Biomedical subjects

Akira Hirose

Publications and source records attributed to Akira Hirose.

13 recordsLinked to original sources

PubMed2006

Developmental learning with behavioral mode tuning by carrier-frequency modulation in coherent neural networks.

We propose a developmental learning architecture with which a motion-control system learns multiple tasks similar to each other or advanced ones incrementally and efficiently by tuning its behavioral mode. The system is based on a coherent neural network whose carrier frequency works as a mode-tuning parameter. In our experiments, we consider two tasks related to bicycle riding. The first is to ride as temporally long as the system can before it falls down (task 1). The second is an advanced one, i.e., to ride as far as possible in a certain direction (task 2). We compare developmental learning to learn task 2 after task 1 with the direct learning of task 2. We also examine the effect of the mode tuning by comparing variable-mode learning (VML), where the carrier frequency is set free to move, with fixed-mode learning (FML), where the frequency is unchanged. We find that VML developmental learning results in the most efficient learning among the possible combinations. We discuss the effects of the incremental task assignment as well as the behavioral mode tuning in developmental learning.

Adaptation, Physiological↗

PubMed2005

Frequency-multiplexed logic circuit based on a coherent optical neural network.

We propose an adaptive logic circuit whose function can be controlled by optical carrier frequency modulation. The circuit learns the desired functions by adjusting the delay time at a spatial light modulator with a complex-valued Hebbian learning rule. After the learning, the circuit can switch its function all at once. A high degree of mechanical stability is achieved by spatial phase-difference coding. Two orthogonal phase components are detected in parallel spatially. Experiments demonstrate that the system works as an AND circuit at a certain frequency and as an XOR at another. The proposal will enhance the design of optical plastic cell architectures.

Journal Article↗

PubMed2004

Tomographic image and visual recovery of acute macula-off rhegmatogenous retinal detachment.

PURPOSE: To observe the macula of acute rhegmatogenous retinal detachment involving the macula with optical coherence tomography (OCT) after scleral buckling and to study the relation between pre- and postoperative visual acuity and the OCT image. METHODS: Prospective study of 15 eyes of 15 patients with macula-off rhegmatogenous retinal detachment. We selected cases with preoperative visual acuity worse than 0.5 to analyze the improvement in postoperative visual acuity. The time period between macula-off retinal detachment and surgery was less than 1 week. RESULTS: Indirect ophthalmoscopy indicated that all retinal detachments were reattached at 2 weeks postoperatively. Accumulation of subretinal fluid at the fovea was observed in nine (60%) cases with OCT. In four of these nine eyes, the accumulation of subretinal fluid persisted up to 6 months after the operation. The presence of residual subretinal fluid did not influence visual recovery during the 6 months' postsurgical follow-up. CONCLUSIONS: OCT revealed postoperative residual subretinal fluid at the macula in some acute macula-off retinal detachment cases. Residual subretinal fluid did not influence the recovery of visual acuity for at least 6 months after surgery.

Acute Disease↗

PubMed2003

Coherent optical neural network that learns desirable phase values in the frequency domain by use of multiple optical-path differences.

A coherent optical neural network is proposed that has the learning ability to achieve desirable phase values in the frequency domain. It is composed of multiple optical-path differences whose lengths are different from one another. The system learns a phase value at each discrete position in the frequency domain by obeying the complex-valued Hebbian rule. The learning curve also agrees with theoretical evolution.

Journal Article↗

PubMed2003

Contribution of ionic currents to magnetoencephalography (MEG) and electroencephalography (EEG) signals generated by guinea-pig CA3 slices.

A mathematical model was used to analyse the contributions of different types of ionic currents in the pyramidal cells of longitudinal CA3 slices to the magnetic fields and field potentials generated by this preparation. Murakami et al. recently showed that a model based on the work of Traub et al. provides a quantitatively accurate account of the basic features of three types of empirical data (magnetic fields outside the slice, extracellular field potentials within the slice and intracellular potentials within the pyramidal neurons) elicited by stimulations of the soma and apical dendrites. This model was used in the present study to compute the net current dipole moment (Q) due to each of the different voltage- and ligand-gated channels in the cells in the presence of fast GABAA inhibition. These values of Q are proportional to the magnetic field and electrical potential far away from the slice. The intrinsic conductances were found to be more important than the synaptic conductances in determining the shape and magnitude of Q. Among the intrinsic conductances, the sodium (gNa) and delayed-rectifier potassium (gK(DR)) channels were found to produce sharp spikes. The high-threshold calcium channel (gCa) and C-type potassium channel (gK(C)) primarily determined the overall current waveforms. The roles of gCa and gK(C) were independent of small perturbations in these channel densities in the apical and basal dendrites. A combination of gNa, gK(DR), gCa, and gK(C) accounted for most of the evoked responses, except for later slow components, which were primarily due to synaptic channels.

Animals↗

PubMed2003

[Three cases of hypotonic maculopathy due to blunt trauma, treated by 360-degree scleral buckling].

BACKGROUND: In hypotonic maculopathy with a shallow anterior chamber, it is difficult to delineate the extent of cyclodialysis. Reoperations are often reported, and a method of management for hypotonic maculopathy is not yet established. CASES: We treated three patients with hypotonic maculopathy due to blunt trauma. Case 1 did not improve after two cryoablations, two cyclopexies, and a laser photocoagulation treatment. Cases 2 and 3 did not improve after a single laser photocoagulation treatment. All cases exhibited retinal breaks, and underwent 360-degree scleral buckling. RESULTS: In all cases, intraocular pressure was normalized soon after the surgery. We found that ultrasound biomicroscopy (UBM) was helpful in clarifying cyclodialysis, and that optical coherence tomography(OCT) was useful to observe morphologic changes of the macula in detail. CONCLUSION: This procedure is considered to be useful in the treatment of hypotonic maculopathy.

Adult↗

PubMed2002

Physiological origins of evoked magnetic fields and extracellular field potentials produced by guinea-pig CA3 hippocampal slices.

This study examined whether evoked magnetic fields and intra- and extracellular potentials from longitudinal CA3 slices of guinea-pig can be interpreted within a single theoretical framework that incorporates ligand- and voltage-sensitive conductances in the dendrites and soma of the pyramidal cells. The 1991 CA3 mathematical model of R. D. Traub is modified to take into account the asymmetric branching patterns of the apical and basal dendrites of the pyramidal cells. The revised model accounts for the magnitude and waveform of the bi- and triphasic magnetic fields evoked by somatic and apical stimulations, respectively, in the slice in the absence of fast inhibition (blocked by 0.1 mM picrotoxin). The revised model also accounts for selective effects of 4-aminopyridine (4-AP) and tetraethylammonium (TEA), which block the potassium channels of A and C type, respectively, on the slow wave of the magnetic fields. Furthermore, the model correctly predicts the laminar profiles of field potential as well as intracellular potentials in the pyramidal cells produced by two classes of cells - those directly activated and those indirectly (synaptically) activated by the applied external stimulus. The intracellular potentials in this validated model reveal that the spikes and slow waves of the magnetic fields are generated in or near the soma and apical dendrites, respectively. These results demonstrate that a single theoretical framework couched within the modern concepts of cellular physiology provides a unified account of magnetic fields outside the slice, extracellular potentials within the slice and intracellular potentials of the pyramidal cells for CA3.

Action Potentials↗

PubMed2002

Inducible expression of vascular endothelial growth factor in adult mice causes severe proliferative retinopathy and retinal detachment.

Transgenic mice with vascular endothelial growth factor (VEGF) driven by the rhodopsin promoter (rho/VEGF mice) develop neovascularization that originates from the deep capillary bed of the retina and grows into the subretinal space. In rho/VEGF mice, VEGF expression in photoreceptors begins between postnatal days 5 and 7, the period when the deep capillary bed is developing. An important question is whether or not the developmental stage of the deep capillary bed is critical for occurrence of neovascularization. Also, although rho/VEGF mice are extremely useful for the study of ocular neovascularization, there are some applications for which the early onset of VEGF expression is a disadvantage. In this study, we used the reverse tetracycline transactivator (rtTA) inducible promoter system coupled to either the rhodopsin or interphotoreceptor retinoid-binding protein (IRBP) promoter to control the time of onset of VEGF transgene expression in photoreceptors. In the absence of doxycycline, adult double-transgenic rho/rtTA-TRE/VEGF or IRBP/rtTA-TRE/VEGF mice showed little VEGF transgene expression and no phenotype. The addition of doxycycline to the drinking water resulted in prominent transgene expression and evidence of neovascularization within 3 to 4 days. Like rho/VEGF mice, the neovascularization originated from the deep capillary bed of the retina, but it was more extensive and caused outer retinal folds followed by total retinal detachment. Real-time polymerase chain reaction and enzyme-linked immunosorbent assay demonstrated that the mice with inducible expression of VEGF that developed retinal detachment had much higher ocular levels of VEGF mRNA and protein compared to rho/VEGF mice that manifest a much milder phenotype. These data demonstrate that regardless of developmental stage of the vascular bed, increased expression of VEGF in the retina is sufficient to cause neovascularization, and high levels of expression cause severe neovascularization and traction retinal detachment. Mice with inducible expression of VEGF in the retina provide a valuable new model of ocular neovascularization.

Animals↗

PubMed2002

A quantitative evaluation of the magnetic field generated by a CA3 pyramidal cell at EPSP and action potential stages.

We evaluate quantitatively which behavioral stage dominantly generates magnetic field adjacent to a CA3 pyramidal cell by using a compartmental model with dendrites and an axon. Generally speaking, there are four stages in the potential behavior, i.e., excitatory and inhibitory postsynaptic potential, firing action potential, bursting action potential, if any, and after hyperpolarization potential stages. Calculated magnetic field also consists of corresponding four stages. We find, first, the dominant origin of the peaks of the magnetic field is counter propagating pulses at the firing and bursting stage at basal and apical dendrites. Second, the amplitude of the magnetic field changes to a great extent by the cancellation timing of the apical- and basal-originating fields depending on the calcium ionic channel spikes. Third, the field generated by the current flowing through the axon is significant enough when the temporal resolution of the measurement system becomes high. The results predict that the magnetic-field waveform measured in physiological experiments represents the dendritic configurations, channel density distributions, and bursting characteristics. These facts enable new investigations of neuronal activities in more detail through the observation of the magnetic-field waveform.

Action Potentials↗

PubMedDate not supplied

Plastic mine detecting radar system using complex-valued self-organizing map that deals with multiple-frequency interferometric images.

Ground penetrating radars (GPR's) have been often applied to underground object imaging. However, conventional radar systems do not work sufficiently to detect anti-personnel plastic landmines. We propose a novel radar imaging system, which processes adaptively interferometric front-end data obtained at multiple-frequency points. The system deals with interferometric images using complex-valued self-organizing map (C-SOM). We demonstrate a successful visualization of a plastic mine buried near the ground surface.

Algorithms↗

PubMedDate not supplied

Choroidal vascular lesions identified by ICG angiography in a case of familial amyloidotic polyneuropathy.

BACKGROUND: To describe a patient with familial amyloidotic polyneuropathy (FAP) whose choroidal vascular lesions were demonstrated dynamically with the use of indocyanine green (ICG) angiography. CASE: A 59-year-old man complained of blurred vision due to vitreal amyloidosis in both eyes. Fundus examination after pars plana vitrectomy showed multiple retinal hemorrhages. OBSERVATIONS: ICG angiography performed after vitrectomy clearly delineated multiple sites of hyperfluorescence indicating tissue staining alongside the major choroidal veins in the lower fundus of his left eye. ICG hyperfluorescence was more evident in the late angiographic phase. Fundus examination and fluorescein angiography revealed no abnormal findings at the corresponding sites of ICG dye leakage. CONCLUSIONS: Choroidal vascular lesions in eyes with FAP were demonstrated in vivo using ICG angiography for the first time. ICG angiography may be very beneficial to evaluate occult choroidal involvement in patients with FAP.

Amyloid Neuropathies, Familial↗

PubMedDate not supplied

Beam forming of ultra-wideband pulses by a complex-valued spatio-temporal multilayer neural network.

We present a neuro-beam former of ultra-wideband (UWB) pulses employing complex-valued spatio-temporal multilayer neural network, where complex-valued back propagation through time (CV-BPTT) is used as a learning algorithm. The system performance is evaluated with a UWB mono-cycle pulse. Simulation results in suppressing multiple UWB interferes and in steering to multiple desired UWB pulses, demonstrates the applicability of the proposed system.

Algorithms↗

PubMedDate not supplied

Optical coherence tomography for retinal detachment with a macular hole in a highly myopic eye.

Optical coherence tomography can facilitate observation of the macula in highly myopic eyes, which may be difficult using an ophthalmoscope because of myopic chorioretinal atrophy. The use of optical coherence tomography to record the process of retinal reattachment and closure of a macular hole in a highly myopic eye following macular buckling surgery is described.

Aged↗