Human subjects ranging in age from 18 to 85 years underwent classical conditioning of the eyeblink response to a tone conditioned stimulus (CS) and an air-puff unconditioned stimulus (UCS). There was a decline in percentage of conditioned responses with age. This decline was most noticeable in subjects over age 50. These conditioning deficits were not due to age-related changes in sensitivity to the tone CS or the air-puff UCS, nor could the conditioning deficits be attributed to an age-related decline in general cognitive abilities or to changes in spontaneous blink rates. The results are discussed in terms of using the classically conditioned eyeblink in humans in conjunction with the classically conditioned nictitating membrane response in rabbits as a model system for studying the neurobiology of age-related conditioning deficits.

The nature of unusual aquatic microbial formations in flooded passages of cave systems in the Nullarbor region of Australia was investigated using electron microscopy and DNA analysis. The caves are located in a semiarid region but intersect the watertable at depths of approximately 100 m below the surface. Throughout submerged portions of the caves divers have noted the presence of unusual microbial formations. These 'microbial mantles' comprise sheets or tongues of mucoid material in which small crystals are embedded. Examination of the biomass revealed it to be primarily composed of densely packed, unbranched filaments, together with spherical-, rod- and spiral-shaped cells, and microcrystals of calcite in a mucoid matrix. Molecular phylogenetic analysis of the community structure revealed approximately 12% of clones showed high similarity to autotrophic nitrite-oxidizing bacteria (Nitrospira moscoviensis). The remainder of the clones exhibited a high proportion of phylogenetically novel sequence types. Chemical analysis of water samples revealed high levels of sulphate and nitrate together with significant nitrite. The community structure, the presence of nitrite in the water, and the apparent absence of aquatic macrofauna, suggest these microbial structures may represent biochemically novel, chemoautotrophic communities dependent on nitrite oxidation.

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