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S Kuriki

Publications and source records attributed to S Kuriki.

At least 37 records · Page 2Linked to original sources
PubMed1995

Event-related magnetic fields at latencies of over 400 ms in silent reading of Japanese Katakana meaningless words.

Event-related magnetic fields (ERFs) were recorded when subjects were presented with meaningless readable words or unreadable words. The ERF averages for readable words and those for unreadable words showed a large difference at latencies of over 400 ms. The equivalent current dipoles were obtained only for readable words, and were located near the cingulate gyrus and the supplementary motor area whose functions are considered to be related to attention and motor planning.

Adult↗
PubMed1995

Cortical sources of middle latency responses of auditory evoked magnetic field.

In the recordings of middle latency responses of auditory evoked magnetic fields in 4 male subjects, we observed distinct components at 11, 19 and 33 ms after click stimulus. Equivalent current dipole sources of these components were located in the supratemporal auditory cortex, where the earliest component source was found at the most medial site.

Acoustic Stimulation↗
PubMed1994

Event-related potentials in silent speech.

Event-related potentials (ERPs) in silent speech using the vowel /a/ were recorded from 12 scalp electrodes and three electrodes monitoring eye and throat movements in eight subjects cued by one of two randomly lit light-emitting diodes (LEDs). The average silent-speech potential minus nonsilent-speech potential showed two significant scalp potential distributions--a positive difference in the occipital scalp area at a 0.30-s latency from the LED onset and a negative difference in the frontal scalp area peaking at electrode Fz at a 0.42-s latency. The occipital scalp potential may include an endogenous component like P3. Possible sites of neural activities underlying the frontal negative difference are discussed in relation to the topography of the scalp potential and functions involved in silent speech.

Adolescent↗
PubMed1994

Characteristics of the background fields in multichannel-recorded magnetic field responses.

We have studied the background fields in the auditory evoked magnetic field responses recorded with a 37-channel SQUID magnetometer. The background fields were found to have a main contribution from the spontaneous fields, which originate in the neural activities of the brain. The spontaneous fields had strong spatial correlation across the recording sites even after averaging over 100 epochs. The spatial distribution of the spontaneous fields consisted of 3 main components of single extremum pattern, dipolar pattern, and a dipolar pattern with some distortion. Computer simulations of the localization of a single dipole source of the evoked field response showed that the spontaneous background field could bring about large location errors in an unpredictable manner, as compared with the location errors caused by a spatially random Gaussian noise field.

Adult↗
PubMed1994

Reduction of brain noise influence in evoked neuromagnetic source localization using noise spatial correlation.

In magnetoencephalographic measurements, magnetic fields caused by spontaneous brain activities not related to the neural activities under study are often referred to as brain noise. This is because the accuracy in neural source localization is considerably degraded by such spontaneous neuromagnetic fields. This paper reports the experimental results of applying the previously proposed noise covariance method to reducing the degradation caused by brain noise and to improving the accuracy in localizing auditory-evoked neural sources. Firstly we present the results of our experiments using measured brain noise and computer-generated signal fields. These results confirm that the covariance method can, in principle, improve the accuracy of evoked neural source localization. Next, the method was applied to source localization for actual neuromagnetic fields evoked by speech sounds. The results obtained strongly suggest that the method is effective in processing actual evoked neuromagnetic data.

Adult↗
PubMed1993

Identification of central sulcus by using somatosensory evoked magnetic fields and brain surface MR images: three dimensional projection analysis.

We present a novel non-invasive technique for identification of the central sulcus on the brain surface by using three-dimensional magnetic resonance imaging (3D-MRI) in combination with somatosensory evoked magnetic fields (SEFs). The central sulcus was supposed anatomically on the brain surface by using 3D-MRI. On the other hand, the primary somatosensory area is determined by using SEF data with median nerve stimulation. Superimposition of the SEFs of the 25 ms response onto the brain surface MR images clearly demonstrated the dipole source located in the gyral fold just behind the supposed central sulcus in all subjects analyzed. Three-dimensional reconstruction of the brain surface image data facilitated visualizing the precise anatomical localization of the magnetic field activities from any angle and measuring the distance from the source to any point of interest. The potential clinical application of this technique is discussed.

Adult↗
PubMed1993

Magnetic field responses to visual stimulation in human parietal association cortex.

The neural activities of the parietal association cortex were studied in humans through the use of a 37-channel SQUID magnetometer system. The magnetic field responses were recorded in the parietal association cortex following visual stimulation with LED light. Main responses peaking at about 120, 170 and 220 msec after LED onset were observed. The estimated current dipole sources of the magnetic field responses at latencies of 160-190 and 210-270 msec were revealed to be located in the intraparietal sulcus. A change in the magnetic field responses with the eye position was found in the amplitude.

Adult↗
PubMed1993

Functional neurosurgical simulation with brain surface magnetic resonance images and magnetoencephalography.

We present a novel noninvasive technique for functional neurosurgical simulation combining three-dimensional magnetic resonance imaging of the brain surface with somatosensory evoked magnetic fields (SEFs) in a case of subcortical brain tumor. The preoperative analysis using this technique revealed that the central sulcus was located between the SEF source projected onto the brain surface and the tumor. At the time of surgery, the central sulcus was clearly identified by phase reversal of the cortical recordings of somatosensory evoked potentials. The actual cortical anatomy and the maximum somatosensory evoked potential location showed excellent agreement with the preoperative analysis of the brain surface magnetic resonance images and the SEF source. The subcortical tumor, which was barely identifiable without reliable functional cortical anatomy, was easily found in the motor area, just before the somatosensory evoked potential (and SEF) source. The potential clinical application of this technique is discussed.

Brain Mapping↗
PubMed1992

[Anatomical analysis of the sources of somatosensory evoked fields (SEFs) using 3D-MRI].

We have recorded short latency somatosensory evoked magnetic fields (SEFs) to left median nerve stimulation in three healthy subjects. The locations of the deduced dipole sources were projected onto the 3-Dimensional magnetic resonance imaging (3D-MRI) of the individual subjects providing an anatomical localization. We found that the deduced sources were located at the primary sensorimotor hand area on the posterior surface of the central sulcus, at an average depth of 26mm (11mm) from the scalp (brain surface). This technique that combined MEG with 3D-MRI was able to precisely determine source locations and analyze the relationships between dipole sources and brain structures. By using this technique, we can confirm functional anatomy of the brain noninvasively, and obtain much useful information preoperatively and during operation.

Adult↗
PubMed1989

Neuromagnetic study of the auditory responses in right and left hemispheres of the human brain evoked by pure tones and speech sounds.

Neuromagnetic responses in the human auditory cortex evoked by various burst stimuli of pure tones and monosyllable speech sounds were measured separately from two hemispheres. Both the pure tones and speech sounds elicited clear responses with two main peaks. The field patterns over the scalp at the peak latencies indicated a single current dipole as an equivalent field generator. The depth of the current dipoles computed from the mapped field data was deeper from the scalp for a tone stimulus of higher frequency, which confirms the tonotopic organization in the auditory cortex. A difference was found in the dipole locations in the horizontal plane for the speech stimuli of a vowel and a consonant-vowel /a/ and a consonant-vowel /ka/. It suggests the sensitivity of the magnetic responses to the acoustic structure of the speech sound.

Adult↗
PubMed1989

Locating accuracy of a current source of neuromagnetic responses: simulation study for a single current dipole in a spherical conductor.

The locating accuracy of a current dipole of neuromagnetic responses in a spherical conductor was examined in terms of the residual field which was a difference between the measured and calculated magnetic fields in a least squares fitting. Characteristics of the residual field as a function of the noise field, dipole depth, and number of measurement points were studied by computer simulations. The confidence region of the dipole location was determined by changing a dipole parameter along a coordinate axis until the sum of squares of the residual field increased by a factor given for each axis. As an example for a dipole at 2.4 cm depth, 95% confidence limits extend 2 mm along the transverse axis, 6 mm along the longitudinal axis, and 5 mm along the radial axis when the signal-to-noise ratio is 2.5 and the measurement points are 42. The method was applied to auditory evoked magnetic responses to examine location differences of the dipoles for different stimuli in the auditory cortex.

Auditory Cortex↗
PubMed1989

Measurements of auditory and somatically evoked magnetic fields and localization of their dipole sources.

We have measured neuromagnetic fields evoked by auditory and somatic stimulations using a SQUID. Responses of the auditory evoked field (AEF) have two peaks at about 100 and 180 ms after the onset of tone burst stimulus. Responses of the somatically evoked field (SEF) have two peaks at about 80 and 160 ms after the stimulus of current pulse. Magnetic field data measured at various positions of the lateral side of the head have been used to calculate parameters of an equivalent current dipole source based on a least-squares fit. The determined source locations indicate the auditory cortex for the AEF and the primary somatosensory cortex for the SEF, in agreement with anatomical structures obtained from NMR images. A simulation study has been done to estimate errors in the calculated dipole parameters due to the field noise. For typical measurement conditions of a signal-to-noise ratio of approximately 5 and measurement points of approximately 40, location errors of the order of 5 mm are estimated.

Auditory Cortex↗
PubMed1987

Biomagnetism in Japan.

The study of biomagnetic fields originating in a biological body is called biomagnetism. Among various fields of biomagnetism, this paper reviews the research and clinical works in magnetocardiogram, neuromagnetism, magneto-oculogram, magnetopneumogram and magnetic measurement for cell motility carried out in Japan.

Biology↗