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N Sadato

Publications and source records attributed to N Sadato.

At least 19 recordsLinked to original sources
PubMed2006

Suppression of the non-dominant motor cortex during bimanual symmetric finger movement: a functional magnetic resonance imaging study.

Patterns of bimanual coordination in which homologous muscles are simultaneously active are more stable than those in which homologous muscles are engaged in an alternating fashion. This may be attributable to the stronger involvement of the dominant motor cortex in ipsilateral hand movements via interaction with the non-dominant motor system, known as neural crosstalk. We used functional magnetic resonance imaging to investigate the neural representation of the interhemispheric interaction during bimanual mirror movements. Thirteen right-handed subjects completed four conditions: sequential finger tapping using the right and left index and middle fingers, bimanual mirror and parallel finger tapping. Auditory cues (3 Hz) were used to keep the tapping frequency constant. Task-related activation in the right primary motor cortex was significantly less prominent during mirror than unimanual left-handed movements. This was mirror- and non-dominant side-specific; parallel movements did not cause such a reduction, and the left primary motor cortex showed no such differential activation across the unimanual right, bimanual mirror, and bimanual parallel conditions. Reducing the contralateral innervation of the left hand may increase the fraction of the force command to the left hand coming from the left primary motor cortex, enhancing the neural crosstalk.

Adult↗
PubMed2004

fMRI activation maps based on the NN-ARx model.

The most significant progresses in the understanding of human brain functions have been possible due to the use of functional magnetic resonance imaging (fMRI), which when used in combination with other standard neuroimaging techniques (i.e., EEG) provides researchers with a potential tool to elucidate many biophysical principles, established previously by animal comparative studies. However, to date, most of the methods proposed in the literature seeking fMRI signs have been limited to the use of a top-down data analysis approach, thus ignoring a pool of physiological facts. In spite of the important contributions achieved by applying these methods to actual data, there is a disproportionate gap between theoretical models and data-analysis strategies while trying to focus on several new prospects, like for example fMRI/EEG data fusion, causality/connectivity patterns, and nonlinear BOLD signal dynamics. In this paper, we propose a new approach which will allow many of the abovementioned hot topics to be addressed in the near future with an underlying interpretability based on bottom-up modeling. In particular, the theta-MAP presented in the paper to test brain activation corresponds very well with the standardized t test of the SPM99 toolbox. Additionally, a new Impulse Response Function (IRF) has been formulated, directly related to the well-established concept of the hemodynamics response function (HRF). The model uses not only the information contained in the signal but also that in the structure of the background noise to simultaneously estimate the IRF and the autocorrelation function (ACF) by using an autoregressive (AR) model with a filtered Poisson process driving the dynamics. The short-range contributions of voxels within the near-neighborhood are also included, and the potential drift was characterized by a polynomial series. Since our model originated from an immediate extension of the hemodynamics approach [Friston, K.J., Mechelli, A., Turner, R., Price C.J. (2000a). Nonlinear responses in fMRI: the balloon model, volterra kernels, and other hemodynamics. NeuroImage 12, 466-477.], a natural interpretability of the results is feasible.

Algorithms↗
PubMed2003

Neural substrates participating in acquisition of facial familiarity: an fMRI study.

The amygdala is related to recognition of faces and emotions, and functional magnetic resonance imaging (fMRI) studies have reported that the amygdala is habituated over time with repetition of facial stimuli. When subjects are presented repeatedly with unfamiliar faces, they come to gradually recognize the unfamiliar faces as familiar. To investigate the brain areas participating in the acquisition of familiarity to repeatedly presented unfamiliar faces, we conducted an fMRI study in 16 healthy subjects. During the task periods, the subjects were instructed to see presented unfamiliar faces repeatedly and to judge whether the face was male or female or whether the face had emotional valences. The experiment consisted of nine sessions. To clarify the brain areas that showed increasing or decreasing activation as the experimental session proceeded, we analyzed the fMRI data using specified linear covariates in the face recognition task from the first session to the ninth session. Imaging data were investigated on a voxel-by-voxel basis for single-group analysis according to the random effect model using Statistical Parametric Mapping. The bilateral posterior cingulate cortices showed significant increases in activity as the experimental sessions proceeded, while the activation in the right amygdala and the left medial fusiform gyrus decreased. Thus, the posterior cingulate cortex may play an important role in the acquisition of facial familiarity.

Adult↗
PubMed2002

Differential amygdala response during facial recognition in patients with schizophrenia: an fMRI study.

Human lesion or neuroimaging studies suggest that amygdala is involved in facial emotion recognition. Although impairments in recognition of facial and/or emotional expression have been reported in schizophrenia, there are few neuroimaging studies that have examined differential brain activation during facial recognition between patients with schizophrenia and normal controls. To investigate amygdala responses during facial recognition in schizophrenia, we conducted a functional magnetic resonance imaging (fMRI) study with 12 right-handed medicated patients with schizophrenia and 12 age- and sex-matched healthy controls. The experiment task was a type of emotional intensity judgment task. During the task period, subjects were asked to view happy (or angry/disgusting/sad) and neutral faces simultaneously presented every 3 s and to judge which face was more emotional (positive or negative face discrimination). Imaging data were investigated in voxel-by-voxel basis for single-group analysis and for between-group analysis according to the random effect model using Statistical Parametric Mapping (SPM). No significant difference in task accuracy was found between the schizophrenic and control groups. Positive face discrimination activated the bilateral amygdalae of both controls and schizophrenics, with more prominent activation of the right amygdala shown in the schizophrenic group. Negative face discrimination activated the bilateral amygdalae in the schizophrenic group whereas the right amygdala alone in the control group, although no significant group difference was found. Exaggerated amygdala activation during emotional intensity judgment found in the schizophrenic patients may reflect impaired gating of sensory input containing emotion.

Adolescent↗
PubMed2002

Functional magnetic resonance imaging evidence for a representation of the ear in human primary somatosensory cortex: comparison with magnetoencephalography study.

Our previous study (T. Nihashi et al., 2001, Neuro- Image 13: 295-304), using magnetoencephalography (MEG), revealed somatotopy of the ear in the human primary somatosensory cortex (SI); that is, the signals following stimulation of the ear reach both the neck and face areas of the SI. However, since this was the first report on somatotopy of the ear in humans, we performed an fMRI activation study to confirm the somatotopic representation, and compared the electrical activity by MEG and the cerebral blood flow change by fMRI. We studied eight healthy subjects using 3-T MRI. We stimulated three parts of the left ear: the helix, the lobulus, and the tragus. First, we identified the location of the ear area in the SI based on our previous MEG study, in which equivalent current dipoles (ECDs) were located in the neck and/or face areas of the SI. Then, we determined the search volume as a sphere with a 15-mm radius, which was placed in the neck and/or face area. We analyzed whether or not fMRI activation occurred inside such spheres. Stimulation of the helix activated the neck area of the SI in four of eight subjects, and both the neck and face areas in two. No activation was observed in two subjects. Stimulation of the lobulus activated the neck area in one subject, the face area in two, both in four, and neither in one. Stimulation of the tragus activated the face in four, both in three, and neither in one. These fMRI findings confirm the result of MEG that the representation of the ear in the SI is separated into neck and face areas.

Adult↗
PubMed2001

Neural interaction of the amygdala with the prefrontal and temporal cortices in the processing of facial expressions as revealed by fMRI.

Some involvement of the human amygdala in the processing of facial expressions has been investigated in neuroimaging studies, although the neural mechanisms underlying motivated or emotional behavior in response to facial stimuli are not yet fully understood. We investigated, using functional magnetic resonance imaging (fMRI) and healthy volunteers, how the amygdala interacts with other cortical regions while subjects are judging the sex of faces with negative, positive, or neutral emotion. The data were analyzed by a subtractive method, then, to clarify possible interaction among regions within the brain, several kinds of analysis (i.e., a correlation analysis, a psychophysiological interaction analysis and a structural equation modeling) were performed. Overall, significant activation was observed in the bilateral fusiform gyrus, medial temporal lobe, prefrontal cortex, and the right parietal lobe during the task. The results of subtraction between the conditions showed that the left amygdala, right orbitofrontal cortex, and temporal cortices were predominantly involved in the processing of the negative expressions. The right angular gyrus was involved in the processing of the positive expressions when the negative condition was subtracted from the positive condition. The correlation analysis showed that activity in the left amygdala positively correlated with activity in the left prefrontal cortex under the negative minus neutral subtraction condition. The psychophysiological interaction revealed that the neural responses in the left amygdala and the right prefrontal cortex underwent the condition-specific changes between the negative and positive face conditions. The right amygdaloid activity also had an interactive effect with activity in the right hippocampus and middle temporal gyrus. These results may suggest that the left and right amygdalae play a differential role in effective processing of facial expressions in collaboration with other cortical or subcortical regions, with the left being related with the bilateral prefrontal cortex, and the right with the right temporal lobe.

Adult↗
PubMed2001

Dynamic changes in glucose metabolism accompanying the expression of the neural phenotype after differentiation in PC12 cells.

To assess what properties of glucose metabolism are most closely related to expression of the neural phenotype, some parameters of glucose metabolism in PC12 cells before (tumor-type) and after differentiation (neuron-type) were investigated. Neuron-type cells exhibited a 2.7-fold higher level of [3H]DG retention than tumor-type cells, accompanied by a higher glucose transport rate and higher levels of hexokinase activity. [14C]CO2 production from [U-14C]glucose in neuron-type was also more than four-times greater than that in tumor-type cells. The levels of [14C]carbon in macromolecules from [14C]glucose in neuron-type cells were also much higher (10.6-fold) than those in tumor-type cells, and the levels of incorporation of [14C]carbon were almost as high as those of [14C]CO2. From the metabolite analysis, amino acids appeared to be the major compounds converted from glucose. On the other hand, the uptakes of [35S]methionine-[35S]cysteine and [3H]uridine in neuron-type cells were lower than those in tumor-type cells. Following depolarization with 50 mM potassium, [14C]CO2 production increased, but the retention of [14C]carbon was not changed in neuron-type cells. The largest change accompanied by acquisition of the neural phenotype was carbon incorporation into the macromolecules derived from glucose. This property may be important for the expression of the neural phenotype as well as the higher levels of both glucose uptake and oxygen consumption.

Animals↗
PubMed2001

Ultrasound activates the auditory cortex of profoundly deaf subjects.

Using three-dimensional PET, the cortical areas activated by bone-conducted ultrasound were measured from five profoundly deaf subjects and compared with the cortical areas of normal-hearing subjects activated by stimuli through bone-conducted ultrasonic, air-conducted, bone-conducted, and vibro-tactile hearing aids. All of the hearing aids, including the ultrasonic hearing aid, consistently activated the medial portion of the primary auditory cortex of the normal volunteers. The same cortical area was also significantly activated in the profoundly deaf subjects although the percentage increase in regional cerebral blood flow (rCBF) was smaller than in normal subjects. These results suggest that extra-cochlear routes convey information to the primary auditory cortex and can therefore produce detectable sound sensation even in the profoundly deaf subjects, who reported a sensation themselves.

Adult↗
PubMed2001

Copper-62 ATSM as a hypoxic tissue tracer in myocardial ischemia.

Copper-62 labeled diacetyl-bis(N4-methylthiosemicarbazone) (62Cu-ATSM) has been proposed as a generator produced positron-emitting tracer for hypoxic tissue imaging. To clarify the usefulness of 62Cu-ATSM for myocardial ischemia, 62Cu-ATSM PET was performed in 7 patients with coronary artery disease. Increased myocardial uptake of 62Cu-ATSM was observed (myocardium/blood ratio: 3.09) in one patient with unstable angina, who had increased 18F-fluorodeoxyglucose (18F-FDG) uptake under the fasting condition. The other 6 patients, who were clinically stable, did not have increased 62Cu-ATSM uptake, although abnormal 18F-FDG uptake was seen in 4 patients. This preliminary study suggests that 62Cu-ATSM is a promising PET tracer for hypoxic imaging in acute ischemia.

Aged↗
PubMed2001

Myocardial FDG-PET examination during fasting and glucose loading states by means of a one-day protocol.

We propose a new method to measure the myocardial FDG uptake during fasting and glucose loading in one day, a myocardial FDG-PET one-day protocol, with both 2- and 3-dimensional data acquisition (2D and 3D) without background activity subtraction. To confirm it, we evaluated the effect of scatter correction in the 2D and 3D modes of a PET scanner both in phantom and patient studies. In the phantom study, we used a cardiac phantom with six divided chambers and two cylindrical phantoms placed as the activity outside the field of view. Each chamber was filled with a different concentration of F- 18 solution. Regions of interest (ROI) were placed on a polar map generated from reconstructed images and were compared to the concentration of the solution in each chamber in both 2D and 3D. In the patient study, 10 non-diabetic patients with coronary artery disease were studied. Each patient received a myocardial FDG study during fasting (F) and glucose loading (L). L images with background subtraction (Lsub(+)) and without background subtraction (Lsub(-)) were compared by polar map analysis. The ROI counts for the true activity in 2D and 3D demonstrated a linear relationship, and quite similar slopes were observed (0.72 in 2D, 0.69 in 3D). The background fraction in Lsub(-) was 3.59+/-1.83%. There were significant differences between Lsub(-) or Lsub(+) and F in both normal and ischemic myocardium. Scatter correction was successfully performed in both 2D and 3D modes. Background activity is thought to be negligible and this proposed method is simple touse in measuring the myocardial FDG uptake in one day.

Aged↗
PubMed2001

Functional mapping of human medial frontal motor areas. The combined use of functional magnetic resonance imaging and cortical stimulation.

Two functional brain-mapping techniques, functional magnetic resonance imaging (fMRI) and cortical stimulation by chronically implanted subdural electrodes, were used in combination for presurgical evaluation of three patients with intractable, partial motor seizures. Brain mapping was focused on characterizing motor-related areas in the medial frontal cortex, where all patients had organic lesions. Behavioral tasks for fMRI involved simple finger and foot movements in all patients and mental calculations in one of them. These tasks allowed us to discriminate several medial frontal motor areas: the presupplementary motor areas (pre-SMA), the somatotopically organized SMA proper, and the foot representation of the primary motor cortex. All patients subsequently underwent cortical stimulation through subdural electrodes placed onto the medial hemispheric wall. In each patient, the cortical stimulation map was mostly consistent with that patient's brain map by fMRI. By integrating different lines of information, the combined fMRI and cortical stimulation map will contribute not only to safe and effective surgery but also to further understanding of human functional neuroanatomy.

Adult↗
PubMed2001

An fMRI study of the functional neuroanatomy of picture encoding in younger and older adults.

Age-related changes in the neural mechanisms of picture encoding were investigated using functional magnetic resonance imaging (fMRI). Seven younger and seven older adults were studied while they were encoding pairs of concrete-related, concrete-unrelated, and abstract pictures. Functional (T2*-weighted) and anatomical (T1-weighted) images of the brain were obtained using a 1.5 T MRI scanner. The results in the younger adults showed that the left dorsal prefrontal cortex (PFC) was activated during associative learning of the concrete-unrelated or abstract pictures. The results also suggest that both ventral and dorsal visual pathways are involved in the encoding of abstract pictures, and that the right superior parietal lobule likely mediates spatial information of the abstract pictures. The older adults showed significant activation in the left dorsal PFC under concrete-unrelated and abstract conditions. However, the older adults failed to activate either the left ventral and right dorsal PFC under the concrete-unrelated condition, or the parietal areas under abstract condition. A direct comparison between the two age groups demonstrates that the older adults had a reduced activation in the bilateral parieto-temporo-occipital areas under abstract condition, and in the right temporo-occipital area extending to the fusiform gyrus under the concrete-unrelated condition. Finally, age difference was found in correlation between memory performance and amplitude of signal change in the parahippocampal gyrus and fusiform gyrus under the concrete-unrelated and abstract conditions. These changes in neural response likely underlie the age-related memory decline in relation to pictorial information.

Adult↗
PubMed2001

Attention to emotion modulates fMRI activity in human right superior temporal sulcus.

A parallel neural network has been proposed for processing various types of information conveyed by faces including emotion. Using functional magnetic resonance imaging (fMRI), we tested the effect of the explicit attention to the emotional expression of the faces on the neuronal activity of the face-responsive regions. Delayed match to sample procedure was adopted. Subjects were required to match the visually presented pictures with regard to the contour of the face pictures, facial identity, and emotional expressions by valence (happy and fearful expressions) and arousal (fearful and sad expressions). Contour matching of the non-face scrambled pictures was used as a control condition. The face-responsive regions that responded more to faces than to non-face stimuli were the bilateral lateral fusiform gyrus (LFG), the right superior temporal sulcus (STS), and the bilateral intraparietal sulcus (IPS). In these regions, general attention to the face enhanced the activities of the bilateral LFG, the right STS, and the left IPS compared with attention to the contour of the facial image. Selective attention to facial emotion specifically enhanced the activity of the right STS compared with attention to the face per se. The results suggest that the right STS region plays a special role in facial emotion recognition within distributed face-processing systems. This finding may support the notion that the STS is involved in social perception.

Adult↗
PubMed2001

Characterization of acetate metabolism in tumor cells in relation to cell proliferation: acetate metabolism in tumor cells.

To reveal the metabolic fate of acetate in neoplasms that may characterize the accumulation patterns of [1-(11)C]acetate in tumors depicted by positron emission tomography. Four tumor cell lines (LS174T, RPMI2650, A2780, and A375) and fibroblasts in growing and resting states were used. In uptake experiments, cells were incubated with[1-(14)C]acetate for 40 min. [(14)C]CO(2) was measured in the tight-air chamber, and the metabolites in cells were identified by thin layer chromatography and paper chromatography. The glucose metabolic rate of each cell line was measured with [2,6-(3)H]2-deoxy-glucose (DG), and the growth activity of each cell line was estimated by measuring the incorporation of [(3)H]methyl thymidine into DNA. Compared with resting fibroblasts, all four tumor cell lines showed higher accumulation of (14)C activity from [1-(14)C]acetate. These tumor-to-normal ratios of [1-(14)C]acetate were larger than those of DG. Tumor cells incorporated (14)C activity into the lipid-soluble fraction, mostly of phosphatidylcholine and neutral lipids, more prominently than did fibroblasts. The lipid-soluble fraction of (14)C accumulation in cells showed a positive correlation with growth activity, whereas the water-soluble and CO(2) fractions did not. These findings suggest that the high tumor-to-normal ratio of [1-(14)C]acetate is mainly due to the enhanced lipid synthesis, which reflects the high growth activity of neoplasms. This in vitro study suggests that [1-(11)C]acetate is appropriate for estimating the growth activity of tumor cells.

Acetates↗
PubMed2001

FDG PET for evaluating the change of glucose metabolism in prostate cancer after androgen ablation.

In the clinical study of prostate cancer, the effect of androgen ablation on glucose metabolism in cancer tissue has not been elucidated. The purpose of this study was to investigate the change in glucose utilization due to endocrine therapy for prostate adenocarcinoma. Ten patients with histologically proven prostate cancer were prospectively investigated with (18)F-fluorodeoxyglucose and positron emission tomography (FDG PET) prior to and after the initiation of endocrine therapy. FDG uptake was calculated to measure glucose utilization in cancer tissue. The change in FDG accumulation was compared with changes in serum prostate specific antigen (PSA) level and prostate size. FDG accumulation in the prostate decreased in all patients 1-5 months after the initiation of hormone therapy. The serum PSA level and prostate size measured on computerized tomography (CT) also decreased in these periods. A decrease in FDG accumulation was also demonstrated in metastatic sites. In this study, there appeared to be a decrease in FDG uptake in prostate cancer after endocrine therapy not only in primary prostate cancer lesions but also at metastatic sites, suggesting that the glucose utilization by tumours was suppressed by androgen ablation.

Adenocarcinoma↗
PubMed2000

Naming of animals and tools: a functional magnetic resonance imaging study of categorical differences in the human brain areas commonly used for naming visually presented objects.

To investigate the neural substrates for naming objects and their category-dependency, we performed functional magnetic resonance imaging (fMRI) with naming of animals and tools. Naming objects, irrespective of their category, activated left frontal to bilateral parietal regions and occipital to posterior temporal regions. Within these areas, naming animals caused more activation of the primary visual cortex bilaterally and the ventral occipital cortex to the inferior temporal area on the right side. Naming tools caused more activation of the posterior part of the left middle temporal area, the rostral part of the left inferior parietal lobule, and the left inferior frontal cortex. These findings suggest that the neural network for naming objects has discrete category-dependent nodes through which pertinent conceptual knowledge may be mediated.

Adult↗
PubMed2000

Brain regions involved in verbal or non-verbal aspects of facial emotion recognition.

To depict the neural substrates for facial emotion recognition and to determine whether their activation is confounded by a verbal factor, we studied eight normal volunteers with functional magnetic resonance imaging (fMRI). Verbal and non-verbal sample stimuli were used in a facial emotion matching task and a gender matching task (control condition). Compared with the gender tasks, the emotion tasks significantly activated the right ventral prefrontal cortex, the right lingual cortex, and the left lateral fusiform cortex, irrespective of sample stimuli. The visual association cortices showed a significant interaction between the task and the material presented, as the activation for verbal materials was higher than for non-verbal materials during the emotion matching tasks. By contrast, no significant interaction was found in the right ventral prefrontal cortex. These results suggest that the verbal factor has a different effect on the neural networks for facial emotion, processing.

Brain Mapping↗