Biomedical subjects

Rieko Kubo

Publications and source records attributed to Rieko Kubo.

3 recordsLinked to original sources

PubMed2005

Interval representative of transmural dispersion of repolarization in children and young adolescents with congenital long QT syndrome.

BACKGROUND: It has been shown experimentally that the interval from the nadir of the initial negative T wave to the end of the T wave is representative of transmural dispersion of repolarization (TDR) when complex T waves are present. In the clinical setting, however, the interval representative of TDR in patients with long QT syndrome (LQTS) is a controversial subject. METHODS AND RESULTS: Five symptomatic patients (3 boys, 2 girls; 3 LQT1, 2 LQT2) were evaluated by a face immersion test before and after treatment to compare the configuration of the T wave. When the notch disappeared after treatment, the single peak of the T wave after treatment coincided with the nadir of the notch before treatment. When the notch remained the same after treatment as before treatment and when the QTc decreased, the corrected interval from the nadir of the notch to the end of the T wave was for the most part shortened. CONCLUSIONS: The present study showed that the interval representative of the TDR in the clinical surface electrocardiogram can be obtained from the nadir of the notch to the end of the T wave in children and adolescents with LQTS, as was shown in the experimental study.

Adolescent↗

PubMed2003

Learning-induced neural plasticity associated with improved identification performance after training of a difficult second-language phonetic contrast.

Adult native Japanese speakers have difficulty perceiving the English /r-l/ phonetic contrast even after years of exposure. However, after extensive perceptual identification training, long-lasting improvement in identification performance can be attained. This fMRI study investigates localized changes in brain activity associated with 1 month of extensive feedback-based perceptual identification training by native Japanese speakers learning the English /r-l/ phonetic contrast. Before and after training, separate functional brain imaging sessions were conducted for identification of the English /r-l/ contrast (difficult for Japanese speakers), /b-g/ contrast (easy), and /b-v/ contrast (difficult), in which signal-correlated noise served as the reference control condition. Neural plasticity, denoted by exclusive enhancement in brain activity for the /r-l/ contrast, does not involve only reorganization in brain regions concerned with acoustic-phonetic processing (superior and medial temporal areas) but also the recruitment of additional bilateral cortical (supramarginal gyrus, planum temporale, Broca's area, premotor cortex, supplementary motor area) and subcortical regions (cerebellum, basal ganglia, substantia nigra) involved with auditory-articulatory (perceptual-motor) mappings related to verbal speech processing and learning. Contrary to what one may expect, brain activity for perception of a difficult contrast does not come to resemble that of an easy contrast as learning proceeds. Rather, the results support the hypothesis that improved identification performance may be due to the acquisition of auditory-articulatory mappings allowing for perception to be made in reference to potential action.

Brain↗

PubMed2003

Cortical evidence of the perceptual backward masking effect on /l/ and /r/ sounds from a following vowel in Japanese speakers.

We examined the influence of stimulus duration of foreign consonant vowel stimuli on the MMNm (magnetic counter part of mismatch negativity). In Experiment 1, /ra/ and /la/ stimuli were synthesized and subjects were native Japanese speakers who are known to have difficulty discriminating the stimuli. "Short" duration stimuli were terminated in the middle of the consonant-to-vowel transition (110 ms). They were nevertheless clearly identifiable by English speakers. A clear MMNm was observed only for short-duration stimuli but not for untruncated long-duration (150-ms) stimuli. We suggest that the diminished MMNm for longer duration stimuli result from more effective masking by the longer vowel part. In Experiment 2 we examined this hypothesis by presenting only the third formant (F3) component of the original stimuli, since the acoustic difference between /la/ and /ra/ is most evident in the third formant, whereas F1 and F2 play a major role in vowel perception. If the MMNm effect depends on the acoustic property of F3, a stimulus duration effect comparable to that found with the original /la/ and /ra/ stimuli might be expected. However, if the effect is attributable to the masking effect from the vowel, no influence of stimulus duration would be expected, since neither stimulus contains F1 and F2 components. In fact, the results showed that the "F3 only" stimuli did not show a duration effect; MMNm was always elicited independent of stimulus duration. The MMN stimulus duration effect is thus suggested to come from the backward masking of foreign consonants by subsequent vowels.

Acoustic Stimulation↗