The impact of letter spacing on reading: a test of the bigram coding hypothesis

Identifying letters and their relative positions is the basis of reading in literate adults. The Local Combinations Detector model hypothesizes that this ability results from the general organization of the visual system, whereby object encoding proceeds through a hierarchy of neural detectors that, in the case of reading, would be tuned to letters, bigrams, or other letter combinations. Given the increase of receptive fields by a factor of 2 to 3 from one neural level to the next, detectors should integrate information only for letters separated by at most 2 other characters. We test this prediction by measuring the impact of letter spacing on reading, purifying this effect from confounding variables. We establish that performance deteriorates non-linearly whenever letters are separated by at least 2 blank spaces, with the concomitant emergence of a word length effect. We then show that this cannot be reduced to an effect of physical size nor of visual eccentricity. Finally, we demonstrate that the threshold of about 2 spaces is constant across variations in font size. Those results support the hypothesis that the fast recognition of combinations of nearby letters plays a central role in the coding of words, such that interfering with this representation prevents the parallel analysis of letter strings.

Spectrin mediates 3D-specific matrix stress-relaxation response in neural stem cell lineage commitment

While extracellular matrix (ECM) stress relaxation is increasingly appreciated to regulate stem cell fate commitment and other behaviors, much remains unknown about how cells process stress-relaxation cues in tissue-like three-dimensional (3D) geometries versus traditional 2D cell culture. Here, we develop an oligonucleotide-crosslinked hyaluronic acid-based ECM platform with tunable stress relaxation properties capable of use in either 2D or 3D. Strikingly, stress relaxation favors neural stem cell (NSC) neurogenesis in 3D but suppresses it in 2D. RNA sequencing and functional studies implicate the membrane-associated protein spectrin as a key 3D-specific transducer of stress-relaxation cues. Confining stress drives spectrin's recruitment to the F-actin cytoskeleton, where it mechanically reinforces the cortex and potentiates mechanotransductive signaling. Increased spectrin expression is also accompanied by increased expression of the transcription factor EGR1, which we previously showed mediates NSC stiffness-dependent lineage commitment in 3D. Our work highlights spectrin as an important molecular sensor and transducer of 3D stress-relaxation cues.

Optimization of Intercropping Modes in Placodon grandiflorus

Intercropping enhances plant growth, increases yield, and boosts the accumulation of secondary metabolites. Platycodon grandiflorus (P. grandiflorus), a traditional Chinese medicinal herb, has limited research available regarding its intercropping practices. We aimed to (1) examine the changes in the physiological and biochemical indicators of plant growth during the intercropping process of P. grandiflorus, (2) assess the quality of P. grandiflorus when intercropped with different crops, and (3) evaluate the optimal intercropping mode for P. grandiflorus. This study utilized the two-year seedlings of P. grandiflorus as the test material in a field study. The intercropping treatments included P. grandiflorus monoculture (JG-JG), intercropping with Achyranthes bidentata (JG-NX), Saposhnikovia divaricata (JG-FF), Adenophora stricta (JG-SS), Zea mays (JG-YM), Setaria italica (JG-GZ), and Glycine max (JG-DD). We investigated the effects of these different intercropping modes on the growth, physiological and biochemical indicators, and the accumulation of five saponins in P. grandiflorus at various growth and development stages. Compared with JG-JG, the chlorophyll and the MDA contents significantly increased and decreased, respectively, in the JG-YM, JG-DD, and JG-NX treatments. All the three treatments enhanced the biomass and exhibited the higher levels of antioxidant enzyme activity and osmoregulatory substance content. JG-YM and JG-SS significantly (p < 0.05) improved the quality of P. grandiflorus, with JG-SS intercropping notably maintaining a high content of platycodin D. The results of this study provide a scientific basis for optimizing intercropping planting systems and advancing the sustainable development of the traditional Chinese medicine industry.

Long-term follow-up of resection of primary benign right ventricular tumours: a 10-year surgical experience

INTRODUCTION

Primary benign right ventricular tumours are rare. They can cause significant mortality without appropriate and timely treatment. We investigated surgical treatment and survival characteristics for right ventricular tumours.

MATERIALS AND METHODS

From 2007 to 2017, 21 patients with primary benign right ventricular tumours who underwent tumour resection were retrospectively reviewed. Clinical findings and follow-up results were analysed.

RESULTS

Thirteen men and eight women were enrolled, with a mean age of 42.3 ± 15.3 years. The most frequent histotypes were myxoma, haemangioma and papillary fibroelastoma. Eight patients underwent concomitant tricuspid valvuloplasty and one had tricuspid valve replacement. No major adverse events or death occurred during the perioperative period. One patient with haemangioma underwent partial tumour resection; however, the tumour regressed gradually during follow-up. Within the 10-year follow-up period (mean 4.8 ± 2.6 years), the recurrence-free and overall survival rates were 81.0% and 85.7%, respectively.

CONCLUSIONS

Tumour resection for primary benign right ventricular tumours is safe and effective, and has a good prognosis. Tricuspid valvuloplasty or tricuspid valve replacement may be necessary for the resection of right ventricular tumours to improve the haemodynamics. Haemangiomas naturally undergo spontaneous regression.

Substrate stress relaxation regulates neural stem cell fate commitment

Adult neural stem cells (NSCs) reside in the dentate gyrus of the hippocampus, and their capacity to generate neurons and glia plays a role in learning and memory. In addition, neurodegenerative diseases are known to be caused by a loss of neurons and glial cells, resulting in a need to better understand stem cell fate commitment processes. We previously showed that NSC fate commitment toward a neuronal or glial lineage is strongly influenced by extracellular matrix stiffness, a property of elastic materials. However, tissues in vivo are not purely elastic and have varying degrees of viscous character. Relatively little is known about how the viscoelastic properties of the substrate impact NSC fate commitment. Here, we introduce a polyacrylamide-based cell culture platform that incorporates mismatched DNA oligonucleotide-based cross-links as well as covalent cross-links. This platform allows for tunable viscous stress relaxation properties via variation in the number of mismatched base pairs. We find that NSCs exhibit increased astrocytic differentiation as the degree of stress relaxation is increased. Furthermore, culturing NSCs on increasingly stress-relaxing substrates impacts cytoskeletal dynamics by decreasing intracellular actin flow rates and stimulating cyclic activation of the mechanosensitive protein RhoA. Additionally, inhibition of motor-clutch model components such as myosin II and focal adhesion kinase partially or completely reverts cells to lineage distributions observed on elastic substrates. Collectively, our results introduce a unique system for controlling matrix stress relaxation properties and offer insight into how NSCs integrate viscoelastic cues to direct fate commitment.