Biomedical subjects

R Kakigi

Publications and source records attributed to R Kakigi.

At least 37 records · Page 2Linked to original sources

PubMed2001

Organizing sound sequences in the human brain: the interplay of auditory streaming and temporal integration.

The present study examined the relationship between two of the early brain processes of sound organization: auditory streaming and the temporal window of integration (TWI). Presented at a fast stimulus delivery rate, two tones alternating in frequency are perceived as separate streams of high and low sounds. However, when two sounds are presented within a ca. 200 ms temporal window, they are often processed as a single auditory event. Both stream segregation and temporal integration occur even in the absence of focused attention as was shown by their effect on the mismatch negativity (MMN) event-related potential. The goal of the present study was to determine the precedence between these two sound organization processes by using the stimulus-omission MMN paradigm. Infrequently omitting one stimulus from a homogeneous tone sequence only elicits an MMN when the stimulus onset asynchrony separating successive tones is shorter than 170 ms. This demonstrates the effect of the TWI. Magnetic brain responses elicited by infrequent stimulus omissions appearing in a sequence of two alternating tones were recorded. The magnetic MMN was elicited by tone omission when the alternating tones formed a single stream (with no or only small frequency separation between the two tones) but not when separate high and low streams emerged in perception (large frequency separation between the two alternating tones). This result shows that auditory streaming takes precedence over the processes of temporal integration.

Acoustic Stimulation↗

PubMed2001

A new method for measuring the conduction velocities of Abeta-, Adelta- and C-fibers following electric and CO(2) laser stimulation in humans.

The conduction velocities of Abeta-, Adelta- and C-fibers of a peripheral nerve of the upper limb in normal subjects were measured by a combination of conventional electric stimulation, painful CO(2) laser stimulation and non-painful CO(2) laser stimulation of a tiny skin surface area, respectively. The values obtained were 69.1+/-7.4 m/s, 10.6+/-2.1 and 1.2+/-0.2 m/s, respectively. These findings demonstrated that the combined methods are useful for experimental and clinical exploration of the physiological function and pathophysiological role of Abeta-, Adelta- and C-fibers of a given peripheral nerve.

Adult↗

PubMed2001

Occipitotemporal activity elicited by viewing eye movements: a magnetoencephalographic study.

The temporal and spatial processing of viewing eye movements was studied by magnetoencephalography (MEG) in six normal subjects. Three visual stimulus types were studied: (1) moving eyes (EYES), (2) moving simulated eyes (SIM), consisting of checks moving in the same spatial location as EYES, and (3) an inwardly moving radial pattern (RADIAL). A large clear MEG component, 1M, with mean peak latency of approximately 170 ms, was seen in the right hemisphere to RADIAL and EYES in all six subjects. The 1M to EYES was significantly longer in latency and smaller in amplitude than that seen to RADIAL. A left hemisphere 1M to EYES and RADIAL was seen in three of six subjects. In all subjects and both hemispheres the equivalent current dipoles (ECD) for EYES and RADIAL were located near the occipitotemporal border, the MT/V5 homologue in humans. The ECD to EYES was significantly more posterior and inferior than that to RADIAL, with a calculated significant separation distance of around 1 cm. No ECD was estimated in the fusiform gyrus, a structure that plays a main role in static face perception. Although the 1M was detected in SIM in all six subjects, our criteria for a reliable ECD could only be satisfied in only one subject. Our results suggest that the cortex of human MT/V5 and its surrounds is active both in the perception of eye motion and motion in general, particularly in the right hemisphere. The areas responsive to eye motion were separable from those responsive to radial motion. These data suggest that there may be specialization within regions of human cortex previously thought to be sensitive to motion in general.

Adult↗

PubMed2001

Representation of the ear in human primary somatosensory cortex.

We studied 13 healthy subjects with a multichannel magnetoencephalography (MEG) system to investigate the somatotopic representation of the ear in the primary somatosensory cortex (SI). We stimulated three parts of the left ear: the helix, the lobulus, and the tragus. The somatosensory-evoked magnetic fields (SEFs) were successfully measured in 7 of 13 subjects. Short-latency responses were analyzed using both single dipole and multidipole models (brain electric source analysis, BESA). From the single dipole model, the equivalent current dipole (ECD) following the helix stimulation was estimated to be near the neck area of SI in all the subjects. In the lobulus stimulation, the ECDs were estimated around the neck area of SI in four subjects, in the face area in one subject, and in the deep white matter in two subjects. In the tragus stimulation, the ECDs were estimated around the neck area of SI in three subjects, in the hand area of SI in two subjects, and in the deep white matter in two subjects. When the ECDs were estimated to be located in unlikely sites (hand area and deep white matter), a two-dipole model, (1) the neck area of SI and (2) face area of SI, was found to be the most appropriate. Although this might be a preliminary study due to a relatively small number of subjects, it revealed that receptive fields of some part of the ear, such as the lobulus and tragus, might be present in both the neck and face areas of SI. These findings suggested that the "ear area" of SI has variability between subjects, unlike the other areas of SI, possibly because the ear is located on the border between the neck and face.

Adult↗

PubMed2001

The effect of stimulus repetition on cortical magnetic responses evoked by words and nonwords.

Stimulus repetition improves performance and modulates event-related brain potentials in word recognition tasks. We recorded evoked magnetic responses from bilateral temporal sites of the brain to determine the cortical area related to the word repetition effect. Fourteen Japanese volunteers read words or pronounceable nonwords, some of which occurred twice with a lag of eight items. Clear magnetic responses were observed bilaterally. In the left hemisphere, a reduction of the magnetic responses by repetition was observed for words but not for nonwords in the latency range of 300-500 ms poststimulus. The sources of the responses were estimated to be in the left perisylvian area adjacent to the auditory cortex and the left parietal area. Only the perisylvian source activity showed the reduction by the word repetition. The left perisylvian area was thus suggested to be related to the word repetition effect. The activity in this area might be associated with the lexical memory process.

Adult↗

PubMed2001

Attention and visual interference stimulation affect somatosensory processing: a magnetoencephalographic study.

In our previous study, continuous visual (cartoon and random dot motion) and auditory (music) stimulation changed the somatosensory evoked magnetic fields following electrical stimulation of the median nerve in human subjects. They enhanced the middle-latency components (3M and 4M) generated in the contralateral primary somatosensory cortex, and reduced the MI component generated in the ipsilateral secondary somatosensory cortex. We speculated that such interference effects were caused by activation of polymodal neurons in areas 5 and/or 7 of the parietal lobe as well as in the medial superior temporal region and superior temporal sulcus. However, we could not exclude the effect of attention on such interference effects. In the present study, to know the effect of attention on visual and auditory interference in these changes, we stimulated the bilateral median nerves unilaterally in a random order, and asked subjects to count the number of times the left median nerve was stimulated while visual or auditory interference was applied. Five components (1M-5M) were identified in the hemisphere contralateral to the stimulated nerve and only one component (MI) was found in the ipsilateral hemisphere. The 3M and 4M components (33-75 ms in latency) were enhanced by both attention and visual interference stimulation but not by auditory stimulation. The 5M component (70-115 ms) and MI component (70-133 ms) were enhanced by attention, but were not changed by attention together with visual or auditory interference. Summarizing the results of our previous study and the present study, (1) visual interference alone enhanced the 3M and 4M but reduced the MI, and (2) attention alone also enhanced the 3M and 4M, and enhanced the 5M and MI. As a result, (3) visual interference with attention enhanced the 3M and 4M more, and showed no significant change of the 5M and MI. This was compatible with a summation of the effects caused by visual interference alone and attention alone, but some interactions between visual interference and attention might have taken place. The locations of dipoles of all components were not significantly changed by attention or any interference stimulation. These findings support the idea that there are significant interactions of activities relating to somatosensory stimulation, visual stimulation and cognitive function, in both the primary and the secondary somatosensory cortex in humans.

Acoustic Stimulation↗

PubMed2001

Neural activities during Wisconsin Card Sorting Test--MEG observation.

The present study recorded activities of magnetoencephalography (MEG) to the presentation of cards, and to the presentation of feedback signals in 12 normal subjects while they performed the Wisconsin Card Sorting Test (WCST), to observe temporal and spatial processing during the task. The MEG responses were compared between two different conditions in the presentation both of cards and of feedback signals: the cards proceeded by the first wrong [W1st(C)] and by the 4th correct feedback signals [C4th(C)]; and the feedback of the first wrong [W1st(FB)] and the 4th correct signals [C4th(FB)]. A multi-dipole model, brain electric source analysis (BESA), was used to explore the dipole sources responsible for the MEG activities. We found that MEG activity differences between the W1st(C) and the C4th(C) condition occurred in the period of 190-220 ms (M190 and M200), and 300-440 ms (M300 and M370) mainly at the supramarginal gyrus, the dorsolateral prefrontal, and the middle and inferior frontal gyrus. MEG differences between the W1st(FB) and the C4th(FB) condition occurred 460-640 ms (M460) after the presentation of the feedback signals, with the activation of the dorsolateral prefrontal cortex and the middle frontal cortex. No significant location differences were found between the frontal responses (M370) of the W1st(C) and M460 of the W1st(FB). Our results proved that the WCST task activates a broad frontal area and the parieto-frontal network across time streaming. Both shifting attention to the wrong feedback and enhanced visual working memory to the sorting shifting condition of the card presentation occur in the same areas at different time points.

Adult↗

PubMed2001

Automatic discriminative sensitivity inside temporal window of sensory memory as a function of time.

Neural representation of preceding sound-patterns stored in the human brain, as reflected by mismatch negativity (MMN) related to the automatic discriminative process, is restricted to a duration of 160-170 ms due to the short form of auditory sensory memory termed the temporal window of integration (TWI). To examine the temporal uniformity of deviation-sensitivity inside TWI of sensory memory, magnetic MMN (MMNm) responses were measured with a dual 37-channel magnetometer for complex sounds of 170 ms duration containing an omitted (silent) segment. Frequent standard stimuli (probability of 80%) consisted of five tone segments. Deviant stimuli were different from standard stimuli in that one of four segments was occasionally (probability of 5%) omitted and replaced by a silent segment. The stimulus duration of 170 ms was intended to correspond to the postulated duration of TWI. When the silent segment occurred later in deviant stimulus, the MMNm peak amplitude was attenuated and MMNm peak latency, measured from the onset of each silent segment, was delayed. Thus, automatic deviation-detection sensitivity declines nonlinearly toward the end of TWI in auditory sensory memory. In the second experiment, two types of deviant stimuli, which differed from each other only in the period after the occurrence of the silent segment, elicited MMNm with the same peak latency but with a different peak amplitude. Thus, mismatch process is triggered at the moment of change but still lasts after the detection of deviation. In other words, both standard and deviant stimuli are treated as a unitary event within a TWI.

Acoustic Stimulation↗

PubMed2001

Auditory response following vocalization: a magnetoencephalographic study.

OBJECTIVE: We recorded vocalization-related cortical fields (VRCF) under complete masking of a subject's own voice to identify the auditory component evoked by a subject's own voice in the VRCF complex. METHODS: We recorded VRCF during simple vowel (/u/) vocalization in 10 right-handed healthy volunteers under two conditions: (1) no masking (control) and (2) masking of the subject's own voice by weighted-white noise during vocalization. In the second experiment, we recorded auditory evoked magnetic fields (AEF) following stimulation of a speech sound applied by voice-recorder. RESULTS: The onset of VRCF appeared gradually before the vocalization onset, and a clear phase-reversed deflection was identified after the onset of vocalization. The difference waveform obtained by subtracting the VRCF of the masking condition from that of the control showed a deflection (1M) at 81.3+/-20.5 (mean+/-SD) ms after the onset of vocalization, but there was no consistent deflection before the vocalization onset. The AEF following voice sound in the second experiment showed the M100 component at 94.3+/-18.4 ms. The equivalent current dipole of the 1M component for different waveforms was located close in the auditory cortex to that of the M100 for AEF waveforms in each hemisphere. CONCLUSION: We successfully separated the auditory feedback response from the VRCF complex, using an adequate masking condition during vocalization of a subject's own voice. The masking effect was crucial to the auditory feedback process after the onset of vocalization. The present results suggested that the 1M component was mainly generated from the auditory feedback process by the subject's own voice. The activated auditory area for simple own voice might be similar to that for simple external sound.

Adult↗

PubMed2001

Two evoked responses with different recovery functions in the primary somatosensory cortex in humans.

OBJECTIVES: We investigated the recovery function of somatosensory evoked magnetic cortical fields (SEFs) to confirm the temporal aspects of the somatosensory process in humans. METHODS: SEFs were recorded following median nerve electrical stimulation in 6 healthy subjects. Double stimulation, with interstimulus intervals (ISIs) from 3 to 100 ms, was applied, and the SEF components for the second stimulation were analyzed. In a supplementary experiment, responses to single stimulations of various intensities from the sensory threshold to the motor threshold were studied. RESULTS: The first SEF component (1M) diminished when the ISI was less than 10 ms, while the second component (2M) remained even when the ISI was 3 ms. The two components showed a very similar attenuation with decrease of stimulus intensity. There was no significant difference in dipole location between 1M and 2M in the primary somatosensory cortex (SI). CONCLUSIONS: The results suggested that at least two independent pathways with different recovery functions exist in a similar area in the SI.

Adult↗

PubMed2001

Effects of attention on pattern-reversal visual evoked potentials: foveal field stimulation versus peripheral field stimulation.

The effects of foveal field attention on pattern reversal visual evoked potential (VEP) were investigated in thirteen normal subjects. Conventional monocular VEP was recorded during the three conditions of control, foveal concentration and reaction time task. Three patterns of checker-board, which were full field (radius, 0-9 degrees), peripheral field (2.5-9 degrees) and foveal field (0-2.5 degrees), were presented for the stimulation in each condition. The P100 and N145 amplitude of the peripheral field VEP were significantly smaller during the concentration and the reaction time task conditions that that in the control session, while the foveal field VEP amplitudes were enhanced in the concentration and reaction time tasks conditions. The full field VEP amplitudes were not significantly changed by the conditions. We concluded that the act of concentration to the foveal field or the task requiring attention to the foveal field, enhanced the VEP response to foveal field stimulation and suppressed the VEP to the peripheral field. A gating effect in area V1 was speculated, although extra-striate cortex might contribute.

Adult↗

PubMed2001

A unique area of the homonculus: the topography of the primary somatosensory cortex in humans following posterior scalp and shoulder stimulation.

We recorded somatosensory evoked magnetic field (SEF) to investigate the differentiation in the receptive area for the face, lower part of the posterior scalp (mastoid) and shoulder, which occupy an unique area in the homunculus. We analyzed the location of the equivalent current dipole (ECD) of SEF following electrical stimulation of the skin at the face, mastoid and shoulder in 20 normal subjects. Three deflections (1M, 2M and 3M) were obtained within 50 ms of the stimulation in 16 of 20 subjects. The peak latency of the 1M and 2M was not significantly different at any stimulus sites. The amplitude of the 1M was significantly larger following the face than mastoid stimulation (p<0.05). The 16 subjects were classified according to the locations of the ECD on stimulation of the mastoid: close to that for shoulder stimulation, but significantly (p<0.05) more superior and medial to that following the face stimulation (Type 1, eleven subjects); close to that for face stimulation, but significantly (P<0.05) more inferior and lateral to that following the shoulder stimulation (Type 2, five subjects). The site of the receptive area for the posterior scalp shows interindividual variation, possibly due to anatomical differences.

Adult↗

PubMed2000

The masking effect in foreign speech sounds perception revealed by neuromagnetic responses.

The backward masking effect on non-native consonants by a following vowel was examined using neuromagnetic responses to synthesized speech sounds. Native speakers of Japanese were presented with sequences of frequent (85%) and infrequent (15%) speech sounds (/ra/ and /la/ respectively, no /l/ /r/ contrast in Japanese language). The duration of the stimuli was 110 ms in a short session and 150 ms in a long session. In the short session, the stimuli were terminated in the course of the transition from the consonant to the vowel to diminish the masking effect from the vowel part. A distinct magnetic counterpart of mismatch negativity (MMNm) was observed for the short session, whereas a smaller MMNm was observed for the long session.

Adult↗

PubMed2000

The dynamic processes for word and picture encoding in the human brain as revealed by magnetoencephalography.

Subjects were asked to memorize either the size or the meaning of the first stimulus (encoding) of a stimulus pair, and to match it to the second stimulus. Words and pictures were used as the stimuli in separate tests. Two components named 1M and 2M in both hemispheres for word or picture stimuli could be detected by magnetoencephalography (MEG). The dipole location of 1M in bilateral hemispheres for words is different from that for pictures, but that of 2M is not. It is considered that picture and word are processed in different systems at the initial stage, mainly in the lateral temporal cortex for words and in the parietal cortex for pictures, whereas they are processed in a common semantic system at the late stage.

Adult↗

PubMed2000

Effects of check size on pattern reversal visual evoked magnetic field and potential.

The effects of different check sizes on the 100m component of pattern reversal visual evoked magnetic fields (VEF) and the P100 component of visual evoked potentials (VEP) in terms of latency, amplitude and source localization were analyzed. Half field stimuli with or without central occlusion with check sizes of 15', 30', 60', 90' and 180' of visual arc were given to 7 healthy subjects. VEF and VEP were recorded simultaneously. The effect of the check size on the peak latency of both 100m and P100 was significant (P<0.01, ANOVA). The latencies for the smaller checks were significantly longer than those for the larger checks. The effect of the check size on the amplitude of the 100m to the stimulation with central occlusion was significant (P<0.05, ANOVA), but was not to the stimulation without central occlusion. That is, the amplitudes for the smaller checks were significantly smaller than those for the larger checks when using the stimulation with central occlusion, but not the stimulation without central occlusion. The effect of the check size on the P100 amplitude was not significant to the stimulation with and without central occlusion. The equivalent current dipoles were located around the calcarine fissure and did not differ significantly in location with check size. In conclusion, check size significantly affects the latency and amplitude of the 100m and/or P100, but not the receptive areas for the stimulation.

Adult↗

PubMed2000

Asymmetry of the human visual field in magnetic response to apparent motion.

Predominance of the lower visual field has been shown in various visual tasks, but whether the upper visual field is involved in a specific neural process is unknown. We used magnetoencephalography to study the effect of orientation and direction on the responses of five subjects to apparent motion from the human extrastriate cortex. The first magnetic response always was the largest, and the peak latency of about 200 ms did not change with the stimulus conditions. Amplitudes of the first responses were highest when motions were oriented at the horizontal meridian, decreasing with the degree of the angle between motion orientation and the horizontal meridian. There was no difference in amplitude between the two directions in the lower visual field, whereas the value of the response to downward motion in the upper visual field was significantly larger than that to upward motion. These amplitude changes are not due to differences in the anatomical distribution of neural activities because the estimated origins for the first responses always were in the same cortical area (around the occipito-parieto-temporal region) and the directions of the current vectors did not change with the stimulus conditions, and the estimated current strength changed with the stimulus conditions as did the response amplitude. These findings suggest that the human extrastriate cortex has a directional preference for downward versus upward motion in the upper visual field.

Adult↗

PubMed2000

Perception of apparent motion is related to the neural activity in the human extrastriate cortex as measured by magnetoencephalography.

To determine the neural correlate of apparent motion perception, we measured magnetic responses to visual stimuli in apparent motion and compared the results with subjective rating of the quality of perceived motion with varied stimulus timing. The latency of the magnetic response was about 150 ms, and its origin was estimated to be in the occipito-parieto-temporal junction. The strength of the first component in the response varied with the stimulus timing, the maximum value being at the interval 0. The change could not be explained by the simple summation of onset and offset responses and this value was related to the subjective rating of quality (smoothness) of motion measured of the stimulus. Results indicate there is a localized cortical region of neural activity which is closely related to the subjective assessment of quality of perceived motion.

Adult↗

PubMed2000

The somatosensory evoked magnetic fields.

Averaged magnetoencephalography (MEG) following somatosensory stimulation, somatosensory evoked magnetic field(s) (SEF), in humans are reviewed. The equivalent current dipole(s) (ECD) of the primary and the following middle-latency components of SEF following electrical stimulation within 80-100 ms are estimated in area 3b of the primary somatosensory cortex (SI), the posterior bank of the central sulcus, in the hemisphere contralateral to the stimulated site. Their sites are generally compatible with the homunculus which was reported by Penfield using direct cortical stimulation during surgery. SEF to passive finger movement is generated in area 3a or 2 of SI, unlike with electrical stimulation. Long-latency components with peaks of approximately 80-120 ms are recorded in the bilateral hemispheres and their ECD are estimated in the secondary somatosensory cortex (SII) in the bilateral hemispheres. We also summarized (1) the gating effects on SEF by interference tactile stimulation or movement applied to the stimulus site, (2) clinical applications of SEF in the fields of neurosurgery and neurology and (3) cortical plasticity (reorganization) of the SI. SEF specific to painful stimulation is also recorded following painful stimulation by CO(2) laser beam. Pain-specific components are recorded over 150 ms after the stimulus and their ECD are estimated in the bilateral SII and the limbic system. We introduced a newly-developed multi (12)-channel gradiometer system with the smallest and highest quality superconducting quantum interference device (micro-SQUID) available to non-invasively detect the magnetic fields of a human peripheral nerve. Clear nerve action fields (NAFs) were consistently recorded from all subjects.

Brain Mapping↗