This Week in PNAS
ENGINEERING
Human-like artificial robot skin
Takao Someya et al. report the development of a flexible, electronic skin capable of detecting both pressure and temperature, an advance that may provide robots with a human-like sense of touch. The research team previously developed artificial skin that could sense pressure but lacked the elasticity and other characteristics of human skin. To improve the artificial skin material, Someya et al. embedded organic transistor-based electronic circuits capable of sensing pressure into a thin plastic film, as well as organic semiconductors that could detect temperature. The net-like matrix was flexible enough to conform to the surface of an egg and could detect pressure and temperature simultaneously. According to the authors, the organic transistors used in the artificial skin are inexpensive and relatively easy to fabricate, and could thus be used in manufacturing robot skin and other commercial products. — M.M.
Pressure sensor matrix on egg.
“Conformable, flexible, large-area networks of pressure and thermal sensors with organic transistor active matrixes” by Takao Someya, Yusaku Kato, Tsuyoshi Sekitani, Shingo Iba, Yoshiaki Noguchi, Yousuke Murase, Hiroshi Kawaguchi, and Takayasu Sakurai (see pages 12321–12325)
DEVELOPMENTAL BIOLOGY
MicroRNAs direct development of taste neurons
Robert Johnston et al. have elucidated the pathway directing the development of the taste receptor neurons ASE left (ASEL) and ASE right (ASER) in the roundworm Caenorhabditis elegans. These neurons each express a distinct array of chemoreceptors essential for C. elegans to navigate complex sensory environments. Both ASEL and ASER arise from identical precursors capable of executing either the ASEL or ASER cell fate. To tease apart the cell fate decisions, Johnston et al. used class I mutants that route both ASE neurons toward the ASEL cell fate, and class II mutants that promote the development of two ASER neurons. These alternative cell fates were shown to be controlled by two microRNAs: lsy-6 and mir-273. Lsy-6 promoted ASEL fate by inhibiting mir-273. Conversely, mir-273 promoted ASER fate by inhibiting lsy-6. The researchers demonstrate that these two microRNAs function in a double-negative feedback loop in which they regulate themselves and each other. — B.T.
Class II lsy-6 mutant neurons initially express both ASEL (red) and ASER (blue) markers.
“MicroRNAs acting in a double-negative feedback loop to control a neuronal cell fate decision” by Robert J. Johnston, Jr., Sarah Chang, John F. Etchberger, Christopher O. Ortiz, and Oliver Hobert (see pages 12449–12454)
ANTHROPOLOGY
Evidence of ancient Chinese salt production
Rowan Flad et al. combined archeological and chemical evidence to demonstrate that significant salt production occurred during the first millennium B.P. at Zhongba, an archeological site lying along the Yangzi River in central China. Large-scale salt production and trade are thought to be critical in the development of complex civilizations, yet no conclusive evidence exists of salt production during the emergence of early Chinese states. Chemical compositions of the soil and nearby brine were found to be similar to other production facilities. Likewise, the form and composition of various ceramics were similar to salt production pottery (briquetage) from other regions of the world. X-ray diffraction analysis of debris residues revealed high levels of calcium oxide, which is used to treat solvable impurities in the brine. Flad et al. also found trace amounts of sodium and chlorine on the interiors of some of the suspected briquetage. The authors conclude that salt production at this site was established well before the start of China's Imperial Era in the 3rd century B.P. — N.Z.
Archaeological site mound in middle of Ganjing River, China.
“Archaeological and chemical evidence for early salt production in China” by Rowan Flad, Jiping Zhu, Changsui Wang, Pochan Chen, Lothar von Falkenhausen, Zhibin Sun, and Shuicheng Li (see pages 12618–12622)
ENVIRONMENTAL SCIENCES
Higher crop yields by Zimbabwean farmers from El Niño forecasts
Anthony Patt et al. report that subsistence farmers in Zimbabwe used seasonal climate forecasts over several years to make different planting decisions, leading to significantly higher harvest yields. Zimbabwe's climate is strongly influenced by El Niño, and its government is currently developing seasonal rainfall forecasts for farmers, aided by improvements in El Niño modeling. To assess the benefit of these forecasts, Patt et al. held annual participatory forecast workshops with a sample of Zimbabwean farmers (≈50 in each of four villages). In addition to being told the probabilities for a normal, rainy, or dry growing season, participants could ask questions about El Niño and forecast development, compare forecasts with traditional indicators, and discuss planting decisions. About 50% of the farmers were found to use weather forecasts to change the timing or type of crops, and workshop participants were more likely to use such information compared with farmers who heard forecasts through other sources. Relative to their historical range of harvests, the farmers' crop yields increased significantly with use of forecast information. Yields increased by 9.4% in the first 2 years of the study and by 18.7% in the second season alone. — R.N.
Map of Zimbabwe showing farming regions and study sites.
“Effects of seasonal climate forecasts and participatory workshops among subsistence farmers in Zimbabwe” by Anthony Patt, Pablo Suarez, and Chiedza Gwata (see pages 12623–12628)
PSYCHOLOGY
Cultural music discrimination in infants and adults
Erin Hannon and Sandra Trehub report that, by 12 months of age, children lose their ability to hear subtle rhythmic variations in foreign music but, unlike adults, regain this ability through limited exposure to such music. Experiences in the first year of life may fine-tune the ability to recognize and respond to species-specific information for communication and survival, such as speech or face recognition. Hannon and Trehub investigated the effects of experience-dependent tuning on responses to musical patterns. Western 12-month-old infants not previously exposed to non-Western, Balkan (Bulgarian and Macedonian) music recognized small structural disruptions in classically Western (isochronous) rhythms, but not in the Balkan (nonisochronous) rhythms. However, with brief, daily exposure to Balkan folk music over 2 weeks, the infants' differentiation of nonisochronous meter variations was as strong as that for isochronous meters. On the other hand, adults similarly instructed to listen daily to Balkan folk music failed to distinguish nonisochronous rhythmic structures. The findings may indicate a sensitive period early in life for acquiring rhythm, or more generally may suggest the existence of socially and biologically important structures for processing information. — R.N.
Nonisochronous (Balkan) music meter familiarization.
“Tuning in to musical rhythms: Infants learn more readily than adults” by Erin E. Hannon and Sandra E. Trehub (see pages 12639–12643)
