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Purpose: The estimation of functional connectivity (FC) measures using resting state functional MRI (fMRI) is often affected by head motion during functional imaging scans. Head motion is more common in the elderly than in young participants and could therefore affect the evaluation of age-related changes in brain networks. Thus, this study aimed to investigate the influence of head motion in FC estimation when evaluating age-related changes in brain networks., Methods: This study involved 132 healthy volunteers divided into 3 groups: elderly participants with high motion (OldHM, mean age (±SD) = 69.6 (±5.31), N = 44), elderly participants with low motion (OldLM, mean age (±SD) = 68.7 (±4.59), N = 43), and young adult participants with low motion (YugLM, mean age (±SD) = 27.6 (±5.26), N = 45). Head motion was quantified using the mean of the framewise displacement of resting state fMRI data. After preprocessing all resting state fMRI datasets, several resting state networks (RSNs) were extracted using independent component analysis (ICA). In addition, several network metrics were also calculated using network analysis. These FC measures were then compared among the 3 groups., Results: In ICA, the number of voxels with significant differences in RSNs was higher in YugLM vs. OldLM comparison than in YugLM vs. OldHM. In network analysis, all network metrics showed significant (P < 0.05) differences in comparisons involving low vs. high motion groups (OldHM vs. OldLM and OldHM vs. YugLM). However, there was no significant (P > 0.05) difference in the comparison involving the low motion groups (OldLM vs. YugLM)., Conclusion: Our findings showed that head motion during functional imaging could significantly affect the evaluation of age-related brain network changes using resting state fMRI data.

Brain activity was recorded using a whole-head magnetoencephalography system followed by coherence analysis to assess neural connectivity in 10 healthy right-handed adults to clarify differences in neural connectivity in brain regions during action observation from several perspectives. The subjects were instructed to observe and memorize or imitate the hand action from a first-person or second-person visual perspective. The brain activity in coherence was modified among frontal and central, sensorimotor, and mirror neuron system-related regions based on the visual perspectives of finger movements. The regional activity in coherence changed similarly under the imitation and observation tasks compared with the condition of observing static hand figures. The information from different visual perspectives of body movements was processed in the frontal-central regions related to sensorimotor processes and partially in mirror neuron system.

Objective: Epileptic spikes are associated with rapidly changing brain activation involving the epileptic foci and other brain regions in the "epileptic network". We aim to resolve these activation changes using simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) recordings., Methods: Simultaneous EEG-fMRI recordings from 9 patients with epilepsy were used in the analysis. Our method employed the whole scalp EEG data to generate regressors for the analysis of fMRI data using the general linear model., Results: We were able to resolve, with milliseconds temporal resolution, changes in activation patterns involving suspected epileptic foci and other brain regions in the epileptic network during spike and slow wave. Using summary maps (called SSWAS maps) which show the activation frequency of voxels, we found that suspected epileptic foci tend to be significantly active during this interval. SSWAS maps also enabled the detection of the epileptic foci in 4 of 5 patients where the conventional event-timing-based analysis failed to identify., Conclusion: These findings demonstrated the efficacy of the method and the potential application of SSWAS maps to identify epileptic foci., Significance: The method could help resolve activation changes during epileptic spike and could provide insights into the underlying pathophysiology of these changes., (Copyright © 2017 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)

Objectives: We investigated whether incomprehensible high-speed auditory speech stimulation was processed and interacted with visual-word discrimination processing. We hypothesised that an interaction might indicate the capacity of working memory (WM) to perform the temporal processing of auditory verbal information., Methods: We recorded P300 for a visual-word discrimination Oddball paradigm in 14 healthy subjects. Auditory speech and reversed speech stimulation were presented at various speeds as task-irrelevant stimuli during the P300 tasks., Results: The P300 latency was prolonged under forward high-speed speech stimuli (× 2.5 and × 3.5) compared with the standard speed and white noise, but there was no effect of reversed speech stimuli on the P300 latency during the word-discrimination paradigm., Conclusions: We considered that high-speed speech stimulation was processed without conscious comprehension and competed with verbal processing during the visual-word-discrimination task, possibly by interfering with the use of WM., Significance: The present study shows the capacity of the brain to process high-speed verbal stimulation and the interaction with a visual-verbal task., (Copyright © 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

We investigated the effects of subliminal stimulation on visible stimulation to demonstrate the priority of facial discrimination processing, using a unique, indiscernible, color-opponent subliminal (COS) stimulation. We recorded event-related magnetic cortical fields (ERF) by magnetoencephalography (MEG) after the presentation of a face or flower stimulus with COS conditioning using a face, flower, random pattern, and blank. The COS stimulation enhanced the response to visible stimulation when the figure in the COS stimulation was identical to the target visible stimulus, but more so for the face than for the flower stimulus. The ERF component modulated by the COS stimulation was estimated to be located in the ventral temporal cortex. We speculated that the enhancement was caused by an interaction of the responses after subthreshold stimulation by the COS stimulation and the suprathreshold stimulation after target stimulation, such as in the processing for categorization or discrimination. We also speculated that the face was processed with priority at the level of the ventral temporal cortex during visual processing outside of consciousness.

Objective: To investigate the somatotopic organization of the facial skin area in the secondary somatosensory cortex (SII) in humans., Methods: Somatosensory evoked magnetic fields following air-puff stimulation of 5 body sites, the foot, the lip and 3 points of the facial skin (forehead, cheek and mandibular angle point), were recorded. We focused on activities in SII following stimulation of these 5 sites and compared dipole locations among them., Results: There was a clear somatotopic organization in SII with lip in the most lateral area, foot in the most medial area and face in an intermediate area close to the lip area. However, there was no significant difference of dipole localization in SII among the 3 areas of facial skin, similar to the overlapped somatotopic organization of facial skin areas in the primary somatosensory cortex in our previous study., Conclusions: The facial skin areas are considered to occupy a small area in SII with insufficient spatial separation to differentiate each area of facial skin even using magnetoencephalography which has a high spatial resolution., Significance: This is the first systematic study of the activated regions in SII following stimulation of the facial skin.

To investigate the representation of facial skin areas in the primary somatosensory cortex (SI), we recorded magnetic fields evoked by air pressure-induced tactile stimulation applied to six points on the face, lower lip and thumb. The thumb area in the SI was located more medial and superior to the lip area, which was consistent with Penfield's homunculus. However, the representations of all skin-covered areas including forehead, cheek, nose and chin in the SI were located between the thumb and lower lip area. There was no significant difference in location among the six facial points. Our results imply that lips occupy a large area of the face representation in the SI, whereas only a small area located between the thumb and lip areas is devoted to skin-covered surfaces. This is the first study showing that the facial skin areas in the human SI are located between the thumb and lower lip areas and close together.

This is the first report to clarify the underlying mechanisms of processing in the modulation of frequencies (tones) in humans using magnetoencephalography (MEG). Volunteers were instructed to vocalize a simple vowel sound (/u/) after receiving a cue (S2) for either one of three (low, middle, or high fundamental frequencies) (F0s). Three tasks, (1) the modulated vocalization task in which the subjects were asked to modulate vocalization tones according to S2, (2) the non-modulated vocalization task in which the subjects were asked to vocalize the same sound (/u/) with a fixed F0, and (3) the image task in which the subjects had to modulate according to S2 and imagine the vowel (/u/) sound, but not vocalize it. In all tasks, two clear components, 1M and 2M, were recorded at approximately 190 and 290 ms after the S2. Since both were identified even in the Image task, they appear to be specifically related to activity for modulation. The equivalent current dipoles of both 1M and 2M were estimated to lie mainly in the inferior frontal lobe or insula in both hemispheres. Therefore, the activity relating to modulation mainly took place in the inferior frontal lobe or insula in both hemispheres starting about 200 ms after the viewing of a cue.

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.

We visualized the brain activity for retrieval imagery of a sound using dual 37-channel magnetometers in seven right-handed healthy subjects. A soundless video image of a hammer striking an anvil was presented on a screen. Significantly larger evoked magnetic fields were recorded, dominantly in the right hemisphere, in six subjects when they imagined the sound than when they did not. The initial peak of the response was 151.0 +/- 26.5 ms (mean +/- s.d.) after the blow. Equivalent current dipoles (ECDs) for the responses recorded from the right hemisphere were located around the inferior frontal sulcus in three subjects and in the insular region in three subjects, but reliable ECDs were not estimated from the left hemisphere. The results suggested that the initial activity for sound retrieval imagery appeared around the inferior frontal and insular areas, dominantly in the right hemisphere.

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.

Visual evoked magnetic field (VEF) and visual evoked potentials (VEP) in response to pattern reversal left half-field central (0-2 degrees, 0-5 degrees) and to left half-field peripheral stimulation (2-15 degrees, 5-15 degrees) were simultaneously recorded in 10 normal subjects. The aim was to localize the origin of the largest wave around 100 ms. By comparing the magnetic evoked 100m wave and electric evoked P100 wave, we found that the response to the small central field (0-2 degrees) stimulation was clearly evident in the VEP and not in the VEF, while the response to the peripheral field (2-15 degrees, 5-15 degrees) stimulation was clearly present in both the VEP and VEF. Our findings show that in contrast to the already recognized predominantly macular origin of VEP activity, VEF activity has a peripheral rather than macular prevalence. Our VEF findings are related to the retinotopic organization of the visual cortex; the 100m dipole to the central field (0-5 degrees) was localized more (1.04 +/- 0.84 cm) posterior than was the 100m dipole to peripheral stimulation (5-15 degrees). The localization of 100m dipoles superimposed on magnetic resonance images (MRI) to central stimuli showed interindividual variations that were in agreement with the known variability of the central field representation in the striate cortex: on the convexity of the occipital pole, in the outer surface of the occipital lobe, and around the calcarine fissure of the right hemisphere. In contrast, following peripheral stimulation, the 100m dipole was located along the medial surface of the hemisphere or in the calcarine fissure. Our results suggest that the main origin of the largest wave around l00ms in response to pattern reversal stimuli is in the striate cortex.

Magnetoencephalograms were recorded from six healthy Japanese subjects in order to investigate the areas in the cortices which are involved in the recognition of Japanese characters (Kanji and Kana). Forty-four Kanji (morphograms), 44 Kana (syllabograms) and 20 alphabet letters were used as stimuli. They were presented randomly and the subjects were required to read each stimulus and count the number of letters. The magnetic responses were recorded with dual 37-channel SQUID (Superconducting Quantum Interference Device) gradiometers from the temporal, parietal and occipital areas of the brain. The magnetic responses to Kanji and Kana were similar and consequently the locations of equivalent current dipoles (ECDs) to Kanji and those to Kana did not differ at any recording site. In all the subjects, ECDs were found in the posterior inferior temporal (PIT) areas approximately corresponding to Brodmann area 37 in the latency range of 150-300 msec. These activities were found in both hemispheres without consistent laterality. The location of the ECD moved forward from posterior to anterior in the PIT area as the latency increased in all but one subject. Only one subject showed activities in the left angular gyrus. Since activities in PIT areas were also found in alphabet letters, the bilateral PIT areas are considered to play an essential role in reading.

We investigated the activation of posterior parietal cortex (PPC) to somatosensory stimulation in humans to determine its fundamental role as a somatosensory associated area using magnetoencephalography (MEG). We studied somatosensory evoked magnetic fields (SEF) after stimulation of median nerve, posterior tibial nerve and lip, and analyzed them by the single dipole model and also by the multidipole model using brain electric source analysis (BESA) system. In single source model analysis, the dipole at the peak latency of short-latency components following each site stimulation were located in the corresponding receptive fields in the primary somatosensory cortex (SI) contralateral to the stimulation. The dipole at the peak latency of the middle latency components were located in bilateral upper bank of Sylvian fissure (SII), By contrast, in the five-dipole model of BESA, the equivalent current dipoles (ECDs) of the middle-latency SEF after stimulation of median nerve and posterior tibial nerve were identified in the contralateral SI and in the bilateral SII and PPC, while all activities of middle-latency SEF after lip stimulation appeared to be restricted in the contralateral SI and bilateral SII. Around 80 msec in latency, the ECD location in PPC after median nerve stimulation was, on the average, 2.4 cm posterior, 2.9 cm medial and 2.6 cm superior to the hand area in SI. The ECD in PPC after posterior tibial nerve stimulation was also located posterior to the foot area in SI, but it was close to the SI area of foot, their distance being approximately 1.3 cm. ECD in PPC was almost equally demonstrated in each hemisphere. These findings suggested that the somatosensory associated cortex in PPC represented somatotopic organization in parallel with 'homunculus' in SI, but the hand area was much wider than the foot area. It was not clear whether the lip area in PPC was absent or was too close to be separated from the SI.

We studied visual evoked magnetic fields to pattern reversal stimulation in six healthy subjects. Similar to the N75-P100-N145 components in visual evoked potentials, triphasic deflections, N75m-P100m-N145m, were clearly observed around the midoccipital position. A very small component, P50m, was occasionally observed preceding the N75m. Equivalent current dipoles (ECDs) of the main deflection, P100m, to quadrant-field stimulation were estimated near or around the calcarine fissure contralateral to the stimulation. The vertical ECD location of the P100m to the upper quadrant-field stimulation was estimated significantly lower (0.81 +/- 0.45 cm) than those to lower stimulation. These results were compatible with the retinotopic organization of the visual cortex (cruciform model) and suggested that the P100m originated in the striate cortex. The small P50m, although only a small number of ECDs could be estimated reliably, was located in the contralateral visual cortex. ECDs of the N75m were estimated mainly near or around the contralateral calcarine fissure. ECDs of the N145m were estimated also retinotopically, but with a greater vertical distance (2.90 +/- 1.09 cm) between upper and lower quadrant-field stimulation. MR-overlaid ECDs of the N145m suggested that these originated in the extrastriate cortex. No ECD was estimated when a probe was placed at the midfrontal position.

The authors investigated magnetoencephalography following stimulation of the posterior tibial (PT) and sural (SU) nerves at the ankle, the peroneal nerve (PE) at the knee, and the femoral nerve (FE) overlying the inguinal ligament in seven normal subjects (14 limbs) and confirmed its usefulness in clarifying the detailed differentiation of the receptive fields in the lower limb area of the primary sensory cortex in humans. The results were summarized as follows: 1) the equivalent current dipoles (ECDs) estimated by the magnetic fields following stimulation of the PT and SU were located very close to each other, along the interhemispheric fissure in all 14 limbs. They were directed horizontally to the hemisphere ipsilateral to the stimulated nerve. 2) The ECD following stimulation of the FE was clearly different from that seen in the other nerves, in terms of the location and/or direction, in all 14 limbs. The ECDs of 14 limbs were classified into two types according to the distance of ECD location between PT and FE; Type 1 (> 1 cm, nine limbs) and Type 2 (< 1 cm, five limbs). The ECD following FE stimulation was located on the crown of the postcentral gyrus or at the edge of the interhemispheric fissure in Type 1 and was close to the ECDs following PT and SU stimulation along the interhemispheric fissure in Type 2. 3) The ECD following PE stimulation was located along the interhemispheric fissure in all 14 limbs as for PT and SU. Its location was slightly but significantly higher than that of PT and SU in Type 1 and was close to ECDs following PT and SU stimulation in Type 2. The present findings indicated that approximately 65% (nine of 14) of the limbs showed the particular receptive fields compatible with the homunculus. Large inter- and the intraindividual (left-right) differences found in the present study indicated a significant anatomical variation in the area of the lower limb in the sensory cortex of humans.

The topography of somatosensory evoked magnetic fields (SEFs) following stimulation of the right and left posterior tibial nerves was investigated in 5 normal subjects (10 nerves). The main deflections N37m-P45m-N60m-P75m and their counterparts P37m-N45m-P60m-N75m were identified in the hemisphere contralateral to the stimulated nerve. Their equivalent current dipoles (ECDs) were located in the foot area of the primary sensory cortex (SI), probably in area 3b. Restricted minor deflections, P40m-N40m and N50m-P50m, were considered to be generated in area 1 in SI. As the generator sources of P37m-N37m, P40m-N40m and N45m-P45m were temporarily changed and interfered with each other, the direction of ECDs appeared to be rotated with the passage of time. Small middle-latency deflections, N100m-P100m, were clearly identified in 2 subjects. ECDs of these deflections were found in the second sensory cortex (SII), in both hemispheres, although they were clearer in the hemisphere contralateral to the stimulated nerve. In conclusion, short- and middle-latency SEFs are mainly generated in area 3b in SI contralateral to the stimulated nerve, and responses generated in area 1 of SI and SII affect the SEFs to some degree, but interindividual differences are large compared with SEFs evoked by upper limb stimulation.