Sex‐related differences in behavioral and amygdalar responses to compound facial threat cues

During face perception, we integrate facial expression and eye gaze to take advantage of their shared signals. For example, fear with averted gaze provides a congruent avoidance cue, signaling both threat presence and its location, whereas fear with direct gaze sends an incongruent cue, leaving threat location ambiguous. It has been proposed that the processing of different combinations of threat cues is mediated by dual processing routes: reflexive processing via magnocellular (M) pathway and reflective processing via parvocellular (P) pathway. Because growing evidence has identified a variety of sex differences in emotional perception, here we also investigated how M and P processing of fear and eye gaze might be modulated by observer's sex, focusing on the amygdala, a structure important to threat perception and affective appraisal. We adjusted luminance and color of face stimuli to selectively engage M or P processing and asked observers to identify emotion of the face. Female observers showed more accurate behavioral responses to faces with averted gaze and greater left amygdala reactivity both to fearful and neutral faces. Conversely, males showed greater right amygdala activation only for M‐biased averted‐gaze fear faces. In addition to functional reactivity differences, females had proportionately greater bilateral amygdala volumes, which positively correlated with behavioral accuracy for M‐biased fear. Conversely, in males only the right amygdala volume was positively correlated with accuracy for M‐biased fear faces. Our findings suggest that M and P processing of facial threat cues is modulated by functional and structural differences in the amygdalae associated with observer's sex.     

Amygdala damage affects event‐related potentials for fearful faces at specific time windows

The amygdala is known to influence processing of threat‐related stimuli in distant brain regions, including visual cortex. The time‐course of these distant influences is unknown, although this information is important for resolving debates over likely pathways mediating an apparent rapidity in emotional processing. To address this, we recorded event‐related potentials (ERPs) to seen fearful face expressions, in preoperative patients with medial temporal lobe epilepsy who had varying degrees of amygdala pathology, plus healthy volunteers. We found that amygdala damage diminished ERPs for fearful versus neutral faces within the P1 time‐range, ∼100–150 ms, and for a later component at ∼500–600 ms. Individual severity of amygdala damage determined the magnitude of both these effects, consistent with a causal amygdala role. By contrast, amygdala damage did not affect explicit perception of fearful expressions nor a distinct emotional ERP effect at 150–250 ms. These results demonstrate two distinct time‐points at which the amygdala influences fear processing. The data also demonstrate that while not all aspects of expression processing are disrupted by amygdala damage, there is a crucial impact on an early P1 component. These findings are consistent with the existence of multiple processing stages or routes for fearful faces that vary in their dependence on amygdala function. Hum Brain Mapp, 2010. © 2009 Wiley‐Liss, Inc.     

Emotion perception and executive control interact in the salience network during emotionally charged working memory processing

Processing of emotional stimuli can either hinder or facilitate ongoing working memory (WM); however, the neural basis of these effects remains largely unknown. Here we examined the neural mechanisms of these paradoxical effects by implementing a novel emotional WM task in an fMRI study. Twenty‐five young healthy participants performed an N‐back task with fearful and neutral faces as stimuli. Participants made more errors when performing 0‐back task with fearful versus neutral faces, whereas they made fewer errors when performing 2‐back task with fearful versus neutral faces. These emotional impairment and enhancement on behavioral performance paralleled significant interactions in distributed regions in the salience network including anterior insula (AI) and dorsal cingulate cortex (dACC), as well as in emotion perception network including amygdala and temporal‐occipital association cortex (TOC). The dorsal AI (dAI) and dACC were more activated when comparing fearful with neutral faces in 0‐back task. Contrarily, dAI showed reduced activation, while TOC and amygdala showed stronger responses to fearful as compared to neutral faces in the 2‐back task. These findings provide direct neural evidence to the emerging dual competition model suggesting that the salience network plays a critical role in mediating interaction between emotion perception and executive control when facing ever‐changing behavioral demands. Hum Brain Mapp 35:5606–5616, 2014. © 2014 Wiley Periodicals, Inc.     

Conscious and unconscious processing of fear after right amygdala damage: A single case ERP-study

In this study, we describe a 58-year-old male patient (FZ) with a right-amygdala lesion after temporal lobe infarction. FZ is unable to recognize fearful facial expressions. Instead, he consistently misinterprets expressions of fear for expressions of surprise. Employing EEG/ERP measures, we investigated whether presentation of fearful and surprised facial expressions would lead to different response patterns. We also measured ERPs to aversively conditioned and unconditioned fearful faces.

We compared ERPs elicited by supraliminally and subliminally presented conditioned fearful faces (CS+), unconditioned fearful faces (CS–) and surprised faces. Despite FZ's inability to recognize fearful facial expressions in emotion recognition tasks, ERP components showed different response patterns to pictures of surprised and fearful facial expressions, indicating that covert or implicit recognition of fear is still intact.

Differences between ERPs to CS+ and CS– were only found when these stimuli were presented subliminally. This indicates that intact right amygdala function is not necessary for aversive conditioning.

Previous studies have stressed the importance of the right amygdala for discriminating facial emotional expressions and for classical conditioning. Our study suggests that the right amygdala is necessary for explicit recognition of fear, while implicit recognition of fear and classical conditioning may still occur following lesion of the right amygdala.     

Multivariate fMRI pattern analysis of fear perception across modalities

The emotional expression of fear can be processed through a number of modalities, and of varying forms, however, much of the functional imaging literature has centered on investigating fear as expressed through faces. Findings point to an active involvement of the amygdala, and remain fairly consistent in other studies of unimodal fear perception; however, few studies have looked at within‐subject cross‐modal responses to fear. Thus, we approached this inquiry by testing 30 healthy young adults with fast, high‐resolution fMRI, recording the neural responses of fear perception, as expressed through faces, bodies, prosody, and vocalizations. The study was analyzed using a multivariate approach (multi‐voxel pattern analysis) and yielded a significant distinction in the responses associated with the perception of fearful vs. neutral emotions. Calculated weights highlighted areas in the amygdala and surrounding subcortical structures as contributing the greatest to the discrimination; however, a whole‐brain analysis was necessary to obtain above‐chance classification accuracy, suggesting that processing fear across modalities likely involves a broad, distributed network. Thus, our findings support a multivariate approach to studying a highly complex construct such as emotion, as it accounts for multiple voxels simultaneously and can accommodate the high subject‐level variability that oftentimes comes with studying emotion perception.     

Withdrawal-associated increases and decreases in functional neural connectivity associated with altered emotional regulation in alcoholism

Alcoholic patients who have undergone multiple detoxifications/relapses show altered processing of emotional signals. We performed functional magnetic resonance imaging during performance of implicit and explicit versions of a task in which subjects were presented with morphs of fearful facial emotional expressions. Participants were abstaining, multiply detoxified (MDTx; n=12) or singly detoxified patients (SDTx; n=17), and social drinker controls (n=31). Alcoholic patients were less able than controls to recognize fearful expressions, and showed lower activation in prefrontal areas, including orbitofrontal cortex and insula, which mediate emotional processing. The decrease in activation was greater in MDTx patients who also showed decreased connectivity between insula and prefrontal areas, and between amygdala and globus pallidus. In the explicit condition, the strength of connectivity between insula and areas involved in regulation of emotion (inferior frontal cortex and frontal pole) was negatively correlated with both the number of detoxifications and dependency (measured by the severity of alcohol dependency (SADQ) and control over drinking score (Impaired Control questionnaire, ICQ)). In contrast, increased connectivity was found between insula and the colliculus neuronal cluster, and between amygdala and stria terminalis bed nucleus. In the implicit condition, number of detoxifications and ICQ score correlated positively with connectivity between amygdala and prefrontal cortical areas involved in attentional and executive processes. Repeated episodes of detoxification from alcohol are associated with altered function both in fear perception pathways and in cortical modulation of emotions. Such changes may confer increased sensitivity to emotional stress and impaired social competence, contributing to relapse.     

Age‐related changes in amygdala–frontal connectivity during emotional face processing from childhood into young adulthood

The ability to process and respond to emotional facial expressions is a critical skill for healthy social and emotional development. There has been growing interest in understanding the neural circuitry underlying development of emotional processing, with previous research implicating functional connectivity between amygdala and frontal regions. However, existing work has focused on threatening emotional faces, raising questions regarding the extent to which these developmental patterns are specific to threat or to emotional face processing more broadly. In the current study, we examined age‐related changes in brain activity and amygdala functional connectivity during an fMRI emotional face matching task (including angry, fearful, and happy faces) in 61 healthy subjects aged 7–25 years. We found age‐related decreases in ventral medial prefrontal cortex activity in response to happy faces but not to angry or fearful faces, and an age‐related change (shifting from positive to negative correlation) in amygdala–anterior cingulate cortex/medial prefrontal cortex (ACC/mPFC) functional connectivity to all emotional faces. Specifically, positive correlations between amygdala and ACC/mPFC in children changed to negative correlations in adults, which may suggest early emergence of bottom‐up amygdala excitatory signaling to ACC/mPFC in children and later development of top‐down inhibitory control of ACC/mPFC over amygdala in adults. Age‐related changes in amygdala–ACC/mPFC connectivity did not vary for processing of different facial emotions, suggesting changes in amygdala–ACC/mPFC connectivity may underlie development of broad emotional processing, rather than threat‐specific processing. Hum Brain Mapp 37:1684–1695, 2016. © 2016 Wiley Periodicals, Inc .     

5‐HTTLPR differentially predicts brain network responses to emotional faces

The effects of the 5‐HTTLPR polymorphism on neural responses to emotionally salient faces have been studied extensively, focusing on amygdala reactivity and amygdala‐prefrontal interactions. Despite compelling evidence that emotional face paradigms engage a distributed network of brain regions involved in emotion, cognitive and visual processing, less is known about 5‐HTTLPR effects on broader network responses. To address this, we evaluated 5‐HTTLPR differences in the whole‐brain response to an emotional faces paradigm including neutral, angry and fearful faces using functional magnetic resonance imaging in 76 healthy adults. We observed robust increased response to emotional faces in the amygdala, hippocampus, caudate, fusiform gyrus, superior temporal sulcus and lateral prefrontal and occipito‐parietal cortices. We observed dissociation between 5‐HTTLPR groups such that L_AL_A individuals had increased response to only angry faces, relative to neutral ones, but S′ carriers had increased activity for both angry and fearful faces relative to neutral. Additionally, the response to angry faces was significantly greater in L_AL_A individuals compared to S′ carriers and the response to fearful faces was significantly greater in S′ carriers compared to L_AL_A individuals. These findings provide novel evidence for emotion‐specific 5‐HTTLPR effects on the response of a distributed set of brain regions including areas responsive to emotionally salient stimuli and critical components of the face‐processing network. These findings provide additional insight into neurobiological mechanisms through which 5‐HTTLPR genotype may affect personality and related risk for neuropsychiatric illness. Hum Brain Mapp 36:2842–2851, 2015. © 2015 Wiley Periodicals, Inc.     

Hypersensitivity to low intensity fearful faces in autism when fixation is constrained to the eyes

Previous studies that showed decreased brain activation in people with autism spectrum disorder (ASD) viewing expressive faces did not control that participants looked in the eyes. This is problematic because ASD is characterized by abnormal attention to the eyes. Here, we collected fMRI data from 48 participants (27 ASD) viewing pictures of neutral faces and faces expressing anger, happiness, and fear at low and high intensity, with a fixation cross between the eyes. Group differences in whole brain activity were examined for expressive faces at high and low intensity versus neutral faces. Group differences in neural activity were also investigated in regions of interest within the social brain, including the amygdala and the ventromedial prefrontal cortex (vmPFC). In response to low intensity fearful faces, ASD participants showed increased activation in the social brain regions, and decreased functional coupling between the amygdala and the vmPFC. This oversensitivity to low intensity fear coupled with a lack of emotional regulation capacity could indicate an excitatory/inhibitory imbalance in their socio‐affective processing system. This may result in social disengagement and avoidance of eye‐contact to handle feelings of strong emotional reaction. Our results also demonstrate the importance of careful control of gaze when investigating emotional processing in ASD. Hum Brain Mapp 38:5943–5957, 2017. © 2017 Wiley Periodicals, Inc.     

Amygdala-prefrontal dissociation of subliminal and supraliminal fear

Facial expressions of fear are universally recognized signals of potential threat. Humans may have evolved specialized neural systems for responding to fear in the absence of conscious stimulus detection. We used functional neuroimaging to establish whether the amygdala and the medial prefrontal regions to which it projects are engaged by subliminal fearful faces and whether responses to subliminal fear are distinguished from those to supraliminal fear. We also examined the time course of amygdala-medial prefrontal responses to supraliminal and subliminal fear. Stimuli were fearful and neutral baseline faces, presented under subliminal (16.7 ms and masked) or supraliminal (500 ms) conditions. Skin conductance responses (SCRs) were recorded simultaneously as an objective index of fear perception. SPM2 was used to undertake search region-of-interest (ROI) analyses for the amygdala and medial prefrontal (including anterior cingulate) cortex, and complementary whole-brain analyses. Time series data were extracted from ROIs to examine activity across early versus late phases of the experiment. SCRs and amygdala activity were enhanced in response to both subliminal and supraliminal fear perception. Time series analysis showed a trend toward greater right amygdala responses to subliminal fear, but left-sided responses to supraliminal fear. Cortically, subliminal fear was distinguished by right ventral anterior cingulate activity and supraliminal fear by dorsal anterior cingulate and medial prefrontal activity. Although subcortical amygdala activity was relatively persistent for subliminal fear, supraliminal fear showed more sustained cortical activity. The findings suggest that preverbal processing of fear may occur via a direct rostral-ventral amygdala pathway without the need for conscious surveillance, whereas elaboration of consciously attended signals of fear may rely on higher-order processing within a dorsal cortico-amygdala pathway.     

Amygdala–prefrontal cortex connectivity increased during face discrimination but not time perception

Time sensitivity is affected by emotional stimuli such as fearful faces. The effect of threatening stimuli on time perception depends on numerous factors, including task type and duration range. We applied a two‐interval forced‐choice task using face stimuli to healthy volunteers to evaluate time perception and emotion interaction using functional magnetic resonance imaging. We conducted finite impulse response analysis to examine time series for the significantly activated brain areas and psycho‐physical interaction to investigate the connectivity between selected regions. Time perception engaged a right‐lateralised frontoparietal network, while a face discrimination task activated the amygdala and fusiform face area (FFA). No voxels were active with regard to the effect of expression (fearful versus neutral). In parallel with this, our behavioural results showed that attending to the fearful faces did not cause duration overestimation. Finally, connectivity of the amygdala and FFA to the middle frontal gyrus increased during the face processing condition compared to the timing task. Overall, our results suggest that the prefrontal–amygdala connectivity might be required for the emotional processing of facial stimuli. On the other hand, attentional load, task type and task difficulty are discussed as possible factors that influence the effects of emotion on time perception.     

Increased amygdala response to masked emotional faces in depressed subjects resolves with antidepressant treatment: an fMRI study.

BACKGROUND: The amygdala has a central role in processing emotions, particularly fear. During functional magnetic resonance imaging (fMRI) amygdala activation has been demonstrated outside of conscious awareness using masked emotional faces. METHODS: We applied the masked faces paradigm to patients with major depression (n = 11) and matched control subjects (n = 11) during fMRI to compare amygdala activation in response to masked emotional faces before and after antidepressant treatment. Data were analyzed using left and right amygdala a priori regions of interest, in an analysis of variance block analysis and random effects model. RESULTS: Depressed patients had exaggerated left amygdala activation to all faces, greater for fearful faces. Right amygdala did not differ from control subjects. Following treatment, patients had bilateral reduced amygdala activation to masked fearful faces and bilateral reduced amygdala activation to all faces. Control subjects had no differences between the two scanning sessions. CONCLUSIONS: Depressed patients have left amygdala hyperarousal, even when processing stimuli outside conscious awareness. Increased amygdala activation normalizes with antidepressant treatment.     

Lower effective connectivity between amygdala and parietal regions in response to fearful faces in schizophrenia

Behavioral abnormalities related to processing negative emotions such as fear have been demonstrated in schizophrenia. The amygdala is strongly associated with fear processing, and alterations in amygdala function and structure have been demonstrated in schizophrenia. Further, functional disconnectivity has been attributed as key to the etiology of schizophrenia, with a number of lines of evidence supporting this theory. In the present study, we examine the effective connectivity corresponding to fear processing, from the amygdala to the whole brain, and compare this between patients with schizophrenia and control participants. An implicit facial emotion processing task was performed by 19 patients with schizophrenia and 24 matched controls during fMRI scanning. During the task, participants made gender judgments from facial images with either neutral or fearful emotion. Neural response to fearful images versus neutral was used as contrast of interest to estimate effective connectivity between the amygdala and the whole brain using the psycho-physiological interactions approach. This connectivity was compared between patients with schizophrenia and healthy controls. We show that when looking at fearful compared to neutral faces patients with schizophrenia show significantly reduced effective connectivity from the amygdala to a large cluster of regions including parts of the precuneus and parietal lobe, compared to healthy controls. These regions have been associated with emotion processing and high level social cognition tasks involving self related processing and mental representations about other people. The reduced amygdala connectivity in schizophrenia shown here further illuminates the neural basis for the behavioral abnormalities in emotional and social function found in the disorder.     

Neural response to emotional faces with and without awareness: event-related fMRI in a parietal patient with visual extinction and spatial neglect

This study examined whether differential neural responses are evoked by emotional stimuli with and without conscious perception, in a patient with visual neglect and extinction. Stimuli were briefly shown in either right, left, or both fields during event-related fMRI. On bilateral trials, either a fearful or neutral left face appeared with a right house, and it could either be extinguished from awareness or perceived. Seen faces in left visual field (LVF) activated primary visual cortex in the damaged right-hemisphere and bilateral fusiform gyri. Extinguished left faces increased activity in striate and extrastriate cortex, compared with right houses only. Critically, fearful faces activated the left amygdala and extrastriate cortex both when seen and when extinguished; as well as bilateral orbitofrontal and intact right superior parietal areas. Comparison of perceived versus extinguished faces revealed no difference in amygdala for fearful faces. Conscious perception increased activity in fusiform, parietal and prefrontal areas of the left-hemisphere, irrespective of emotional expression; while a differential emotional response to fearful faces occurring specifically with awareness was found in bilateral parietal, temporal, and frontal areas. These results demonstrate that amygdala and orbitofrontal cortex can be activated by emotional stimuli even without awareness after parietal damage; and that substantial unconscious residual processing can occur within spared brain areas well beyond visual cortex, despite neglect and extinction.     

Thalamocortical interactions underlying visual fear conditioning in humans

Despite a strong focus on the role of the amygdala in fear conditioning, recent works point to a more distributed network supporting fear conditioning. We aimed to elucidate interactions between subcortical and cortical regions in fear conditioning in humans. To do this, we used two fearful faces as conditioned stimuli (CS) and an electrical stimulation at the left hand, paired with one of the CS, as unconditioned stimulus (US). The luminance of the CS was rhythmically modulated leading to “entrainment” of brain oscillations at a predefined modulation frequency. Steady‐state responses (SSR) were recorded by MEG. In addition to occipital regions, spectral analysis of SSR revealed increased power during fear conditioning particularly for thalamus and cerebellum contralateral to the upcoming US. Using thalamus and amygdala as seed‐regions, directed functional connectivity was calculated to capture the modulation of interactions that underlie fear conditioning. Importantly, this analysis showed that the thalamus drives the fusiform area during fear conditioning, while amygdala captures the more general effect of fearful faces perception. This study confirms ideas from the animal literature, and demonstrates for the first time the central role of the thalamus in fear conditioning in humans. Hum Brain Mapp 36:4592–4603, 2015. © 2015 Wiley Periodicals, Inc.     

Amygdalar activation associated with positive and negative facial expressions

Most theories of amygdalar function have underscored its role in fear. One broader theory suggests that neuronal activation of the amygdala in response to fear-related stimuli represents only a portion of its more widespread role in modulating an organism's vigilance level. To further explore this theory, the amygdalar response to happy, sad, angry, fearful, and neutral faces in 17 subjects was characterized using 3 T fMRI. Utilizing a random effects model and hypothesis-driven analytic strategy, it was observed that each of the four emotional faces was associated with reliable bilateral activation of the amygdala compared with neutral. These findings suggest a broader role for the amygdala in modulating the vigilance level during the perception of several negative and positive facial emotions.     

Distributed and interactive brain mechanisms during emotion face perception: evidence from functional neuroimaging

Brain imaging studies in humans have shown that face processing in several areas is modulated by the affective significance of faces, particularly with fearful expressions, but also with other social signals such gaze direction. Here we review haemodynamic and electrical neuroimaging results indicating that activity in the face-selective fusiform cortex may be enhanced by emotional (fearful) expressions, without explicit voluntary control, and presumably through direct feedback connections from the amygdala. fMRI studies show that these increased responses in fusiform cortex to fearful faces are abolished by amygdala damage in the ipsilateral hemisphere, despite preserved effects of voluntary attention on fusiform; whereas emotional increases can still arise despite deficits in attention or awareness following parietal damage, and appear relatively unaffected by pharmacological increases in cholinergic stimulation. Fear-related modulations of face processing driven by amygdala signals may implicate not only fusiform cortex, but also earlier visual areas in occipital cortex (e.g., V1) and other distant regions involved in social, cognitive, or somatic responses (e.g., superior temporal sulcus, cingulate, or parietal areas). In the temporal domain, evoked-potentials show a widespread time-course of emotional face perception, with some increases in the amplitude of responses recorded over both occipital and frontal regions for fearful relative to neutral faces (as well as in the amygdala and orbitofrontal cortex, when using intracranial recordings), but with different latencies post-stimulus onset. Early emotional responses may arise around 120ms, prior to a full visual categorization stage indexed by the face-selective N170 component, possibly reflecting rapid emotion processing based on crude visual cues in faces. Other electrical components arise at later latencies and involve more sustained activities, probably generated in associative or supramodal brain areas, and resulting in part from the modulatory signals received from amygdala. Altogether, these fMRI and ERP results demonstrate that emotion face perception is a complex process that cannot be related to a single neural event taking place in a single brain regions, but rather implicates an interactive network with distributed activity in time and space. Moreover, although traditional models in cognitive neuropsychology have often considered that facial expression and facial identity are processed along two separate pathways, evidence from fMRI and ERPs suggests instead that emotional processing can strongly affect brain systems responsible for face recognition and memory. The functional implications of these interactions remain to be fully explored, but might play an important role in the normal development of face processing skills and in some neuropsychiatric disorders.     

Variation of human amygdala response during threatening stimuli as a function of 5'HTTLPR genotype and personality style.

BACKGROUND: In the brain, processing of fearful stimuli engages the amygdala, and the variability of its activity is associated with genetic factors as well as with emotional salience. The objective of this study was to explore the relevance of personality style for variability of amygdala response. METHODS: We studied two groups (n=14 in each group) of healthy subjects categorized by contrasting cognitive styles with which they attribute salience to fearful stimuli: so-called phobic prone subjects who exaggerate potential environmental threat versus so-called eating disorders prone subjects who tend to be much less centered around fear. The two groups underwent functional magnetic resonance imaging (fMRI) at 3T during performance of a perceptual task of threatening stimuli and they were also matched for the genotype of the 5' variable number tandem repeat (VNTR) polymorphism in the serotonin transporter. RESULTS: The fMRI results indicated that phobic prone subjects selectively recruit the amygdala to a larger extent than eating disorders prone subjects. Activity in the amygdala was also independently predicted by personality style and genotype of the serotonin transporter. Moreover, brain activity during a working memory task did not differentiate the two groups. CONCLUSIONS: The results of the present study suggest that aspects of personality style are rooted in biological responses of the fear circuitry associated with processing of environmental information.     

Neural responses to emotional faces in women recovered from anorexia nervosa

Impairments in emotional processing have been associated with anorexia nervosa. However, it is unknown whether neural and behavioural differences in the processing of emotional stimuli persist following recovery. The aim of this study was to investigate the neural processing of emotional faces in individuals recovered from anorexia nervosa compared with healthy controls. Thirty-two participants (16 recovered anorexia nervosa, 16 healthy controls) underwent a functional magnetic resonance imaging (fMRI) scan. Participants viewed fearful and happy emotional faces and indicated the gender of the face presented. Whole brain analysis revealed no significant differences between the groups to the contrasts of fear versus happy and vice versa. Region of interest analysis demonstrated no significant differences in the neural response to happy or fearful stimuli between the groups in the amygdala or fusiform gyrus. These results suggest that processing of emotional faces may not be aberrant after recovery from anorexia nervosa.     

Shyness and the first 100 ms of emotional face processing

Although shyness is presumed to be related to an increased sensitivity to detect motivationally salient social stimuli, we know little of how shyness affects the early perception of facial emotions. We demonstrate here that individual differences in normative shyness were related to brain responses to some emotional faces as early as the P1 electrocortical component, 80-130 ms after stimulus onset. High-shy individuals showed reduced P1 amplitude for fearful faces compared to neutral faces. Low-shy individuals processed happy faces faster than other emotions and showed increased P1 amplitudes for happy faces over neutral faces. Regardless of shyness level, participants showed increased amplitudes in the N170 component (130-200 ms) for all emotions over neutral conditions, particularly for the emotion of fear. This study presents the first evidence that shyness is related to early electrocortical responses to the processing of fearful faces, consistent with a fast-path amygdala sensitivity model.