Week in Review: Number 26

A Group of Cells in the Brain's Temporal Pole Specializes in Recognizing Familiar Faces
The fabled "grandmother neuron," a neuron that in itself encodes the recognition of an individual person—such as one's grandmother or a celebrity—is a theoretical concept at the culmination of visual processing from the retina to the brain, including input from memory and emotions. While such a singular neuron remains hypothetical, researchers have discovered a group of "hybrid" neurons in the brain’s temporal pole (TP) region that represents the connection between the sensory and memory domains. These neurons behave like sensory cells in the sense that they have reliable and fast responses to visual stimuli, while at the same time responding only to stimuli that the brain has seen previously, much like memory cells. Earlier research by the investigators localized a small region in the anterior temporal cortex of the brain as involved in facial recognition. In the new experiments, they explored this region with fMRI in two Rhesus macaques as the monkeys watched familiar and unfamiliar faces. The researchers found that the neurons in the TP region were fast, immediately discriminating between familiar faces seen in-person and unfamiliar faces seen virtually. Furthermore, these neurons were highly selective, responding threefold more strongly to the familiar faces than to the unfamiliar faces. Interestingly, because the unfamiliar faces were presented virtually compared to the familiar faces having been seen in-person, the researchers hypothesized about the brain's preference for in-person recognition. The first author of the study comments, “Given the tendency nowadays to go virtual, it is important to note that faces that we have seen on a screen may not evoke the same neuronal activity as faces that we meet in-person.” While this population or "collective" of neurons is more accurately described as a "grandmother face area" of the brain rather than the still elusive face-specific grandmother neuron, their discovery is a step forward in investigating how brain cells encode facial recognition. The findings could also one day inform clinical strategies to help people suffering from prosopagnosia or face blindness.

Scintillating Starburst Optical Illusion
Comprised of concentric star polygons that induce illusory ray patterns, "scintillating starbursts" are a newly studied type of optical illusion that highlights the subjective, constructive nature of visual perception. Originally created as a logo for his design company, Recursia Studios, the artist behind scintillating starbursts then teamed up with a psychology researcher and data scientist to conduct a study on the mechanisms underlying the effect. Their study involved 122 participants who viewed 162 different versions of the scintillating starburst varying in shape, complexity, and brightness. The results showed that factors such as contrast, line width, and number of vertices influenced how strongly the rays were perceived. The authors argue that scintillating starbursts are a new optical illusion, distinct from grid illusions such as the scintillating grid, Hermann grid, Motokawa grid, and pincushion grid illusions. One of the authors explains, "[T]he rays are stronger and more striking and at the same time fleeting or scintillating, traversing the background." They suggest instead that scintillating starburst is a compound illusion, combining the perception of short Motokowa line segments that serve as guideposts for the illusory rays with a scintillating effect from saccadic eye movements that alternate between peripheral and foveal vision, with the effect being more pronounced to peripheral vision. The effect is further enhanced when rotating. The researchers also note that the illusion is an effect of luminance rather than of chromaticity (color). One of the authors explains, "If the background is brighter than the shape, the illusory rays will appear brighter than the background. If the background is darker than the shape, the illusory rays will appear darker than the background. If background and shape are isoluminant [regardless of color], no rays appear." While a technical study of optical illusions might seem extraneous, it reveals the subjective and constructive nature of visual perception. The existence and effectiveness of optical illusions challenges the belief that what we see always corresponds with reality. One of the authors states that a future direction could be studying the propensity to see optical illusions with personality characteristics.

A Synthetic Norrin/Wnt Antibody Restores Blood-Retina Barrier in Diabetic Retinopathy
A team of researchers at University of Toronto are developing a new antibody as a potential treatment for diabetic retinopathy and other diseases caused by defects in the blood-retina barrier. Specifically, the researchers studied the Norrin/Wnt cell signalling pathway, which is crucial for the formation and maintenance of the blood-retina barrier. When this signalling pathway is disrupted, such as in diabetic retinopathy, the blood vessels become leaky, compromising the blood-retina barrier. The current publication describes how a synthetic antibody (F4L5.13) activating the Frizzled4-LRP5 receptor complex successfully stimulated Norrin/Wnt signalling to restore barrier function. This antibody activates the Norrin/Wnt pathway by attaching to two key cell surface receptors (Frizzled4 and LRP5) and bringing them into close proximity. The researchers have thus far tested their antibody in cell cultures and in two mouse models, one representing a genetic eye condition (for Norrie disease) and one for diabetic retinopathy. In the cell culture model, the antibody restored barrier function "in part by promoting surface expression of junction proteins." Treatment of the antibody in mice restored barrier function and "significantly normalized neovascularization in an oxygen-induced retinopathy." The investigators have founded a start-up company to proceed with translation of their work to clinical studies. One century ago in 1921, researchers at University of Toronto developed insulin, the life-saving medication to treat diabetes. It is especially fitting, therefore, that U of T researchers continue that legacy, in this case to develop a drug therapy for a common ocular complication of diabetes. Because of similarities between the blood-retina and blood-brain barriers, they also plan to extend their research to other contexts.

Metabolic Responses to LED and OLED Light at Night
Exposure to blue light has various effects on human health, such as in the regulation of circadian rhythm. Researchers in Japan wanted to explore the effect of blue light on physiological processes such as metabolism during sleep. In particular, they compared polychromatic white LEDs (light-emitting diodes) and polychromatic white OLEDs (organic light-emitting diodes). LEDs have been widely adopted for their energy-saving advantages. However, polychromatic white LEDs also emit more blue light compared to polychromatic white OLEDs, sparking curiosity as to their potential effects on health. The study involved ten male participants exposed to LED, OLED (1000 lux), or dim (< 10 lux) light for 4 hours before sleep in a metabolic chamber. The researchers then measured energy expenditure, core body temperature, fat oxidation, and 6-sulfatoxymelatonin (melatonin) levels during sleep. The study's senior author reports, "Although no effect on sleep architecture was observed, energy expenditure and core body temperature during sleep were significantly decreased after OLED exposure. Furthermore, fat oxidation during sleep was significantly lower after exposure to LED compared with OLED." The results also showed a weak but significant correlation between 6-sulfatoxymelatonin levels and fat oxidation under OLED lighting. The sample size of ten male participants is extremely small and homogeneous. Nonetheless, given that some differences in metabolic responses were observed among different artificial lighting conditions, connections between artificial lighting and metabolism could be further explored in larger studies.

Illusory Faces Elicit Similar Responses as Real Faces
Face pareidolia, the perception of illusory faces in inanimate objects, lies at the intersection between optical illusions and facial recognition. Although technically an error in visual processing, the ability to quickly perceive faces with a crude template of two eyes, a nose, and a mouth—and the emotions they express—is an evolutionary benefit for judging friend or foe, a side effect that is so common that we simply accept it as normal. Neuroscientists in Australia wanted to study the psychology behind the phenomenon, especially as it pertains to the perception of emotions. “We know these objects are not truly faces, yet the perception of a face lingers,” the first author of the study explained, “We end up with something strange: a parallel experience that it is both a compelling face and an object. Two things at once. The first impression of a face does not give way to the second perception of an object.” Their study asked 17 participants to view sequences of dozens of real and illusory faces and rate the perceived emotion on a scale from happy to angry. The results showed that perception of facial expression was consistent across observers, despite variations in visual features. Secondly, the expression on prior faces influenced the perception of subsequent faces. For example, seeing happy faces caused the viewer to more likely perceive the next face as happier. Lastly, this bias was observed even when the real faces and illusory faces were interleaved in the sequence. Such a "cross-over" condition revealed that rather than being discarded as false detections, analysis of facial expression applied to the illusory faces in the same way as for real faces. The lead researcher concluded, “When objects look compellingly face-like, it is more than an interpretation: they really are driving your brain’s face detection network. And that scowl, or smile; that’s your brain’s facial expression system at work. For the brain, fake or real, faces are all processed the same way.”

In Other News
(1) Art: Optical illusion with a message about conservation
(2) Research project aims to use fluorescein video-angiogram to measure diabetic retinopathy
(3) Patients enrolled in clinical trials for presbyopia-correcting contact lenses