Altered white-matter architecture in treatment-naive adolescents with clinical depression.

BACKGROUND: Depressive disorders are highly prevalent in adolescence and confer a heightened risk of recurrence in adulthood. Insight into the developmental neurocircuitry of depression could advance our understanding of depression and aid the development of effective treatment strategies. Whereas white-matter (WM) abnormalities are strongly implicated in adult depression, we still lack a firm understanding of WM architecture in adolescent depression. Using diffusion tensor imaging (DTI), we set out to investigate WM microstructure in a sample of clinically depressed adolescents relative to matched controls. METHOD: We employed tract-based spatial statistics (TBSS) to examine WM microstructure in 25 treatment-naive adolescents with clinical depression relative to 21 matched controls. Using TBSS, we examined fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD) and mean diffusivity (MD). Threshold-free cluster enhancement (TFCE) with family-wise error (FWE) correction was used to control for multiple comparisons. RESULTS: Our analysis revealed abnormal WM microstructure in clinically depressed adolescents. More specifically, whole-brain analysis revealed that patients had lower FA values in the body of the corpus callosum (CC), coupled with elevated RD and MD, and preserved AD. Conversely, region-of-interest analysis revealed that patients had higher FA values in the uncinate fasciculus (UF), coupled with elevated AD, reduced RD and preserved MD. CONCLUSIONS: In line with neurocircuitry models of depression, our findings suggest that WM abnormalities within pathways facilitating cognitive and emotional functioning are involved in the pathophysiology of depression. Importantly, our findings show that these WM abnormalities are already present early in the course of the disorder.

A new symptom model for autism cross-validated in an independent sample.

BACKGROUND: Results from several studies indicated that a symptom model other than the DSM triad might better describe symptom domains of autism. The present study focused on a) investigating the stability of a new symptom model for autism by cross-validating it in an independent sample and b) examining the invariance of the model regarding three covariates: symptom severity, intelligence, and age. METHOD: The validity of the symptom model was examined in an independent sample of N = 263 children and adolescents with autism spectrum disorders, and model invariance was studied in a larger sample of N = 356 children and adolescents with autism spectrum disorders. The fit of the symptom model to the sample data was compared to that of alternative models (including the DSM triad), and the invariance of the new model was investigated for each covariate by multiple-group comparisons. RESULTS: The fit of the new symptom model was better than that of two alternative models. It could not be compared to that of the DSM triad, because the latter encountered empirical identification problems. There were no significant or substantive differences between the estimated model in each of the dichotomised groups for any of the three covariates, which indicated factorial invariance of both structural form and factor loadings. CONCLUSIONS: The symptom model appeared to be relatively stable: It could be cross-validated in the independent sample and factorial invariance was shown between the dichotomised groups for each covariate. Further model validation with instruments other than the Autism Diagnostic Interview-Revised (ADI-R) is recommended.

Measurement of the conductance of a hydrogen molecule.

Recent years have shown steady progress towards molecular electronics, in which molecules form basic components such as switches, diodes and electronic mixers. Often, a scanning tunnelling microscope is used to address an individual molecule, although this arrangement does not provide long-term stability. Therefore, metal-molecule-metal links using break-junction devices have also been explored; however, it is difficult to establish unambiguously that a single molecule forms the contact. Here we show that a single hydrogen molecule can form a stable bridge between platinum electrodes. In contrast to results for organic molecules, the bridge has a nearly perfect conductance of one quantum unit, carried by a single channel. The hydrogen bridge represents a simple test system in which to understand fundamental transport properties of single-molecule devices.

Current-induced forces in molecular wires.

We report first-principles calculations of current-induced forces in molecular wires for which experiments are available. We investigate, as an example, the effect of current-induced forces on a benzene molecule connected to two bulk electrodes via sulfur end groups. We find that the molecule twists around an axis perpendicular to its plane and undergoes a "breathing" oscillation at resonant tunneling via antibonding states. However, current-induced forces do not substantially affect the absolute value of the current for biases as high as 5 V, suggesting that molecular wires can operate at very large electric fields without current-induced breakdown.

Atomic-beam alignment of inorganic materials for liquid-crystal displays.

The technique used to align liquid crystals-rubbing the surface of a substrate on which a liquid crystal is subsequently deposited-has been perfected by the multibillion-dollar liquid-crystal display industry. However, it is widely recognized that a non-contact alignment technique would be highly desirable for future generations of large, high-resolution liquid-crystal displays. A number of alternative alignment techniques have been reported, but none of these have so far been implemented in large-scale manufacturing. Here, we report a non-contact alignment process, which uses low-energy ion beams impinging at a glancing angle on amorphous inorganic films, such as diamond-like carbon. Using this approach, we have produced both laptop and desktop displays in pilot-line manufacturing, and found that displays of higher quality and reliability could be made at a lower cost than the rubbing technique. The mechanism of alignment is explained by adopting a random network model of atomic arrangement in the inorganic films. Order is induced by exposure to an ion beam because unfavourably oriented rings of atoms are selectively destroyed. The planes of the remaining rings are predominantly parallel to the direction of the ion beam.

Temperature effects on the transport properties of molecules.

Recent experiments found an unusual temperature-induced large shift in the resonant-tunneling voltage of certain molecules. We report first-principles calculations showing that such behavior can be caused by the excitation of rotational modes of ligands. These modes have classical characteristics, i.e., the maximum excursion is dominant, while at the same time they have a significant effect on the energy levels responsible for resonant tunneling. The proposed mechanism of ligand rotations is unique to molecules and accounts for the fact that the effect is not seen in semiconductor nanostructures.