Biomedical subjects

Masahiko Morita

Publications and source records attributed to Masahiko Morita.

5 recordsLinked to original sources

PubMed2006

DISC1-NDEL1/NUDEL protein interaction, an essential component for neurite outgrowth, is modulated by genetic variations of DISC1.

Disrupted-In-Schizophrenia-1 (DISC1) is a unique susceptibility gene for major mental conditions, because of the segregation of its genetic variant with hereditary psychosis in a Scottish pedigree. Genetic association studies reproducibly suggest involvement of DISC1 in both schizophrenia and bipolar disorder in several ethnic groups. The DISC1 protein is multifunctional, and a pool of DISC1 in the dynein motor complex is required for neurite outgrowth in PC12 cells as well as proper neuronal migration and dendritic arborization in the developing cerebral cortex in vivo. Here, we show that a specific interaction between DISC1 and nuclear distribution element-like (NDEL1/NUDEL) is required for neurite outgrowth in differentiating PC12 cells. Among several components of the dynein motor complex, DISC1 and NDEL1 are selectively upregulated during neurite outgrowth upon differentiation in PC12 cells. The NDEL1 binding site of DISC1 was narrowed down to a small portion of exon 13, corresponding to amino acids 802-835 of DISC1. We demonstrate that genetic variants of DISC1, proximal to the NDEL1 binding site, affect the interaction between DISC1 and NDEL1.

Animals↗

PubMed2003

Integration process of contours defined by different attributes.

We examined how contours defined by different attributes are integrated into a shape using the visual search paradigm and found that the search for the bar orientation is particularly difficult when each bar is composed of motion-defined and luminance- or color-defined contours. This does not support the view that the shape integration process is based on the unified contour representation entirely common to all attributes, but suggests that motion-defined contours are integrated through a different process.

Color Perception↗

PubMed2002

Photosynthetic productivity of conical helical tubular photobioreactor incorporating Chlorella sorokiniana under field conditions.

The photosynthetic performance of a conical, helical tubular photobioreactor (HTP) incorporating Chlorella sorokiniana was investigated under conditions of high temperature and light intensity during midsummer in an outdoor environment. Although the culture medium temperature exceeded 40 degrees C for approximately 5 h each day, peaking at 47.5 degrees C under sunny conditions, a photosynthetic productivity of 30.0 g x m(-2) (installation area) x day(-1) and a photosynthetic efficiency of 8.66% [photosynthetically active radiation (PAR), 400-700 nm] were achieved. A maximum photosynthetic productivity of 33.2 g x m(-2) x day(-1) was achieved on a sunny day, when solar energy input was also maximal (11.5 MJ x m(-2) x day(-1) [PAR]). On the other hand, a maximum photosynthetic efficiency of 9.54% was obtained on a day that was rainy in the morning and cloudy in the afternoon, and there was relatively little solar energy input. The average daily photosynthetic efficiency over the two culture periods (August 4 to 7 and August 10 to 13, 1999) was 7.25%. Thus, a high level of photosynthetic performance was achieved in the conical HTP incorporating Chlorella sorokiniana despite the fact that culture medium temperature was not controlled. The use of Chlorella sorokiniana in the conical HTP should be a good choice to produce microalgal biomass during the summer under field conditions.

Biomass↗

PubMed2002

Computational modeling of pair-association memory in inferior temporal cortex.

Distinctive neuronal activities related to visual stimulus-stimulus association have been found in the inferior temporal (IT) cortex of monkeys. They provide an important clue to elucidating the memory mechanisms of the brain, but do not accord with existing neural network models. In the present paper, we clarify the computational principle required for reproducing the empirical data and construct a biologically feasible model that learns and performs a delayed pair-association task. This model is composed of two neural networks, association network N1 and trainer network N2, and pair-association memories are formed by their interactions. Specifically, N2 receives the output of N1 in addition to an external input, and sends a learning signal back to N1; this signal works as a guide for shifts in output pattern or state transitions of N1, and memory traces are engraved along its path, so that a trajectory attractor connecting from the cue-coding to the target-coding state is formed in N1. Computer simulation shows that the model not only distinguishes the target in the task, but also explains the activity of the IT neurons very well. It is reasonable to presume that N1 and N2 correspond to area TE and the rhinal cortex, respectively; based on this theory, we explain some physiological findings on learning and memory, and also make several predictions.

Algorithms↗

PubMed1996

Memory and Learning of Sequential Patterns by Nonmonotone Neural Networks.

Conventional neural network models for temporal association generally do not work well in the absence of synchronizing neurons. This is because their dynamical properties are fundamentally not suitable for storing sequential patterns, no matter what storage or learning algorithm is used. The present article describes a nonmonotone neural network (NNN) model in which sequential patterns are stored by being embedded in a trajectory attractor of the dynamical system, and recalled stably and smoothly without synchronization; recall is done in such a way that the network state successively moves along the trajectory. A simple and natural learning algorithm for the NNN is also presented, where one only has to vary the input pattern gradually and modify the synaptic weights according to a kind of covariance rule; then the network state follows slightly behind the input pattern, and its trajectory grows to be an attractor with a small number of repetitions. Copyright 1996 Elsevier Science Ltd.

Journal Article↗