memory for life events that undergoes substantial developmental changes from childhood to adulthood. Relatively little is known regarding the functional neural correlates of AM retrieval in children as assessed with fMRI, and how they may differ from adults. We investigated this question with 14 children ages 8-11 years and 14 adults ages 19-30 years, contrasting AM retrieval with semantic memory (SM) retrieval. During scanning, participants were cued by verbal prompts to retrieve previously selected recent AMs or to verify semantic properties of words. As predicted, both groups showed AM retrieval-related increased activation in regions implicated in prior studies, including bilateral hippocampus, and prefrontal, posterior cingulate, and parietal cortices. Adults showed greater activation in the hippocampal/parahippocampal region as well as prefrontal and parietal cortex, relative to children; age-related differences were most prominent in the first 8 sec versus the second 8 sec of AM retrieval and when AM retrieval was contrasted with semantic retrieval. This study is the first to characterise similarities and differences during AM retrieval in children and adults using fMRI.

Social memory associated with estrogen receptor polymorphisms in women

The ability to recognize the identity of faces and voices is essential for social relationships. Although the heritability of social memory is high, knowledge about the contributing genes is sparse. Since sex differences and rodent studies support an influence of estrogens and androgens on social memory, polymorphisms in the estrogen and androgen receptor genes (ESR1, ESR2, AR) are candidates for this trait. Recognition of faces and vocal sounds, separately and combined, was investigated in 490 subjects, genotyped for 10 single nucleotide polymorphisms (SNPs) in ESR1, four in ESR2 and one in the AR Four of the associations survived correction for multiple testing: women carrying rare alleles of the three ESR2 SNPs, rs928554, rs1271572 and rs1256030, in linkage disequilibrium with each other, displayed superior face recognition compared with non-carriers. Furthermore, the uncommon genotype of the ESR1 SNP rs2504063 was associated with better recognition of identity through vocal sounds, also specifically in women. This study demonstrates evidence for associations in women between face recognition and variation in ESR2, and recognition of identity through vocal sounds and variation in ESR1. These results suggest that estrogen receptors may regulate social memory function in humans, in line with what has previously been established in mice.

Amygdala subnuclei resting-state functional connectivity sex and estrogen differences

The amygdala is a hub in emotional processing, including that of negative affect. Healthy men and women have distinct differences in amygdala responses, potentially setting the stage for the observed sex differences in the prevalence of fear, anxiety, and pain disorders. Here, we examined how amygdala subnuclei resting-state functional connectivity is affected by sex, as well as explored how the functional connectivity is related to estrogen levels. Resting-state functional connectivity was measured using functional magnetic resonance imaging (fMRI) with seeds placed in the left and right laterobasal (LB) and centromedial (CM) amygdala. Sex differences were studied in 48 healthy men and 48 healthy women, matched for age, while the association with estrogen was analyzed in a subsample of 24 women, for whom hormone levels had been assessed. For the hormone analyses, the subsample was further divided into a lower and higher estrogen levels group based on a median split. We found distinct sex differences in the LB and CM amygdala resting-state functional connectivity, as well as preliminary evidence for an association between estrogen levels and connectivity patterns. These results are potentially valuable in explaining why women are more afflicted by conditions of negative affect than are men, and could imply a mechanistic role for estrogen in modulating emotion.

Effects of sex and gonadectomy on social investigation and social recognition in mice

Background

An individual’s ability to recognise and pay attention to others is crucial in order to behave appropriately in various social situations. Studies in humans have shown a sex bias in sociability as well as social memory, indicating that females have better face memory and gaze more at the eyes of others, but information about the factors that underpin these differences is sparse. Our aim was therefore to investigate if sociability and social recognition differ between female and male mice, and if so, to what extent gonadal hormones may be involved. Intact and gonadectomised male and female mice were assessed for sociability and social recognition using the three-chambered sociability paradigm, as well as the social discrimination test. Furthermore, we conducted a novel object recognition test, a locomotor activity test and an odour habituation/dishabituation test.

Results

The present study showed that the ability to recognise other individuals is intact in males with and without gonads, as well as in intact females, whereas it is hampered in gonadectomised females. Additionally, intact male mice displayed more persistent investigatory behaviour compared to the other groups, although the intact females showed elevated basal locomotor activity. In addition, all groups had intact object memory and habituated to odours.

Conclusions

Our results suggest that intact male mice investigate conspecifics more than females do, and these differences seem to depend upon circulating hormones released from the testis. As these results seem to contrast what is known from human studies, they should be taken into consideration when using the three-chambered apparatus, and similar paradigms as animal models of social deficits in e.g. autism. Other behavioural tests, and animal models, may be more suitable for translational studies between patients and experimental animals.

Orienting to face expression during encoding improves men's recognition of own gender faces

It is unclear why women have superior episodic memory of faces, but the benefit may be partially the result of women engaging in superior processing of facial expressions. Therefore, we hypothesized that orienting instructions to attend to facial expression at encoding would significantly improve men's memory of faces and possibly reduce gender differences. We directed 203 college students (122 women) to study 120 faces under instructions to orient to either the person's gender or their emotional expression. They later took a recognition test of these faces by either judging whether they had previously studied the same person or that person with the exact same expression; the latter test evaluated recollection of specific facial details. Orienting to facial expressions during encoding significantly improved men's recognition of own-gender faces and eliminated the advantage that women had for male faces under gender orienting instructions. Although gender differences in spontaneous strategy use when orienting to faces cannot fully account for gender differences in face recognition, orienting men to facial expression during encoding is one way to significantly improve their episodic memory for male faces.

Face-n-Food: Gender Differences in Tuning to Faces

Faces represent valuable signals for social cognition and non-verbal communication. A wealth of research indicates that women tend to excel in recognition of facial expressions. However, it remains unclear whether females are better tuned to faces. We presented healthy adult females and males with a set of newly created food-plate images resembling faces (slightly bordering on the Giuseppe Arcimboldo style). In a spontaneous recognition task, participants were shown a set of images in a predetermined order from the least to most resembling a face. Females not only more readily recognized the images as a face (they reported resembling a face on images, on which males still did not), but gave on overall more face responses. The findings are discussed in the light of gender differences in deficient face perception. As most neuropsychiatric, neurodevelopmental and psychosomatic disorders characterized by social brain abnormalities are sex specific, the task may serve as a valuable tool for uncovering impairments in visual face processing.

Biases in spatial bisection induced by viewing male and female faces

Research on visual attention triggered by face gender is still relatively sparse. In the present study, three experiments are reported in which male and female participants were required to estimate the midpoint of a line (i.e., the "line bisection task"): at each end of the line a face was presented. Depending on the experimental condition, faces could be of the same gender (i.e., two males or two females) or the opposite gender. Experiments 1 and 2 converged in showing that when a male face was presented at the right and a female face at the left endpoint of the line, a clear rightward bias emerged compared to the other experimental conditions, indicating that male faces captured attention more than female faces. Importantly, male faces used across Experiments 1 and 2 were rated as more threatening than female faces, suggesting that perceived level of threat may have been responsible for the observed bias toward the male face. Experiment 3 corroborated this hypothesis by finding an attentional bias toward the male face with high threat (angry) faces but not with low threat (smiling) faces.

Influence of repressive coping style on cortical activation during encoding of angry faces

BACKGROUND

Coping plays an important role for emotion regulation in threatening situations. The model of coping modes designates repression and sensitization as two independent coping styles. Repression consists of strategies that shield the individual from arousal. Sensitization indicates increased analysis of the environment in order to reduce uncertainty. According to the discontinuity hypothesis, repressors are sensitive to threat in the early stages of information processing. While repressors do not exhibit memory disturbances early on, they manifest weak memory for these stimuli later. This study investigates the discontinuity hypothesis using functional magnetic resonance imaging (fMRI).

METHODS

Healthy volunteers (20 repressors and 20 sensitizers) were selected from a sample of 150 students on the basis of the Mainz Coping Inventory. During the fMRI experiment, subjects evaluated and memorized emotional and neutral faces. Subjects performed two sessions of face recognition: immediately after the fMRI session and three days later.

RESULTS

Repressors exhibited greater activation of frontal, parietal and temporal areas during encoding of angry faces compared to sensitizers. There were no differences in recognition of facial emotions between groups neither immediately after exposure nor after three days.

CONCLUSIONS

The fMRI findings suggest that repressors manifest an enhanced neural processing of directly threatening facial expression which confirms the assumption of hyper-responsivity to threatening information in repression in an early processing stage. A discrepancy was observed between high neural activation in encoding-relevant brain areas in response to angry faces in repressors and no advantage in subsequent memory for these faces compared to sensitizers.

The social network-network: size is predicted by brain structure and function in the amygdala and paralimbic regions

The social brain hypothesis proposes that the large size of the primate neocortex evolved to support complex and demanding social interactions. Accordingly, recent studies have reported correlations between the size of an individual's social network and the density of gray matter (GM) in regions of the brain implicated in social cognition. However, the reported relationships between GM density and social group size are somewhat inconsistent with studies reporting correlations in different brain regions. One factor that might account for these discrepancies is the use of different measures of social network size (SNS). This study used several measures of SNS to assess the relationships SNS and GM density. The second goal of this study was to test the relationship between social network measures and functional brain activity. Participants performed a social closeness task using photos of their friends and unknown people. Across the VBM and functional magnetic resonance imaging analyses, individual differences in SNS were consistently related to structural and functional differences in three regions: the left amygdala, right amygdala and the right entorhinal/ventral anterior temporal cortex.

Own-age and own-sex biases in recognition of aged faces

It is surprising how easily we are able to recognize people whom we have not seen in many years, somehow compensating for the aging-related facial changes that occurred. We measured the limits of the ability to recognize faces across the lifespan by young versus old men and women. Images of five males and five females at young and middle ages were morphed in 10% increments to create aged face images across the lifespan. Fifty-eight participants (28 females) judged whether pairs of photographs were of the same or different identity. Women outperformed men for female faces, exhibiting a sex difference and own-sex bias. Additionally, older participants showed an own-age bias and outperformed their younger counterparts with older stimuli. It appears that the recognition of faces is affected by the own-age and own-sex biases, potentially allowing us to remember some people better than others, thus mediating our interaction with the world.

Face gender modulates women's brain activity during face encoding

Women typically remember more female than male faces, whereas men do not show a reliable own-gender bias. However, little is known about the neural correlates of this own-gender bias in face recognition memory. Using functional magnetic resonance imaging (fMRI), we investigated whether face gender modulated brain activity in fusiform and inferior occipital gyri during incidental encoding of faces. Fifteen women and 14 men underwent fMRI while passively viewing female and male faces, followed by a surprise face recognition task. Women recognized more female than male faces and showed higher activity to female than male faces in individually defined regions of fusiform and inferior occipital gyri. In contrast, men's recognition memory and blood-oxygen-level-dependent response were not modulated by face gender. Importantly, higher activity in the left fusiform gyrus (FFG) to one gender was related to better memory performance for that gender. These findings suggest that the FFG is involved in the gender bias in memory for faces, which may be linked to differential experience with female and male faces.

Anterior temporal face patches: a meta-analysis and empirical study

Evidence suggests the anterior temporal lobe (ATL) plays an important role in person identification and memory. In humans, neuroimaging studies of person memory report consistent activations in the ATL to famous and personally familiar faces and studies of patients report resection or damage of the ATL causes an associative prosopagnosia in which face perception is intact but face memory is compromised. In addition, high-resolution fMRI studies of non-human primates and electrophysiological studies of humans also suggest regions of the ventral ATL are sensitive to novel faces. The current study extends previous findings by investigating whether similar subregions in the dorsal, ventral, lateral, or polar aspects of the ATL are sensitive to personally familiar, famous, and novel faces. We present the results of two studies of person memory: a meta-analysis of existing fMRI studies and an empirical fMRI study using optimized imaging parameters. Both studies showed left-lateralized ATL activations to familiar individuals while novel faces activated the right ATL. Activations to famous faces were quite ventral, similar to what has been reported in previous high-resolution fMRI studies of non-human primates. These findings suggest that face memory-sensitive patches in the human ATL are in the ventral/polar ATL.

Greater visual averaging of face identity for own-gender faces

Recent evidence suggests that observers can rapidly form an average representation based on a set of simultaneously presented faces. Here, we replicate this finding and show that the tendency to process sets of faces in terms of an average representation is greater for own-gender faces. Male and female participants viewed sets of four male or female faces before deciding whether or not a subsequently presented single test face had been present in the set. Incorrect endorsement that it was one of the set members was greater when the test face was a morphed average of the four faces than when it was an actual set member, and this effect was strongest when the gender of the faces was the same as the observer's. The finding that observers were more likely to incorrectly endorse own-gender (vs. other-gender) faces forms an exception to the often reported own-gender advantage in face recognition.

Social cognition, the male brain and the autism spectrum

Behavioral studies have shown that, at a population level, women perform better on tests of social cognition and empathy than men. Furthermore Autism Spectrum Disorders (ASDs), which are characterized by impairments in social functioning and empathy, occur more commonly in males than females. These findings have led to the hypothesis that differences in the functioning of the social brain between males and females contribute to the greater vulnerability of males to ASD and the suggestion that ASD may represent an extreme form of the male brain. Here we sought to investigate this hypothesis by determining: (i) whether males and females differ in social brain function, and (ii) whether any sex differences in social brain function are exaggerated in individuals with ASD. Using fMRI we show that males and females differ markedly in social brain function when making social decisions from faces (compared to simple sex judgements) especially when making decisions of an affective nature, with the greatest sex differences in social brain activation being in the inferior frontal cortex (IFC). We also demonstrate that this difference is exaggerated in individuals with ASD, who show an extreme male pattern of IFC function. These results show that males and females differ significantly in social brain function and support the view that sex differences in the social brain contribute to the greater vulnerability of males to ASDs.

A review on sex differences in processing emotional signals

Interest in sex-related differences in psychological functioning has again come to the foreground with new findings about their possible functional basis in the brain. Sex differences may be one way how evolution has capitalized on the capacity of homologous brain regions to process social information between men and women differently. This paper focuses specifically on the effects of emotional valence, sex of the observed and sex of the observer on regional brain activations. We also discuss the effects of and interactions between environment, hormones, genes and structural differences of the brain in the context of differential brain activity patterns between men and women following exposure to seen expressions of emotion and in this context we outline a number of methodological considerations for future research. Importantly, results show that although women are better at recognizing emotions and express themselves more easily, men show greater responses to threatening cues (dominant, violent or aggressive) and this may reflect different behavioral response tendencies between men and women as well as evolutionary effects. We conclude that sex differences must not be ignored in affective research and more specifically in affective neuroscience.

Creating probabilistic maps of the face network in the adolescent brain: a multicentre functional MRI study

Large-scale magnetic resonance (MR) studies of the human brain offer unique opportunities for identifying genetic and environmental factors shaping the human brain. Here, we describe a dataset collected in the context of a multi-centre study of the adolescent brain, namely the IMAGEN Study. We focus on one of the functional paradigms included in the project to probe the brain network underlying processing of ambiguous and angry faces. Using functional MR (fMRI) data collected in 1,110 adolescents, we constructed probabilistic maps of the neural network engaged consistently while viewing the ambiguous or angry faces; 21 brain regions responding to faces with high probability were identified. We were also able to address several methodological issues, including the minimal sample size yielding a stable location of a test region, namely the fusiform face area (FFA), as well as the effect of acquisition site (eight sites) and scanner (four manufacturers) on the location and magnitude of the fMRI response to faces in the FFA. Finally, we provided a comparison between male and female adolescents in terms of the effect sizes of sex differences in brain response to the ambiguous and angry faces in the 21 regions of interest. Overall, we found a stronger neural response to the ambiguous faces in several cortical regions, including the fusiform face area, in female (vs. male) adolescents, and a slightly stronger response to the angry faces in the amygdala of male (vs. female) adolescents.

Women’s Own-Gender Bias in Face Recognition Memory

Women remember more female than male faces, whereas men do not seem to display an own-gender bias in face recognition memory. Why women remember female faces to a greater extent than male faces is unclear; one proposition is that women attend more to and thereby process female faces more effortfully than male faces during encoding. A manipulation that distracts attention and reduces effortful processing may therefore decrease women’s own-gender bias by reducing memory for female faces relative to male faces. In three separate experiments, women and men encoded female and male faces for later recognition in full attention and divided attention conditions. Results consistently showed that women, in contrast to men, displayed a reliable own-gender bias. Importantly, the magnitude of women’s own-gender bias was not reduced in divided attention conditions, indicating that it is not a result of effortful processing of female faces. We suggest these results reflect that women have greater perceptual expertise for female faces, facilitating recognition memory.

The Gender of Face Stimuli is Represented in Multiple Regions in the Human Brain

Face perception in humans is mediated by activation in a network of brain areas. Conventional univariate fMRI data analysis has not localized differential responses to viewing male as compared with viewing female faces within this network. We tested whether we could detect neural response patterns specific to viewing male vs. female faces in 40 participants. Replicating earlier work, face stimuli evoked activation in the core (inferior occipital gyrus, IOG; fusiform gyrus, FG; and superior temporal sulcus, STS), as well as extended (amygdala, inferior frontal gyrus, IFG; insula, INS; and orbitofrontal cortex, OFC) regions of the face network. Multivariate pattern classification of activity within these regions revealed successful decoding of gender information, significantly above chance, in the IOG, FG, STS, IFG, INS, and OFC, but not in the amygdala. Multiple control regions indicated that this result might be restricted to face-responsive regions. Our findings suggest that gender information is distributed across the face network and is represented in the core regions that process invariant facial features, as well as the extended regions that process changeable aspects of faces.