914 research outputs found
Maximization of Learning Speed in the Motor Cortex Due to Neuronal Redundancy
Many redundancies play functional roles in motor control and motor learning. For example, kinematic and muscle redundancies contribute to stabilizing posture and impedance control, respectively. Another redundancy is the number of neurons themselves; there are overwhelmingly more neurons than muscles, and many combinations of neural activation can generate identical muscle activity. The functional roles of this neuronal redundancy remains unknown. Analysis of a redundant neural network model makes it possible to investigate these functional roles while varying the number of model neurons and holding constant the number of output units. Our analysis reveals that learning speed reaches its maximum value if and only if the model includes sufficient neuronal redundancy. This analytical result does not depend on whether the distribution of the preferred direction is uniform or a skewed bimodal, both of which have been reported in neurophysiological studies. Neuronal redundancy maximizes learning speed, even if the neural network model includes recurrent connections, a nonlinear activation function, or nonlinear muscle units. Furthermore, our results do not rely on the shape of the generalization function. The results of this study suggest that one of the functional roles of neuronal redundancy is to maximize learning speed
Studies on the Formation and Aging of Precipitates. (I) : Electron Microscopic Investigation of Formation of Barium Sulfate Precipitate
Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS): Clinical, Radiological and Epidemiological Aspects
MRI Findings in Neuroferritinopathy
Neuroferritinopathy is a neurodegenerative disease which
demonstrates brain iron accumulation caused by the mutations in
the ferritin light chain gene. On brain MRI in
neuroferritinopathy, iron deposits are observed as low-intensity
areas on T2WI and as signal loss on T2∗WI. On T2WI, hyperintense
abnormalities reflecting tissue edema and gliosis are also seen.
Another characteristic finding is the presence of symmetrical
cystic changes in the basal ganglia, which are seen in the
advanced stages of this disorder. Atrophy is sometimes noted in
the cerebellar and cerebral cortices. The variety in the MRI
findings is specific to neuroferritinopathy. Based on observations
of an excessive iron content in patients with chronic neurologic
disorders, such as Parkinson disease and Alzheimer disease, the
presence of excess iron is therefore recognized as a major risk
factor for neurodegenerative diseases. The future development of
multimodal and advanced MRI techniques is thus expected to play an
important role in accurately measuring the brain iron content and
thereby further elucidating the neurodegenerative process
Cathode Sheath Thickness of a Microhollow Cathode Discharge Plasma In Argon High Gas Pressures
In a glow discharge, the sheath region that is formed around the cathode surface has a decisive effect on the generation of plasmas. In order to investigate the sheath structure in an atmospheric pressure plasma, we developed a microhollow cathode discharge (MHCD) device. The MHCD device had a cathode diameter of 0.5 mm and its length of 2.0 mm. The discharge was operated at a discharge voltage and current of -220 V and 15 mA, respectively, up to 20 kPa of He-Ar mixtures. We carried out the visible/UV emission spectroscopy, which enabled us to understand the characteristics in the cathode sheath. It was found that two dimensional emission images attributed to Ar+ ion and neutral atom showed significantly different behavior with increasing gas pressure. By comparing the results obtained by an ionizing sheath theory with experimental ones, the detail of the sheath structure is clarified
An analysis of competition based on the revision of rules in wrestling―A comparison of technique frequency and scoring of the gold medalists from the Games of the 29th Olympiad in Barcelona and Japanese national team members
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