Decomposition Process of Woody Debris and Fungal Community Structure

We examined the relationship between the community structure of wood-decaying fungi, detected by high-throughput sequencing, and the decomposition rate using 13 years of data from a forest dynamics plot. For molecular analysis and wood density measurements, drill dust samples were collected from logs and stumps of Fagus and Quercus in the plot. Regression using a negative exponential model between wood density and time since death revealed that the decomposition rate of Fagus was greater than that of Quercus. The residual between the expected value obtained from the regression curve and the observed wood density was used as a decomposition rate index. Principal component analysis showed that the fungal community compositions of both Fagus and Quercus changed with time since death. Principal component analysis axis scores were used as an index of fungal community composition. A structural equation model for each wood genus was used to assess the effect of fungal community structure traits on the decomposition rate and how the fungal community structure was determined by the traits of coarse woody debris. Results of the structural equation model suggested that the decomposition rate of Fagus was affected by two fungal community composition components: one that was affected by time since death and another that was not affected by the traits of coarse woody debris. In contrast, the decomposition rate of Quercus was not affected by coarse woody debris traits or fungal community structure. These findings suggest that, in the case of Fagus coarse woody debris, the fungal community structure is related to the decomposition process of its host substrate. Because fungal community structure is affected partly by the decay stage and wood density of its substrate, these factors influence each other. Further research on interactive effects is needed to improve our understanding of the relationship between fungal community structure and the woody debris decomposition process

Active damping of the scanner for high-speed atomic force microscopy

金沢大学大学院自然科学研究科物理学金沢大学理学部The scanner that moves the sample stage in three dimensions is a crucial device that limits the imaging rate of atomic force microscopy. This limitation derives mainly from the resonant vibrations of the scanner in the z direction (the most frequent scanning direction). Resonance originates in the scanner\u27s mechanical structure as well as in the z piezoactuator itself. We previously demonstrated that the resonance originating in the structure can be minimized by a counterbalancing method. Here we report that the latter resonance from the actuator can be eliminated by an active damping method, with the result the bandwidth of the z scanner nearly reaches the first resonant frequency (150 kHz) of the z piezoactuator. © 2005 American Institute of Physics

A Neurorobotics Simulation of Autistic Behavior Induced by Unusual Sensory Precision

Recently, applying computational models developed in cognitive science to psychiatric disorders has been recognized as an essential approach for understanding cognitive mechanisms underlying psychiatric symptoms. Autism spectrum disorder is a neurodevelopmental disorder that is hypothesized to affect information processes in the brain involving the estimation of sensory precision (uncertainty), but the mechanism by which observed symptoms are generated from such abnormalities has not been thoroughly investigated. Using a humanoid robot controlled by a neural network using a precision-weighted prediction error minimization mechanism, it is suggested that both increased and decreased sensory precision could induce the behavioral rigidity characterized by resistance to change that is characteristic of autistic behavior. Specifically, decreased sensory precision caused any error signals to be disregarded, leading to invariability of the robot’s intention, while increased sensory precision caused an excessive response to error signals, leading to fluctuations and subsequent fixation of intention. The results may provide a system-level explanation of mechanisms underlying different types of behavioral rigidity in autism spectrum and other psychiatric disorders. In addition, our findings suggest that symptoms caused by decreased and increased sensory precision could be distinguishable by examining the internal experience of patients and neural activity coding prediction error signals in the biological brain

Emergence of sensory attenuation based upon the free-energy principle

The brain attenuates its responses to self-produced exteroceptions (e.g., we cannot tickle ourselves). Is this phenomenon, known as sensory attenuation, enabled innately, or acquired through learning? Here, our simulation study using a multimodal hierarchical recurrent neural network model, based on variational free-energy minimization, shows that a mechanism for sensory attenuation can develop through learning of two distinct types of sensorimotor experience, involving self-produced or externally produced exteroceptions. For each sensorimotor context, a particular free-energy state emerged through interaction between top-down prediction with precision and bottom-up sensory prediction error from each sensory area. The executive area in the network served as an information hub. Consequently, shifts between the two sensorimotor contexts triggered transitions from one free-energy state to another in the network via executive control, which caused shifts between attenuating and amplifying prediction-error-induced responses in the sensory areas. This study situates emergence of sensory attenuation (or self-other distinction) in development of distinct free-energy states in the dynamic hierarchical neural system

Structural changes in bacteriorhodopsin in response to alternate illumination observed by high-speed atomic force microscopy

金沢大学理工研究域数物科学系Blue light, green light: High-speed atomic force microscopy visualized light-induced structural changes of the D96N bacteriorhodopsin (bR) mutant under alternate two-color illumination. With green light, each bR molecule is displaced outward from the trimer center. This activated structure is driven back to the ground state by the subsequent blue-light illumination (see picture). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

High-speed atomic force microscopy shows dynamic molecular processes in photoactivated bacteriorhodopsin

金沢大学理工研究域数物科学系Dynamic changes in protein conformation in response to external stimuli are important in biological processes, but it has proved difficult to directly visualize such structural changes under physiological conditions1-10. Here, we show that high-speed atomic force microscopy7 can be used to visualize dynamic changes in stimulated proteins. High-resolution movies of a light-driven proton pump, bacteriorhodopsin, reveal that, upon illumination, a cytoplasmic portion of each bacteriorhodopsin monomer is brought into contact with adjacent trimers. The bacteriorhodopsin-bacteriorhodopsin11,12 interaction in the transiently formed assembly engenders both positive and negative cooperative effects in the decay kinetics as the initial bacteriorhodopsin recovers and, as a consequence, the turnover rate of the photocycle is maintained constant, on average, irrespective of the light intensity. These results confirm that high-resolution visualization is a powerful approach for studying elaborate biomolecular processes under realistic conditions. © 2010 Macmillan Publishers Limited. All rights reserved