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Biomedical subjects

Ryusuke Kakigi

Publications and source records attributed to Ryusuke Kakigi.

90 records · Page 5Linked to original sources
PubMed2003

Gating of somatosensory evoked magnetic fields during the preparatory period of self-initiated finger movement.

The temporal change in somatosensory evoked magnetic fields (SEFs) in the preparatory period of self-initiated voluntary movement was investigated. The SEF following stimulation of the right median nerve was recorded, using a 204-channel whole-head MEG system, in nine healthy subjects during a self-initiated extension of the right index finger every 5 to 7 s. The preparatory period before finger movement was divided into six subperiods, and the MEG signals following the stimulation in each subperiod were averaged separately. SEFs were also recorded in the resting state. The ECD strengths for N20m and P60m were not significantly changed in any subperiod before movement compared with those in the resting state. The ECD strength for P30m was significantly smaller 500 ms or less before movement than during the resting state and 1,500 ms or less before movement compared to that during the period from 3,000 to 4,000 ms before movement. Thus, we confirmed that the SEF components were attenuated even during a period of self-initiated voluntary movement. The modulation started at least 1,500 ms before movement and was greater for the P30m than the N20m component. These findings suggested that motor-associated cortices attenuated SEF components by a centrifugal gating process.

Adult↗
PubMed2003

Changes in somatosensory evoked responses by repetition of the median nerve stimulation.

OBJECTIVE: We investigate the synaptic factor for the recovery function of evoked responses using a repetitive stimulation technique. METHODS: Somatosensory evoked cortical magnetic field (SEF) was recorded following stimulation of the median nerve using single to 6-train stimulation in 8 healthy subjects. The SEF responses after each stimulus in the train stimulation were extracted by subtraction of the waveforms. RESULTS: An attenuation of the SEF components was recognized after the second of the stimuli, but there was no significant attenuation with the third or later stimulations. The root mean square (RMS) of the 1M (peak latency at 20 ms after stimulation) and 4M (70 ms) components were smaller than that of the single stimulation during the train stimulation, while the 2M (30 ms) and 3M (45 ms) components were not attenuated, but the 3M was facilitated at the fourth to sixth stimulation. CONCLUSION: The synaptic factor was not responsible for the attenuation of the SEF components during repetitive stimulation in healthy subjects. The SEF change disclosed a functional difference among the SEF components during the train stimulation, especially among the later components.

Adult↗
PubMed2003

Sensory perception during sleep in humans: a magnetoencephalograhic study.

We reported the changes of brain responses during sleep following auditory, visual, somatosensory and painful somatosensory stimulation by using magnetoencephalography (MEG). Surprisingly, very large changes were found under all conditions, although the changes in each were not the same. However, there are some common findings. Short-latency components, reflecting the primary cortical activities generated in the primary sensory cortex for each stimulus kind, show no significant change, or are slightly prolonged in latency and decreased in amplitude. These findings indicate that the neuronal activities in the primary sensory cortex are not affected or are only slightly inhibited during sleep. By contrast, middle- and long-latency components, probably reflecting secondary activities, are much affected during sleep. Since the dipole location is changed (auditory stimulation), unchanged (somatosensory stimulation) or vague (visual stimulation) between the state of being awake and asleep, different regions responsible for such changes of activity may be one explanation, although the activated regions are very close to each other. The enhancement of activities probably indicates two possibilities, an increase in the activity of excitatory systems during sleep, or a decrease in the activity of some inhibitory systems, which are active in the awake state. We have no evidence to support either, but we prefer the latter, since it is difficult to consider why neuronal activities would be increased during sleep.

Adult↗
PubMed2003

Mechanisms of differences in gating effects on short-and long-latency somatosensory evoked potentials relating to movement.

We investigated the mechanisms underlying the differences in gating effects on short- and long-latency somatosensory evoked potentials (SEPs) relating to movement. SEPs were recorded in normal subjects for 6 different tasks in Experiment 1: Control, Movement, Distraction, Attention, Movement during Distraction and Movement during Attention, and for 4 different tasks in Experiment 2: Control, Passive Movement, Contralateral Movement and Movement Imagery. The amplitudes of short-latency SEPs were significantly reduced by active and passive movement of the stimulated hand, but long-latency SEPs (N140-P200) were significantly enhanced by active movement of the stimulated hand. Attention, Distraction, Contralateral Movement and Movement Imagery did not affect the amplitudes of SEPs. The degree of enhancement of long-latency SEPs by active Movement was greater than that by active movement with Attention or Distraction. Gating effects on long-latency SEPs were different from those on short-latency SEPs. Since this effect was not related to Attention/Distraction, Passive Movement, Movement Imagery or Movement of another site, it is probably due to specific centrifugal effects, which are different from more direct gating effects on short-latency components. This study showed the difference in gating effects on somatosensory perception depending on time periods following stimulation, which may indicate an interaction between motor and somatosensory cortex.

Adult↗
PubMed2003

Tonotopic representation of missing fundamental complex sounds in the human auditory cortex.

The N1m component of the auditory evoked magnetic field in response to tones and complex sounds was examined in order to clarify whether the tonotopic representation in the human secondary auditory cortex is based on perceived pitch or the physical frequency spectrum of the sound. The investigated stimulus parameters were the fundamental frequencies (F0 = 250, 500 and 1000 Hz), the spectral composition of the higher harmonics of the missing fundamental sounds (2nd to 5th, 6th to 9th and 10th to 13th harmonic) and the frequencies of pure tones corresponding to F0 and to the lowest component of each complex sound. Tonotopic gradients showed that high frequencies were more medially located than low frequencies for the pure tones and for the centre frequency of the complex tones. Furthermore, in the superior-inferior direction, the tonotopic gradients were different between pure tones and complex sounds. The results were interpreted as reflecting different processing in the auditory cortex for pure tones and complex sounds. This hypothesis was supported by the result of evoked responses to complex sounds having longer latencies. A more pronounced tonotopic representation in the right hemisphere gave evidence for right hemispheric dominance in spectral processing.

Acoustic Stimulation↗
PubMed2003

Pain processing within the primary somatosensory cortex in humans.

To investigate the processing of noxious stimuli within the primary somatosensory cortex (SI), we recorded magnetoencephalography following noxious epidermal electrical stimulation (ES) and innocuous transcutaneous electrical stimulation (TS) applied to the dorsum of the left hand. TS activated two sources sequentially within SI: one in the posterior bank of the central sulcus and another in the crown of the postcentral gyrus, corresponding to Brodmann's areas 3b and 1, respectively. Activities from area 3b consisted of 20- and 30-ms responses. Activities from area 1 consisted of three components peaking at 26, 36 and 49 ms. ES activated one source within SI whose location and orientation were similar to those of the TS-activated area 1 source. Activities from this source consisted of three components peaking at 88, 98 and 109 ms, later by 60 ms than the corresponding TS responses. ES and TS subsequently activated a similar region in the upper bank of the sylvian fissure, corresponding to the secondary somatosensory cortex (SII). The onset latency of the SII activity following ES (109 ms) was later by 29 ms than that of the first SI response (80 ms). Likewise, the onset latency of SII activity following TS (52 ms) was later by 35 ms than that of area 1 of SI (17 ms). Therefore, our results showed that the processing of noxious and innocuous stimuli is similar with respect to the source locations and activation timings within SI and SII except that there were no detectable activations within area 3b following noxious stimulation.

Adult↗
PubMed2002

Structure of visual evoked magnetic field during sleep in humans.

To investigate the effects of sleep on the visual evoked magnetic fields (VEF), we recorded VEF following flash light stimulation in healthy adults during sleep. The awake VEF contained several components with approximate latencies of 40, 55, 65, 80, 100, 110, 150, and 180 ms. In contrast, the sleep VEF contained mainly three components with approximate latencies of 65, 100 and 115 ms. By comparing the magnetic components between the awake and sleep conditions based on similarities in the contour pattern of the isomagnetic field, three components for the sleep condition were found to be enhanced, those at 55, 80-100 and 100-110 ms in the awake VEF. Other components of the awake VEF may be reduced or disappear during sleep. This large change in the VEF during sleep suggests that some qualitative changes occur in the cortical visual processing, for example, a reduction in the inhibitory activities at works while awake.

Adult↗
PubMed2002

Gaze direction affects face perception in humans.

We recorded event-related potentials (ERP) in response to images of faces with a straight gaze (straight eyes) and eyes averted (averted eyes). Peak latencies of ERP components showed no significant change between straight eyes and averted eyes, but amplitude for averted eyes, particularly when averted to the right, was significantly larger than that for straight eyes at the lateral temporal electrode of the right hemisphere. Single-unit recordings in monkeys and neuroimaging studies in humans have revealed activity in the lateral temporal region, mainly the superior temporal sulcus, and a clinical study demonstrated the importance of the right hemisphere when viewing gaze direction. This is the first systematic neurophysiological report to confirm these findings using ERP.

Adult↗
PubMed2002

Visual detection of motion speed in humans: spatiotemporal analysis by fMRI and MEG.

Humans take a long time to respond to the slow visual motion of an object. It is not known what neural mechanism causes this delay. We measured magnetoencephalographic neural responses to light spot motion onset within a wide speed range (0.4-500 degrees /sec) and compared these with human reaction times (RTs). The mean response latency was inversely related to the speed of motion up to 100 degrees /sec, whereas the amplitude increased with the speed. The response property at the speed of 500 degrees /sec was different from that at the other speeds. The speed-related latency change was observed when the motion duration was 10 msec or longer in the speed range between 5 and 500 degrees /sec, indicating that the response is directly related to the speed itself. The source of the response was estimated to be around the human MT+ and was validated by functional magnetic imaging study using the same stimuli. The results indicate that the speed of motion is encoded in the neural activity of MT+ and that it can be detected within 10 msec of motion observation. RT to the same motion onset was also inversely related to the speed of motion but the delay could not be explained by the magnetic response latency change. Instead, the reciprocal of RT was linearly related to the reciprocal of the magnetic response latency, suggesting that the visual process interacts with other neural processes for decision and motor preparation.

Adult↗
PubMed2002

Human cortical responses to coherent and incoherent motion as measured by magnetoencephalography.

To investigate the detail response properties for the incoherent motion of the human visual system, we measured the magnetoencephalographic neural responses to both coherent and incoherent motions at various speeds (from 0.65 to 20.6 degrees /s). The peak latency of the first component of the response from the extrastriate area was inversely related to the speed of motion (from 228 to 155 ms in mean) and there was no significant difference in the latency change between the two types of motion. There were significant differences in the peak amplitude change with the motion speed and a difference in the distribution of the magnetic fields of the responses was seen in six of the seven subjects. The results show that the speed of the incoherently moving dots is represented in the human visual system in the same manner as that of coherently moving dots. The differences in the magnetic fields between the two responses indicate that the same speed-related response changes can occur with different neural populations responsible for both motions.

Adult↗
PubMed2002

Conduction velocity of the spinothalamic tract following CO2 laser stimulation of C-fibers in humans.

Pain-related somatosensory-evoked potential following CO(2) laser stimulation (laser-evoked potential (LEP)) is now used not only for research objectives, but also for clinical applications. Estimating the conduction velocity (CV) of the spinothalamic tract (STT) by analyzing LEP following activation of Adelta-fibers (Adelta-CVSTT) by CO(2) laser stimulation has been performed previously, but estimating the CV of STT following activation of C-fibers (C-CVSTT) has not. This is the first report to estimate the C-CVSTT in humans; by using the novel method of CO(2) laser stimulation applied to tiny skin areas. The calculation method was based on that of Kakigi and Shibasaki (Electroenceph clin Neurophysiol 80 (1991) 39) who measured Adelta-CVSTT by conventional CO(2) laser stimulation. The C-CVSTT ranged between 1.4 and 4.0 m/s, and its mean+/-SD was 2.9+/-0.8 m/s. This C-CVSTT was significantly slower than the Adelta-CVSTT, which ranged approximately from 10 to 21 m/s. The nociceptive signal of the C-fibers in STT is probably conveyed by unmyelinated axons of projection neurons to reach the thalamus. Our findings provide the first physiological evidence of the signals ascending through unmyelinated axons in the spinal cord in humans. In addition, estimating C-CVSTT and Adelta-CVSTT combined with conventional methods to measure the CV of the posterior column using electrical stimulation should be useful and have important clinical applications, particularly in patients with spinal cord lesions showing various kinds of sensory disturbances.

Adult↗
PubMed2002

Preferential stimulation of Adelta fibers by intra-epidermal needle electrode in humans.

We recorded evoked potentials (EPs) induced by conventional transcutaneous electrical stimulation (TS), laser stimulation (LS) and epidermal electrical stimulation (ES) using a specially made needle electrode. We evaluated the activated fibers by epidermal stimulation by assessing the conduction velocity (CV) of the peripheral nerves. The EPs were recorded from Cz electrode (vertex) of the International 10-20 system in 12 healthy subjects. For the ES, the tip of a stainless steel needle electrode was inserted in the epidermis of the skin (0.2 mm in depth). Distal and proximal sites of the upper limb were stimulated by the LS and ES with an intensity which induced a definite pain sensation. Similar sites were stimulated by TS with an intensity of two times the sensory threshold. A major EP positive response (P1) was obtained by stimulation by all three types of stimuli. The P1 latency for the TS (245+/-22 ms) was significantly shorter than that for the ES (302+/-17 ms, P<0.0001) and LS (341+/-21 ms, P<0.0001) and the peak latency P1 by the LS was also significantly longer, approximately 40 ms, than that by the ES (P<0.0001). The CVs were 15.1, 15.3 and 44.1 m/s obtained by ES, LS and TS, respectively. The CV indicated that the fibers activated by the ES were mainly A fibers, which corresponded to the fibers stimulated by the LS. We considered that the ES with our newly developed needle electrode was a very convenient method for the selective stimulation of the A fibers, since it was very simple, not requiring any special apparatus, did not cause bleeding or burns and caused minimum uncomfortable feeling.

Adult↗
PubMed2002

Pain-related magnetic fields evoked by intra-epidermal electrical stimulation in humans.

OBJECTIVES: We recently developed a new method for the preferential stimulation of Adelta fibers in humans. The aim of the present study was to examine whether this method can serve as an appropriate stimulus in a magnetoencephalographic study. METHODS: We recorded somatosensory-evoked magnetic fields (SEFs) following intra-epidermal electrical stimulation applied to the hand and elbow. Superficial parts of the skin were electrically stimulated through a needle electrode whose tip was inserted in the epidermis. RESULTS: In all 13 subjects, the equivalent current dipole was estimated in the secondary somatosensory cortices (SII). In 5 out of 13 subjects, simultaneous activation of the primary somatosensory cortex (SI) in the hemisphere contralateral to the stimulation was identified. The mean peak latencies of magnetic fields corresponding to contralateral SI, SII and ipsilateral SII activation following hand stimulation were 162, 158 and 171 ms, respectively. The respective latency following elbow stimulation was 137, 139 and 157 ms, respectively. Estimated peripheral conduction velocity was 15.6m/s. CONCLUSIONS: All the results were consistent with previous findings in pain SEF studies. We concluded that our novel intra-epidermal electrical stimulation is useful for pain SEF studies since it does not need special equipment and is easy to control.

Adult↗
PubMed2002

New concept for the recovery function of short-latency somatosensory evoked cortical potentials following median nerve stimulation.

OBJECTIVES: We investigated the recovery function of the cortical components of somatosensory evoked potentials (SEP) at a very short interstimulus interval (ISI, less than 10 ms) using an integrative computer system in 10 healthy subjects (age, 27-38 years). METHODS: The SEP and nerve action potentials were recorded at P3 with a reference of Fz in the International 10-20 System and the ipsilateral Erb's point, respectively. Double stimulation of the right median nerve with an ISI from 0.5 to 100 ms was performed to analyze the N20 and P30 components at less than 10 ms. RESULTS: The P30 component was recognized following the second stimulation at an ISI of over 1 ms, while N20 was not identified at an ISI of less than 9 ms. There appeared a sub-component of SEP at 1-12 ms ISI, which was not identified following a single stimulation under control conditions. CONCLUSIONS: The results indicated that the recovery function of given SEP components was not simply determined by the number of synapses interposed between the stimulus site and the generator source of the response in the central nervous system, but there might be a structural or functional process of low-cut filtering in the primary sensory cortex. We also considered that the final SEP waveform determined by the excitatory and inhibitory balance of the components, which could be changed with ISI, and that the existence of the sub-component might cause the complexity of the recovery curve and large inter-individual difference of the waveform.

Action Potentials↗
PubMed2002

Effects of attention, distraction and sleep on CO(2) laser evoked potentials related to C-fibers in humans.

OBJECTIVES: The objective of this study is to evaluate the effects of attention, distraction and sleep on CO(2) laser-evoked potentials (LEP) relating to C-fibers (ultra-late LEP). METHODS: Non-painful CO(2) laser pulses were delivered to a tiny skin area of the dorsum of the right hand. Ultra-late LEP were recorded from 10 normal subjects in 5 different conditions: control (wakefulness), attention, distraction, drowsiness and sleep (stage 2). RESULTS: The amplitude of ultra-late LEP was slightly increased during attention and significantly decreased during distraction, relative to the control. The ultra-late LEP decreased much in amplitude or almost disappeared during sleep. However, significant differences in latency among the conditions were not found. CONCLUSIONS: We confirmed that the brain responses relating to signals ascending through C-fibers were much affected by the level of consciousness, being consistent with the findings of late LEP relating to Adelta-fibers. This is the first study to indicate the important characteristics of ultra-late LEP relating to consciousness, suggesting that they include cognitive function and also that one has to be careful of the change in alertness when recording.

Adult↗
PubMed2002

Visual information process in Williams syndrome: intact motion detection accompanied by typical visuospatial dysfunctions.

It has been suggested that visuospatial cognitive disabilities seen in children with Williams syndrome (WMS) are related to a dysfunction of the dorsal stream in the visual information analysis system. We investigated whether visual motion detection is also impaired in WMS because it is one of the main functions of the dorsal stream. Using various psychophysical examinations and magnetoencephalography, we studied a child with WMS who had the typical features of the syndrome. We found profound impairments in the visuospatial cognitions, as previously reported in WMS. In contrast, he had normal ability for the direction discrimination of coherent motion on a background of randomly moving dots, and he perceived apparent motion as do normal children. Furthermore, the latencies of both responses to the coherent and incoherent motions as measured by magnetoencephalography were within the mean +/- 2 SD among normal adults and the estimated origins were near the human homologue of V5/MT (visual area 5/middle temporal area). The results indicate that the visuospatial cognitive deficits in WMS can occur without impairment of the visual motion detection. We consider that the deficits are caused by a restricted dysfunction of the neural groups for position and three-dimensional form perceptions in the dorsal stream of the visual system, though other possibilities are not excluded.

Brain Mapping↗
PubMedDate not supplied

Musical training enhances automatic encoding of melodic contour and interval structure.

In music, melodic information is thought to be encoded in two forms, a contour code (up/down pattern of pitch changes) and an interval code (pitch distances between successive notes). A recent study recording the mismatch negativity (MMN) evoked by pitch contour and interval deviations in simple melodies demonstrated that people with no formal music education process both contour and interval information in the auditory cortex automatically. However, it is still unclear whether musical experience enhances both strategies of melodic encoding. We designed stimuli to examine contour and interval information separately. In the contour condition there were eight different standard melodies (presented on 80% of trials), each consisting of five notes all ascending in pitch, and the corresponding deviant melodies (20%) were altered to descending on their final note. The interval condition used one five-note standard melody transposed to eight keys from trial to trial, and on deviant trials the last note was raised by one whole tone without changing the pitch contour. There was also a control condition, in which a standard tone (990.7 Hz) and a deviant tone (1111.0 Hz) were presented. The magnetic counterpart of the MMN (MMNm) from musicians and nonmusicians was obtained as the difference between the dipole moment in response to the standard and deviant trials recorded by magnetoencephalography. Significantly larger MMNm was present in musicians in both contour and interval conditions than in nonmusicians, whereas MMNm in the control condition was similar for both groups. The interval MMNm was larger than the contour MMNm in musicians. No hemispheric difference was found in either group. The results suggest that musical training enhances the ability to automatically register abstract changes in the relative pitch structure of melodies.

Acoustic Stimulation↗