Brain activity supporting alternating speech for semantic words: simultaneous magnetoencephalographic recording.

Communication, especially conversation, is essential for human social life. Many previous studies have examined the neuroscientific underpinnings of conversation, i.e. language comprehension and speech production. However, conversation inherently involves two or more people, and unless two people actually interact with one another, the nature of the conversation cannot be truly revealed. Therefore, in this study, we used two magnetoencephalographs that were connected together, and simultaneously recorded brain activity while two people took turns speaking in a word association/alphabet completion task. We compared the amplitude modulation of the alpha- and beta-band rhythms within each of the 62 brain regions under semantic (word association; less predictable) and non-semantic (alphabet completion; more predictable) conditions. We found that the amplitudes of the rhythms were significantly different between conditions in a wide range of brain regions. Additionally, significant differences were observed in nearly the same group of brain regions after versus before each utterance, indicating that a wide range of brain areas is involved in predicting a conversation partner's next utterance. This result supports the idea that mentalizing, e.g. predicting another person's speech, plays an important role in conversation, and suggests that the neural network implicated in mentalizing extends over a wide range of brain regions.

Electrochemical control of bone microstructure on electroactive surfaces for modulation of stem cells and bone tissue engineering.

Controlling stem cell behavior at the material interface is crucial for the development of novel technologies in stem cell biology and regenerative medicine. The composition and presentation of bio-factors on a surface strongly influence the activity of stem cells. Herein, we designed an electroactive surface that mimics the initial process of trabecular bone formation, by immobilizing chondrocyte-derived plasma membrane nanofragments (PMNFs) on its surface for rapid mineralization within 2 days. Moreover, the electroactive surface was based on the conducting polymer polypyrrole (PPy), which enabled dynamic control of the presentation of PMNFs on the surface via electrochemical redox switching, further resulting in the formation of bone minerals with different morphologies. Furthermore, bone minerals with contrasting surface morphologies had differential effects on the differentiation of human bone marrow-derived stem cells (hBMSCs) cultured on the surface. Together, this electroactive surface showed multifunctional characteristics, not only allowing dynamic control of PMNF presentation but also promoting the formation of bone minerals with different morphologies within 2 days. This electroactive substrate could be valuable for more precise control of stem cell growth and differentiation, and further development of more suitable microenvironments containing bone apatite for housing a bone marrow stem cell niche, such as biochips/bone-on-chips.

Important roles of odontoblast membrane phospholipids in early dentin mineralization.

The objective of this study was to first identify the timing and location of early mineralization of mouse first molar, and subsequently, to characterize the nucleation site for mineral formation in dentin from a materials science viewpoint and evaluate the effect of environmental cues (pH) affecting early dentin formation. Early dentin mineralization in mouse first molars began in the buccal central cusp on post-natal day 0 (P0), and was first hypothesized to involve collagen fibers. However, elemental mapping indicated the co-localization of phospholipids with collagen fibers in the early mineralization area. Co-localization of phosphatidylserine and annexin V, a functional protein that binds to plasma membrane phospholipids, indicated that phospholipids in the pre-dentin matrix were derived from the plasma membrane. A 3-dimensional in vitro biomimetic mineralization assay confirmed that phospholipids from the plasma membrane are critical factors initiating mineralization. Additionally, the direct measurement of the tooth germ pH, indicated it to be alkaline. The alkaline environment markedly enhanced the mineralization of cell membrane phospholipids. These results indicate that cell membrane phospholipids are nucleation sites for mineral formation, and could be important materials for bottom-up approaches aiming for rapid and more complex fabrication of dentin-like structures.

Mechanotransductive Mechanisms of Biomimetic Hydrogel Cues Modulating Meckel's Cartilage Degeneration.

Meckel's cartilage, a cartilage rod present in the mandible during developmental stages, shows a unique developmental fate: while the anterior and posterior portions undergo ossification, the middle part degenerates. Previously, it was shown that a stiff environment promoted cartilage degeneration in the middle region, while a soft environment enhanced the mineralization in the anterior region of Meckel's cartilage. This study aims to elucidate the spatio-temporal changes in the mechanosensing properties of Meckel's cartilage during its early developmental stages and clarify the mechanotransduction-related mechanisms involved in its degeneration. The results show that the expression of Hippo pathway effector yes-associated protein (YAP) is only detectable in the Meckel's cartilage onward embryonic day (E)14.5, indicating that mechanosensing is dependent on the tissue developmental stage. Consistently, microenvironmental stiffness-induced cartilage degeneration can only be induced in cartilages onward E14.5, but not in those at earlier developmental stages. Expressions of integrin-ß1 and cartilage matrix-degrading enzymes, matrix metalloproteinase 1 (MMP-1) and MMP-13, are significantly enhanced in the degeneration area. Moreover, verteporfin (YAP inhibitor) and integrin-ß1 antibody block the substrate stiffness-induced degeneration by suppressing the expressions of MMP-1 and MMP-13. These data provide new insights into the interplay between biochemical and mechanical cues determining the fate of Meckel's cartilage.