Biomedical subjects

K Kansaku

Publications and source records attributed to K Kansaku.

11 recordsLinked to original sources

PubMed2006

Neural correlates of tic generation in Tourette syndrome: an event-related functional MRI study.

Little is known about the neural correlates of tics and associated urges. In the present study, we aimed to explore the neural basis of tics in patients with Tourette syndrome by using event-related functional MRI (fMRI). Ten patients (6 women, 4 men; age: mean +/- SD = 31 +/- 11.2) were studied while spontaneously exhibiting a variety of motor and vocal tics. On the basis of synchronized video/audio recordings, fMRI activities were analysed 2 s before and at tic onset irrespective of the clinical phenomenology. We identified a brain network of paralimbic areas such as anterior cingulate and insular cortex, supplementary motor area (SMA) and parietal operculum (PO) predominantly activated before tic onset (P < 0.05, corrected for multiple comparisons). In contrast, at the beginning of tic action, significant fMRI activities were found in sensorimotor areas including superior parietal lobule bilaterally and cerebellum. The results of this study indicate that paralimbic and sensory association areas are critically implicated in tic generation, similar to movements triggered internally by unpleasant sensations, as has been shown for pain or itching.

Adult↗

PubMed2001

Retinotopic hemodynamic activation of the human V5/MT area during optokinetic responses.

To detect retinotopic activation in the human V5/MT, we obtained fMRI signals during optokinetic responses (OKR). We used two types of patterns, consisting of random dots plotted in either the central or peripheral regions, to stimulate the central and peripheral visual fields, respectively. These patterns moved at a constant speed of 20 degrees/s rightward and leftward alternately. Subjects were required to track the patterns with their eyes. The two types of visual stimuli elicited different patterns of brain activation; the area with the most significant response to central visual field stimuli was located posteriorly to that responding to peripheral visual field stimuli.

Adult↗

PubMed2001

Demonstration of the postcommissural fibres of the fornix in short-inversion time inversion-recovery imaging on a high-field system.

Short-inversion time inversion-recovery (STIR) imaging using a 3 tesla system was assessed to reveal the postcommissural fibres (PF) of the fornix, which have rarely been highlighted neuroradiologically in the clinical setting. We studied 27 normal subjects. Sequence parameters were TR/TE/TI 8000/52/ 150 ms. STIR was expected to take advantage of the high signal-to-noise ratio of a high-field system, due to the long repetition time. PF were identifiable in axial and coronal slices in all cases. They were bordered anteriorly and superiorly by the anterior commissure and posteriorly and inferiorly by the mamillary body. Behind the anterior commissure, they ran in an arch-shaped posterior and inferior course in the hypothalamic nuclei and joined the mamillary body anterolaterally. They usually extended through three 3-mm slices (with 1 mm interslice gap) in anteroposterior and vertical dimensions. Little variation was observed in their course or size. Demonstration of the PF would provide a more detailed correlation of human neuroanatomy to hypothalamic function and individualised understanding of hypothalamic pathology and influence therapy.

Adolescent↗

PubMed2001

Imaging studies on sex differences in the lateralization of language.

It has been proposed that language is more strongly lateralized in males than in females. Recent imaging studies, however, have yielded a variety of seemingly contradictory observations. Here, we categorize these observations into three groups: (1) studies that employed sub-lexical tasks applicable to nonwords, which found sex-differences in the anterior language areas; (2) studies that employed tasks applicable to real individual words, which reported lateralized activation in both sexes (and thus no sex-differences); and (3) studies that employed passive listening to stories with a global language structure, which found clear sex-differences in the posterior language areas. We suggest that these differences in observations are explained, at least in part, by the amount of time demanded relative to the interhemispheric conduction delay.

Adult↗

PubMed2000

Sex differences in lateralization revealed in the posterior language areas.

It has been hypothesized that language functions are more strongly lateralized to the left hemisphere in males than in females. Previous anatomical data and patient studies have suggested that the posterior language areas should exhibit sex differences. However, neuroimaging studies to date have only provided support for differences in the anterior language areas. To look for differences in the posterior language areas, functional magnetic resonance imaging scans were obtained while male and female subjects listened attentively to a story read aloud and to the same story replayed in reverse. Comparing activation in the superior and the middle temporal gyri during a story to activation during reverse replay of the story showed lateralization to the left in males but not in females. There was no lateralization in either sex when comparing activation during random fragmentation of the story to reverse replay. In the angular and the supramarginal gyri, however, activation was lateralized to the left hemisphere in both sexes, unlike the sex-dependent activation of the posterior temporal lobes. We infer that females use the posterior temporal lobes more bilaterally during linguistic processing of global structures in a narrative than males do.

Adult↗

PubMed1998

Sequential hemodynamic activation of motor areas and the draining veins during finger movements revealed by cross-correlation between signals from fMRI.

Activity in the human supplementary motor area (SMA), primary motor cortex (M1), and the draining vein of the motor cortex during a visually triggered finger opposition task was measured by functional magnetic resonance imaging with a repetition time of 1 s. Sequential hemodynamic activation in these areas was revealed by cross-correlating a signal sequence in M1 directly with signal sequences from SMA and the draining vein, and applying polynomial fitting with the aid of Akaike's information criterion. We succeeded in detecting a time delay of approximately 0.5 s between the activations of SMA and M1, and a delay of nearly 1.3 s between the activations of M1 and its draining vein. The new combination of fMRI and data analysis techniques has attained a time resolution comparable to those in preceding studies that used shorter fMRI repetition times of 100-200 ms.

Adult↗

PubMed1998

Functional magnetic resonance imaging during recognition of written words: Chinese characters for concrete objects versus abstract concepts.

An attempt was made to apply functional magnetic resonance imaging (fMRI) to reveal cortical areas activated upon presentation of two groups of Chinese characters in six normal right-handed, male, Japanese subjects. Presentation of the characters representing 'abstract concepts' activated the bilateral occipital region without a significant difference between the bilateral occipital and temporal regions. Presentation of the characters representing 'concrete objects' resulted in significantly stronger activation in the left occipital and temporal regions. These results suggest that recognition of concrete characters involves a stronger initial process in the left occipital temporal cortices than recognition of abstract characters.

Adult↗

PubMed1998

Functional magnetic resonance imaging during recognition of written words: Chinese characters for concrete objects versus abstract concepts.

Adult↗

PubMed1998

Serial magnetic resonance imaging of acute spontaneous thrombosis of a giant intracranial aneurysm--case report.

A 46-year-old female presented with decreased bilateral visual acuity due to an unruptured non-thrombosed giant aneurysm arising from the left internal carotid artery. After admission, acute thrombosis of the aneurysm occurred spontaneously. Her consciousness and visual acuity temporarily worsened. Serial T2-weighted magnetic resonance (MR) imaging showed the size of the low intensity area near the orifice increased, and the aneurysm ruptured thereafter. Trapping of the aneurysm with a high-flow bypass was performed. Serial MR imaging findings clearly demonstrated the intraluminal structure of the thrombosed giant aneurysm. The aneurysm grew in size after thrombosis. The enlarging signal-void area on T2-weighted MR images were indicative of aneurysmal rupture. MR imaging is quite helpful to evaluate the changes of intraluminal thrombosis and size in giant aneurysms.

Acute Disease↗

PubMed1998

Differences in auditory scalp potentials evoked by meaningful words and nonlinguistic stimuli.

Differences in auditory evoked potentials with meaningful words and their reverse playback may reflect different neural processes in recognizing auditory stimuli. Auditory evoked potentials with the words and their reverse playback were analyzed for eight volunteers, and a maximal difference was observed at a latency around 400 msec. over the left middle temporal central area.

Cerebral Cortex↗

PubMedDate not supplied

Binocular interactions in visual evoked cortical potentials with two light-emitting-diodes.

Binocular interaction for a central field was studied with transient scalp visual evoked cortical potentials (VECPs) using two light-emitting-diodes. VECPs were obtained for binocular and monocular visions with dominant and non-dominant eyes, and arithmetical sums of monocular VECPs with dominant and non-dominant eyes were calculated. Amplitude and latency of remarkable initial three peaks were tested with the multivariate analysis of variance. Significant differences were noted among the four VECPs. Pairwise comparisons showed that (1) the amplitude of the first peak for the binocular VECPs was larger than that for the monocular VECPs but smaller than that for the sum-VECPs; the latency of the first peaks for the binocular VECPs were earlier than that for the monocular VECPs with the non-dominant eye; (2) the amplitude of the first negative peak for the sum-VECPs was larger than that for the binocular VECPs, and the peak latency for the sum-VECPs showed later than that for the binocular VECPs; (3) the amplitude of the second positive peak for the binocular VECPs and monocular VECPs with the dominant eye was larger than that with the non-dominant eye, but smaller for the binocular VECPS than that for the sum-VECPs; the latency for the binocular VECPs showed earlier than that for the monocular VECPs with the dominant eye and for the sum-VECPs. Binocular suppression was noted in amplitude for the three peaks and binocular facilitation was noted in latency for the latter two peaks.

Adult↗