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In magnetic resonance imaging (MRI), protons (part of the nucleus of an atom) are exposed to rotating magnetic fields in the radio frequency range. When the frequency is stopped, the protons emit energy as they return to their former state. Computer analysis of this emitted energy portrays a spatial image of the distribution of specific elements (e.g., hydrogen). An important measure obtained during MRI is the time taken for the protons to return to a resting state after excitation (T-1). Using MRI, significant increases have been found in the white-matter T-1 of patients with Alzheimer's disease (AD). Another diagnostic procedure, single-photon emission computerized tomography (SPECT), in which variations in the density of brain tissue are measured from an X-ray source and detectors placed around the head, has demonstrated reduced cerebral blood flow (perfusion) in AD patients. To assess whether localized changes in white matter T-1 were related to cognitive deficits or to perfusion changes in the adjoining gray matter of AD patients, 21 right-handed patients with a clinical diagnosis of probable AD were evaluated with MRI. Thirteen of these patients were also evaluated with SPECT. All the patients were given a battery of cognitive tests. Significant relationships were found between localized perfusion reductions, T-1, and localized cognitive deficits. In general, the greater the T-1, the greater the perfusion reduction in adjoining gray matter. Significant relationships were also found between the T-1 of particular brain regions and performance on psychometric tests which tapped into those same regions. For instance, vocabulary test scores were significantly related to the T-1 of left hemisphere structures, which is in keeping with findings of vocabulary impairment in left-hemisphere disorder (of right-handed people). Relationships found between T-1 and pathological change may lead to a way of definitively diagnosing AD in living patients. To date, definitive diagnosis can only be accomplished by the post-mortem examination of white matter. (Consumer Summary produced by Reliance Medical Information, Inc.)

Arid and semi-arid environments are characterized by extreme fluctuations in temperature and low rainfall, which present significant challenges to the animals inhabiting these areas. However, the presence of burrows may allow animals to avoid climatic extremes and predators and may act as valuable foraging sites. We assessed the microhabitat conditions (maximum and minimum temperature, relative humidity and seed abundance) of aardvark (Orycteropus afer) burrows in relation to paired non-burrow areas at three sites in South Africa. We also describe the extent to which they are used as resources by other vertebrates. Maximum temperatures were significantly lower and minimum temperatures and relative humidity values were significantly higher inside the burrows than outside. The concentration of seeds inside the burrows and at the paired non-burrow sites was similar. Twenty-seven vertebrate species (21 mammals, two birds, three reptiles and one amphibian) were recorded making use of the burrows and it is likely that these species accrue benefits (e.g. a buffered microclimate) from burrow use. However, our sampling was biased towards mammals and nocturnal species. Consequently, we recommend further work to establish the overall reliance of vertebrate taxa on aardvark burrows in arid and semi-arid environments.

Bushclumps are scattered islands of thicket-like vegetation within a matrix of more open vegetation. We investigated the role of bushclumps as refugia for small mammals, and examined the effect of a limited number of abiotic and biotic factors on their richness, diversity and abundance. Small mammals were surveyed using Sherman small mammal traps at two sites in the Eastern Cape Province, South Africa (Mountain Zebra National Park and Kwandwe Private Game Reserve). Soil hardness and seed abundance, inside and outside bushclumps, were determined. Trap success was significantly higher inside bushclumpsthan in areas outside, and species diversity and the abundance of small mammals were greater within bushclumps compared tooutside. Bushclumps also had significantly softer soil and a higher concentration of seeds. We conclude that bushclumps provide a concentrated source of food and protection from predators for small mammals, and are thus used significantly more than adjacent open areas. The conservation of bushclumps is therefore important for the overall maintenance of ecosystem functioning.

Presents a letter to the editor about the trial of Leo Frank in Georgia.