Biomedical subjects

Tadashi Yamazaki

Publications and source records attributed to Tadashi Yamazaki.

12 recordsLinked to original sources

PubMed2006

Chronically mountable goggles for persistent exposure to single orientation.

To examine the effect of experience on the developmental plasticity of functional maps in the visual cortex, we need to establish a method for a stable visual experience manipulation under the freely moving condition. For this purpose, we fabricated goggles that are chronically mounted stably on the animal's head, but easy to replace according to the animal's growth. Here we report the design of the goggles and the method of mounting them on the head of animals. By this method, combined with the intrinsic signal optical imaging technique, we were able to observe a rapid and robust reorganization of orientation maps.

Aging↗

PubMed2006

Focalized contractile impairment at hypertrophied myocardium proven in consideration of wall stress in patients with hypertrophic cardiomyopathy.

In hypertrophic cardiomyopathy (HCM) a hyperkinetic state is sometimes observed in spite of impaired systolic function in the hypertrophied myocardium. The aim of the present study was to determine the mechanism of this paradox. Seventeen patients with HCM and 10 normal subjects underwent cine magnetic resonance (MR) imaging to measure percent systolic wall thickening and percent fractional shortening. The ratio of systolic radial wall stress of the LV at the hypertrophied myocardium over that at the nonhypertrophied myocardium was evaluated to describe the focal advantageous condition for wall thickening. The ratio was 0.66 +/- 0.36 at the start of contraction and 0.78 +/- 0.31 at early-systole, indicating consistently smaller radial wall stress at the hypertrophied myocardium. Although the condition for contraction was favorable (a ratio less than 1.00), percent systolic wall thickening at the hypertrophied myocardium (23.0 +/- 11.8%) was smaller than that at the nonhypertrophied myocardium (70.5 +/- 32.3%). Smaller end-diastolic dimension (HCM group; 45.2 +/- 4.2 mm, reference group; 48.9 +/- 4.1 mm, P = 0.04) with a statistically identical value of systolic decrease in intraventricular dimension (HCM group; 19.7 +/- 3.9 mm, reference group; 18.9 +/- 3.2 mm, P = 0.60) yielded high percent fractional shortening in patients with HCM (43.5 +/- 7.6%). Although contractile impairment was proven at the hypertrophied region with low radial wall stress in the HCM group, the smaller end-diastolic dimension in this group resulted in high percent fractional shortening.

Cardiomyopathy, Hypertrophic↗

PubMed2005

Neural modeling of an internal clock.

We studied a simple random recurrent inhibitory network. Despite its simplicity, the dynamics was so rich that activity patterns of neurons evolved with time without recurrence due to random recurrent connections among neurons. The sequence of activity patterns was generated by the trigger of an external signal, and the generation was stable against noise. Moreover, the same sequence was reproducible using a strong transient signal, that is, the sequence generation could be reset. Therefore, a time passage from the trigger of an external signal could be represented by the sequence of activity patterns, suggesting that this model could work as an internal clock. The model could generate different sequences of activity patterns by providing different external signals; thus, spatiotemporal information could be represented by this model. Moreover, it was possible to speed up and slow down the sequence generation.

Action Potentials↗

PubMed2004

Sound frequency representation in cat auditory cortex.

Using the intrinsic signal optical recording technique, we reconstructed the two-dimensional pattern of stimulus-evoked neuronal activities in the auditory cortex of anesthetized and paralyzed cats. The average magnitude of intrinsic signal in response to a pure tone stimulus increased steadily as the sound pressure level increased. A detailed analysis demonstrated that the evoked signals at early frames were scaled by the sound pressure level, which in turn indicated the presence of a minimum level of sound pressure beyond which stimulus-related intrinsic signal can be generated. Intrinsic signals evoked significantly by pure tone stimuli of different frequencies were localized and arranged in an orderly manner in the middle ectosylvian gyrus, which indicates that the primary auditory field (AI) is tonotopically organized. The arrangement of optimal frequencies obtained from optical recordings of the same auditory cortex, which were conducted on different days, was highly reproducible. Furthermore, other auditory fields surrounding AI in the recorded area were allocated based on the observed tonotopicity. We also conducted unit recordings on the cats used for optical recording with the same set of acoustic stimuli. The gross feature of the arrangement of optimal frequencies determined by unit recordings agreed with the tonotopic arrangement determined by the optical recording, although the precise agreement was not obtained.

Acoustic Stimulation↗

PubMed2004

Development of a pioneering clinical support system utilizing information technology.

Nowadays, evidence-based medicine has entered the mainstream of clinical judgement and the human genome has been completely decoded. Even the concept of individually designed medicine, that is, tailor-made medicine, is now being discussed. Due to their complexity, however, management methods for clinical information have yet to be established. We have conducted a study on a universal technique which enables one to select or produce by employing information processing technology clinical findings from various clinical information generated in vast quantity in day-to-day clinical practice, and to share such information and/or the results of analysis between two or more institutions. In this study, clinically useful findings have been successfully obtained by systematizing actual clinical information and genomic information obtained by an appropriate collecting and management method of information with due consideration to ethical issues. We report here these medical achievements as well as technological ones which will play a role in propagating such medical achievements.

Artificial Intelligence↗

PubMed2003

Serous cystadenoma of the pancreas associated with obstructive jaundice.

We herein report a case of pancreatic serous cystadenoma in a patient who presented with jaundice, and we provide a review of the literature. A 53-year-old man was admitted with complaints of jaundice and weight loss. With a preoperative diagnosis of pancreatic serous cystadenoma with obstructive jaundice, he underwent pylorus-preserving pancreatoduodenectomy. A cystic tumor partially protruding into the bile duct was observed in the pancreatic head. Histology verified serous cystadenoma of the pancreas. Histologically, no atypia was proven in the epithelium. There have been only eight case reports dealing with serous cystadenoma of the pancreas with obstructive jaundice. Although serous cystadenoma of the pancreas has essentially a benign nature, pylorus-preserving pancreatoduodenectomy is the treatment of choice when available to avoid the recurrence of obstructive jaundice.

Cholangiopancreatography, Endoscopic Retrograde↗

PubMed2003

A common Ile 823 Met variant of ATP-binding cassette transporter A1 gene (ABCA1) alters high density lipoprotein cholesterol level in Japanese population.

Recently, variants in ATP-binding cassette transporter A1 (ABCA1) were demonstrated to be associated with increased level of high density lipoprotein cholesterol (HDL-C) and decreased risk of coronary artery disease (CAD) in Caucasians. However, this is not universally applicable due to the ethnic or environmental differences. In this context, to clarify the effect of ABCA1 in Japanese, we evaluated the phenotypic effects of I/M 823 and R/K 219 variants on the plasma level of HDL-C in 410 patients recruited in our hospital. Subjects with M 823 allele had significantly higher level of HDL-C than those without M823 allele (49.0+/-15.1 vs. 44.9+/-11.5 mg/dl, respectively, P<0.05). This statistical significance did not change even after multiple regression analysis. In contrast, there was no difference in HDL-C level among the genotypes in R/K 219 polymorphism. Further, in our study population an inverse relationship was shown to exist between HDL-C level and incidence of CAD. However, no positive association was observed between those variants and susceptibility to CAD. In this study, we provide evidence that I/M 823 variant, not R/K 219 variant, in ABCA1 is one of the determinants of HDL-C level, suggesting the importance of this gene on lipid metabolism in Japanese.

ATP Binding Cassette Transporter 1↗

PubMed2003

Mathematical analysis of a correlation-based model for orientation map formation.

We consider a correlation-based model for the orientation map formation proposed by Miller [Journal of Neuroscience 14 (1994) 409] and study the formation mathematically. We perform the Fourier transform and compute the principal component of the model. With our analysis, the roles of functions are clarified and the result indicates that the developed orientation maps have the following properties. (1) Maps have oriented receptive fields. (2) Preferred orientations smoothly change on the cortical surface. (3) Periodicity of preferred orientations does not appear. (4) Periodicity of phases appears. (5) Singular points appear irregularly on the cortical surface. Our analytical results are justified by computer simulations.

Algorithms↗

PubMed2002

A mathematical analysis of the development of oriented receptive fields in Linsker's model.

We consider Linsker's neural network model and study how oriented receptive fields (RFs) are developed at layer F-->G mathematically. We concentrate on the Mexican-hat correlation function and show that this function determines the spatial frequency of RFs. We also focus on the role of the arbor function. Two types of arbor functions, a Gaussian type and a step type, are considered, and it is shown that the Gaussian arbor function develops center-surround RFs while the step arbor function enables the development of multi-lobed RFs in addition to center-surround RFs. The roles of Linsker's parameters k1, k2 are also discussed.

Fourier Analysis↗

PubMed2002

Vector analysis of the wall shear rate at the human aortoiliac bifurcation using cine MR velocity mapping.

OBJECTIVE: Small or oscillatory wall shear stress accelerates atherosclerosis. MR velocity mapping is feasible for vector analysis of wall shear rate (a spatial gradient of blood flow velocity at the vessel wall) in humans. A relationship between anatomic variations at the aortoiliac bifurcation and characteristics of wall shear rate was evaluated. SUBJECTS AND METHODS: To obtain two components of wall shear rate vectors, an axial component along the vessel axis and a nonaxial component perpendicular to the former at the inner and outer walls of the common iliac arteries just distal to the aortoiliac bifurcation, we performed cine MR velocity mapping with three orthogonal velocity-encoded directions in seven volunteers. RESULTS: The peak axial component at the outer wall (120.6 +/- 37.2 sec(-1)) was smaller than that at the inner wall (196.0 +/- 53.7 sec(-1)) (p < 0.01). Oscillation described by a time integral of the axial component in recessive blood flow direction over integrals in dominant and recessive directions at the outer wall was greater (0.24 +/- 0.11) than that at the inner wall (0.15 +/- 0.08) (p < 0.01). The intersecting angle between the extrapolation of the aortic axis and the direction of the axis of the common iliac artery correlated positively with the peak axial component (r = 0.577, p < 0.05) and inversely with oscillation (r = 0.603, p < 0.05). CONCLUSION: Three-dimensional vector analysis with MR velocity mapping revealed that the outer wall at the aortoiliac bifurcation showed low and oscillatory shear rate, and this inclination was increased when the takeoff angle of the iliac artery was small.

Adult↗

PubMedDate not supplied

A neural network model for trace conditioning.

We studied the dynamics of a neural network that has both recurrent excitatory and random inhibitory connections. Neurons started to become active when a relatively weak transient excitatory signal was presented and the activity was sustained due to the recurrent excitatory connections. The sustained activity stopped when a strong transient signal was presented or when neurons were disinhibited. The random inhibitory connections modulated the activity patterns of neurons so that the patterns evolved without recurrence with time. Hence, a time passage between the onsets of the two transient signals was represented by the sequence of activity patterns. We then applied this model to represent the trace eye blink conditioning, which is mediated by the hippocampus. We assumed this model as CA3 of the hippocampus and considered an output neuron corresponding to a neuron in CA1. The activity pattern of the output neuron was similar to that of CA1 neurons during trace eye blink conditioning, which was experimentally observed.

Animals↗

PubMedDate not supplied

Effusive constrictive pericarditis due to rheumatoid arthritis revealed by pericardiocentesis with simultaneous pressure recording--a case report.

A 59-year-old man had a history of rheumatoid arthritis. He presented with incurable pericardial effusion. He was repeatedly treated with pericardiocentesis with only transient attenuation of his symptoms because the underlying pericardial constriction had been overlooked. This time the authors diagnosed effusive constrictive pericarditis due to rheumatoid arthritis using the hemodynamic findings observed before and after pericardiocentesis.

Arthritis, Rheumatoid↗