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

A deep neural network model of the primate superior colliculus for emotion recognition

Although sensory processing is pivotal to nearly every theory of emotion, the evaluation of the visual input as ‘emotional’ (e.g. a smile as signalling happiness) has been traditionally assumed to take place in supramodal ‘limbic’ brain regions. Accordingly, subcortical structures of ancient evolutionary origin that receive direct input from the retina, such as the superior colliculus (SC), are traditionally conceptualized as passive relay centres. However, mounting evidence suggests that the SC is endowed with the necessary infrastructure and computational capabilities for the innate recognition and initial categorization of emotionally salient features from retinal information. Here, we built a neurobiologically inspired convolutional deep neural network (DNN) model that approximates physiological, anatomical and connectional properties of the retino-collicular circuit. This enabled us to characterize and isolate the initial computations and discriminations that the DNN model of the SC can perform on facial expressions, based uniquely on the information it directly receives from the virtual retina. Trained to discriminate facial expressions of basic emotions, our model matches human error patterns and above chance, yet suboptimal, classification accuracy analogous to that reported in patients with V1 damage, who rely on retino-collicular pathways for non-conscious vision of emotional attributes. When presented with gratings of different spatial frequencies and orientations never ‘seen’ before, the SC model exhibits spontaneous tuning to low spatial frequencies and reduced orientation discrimination, as can be expected from the prevalence of the magnocellular (M) over parvocellular (P) projections. Likewise, face manipulation that biases processing towards the M or P pathway affects expression recognition in the SC model accordingly, an effect that dovetails with variations of activity in the human SC purposely measured with ultra-high field functional magnetic resonance imaging. Lastly, the DNN generates saliency maps and extracts visual features, demonstrating that certain face parts, like the mouth or the eyes, provide higher discriminative information than other parts as a function of emotional expressions like happiness and sadness. The present findings support the contention that the SC possesses the necessary infrastructure to analyse the visual features that define facial emotional stimuli also without additional processing stages in the visual cortex or in ‘limbic’ areas.

This article is part of the theme issue ‘Cracking the laugh code: laughter through the lens of biology, psychology and neuroscience’.

The role of sex and emotion on emotion perception in artificial faces: An ERP study

Sex has a significant impact on the perception of emotional expressions. However, it remains unclear whether sex influences the perception of emotions in artificial faces, which are becoming popular in emotion research. We used an emotion recognition task with FaceGen faces portraying six basic emotions aiming to investigate the effect of sex and emotion on behavioural and electrophysiological parameters. 71 participants performed the task while EEG was recorded. The recognition of sadness was the poorest, however, females recognized sadness better than males. ERP results indicated that fear, disgust, and anger evoked higher amplitudes of late positive potential over the left parietal region compared to neutral expression. Females demonstrated higher values of global field power as compared to males. The interaction between sex and emotion on ERPs was not significant. The results of our study may be valuable for future therapies and research, as it emphasizes possibly distinct processing of emotions and potential sex differences in the recognition of emotional expressions in FaceGen faces.

The Neurobiological Correlates of Gaze Perception in Healthy Individuals and Neurologic Patients

The ability to adaptively follow conspecific eye movements is crucial for establishing shared attention and survival. Indeed, in humans, interacting with the gaze direction of others causes the reflexive orienting of attention and the faster object detection of the signaled spatial location. The behavioral evidence of this phenomenon is called gaze-cueing. Although this effect can be conceived as automatic and reflexive, gaze-cueing is often susceptible to context. In fact, gaze-cueing was shown to interact with other factors that characterize facial stimulus, such as the kind of cue that induces attention orienting (i.e., gaze or non-symbolic cues) or the emotional expression conveyed by the gaze cues. Here, we address neuroimaging evidence, investigating the neural bases of gaze-cueing and the perception of gaze direction and how contextual factors interact with the gaze shift of attention. Evidence from neuroimaging, as well as the fields of non-invasive brain stimulation and neurologic patients, highlights the involvement of the amygdala and the superior temporal lobe (especially the superior temporal sulcus (STS)) in gaze perception. However, in this review, we also emphasized the discrepancies of the attempts to characterize the distinct functional roles of the regions in the processing of gaze. Finally, we conclude by presenting the notion of invariant representation and underline its value as a conceptual framework for the future characterization of the perceptual processing of gaze within the STS.

Sex-specific effects of low-dose hydrocortisone on threat detection in HIV

One sex differences in the perception of emotion is that females, particularly those with high anxiety, often show heightened identification of fearful faces. To better understand the causal role of glucocorticoids in this sex difference, we examine these associations in people with HIV(PWH) where emotion perception is impaired and mental health disorders are frequent. In a double-blind, placebo-controlled, cross-over study, we used a single low-dose of hydrocortisone (10 mg; LDH) as a mechanistic probe of the effects of elevated glucocorticoids on negative emotion perception in 65 PWH (31 women). The primary outcome was accuracy in identifying emotional expressions on the Facial Emotion Perception Test (FEPT). Salivary cortisol, self-reported stress/anxiety, and childhood trauma were also assessed. LDH increased salivary cortisol levels versus placebo. The effect of LDH versus placebo on FEPT accuracy depended on the combined influence of facial expression and sex (P = 0.03). LDH influenced accuracy only for women (P = 0.03), specifically for fearful faces (Cohen's d = 0.44, P = 0.04). Women's enhanced threat detection varied with psychological burden (mood, anxiety, and post-traumatic stress symptoms), more pronounced among those with lower burden and trauma (P < 0.05). This result suggests a role of the HPA axis in sex differences for perception of fearful faces in women with HIV, potentially due to changes in glucocorticoid receptor availability/activity, or improved integration of signals from facial recognition and emotion processing regions. The blunting of this effect in men and in individuals with more severe trauma suggests that the mechanisms underlying threat detection differ by sex and trauma history and warrant further investigation.

Resting EEG in alpha band predicts individual differences in visual size perception

Human visual size perception results from an interaction of external sensory information and internal state. The cognitive mechanisms involved in the processing of context-dependent visual size perception have been found to be innate in nature to some extent, suggesting that visual size perception might correlate with human intrinsic brain activity. Here we recorded human resting alpha activity (8-12 Hz), which is an inverse indicator of sustained alertness. Moreover, we measured an object's perceived size in a two-alternative forced-choice manner and the Ebbinghaus illusion magnitude which is a classic illustration of context-dependent visual size perception. The results showed that alpha activity along the ventral visual pathway, including left V1, right LOC and bilateral inferior temporal gyrus, negatively correlated with an object's perceived size. Moreover, alpha activity in the left superior temporal gyrus positively correlated with size discrimination threshold and size illusion magnitude. The findings provide clear evidence that human visual size perception scales as a function of intrinsic alertness, with higher alertness linking to larger perceived size of objects and better performance in size discrimination and size illusion tasks, and suggest that individual variation in resting-state brain activity provides a neural explanation for individual variation in cognitive performance of normal participants.

Fast saccadic and manual responses to faces presented to the koniocellular visual pathway

The parallel pathways of the human visual system differ in their tuning to luminance, color, and spatial frequency. These attunements recently have been shown to propagate to differential processing of higher-order stimuli, facial threat cues, in the magnocellular (M) and parvocellular (P) pathways, with greater sensitivity to clear and ambiguous threat, respectively. The role of the third, koniocellular (K) pathway in facial threat processing, however, remains unknown. To address this gap in knowledge, we briefly presented peripheral face stimuli psychophysically biased towards M, P, or K pathways. Observers were instructed to report via a key-press whether the face was angry or neutral while their eye movements and manual responses were recorded. We found that short-latency saccades were made more frequently to faces presented in the K channel than to P or M channels. Saccade latencies were not significantly modulated by expressive and identity cues. In contrast, manual response latencies and accuracy were modulated by both pathway biasing and by interactions of facial expression with facial masculinity, such that angry male faces elicited the fastest, and angry female faces, the least accurate, responses. We conclude that face stimuli can evoke fast saccadic and manual responses when projected to the K pathway.

Magnocellular and parvocellular pathway contributions to facial threat cue processing

Human faces evolved to signal emotions, with their meaning contextualized by eye gaze. For instance, a fearful expression paired with averted gaze clearly signals both presence of threat and its probable location. Conversely, direct gaze paired with facial fear leaves the source of the fear-evoking threat ambiguous. Given that visual perception occurs in parallel streams with different processing emphases, our goal was to test a recently developed hypothesis that clear and ambiguous threat cues would differentially engage the magnocellular (M) and parvocellular (P) pathways, respectively. We employed two-tone face images to characterize the neurodynamics evoked by stimuli that were biased toward M or P pathways. Human observers (N = 57) had to identify the expression of fearful or neutral faces with direct or averted gaze while their magnetoencephalogram was recorded. Phase locking between the amygdaloid complex, orbitofrontal cortex (OFC) and fusiform gyrus increased early (0–300 ms) for M-biased clear threat cues (averted-gaze fear) in the β-band (13–30 Hz) while P-biased ambiguous threat cues (direct-gaze fear) evoked increased θ (4–8 Hz) phase locking in connections with OFC of the right hemisphere. We show that M and P pathways are relatively more sensitive toward clear and ambiguous threat processing, respectively, and characterize the neurodynamics underlying emotional face processing in the M and P pathways.

Differential magnocellular versus parvocellular pathway contributions to the combinatorial processing of facial threat

Recently, speed of presentation of facially expressive stimuli was found to influence the processing of compound threat cues (e.g., anger/fear/gaze). For instance, greater amygdala responses were found to clear (e.g., direct gaze anger/averted gaze fear) versus ambiguous (averted gaze anger/direct gaze fear) combinations of threat cues when rapidly presented (33 and 300ms), but greater to ambiguous versus clear threat cues when presented for more sustained durations (1, 1.5, and 2s). A working hypothesis was put forth (Adams et al., 2012) that these effects were due to differential magnocellular versus parvocellular pathways contributions to the rapid versus sustained processing of threat, respectively. To test this possibility directly here, we restricted visual stream processing in the fMRI environment using facially expressive stimuli specifically designed to bias visual input exclusively to the magnocellular versus parvocellular pathways. We found that for magnocellular-biased stimuli, activations were predominantly greater to clear versus ambiguous threat-gaze pairs (on par with that previously found for rapid presentations of threat cues), whereas activations to ambiguous versus clear threat-gaze pairs were greater for parvocellular-biased stimuli (on par with that previously found for sustained presentations). We couch these findings in an adaptive dual process account of threat perception and highlight implications for other dual process models within psychology.

Sex differences in the effects of PARP inhibition on microglial phenotypes following neonatal stroke

Neonatal acute ischemic stroke is a cause of neonatal brain injury that occurs more frequently in males, resulting in associated neurobehavioral disorders. The bases for these sex differences are poorly understood but might include the number, morphology and activation of microglia in the developing brain when subjected to stroke. Interestingly, poly (ADP-ribose) polymerase (PARP) inhibition preferentially protects males against neonatal ischemia. This study aims to examine the effects of PJ34, a PARP inhibitor, on microglial phenotypes at 3 and 8 days and on neurobehavioral disorders in adulthood for both male and female P9 mice subjected to permanent middle cerebral artery occlusion (pMCAo). PJ34 significantly reduced the lesion size by 78% and reduced the density of CX3CR1^gfp-labeled microglial cells by 46% when examined 3 days after pMCAo in male but not in female mice. Eight days after pMCAo, the number of Iba1⁺/Cox-2⁺ cells did not differ between male and female mice in the cortical peri-infarct region. In the amygdala, Iba1⁺/Cox-2⁺ (M1-like) cell numbers were significantly decreased in PJ34-treated males but not in females. Conversely, Iba1⁺/Arg-1⁺ (M2-like) and Arg-1⁺/Cox-2⁺ (Mtransitional) cell numbers were significantly increased in PJ34-treated females. Regarding neurobehavioral disorders during adulthood, pMCAo induced a motor coordination deficit and a spatial learning deficit in female mice only. PJ34 prevented MBP fibers, motor coordination and learning disorders during adulthood in female mice. Our data show significant sex differences in the effects of PARP inhibition on microglia phenotypes following neonatal ischemia, associated with improved behavior and myelination during adulthood in females only. Our findings suggest that modulating microglial phenotypes may play key roles in behavior disorders and white matter injury following neonatal stroke.

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.

Observer's anxiety facilitates magnocellular processing of clear facial threat cues, but impairs parvocellular processing of ambiguous facial threat cues

Facial expression and eye gaze provide a shared signal about threats. While a fear expression with averted gaze clearly points to the source of threat, direct-gaze fear renders the source of threat ambiguous. Separable routes have been proposed to mediate these processes, with preferential attunement of the magnocellular (M) pathway to clear threat, and of the parvocellular (P) pathway to threat ambiguity. Here we investigated how observers’ trait anxiety modulates M- and P-pathway processing of clear and ambiguous threat cues. We scanned subjects (N = 108) widely ranging in trait anxiety while they viewed fearful or neutral faces with averted or directed gaze, with the luminance and color of face stimuli calibrated to selectively engage M- or P-pathways. Higher anxiety facilitated processing of clear threat projected to M-pathway, but impaired perception of ambiguous threat projected to P-pathway. Increased right amygdala reactivity was associated with higher anxiety for M-biased averted-gaze fear, while increased left amygdala reactivity was associated with higher anxiety for P-biased, direct-gaze fear. This lateralization was more pronounced with higher anxiety. Our findings suggest that trait anxiety differentially affects perception of clear (averted-gaze fear) and ambiguous (direct-gaze fear) facial threat cues via selective engagement of M and P pathways and lateralized amygdala reactivity.