Biomedical subjects

R Kakigi

Publications and source records attributed to R Kakigi.

At least 55 records · Page 3Linked to original sources

PubMed2000

Magnetic response of human extrastriate cortex in the detection of coherent and incoherent motion.

Although direction selectivity is a cardinal property of neurons in the visual motion detection system, movement of numerous elements without global direction (incoherent motion) has been shown to activate human and monkey visual systems, as does coherent motion which has global direction. We used magnetoencephalography to investigate the neural process underlying responses to these types of motions in the human extrastriate cortex. Both motions were created using a random dot kinematogram and four speeds (0, 0.6, 9.6 and 25 degrees /s). The visual stimuli were composed of two successive motions at different speeds; a coherent motion at a certain speed that changed to incoherent motion at another speed or vice versa. Magnetic responses to the change in motion consisted of a few components, the first of which was always largest. The peak latency of the first component was inversely related to the speed of the preceding motion, but for both motions it was not affected by the speed of the subsequent motion. For each subject, the estimated origin of the first component was always in the extrastriate cortex, and this changed with the speed of the preceding motion. For both motions, the location for the slower preceding motion was lateral to that for the faster preceding motion. Although the latency changes of the two motions differed, their overall response properties were markedly similar. These findings show that the speed of incoherent motion is represented in the human extrastriate cortex neurons to the same degree as coherent motion. We consider that the human visual system has a distinct neural mechanism to perceive random dots' motion even though they do not move in a specific direction as a whole.

Adult↗

PubMed2000

Cortical activity related to cue-invariant shape perception in humans.

We used magnetoencephalography to search spatio-temporally for cortical activity related to the perception of shape defined by various visual cues in humans. The visual stimuli were three kinds of two-dimensional figures: two had fixed shapes (Diamond and Cross), the other did not (Noise). These figures were defined by three visual cues: difference of flicker, texture or luminance between the foreground and the background in the random dot pattern. Using this stimulus, we recorded the magnetic responses from the temporo-occipital regions of nine healthy subjects. Additionally, we measured the reaction time for the subjects to detect the figure by button-pressing. A magnetic component was identified in the responses. The properties of the first magnetic component differed for stimulus condition. The peak latency of the first magnetic component was different for the cues (270 ms for flicker, 360 ms for texture and 250 ms for luminance), but not for the figures. In contrast, the peak amplitude of the first magnetic component was different for the figures (96-144 fT for Diamond or Cross and 52-80 fT for Noise), but not for the cues. The signal source of the first magnetic component was estimated to lie on the ventral side of the extrastriate cortex: In the posterior part of the inferior temporal cortex, probably in the fusiform gyrus in four subjects, and in the lateral part of the occipital cortex which was outside of the primary visual cortex (visual area 1) in one subject. The signal source location was different inter-individually, but almost the same within each subject. Reaction time was 471 ms for flicker, 569 ms for texture and 426 ms for luminance, but the interval between the reaction time and the peak latency was constant (about 200 ms) for each cue. The first magnetic component was more clearly recorded from the right hemisphere than from the left.We found that the shape defined by the different visual cues activates the same localized site in the lateral extrastriate cortex. This spatial convergence suggests that there is a restricted locus that processes the visual shape regardless of the difference of the visual cue. The correspondence between the peak latency and the reaction time suggests that the activity of the area is responsible for the perception of visual shape. The inter-hemispheric difference suggests a dominance of the right hemisphere in visual shape processing.

Adult↗

PubMed2000

Hemispheric lateralization in an analysis of speech sounds. Left hemisphere dominance replicated in Japanese subjects.

Evoked magnetic responses to speech sounds [R. Näätänen, A. Lehtokoski, M. Lennes, M. Cheour, M. Huotilainen, A. Iivonen, M. Vainio, P. Alku, R.J. Ilmoniemi, A. Luuk, J. Allik, J. Sinkkonen and K. Alho, Language-specific phoneme representations revealed by electric and magnetic brain responses. Nature, 385 (1997) 432-434.] were recorded from 13 Japanese subjects (right-handed). Infrequently presented vowels ([o]) among repetitive vowels ([e]) elicited the magnetic counterpart of mismatch negativity, MMNm (Bilateral, nine subjects; Left hemisphere alone, three subjects; Right hemisphere alone, one subject). The estimated source of the MMNm was stronger in the left than in the right auditory cortex. The sources were located posteriorly in the left than in the right auditory cortex. These findings are consistent with the results obtained in Finnish [R. Näätänen, A. Lehtokoski, M. Lennes, M. Cheour, M. Huotilainen, A. Iivonen, M.Vainio, P.Alku, R.J. Ilmoniemi, A. Luuk, J. Allik, J. Sinkkonen and K. Alho, Language-specific phoneme representations revealed by electric and magnetic brain responses. Nature, 385 (1997) 432-434.][T. Rinne, K. Alho, P. Alku, M. Holi, J. Sinkkonen, J. Virtanen, O. Bertrand and R. Näätänen, Analysis of speech sounds is left-hemisphere predominant at 100-150 ms after sound onset. Neuroreport, 10 (1999) 1113-1117.] and English [K. Alho, J.F. Connolly, M. Cheour, A. Lehtokoski, M. Huotilainen, J. Virtanen, R. Aulanko and R.J. Ilmoniemi, Hemispheric lateralization in preattentive processing of speech sounds. Neurosci. Lett., 258 (1998) 9-12.] subjects. Instead of the P1m observed in Finnish [M. Tervaniemi, A. Kujala, K. Alho, J. Virtanen, R.J. Ilmoniemi and R. Näätänen, Functional specialization of the human auditory cortex in processing phonetic and musical sounds: A magnetoencephalographic (MEG) study. Neuroimage, 9 (1999) 330-336.] and English [K. Alho, J. F. Connolly, M. Cheour, A. Lehtokoski, M. Huotilainen, J. Virtanen, R. Aulanko and R.J. Ilmoniemi, Hemispheric lateralization in preattentive processing of speech sounds. Neurosci. Lett., 258 (1998) 9-12.] subjects, prior to the MMNm, M60, was elicited by both rare and frequent sounds. Both MMNm and M60 sources were posteriorly located in the left than the right hemisphere.

Adult↗

PubMed2000

Spatiotemporal source analysis of vocalization-associated magnetic fields.

The vocalization-related cortical fields (VRCF) following vowel vocalization were studied by magnetoencephalography (MEG) in eight normal subjects. A multiple-source model, BESA (Brain Electric Source Analysis), was applied to elucidate the generating mechanism of VRCF in the period from 150 ms before to 150 ms after the onset of vocalization. Six sources provided satisfactory solutions for VRCF activities during that period. Sources 1 and 2, which were activated from approximately 150 ms before the vocalization onset, were located in laryngeal motor areas of the left and right hemispheres, respectively. Sources 5 and 6 were located in the truncal motor area in each hemisphere, and they were very similar to sources 1 and 2 in terms of temporal change of activities. Sources 3 and 4 were located in the auditory cortices of the left and right hemispheres, respectively, and they appeared to be activated just after the vocalization onset. However, all six sources were temporally overlapped in the period approximately 0-100 ms after the vocalization onset. The present results suggested that the bilateral motor cortices, probably laryngeal and truncal areas, were activated just before the vocalization. We considered that the activities of the bilateral auditory areas after the vocalization were the response of the subject's central auditory system to his/her own voice. The motor and auditory activities were temporally overlapped, and BESA was very useful to separate the activities of each source.

Adult↗

PubMed2000

Effects of distraction on pain-related somatosensory evoked magnetic fields and potentials following painful electrical stimulation.

We aimed to compare the effects of distraction on pain-related somatosensory evoked magnetic fields (pain SEF) following painful electrical stimulation with simultaneous recordings of evoked potentials (pain SEP). Painful electrical stimuli were applied to the right index finger of eleven healthy subjects. A table with 25 random two-digit numbers was shown to the subjects, who were asked to add 5 numbers of each line in their mind (calculation task) or to memorize the numbers (memorization task) during the recording. In the SEF recording, 3 short-latency components within 50 ms of the stimulation were generated in the primary sensory cortex (SI) of the hemisphere contralateral to the stimulated finger. Middle-latency components between 100 and 250 ms after the stimuli were recorded from the secondary somatosensory cortex (SII) in the bilateral hemispheres or the cingulate cortex. No SEF components were significantly affected by either task. In the SEP recording, the middle-latency components (N140 and P230) were identified as being maximal around the vertex. Amplitudes of the N140 and P230 were not affected by each task, but the peak-to-peak amplitude (N140-P230) was significantly decreased by both the calculation and memorization tasks, particularly by the former. Subjective pain rating was decreased in both the calculation and memorization tasks, particularly in the former. We concluded that distraction tasks reduced activities in the limbic system, in which the middle-latency EEG component probably generated, while neither the short-latency SEF components generated in SI nor the primary pain-related SEF components generated in SII-insula are affected.

Adult↗

PubMed2000

Vibratory stimulation of proximal muscles does not affect cortical components of somatosensory evoked potential following distal nerve stimulation.

OBJECTIVES: The effects of the proprioceptive activity of the proximal muscles on somatosensory evoked potentials (SEPs) were investigated, using vibratory stimulation of proximal muscle tendons. METHODS: SEPs were recorded following electrical median nerve stimulation at the wrist during vibratory stimulation of tendon of pronator teres, biceps and trapezius muscles and fingers in 8 normal subjects. RESULTS: The cortical SEP components, N20, P25 and N33 recorded from the parietal area, and P20 and N30 recorded from frontal area contralateral to the stimulated side, were markedly attenuated by vibratory stimulation applied to the fingers, but unaffected by vibratory stimulation of the proximal muscles. CONCLUSION: The proprioceptive afferent, especially group Ia muscle spindle afferent, in the relaxed proximal muscles is not likely to contribute to the gating of SEP following distal nerve stimulation.

Brain↗

PubMed2000

Identification of auditory evoked potentials of one's own voice.

OBJECTIVE: We recorded vocalization related cortical potentials (VRCP) with complete masking of one's own voice, and separated the feedback auditory potentials following vocalization from the VRCP complex. METHODS: We used 9 right-handed healthy subjects. We recorded VRCP during simple vowel vocalizing under two conditions, (1) without masking (control); (2) with masking. Electroencephalography (EEG) was recorded from seven areas, Fz, Cz, Pz, C3, C4, T3 and T4, of the International 10-20 system. The trigger point was the onset of vocalized sound recorded through a microphone. RESULTS: In both control and masking conditions, similar negative potentials prior to the vocalization were observed. However, the amplitude just after the onset of vocalization was significantly smaller in the masking than the control condition. The difference waveform, obtained by subtracting the waveforms in the masking from those in the control condition, showed a simple negative peak after the vocalization onset. CONCLUSIONS: We considered that the difference waveform indicated the auditory evoked potentials following own voice in the auditory feedback process. Since there was no difference of the negative potentials before vocalization between the two conditions, we speculated that the masking effect on auditory feedback following vocalization was crucial, while its effect on the preparatory process of simple vocalization might be minimal.

Acoustic Stimulation↗

PubMed2000

Dermatome versus homunculus; detailed topography of the primary somatosensory cortex following trunk stimulation.

OBJECTIVE: Identification of a detailed topography of the receptive area for each of the thoracic dermatomes in humans using somatosensory evoked magnetic fields (SEF). METHODS: We analyzed the location of the equivalent current dipole (ECD) of SEF following electrical stimulation of the skin at Th4, Th6, Th8, Th10 and Th12 dermatomes in 14 normal subjects. RESULTS: Three deflections, M18, M25 and M40, were obtained within 60 ms of stimulation of Th6, Th8 and Th10 dermatomes. No consistent deflection could be identified following Th4 and Th12 dermatomal stimulation, probably due to a poor signal-to-noise ratio and difficulty in fixing the stimulation electrodes. M18 was absent or small in amplitude. The latency of M25 ranged from short to long in the order Th6, Th8 and Th10 (P<0.05). ECDs of all components for each site stimulation were located in the truncal area of the primary somatosensory cortex. Although the locations of the ECDs tend to be arranged from lateral to medial in the sequence Th6, Th8 and Th10, the difference was not significant. CONCLUSION: The representation area of the trunk is small, and the receptive areas for the stimulation of Th6, Th8 and Th10 dermatomes are considered to be very close or to overlap.

Adult↗

PubMed2000

After-effect of transcutaneous electrical nerve stimulation (TENS) on pain-related evoked potentials and magnetic fields in normal subjects.

OBJECTIVES: The after-effect of transcutaneous electrical nerve stimulation (TENS) on pain-related brain responses was investigated using electroencephalography (EEG) and magnetoencephalography (MEG). METHODS: We studied 13 healthy volunteers for the main experiment and 7 for the control experiment. The pain-related evoked cerebral potentials (PREP) at Cz and magnetic cortical fields (PRCF) on both hemispheres following painful electrical finger stimulation were simultaneously recorded before and after TENS on the right forearm of the median nerve territory at 50 Hz for 30 min. PREP and PRCF were similarly recorded without TENS in the control experiment. RESULTS: The PREP components, N150 and P220, were significantly attenuated after TENS, compared to those before TENS (P<0.01, two-way repeated ANOVA). However, there was no consistent change of the PRCF components. Eleven of 13 subjects reported no change of pain sensation after TENS. There was no change of PREP in control experiment without TENS. CONCLUSIONS: The results indicated that TENS reduced PREP following painful electrical stimulation, and that the origin of PREP was, at least partially, different from that of PRCF which was not changed after TENS. An after-effect of TENS significantly affected the generation process of PREP, but it was not enough to relieve the subjective painful feeling.

Adult↗

PubMed2000

Pain-Related somatosensory evoked potentials.

The authors reviewed basic and clinical reports of pain-related somatosensory evoked potentials (SSEP) after high-intensity electrical stimulation [pain SSEP(E)] and painful laser stimulation [pain SSEP(L)]. The conduction velocity of peripheral nerves for both pain SSEP(E) and pain SSEP(L) is approximately 10 to 15 m/second, in a range of Adelta fibers. The generator sources are considered to be the secondary somatosensory cortex and insula, and the limbic system, including the cingulate cortex, amygdala, or hippocampus of the bilateral hemispheres. The latencies and amplitudes are clearly affected by vigilance, attention-distraction, and various kinds of stimulation applied simultaneously with pain. Abnormalities of pain SSEP(L) reflect an impairment of pain-temperature sensation, probably relating to dysfunction of A5 fibers of the peripheral nerve and spinothalamic tract. In contrast, conventional SSEP after nonpainful electrical stimulation reflects an impairment of tactile, vibratory, and deep sensation, probably relating to dysfunction of Aalpha or Abeta fibers of the peripheral nerve and dorsal column. Therefore, combining the study of pain SSEP(L) and conventional SSEP is useful to detect physiologic abnormalities, and sometimes subclinical abnormalities, of patients with peripheral and central nervous system lesions.

Afferent Pathways↗

PubMed2000

Human visual motion areas determined individually by magnetoencephalography and 3D magnetic resonance imaging.

We used magnetoencephalography to study inter-individual locational difference in the extrastriate region which responds to visual motion. Magnetic responses to visual motion onset from the right temporo-occipital area were recorded from 12 subjects. All the subjects had clear responses to apparent or random dot coherent motion. The origins of these responses was investigated by use of the single equivalent current dipole model. The nearest scalp to the origin also was identified for each subject, which may be useful in transcranial stimulation studies. Although the magnetic responses of all the subjects should have the same functional properties; be related to neural activities synchronized exclusively to the onset of motion, the estimated origins varied greatly among the subjects. The location of origin could be classified as one of three types: temporo-occipital, occipital, or parietal, according to the sulcal anatomy investigated in the individual's three-dimensional magnetic resonance image. Temporo-occipital types were found for seven subjects, and anatomically the regions were around human MT/V5. Two subjects had the occipital type, with regions posterior to the anatomical MT/V5 and corresponding to V3A anatomically. The other three subjects had origins classified as the parietal type dorso-rostral to the anatomical MT/V5, with regions around the posterior end of the superior temporal sulcus. Although all these cortical regions appear to be related to the neural process of visual motion, whether they correspond functionally to the same names or migrated MT/V5 must now be determined.

Adult↗

PubMed1999

Individual differences in working memory and the peak alpha frequency shift on magnetoencephalography.

The effect of the working memory demands on the peak alpha frequency of the power spectrum of magnetoencephalography (MEG) was investigated. There were one control condition and four listening span test (LST) conditions demanding the use of working memory. The results showed that the peak alpha frequency of the averaged MEG power shifted to the higher frequency region in the LST condition dominantly in the fronto-temporal region. Individual differences in working memory capacities were observed in the shift of peak alpha frequency of MEG.

Adult↗

PubMed1999

Peripheral nerve conduction recorded by a micro gradiometer system (micro-SQUID) in humans.

We developed a new multi (twelve) -channel gradiometer system with the smallest and highest quality superconducting quantum interference device (micro-SQUID). A very small distance (3.80 mm) between the sensor coils and the skin provides quite high spatial resolution. The actual whole image of the sensory nerve action fields (NAF) of the human median nerve at the wrist were successfully recorded following digital nerve stimulation by using the micro-SQUID. The NAF showed the biphasic waveform at each of the 12 channels, and the isomagnetic field map clearly showed the moving quadrupole pattern. The quadrupole comprised a dipole for depolarization followed by another dipole with the opposite direction for repolarization. The polarized length of the nerve obtained by reconstructing the magnetic field maps was approximately 17 cm, and the magnetic field complex moved along the nerve from the distal to the proximal part of the wrist at 58.7 m/s.

Adult↗

PubMed1999

Magnetoencephalographic responses to painful impact stimulation.

Magnetoencephalographic (MEG) field recordings are unique to detect current dipoles in SI and SII. Few devices are available for painful mechanical stimulation in magnetically shielded MEG rooms. The aim of the present MEG (dual 37-channel biomagnetometer) study was to investigate the location of the cortical generators evoked by painful impact stimuli of different intensities. An airgun was placed outside the shielded MEG room, and small plastic bullets were fired at the arm and trunk of the subjects in the room. The velocity of the bullet was measured and related to the evoked pain intensity. Stimuli were delivered for each of the following three conditions: strong pain intensity elicited from the upper arm and upper trunk; weak pain intensity elicited from the upper trunk. The evoked MEG responses had a major component with the characteristically polarity-reversal deflections indicating a dipole located beneath the coils. The response could be estimated by a single current dipole. When the estimated locations of the dipoles were superimposed on the individual magnetic resonance images (MRIs), consistent bilateral activation of areas corresponding to the secondary sensory cortices (SII) was found.

Adult↗

PubMed1999

Human face perception traced by magneto- and electro-encephalography.

The temporal and spatial processing of face perception in normal subjects was traced by magnetoencephalography (MEG) and electroencephalography (EEG). We used 5 different visual stimuli: (1) face with opened eyes, (2) face with closed eyes, (3) eyes, (4) scrambled face, and (5) hand, and they were shown in random order. Subjects were asked to count the number of hand stimuli. To analyze the complicated brain responses to visual stimuli, we used brain electric source analysis (BESA) as the spatio-temporal multiple source model. In MEG recording, the 1M and 2M components were identified in all subjects. The 1M component was recorded to all kinds of stimuli. The 2M component was clearly identified only to face stimulation in all subjects, but to eyes stimulation in only 3 subjects with a small amplitude. The 2M component was not identified to scrambled face nor hand stimulation. The 2M component was recorded from the right hemisphere in all subjects, but in only 5 of 10 subjects from the left hemisphere. The mean peak latencies of the 1M and 2M components were approximately 132 and 179 ms, respectively. The interpeak latency between 1M and 2M was approximately 47 ms on average but the interindividual difference was large. There was no significant difference of the 2M latency between face with opened eyes and face with closed eyes. The 1M component was generated in the primary visual cortex in the bilateral hemispheres, and the 2M component was generated in the inferior temporal cortex, around the fusiform gyrus. In the EEG recording, face-specific components, positive at the vertex, P200 (Cz), and the negative at the temporal areas, N190 (T5') and N190 (T6'), were clearly recorded. The EEG results were fundamentally compatible with the MEG results. The amplitude of the component recorded from the right hemisphere was significantly larger than that from the left hemisphere. These findings suggest that the fusiform gyrus is considered to play an important role in face perception in humans, and that the right hemisphere is more dominant. Face perception takes place approximately 47 ms after the primary response to visual stimulation in the primary visual cortex, but the period of information transfer to the fusiform gyrus is variable among subjects. Detailed temporal and spatial analyses of the processing of face perception can be achieved with MEG.

Adult↗

PubMed1999

It takes longer to recognize the eyes than the whole face in humans.

Brain responses to eyes and whole face were studied by magnetoencephalography (MEG). We used five different visual stimuli, face with opened eyes, face with closed eyes, eyes, scrambled face, and hand. 1M was evoked in response to all kinds of stimuli but 2M peaking at approximately 180 ms was recorded only for face and eyes. The peak latencies of 1M and 2M and the interpeak latency 1M-2M to eyes were significantly longer than those to face, and there was no significant difference of latency between face with opened eyes and face with closed eyes. The 2M both for face and eyes was generated in the same area, the inferior temporal cortex, around the fusiform gyrus.

Adult↗

PubMed1999

Changes of somatosensory evoked potentials during writing with the dominant and non-dominant hands.

Since close attention and special effort are necessary to perform difficult unskilled movements, particular brain activities underlying such movements could be expected to take place in the primary sensori-motor cortices (SI and MI). In this study we focused on such activities by analyzing the difference in the somatosensory evoked potential (SEP) in presence to the electrical stimulation of the median nerve during writing using the dominant and non-dominant hands in twelve right-handed and eight left-handed normal subjects. By alternately stimulating the right and left median nerves during the writing with either hand, SEPs were recorded from both hemispheres. During the dominant hand writing, the middle latency SEP components, i.e., parietal P25 and N33 and frontal N30, were significantly attenuated only in the hemisphere contralateral to the writing hand, corresponding to the conventional gating effect. During the non-dominant hand writing, not only those components recorded from the hemisphere contralateral to the writing hand, but also those from the hemisphere ipsilateral to the writing hand were significantly attenuated. In addition, N20 in the hemisphere contralateral to the writing hand was also significantly attenuated. There was no significant difference in the attenuation between the right-handed and left-handed subjects. The results indicated that the specific interaction between the signals after electrical stimulation and the sensory cortical activities related to the writing using the non-dominant hand occurred in both hemispheres, while it was recognized only in the hemisphere contralateral to the writing hand during the dominant hand writing. We speculate that the somatosensory cortex was more activated and thus interacted with the applied stimulation during the unskilled movement of the non-dominant hand compared to the movement of the dominant hand.

Adult↗

PubMed1999

Topography of the secondary somatosensory cortex in humans: a magnetoencephalo-graphic study.

The topography of the secondary somatosensory cortex (SII) responses to somatosensory stimulation applied to various parts of the body of normal volunteers was analyzed using magnetoencephalography (MEG). Although there were large inter-individual differences, the following orders of a location of equivalent current dipoles (ECDs) were found; (1) Anterior-posterior direction: lower lip-upper lip-thumb-middle finger-foot, (2) Medial-lateral direction: foot-middle finger-thumb-upper lip-lower lip, and (3) Lower-upper direction: lower lip-upper-lip-thumb-middle finger-foot. In general, these findings are similar to those obtained in studies of monkeys. However, the differentiation was not as clear as that seen in the homunculus in the primary somatosensory cortex (SI). The auditory cortex is located at a site more posterior, lateral and lower than the SII.

Adult↗