Dissociated roles of the middle frontal gyri in the processing of Chinese characters.

The present study examined a hypothesis that the right middle frontal gyrus participates in processing orthography of Chinese characters, while the left middle frontal gyrus mediates access to phonology and semantics. Brain activation during three character tasks, which required processing orthography, phonology, or semantics of Chinese characters, respectively, was measured by functional magnetic resonance imaging. Comparable neural activity in the right middle frontal gyrus was observed in all three character tasks that always demand orthographical processing. In contrast, the left middle frontal gyrus showed greater activation in the phonological and semantic tasks than in the orthographic task. These results suggest that the right and left middle frontal gyrus have dissociable functions in achieving Chinese character recognition.

Lateral modulation of BOLD activation in unstimulated regions of the human visual cortex.

After staring at a blank region surrounded by a dynamic background for a few seconds, observers report a twinkle aftereffect in the unstimulated blank region. The significance of this twinkle aftereffect is that it occurs at a location that received no stimulation, and therefore reflects a rebound from lateral inhibition within the dynamic processing system. To study this inhibitory rebound effect, the blood oxygenation level dependent (BOLD) activation in the visual cortex was measured while the observers were viewing a flickering pin-wheel pattern alternating with a blank test. Retinotopic regions corresponding to the inter-wedge regions in the pin-wheel pattern showed activation negatively correlated with the test sequence. While the BOLD activation in the visual cortex is generally considered to be retinotopically driven by the visual stimuli, we were able to show a sustained negative activation in the unstimulated regions, with properties that correspond to those of the inhibitory rebound of the perceived aftereffect.

Understanding viral partitioning in two-phase aqueous nonionic micellar systems: 1. Role of attractive interactions between viruses and micelles.

The partitioning behavior of viruses in the two-phase aqueous nonionic n-decyl tetra(ethylene oxide) (C10E4) micellar system cannot be fully explained by considering solely the repulsive, steric, excluded-volume interactions that operate between the viruses and the nonionic C10E4 micelles. Specifically, an excluded-volume theory developed recently by our group is not able to quantitatively predict the observed viral partition coefficients, even though this theory is capable of providing reasonable quantitative predictions of protein partition coefficients. To shed light on the discrepancy between the theoretically predicted and the experimentally measured viral partition coefficients, a central assumption underlying the excluded-volume theory that the viruses and the C10E4 micelles interact solely through repulsive, excluded-volume interactions was challenged in this study. In particular, utilizing bacteriophage P22 as a model virus, a competitive inhibition test and a partitioning study of the capsids of bacteriophage P22 were conducted. Based on the results of these two experimental studies, it was concluded that any attractive interactions between the tailspikes of bacteriophage P22 and the C10E4 micelles are negligible. Another experimental study was carried out wherein the partition coefficients of the model viruses, bacteriophages P22 and T4, were measured at various temperatures, and compared with those previously obtained for bacteriophage phiX174. This comparison also indicated that possible attractive, electromagnetic-induced interactions between the bacteriophage particles and the C10E4 micelles cannot be invoked to rationalize the observed discrepancy between the theoretically predicted and the experimentally measured viral partition coefficients.