Biomedical subjects

Keiichi Tajima

Publications and source records attributed to Keiichi Tajima.

3 recordsLinked to original sources

PubMed2006

Neural processes involved with perception of non-native durational contrasts.

Neural processes underlying identification of durational contrasts were studied by comparing English and Japanese speakers for Japanese short/long vowel identification relative to consonant identification. Enhanced activities for non-native contrast (Japanese short/long vowel identification by English speakers) were observed in brain regions involved with articulatory-auditory mapping (Broca's area, superior temporal gyrus, planum temporale, and cerebellum), but not in the supramarginal gyrus. Greater activity in the supramarginal gyrus found for the consonant identification over short/long vowel identification by Japanese speakers implies that it is more important for phonetic contrasts differing in place of articulation than for vowel duration. These results support the hypothesis that neural processes used to facilitate perception depend on the relative contribution of information important for articulatory planning control.

Adult↗

PubMed2003

Olprinone, a phosphodiesterase III inhibitor, does not affect hypoxia-induced pial arteriolar dilatation in rabbits.

PURPOSE: Olprinone, a phosphodiesterase III inhibitor, is used for the treatment of heart failure or asthma. Such patients may suffer from hypoxia. However, the effect of olprinone on the cerebral vasodilator response to hypoxia remains unclear. METHODS: Rabbits were anesthetized and ventilated mechanically. The pial arteriolar diameter was determined using a cranial window and intravital microscopy. Hypoxia was induced twice in the same animal by reducing FIO(2) to 0.1. The first episode was induced during an infusion of saline, and the second during an infusion of saline (saline group; n = 8) or olprinone (1 microg x kg(-1) x min(-1), OLP1 group; n = 8 or 10 microg x kg(-1) x min(-1), OLP10 group; n = 8). The pial arteriolar responses to hypoxia were recorded and compared between the two episodes of hypoxia in each group. RESULTS: Blood gas data in the first hypoxic challenge were identical to those in the second challenge in each group. Pial arteriolar diameter increased significantly during hypoxia. In arterioles between 50-100 microm diameter, first and second hypoxia-induced pial arteriolar dilatation in OLP1 were 13 +/- 6% and 10 +/- 7% respectively (P = 0.574 ) and those in OLP10 were 16 +/- 6% and 15 +/- 7% respectively (P = 0.606). In arterioles between 25-50 microm, the results were the same as in arterioles between 50-100 microm. CONCLUSION: Olprinone does not affect the hypoxia-induced dilatation of pial arterioles in pentobarbital anesthetized rabbits.

Animals↗

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↗