In This Issue

CO₂ ice crystallization examined under space-like conditions

Amorphous and crystalline CO₂ ice with characteristic infrared spectra.

Carbon dioxide ice has been identified in a variety of astrophysical settings, from the interior of dense interstellar clouds to the envelopes around young stars and on bodies within our own solar system. Although this molecular species has been the focus of increased research due to the potential insights it offers into astrophysical processes, many details about its structure remain unknown. Combining laboratory infrared spectroscopy, theoretical modeling, and real-world astronomical observations, Rafael Escribano et al. (pp. 12899–12904) generated a highly amorphous form of CO₂ ice and studied how it crystallizes both by high-temperature annealing and by slow accumulation of monolayers from the gas phase under an ultrahigh vacuum. Based on their findings, the authors present theoretical models for different CO₂ ice structures and identify a preferred in-plane orientation for certain vibrational modes of crystalline CO₂. In addition, the authors reveal the infrared characteristics of amorphous CO₂ ice, including a key band that dominates the amorphous phase but disappears when the crystallization is complete. The absence of this band in the published spectra of CO₂ ice strongly suggests that pure CO₂ ice in space cannot be completely amorphous, according to the authors. — T.J.

Cantilever-free technique may lead to desktop nanoprinting

Scanning probe lithography (SPL) refers to technologies that combine movable high-resolution probes with various printing techniques to construct nanoscale patterns on surfaces. Although SPL offers a potential means to fabricate devices—such as integrated circuits in a desktop format—the technology is currently limited by its high cost, mechanical fragility, and inflexibility. To address these limitations, Keith Brown et al. (pp. 12921–12924) devised a cantilever-free SPL architecture that can generate molecular features at the 100 nanometer scale using a 2D array of independently actuated probes. Unlike previously reported cantilever-free systems, in which each probe can only reproduce a single, preassigned pattern, the authors’ technique uses local heating to thermally expand an elastomeric film and actuate individual probes, creating what is in effect a nanoscale-resolution dot-matrix printer. According to the authors, the approach is both simple and scalable and can be tuned to compensate for the unavoidable imperfections that arise in real-world applications, a fundamental drawback of current SPL systems. The findings demonstrate that cantilever-free printing can produce arbitrary, high-resolution patterns, and the authors suggest that the technique could lead to desktop SPL fabrication. — T.J.

Effects of televised advertisements on drug efficacy

Drug advertisements and efficacy.

The placebo effect allows patients to achieve therapeutic benefits merely through the mistaken belief that an administered treatment contains an active drug. To determine whether exposure to direct-to-consumer drug advertisements can influence the drugs’ efficacy, Emir Kamenica et al. (pp. 12931–12935) conducted a trial of 340 healthy individuals, divided into two similarly sized groups depending on whether or not they exhibited an allergic response to at least one of several common allergens, such as grass, dust mites, and ragweed. The volunteers were asked about their preexisting beliefs about the efficacy of Claritin, a widely used allergy drug, and then administered a skin injection of histamine, which induces an allergic reaction, followed by 10 mg of Claritin. The authors then showed half the volunteers in each group a televised feature film with natural advertisement breaks containing advertisements that showed Claritin in a positive light; the rest of the volunteers viewed the same film with advertisements claiming that a competing drug, Zyrtec, was more effective than Claritin. At various times during the film, the authors measured the volunteers’ response to the histamine injection through a skin test. The authors report that, among the volunteers who did not have common allergies, exposure to Claritin—rather than Zyrtec—advertisements increased not only the volunteers’ perceptions of Claritin’s efficacy but also the efficacy of Claritin in reducing the allergic response to histamine. According to the authors, advertisements might affect the physiological efficacy of drugs among individuals whose beliefs about the drugs are relatively malleable. — P.N.

Tracing the origin of the mammalian neocortex

To uncover the evolutionary origin of the mammalian brain’s outer layer, known as the neocortex, researchers have long attempted to identify the layer’s counterparts in birds and reptiles, but the precise developmental source of the mammalian neocortex remains unclear. T. Grant Belgard et al. (pp. 13150–13155) performed comparative gene expression analysis to obtain expression profiles of 5,130 highly transcribed genes in a set of structures in the adult mouse and chicken brain that develop from one of four sectors of the pallium, the dorsal portion of a brain region known as the telencephalon. The authors report that structures that share a developmental origin but show functional divergence between birds and mammals did not exhibit greater similarity in transcription profiles than developmentally unrelated but functionally equivalent structures. However, regions such as the striatum and hippocampus, which share homology and function between birds and mammals, displayed conservation among groups of coexpressed genes. The authors suggest that the findings enable a molecular understanding of the development of specialized mammalian and avian brain regions. According to the authors, future studies of the evolution of the neocortex must include both gene expression data and homology studies based on cell lineages to uncover how molecular mechanisms were repurposed for neocortical evolution in mammals. — P.N.

Bottlenose dolphins use signature whistles to “name” individuals

Bottlenose dolphin leaping in the North Sea.

Among animals that develop distinctive calls by copying sounds in their environments, parrots and dolphins stand out because of their ability to use learned signals to label objects under experimental conditions. To determine whether this ability is part of the natural communication system of bottlenose dolphins, Stephanie King and Vincent Janik (pp. 13216–13221) tested whether the dolphins use signature whistles—voice-independent calls unique to individuals and exchanged when the animals meet at sea—to address individuals. The authors followed a population of wild, free-ranging dolphins off the east coast of Scotland, and monitored their responses to different whistles. The researchers either played back a synthetic version of a dolphin’s own recorded signature whistle, played the whistles of familiar dolphins from the same population or of unfamiliar dolphins from a different population. Wild bottlenose dolphins responded to their own signature whistles by calling back, but did not respond to the other whistles. The authors suggest that dolphins might use signature whistles as labels to address or contact individuals of the same species, and their use of identity signals mirrors the human convention of naming individuals, a practice long believed to be a human prerogative in the animal kingdom. According to the authors, the results demonstrate that bottlenose dolphins are the only known nonhuman mammals capable of using labels to address social companions during natural communication. — P.N.

Gray matter changes may predict autism severity in adults

Intrinsic wiring costs of the brain.

The neural changes that occur in people with autism spectrum disorder (ASD) have eluded researchers for years. Neuroimaging studies have revealed abnormal connections within the white matter of people with ASD, but how neural wiring is affected within the cortex, a sheet of gray matter that covers the brain and influences conscious thought, memory, language, and other functions, remains unclear. Christine Ecker et al. (pp. 13222–13227) explored how the length of connections required to wire the cortex—known as the wiring cost—differs in people with ASD compared with the general population. The authors performed MRI scans on 68 adults with and without ASD, and found that wiring costs were much lower in people with ASD than those without, particularly in the frontotemporal regions of the brain. Differences in wiring costs reflected the severity of social and repetitive symptoms in adults with ASD, the authors report. According to the authors, the findings suggest that differences in connectivity exist in both the white and gray matter of the brain in people with ASD, providing a basis for the core set of neural changes that underlie the symptoms of autism.— A.G.