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Ippeita Dan

Publications and source records attributed to Ippeita Dan.

15 recordsLinked to original sources
PubMed2007

10/20, 10/10, and 10/5 systems revisited: their validity as relative head-surface-based positioning systems.

With the advent of multi-channel EEG hardware systems and the concurrent development of topographic and tomographic signal source localization methods, the international 10/20 system, a standard system for electrode positioning with 21 electrodes, was extended to higher density electrode settings such as 10/10 and 10/5 systems, allowing more than 300 electrode positions. However, their effectiveness as relative head-surface-based positioning systems has not been examined. We previously developed a virtual 10/20 measurement algorithm that can analyze any structural MR head and brain image. Extending this method to the virtual 10/10 and 10/5 measurement algorithms, we analyzed the MR images of 17 healthy subjects. The acquired scalp positions of the 10/10 and 10/5 systems were normalized to the Montreal Neurological Institute (MNI) stereotactic coordinates and their spatial variability was assessed. We described and examined the effects of spatial variability due to the selection of positioning systems and landmark placement strategies. As long as a detailed rule for a particular system was provided, it yielded precise landmark positions on the scalp. Moreover, we evaluated the effective spatial resolution of 329 scalp landmark positions of the 10/5 system for multi-subject studies. As long as a detailed rule for landmark setting was provided, 241 scalp positions could be set effectively when there was no overlapping of two neighboring positions. Importantly, 10/10 positions could be well separated on a scalp without overlapping. This study presents a referential framework for establishing the effective spatial resolutions of 10/20, 10/10, and 10/5 systems as relative head-surface-based positioning systems.

Body Surface Area↗
PubMed2007

Virtual spatial registration of stand-alone fNIRS data to MNI space.

The registration of functional brain data to common stereotaxic brain space facilitates data sharing and integration across different subjects, studies, and even imaging modalities. Thus, we previously described a method for the probabilistic registration of functional near-infrared spectroscopy (fNIRS) data onto Montreal Neurological Institute (MNI) coordinate space that can be used even when magnetic resonance images of the subjects are not available. This method, however, requires the careful measurement of scalp landmarks and fNIRS optode positions using a 3D-digitizer. Here we present a novel registration method, based on simulations in place of physical measurements for optode positioning. First, we constructed a holder deformation algorithm and examined its validity by comparing virtual and actual deformation of holders on spherical phantoms and real head surfaces. The discrepancies were negligible. Next, we registered virtual holders on synthetic heads and brains that represent size and shape variations among the population. The registered positions were normalized to MNI space. By repeating this process across synthetic heads and brains, we statistically estimated the most probable MNI coordinate values, and clarified errors, which were in the order of several millimeters across the scalp, associated with this estimation. In essence, the current method allowed the spatial registration of completely stand-alone fNIRS data onto MNI space without the use of supplementary measurements. This method will not only provide a practical solution to the spatial registration issues in fNIRS studies, but will also enhance cross-modal communications within the neuroimaging community.

Adult↗
PubMed2006

Exploring the false discovery rate in multichannel NIRS.

Near infrared spectroscopy (NIRS), an emerging non-invasive tool for functional neuroimaging, has evolved as a multichannel technique allowing simultaneous measurements through many channels ranging from below ten to above hundred. Simultaneous testing of such a large number of channels escalates the risk of Type I error, therefore multiplicity correction is unavoidable. To date, only a few studies have considered this issue using Bonferroni correction, which is an effective conservative solution, but may be too severe for neuroimaging. Its power varies in inverse proportion of the number of channels, which varies among NIRS studies depending on selected region of interest (ROI), thereby leading to a subjective inference. This problem may be well circumvented by a more contemporary approach, called false discovery rate (FDR) that is widely being adopted in functional neuroimaging. An FDR-based procedure controls the expected proportion of erroneously rejected hypotheses among the rejected hypotheses, which offers a more objective, powerful, and consistent measure of Type I error than Bonferroni correction and maintains a better balance between power and specificity. In this technical note, we examine FDR approach using examples from simulated and real NIRS data. The FDR-based procedure could yield 52% more power than Bonferroni correction in a 172-channel real NIRS study and proved to be more robust against the changing number of channels.

Brain↗
PubMed2006

Prefrontal activity during flavor difference test: application of functional near-infrared spectroscopy to sensory evaluation studies.

Sensory evaluation (SE) of food attributes involves various levels of cognitive functions, yet not much has been studied about its neural basis. Using multi-channel functional near-infrared spectroscopy (fNIRS), we examined the activation of the anterior portion of the lateral prefrontal cortex (LPFC) of 12 healthy volunteers during the SE of tea samples. The experimental task used corresponded to the early phase of the same-different test, and required subjects to attentively taste tea samples and memorize their flavors. To isolate activation associated with the cognitive functions involved in the task, we contrasted the results with those achieved by a control (Ctl) task during which subjects held familiar tea samples in their mouths without actively evaluating their flavor. We probabilistically registered the fNIRS data to the Montreal Neurological Institute standard brain space to examine the results as they correspond with other published neuroimaging studies. We found significant activation in the left LPFC and in the right inferior frontal gyrus. The activation pattern was consistent with earlier studies on encoding of other sensory stimuli, with cortical regions supposed to be involved in semantic and perceptual processing. This research makes a start on characterizing the cognitive process employed during SE from the neuroimaging perspective.

Adult↗
PubMed2006

Prefrontal activity during taste encoding: an fNIRS study.

To elucidate the function of the lateral prefrontal cortex (LPFC) in taste encoding, it is worth applying to taste, the psychological paradigms of intentional memorization that have been used with other extensively studied senses, and thus updating current models for LPFC functions to include a taste modality. Using multichannel functional near-infrared spectroscopy (fNIRS), we examined the LPFC's of healthy volunteers (N = 18) during the intentional memorization of a basic taste. In order to minimize the confounding effects of verbal processes that are known to employ the left LPFC, we used quaternary taste mixtures that were difficult to verbalize, and confined analysis to those who did not use a verbal strategy during memorization (N = 10). In order to examine the results in association with data in the literature, the location of activity was probabilistically estimated and anatomically labeled in the Montreal Neurological Institute (MNI) standard brain space. By contrasting the cortical activation under encoding conditions with that under control conditions without memory requirement, we found activation in the bilateral ventro-LPFC and the right posterior portion of the LPFC. The activation pattern was consistent with previous studies on the encoding of nonverbal materials using other senses. This suggests that models for LPFC functions that derive from previous studies can be generalized to intentional encoding processes of taste information, at least at a macro-structural level. The current study also demonstrates that, by using fNIRS, LPFC functions on taste can be examined with experimental paradigms relevant to those used for other senses.

Adult↗
PubMed2005

Spatial registration of multichannel multi-subject fNIRS data to MNI space without MRI.

The registration of functional brain data to the common brain space offers great advantages for inter-modal data integration and sharing. However, this is difficult to achieve in functional near-infrared spectroscopy (fNIRS) because fNIRS data are primary obtained from the head surface and lack structural information of the measured brain. Therefore, in our previous articles, we presented a method for probabilistic registration of fNIRS data to the standard Montreal Neurological Institute (MNI) template through international 10-20 system without using the subject's magnetic resonance image (MRI). In the current study, we demonstrate our method with a new statistical model to facilitate group studies and provide information on different components of variability. We adopt an analysis similar to the single-factor one-way classification analysis of variance based on random effects model to examine the variability involved in our improvised method of probabilistic registration of fNIRS data. We tested this method by registering head surface data of twelve subjects to seventeen reference MRI data sets and found that the standard deviation in probabilistic registration thus performed for given head surface points is approximately within the range of 4.7 to 7.0 mm. This means that, if the spatial registration error is within an acceptable tolerance limit, it is possible to perform multi-subject fNIRS analysis to make inference at the population level and to provide information on positional variability in the population, even when subjects' MRIs are not available. In essence, the current method enables the multi-subject fNIRS data to be presented in the MNI space with clear description of associated positional variability. Such data presentation on a common platform, will not only strengthen the validity of the population analysis of fNIRS studies, but will also facilitate both intra- and inter-modal data sharing among the neuroimaging community.

Adult↗
PubMed2005

Virtual 10-20 measurement on MR images for inter-modal linking of transcranial and tomographic neuroimaging methods.

It is important to create a link between stereotaxic coordinates and head-surface-based positioning systems in order to share data between tomographic and transcranial brain mapping studies. In our previous studies, we established the probabilistic correspondence of the international 10-20 positions to the standard stereotaxic coordinate systems and made a reference database. However, its expansion required the physical marking of the 10-20 positions and the subsequent acquisition of MR images. To avoid such tedious procedures, we developed a virtual 10-20 measurement algorithm that can be applied to re-analyze any structural MR image that covers the whole head. As in the physical 10-20 measurements, with the reference points given, the algorithm automatically determines each 10-20 position step by step. Using the virtual 10-20 measurement method, we re-analyzed the MR images of 17 healthy subjects for whom we had determined 10-20 positions by physical marking in our previous study. The acquired 10-20 positions were normalized to the Montreal Neurological Institute (MNI) stereotactic coordinates and compared with the positions previously determined by physical measurements. 10-20 positions determined using the virtual and physical methods were roughly consistent. Average standard deviations for virtual and physical methods were 7.7 mm and 9.0 mm, respectively. There was a systematic shift in the virtual method, likely due to the absence of hair interference. We corrected the shift with affine transformation. The virtual 10-20 measurement method proved to be an effective alternative to physical marking. This method will serve as an essential tool for expanding the reference database and will further strengthen the link between tomographic and transcranial brain mapping methods.

Adult↗
PubMed2005

Automated cortical projection of head-surface locations for transcranial functional brain mapping.

Recent advancements in two noninvasive transcranial neuroimaging techniques, near-infrared spectroscopy (NIRS) and transcranial magnetic stimulation (TMS), signify the increasing importance of establishing structural compatibility between transcranial methods and conventional tomographic methods, such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET). The transcranial data obtained from the head surface should be projected onto the cortical surface to present the transcranial brain-mapping data on the same platform as tomographic methods. Thus, we developed two transcranial projection algorithms that project given head-surface points onto the cortical surface in structural images, and computer programs based on them. The convex-hull algorithm features geometric handling of the cortical surface, while the balloon-inflation algorithm is faster, and better reflects the local cortical structure. The automatic cortical projection methods proved to be as effective as the manual projection method described in our previous study. These methods achieved perfect correspondence between any given point on the head surface or a related nearby point in space, and its cortical projection point. Moreover, we developed a neighbor-reference method that enables transcranial cortical projection of a given head-surface point in reference to three neighboring points and one additional standard point, even when no structural image of the subject is available. We also calculated an error factor associated with these probabilistic estimations. The current study presents a close topological link between transcranial and tomographic brain-mapping modalities, which could contribute to inter-modal data standardization.

Adult↗
PubMed2004

Signaling by the kinase MINK is essential in the negative selection of autoreactive thymocytes.

Signaling through the T cell antigen receptor leading to elimination (negative selection) or differentiation (positive selection) of developing thymocytes generates a self-tolerant T cell repertoire. Here we report that the serine-threonine kinase MINK selectively connects the T cell receptor to a signaling pathway that mediates negative but not positive selection. Analysis of this pathway suggested that the essential function of MINK in the elimination of self-reactive thymocytes may be associated with 'downstream' activation of Jun kinase and enhancement of expression of the proapoptotic molecule Bim.

Animals↗
PubMed2004

Three-dimensional probabilistic anatomical cranio-cerebral correlation via the international 10-20 system oriented for transcranial functional brain mapping.

The recent advent of multichannel near-infrared spectroscopy (NIRS) has expanded its technical potential for human brain mapping. However, NIRS measurement has a technical drawback in that it measures cortical activities from the head surface without anatomical information of the object to be measured. This problem is also found in transcranial magnetic stimulation (TMS) that transcranially activates or inactivates the cortical surface. To overcome this drawback, we examined cranio-cerebral correlation using magnetic resonance imaging (MRI) via the guidance of the international 10-20 system for electrode placement, which had originally been developed for electroencephalography. We projected the 10-20 standard cranial positions over the cerebral cortical surface. After examining the cranio-cerebral correspondence for 17 healthy adults, we normalized the 10-20 cortical projection points of the subjects to the standard Montreal Neurological Institute (MNI) and Talairach stereotactic coordinates and obtained their probabilistic distributions. We also expressed the anatomical structures for the 10-20 cortical projection points probabilistically. Next, we examined the distance between the cortical surface and the head surface along the scalp and created a cortical surface depth map. We found that the locations of 10-20 cortical projection points in the standard MNI or Talairach space could be estimated with an average standard deviation of 8 mm. This study provided an initial step toward establishing a three-dimensional probabilistic anatomical platform that enables intra- and intermodal comparisons of NIRS and TMS brain imaging data.

Adult↗
PubMed2004

Multimodal assessment of cortical activation during apple peeling by NIRS and fMRI.

An intriguing application of neuroimaging is directly measuring actual human brain activities during daily living. To this end, we investigated cortical activation patterns during apple peeling. We first conducted a pilot study to assess the activation pattern of the whole lateral cortical surface during apple peeling by multichannel near-infrared spectroscopy (NIRS) and detected substantial activation in the prefrontal region in addition to expected activations extending over the motor, premotor and supplementary motor areas. We next examined cortical activation during mock apple peeling by simultaneous measurement using multichannel NIRS and functional magnetic resonance imaging (fMRI) in four subjects. We detected activations extending over the motor, premotor and supplementary motor areas, but not in the prefrontal cortex. Thus, we finally focused on the prefrontal cortex and examined its activation during apple peeling in 12 subjects using a multichannel NIRS. We subsequently found that regional concentrations of oxygenated hemoglobin significantly increased in the measured region, which encompassed portions of the dorsolateral, ventrolateral and frontopolar areas of the prefrontal cortex. The current study demonstrated that apple peeling as practiced in daily life recruited the prefrontal cortex but that such activation might not be detected for less laborious mock apple peeling that can be performed in an fMRI environment. We suggest the importance of cortical study of an everyday task as it is but not as a simplified form; we also suggest the validity of NIRS for this purpose. Studies on everyday tasks may serve as stepping stone toward understanding human activities in terms of cortical activations.

Activities of Daily Living↗
PubMed2002

Overlapping of MINK and CHRNE gene loci in the course of mammalian evolution.

Overlapping of genes, especially in an anti-parallel fashion, is quite rare in eukaryotic genomes. We have found a rare instance of exon overlapping involving CHRNE and MINK gene loci on chromosome 17 in humans. CHRNE codes for the epsilon subunit of the nicotinic acetylcholine receptor (AChRepsilon) whereas MINK encodes a serine/threonine kinase belonging to the GCK family. To elucidate the evolutionary trail of this gene overlapping event, we examined the genomes of a number of primates and found that mutations in the polyadenylation signal of the CHRNE gene in early hominoids led to the overlap. Upon extending this analysis to genomes of other orders of placental mammals, we observed that the overlapping occurred at least three times independently during the course of mammalian evolution. Because CHRNE and MINK are differentially expressed, the potentially hazardous mutations responsible for the exon overlap seem to have escaped evolutionary pressures by differential temporo-spatial expression of the two genes.

Animals↗
PubMed2002

Cloning and characterization of PAK5, a novel member of mammalian p21-activated kinase-II subfamily that is predominantly expressed in brain.

The p21-activated kinase (PAK) family of protein kinases has recently attracted considerable attention as an effector of Rho family of small G proteins and as an upstream regulator of MAPK signalling pathways during cellular events such as re-arrangement of the cytoskeleton and apoptosis. We have cloned a novel human PAK family kinase that has been designated as PAK5. PAK5 contains a CDC42/Rac1 interactive binding (CRIB) motif at the N-terminus and a Ste20-like kinase domain at the C-terminus. PAK5 is structurally most related to PAK4 and PAK6 to make up the PAK-II subfamily. We have shown that PAK5 preferentially binds to CDC42 in the presence of GTP and that CRIB motif is essential for this interaction. PAK5 is a functional protein kinase but unlike PAK-I family kinases (PAK1, 2, and 3), the kinase activity of PAK5 does not seem to require the binding of CDC42. Overexpression of PAK5 activates the JNK kinase pathway but not p38 or ERK pathways. PAK5 transcript is predominantly expressed in brain as revealed by Northern blot and in situ hybridization. The expression pattern of PAK5 is distinct from that of PAK4 and PAK6, suggesting a functional division among PAK-II subfamily kinases based on differential tissue distribution.

Amino Acid Motifs↗
PubMed2001

Cloning of MASK, a novel member of the mammalian germinal center kinase III subfamily, with apoptosis-inducing properties.

We have cloned a novel human GCK family kinase that has been designated as MASK (Mst3 and SOK1-related kinase). MASK is widely expressed and encodes a protein of 416 amino acid residues, with an N-terminal kinase domain and a unique C-terminal region. Like other GCK-III subfamily kinases, MASK does not activate any mitogen-activated protein kinase pathways. Wild type MASK, but not a form lacking the C terminus, exhibits homophilic binding in the yeast two-hybrid system and in coimmunoprecipitation experiments. Additionally, deletion of this C-terminal region of MASK leads to an increased kinase activity toward itself as well as toward an exogenous substrate, myelin basic protein. A potential caspase 3 cleavage site (DESDS) is present in the C-terminal region of MASK, and we show that MASK is cleaved in vitro by caspase 3. Finally, wild type and C-terminally truncated forms of MASK can both induce apoptosis upon overexpression in mammalian cells that is abrogated by CrmA, suggesting involvement of MASK in the apoptotic machinery in mammalian cells.

Amino Acid Motifs↗