Biomedical subjects

Tatsuo Nagasaka

Publications and source records attributed to Tatsuo Nagasaka.

6 recordsLinked to original sources

PubMed2003

Changes in brain activation patterns associated with learning of Korean words by Japanese: an fMRI study.

We used functional magnetic resonance imaging (fMRI) to explore the change in brain activation associated with the learning of Korean words written in Han-gul characters (K-words) by young Japanese at two stages. Subjects were 12 right-handed native Japanese without previous knowledge of Korean words and characters. On the first day they were taught the pronunciation and meaning of 20 K-words. Then, after the first fMRI session (on day 2), they were given a set of 20 cards with the words and corresponding photographs. They also received a tape and were instructed to memorize the 20 K-words by studying them every day until the day of the second fMRI session (day 16). During the fMRI sessions, 20 Japanese words written in kana syllabograms (J-words) and the 20 previously presented K-words, as well as 20 new K-words (Kn-words) were presented visually for silent reading. The first J-word reading, relative to the first K-word reading, showed activation in the left angular gyrus. K-word reading relative to J-word reading during both sessions showed activation in occipital regions. Within these activated areas, session by condition interaction was found only in the left angular gyrus. The interaction between session and condition resulted from the fact that the differences in blood oxygenation-level-dependent signals between K-words and J-words and between Kn-words and J-words were significantly greater in the first session than in the second session. From the results, we concluded that patterns of brain activation changed as the memory of the 20 K-words became fixed through daily practice and that reading of both Korean words and Japanese syllabograms engaged the left angular gyrus.

Adult↗

PubMed2003

Metabolic properties of band heterotopia differ from those of other cortical dysplasias: a proton magnetic resonance spectroscopy study.

PURPOSE: To assess the biochemical properties of band heterotopia in comparison with other cortical developmental malformations (CDMs) by using proton magnetic resonance spectroscopy (1H-MRS). METHODS: We performed localized single-voxel 1H-MRS studies on 13 patients [five band heterotopia (BH), two focal cortical dysplasia (CD), two unilateral CD, one bilateral perisylvian dysplasia, three hemimegalencephaly]. CDMs other than BH were categorized as CD. Spectra were acquired from volumes of interest (VOIs) localized in the CD and in normal-appearing cortex on the contralateral side. In BH patients, the VOIs were the external cortex and the laminar heterotopia. For the BH study, spectra also were obtained from the cortex of age-matched normal volunteers. RESULTS: The spectra of CD lesions were characterized by significantly lower ratios of N-acetyl aspartate to creatine (NAA/Cr) and by higher choline to Cr (Cho/Cr) ratios than in the contralateral remote cortex (p = 0.01 and 0.01, respectively). The NAA/Cr and Cho/Cr ratios of the external cortex of BH were not significantly different from those of normal volunteers. The NAA/Cr ratio of the laminar heterotopia was not significantly different from that of the external cortex (p = 0.12) or normal volunteers (p = 0.60), whereas Cho/Cr was significantly higher in laminar heterotopias than in the external cortex (p = 0.04) or controls (p = 0.03). CONCLUSIONS: 1H-MRS can distinguish between the metabolic properties of BH and CD.

Adolescent↗

PubMed2002

Neural basis of the retrieval of people's names: evidence from brain-damaged patients and fMRI.

The aim of this study was to identify the neuroanatomical basis of the retrieval of people's names. Lesion data showed that patients with language-dominant temporal lobectomy had impairments in their ability to retrieve familiar and newly learned people's names, whereas patients with language-nondominant temporal lobectomy had difficulty retrieving newly learned people's names. Functional magnetic resonance imaging experiments revealed activations in the left temporal polar region during the retrieval of familiar and newly learned people's names, and in the right superior temporal and bilateral prefrontal cortices during the retrieval of newly learned information from face cues. These data provide new evidence that the left anterior temporal region is crucial for the retrieval of people's names irrespective of their familiarity and that the right superior temporal and bilateral prefrontal areas are crucial for the process of associating newly learned people's faces and names.

Adolescent↗

PubMed2002

A formal total synthesis of (+/-)-cephalotaxine using sequential N-acyliminium ion reactions.

[reaction: see text] Novel synthesis of cephalotaxine 1 based on tertiary N-acyliminium ion chemistry starting from alkynylamide 2 was achieved. The key steps include the preparation of pyrroloisoquinoline 4 from alkynylamide 2, the ring expansion of pyrroloisoquinoline 4 to pyrrolobenzazepine 12, and the construction of cyclopentapyrrolobenzazepine ring system 6, all of which are derived from N-acyliminium ion intermediates.

Harringtonines↗

PubMed2002

Neural basis of temporal context memory: a functional MRI study.

Temporal context information is crucial to understanding human episodic memory. Human lesion and neuroimaging data indicate that prefrontal regions are important for retrieving temporal context memory, although the exact nature of their involvement is still unclear. We employed functional magnetic resonance imaging (fMRI) to elucidate the neural basis of two kinds of temporal context memory: the temporal order of items between lists and within a list. On the day of the fMRI experiment, subjects memorized a list of 30 pictures in the morning and another list of 30 pictures in the afternoon. During the scanning session, the subjects performed three tasks. In a between-lists task, they were asked to judge the temporal order between two items that had been presented in different lists. In a within-list task, they were asked to judge the temporal order between two items that had been presented in a single list. We found bilateral prefrontal activities during these two temporal context memory tasks compared with a simple item-recognition task. Furthermore, in direct comparison between these two tasks, we found differential prefrontal activities. Thus, right prefrontal activity was associated with temporal order judgment of items between lists, whereas left prefrontal activity was related to temporal order judgment of items within a list. These results indicate that retrieval processes of two kinds of temporal context memory are supported by different, but overlapping, sets of cerebral regions. We speculate that this reflects different cognitive processes for retrieving temporal context memory between separate episodes and within a single episode.

Adult↗

PubMed1998

Stereoselective Synthesis of Tilivalline(1).

Tilivalline 1, a metabolite from Klebsiella pneumoniae var. ocytoca, was easily synthesized in five steps from (S)-proline and 3-(benzyloxy)isatoic anhydride 4g. This synthesis is based on modified Curtius reactions of 3-substituted phthalic anhydrides 11 to 3-substituted isatoic anhydrides 4, conversion of lactams 6 to the acyliminium precursors 7 and stereoselective introduction of indole from the less hindered side of 7.

Journal Article↗