Musical imagery: sound of silence activates auditory cortex

Auditory imagery occurs when one mentally rehearses telephone numbers or has a song 'on the brain'--it is the subjective experience of hearing in the absence of auditory stimulation, and is useful for investigating aspects of human cognition. Here we use functional magnetic resonance imaging to identify and characterize the neural substrates that support unprompted auditory imagery and find that auditory and visual imagery seem to obey similar basic neural principles.     

Significant decadal-scale impact of volcanic eruptions on sea level and ocean heat content

Ocean thermal expansion contributes significantly to sea-level variability and rise. However, observed decadal variability in ocean heat content and sea level has not been reproduced well in climate models. Aerosols injected into the stratosphere during volcanic eruptions scatter incoming solar radiation, and cause a rapid cooling of the atmosphere and a reduction in rainfall, as well as other changes in the climate system. Here we use observations of ocean heat content and a set of climate simulations to show that large volcanic eruptions result in rapid reductions in ocean heat content and global mean sea level. For the Mt Pinatubo eruption, we estimate a reduction in ocean heat content of about 3 x 10(22) J and a global sea-level fall of about 5 mm. Over the three years following such an eruption, we estimate a decrease in evaporation of up to 0.1 mm d(-1), comparable to observed changes in mean land precipitation. The recovery of sea level following the Mt Pinatubo eruption in 1991 explains about half of the difference between the long-term rate of sea-level rise of 1.8 mm yr(-1) (for 1950-2000), and the higher rate estimated for the more recent period where satellite altimeter data are available (1993-2000).     

Admixture mapping for hypertension loci with genome-scan markers

Identification of genetic variants that contribute to risk of hypertension is challenging. As a complement to linkage and candidate gene association studies, we carried out admixture mapping using genome-scan microsatellite markers among the African American participants in the US National Heart, Lung, and Blood Institute's Family Blood Pressure Program. This population was assumed to have experienced recent admixture from ancestral groups originating in Africa and Europe. We used a set of unrelated individuals from Nigeria to represent the African ancestral population and used the European Americans in the Family Blood Pressure Program to provide estimates of allele frequencies for the European ancestors. We genotyped a common set of 269 microsatellite markers in the three groups at the same laboratory. The distribution of marker location-specific African ancestry, based on multipoint analysis, was shifted upward in hypertensive cases versus normotensive controls, consistent with linkage to genes conferring susceptibility. This shift was largely due to a small number of loci, including five adjacent markers on chromosome 6q and two on chromosome 21q. These results suggest that chromosome 6q24 and 21q21 may contain genes influencing risk of hypertension in African Americans.     

Late Eocene of Burma yields earliest anthropoid primate, Pondaungia cotteri.

In April 1978, a fragment of a primate lower jaw containing the second and third molar teeth was found in late Eocene exposures of the Pondaung Hills about 1 mile north-west of Mogaung village in northwestern Central Burma. This approximately 40-Myr-old specimen is the first fossil primate found in Burma since the fragmentary remains of the controversial earliest anthropoids Pondaungia cotteri Pilgrim and Amphipithecus mogaungensis Colbert were recovered more than 50 yr ago. The jaw described here is believed to represent further evidence of P. cotteri. Its recovery from undoubled late Eocene exposures coupled with its salient higher primate characters and excellent state of preservation provides the opportunity to substantiate further that the Pondaung primates of Burma are the earliest known record of the Anthropoidea.     

HIV in Africa (Communication arising): chemokine-receptor genes and AIDS risk

Schliekelman et al. have provided a model to quantify the speed at which HIV-resistance haplotypes can become enriched in a susceptible population through a delay in the onset of AIDS, permitting greater lifetime reproduction and the selection of AIDS-delaying haplotypes. But we question their conclusion that there could be a rapid evolution of resistance to AIDS onset in some African populations if the current HIV epidemic persists, as this depends on an untested assumption: that variant forms of the chemokine-receptor-5 (CCR5) gene impart selective advantages or disadvantages in Africa that are comparable to those reported for African Americans. Here we test this premise in a large Ugandan population, and find that CCR5 variants are not associated with HIV/AIDS disease risk in Africa--the origin and centre of the current AIDS pandemic. This gene may therefore not be subject to rapid evolutionary change as a result of the HIV epidemic in Africa.     

Nanomechanics: response of a strained semiconductor structure

The nanomechanical properties of thin silicon films will become increasingly critical in semiconductor devices, particularly in the context of substrates that consist of a silicon film on an insulating layer (known as silicon-on-insulator, or SOI, substrates). Here we use very small germanium crystals as a new type of nanomechanical stressor to demonstrate a surprising mechanical behaviour of the thin layer of silicon in SOI substrates, and to show that there is a large local reduction in the viscosity of the oxide on which the silicon layer rests. These findings have implications for the use of SOI substrates in nanoelectronic devices.