Emotional Facial Expression Detection in the Peripheral Visual Field

BACKGROUND: In everyday life, signals of danger, such as aversive facial expressions, usually appear in the peripheral visual field. Although facial expression processing in central vision has been extensively studied, this processing in peripheral vision has been poorly studied. METHODOLOGY/PRINCIPAL FINDINGS: Using behavioral measures, we explored the human ability to detect fear and disgust vs. neutral expressions and compared it to the ability to discriminate between genders at eccentricities up to 40°. Responses were faster for the detection of emotion compared to gender. Emotion was detected from fearful faces up to 40° of eccentricity. CONCLUSIONS: Our results demonstrate the human ability to detect facial expressions presented in the far periphery up to 40° of eccentricity. The increasing advantage of emotion compared to gender processing with increasing eccentricity might reflect a major implication of the magnocellular visual pathway in facial expression processing. This advantage may suggest that emotion detection, relative to gender identification, is less impacted by visual acuity and within-face crowding in the periphery. These results are consistent with specific and automatic processing of danger-related information, which may drive attention to those messages and allow for a fast behavioral reaction

Organization of pioneer retinal axons within the optic tract of the rhesus monkey.

Retinal ganglion cell axons must make a decision at the embryonic optic chiasm to grow into the appropriate optic tract. To gain insight into the cues that play a role in sorting out the crossed from the uncrossed optic axons, we investigated the sequence of their initial ingrowth in rhesus monkey embryos. Two carbocyanine dyes, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate and 4-(4-dihexadecylaminostyryl)-N-methylpyridinium iodide, were placed, respectively, into the left and right retinas to identify the course of uncrossed and crossed retinal axons through the optic chiasm and tract. Our results show that at embryonic day 36 the most advanced retinal projections are uncrossed. At this age the leading crossed axons are just reaching the chiasmatic midline, whereas the uncrossed fibers have already entered the optic tract. This indicates that the pathfinding of these pioneer uncrossed fibers does not require the presence of retinal axons from the opposite eye. At subsequent stages of development (embryonic days 40 and 42) there is a clear partial segregation of the uncrossed and crossed retinal axons within the optic tract: the uncrossed-component course is in the deeper portion of the optic tract, whereas the crossed component lies in a more superficial region. Thus, the spatial organization of retinal axons within the primordial optic tract reflects the sequential addition of the uncrossed and crossed retinal fibers. The orderly and sequential ingrowth of these pioneer retinal axons indicates that specific chiasmatic cues are expressed early in development and that such pioneer fibers may serve as guides for the later-arriving retinal fibers

Early divergence of magnocellular and parvocellular functional subsystems in the embryonic primate visual system

In both human and Old World primates visual information is conveyed by two parallel pathways: the magnocellular (M) and parvocellular (P) streams that project to separate layers of the lateral geniculate nucleus and are involved primarily in motion and color/form discrimination. The present study provides evidence that retinal ganglion cells in the macaque monkey embryo diverge into M and P subtypes soon after their last mitotic division and that optic axons project directly and selectively to either the M or P moieties of the developing lateral geniculate nucleus. Thus, initial M projections from the eyes overlap only in prospective layers 1 and 2, whereas initial P projections overlap within prospective layers 3-6. We suggest that the divergence of the M and P pathways requires developmental mechanisms different from those underlying competition-driven segregation of initially intermixed eye-specific domains in the primate visual system

A critical role for VEGF and VEGFR2 in NMDA receptor synaptic function and fear-related behavior

Vascular endothelial growth factor (VEGF) is known to be required for the action of antidepressant therapies but its impact on brain synaptic function is poorly characterized. Using a combination of electrophysiological, single-molecule imaging and conditional transgenic approaches, we identified the molecular basis of the VEGF effect on synaptic transmission and plasticity. VEGF increases the postsynaptic responses mediated by the N-methyl-d-aspartate type of glutamate receptors (GluNRs) in hippocampal neurons. This is concurrent with the formation of new synapses and with the synaptic recruitment of GluNR expressing the GluN2B subunit (GluNR-2B). VEGF induces a rapid redistribution of GluNR-2B at synaptic sites by increasing the surface dynamics of these receptors within the membrane. Consistently, silencing the expression of the VEGF receptor 2 (VEGFR2) in neural cells impairs hippocampal-dependent synaptic plasticity and consolidation of emotional memory. These findings demonstrated the direct implication of VEGF signaling in neurons via VEGFR2 in proper synaptic function. They highlight the potential of VEGF as a key regulator of GluNR synaptic function and suggest a role for VEGF in new therapeutic approaches targeting GluNR in depression