A major question in neocortical research is the extent to which neuronal organization is stereotyped. Previous studies have revealed functional clustering and neuronal interactions among cortical neurons located within tens of micrometers in the tangential orientation (orientation parallel to the pial surface). In the tangential orientation at this scale, however, it is unknown whether the distribution of neuronal subtypes is random or has any stereotypy. We found that the tangential arrangement of subcerebral projection neurons, which are a major pyramidal neuron subtype in mouse layer V, was not random but significantly periodic. This periodicity, which was observed in multiple cortical areas, had a typical wavelength of 30 m. Under specific visual stimulation, neurons in single repeating units exhibited strongly correlated c-Fos expression. Therefore, subcerebral projection neurons have a periodic arrangement, and neuronal activity leading to c-Fos expression is similar among neurons in the same repeating units. These results suggest that the neocortex has a periodic functional micro-organization composed of a major neuronal subtype in layer V.

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The method of rotating bending fatigue test under an electrochemical hydrogen charging was established, by which the fatigue tests were carried out for a JIS SCM435 to study the effect of hydrogen on fatigue strength. The fatigue life of the specimen was degraded by hydrogen charging in relatively low fatigue life regime, where the slope of S N curve for the hydrogen charged specimens was equivalent to that for no charged specimens. The fatigue strength on 50 failure probability at 10 7 cycles under the hydrogen charging was slightly lower than that under the hydrogen free condition. On the surface of the non charged specimen that was run out at 10 7 cycles, a number of cracks up to ≈ 100 µm in length was observed. By contrast, in the hydrogen charged specimen, no crack was observed after the fatigue testing. These results suggested that the hydrogen charging had a negative in uence on the fatigue limit as well as fatigue life of the alloy used in this study.