Face cells in orbitofrontal cortex represent social categories.

Perceiving social and emotional information from faces is a critical primate skill. For this purpose, primates evolved dedicated cortical architecture, especially in occipitotemporal areas, utilizing face-selective cells. Less understood face-selective neurons are present in the orbitofrontal cortex (OFC) and are our object of study. We examined 179 face-selective cells in the lateral sulcus of the OFC by characterizing their responses to a rich set of photographs of conspecific faces varying in age, gender, and facial expression. Principal component analysis and unsupervised cluster analysis of stimulus space both revealed that face cells encode face dimensions for social categories and emotions. Categories represented strongly were facial expressions (grin and threat versus lip smack), juvenile, and female monkeys. Cluster analyses of a control population of nearby cells lacking face selectivity did not categorize face stimuli in a meaningful way, suggesting that only face-selective cells directly support face categorization in OFC. Time course analyses of face cell activity from stimulus onset showed that faces were discriminated from nonfaces early, followed by within-face categorization for social and emotion content (i.e., young and facial expression). Face cells revealed no response to acoustic stimuli such as vocalizations and were poorly modulated by vocalizations added to faces. Neuronal responses remained stable when paired with positive or negative reinforcement, implying that face cells encode social information but not learned reward value associated to faces. Overall, our results shed light on a substantial role of the OFC in the characterizations of facial information bearing on social and emotional behavior.

Sympathy for the underdog: people are inclined to adopt the emotional perspective of powerless (versus powerful) others.

Upon learning of the story of Cinderella, most people spontaneously adopt the emotional perspective of this helpless young woman rather than of her older sisters who oppress her. The present research examines whether this pattern reveals a general human tendency to empathise more with the emotions of individuals with low (versus high) power. Six experiments (N = 878) examined how power influences the focus of people's emotional attributions. Participants were presented with situations in which one character exercised power over another one and had to resolve a referential ambiguity by considering the perspective of one or the other character. Results show that participants largely privileged the emotional states of the low-power character over those of the high-power character. This effect was observed with different types of stimuli (comics and video clips), with high- and low-power roles attributed to pairs of different genders (Experiments 1-4) or same gender (Experiments 5-6). Finally, the tendency persisted - though it was reduced - when participants adopted a less passive role with respect to the characters (Experiment 3) and when power occurred in a less despotic way (Experiment 6). Results are discussed with respect to social attention and sensitivity to fairness.

Implicit preference for human trustworthy faces in macaque monkeys.

It has been shown that human judgements of trustworthiness are based on subtle processing of specific facial features. However, it is not known if this ability is a specifically human function, or whether it is shared among primates. Here we report that macaque monkeys (Macaca Mulatta and Macaca Fascicularis), like humans, display a preferential attention to trustworthiness-associated facial cues in computer-generated human faces. Monkeys looked significantly longer at faces categorized a priori as trustworthy compared to untrustworthy. In addition, spatial sequential analysis of monkeys' initial saccades revealed an upward shift with attention moving to the eye region for trustworthy faces while no change was observed for the untrustworthy ones. Finally, we found significant correlations between facial width-to-height ratio- a morphometric feature that predicts trustworthiness' judgments in humans - and looking time in both species. These findings suggest the presence of common mechanisms among primates for first impression of trustworthiness.

Subthalamic nucleus electrical stimulation modulates calcium activity of nigral astrocytes.

BACKGROUND: The substantia nigra pars reticulata (SNr) is a major output nucleus of the basal ganglia, delivering inhibitory efferents to the relay nuclei of the thalamus. Pathological hyperactivity of SNr neurons is known to be responsible for some motor disorders e.g. in Parkinson's disease. One way to restore this pathological activity is to electrically stimulate one of the SNr input, the excitatory subthalamic nucleus (STN), which has emerged as an effective treatment for parkinsonian patients. The neuronal network and signal processing of the basal ganglia are well known but, paradoxically, the role of astrocytes in the regulation of SNr activity has never been studied. PRINCIPAL FINDINGS: In this work, we developed a rat brain slice model to study the influence of spontaneous and induced excitability of afferent nuclei on SNr astrocytes calcium activity. Astrocytes represent the main cellular population in the SNr and display spontaneous calcium activities in basal conditions. Half of this activity is autonomous (i.e. independent of synaptic activity) while the other half is dependent on spontaneous glutamate and GABA release, probably controlled by the pace-maker activity of the pallido-nigral and subthalamo-nigral loops. Modification of the activity of the loops by STN electrical stimulation disrupted this astrocytic calcium excitability through an increase of glutamate and GABA releases. Astrocytic AMPA, mGlu and GABA(A) receptors were involved in this effect. SIGNIFICANCE: Astrocytes are now viewed as active components of neural networks but their role depends on the brain structure concerned. In the SNr, evoked activity prevails and autonomous calcium activity is lower than in the cortex or hippocampus. Our data therefore reflect a specific role of SNr astrocytes in sensing the STN-GPe-SNr loops activity and suggest that SNr astrocytes could potentially feedback on SNr neuronal activity. These findings have major implications given the position of SNr in the basal ganglia network.