Shigeaki Matsuoka

Origin of scalp far-field N18 of SSEPs in response to median nerve stimulation

To identify the origin of scalp-recorded far-field negativity of short-latency somatosensory evoked potentials to median nerve stimulation (designated N18), direct records were made from the thalamus and ventricular system during 4 stereotaxic and 3 posterior fossa operations. In the thalamus a negative potential with almost the same latency as the scalp N18 was restricted to the Vim nucleus, but there was a large positive potential in the VC nucleus and medial lemniscus. Vim negativity increased in amplitude when high frequency stimulation was given to the median nerve, indicative of a facilitation effect. In contrast, the amplitude of scalp N18 decreased at high frequency stimulus. Direct recordings made through the medulla oblongata to the mid-brain showed a negative potential with gradually increasing latency. Above the upper pons, there was stationary negativity with no latency shift. The similarity between this negative potential and N18 is shown by their having the same latency and same response to the amplitude reduction and latency prolongation produced by high frequency stimulus. Our data suggest that scalp N18 comes from brain-stem activity between the upper pons and the mid-brain rather than from the thalamus.

MEG and EEG topography of frontal midline theta rhythm and source localization

SummaryIn this paper, we report on our study of frontal midline theta (Fmθ) activity in human subjects, recorded during mental processes such as arithmetic calculation. The Fmθ is a 6–7 Hz rhythmic wave with a duration of few seconds. The Fmθ activity is observed in the central region at the front of the head. EEGs and MEGs of Fmθ were measured simultaneously during mental calculation, and we analyzed these waveforms based on both topographic EEG maps and magnetic fields measurements. A single dipole simulated the EEG topography adequately, but there are many other dipole models which can generate a similar EEG pattern. It is difficult to estimate the source location of the Fmθ from the EEG topography alone because the EEG technique has a certain ambiguity associated with source estimation. Therefore, we considered the spatial relationships between the sources and the patterns of EEG and MEG that were simulated. Although it is not possible to obtain a unique solution for the source location of Fmθ from the EEG data alone, the simultaneous recording of MEGs from a large scalp area may result in an unambiguous solution. We therefore conclude that the simultaneous recording of both MEG and EEG data is more useful for accurate localization, than the EEG alone.

Arachnoid cyst in the quadrigeminal cistern

Two cases of arachnoid cysts in the quadrigeminal cistern are presented, and one occurred in an adult. Signs and symptoms of increased intracranial pressure were noted, and obstructive hydrocephalus was shown by computed tomography scans in both cases. Arachnoid cysts in the quadrigeminal cistern have rarely been reported, especially in adults. The definition, classification, and etiology of arachnoid cyst are still confused in the literature, and various terms have also been used to indicate this particular location of cyst. In this study, these confusing problems are reviewed, and the usefulness of metrizamide computed tomographic cisternography is emphasized as a noninvasive method of diagnosis.

Our new methods of clinical evaluation in computer audiometry

ZusammenfassungVersucht wurde eine Frequenzanalyse der langsamen Komponente der gemittelten akustischen Reizantwort bei wachen Erwachsenen mit normalem Gehör und mit Innen- und Mittelohrschwerhörigkeit. Sinutöne von 0,5, 1,0, 2,0 und 4,0 Khz von 100 msec Dauer und einer An- und Abschwellzeit von 10 msec wurden über Kopfhörer 100mal bei Intensität von 20, 40 und 60 dB gegeben. Dabei ließ sich feststellen, daß die langsame Komponente einem engen Frequenzband von 3–7 Hz entspricht. Wie Abb. 1 a zeigt, wurden eine Versuchsanordnung mit engem, auf 3–7 Hz abgestimmten Frequenzfilter eingerichtet und damit an normalen, wachen Erwachsenen Vergleichsmessungen, einerseits mit der üblichen averaged evoked response (AER), andererseits mit frequency-analysed evoked response (FAER), ausgeführt. Fig.1 b und c zeigen die entsprechenden Kurvenformen bei 100mal Reizung mit einem Ton von 1 Khz bei 60 dB. Die signal/noise-relation konnte, wie in Fig. 1 c zu sehen, durch Verwendung des Filters wesentlich verbessert werden. Dadurch läßt sich bei klinischer Anwendung bei schwellennahen Messungen eine positive Antwort sicherer und schon bei geringer Reizzahl identifizieren (Fig.2); Artefakte lassen sich ausschließen und die Meßzeiten verkürzen.

Tuning method of modified wavelet transform in human sleep EEG analysis

We have developed an automatic discrimination system of human sleep EEG (electroencephalogram) stages based on a wave-shape recognition method. These systems can detect discrete stages (stage MT, W, 1, 2, 3, 4 and REM). But, it is impossible to extract much information in detail by them. Therefore, we tried to continuous wavelet analysis applied to EEG signals in order to extract more precise information for the stages. We have proposed a modified wavelet transform method and an extraction method of time series of peak frequency based on time-frequency analysis. It was confirmed that the modified wavelet transform method was effective, although it was necessary to tune the parameter in the modified wavelet transform in order to get more effective features. In this paper, tuning method of modified wavelet transform is discussed from viewpoint of the feature extraction about human sleep EEG stages. Two types (linear and nonlinear) of tuning methods are proposed. And it is confirmed that nonlinear tuning method based on sigmoid function is effective through the experimental studies.

Epileptic Convulsion in Chimera Mice

Using a method of aggregation of embryos from the Fl progenies of ddY X El and ddY X C57BL/6J, seven chimera mice were produced. These seven chimera mice manifested various distributions of the white coat color derived from the Fl progeny of ddY X El. It was found that the chimera mouse, which had a larger percent of the white coat color, had a higher susceptibility to epileptic convulsion, the susceptibility having been proportional to the degree of the tissue mosaicism.