[Objective] We quantitatively evaluated the influences of the stimulus pattern and the color combination for visual evoked potentials (VEPs).
[Method] Steady-state VEPs were recorded from 11 healthy young adults (aged 21–24). Two isoluminant color combinations (red/blue (R/B) and red/green (R/G)) and two stimulus patterns (sinusoidal (Sin.) and square (Sq.) pattern) were combined for constructing the visual target. Temporal frequencies of 4–18 Hz were used. Amplitude of first harmonic and second harmonic components were defined as characteristic parameters. Difference of those parameters between two stimulus conditions were also evaluated.
[Result] VEP amplitudes were gradually increased according to the temporal frequency increased from 7–10 Hz, and were more remarkable for Sin. than for Sq. VEP amplitudes on R/B were larger than that of R/G in temporal frequency of 12–18 Hz. Difference of VEP amplitudes between R/B Sin. and R/B Sq. were Sin. dominance, especially of temporal frequency of 9 Hz.
[Discussion] Difference of response between stimulus patterns was supposed to be derived from the intensity of color change. The influence of the antagonistic effects in primary visual cortex was taken into account the reason for the difference of VEP responses between color combinations. Characteristic of response for each stimulus condition depends on interaction of the effect of stimulus patterns and that of color combinations.

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[Objective] This study was aimed to evaluate our previously proposed method of estimating the target signal sources in the human brain, with using the electroencephalogram (EEG) data during a simple motor task. And the locations and frequencies of the signal sources estimated by our method are compared with results of the conventional event-related de-/synchronization (ERD/ERS) analysis.
[Method] Eight healthy male volunteers were asked to perform a voluntary finger single-tapping every around 10 s, but without counting, for 5 min per a session; two sessions were made with in each of the subjects. EEG signals were recorded from 19 scalp locations according to the International 10-20 EEG System with a linked earlobe reference. The electromyogram (EMG) was also recorded from the right first dorsal interosseous muscle. Both EEG and EMG data were sectioned by a 1-s Hanning window with 50% overlap for the Fourier transform. The Spearman’s rank-order correlation coefficients in the frequency domain were calculated for all spectral pairs between the EEG signal of each sensor and the EMG signal. Hence, the cross-frequency EEG-EMG correlation matrices were obtained for the 19 EEG sensors. For the spectral pairs showing the statistically significant correlation, spatial distributions of the correlation coefficients over the scalp were plotted as the correlation topographies. Also, the corresponding EMG spectra were extracted as the time series. By these EEG-EMG correlation topographies and the EMG spectra time series, the original EEG data were weighted so that the specific frequency signals were exclusively enhanced. On the weighted EEG data, the standardized low-resolution brain electromagnetic tomography (sLORETA) was applied to each of 1-s time sections, and the source locations were estimated by averaging the sources calculated for all sections with sLORETA modified for quantitative method (sLORETA-qm), using a four-layer anisotropic spheres model with a reference MR image. For the ERD/ERS analysis, the event timing of the finger tapping was determined based on the EMG signal. The EEG signals were extracted for a time frame of a 2.5-s pre-event and a 5-s post-event and the short-time Fourier transform was computed for the spectral power time series.
[Results] The cross-frequency EEG-EMG correlation matrices showed that distinct alpha-band and beta-band EEG signals negatively correlated with the EMG signals by a statistically significant amount. Corresponding to those frequency bands, multiple signal sources were estimated by our proposed method: alpha-band signal sources located in parietal-occipital as well as temporal lobes, and beta-band signal sources located in contra-/ipsilateral regions around central sulcus. The ERD/ERS analysis demonstrated also the alpha-band post-event synchronizations in parietal-occipital lobe, the beta-band desynchronization during the muscle contraction in ipsilateral central region, and the beta-band post-event synchronizations in contralateral central-parietal regions.
[Conclusion] It was shown that our proposed method of the targeted signal source estimation can be useful for localizing the specific neural activities in human brains. And the frequencies and locations of the estimated signal sources were consistent with previous anatomical and physiological studies, and also with the results of conventional ERD/ERS analysis.

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Transcranial direct current stimulation (tDCS) is a noninvasive, painless cortical stimulation technique. Depending on the polarity of the current flow, brain excitability can either be increased by the anodal tDCS or decreased by the cathodal tDCS. The aim of the present study was to examine the behavioral effects of direct current delivery on left posterior temporal and inferior parietal cortices during the Rey’s auditory verbal learning test (RAVLT) that examine audioverbal short-term memory. The RAVLT includes a list of 15 common words to be read one-by-one. After the presentation of 15 words, the subjects are required to repeat as many words as they can. The encoding-recall procedure is repeated five times. Twelve healthy subjects performed the RAVLT, during which, 10 minutes anodal and 15 seconds sham current was applied on left posterior temporal and inferior parietal cortex from the second encoding process. There was a significant difference in the mean number of remembered words between anodal and sham stimulation on the second process. Anodal tDCS increased the number of remembered words when compared to sham stimulation. Our results imply that anodal tDCS induced short-term modulation of the left posterior temporal and inferior parietal cortex while learning auditory presented words. tDCS is a promising tool for improving memory performance.

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Although ring electrodes generally used in antidromic sensory nerve conduction studies of the hand, disposable surface electrodes for recording, which offer numerous advantages in terms of infection control and usability, are becoming increasingly popular. However, no studies on optimal electrode placement for disposable surface electrodes have been reported. The aim of this study was to determine optimal surface recording electrode placement in antidromic median sensory nerve conduction studies. The sensory nerve action potentials (SNAP) recorded in both hands of the ten healthy subjects evoked by median nerve stimulation at the wrist. The potentials were recorded from ring electrode at the base of the second digit as commonly used and disposable surface electrodes placed at 4 different locations (radial, volar, and medial aspects of the second digit, and radial aspect of the third digit). The latency and the amplitude of the SNAP delivered by disposable surface electrodes placed on midline volar aspect of the second digit were similar to measurements obtained by using ring electrodes. The responses delivered by surface electrode placement on radial aspect of the second digit had lower amplitude and shorter latency than responses using ring electrodes with statistically significance (p<0.001, paired t-test), suggesting that responses were influenced by volume conduction. These data indicate that disposable surface recording electrodes must be placed on the second digit volar midline in order to obtain similar results using ring electrodes in antidromic median sensory nerve conduction studies.

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Magnetoencephalography (MEG) is a powerful tool of basic and clinical neuroscience to detect real neuronal activities directly and non-invasively with good time and spatial resolution. Since the ministry of health in Japan approved MEG as clinical examination covered by health insurance in 2004, many patients suffering from various brain disorders benefitted from this method for these years. We reviewed clinical MEG studies regarding psychiatry diseases and dementia based on a website bibliographic survey before March 2012 on MEDLINE using the keywords of each disease AND (MEG OR magnetoencephalography). We found 95 papers about schizophrenia, 23 about mood disorders, 29 about developmental disorders, 13 about epilepsy psychosis, 71 about dementia. Then, we selected several papers with evidence level higher than 3 to assess the clinical utility of MEG. Although a few studies stressed the superiority of MEG compared to EEG for the diagnosis or treatment indication for psychiatric diseases and dementia, we could not find any papers with evidence level higher than 2 except two about dementia. Future development is needed for more objective analysis of MEG findings in psychiatry diseases and dementia.

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In addition to the histological diagnosis of brain tumor, functional brain mapping is indispensable for neurosurgeons to delineate the boundary between a pathological lesion and normally functioning adjacent brain areas. Magnetoencephalography (MEG) is one of key diagnostic tools for the brain mapping and has been approved as a health insurance treatment in Japan since 2004. In this study, we reviewed MEG studies regarding brain tumor treatment by using website bibliography to show scientific evidence of clinical MEG. We searched brain tumor-related manuscripts published between 1985 and July 2012. on MEDLINE by using keywords as (brain tumor OR neoplasm) AND (MEG OR magnetoencephalography). We selected 56 abstracts from 970 titles, which hit to the keywords. Twenty-three papers with high enough evidence levels and abstract contents were carefully reviewed from scientific and practical point of views. Somatosensory evoked magnetic fields (SEF) were the initial clinical application of MEG to identify the central sulcus (CS) non-invasively. The accuracy of SEF-based CS localization reached approximately 100% and has become a gold standard clinical modality. Several groups applied MEG for identification of language dominancy. Although the accuracy of MEG-based language lateralization was less than 90%, compared to Wada test, it has been widely available in clinical practice. The new trend of MEG utility is spontaneous MEG analysis, which contains potentials to visualize functional neural network at the resting state of the human brain. Combining all MEG investigations enables us to perform non-invasive functional brain mapping for patients diagnosed as having brain tumor.

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