Biomedical subjects

Naoki Masuda

Publications and source records attributed to Naoki Masuda.

6 recordsLinked to original sources

PubMed2003

Duality of rate coding and temporal coding in multilayered feedforward networks.

A functional role for precise spike timing has been proposed as an alternative hypothesis to rate coding. We show in this article that both the synchronous firing code and the population rate code can be used dually in a common framework of a single neural network model. Furthermore, these two coding mechanisms are bridged continuously by several modulatable model parameters, including shared connectivity, feedback strength, membrane leak rate, and neuron heterogeneity. The rates of change of these parameters are closely related to the response time and the timescale of learning.

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PubMed2003

Ergodicity of spike trains: when does trial averaging make sense?

Neuronal information processing is often studied on the basis of spiking patterns. The relevant statistics such as firing rates calculated with the peri-stimulus time histogram are obtained by averaging spiking patterns over many experimental runs. However, animals should respond to one experimental stimulation in real situations, and what is available to the brain is not the trial statistics but the population statistics. Consequently, physiological ergodicity, namely, the consistency between trial averaging and population averaging, is implicitly assumed in the data analyses, although it does not trivially hold true. In this letter, we investigate how characteristics of noisy neural network models, such as single neuron properties, external stimuli, and synaptic inputs, affect the statistics of firing patterns. In particular, we show that how high membrane potential sensitivity to input fluctuations, inability of neurons to remember past inputs, external stimuli with large variability and temporally separated peaks, and relatively few contributions of synaptic inputs result in spike trains that are reproducible over many trials. The reproducibility of spike trains and synchronous firing are contrasted and related to the ergodicity issue. Several numerical calculations with neural network examples are carried out to support the theoretical results.

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PubMed2002

Bridging rate coding and temporal spike coding by effect of noise.

It is controversial whether temporal spike coding or rate coding is dominant in the information processing of the brain. We show by a two-layered neural network model with noise that, when noise is small, cortical neurons fire synchronously and intervals of synchronous firing robustly encode the signal information, but that the neurons desynchronize with moderately strong noise to encode waveforms of the signal more accurately. Further increase of noise just deteriorates the encoding. A positive role of noise in the brain is suggested in a meaning different from stochastic resonance, coherence resonance, and deterministic chaos.

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PubMed2002

Spatiotemporal spike encoding of a continuous external signal.

Interspike intervals of spikes emitted from an integrator neuron model of sensory neurons can encode input information represented as a continuous signal from a deterministic system. If a real brain uses spike timing as a means of information processing, other neurons receiving spatiotemporal spikes from such sensory neurons must also be capable of treating information included in deterministic interspike intervals. In this article, we examine functions of neurons modeling cortical neurons receiving spatiotemporal spikes from many sensory neurons. We show that such neuron models can encode stimulus information passed from the sensory model neurons in the form of interspike intervals. Each sensory neuron connected to the cortical neuron contributes equally to the information collection by the cortical neuron. Although the incident spike train to the cortical neuron is a superimposition of spike trains from many sensory neurons, it need not be decomposed into spike trains according to the input neurons. These results are also preserved for generalizations of sensory neurons such as a small amount of leak, noise, inhomogeneity in firing rates, or biases introduced in the phase distributions.

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PubMed2002

[A case of severe septicemia due to Aeromonas hydrophila].

Septicemia by Aeromonas hydrophila (A. hydrophila) developed in a 69-year-old female with a history of uncompensated liver cirrhosis. She was admitted to our hospital, complaining of fever, vomiting, diarrhea, and pain as well as swelling of the left lower extremity. Seven hours later, skin of the left extremity developed bullae and became discolored. Although she was treated with infusion of antibiotics plus dopamine, continuous hemodiafiltration, glucose-insulin therapy and mechanical ventilation, she fell in severe septic shock, and died 23 hours after admission. A. hydrophila was isolated from both blood and bullous fluid. Mortality rate of septicemia due to A. hydrophila is reported ranging from 29% to 73%. Patients with liver disease have poor prognosis. Morbidity of this septicemia depends on pre-infection conditions, especially on liver functions. Early surgical debridement and antimicrobial therapy is recommended, but rapid worsening often results in death. We have to pay attention to infection of A. hydrophila especially in patients with liver cirrhosis.

Aeromonas hydrophila↗

PubMed2002

[Spinal anesthesia with bupivacaine for a patient with a history of severe leg pain after intrathecal dibucaine].

An 87-year-old man was scheduled for the 11th transurethral bladder tumor resection (TURBT). He had a history of non-active syphilis for 21 years, diabetes mellitus for 7 years, and severe emphysema. Preoperative physical examination of the lower extremities, revealed loss of knee-jerk reflex, and loss of vibratory and proprioceptive perception. Four years previously, he underwent TURBT twice under spinal anesthesia with dibucaine, which caused severe leg pain during anesthesia. Therefore, subsequent TURBTs (eight times) were performed under general anesthesia with tracheal intubation, which frequently caused postoperative respiratory distress. Recently, bupivacaine, less neurotoxic than dibucaine, was on the market in Japan for use in spinal anesthesia. Therefore we planned spinal anesthesia using 0.5% bupivacaine, 2.0 ml. This time, he did not complain of leg pain during anesthesia, and postoperative conditions were satisfactory. We can conclude that bupivacaine is very useful for spinal anesthesia especially in patients with a history of leg pain by spinal anesthesia with dibucaine.

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