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Repetitive transcranial magnetic stimulation (rTMS) has been proposed as a possible treatment for psychiatric and neurological disorders characterized by focal brain excitability, such as major depression and action myoclonus. However, the mechanism of modulating excitability by rTMS is unclear. We examined the changes in high frequency oscillations (HFOs) of somatosensory evoked potentials (SEPs) before and after slow rTMS over the right primary somatosensory cortex (0.5 Hz, 50 pulses, 80% motor threshold intensity). The HFOs, which represent a localized activity of intracortical inhibitory interneurons, were significantly increased after slow rTMS, while the SEPs were not changed. Our results suggest that slow rTMS affects cortical excitability by modulating the activity of the intracortical inhibitory interneurons beyond the time of the stimulation and that rTMS may have therapeutic effects on such disorders.

Parallel distributed processing neuroimaging in the Stroop color word interference task in five healthy subjects was studied. The total reaction time was set at 650 ms with a time window of 200 ms in steps of 50 ms. Spatially filtered magnetoencephalography analysis, as used in synthetic aperture magnetometry, was used. Neural activation began in the left posterior parietal-occipital area (150-250 ms post-stimulus), followed by the right prefrontal polar area (250-350 ms), the left dorsolateral prefrontal cortex (250-400 ms), and the mid- to lower- primary motor area (350-400 ms). Successive and temporally overlapping activation of various cortical regions were successfully estimated within a short 200 ms time interval, contrary to previous positron emission tomography and fMRI studies., (Copyright 2002 Elsevier Science Ireland Ltd.)

Abnormality of cytoskeletal proteins is closely related to the pathology of Alzheimer's disease. As neurofilament proteins are major cytoskeletal components of neurons, abnormality of neurofilaments is proposed in brain with Alzheimer's disease. Free-floating sections of the hippocampus with Alzheimer's disease were studied immunohistochemically, using a polyclonal antibody specifically bound to the tail region of neurofilament L (NF-L). In brains with early onset type of Alzheimer's disease, many neurons and dystrophic neurites were labeled by the antibody, while these observations were not seen in either brains with late onset type or control brains. Double immunohistochemical staining of NF-L and tau protein demonstrated that abnormal deposition of NF-L was not always accompanied with that of tau protein, indicating that the abnormal deposition of NF-L might not occur in parallel with that of tau protein. These observations suggest the involvement of neurofilament proteins on the pathology of Alzheimer's disease in a different way than tau protein.

The movement of potential field of alpha activity was investigated with a potential flow technique, alpha activity was divided into slow, medium and fast subbands. The peak-to-peak amplitude and source density distribution of each subband was also constructed. The potential flow of medium alpha was from medial to lateral in the anterior region, and from lateral to medial in the posterior region. The flow patterns of slow and fast alpha were more complicated. Similar flow directions formed a group. Different groups met or diverged at discontinuous grid points around the local maxima of potential distribution. The discontinuous points of medium alpha were centered in the parieto-occipital region, and those of slow and fast alpha were more equally distributed over the scalp. Against potential gradients, several groups of similar flow directions participated in the formation of potential field. The generation of potential field was assumed to be controlled widely for medium alpha and locally for slow and fast alpha.

Changes in the fractal dimension of the waxing and waning of alpha activity from wakefulness to drowsiness were investigated in 10 normal subjects. The envelope of filtered alpha activity was estimated with the Hilbert transform. A subset time series was constructed from the alpha envelope data taken at an interval (k). The points of the logarithm of interval k vs. the logarithm of the curve length of the subset time series (log L(k)) were fitted by a two-segment curve, consisting of small and long line segments (segments 1 and 2). The fractal dimension was estimated from the slope of straight line for each segment by using Higuchi's method. The mean fractal dimension was 1.16 for segment 1 and 1.95 for segment 2 during wakefulness and 1.15 for segment 1 and 1.89 for segment 2 during drowsiness. The fractal dimension significantly decreased in both segments during drowsiness, thus, indicating decreases in the complexity of alpha envelope.

Moment-to-moment electroencephalogram (EEG) changes just before spike and wave complexes (SWCs) were investigated by using a non-stationary power spectral analysis in 10 epileptic patients with asymmetric SWCs. The instantaneous power spectra of background EEG were estimated for a 10-s period just before SWCs in 10 locations. The spectral shape, showing a l/f amplitude characteristic, was assessed by the negative slope (spectral slope) of a straight line on a plot of log power versus frequency. Spectral slope significantly increased toward SWCs at locations with greater SWCs. This finding suggested structural changes in EEG frequency composition just before SWCs because of an epileptogenic process.

The movement of potential field (potential flow) of frontal midline theta activity (Fm theta) as well as its potential distribution was examined in 7 subjects by using optical flow detection techniques in image processing. Electroencephalograms (EEGs) over the fronto-central region were recorded from 13 electrodes near the frontal midline (Fz) while the subjects were performing a mental task. The potential flow of Fm theta was estimated on a frame consisting of a square grid with Fz at its center. In regions anterior to Fz, the direction of potential flow was from lateral to medial, whereas it was from medial to lateral in regions posterior to Fz. The peak-to-trough amplitude distribution was round or oval with a maximum just anterior to Fz. The source density distribution showed the greatest potential along the midline in the frontal region and bilaterally symmetric smaller maximum areas mostly in the prefrontal regions. Our findings suggested the presence of 2 different source areas of opposite direction in each hemisphere in spite of a round or oval amplitude distribution.