What surprises the Mona Lisa? The relative importance of the eyes and eyebrows for detecting surprise in briefly presented face stimuli.

The classification image (CI) technique has been used to derive templates for judgements of facial emotion and reveal which facial features inform specific emotional judgements. For example, this method has been used to show that detecting an up- or down-turned mouth is a primary strategy for discriminating happy versus sad expressions. We explored the detection of surprise using CIs, expecting widened eyes, raised eyebrows, and open mouths to be dominant features. We briefly presented a photograph of a female face with a neutral expression embedded in random visual noise, which modulated the appearance of the face on a trial-by-trial basis. In separate sessions, we showed this face with or without eyebrows to test the importance of the raised eyebrow element of surprise. Noise samples were aggregated into CIs based on participant responses. Results show that the eye-region was most informative for detecting surprise. Unless attention was specifically directed to the mouth, we found no effects in the mouth region. The eye effect was stronger when the eyebrows were absent, but the eyebrow region was not itself informative and people did not infer eyebrows when they were missing. A follow-up study was conducted in which participants rated the emotional valence of the neutral images combined with their associated CIs. This verified that CIs for 'surprise' convey surprised expressions, while also showing that CIs for 'not surprise' convey disgust. We conclude that the eye-region is important for the detection of surprise.

Growth and differentiation factor 15 is secreted by skeletal muscle during exercise and promotes lipolysis in humans.

We hypothesized that skeletal muscle contraction produces a cellular stress signal, triggering adipose tissue lipolysis to sustain fuel availability during exercise. The present study aimed at identifying exercise-regulated myokines, also known as exerkines, able to promote lipolysis. Human primary myotubes from lean healthy volunteers were submitted to electrical pulse stimulation (EPS) to mimic either acute intense or chronic moderate exercise. Conditioned media (CM) experiments with human adipocytes were performed. CM and human plasma samples were analyzed using unbiased proteomic screening and/or ELISA. Real-time qPCR was performed in cultured myotubes and muscle biopsy samples. CM from both acute intense and chronic moderate exercise increased basal lipolysis in human adipocytes. Growth and differentiation factor 15 (GDF15) gene expression and secretion increased rapidly upon skeletal muscle contraction. GDF15 protein was upregulated in CM from both acute and chronic exercise-stimulated myotubes. We further showed that physiological concentrations of recombinant GDF15 protein increased lipolysis in human adipose tissue, while blocking GDF15 with a neutralizing antibody abrogated EPS CM-mediated lipolysis. We herein provide the first evidence to our knowledge that GDF15 is a potentially novel exerkine produced by skeletal muscle contraction and able to target human adipose tissue to promote lipolysis.