Norio Hirabuki

Medial prefrontal cortex generates frontal midline theta rhythm

Frontal midline theta rhythm (Fm theta) is a distinct theta activity of EEG in the frontal midline area that appears during concentrated performance of mental tasks in normal subjects and reflects focused attentional processing. To tomographically visualize the source current density distributions of Fm theta, we recorded Fm theta by using a 64-channel whole-head MEG system from four healthy subjects, and applied a new analysis method, synthetic aperture magnetometry (SAM), an adaptive beam forming method. Fm theta was observed in the MEG signals over the bilateral frontal regions. SAM analysis showed bilateral medial prefrontal cortices, including anterior cingulate cortex, as the source of Fm theta. This result suggests that focused attention is mainly related to medial prefrontal cortex.

Movement-Related Desynchronization of the Cerebral Cortex Studied with Spatially Filtered Magnetoencephalography

Event-related desynchronization (ERD) within the alpha and beta bands on unilateral index finger extension and hand grasping was investigated on six normal volunteers with magnetoencephalography (MEG). A novel spatial filtering technique for imaging cortical source power, synthetic aperture magnetometry (SAM), was employed for the tomographic demonstration of ERD. SAM source image results were transformed into statistical parametric images. On the same hand grasping task, a functional MRI (fMRI) study was conducted on two subjects and compared with the ERD result. When the MEG data were analyzed with the fast Fourier transformation, power attenuation within the alpha and beta bands was evident on the contralateral sensorimotor area just prior to movement onset. The tomographic distribution of ERD was clearly obtained with SAM statistical imaging analysis. The equivalent current dipole (ECD) for the signal-averaged motor field was localized to the hemisphere contralateral to the hand movement, roughly at the center of the region displaying beta-band ERD. The signal increase on fMRI roughly colocalized with the ERD on the contralateral sensorimotor area. In conclusion, with the novel spatial filtering technique for the brain magnetic field, SAM, cortical regions contributing to ERD on finger movement were successfully demonstrated in a tomographic manner. The relative colocalization of the contralateral SAM ERD with ECD as well as the fMRI activation suggests that SAM is a practically useful technique to extract event-related signals from brain noise.

Frequency-dependent spatial distribution of human somatosensory evoked neuromagnetic fields

Using synthetic aperture magnetometry (SAM), we examined the spatial distribution of frequency changes in magnetoencephalography signal rhythms on individual magnetic resonance images following somatosensory stimulation. SAM is a novel statistical spatial filtering method that uses an adaptive beamformer. Electrical stimulation of the right median nerve demonstrated high-frequency event-related synchronization (ERS) in the 50-200-Hz range, consistently localized in the contralateral primary sensorimotor area in all subjects (n=7). Event-related desynchronization (ERD) was demonstrated in the 8-13, 13-25 and 25-50-Hz ranges bilaterally in the area surrounding the central sulcus. The differences in the spatial distribution as well as the frequency bands between ERS and ERD suggest that ERS and ERD reflect the responses of different cell assemblies rather than a frequency shift of the same cell assembly.

Theta rhythm increases in left superior temporal cortex during auditory hallucinations in schizophrenia : a case report

Auditory hallucinations (AH), the perception of sounds and voices in the absence of external stimuli, remain a serious problem for a large subgroup of patients with schizophrenia. Functional imaging of brain activity associated with AH is difficult, since the target event is involuntary and its timing cannot be predicted. Prior efforts to image the patterns of cortical activity during AH have yielded conflicting results. In this study, MEG was used to directly image the brain electrophysiological events associated with AH in schizophrenia. We observed an increase in theta rhythm, as sporadic bursts, in the left superior temporal area during the AH states, whereas there was steady theta band activity in the resting state. The present finding suggests strong association of the left superior temporal cortex with the experience of AH in this patient. This is consistent with the hypothesis that AH arises from areas of auditory cortex subserving receptive language processing.

Proton magnetic resonance spectroscopy of patients with parkinsonism

We studied cerebral metabolism in 82 patients with nonfamilial parkinsonism, including Parkinsons disease (PD; n = 23), progressive supranuclear palsy (PSP; n = 12), corticobasal degeneration (CBD; n = 19), multiple systemic atrophy (MSA; n = 18) and vascular parkinsonism (VP; n = 10) by using proton magnetic resonance spectroscopy ((1)H-MRS), which allowed noninvasive measurement of signal intensities from N-acetylasparate (NAA), choline-containing compounds (CHO) and creatine plus phosphocreatine (CRE). As compared to normal controls, patients with PSP, CBD, MSA and VP, but not PD, had significant reduction of the NAA/CRE ratio in the frontal cortex, whereas patients with PSP, CBD, MSA and PD, but not VP, had significant reduction of the NAA/CRE ratio in the putamen. Patients with CBD had significant reduction of the NAA/CRE ratio in the frontal cortex and putamen as compared to patients with PD, MSA and VP. Patients with PSP showed a significant reduction of the NAA/CRE ratio in the putamen as compared with patients with PD and MSA. Patients with CBD showed clear asymmetry in the putamen as compared to controls and other patients. The reduction of the NAA/CRE ratio in the putamen correlated well with the severity of parkinsonism. (1)H-MRS may be useful in monitoring patients with various types of parkinsonism.

Decrease in N-acetylaspartate/creatine ratio in the motor area and the frontal lobe in amyotrophic lateral sclerosis.

Abstract We studied whether N-acetylaspartate (NAA), a neuronal marker, is reduced in the brain of 14 patients with clinically definite amyotrophic lateral sclerosis (ALS) and whether NAA levels in the motor area and frontal lobe correlate with the clinical features, including frontal lobe function. We also studied 14 normal controls were evaluated. We obtained peak integrals in 1H magnetic resonance spectroscopy (MRS) for NAA, creatine (Cr), and choline-containing compounds (Cho). Severity of the disease was determined using the manual muscle strength test, and the Norris limb and bulbar scales. In the patients, the NAA/Cr ratio was reduced in the motor area and frontal lobe, while the Cho/Cr ratio was normal throughout the brain. There were significant correlations between the NAA/Cr ratio in the motor area and the Norris limb scale (r = 0.50; P < 0.01) and between the NAA/Cr ratio in the frontal lobe and the number of categories achieved in the Wisconsin Card Sorting test (r = 0.71; P < 0.05), implying frontal lobe dysfunction. These correlations suggest that a reduced NAA/Cr ratio is a marker of cortical neuronal loss and dysfunction in ALS.

Functional mapping of pain-related activation with echo-planar MRI : Significance of the SII-insular region

ACTIVATION in numerous regions of the brain is likely to be involved in the complex neural network function of pain perception. To detect the cortical representation during nonpainful and painful stimuli, which were presented using electrical finger stimulation in six normal right-handed male volunteers, we performed echo-planar functional magnetic resonance imaging (fMRI). Using a 1.5-T MR system that scanned the supratentorial region of the brain, we obtained multislice BOLD-based functional MR images with single-shot gradient-echo echo-planar imaging (EPI). The data show that dispersed brain regions are activated during painful stimulation, and especially demonstrate the significance of the SII-insular region in pain perception.

Neuromagnetic fields preceding unilateral movements in dextrals and sinistrals.

MOVEMENT -related magnetic fields were recorded with a whole-head magnetoencephalographic system in three dextrals and three sinistrals during right or left index finger extension. The motor field (MF) demonstrated an asymmetrical isofield map pattern with larger field reversal over the contralateral hemisphere for dominant hand movement and an almost symmetrical pattern for non-dominant hand movement in each subject. The equivalent current dipole moment of the MF for the contralateral hemisphere was significantly larger than the ipsilateral hemisphere for dominant hand movement, and almost equal for both hemispheres for non-dominant hand movement. These results were congruent for both dextrals and sinistrals, suggesting a more important role of the hemisphere contralateral to the dominant hand in unilateral voluntary movement, regardless of handedness.

Computed tomographic findings of nasopharyngeal carcinoma with skull base and intracranial involvement

Twenty‐nine patients with nasopharyngeal carcinoma (NPC) with skull base or intracranial involvement were analyzed by high‐resolution computed tomography (CT). We divided the path of the primary tumor spread into six directions from the nasopharynx. The most common direction of spread was the anterior region, and the second most common was the posterolateral region. Recently, high resolution CT has been used for the diagnosis of the nasopharynx. T‐staging of NPC was made according to the International Union Against Cancer (UICC) TNM classification system, depending on clinical findings and conventional radiograph examinations (not including CT). CT images were valuable for detection of the primary tumor involvement of the skull base region in NPC. Furthermore, bone target CT images were better for searching for subtle bony changes. Therefore, we recommend that CT should be used in T‐staging of NPC systematically. When CT is used as one of the staging criteria, some patients with NPC with subtle bony changes will be upstaged.

Effects of stimulus rate on the auditory cortex using fmri with ‘sparse’ temporal sampling

The purpose of this study was to evaluate the effects of the auditory stimulus presentation rate on signal response during fMRI with a minimal effect of scanner acoustic noise. Six subjects received auditory stimulus with a pure tone (1000 Hz, 30 ms duration) at presentation rates of 0.5, 2, 5, 10 and 20 Hz. Echo planar images were obtained with a long TR of 12 s and clustered multi-slice acquisition. The number of activated pixels and percentage signal change were measured in the transverse temporal gyri, which revealed that these values at 5 Hz were significantly greater than those at 0.5 Hz and at 20 Hz.