In the responses of magnetoencephalography (MEG) related to higher brain functions, components that result in a failure of the estimation of single equivalent-current dipoles often appear. For example, a single dipole source with a very deep location and a very large moment is calculated. This is unacceptable for MEG researchers, though it satisfies the criteria for inspecting the reliability of the dipole, such as goodness-of-fit (GOF) and correlation coefficient. We have developed a new algorithm to avoid these false solutions and to obtain better accuracy of source locations. In the proposed method, a term including the moment and signal-to-noise ratio (SNR) was added to the cost function of the rotating dipole estimation. Two dipoles were successfully localized from the simulated MEG responses that gave an unacceptably deep solution if the conventional cost function was used. The location error was at a distance of less than 5mm between the estimated and original dipoles when the SNR of the response was larger than 10. By use of the present method, the possibility of getting unacceptable solutions from the actual MEG responses will be reduced.

View full abstract

A device was developed that enables in situ optical and electrical observations of a single cell under exposure to a magnetic field. Electric current through a flat conductor sheet made a homogeneous magnetic field above the sheet. The sheet was made of brass, 30mm×30mm to 60mm×660mm and 0.3mm thick, with a hole 2mm in diameter in the center of the sheet for the light path of a microscope. An electric current of diverse waveforms was supplied by a function generator through an amplifier, generating a magnetic field of the same waveform up to 0.14mT. The sheet was laid concentrically on the stage of a microscope. The homogeneity of the field over a 40mm×40mm sheet was estimated to be 5% in the vertical and 0.1% in the horizontal directions for a 1mm shift of a cell. A sheet does not hinder movement of the patch-clamp attachments and leaves space for a pair of coils to compensate the geomagnetic field on the stage of the microscope. The electric noise caused by the field was so small that it could be canceled in the data collection process.

View full abstract

To clarify the flow dynamics of intracranial cerebrospinal fluid (CSF) in normal pressure hydrocephalus (NPH), frequency analyses of CSF flow measured with an ECG-gated phase contrast cine magnetic resonance imaging (MRI) were performed. The amplitude and phase in the CSF flow spectra in the aqueduct were determined in patients with NPH after a subarachnoid hemorrhage (SAH-NPH group, n=26), an idiopathic NPH (I-NPH group, n=4), an asymptomatic ventricular dilation or a brain atrophy (VD group, n=21), and in healthy volunteers (control group, n=25). The changes of CSF flow spectra were also, analyzed 5 and 15 minutes after an intravenous injection of acetazolamide. Moreover, a phase transfer function (PTF) calculated from the spectra of the driving vascular pulsation and CSF flow in the aqueduct were assessed in patients with SAH-NPH and control groups before and after acetazolamide injection. These values were compared with the pressure volume response (PVR). The amplitude of the 1st-3rd harmonics in the SAH-NPH or I-NPH group was significantly larger than in the control or VD group because of a decrease in compliance (increase in PVR). The phase of the 1st harmonic in the SAH-NPH group was significantly different from that in the control or VD group, but no difference was found between the control and VD groups. The amplitude of the 0-3rd harmonics increased, and the phase of the 1st harmonic changed in all groups after an acetazolamide injection. An evaluation of the time course of the direct current of CSF flow provided further information about the compensatory faculty of the cerebrospinal cavity. A PTF of the 1st harmonic in the SAH-NPH group was significantly larger than in the control group, and a positive correlation was noted between PTF of the 1st harmonic and PVR. In conclusion, frequency analyses of CSF flow measured by cine-MRI make it possible to obtain noninvasively a more detailed picture of the pathophysiology of NPH and of changes in intracranial conditions.

View full abstract

The motion aftereffect (MAE) is a modification of motion perception following prolonged observation of a regularly moving stimulus (adaptation to the stimulus). The MAE involves the apparent motion of a stationary stimulus in the direction opposite to a previously observed one. Many psychophysical studies on the MAE have been reported to investigate the mechanisms of motion perception. On the other hand, some noninvasive functional brain imaging studies have reported the brain activity in area MT/V5 during the MAE. However, only static stimuli were used in these studies; therefore insufficient study on the relationship between brain activity and velocity perception during the MAE has been conducted. So we investigated this relationship by using both moving and static stimuli presented after adaptation, which were perceived to move with a velocity different from the physical velocity by the MAE. We used concentric half rings that moved in either a contracting or an expanding direction as visual stimuli. MEG responses were recorded in synchrony with the instance of change in the direction of motion or of the termination of motion under adapted or nonadapted states. Perceived velocities were measured before and after the velocity changes of the stimuli. We also measured the MEG responses when subjects' perceptions were equal (subjectively static) between adapted and nonadapted conditions to investigate the effect of adaptation on brain activity. Subjectively static stimuli were defined by psychophysical measurement in a preliminary session. The results: (1) MEG peak latency did not change by adaptation; (2) There exists a brain area whose activity increases by adaptation; (3) Measured MEG intensity was not simply related to the perceived velocity, and an effect of adaptation on the intensity is significant. These results with previous electrophysiological studies suggest the possibility that the direction-selective cells sensitive to the direction opposite to adaptation stimuli increase in firing rates.

View full abstract

Awake background electroencephalograms (EEGs) are interpreted by an electroencephalographer (EEGer), and the results of EEG interpretation are described in EEG reports. These reports, which include enough contents so that the time series of raw EEG can be imaged from them, are desired. In this study, a method for constructing an EEG model in consideration of an EEGer's visual interpretation was proposed. First, the values of specific EEG parameters for EEG interpretation items were determined based on EEGer's EEG report, and the model parameters were calculated from the determined EEG parameters by using the relationship between the model parameters and the EEG parameters. The proposed models were constructed for the EEG data of 8 subjects. The time series of constructed models were evaluated by use of the automatic EEG interpretation method, which was previously proposed by us, and it was seen that the results of EEG interpretation for models were almost equal to those for raw EEG.

View full abstract

It is more than a half-century since Dr. Hans Selye proposed that the reaction to an external stimulus to a human be called a “stress.” However, an index that can quantitatively evaluate the stress has not yet been established. We have focused on the change of α-amylase activity in saliva (salivary amylase) and carried out an in vivo evaluation in six normal subjects to define the levels of mental stress through amylase activity. In this evaluation, the Kraepelin Psychodiagnostic Test was used as a mental stressor for the subjects. In normal subjects, a comparatively quick response was observed by the experiment for stress load, which verified a correlation between mental stress and salivary amylase activity. The sign of gradient calculated from the salivary amylase activity was negative or positive, depending on whether the stress reaction is comfortable. Furthermore, when the salivary amylase activity and salivary total protein were measured, the effect of the salivary flow rate could be estimated. The change of salivary amylase activity was confirmed as being originated from stress. These results suggest that the monitoring of salivary amylase could be used as a noninvasive indicator of stress reaction.

View full abstract