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Biomedical subjects

Ryusuke Kakigi

Publications and source records attributed to Ryusuke Kakigi.

At least 55 records · Page 3Linked to original sources
PubMed2005

Gating of SEPs by contraction of the contralateral homologous muscle during the preparatory period of self-initiated plantar flexion.

To investigate the centrifugal change in somatosensory information processing caused by contraction of the contralateral homologous muscle, we recorded the somatosensory-evoked potentials (SEPs) during the preparatory period of a self-initiated plantar flexion. The SEPs following stimulation of the right tibial nerve at the popliteal fossa were recorded in nine healthy subjects. Self-initiated plantar flexion of the left ankle was performed once every 5 to 7 s. The electrical stimulation was delivered continuously, and the subjects were instructed to concentrate on the movement and not to pay attention to the electrical stimulation. Based on the components of movement-related cortical potential, Bereitschaftspotential (BP) and Negative slope (NS), the preparatory period was divided into four sub-periods (NS, BP-1, BP-2, and Pre-BP). To obtain pre-movement SEPs, the signals following stimulation in each sub-period were averaged. SEPs were attenuated in the preparatory period, especially in the NS sub-period. The amplitude of N40 component was significantly attenuated compared with that in the stationary state and other sub-periods. The amplitude of P53 and N70 was smaller in the NS sub-period than other pre-movement sub-periods. Since there was no centripetal effect on SEPs in the preparatory period, these findings suggested that the activity of motor-related areas modulated the somatosensory information from the contralateral non-movement limb (centrifugal gating). It was assumed that an inhibition on the somatosensory inputs from contralateral limb was caused by the projection via either the corpus callosum or ipsilateral cortico-cortical projections.

Adult↗
PubMed2005

Mismatch responses related to temporal discrimination of somatosensory stimulation.

OBJECTIVE: To determine the existence of a pre-attentively evoked somatosensory mismatch negativity component and to investigate the use of that component in objective clinical diagnostics. METHODS: First we determined the temporal discrimination threshold (DT) of paired stimuli in each subject, and applied two sequential electrical stimuli to the hand with paired stimulus times of (1) DT-10 ms, (2) DT-30 ms and (3) DT+50 ms. Then, we recorded ERPs using an oddball paradigm, frequent (standard) and rare (deviant). We used two stimuli, DT-30 ms and DT-10 ms, in the first experiment, and DT-30 ms and DT+50 ms, in the second experiment. RESULTS: In each experiment, two specific components, a negative component peaking at approximately 60ms (N60) and a large positive component peaking around 100-200 ms (P150), were identified, mainly following the deviant stimulus, which were considered somatosensory mismatch components. N60 was more remarkably identified in the second experiment and P150 in the first. CONCLUSIONS: N60 might be generated during tasks which subjects can clearly discriminate, but P150, which seems to correspond to auditory mismatch negativity, might be generated in tasks which require fine discrimination. SIGNIFICANCE: We confirmed that our new method could be used for the objective examination of temporal discrimination.

Adult↗
PubMed2005

Mechanisms of face perception in humans: a magneto- and electro-encephalographic study.

We have been studying the underlying mechanisms of face perception in humans using magneto- (MEG) and electro-encephalography (EEG) including (1) perception by viewing the static face, (2) differences in perception by viewing the eyes and whole face, (3) the face inversion effect, (4) the effect of gaze direction, (5) perception of eye motion, (6) perception of mouth motion, and (7) the interaction between auditory and visual stimuli related to the vowel sounds. In this review article, we mainly summarize our results obtained on 3, 5, and 6 above. With the presentation of both upright and inverted unfamiliar faces, the inferior temporal cortex (IT) centered on the fusiform gyrus, and the lateral temporal cortex (LT) near the superior temporal sulcus were activated simultaneously, but independently, between 140 and 200 ms post-stimulus. The right hemisphere IT and LT were both active in all subjects, and those in the left hemisphere in half of the subjects. Latencies with inverted faces relative to those with upright faces were longer in the right hemisphere, and shorter in the left hemisphere. Since the activated regions under upright and those under inverted face stimuli did not show a significant difference, we consider that differences in processing upright versus inverted faces are attributable to temporal processing differences rather than to processing of information by different brain regions. When viewing the motion of the mouth and eyes, a large clear MEG component, 1M (mean peak latency of approximately 160 ms), was elicited to both mouth and eye movement, and was generated mainly in the occipito-temporal border, at human MT/V5. The 1M to mouth movement and the 1M to eye movement showed no significant difference in amplitude or generator location. Therefore, our results indicate that human MT/V5 is active in the perception of both mouth and eye motion, and that the perception of movement of facial parts is probably processed similarly.

Adult↗
PubMed2005

Functional relationship between human rolandic oscillations and motor cortical excitability: an MEG study.

Synchronization and desynchronization of the neural rhythm in the brain play an important role in the orchestration of perception, motor action and conscious experience. Based on the results of electrocorticographic and magnetoencephalographic (MEG) recordings, it has been considered that human rolandic oscillations originate in the anterior bank of the central sulcus (20-Hz rhythm) and the postcentral cortex (10-Hz rhythm): the 20-Hz oscillation is closely related to motor function, while the 10-Hz rhythm is attributed mainly to sensory function. To test whether the rolandic oscillations are functionally relevant to the motor cortical excitability, we examined effects of 1-Hz repetitive transcranial magnetic stimulation (rTMS) of the left primary motor cortex (M1) on movement-related changes of the rolandic oscillations in 12 normal subjects. MEG data recorded during brisk extension of the right index finger in two different sessions (with and without rTMS conditioning) were compared. Motor-evoked potential (MEP) of the right hand muscle was also measured before and after rTMS to assess the motor cortical excitability. We found that 1-Hz rTMS over M1 significantly reduced the movement-related rebound of the 20-Hz oscillation in association with decreased motor cortical excitability. In particular, movement-related rebound of the 20-Hz rhythm was closely tied with motor cortical excitability. These findings further strengthen the notion of functional relevance of 20-Hz cortical oscillation to motor cortical excitability. In the framework of previous studies, the decrease in movement-related rebound may be regarded as a compensatory reaction to the inhibited cortical activity.

Adult↗
PubMed2005

Differential modulation in human primary and secondary somatosensory cortices during the preparatory period of self-initiated finger movement.

To elucidate the mechanisms underlying sensorimotor integration, we investigated modulation in the primary (SI) and secondary (SII) somatosensory cortices during the preparatory period of a self-initiated finger extension. Electrical stimulation of the right median nerve was applied continuously, while the subjects performed a self-initiated finger extension and were instructed not to pay attention to the stimulation. The preparatory period was divided into five sub-periods from the onset of the electromyogram to 3000 ms before movement and the magnetoencephalogram signals following stimulation in each sub-period were averaged. Multiple source analysis indicated that the equivalent current dipoles (ECDs) were located in SI and bilateral SII. Although the ECD moment for N 20 m (the upward deflection peaking at around 20 ms) was not significantly changed, that for P 30 m (the downward deflection peaking at around 30 m) was significantly smaller in the 0- to -500-ms sub-period than the -2000- to -3000-ms sub-period. As for SII, the ECD moment for the SII ipsilateral to movement showed no significant change, while that for the contralateral SII was significantly larger in the 0- to -500-ms sub-period than the -1500- to -2000-ms or -2000- to -3000-ms sub-period. The opposite effects of movement on SI and SII cortices indicated that these cortical areas play a different role in the function of the sensorimotor integration and are affected differently by the centrifugal process.

Adult↗
PubMed2005

Somato-motor inhibitory processing in humans: a study with MEG and ERP.

The go/nogo task is a useful paradigm for recording event-related potentials (ERPs) to investigate the neural mechanisms of response inhibition. In nogo trials, a negative deflection at around 140-300 ms (N2), which has been called the 'nogo potential', is elicited at the frontocentral electrodes, compared with ERPs recorded in go trials. In the present study, we investigated the generators of nogo potentials by recording ERPs and by using magnetoencephalography (MEG) simultaneously during somatosensory go/nogo tasks to elucidate the regions involved in generating nogo potentials. ERP data revealed that the amplitude of the nogo-N140 component, which peaked at about 155 ms from frontocentral electrodes, was significantly more negative than that of go-N140. MEG data revealed that a long-latency response peaking at approximately 160 ms, termed nogo-M140 and corresponding to nogo-N140, was recorded in only nogo trials. The equivalent current dipole of nogo-M140 was estimated to lie around the posterior part of the inferior frontal sulci in the prefrontal cortex. These results revealed that both nogo-N140 and nogo-M140 evoked by somatosensory go/nogo tasks were related to the neural activity generated from the prefrontal cortex. Our findings combining MEG and ERPs clarified the spatial and temporal processing related to somato-motor inhibition caused in the posterior part of the inferior frontal sulci in the prefrontal cortex in humans.

Adult↗
PubMed2005

An ERP study of second language learning after childhood: effects of proficiency.

Whether there is an absolute critical period for acquiring language is a matter of continuous debate. One approach to address this issue is to compare the processes of second language (L2) learning after childhood and those of first language (L1) learning during childhood. To study the cortical process of postchildhood L2 learning, we compared event-related brain potentials recorded from two groups of adult Japanese speakers who attained either high or intermediate proficiency in English after childhood (J-High and J-Low), and adult native English speakers (ENG). Semantic anomalies embedded in English sentences evoked a clear N400 component in all three groups, with only the time course of the brain activation varying among the groups. Syntactic violations elicited a left-lateralized negativity similar to the left anterior negativity in ENG and J-High, but not in J-Low. In ENG, a P600 component was additionally found. These results suggest that semantic processing is robust from early on in L2 learning, whereas the development of syntactic processing is more dependent on proficiency as evidenced by the lack of the left-lateralized negativity in J-Low. Because early maturation and stability of semantic processing as opposed to syntactic processing are also a feature of L1 processing, postchildhood L2 learning may be governed by the same brain properties as those which govern childhood L1 learning. We argue that these processes are qualitatively similar in many respects, with only restricted domains of language processing being subject to absolute critical period effects.

Adult↗
PubMed2005

Automatic encoding of polyphonic melodies in musicians and nonmusicians.

In music, multiple musical objects often overlap in time. Western polyphonic music contains multiple simultaneous melodic lines (referred to as "voices") of equal importance. Previous electrophysiological studies have shown that pitch changes in a single melody are automatically encoded in memory traces, as indexed by mismatch negativity (MMN) and its magnetic counterpart (MMNm), and that this encoding process is enhanced by musical experience. In the present study, we examined whether two simultaneous melodies in polyphonic music are represented as separate entities in the auditory memory trace. Musicians and untrained controls were tested in both magnetoencephalogram and behavioral sessions. Polyphonic stimuli were created by combining two melodies (A and B), each consisting of the same five notes but in a different order. Melody A was in the high voice and Melody B in the low voice in one condition, and this was reversed in the other condition. On 50% of trials, a deviant final (5th) note was played either in the high or in the low voice, and it either went outside the key of the melody or remained within the key. These four deviations occurred with equal probability of 12.5% each. Clear MMNm was obtained for most changes in both groups, despite the 50% deviance level, with a larger amplitude in musicians than in controls. The response pattern was consistent across groups, with larger MMNm for deviants in the high voice than in the low voice, and larger MMNm for in-key than out-of-key changes, despite better behavioral performance for out-of-key changes. The results suggest that melodic information in each voice in polyphonic music is encoded in the sensory memory trace, that the higher voice is more salient than the lower, and that tonality may be processed primarily at cognitive stages subsequent to MMN generation.

Acoustic Stimulation↗
PubMed2004

Sound perception affected by nonlinear variation of accuracy in memory trace.

The mismatch negativity (MMN) reflects the neural representation of the acoustic environment stored in sensory memory. The short phase of sensory memory corresponds to the temporal window of integration (TWI) which integrates the neighboring sounds into a unitary event. We measured the magnetic MMN (MMNm) and the discriminative reaction time (RT) responding to an omitted segment incorporated into a complex sound. Consequently, for the late omitted segments, the MMNm amplitudes were decreased, and those latencies and the RTs were prolonged. The percentages of the correct responses were also reduced for the late omitted segments. In sum, the discriminative sensitivity nonlinearly declined toward the end of the TWI, suggesting that the time-wise accuracy of the neural trace nonlinearly varies in sensory memory.

Acoustic Stimulation↗
PubMed2004

Effects of ISI and stimulus probability on event-related go/nogo potentials after somatosensory stimulation.

The present study investigated the characteristics of the middle-latency negative potential of event-related potentials (ERPs) using somatosensory go/nogo tasks. We manipulated interstimulus interval (ISI) in Experiment 1 and stimulus probability in Experiment 2 and analyzed the subtracted difference waveform resulting from subtraction of the ERP evoked by the go stimulation from that evoked by the nogo stimulation. In Experiment 1, the peak latency of negativity became significantly longer as the ISI increased, but the peak amplitude was unchanged. The reaction time (RT) was longer with increasing ISI. In Experiment 2, manipulation of the stimulus probability yielded an increase in peak amplitude with decreasing probability of the nogo stimulus, but did not affect the latency. The RT increased as the probability of a nogo stimulus rose. Because manipulation of the ISI and stimulus probability elicited different brain activities, we hypothesized that manipulation of the ISI elicited a delay of the stimulus evaluation process including response inhibition, and that stimulus probability significantly affected the strength of the response inhibition process.

Adult↗
PubMed2004

Temporal dynamics of neural adaptation effect in the human visual ventral stream.

When the same visual stimulus is repeatedly presented with a brief interval, the brain responses to that stimulus are attenuated relative to those at first presentation [neural adaptation (NA)]. Although this effect has been widely observed in various regions of human brain, its temporal dynamics as a neuronal population has been mostly unclear. In the present study, we used a magnetoencephalography (MEG) and conducted a macrolevel investigation of the temporal profiles of the NA occurring in the human visual ventral stream. The combination of MEG with our previous random dot blinking method isolated the neural responses in the higher visual cortex relating to shape perception. We dissociated three dimensions of the NA: activation strength, peak latency, and temporal duration of neural response. The results revealed that visual responses to the repeated compared with novel stimulus showed a significant reduction in both activation strength and peak latency but not in the duration of neural processing. Furthermore, this acceleration of peak latency showed a significant correlation with reaction time of the subjects, whereas no correlation was found between the reaction time and the temporal duration of neural responses. These results indicate that (1) the NA involves the brain response changes in the temporal domain as well as the response attenuation reported previously, and (2) this temporal change is primarily observed as a rapid rising of "what" responses, rather than a temporal shortening of neural response curves within the visual ventral stream as considered previously.

Adult↗
PubMed2004

Serial processing in the human somatosensory system.

Although numerous anatomical and electrophysiological findings in animal studies have supported a hierarchical scheme of somatosensory processing, precise activation timings of each cortical area are not known. Therefore we examined the temporal relationship of activities among multiple cortical areas using magnetoencephalography in humans. We found activations in Brodmann's areas 3b, 4, 1, 5 and the secondary somatosensory cortex region in the right hemisphere following transcutaneous electrical stimulation of the dorsum of the left hand. The mean onset latencies of each cortical activity were 14.4, 14.5, 18.0, 22.4 and 21.7 ms, respectively. The differences of onset latencies among these activations indicated the serial mode of processing both through the postcentral gyrus and through the primary and secondary somatosensory cortices.

Adult↗
PubMed2004

Interaction between auditory and visual stimulus relating to the vowel sounds in the auditory cortex in humans: a magnetoencephalographic study.

We investigated the interaction between auditory and visual stimulus relating to the vowel sounds in the auditory cortex in humans, using magnetoencephalography. We compared the difference in the main component, M100 generated in the auditory cortex, in terms of peak latency, amplitude, dipole location and moment, following the vowel sound_/a/_between two conditions: (1) showing a face with closed mouth; and (2) showing the same face with mouth movement appearing to pronounce/a/using an apparent motion method. We found no significant difference in the M100 component between the two conditions within or between the right and left hemispheres. These findings indicated that the vowel sound perception in the auditory cortex, at least in the primary processing stage, was not affected by viewing mouth movement.

Acoustic Stimulation↗
PubMed2004

Temporal discrimination threshold on various parts of the body.

The temporal discrimination threshold (TDT) of various parts of the body was investigated in 35 healthy volunteers, and the effect of aging on the TDT was studied in 80 subjects (aged 18-82 years). Ascending (ATDT) and descending (DTDT) TDT values were measured in 13 areas using a pair of electrical stimuli. Both ATDT and DTDT differed significantly among the body parts (P < 0.01, one-way repeated ANOVA), and the TDT was shortest on the index finger and longest on the lower leg, where it was approximately 156% of that on the finger. There was no difference of the TDT value with gender or between sides. There was no effect of aging on the TDT in subjects aged 18-64 years, but the value was prolonged in subjects over 65 years. We suggest that the TDT difference among body parts is mainly due to the difference in sensory processes in the central nervous system, and that it may provide information about changes in the system related to aging.

Adolescent↗
PubMed2004

Effects of a go/nogo task on event-related potentials following somatosensory stimulation.

OBJECTIVE: We investigated the effects of a go/nogo task on event-related potentials (ERPs) evoked by somatosensory stimuli. METHODS: ERPs following electrical stimulation of the second (go stimulus) or fifth (nogo stimulus) left-handed digit were recorded from 9 subjects. The recordings were conducted in 3 conditions: Control, Count and Movement. The subjects were instructed to count the go stimuli silently in Count, and respond to the go stimuli by grasping right hands in Movement. Go and nogo stimuli were presented at an even probability. RESULTS: N140 was recorded in all conditions and P300 in Count and Movement. The mean amplitudes of the nogo stimuli in the interval 140-200 msec and nogo-N140 amplitude were significantly more negative than those of the go stimuli in Count or Movement. Nogo-P300 was larger in amplitude than go-P300 in Movement but not Count. The effect of P300 was applied to Fz and Cz, but not at Pz. CONCLUSIONS: In the present study, effects of a somatosensory go/nogo task on ERPs were investigated, and our findings were very similar to those of previous studies using visual and auditory go/nogo tasks. Therefore, we suggest that cortical activities relating to go/nogo tasks are not dependent on sensory modalities. SIGNIFICANCE: The present study showed for the first time the go/nogo effects on somatosensory-evoked ERPs. These effects were similar to those in visual and auditory ERP studies.

Acoustic Stimulation↗
PubMed2004

Effects of distraction on magnetoencephalographic responses ascending through C-fibers in humans.

OBJECTIVE: Using magnetoencephalography (MEG), we evaluated the cerebral regions relating to second pain perception ascending through C-fibers and investigated the effect of distraction on each region. METHODS: Thirteen normal subjects participated in this study. CO2 laser pulses were delivered to the dorsum of the left hand to selectively activate C-fibers. The MEG responses were analyzed using a multi-dipole model. RESULTS: (1) primary somatosensory cortex (SI), and (2) secondary somatosensory cortex (SII)--insula were the main generators for the primary component, 1M, whose mean peak latency was 744 ms. In addition to (1) and (2), (3) cingulate cortex and (4) medial temporal area (MT) were also activated for the subsequent component, 2M, whose mean peak latency was 947 ms. During a mental calculation task (Distraction), all 6 sources were significantly reduced in amplitude, but the SII-insula (P < 0.01) and cingulate cortex (P < 0.001) were more sensitive than the SI (P < 0.05) and MT (P < 0.05). CONCLUSIONS: We confirmed that SI in the contralateral hemisphere and SII-insula, cingulate cortex and MT in bilateral hemispheres play a major role in second pain perception, and all sites were much affected by a change of attention, indicating that these regions are related to the cognitive aspect of second pain perception. SIGNIFICANCE: The SI, SII, cingulate and MT were activated during the C-fiber-related MEG response, and responses in these regions were significantly diminished during mental distraction.

Adult↗
PubMed2004

Magnetoencephalographic study of occipitotemporal activity elicited by viewing mouth movements.

OBJECTIVE: We studied the temporal and spatial characteristics of neural responses elicited by viewing mouth movements using magnetoencephalography. METHODS: We focused on differences in responses to mouth opening and closing movements by apparent motion, using an averting eyes condition as a control. RESULTS: A large clear MEG component, 1 M (mean peak latency of approximately 160 ms), was elicited by both mouth movements. We modeled the neural sources using a brain electric source analysis (BESA) method and placed the sources around: (1) the occipitotemporal border at human MT/V5, (2) the primary visual cortex (V1), and (3) fusiform gyrus. The calculated activity of Source (1) was large whereas the activity of the others was small or negligible. Source (1), as calculated separately for mouth closing and opening movements and eye movement, showed no significant different amplitude and locations. We did not find any activity in the superior temporal sulcus (STS). CONCLUSIONS: Our results indicate that human MT/V5 is active in the perception of both mouth and eye motions. Viewing mouth and eye movements elicits no significant differences in MT/V5 activity, indicating that the perception of movement of facial parts is probably processed in the same manner. SIGNIFICANCE: Characteristic activities in the human MT/V5 elicited by viewing mouth movement were clarified by MEG.

Adult↗