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Objective : We present a benchmarking protocol for quantitatively comparing emerging on-scalp magnetoencephalography (MEG) sensor technologies to their counterparts in state-of-the-art MEG systems. Methods: As a means of validation, we compare a high-critical-temperature superconducting quantum interference device (high $T_{{c}}$ SQUID) with the low- $T_{{c}}$ SQUIDs of an Elekta Neuromag TRIUX system in MEG recordings of auditory and somatosensory evoked fields (SEFs) on one human subject. Results: We measure the expected signal gain for the auditory-evoked fields (deeper sources) and notice some unfamiliar features in the on-scalp sensor-based recordings of SEFs (shallower sources). Conclusion: The experimental results serve as a proof of principle for the benchmarking protocol. This approach is straightforward, general to various on-scalp MEG sensors, and convenient to use on human subjects. The unexpected features in the SEFs suggest on-scalp MEG sensors may reveal information about neuromagnetic sources that is otherwise difficult to extract from state-of-the-art MEG recordings. Significance: As the first systematically established on-scalp MEG benchmarking protocol, magnetic sensor developers can employ this method to prove the utility of their technology in MEG recordings. Further exploration of the SEFs with on-scalp MEG sensors may reveal unique information about their sources.

Accepted manuscript online: 28 October 2016 Shortening of the interstimulus interval (ISI) generally leads to attenuation of cortical sensory responses. For proprioception, however, this ISI effect is still poorly known. Our aim was to characterize the ISI dependence of movement-evoked proprioceptive cortical responses and to find the optimum ISI for proprioceptive stimulation. We measured, from 15 healthy adults, magnetoencephalographic responses to passive flexion and extension movements of the right index finger. The movements were generated by a movement actuator at fixed ISIs of 0.5, 1, 2, 4, 8, and 16 s, in separate blocks. The responses peaked at ~ 70 ms (extension) and ~ 90 ms (flexion) in the contralateral primary somatosensory cortex. The strength of the cortical source increased with the ISI, plateauing at the 8-s ISI. Modeling the ISI dependence with an exponential saturation function revealed response lifetimes of 1.3 s (extension) and 2.2 s (flexion), implying that the maximum signal-to-noise ratio (SNR) in a given measurement time is achieved with ISIs of 1.7 s and 2.8 s respectively. We conclude that ISIs of 1.5–3 s should be used to maximize SNR in recordings of proprioceptive cortical responses to passive finger movements. Our findings can benefit the assessment of proprioceptive afference in both clinical and research settings. This work was supported by the Academy of Finland (Grants #131483 and #263800 to Riitta Hari and Grants #266133 and #296240 to Harri Piitulainen), Tekes – the Finnish Funding Agency for Technology and Innovation (Grant 1104/10), the European Research Council (Advanced Grant #232946 to Riitta Hari), the Emil Aaltonen Foundation (Eero Smeds), and the Research Programs Unit of the University of Helsinki (Eero Smeds).

Two major concerns with respect to task-based motor functional magnetic resonance imaging (fMRI) are inadequate participants' performance as well as intra- and inter-subject variability in execution of the motor action., SCOPUS: ar.j, info:eu-repo/semantics/published

Motor symptoms are defining traits in the diagnosis of Parkinson’s disease (PD). A crucial component in motor function and control of movements is the integration of efferent signals from the motor network to the peripheral motor system, and afferent proprioceptive sensory feedback. Previous studies have indicated abnormal movement-related cortical oscillatory activity in PD, but the role of the proprioceptive afference on abnormal oscillatory activity in PD has not been elucidated. In the present study, we examine the role of proprioception by studying the cortical processing of proprioceptive stimulation in PD patients, ON/OFF levodopa medication, as compared to that of healthy controls (HC). We used a proprioceptive stimulator that generated precisely controlled passive movements of the index finger and measured the induced cortical oscillatory responses following the proprioceptive stimulation using magnetoencephalography (MEG). Both PD patients and HC showed a typical initial mu/beta-band (8–30 Hz) desynchronization during the passive movement. However, the subsequent beta rebound after the passive movement that was apparent in HC was much attenuated and almost absent in PD patients. Furthermore, we found no difference in the degree of beta rebound attenuation between patients ON and OFF levodopa medication. Our results hence demonstrate a disease-related deterioration in cortical processing of proprioceptive afference in PD, and further suggest that such disease-related loss of proprioceptive function is due to processes outside the dopaminergic system affected by levodopa medication.

This magnetoencephalography (MEG) study aims at characterizing the coupling between cerebellar activity and the kinematics of repetitive self-paced finger movements. Neuromagnetic signals were recorded in 11 right-handed healthy adults while they performed repetitive flexion-extensions of right-hand fingers at three different movement rates: slow (~ 1 Hz), medium (~ 2 Hz), and fast (~ 3 Hz). Right index finger acceleration was monitored with an accelerometer. Coherence analysis was used to index the coupling between right index finger acceleration and neuromagnetic signals. Dynamic imaging of coherent sources was used to locate coherent sources. Coupling directionality between primary sensorimotor (SM1), cerebellar, and accelerometer signals was assessed with renormalized partial directed coherence. Permutation-based statistics coupled with maximum statistic over the entire brain volume or restricted to the cerebellum were used. At all movement rates, maximum coherence peaked at SM1 cortex contralateral to finger movements at movement frequency (F0) and its first harmonic (F1). Significant (statistics restricted to the cerebellum) coherence consistently peaked at the right posterior lobe of the cerebellum at F0 with no influence of movement rate. Coupling between Acc and cerebellar signals was significantly stronger in the afferent than in the efferent direction with no effective contribution of cortico-cerebellar or cerebello-cortical pathways. This study demonstrates the existence of significant coupling between finger movement kinematics and neuromagnetic activity at the posterior cerebellar lobe ipsilateral to finger movement at F0. This coupling is mainly driven by spinocerebellar, presumably proprioceptive, afferences., SCOPUS: ar.j, info:eu-repo/semantics/published

highlights abstract Objective: Corticokinematic coherence (CKC) is the coupling between magnetoencephalographic (MEG) signals and limb kinematics during fast movements. Our objective was to assess the robustness of CKC-based identification of the primary sensorimotor (SM1) cortex of subjects producing strong mag- netic artifacts when the MEG signals were cleaned with temporal signal space separation (tSSS). Methods: We recorded MEG during active and passive forefinger movements and during median-nerve stimulation in the following conditions: (1) artifact-free, (2) a magnetic wire attached to the scalp at C3 location, and (3) a magnetic wire attached behind the lower central incisors. Data were pre- processed with tSSS and analyzed using standard CKC methods, somatosensory evoked fields (SEFs), and dipole modeling. Result: Artifacts were effectively suppressed by tSSS, enabling successful identification of the SM1 cortex in all subjects based on CKC and SEFs. The sources were in artifact conditions 5 mm away from the sources identified in artifact-free conditions. Conclusion: tSSS suppressed artifacts strongly enough to enable reliable identification of the SM1 cortex on the basis of CKC mapping, with localization accuracy comparable to SEF-based mapping. Significance: The results suggest that CKC can be used for SM1 cortex identification and for studies of proprioception even in patients implanted with magnetic material.

Summary Aims of the study This study investigates the effect of movement rate on the coupling between cortical magnetoencephalographic (MEG) signals and the kinematics of repetitive active finger movements, i.e., the corticokinematic coherence (CKC). Material and methods CKC was evaluated in ten right-handed healthy adults performing repetitive flexion–extension of the right-hand fingers in three different movement rate conditions: slow (∼1 Hz, duration: 11 min), medium (∼2 Hz, duration: 5 min) and fast (∼3 Hz, duration: 3 min). Neuromagnetic signals were recorded with a whole-scalp-covering MEG (Elekta Oy) and index acceleration was monitored with a 3-axis accelerometer. Coherent sources were estimated on the time-course of the cross-correlogram using equivalent current dipole (ECD) modeling. Results Significant coherence was found at movement frequency or its first harmonics in all subjects and movement conditions. ECDs clustered at the primary sensorimotor cortex contralateral to hand movements. Movement rate had no effect on the coherence levels and the location of coherent sources. Conclusions This study demonstrates that the movement rate does not affect coherence levels and CKC source location during active finger movements. This finding has direct implications for CKC functional mapping applications and studies investigating the pathophysiology of central nervous disorders affecting proprioceptive pathways.

Cortex-muscle coherence (CMC) reflects coupling between magnetoencephalography (MEG) and surface electromyography (sEMG), being strongest during isometric contraction but absent, for unknown reasons, in some individuals. We used a novel nonmagnetic high-density sEMG (HD-sEMG) electrode grid (36 mm × 12 mm; 60 electrodes separated by 3 mm) to study effects of sEMG recording site, electrode derivation, and rectification on the strength of CMC. Monopolar sEMG from right thenar and 306-channel whole-scalp MEG were recorded from 14 subjects during 4-min isometric thumb abduction. CMC was computed for 60 monopolar, 55 bipolar, and 32 Laplacian HD-sEMG derivations, and two derivations were computed to mimic “macroscopic” monopolar and bipolar sEMG (electrode diameter 9 mm; interelectrode distance 21 mm). With unrectified sEMG, 12 subjects showed statistically significant CMC in 91–95% of the HD-sEMG channels, with maximum coherence at ∼25 Hz. CMC was about a fifth stronger for monopolar than bipolar and Laplacian derivations. Monopolar derivations resulted in most uniform CMC distributions across the thenar and in tightest cortical source clusters in the left rolandic hand area. CMC was 19–27% stronger for HD-sEMG than for “macroscopic” monopolar or bipolar derivations. EMG rectification reduced the CMC peak by a quarter, resulted in a more uniformly distributed CMC across the thenar, and provided more tightly clustered cortical sources than unrectifed sEMGs. Moreover, it revealed CMC at ∼12 Hz. We conclude that HD-sEMG, especially with monopolar derivation, can facilitate detection of CMC and that individual muscle anatomy cannot explain the high interindividual CMC variability.

To maintain steady motor output, distracting sensory stimuli need to be blocked. To study the effects of brief auditory and visual distractors on the human primary motor (M1) cortex, we monitored magnetoencephalographic (MEG) cortical rhythms, electromyogram (EMG) of finger flexors, and corticomuscular coherence (CMC) during right‐hand pinch (force 5–7% of maximum) while 1‐kHz tones and checkerboard patterns were presented for 100 ms once every 3.5–5 s. Twenty‐one subjects (out of twenty‐two) showed statistically significant ∼20‐Hz CMC. Both distractors elicited a covert startle‐like response evident in changes of force and EMG (∼50% of the background variation) but without any visible movement, followed by ∼1‐s enhancement of CMC (auditory on average by 75%, P

Magnetoencephalographic (MEG) signals recorded from the primary sensorimotor (SM1) cortex are coherent with kinematics of both active and passive finger movements. The coherence mainly reflects movement-related proprioceptive afference to the cortex. Here we describe a novel MEG-compatible stimulator to generate computer-controlled passive finger and toe movements that can be used as stimuli in functional brain-imaging experiments. The movements are produced by pneumatic artificial muscle (PAM), elastic actuator that shortens with increasing air pressure. To test the applicability of the stimulator to functional brain-imaging, 4-min trains of passive repetitive 5-mm flexion-extension movements of the right and left index finger and the right hallux were produced at 3Hz while the subject's brain activity was measured with whole-scalp MEG and finger or toe kinematics with an accelerometer. In all ten subjects studied, statistically significant coherence (up to 0.78) occurred between the accelerometer and MEG signals at the movement frequency or its first harmonic. Sources of coherent activity were in the contralateral hand or foot SM1 cortices. Movement-evoked fields elicited with intermittent movements of the right index finger (once every 3.2-4.0s; mean±SD peak response latency 88±25ms) were co-located with the respective coherent sources. We further moved the right index finger at 3, 6, and 12Hz (movement ranges 5, 3, and 2mm, respectively), and analyzed the first 1, 2, and 4-min epochs of data. One minute of data was sufficient to locate the left hand area of the SM1 cortex at all movement frequencies. Sound-induced spurious coherence was reliably ruled out in a control experiment. Our novel movement stimulator thus provides a robust and reliable tool to track proprioceptive afference to the cortex and to locate the SM1 cortex., info:eu-repo/semantics/published

To gain fundamental knowledge on how the brain controls motor actions, we studied in detail the interplay between MEG signals from the primary sensorimotor (SM1) cortex and the contraction force of 17 healthy adult humans (7 females, 10 males). SM1 activity was coherent at ~20 Hz with surface electromyogram (as already extensively reported) but also with contraction force. In both cases, the effective coupling was dominant in the efferent direction. Across subjects, the level of ~20 Hz coherence between cortex and periphery positively correlated with the “burstiness” of ~20 Hz SM1 (Pearson r ≈ 0.65) and peripheral fluctuations (r ≈ 0.9). Thus, ~20 Hz coherence between cortex and periphery is tightly linked to the presence of ~20 Hz bursts in SM1 and peripheral activity. However, the very high correlation with peripheral fluctuations suggests that the periphery is the limiting factor. At frequencies, SCOPUS: ar.j, info:eu-repo/semantics/published

This study investigates whether movement kinematics modulates similarly the rolandic α and β rhythm amplitude during executed and observed goal-directed hand movements. It also assesses if this modulation relates to the corticokinematic coherence (CKC), which is the coupling observed between cortical activity and movement kinematics during such motor actions. Magnetoencephalography (MEG) signals were recorded from 11 right-handed healthy subjects while they performed or observed an actor performing the same repetitive hand pinching action. Subjects' and actor's forefinger movements were monitored with an accelerometer. Coherence was computed between acceleration signals and the amplitude of α (8-12 Hz) or β (15-25 Hz) oscillations. The coherence was also evaluated between source-projected MEG signals and their β amplitude. Coherence was mainly observed between acceleration and the amplitude of β oscillations at movement frequency within bilateral primary sensorimotor (SM1) cortex with no difference between executed and observed movements. Cross-correlation between the amplitude of β oscillations at the SM1 cortex and movement acceleration was maximal when acceleration was delayed by ~ 100 ms, both during movement execution and observation. Coherence between source-projected MEG signals and their β amplitude during movement observation and execution was not significantly different from that during rest. This study shows that observing others' actions engages in the viewer's brain similar dynamic modulations of SM1 cortex β rhythm as during action execution. Results support the view that different neural mechanisms might account for this modulation and CKC. These two kinematic-related phenomena might help humans to understand how observed motor actions are actually performed., SCOPUS: ar.j, info:eu-repo/semantics/published

Contains fulltext : 181359.pdf (Publisher’s version ) (Open Access) The development of new magnetic sensor technologies that promise sensitivities approaching that of conventional MEG technology while operating at far lower operating temperatures has catalysed the growing field of on-scalp MEG. The feasibility of on-scalp MEG has been demonstrated via benchmarking of new sensor technologies performing neuromagnetic recordings in close proximity to the head surface against state-of-the-art in-helmet MEG sensor technology. However, earlier work has provided little information about how these two approaches compare, or about the reliability of observed differences. Herein, we present such a comparison, based on recordings of the N20m component of the somatosensory evoked field as elicited by electric median nerve stimulation. As expected from the proximity differences between the on-scalp and in-helmet sensors, the magnitude of the N20m activation as recorded with the on-scalp sensor was higher than that of the in-helmet sensors. The dipole pattern of the on-scalp recordings was also more spatially confined than that of the conventional recordings. Our results furthermore revealed unexpected temporal differences in the peak of the N20m component. An analysis protocol was therefore developed for assessing the reliability of this observed difference. We used this protocol to examine our findings in terms of differences in sensor sensitivity between the two types of MEG recordings. The measurements and subsequent analysis raised attention to the fact that great care has to be taken in measuring the field close to the zero-line crossing of the dipolar field, since it is heavily dependent on the orientation of sensors. Taken together, our findings provide reliable evidence that on-scalp and in-helmet sensors measure neural sources in mostly similar ways.

We introduce a novel multimodal scheme for primary sensorimotor hand area (SM1ha) mapping integrating multiple functional indicators from functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG). Ten right-handed healthy subjects (19–33 years; 5 females, 5 males) and four patients (24–64 years; 2 females, 2 males) suffering from space-occupying brain lesion close to the central sulcus were studied. Functional indicators of the SM1ha were obtained from block-design fMRI motor protocol, and six MEG protocols: somatosensory evoked fields to electrical median-nerve stimulation, mu-rhythm suppression (~10 and ~20 Hz), corticomuscular coherence, and corticokinematic coherence with and without finger contacts. To assess the spatial spread of the functional indicators, their coordinates were subjected to principal component analysis to produce a centered ellipsoid with axis along principal components. Five to seven functional indicators were obtained for each participant. In all participants, the ellipsoid co-localized with the anatomical SM1ha. In healthy subjects, 50–100 % of functional indicators were located within 10 mm from the center of the ellipsoid. In patients, 17–100 % of functional indicators were located within 10 mm from the center of the ellipsoid. In conclusion, the multimodal scheme proposed led to a functional mapping of SM1ha that co-localized with anatomical SM1ha in all participants. The spread of the SM1ha functional indicators in some patients with brain lesions highlights the potential benefit of the proposed multimodal approach to assess the reliability of the non-invasive SM1ha mapping.

Objective Our aim was to assess the effectiveness and reliability of spatiotemporal signal space separation (tSSS) and movement correction (MC) in magnetoencephalography (MEG) recordings disturbed by head movements and magnetized material on the head. Methods We recorded MEG from 20 healthy adults in stationary (reference) head position and during controlled head movements. Nearby magnetic interference sources were simulated by attaching magnetized particles on the subject’s head. Auditory and somatosensory stimuli were presented. MC, tSSS and averaging were performed to obtain auditory (AEF) and somatosensory (SEF) evoked fields. Neuronal sources were modeled as equivalent current dipoles. MC was also validated by reconstructing signals generated by current dipoles in a phantom. Results After MC, the AEF and SEF responses recorded during intermittent head movements were similar in amplitude to the reference recordings and differed by 5–7 mm in source location. The tSSS method removed artifacts due to the attached magnetized particles but did not affect the reference data. Conclusions The methods are able to reliably recover MEG responses contaminated by movements and magnetic artifacts on the head. Significance The combination of tSSS and MC methods is especially useful in clinical measurements, where movements and magnetic disturbances are commonly present.

Reading epilepsy (RE) is an idiopathic reflex epilepsy syndrome characterized by perioral myoclonic jerks (PMJs) during reading associated with left-dominant frontotemporal spike-wave discharges (SWDs). To better understand the pathophysiology of this syndrome, we studied a 45-year-old patient using magnetic source imaging (MSI). The patient underwent two whole-head magnetoencephalography (MEG) recordings (Elekta Neuromag Oy) within 2 months while reading aloud. Forty-two SWDs associated with PMJs were recorded and averaged with respect to SWDs peak power. Epileptic discharges were then reconstructed using conventional equivalent current dipoles (ECDs) modeling, distributed sources sLORETA modeling, and beamformer approach. These methods identified two brain sources located in the left supplementary motor cortex (SMC) and the left primary sensorimotor face area (PSMFA). The spatiotemporal pattern of the sources was characterized by a cross-talk between these two brain regions, with an initial source in the left SMC. This MSI investigation suggests that RE-PMJs are associated with reading-induced activation of hyperexcitable neurons in the left SMC, followed by secondary propagation to the left PSMFA producing the myoclonus.

We used magnetoencephalography to show that the human primary somatosensory (SI) cortex is activated by mere observation of touch. Somatosensory evoked fields were measured from adult human subjects in two conditions. First, the experimenter touched the subject's right hand with her index finger (Experienced touch). In the second condition, the experimenter touched her own hand in a similar manner (Observed touch). Minimum current estimates were computed across three consecutive 300-ms time windows (0-300, 300-600 and 600-900 ms) with respect to touch onset. During 'Experienced touch', as expected, the contralateral (left) SI cortex was strongly activated in the 0-300 ms time window. In the same time window, statistically significant activity also occurred in the ipsilateral SI, although it was only 2.5% of the strength of the contralateral activation; the ipsilateral activation continued in the 300-600 ms time window. During 'Observed touch', the left SI cortex was activated during the 300-600 ms interval; the activation strength was 7.5% of that during the significantly activated period (0-300 ms) of 'Experienced touch'. The results suggest that when people observe somebody else being touched, activation of their own somatosensory circuitry may contribute to understanding of the other person's somatosensory experience.

Controversy persists over the role of the primary somatosensory cortex (SI) in processing small-fiber peripheral afferent input. We therefore examined subject I.W, who, due to sensory neuronopathy syndrome, has no large-fiber afferents below C3 level. Cortical evoked responses were recorded with a whole-scalp neuromagnetometer to high-intensity electrical stimulation of the distal right radial, median, and tibial nerves and skin over the forearm and mechanical stimulation of (neurologically intact) lip. The responses to electrical stimulation in the Abeta-denervated limbs peaked at 110-140 ms in contralateral SI and at 140-220 ms in contralateral secondary somatosensory cortex (SII), consistent with Adelta-mediated input. I.W. was able to localize pin-prick stimuli with 4 cm accuracy. Responses to laser stimuli on the radial dorsum of the hand peaked in contralateral SII cortex at 215 ms, also compatible with Adelta-mediated input. These results support the role of the SI cortex in processing the sensory discriminative aspects of Adelta-mediated input.

Sensory stimulation resulting from one's own behavior or the outside world is easily differentiated by healthy persons who are able to predict the sensory consequences of their own actions. This ability has been related to cortical attenuation of activation elicited by self-produced stimulation. To date, however, the neural processes underlying this modulation remain to be elucidated. We therefore recorded whole-scalp magnetoencephalographic (MEG) signals from 10 young adults either when they were touched by another person with a brush or when they touched themselves with the same device. The main MEG responses peaked at the primary somatosensory cortex at 54+/-2 ms. Signals and source strengths were about a fifth weaker to self-produced than external touch. Importantly, attenuation was present in each subject. Control recordings indicated that the suppression was neither caused by hand movements as such nor by visual cues. The very early start of the attenuation already about 30 ms after stimulation onset is in line with the hypothesis of forward mechanisms, based on motor commands, as the basis of differentiation between self-produced and externally produced tactile sensations.

Using a continuous listening task, we evaluated the coupling between the listener's cortical activity and the temporal envelopes of different sounds in a multitalker auditory scene using magnetoencephalography and corticovocal coherence analysis. Neuromagnetic signals were recorded from 20 right-handed healthy adult humans who listened to five different recorded stories (attended speech streams), one without any multitalker background (No noise) and four mixed with a “cocktail party” multitalker background noise at four signal-to-noise ratios (5, 0, −5, and −10 dB) to produce speech-in-noise mixtures, here referred to as Global scene. Coherence analysis revealed that the modulations of the attended speech stream, presented without multitalker background, were coupled at ∼0.5 Hz to the activity of both superior temporal gyri, whereas the modulations at 4–8 Hz were coupled to the activity of the right supratemporal auditory cortex. In cocktail party conditions, with the multitalker background noise, the coupling was at both frequencies stronger for the attended speech stream than for the unattended Multitalker background. The coupling strengths decreased as the Multitalker background increased. During the cocktail party conditions, the ∼0.5 Hz coupling became left-hemisphere dominant, compared with bilateral coupling without the multitalker background, whereas the 4–8 Hz coupling remained right-hemisphere lateralized in both conditions. The brain activity was not coupled to the multitalker background or to its individual talkers. The results highlight the key role of listener's left superior temporal gyri in extracting the slow ∼0.5 Hz modulations, likely reflecting the attended speech stream within a multitalker auditory scene.SIGNIFICANCE STATEMENTWhen people listen to one person in a “cocktail party,” their auditory cortex mainly follows the attended speech stream rather than the entire auditory scene. However, how the brain extracts the attended speech stream from the whole auditory scene and how increasing background noise corrupts this process is still debated. In this magnetoencephalography study, subjects had to attend a speech stream with or without multitalker background noise. Results argue for frequency-dependent cortical tracking mechanisms for the attended speech stream. The left superior temporal gyrus tracked the ∼0.5 Hz modulations of the attended speech stream only when the speech was embedded in multitalker background, whereas the right supratemporal auditory cortex tracked 4–8 Hz modulations during both noiseless and cocktail-party conditions.

Short laser pulses applied to the skin are used increasingly in both clinical and basic assessment of nociceptive brain mechanisms. The authors aimed to characterize further the cortical responses to noxious laser stimuli and to define the interstimulus interval (ISI) for the optimum signal-to-noise ratio during a fixed measurement time. Three hundred six-channel whole-scalp magnetoencephalographic (MEG) and midline EEG signals were recorded from nine healthy adults during painful thulium laser stimulation. The stimuli were delivered on the dorsum of the left hand at ISIs of 0.5, 1, 2, 4, 8, and 16 seconds. The MEG responses peaked at 160 to 195 msec around the contralateral primary somatosensory (SI) cortex, at 150 to 190 msec in the contralateral secondary somatosensory (SII) cortex, and at 160 to 205 msec in the ipsilateral SII cortex. The simultaneously measured electrical vertex potentials peaked at 190 to 230 msec and 310 to 330 msec (N200-P300). All these responses showed rather similar refractory times: The amplitudes increased strongly from 0.5 to 4-second ISIs and thereafter saturated at ISIs of 8 to 16 seconds. On the basis of the time constants of the recovery cycles, the optimum ISI for obtaining the best signal-to-noise ratio for laser-evoked MEG and EEG responses during a fixed measurement interval is 4 to 5 seconds.

Background The use of navigated repetitive transcranial magnetic stimulation (rTMS) in mapping of speech-related brain areas has recently shown to be useful in preoperative workflow of epilepsy and tumor patients. However, substantial inter- and intraobserver variability and non-optimal replicability of the rTMS results have been reported, and a need for additional development of the methodology is recognized. In TMS motor cortex mappings the evoked responses can be quantitatively monitored by electromyographic recordings; however, no such easily available setup exists for speech mappings. New method We present an accelerometer-based setup for detection of vocalization-related larynx vibrations combined with an automatic routine for voice onset detection for rTMS speech mapping applying naming. Comparison with existing method(s) The results produced by the automatic routine were compared with the manually reviewed video-recordings. Results The new method was applied in the routine navigated rTMS speech mapping for 12 consecutive patients during preoperative workup for epilepsy or tumor surgery. The automatic routine correctly detected 96% of the voice onsets, resulting in 96% sensitivity and 71% specificity. Majority (63%) of the misdetections were related to visible throat movements, extra voices before the response, or delayed naming of the previous stimuli. The no-response errors were correctly detected in 88% of events. Conclusion The proposed setup for automatic detection of voice onsets provides quantitative additional data for analysis of the rTMS-induced speech response modifications. The objectively defined speech response latencies increase the repeatability, reliability and stratification of the rTMS results.

HyperscanningMost neuroimaging studies of human social cognition have focused on brain activity of single subjects. More recently, "two-person neuroimaging" has been introduced, with simultaneous recordings of brain signals from two subjects involved in social interaction. These simultaneous "hyperscanning" recordings have already been carried out with a spectrum of neuroimaging modalities, such as functional magnetic resonance imaging (fMRI), electroencephalography (EEG), and functional near-infrared spectroscopy (fNIRS).Dual meg setupWe have recently developed a setup for simultaneous magnetoencephalographic (MEG) recordings of two subjects that communicate in real time over an audio link between two geographically separated MEG laboratories. Here we present an extended version of the setup, where we have added a video connection and replaced the telephone-landline-based link with an Internet connection. Our setup enabled transmission of video and audio streams between the sites with a one-way communication latency of about 130 ms. Our software that allows reproducing the setup is publicly available.ValidationWe demonstrate that the audiovisual Internet-based link can mediate real-time interaction between two subjects who try to mirror each others' hand movements that they can see via the video link. All the nine pairs were able to synchronize their behavior. In addition to the video, we captured the subjects' movements with accelerometers attached to their index fingers; we determined from these signals that the average synchronization accuracy was 215 ms. In one subject pair we demonstrate inter-subject coherence patterns of the MEG signals that peak over the sensorimotor areas contralateral to the hand used in the task.

Activation of peripheral mixed and cutaneous nerves activates a distributed cortical network including the second somatosensory cortex (SII) in the parietal operculum. SII activation has not been previously reported in the stimulation of the dorsal penile nerve (DPN). We recorded somatosensory evoked fields (SEFs) to DPN stimulation from 7 healthy adults with a 122-channel whole-scalp neuromagnetometer. Electrical pulses were applied once every 0.5 or 1.5 sec to the left and right DPN. For comparison, left and right median and tibial nerves were stimulated alternatingly at 1.5-sec intervals. DPN stimuli elicited weak, early responses in the vicinity of responses to tibial nerve stimulation in the primary somatosensory cortex. Strong later responses, peaking at 107-126 msec were evoked in the SII cortices of both hemispheres, with left-hemisphere dominance. In addition to tactile processing, SII could also contribute to mediating emotional effects of DPN stimuli.

Sounds convolved with individual head-related transfer functions and presented through headphones can give very natural percepts of the three-dimensional auditory space. We recorded whole-scalp neuromagnetic responses to such stimuli to compare reactivity of the human auditory cortex to sound azimuth and elevation. The results suggest that the human auditory cortex analyses sound azimuth, based on both binaural and monaural localization cues, mainly in the hemisphere contralateral to the sound, whereas elevation in the anterior space and in the lateral auditory space in general, both strongly relying on monaural spectral cues, are analyzed in more detail in the right auditory cortex. The binaural interaural time and interaural intensity difference cues were processed in the auditory cortex around 100-150 ms and the monaural spectral cues later around 200-250 ms.

Corticokinematic coherence (CKC) reflects coupling between magnetoencephalographic (MEG) signals and hand kinematics, mainly occurring at hand movement frequency (F0) and its first harmonic (F1). Since CKC can be obtained for both active and passive movements, it has been suggested to mainly reflect proprioceptive feedback to the primary sensorimotor (SM1) cortex. However, the directionality of the brain-kinematics coupling has not been previously assessed and was thus quantified in the present study by means of renormalized partial directed coherence (rPDC).MEG data were obtained from 15 subjects who performed right index-finger movements and whose finger was, in another session, passively moved, with or without tactile input. Four additional subjects underwent the same task with slowly varying movement pace, spanning the 1-5. Hz frequency range. The coupling between SM1 activity recorded with MEG and finger kinematics was assessed with coherence and rPDC.In all conditions, the afferent rPDC spectrum, which resembled the coherence spectrum, displayed higher values than the efferent rPDC spectrum. The afferent rPDC was 37% higher when tactile input was present, and it was at highest at F1 of the passive conditions; the efferent rPDC level did not differ between conditions. The apparent latency for the afferent input, estimated within the framework of the rPDC analysis, was 50-100. ms.The higher directional coupling between hand kinematics and SM1 activity in afferent than efferent direction strongly supports the view that CKC mainly reflects movement-related somatosensory proprioceptive afferent input to the contralateral SM1 cortex., SCOPUS: ar.j, info:eu-repo/semantics/published

The voice we most often hear is our own, and proper interaction between speaking and hearing is essential for both acquisition and performance of spoken language. Disturbed audiovocal interactions have been implicated in aphasia, stuttering, and schizophrenic voice hallucinations, but paradigms for a noninvasive assessment of auditory self‐monitoring of speaking and its possible dysfunctions are rare. Using magnetoencephalograpy we show here that self‐uttered syllables transiently activate the speaker's auditory cortex around 100 ms after voice onset. These phasic responses were delayed by 11 ms in the speech‐dominant left hemisphere relative to the right, whereas during listening to a replay of the same utterances the response latencies were symmetric. Moreover, the auditory cortices did not react to rare vowel changes interspersed randomly within a series of repetitively spoken vowels, in contrast to regular change‐related responses evoked 100–200 ms after replayed rare vowels. Thus, speaking primes the human auditory cortex at a millisecond time scale, dampening and delaying reactions to self‐produced “expected” sounds, more prominently in the speech‐dominant hemisphere. Such motor‐to‐sensory priming of early auditory cortex responses during voicing constitutes one element of speech self‐monitoring that could be compromised in central speech disorders. Hum. Brain Mapping 9:183–191, 2000. © 2000 Wiley‐Liss, Inc.

We describe a method to apply large-area vibrotactile stimuli, based on a vibrating balloon, on the palms of both hands during evoked response studies. Magnetoencephalographic (MEG) signals were recorded with a whole-scalp neuromagnetometer from six healthy subjects while they held their hands on a balloon which was made to vibrate by delivering tones to it through a loudspeaker and a tube. The 200 Hz stimuli, presented once every 1 or 2 s in separate sessions, elicited prominent and replicable somatosensory evoked fields (SEFs) and also auditory evoked fields (AEFs) due to the concomitant sound. Source modelling allowed reliable differentiation between bilateral activation of the primary somatosensory (SI) cortices (peaks at 46–61 ms after the stimulus onset) and of the supratemporal auditory cortices (peaks at 104–126 ms). These simple vibrotactile stimuli could be useful for rapid and reliable identification of the somatosensory and auditory cortices, for example in presurgical evaluation of children.

The planning and execution of movements involve areas of the cerebral cortex that are separated in their activity both temporally and spatially. However, the mechanism by which these areas combine to produce a co-ordinated movement is unknown. Studies of the activity of neurones in the sensorimotor cortex in monkeys and humans have shown synchronous oscillatory activity in the 15-30 Hz range (Murthy & Fetz, 1992, 1996a; Sanes & Donoghue, 1993; Stancak & Pfurtscheller, 1996; Baker et al. 1997; Donoghue et al. 1998). These synchronous oscillations have been suggested to link the disparate motor signals together in a manner analogous to the perceptual ‘binding’ of stimulus attributes in the visual cortex (Singer & Gray, 1995), where the observed neuronal synchronization is attributed to neurones that participate in the encoding of related information. Sanes & Donoghue (1993) and Murthy & Fetz (1996a) have shown that oscillations in monkey sensorimotor cortex are synchronous over large distances (up to 14 mm), suggesting the involvement of large neuronal populations. However, Murthy & Fetz (1996b) concluded that the oscillatory episodes had no consistent relationship with a variety of motor tasks, and suggested that rather than being involved directly in ‘binding’ during movement execution, the oscillations could be a neuronal correlate of attention during sensorimotor tasks. By contrast, a number of studies have shown that 15-30 Hz oscillations recorded over the sensorimotor cortex in man disappear during a self-paced finger movement, but reappear following movement completion (Jasper & Penfield, 1949; Gastaut, 1952; Salmelin & Hari, 1994; Stancak & Pfurtscheller, 1996). Baker et al. (1997) found that 15-30 Hz local field potential oscillations recorded in monkey primary motor cortex during a precision grip task showed a marked increase during the hold phase of the task. They suggested that the synchronous oscillations could reflect a mode of processing suited to the maintenance of a maintained grip. Oscillatory activity in motor cortex is coherent with the electromyogram (EMG) of active contralateral hand and forearm muscles (Conway et al. 1995; Salenius et al. 1996, 1997a; Baker et al. 1997). In the monkey, Baker et al. (1997) demonstrated that EMG-EMG coherence showed the same task dependence as the cortical signals, indicating that this coherence could be used to gain important insights into the temporal modulation of oscillatory activity at the cortical level. In this study we have extended this investigation to man, searching for modulation of coherent oscillatory activity during different precision grip tasks. We confirm the disappearance of oscillations during even a slow, low force movement, and further show a ‘rebound’ phenomenon whereby coherence is increased following a movement over and above that seen before movement. Using combined magnetoencephalogram (MEG) and EMG in one of the tasks studied, we show that at least part of the coherent oscillations seen in the periphery is likely to be generated in the primary motor cortex. A preliminary account of this work has been published previously (Kilner et al. 1998).

We recorded somatosensory evoked magnetic fields (SEFs) to left median nerve electric stimulation from seven healthy subjects. The stimulus intensity was varied in three sessions: sensory stimuli evoked a clear tactile sensation without any movement, weak motor stimuli exceeded the motor threshold, and strong motor stimuli caused a vigorous movement. Responses were modelled with sources in the contralateral primary somatosensory cortex (SI), the contralateral and ipsilateral secondary somatosensory cortices (SIIs) and the contralateral posterior parietal cortex (PPC). The amplitude of the 20 ms response from the SI cortex and the subjective magnitude estimations followed the stimulus intensity whereas signals from the three other areas saturated already at the level of the motor threshold. The results implicate differential roles for various somatosensory cortices in intensity coding.

Considerable changes take place in the number of cerebral neurons, synapses and axons during development, mainly as a result of competition between different neural activities [1–4]. Studies using animals suggest that when input from one sensory modality is deprived early in development, the affected neural structures have the potential to mediate functions for the remaining modalities [5–8]. We now show that similar potential exists in the human auditory system: vibrotactile stimuli, applied on the palm and fingers of a congenitally deaf adult, activated his auditory cortices. The recorded magnetoencephalographic (MEG) signals also indicated that the auditory cortices were able to discriminate between the applied 180 Hz and 250 Hz vibration frequencies. Our findings suggest that human cortical areas, normally subserving hearing, may process vibrotactile information in the congenitally deaf.

This is a whole head magnetoencephalographic (MEG) study of the neural processing of briefly presented images of human faces in 14 normal subjects. The experiments involved three tasks of increasing complexity, involving image categorisation, image comparison and the identification of emotion. The analyses were based on average responses to repeated stimuli in the different image categories. These averages were processed to give numerical measures of the power within defined regions and latency spans. The only statistically significant difference in these data between the response to faces and other images is in the right occipito-temporal channels at a latency of 140 ms. The face-specific response is largely independent of the task. Source modelling suggests an extended source in the ventral occipito-temporal region. The analysis supports the notions of both face-specificity and right hemisphere dominance for all image types at early latencies.

We describe patient E.P. who occasionally perceives a 'ghost' hand which copies the previous positions of the left hand with a 0.5-1 min time lag, but follows the movement patterns of the right hand. The symptoms started after an operation of a ruptured aneurysm, followed by an infarction of the right frontal lobe; E.P. also has a previously lesioned corpus callosum. Neuromagnetic recordings revealed that activity of the left secondary somatosensory cortex was strongly suppressed during the ghost arm percept, thereby providing an objective correlate for E.P.'s sensations. We conclude that simultaneous mental contents about body scheme may be based on neural information extracted at considerably different times, resulting in fragmentation of bodily awareness.

When your favourite athlete flops over the high-jump bar, you may twist your body in front of the TV screen. Such automatic motor facilitation, 'mirroring' or even overt imitation is not always appropriate. Here, we show, by monitoring motor-cortex brain rhythms with magnetoencephalography (MEG) in healthy adults, that viewing intermittent hand actions of another person, in addition to activation, phasically stabilizes the viewer's primary motor cortex, with the maximum of half a second after the onset of the seen movement. Such a stabilization was evident as enhanced cortex-muscle coherence at 16-20 Hz, despite signs of almost simultaneous suppression of rolandic rhythms of approximately 7 and 15 Hz as a sign of activation of the sensorimotor cortex. These findings suggest that inhibition suppresses motor output during viewing another person's actions, thereby withholding unintentional imitation. © 2014 The Authors., SCOPUS: ar.j, info:eu-repo/semantics/published

Motor information conveyed by viewing the kinematics of an agent's action helps to predict how the action will unfold. Still, how observed movement kinematics is processed in the brain remains to be clarified. Here, we used magnetoencephalography (MEG) to determine at which frequency and where in the brain, the neural activity is coupled with the kinematics of executed and observed motor actions. Whole-scalp MEG signals were recorded from 11 right-handed healthy adults while they were executing (Self) or observing (Other) similar goal-directed hand actions performed by an actor placed in front of them. Actions consisted of pinching with the right hand green foam-made pieces mixed in a heap with pieces of other colors placed on a table, and put them in a plastic pot on the right side of the heap. Subjects' and actor's forefinger movements were monitored with an accelerometer. The coherence between movement acceleration and MEG signals was computed at the sensor level. Then, cortical sources coherent with movement acceleration were identified with Dynamic Imaging of Coherent Sources. Statistically significant sensor-level coherence peaked at the movement frequency (F0) and its first harmonic (F1) in both movement conditions. Apart from visual cortices, statistically significant local maxima of coherence were observed in the right posterior superior temporal gyrus (F0), bilateral superior parietal lobule (F0 or F1) and primary sensorimotor cortex (F0 or F1) in both movement conditions. These results suggest that observing others' actions engages the viewer's brain in a similar kinematic-related manner as during own action execution. These findings bring new insights into how human brain activity covaries with essential features of observed movements of others.

Functional brain imaging studies have indicated that several cortical and subcortical areas active during actual motor performance are also active during imagination or mental rehearsal of movements. Recent evidence shows that the primary motor cortex may also be involved in motor imagery. Using whole-scalp magnetoencephalography, we monitored spontaneous and evoked activity of the somatomotor cortex after right median nerve stimuli in seven healthy right-handed subjects while they kinesthetically imagined or actually executed continuous finger movements. Manipulatory finger movements abolished the poststimulus 20-Hz activity of the motor cortex and markedly affected the somatosensory evoked response. Imagination of manipulatory finger movements attenuated the 20-Hz activity by 27% with respect to the rest level but had no effect on the somatosensory response. Slight constant stretching of the fingers suppressed the 20-Hz activity less than motor imagery. The smallest possible, kinesthetically just perceivable finger movements resulted in slightly stronger attenuation of 20-Hz activity than motor imagery did. The effects were observed in both hemispheres but predominantly contralateral to the performing hand. The attempt to execute manipulatory finger movements under experimentally induced ischemia causing paralysis of the hand also strongly suppressed 20-Hz activity but did not affect the somatosensory evoked response. The results indicate that the primary motor cortex is involved in motor imagery. Both imaginative and executive motor tasks appear to utilize the cortical circuitry generating the somatomotor 20-Hz signal.

The cortical mechanisms of auditory sensory memory were investigated by analysis of neuromagnetic evoked responses. The major deflection of the auditory evoked field (N100m) appears to comprise an early posterior component (N100mP) and a late anterior component (N100mA) which is sensitive to temporal factors. When pairs of identical sounds are presented at intervals less than about 250 msec, the second sound evokes N100mA with enhanced amplitude at a latency of about 150 msec. We suggest that N100mA may index the activity of two distinct processes in auditory sensory memory. Its recovery cycle may reflect the activity of a memory trace which, according to previous studies, can retain processed information about an auditory sequence for about 10 sec. The enhancement effect may reflect the activity of a temporal integration process, whose time constant is such that sensation persists for 200–300 msec after stimulus offset, and so serves as a short memory store. Sound sequences falling within this window of integration seem to be coded holistically as unitary events.

We studied cardiac contamination of magnetoencephalographic signals in eight healthy volunteers. The signals were recorded in a magnetically shielded room while the subject was sitting under a whole-scalp neuromagnetometer and were averaged time-locked to the R wave of the electrocardiogram. The maximum amplitude of the cardiac artifact varied between the subjects and was on average 130 fT/cm. The number of significantly contaminated channels was higher over the left than the right hemisphere. The electric and magnetic signals varied over time in the same way, implying that the artifacts are generated by cardiac currents, without any significant contribution from blood-flow-related pulsations or body movements. These artifacts may have a considerable effect on unaveraged data, i.e., recordings of spontaneous brain activity, and thus should be taken into account in the analysis.

Neuromagnetic responses to median nerve stimulation were studied in six healthy right-handed subjects. In the rest condition, only the right and left median nerves were alternately stimulated at the wrists. In two other conditions, continuous superficial tactile stimulation was concurrently applied to either the left or right hand. Tactile stimulation of palm and fingers of one hand enhanced, in the ipsilateral primary somatosensory cortex (SI), responses to median nerve stimulation of the other hand. This effect was stronger in the left than the right SI. Our data provide evidence in humans for the access of cutaneous information from the hands to ipsilateral SI, probably via excitatory transcallosal pathways. This interhemispheric information transfer may represent a neurophysiological substrate of somatosensory fusion between the hands.

To find out in which detail the kinematics of observed movements is represented in the viewer's brain, we searched for brain areas displaying coherent magnetoencephalographic (MEG) activity with observed repetitive hand movements. Whole-scalp MEG signals were recorded from 10 right-handed young adults who observed repetitive 3-Hz right-hand flexion-extension movements performed by the experimenter. The coherence between the subject's MEG signals and the experimenter's index-finger acceleration was computed to index the level of actor-observer coupling. The underlying cortical activity was identified with Dynamic Imaging of Coherent Sources. In all subjects, coherence spectra showed statistically significant peaks at movement frequency (F0) and its first harmonic (F1), strongest at visual areas. At F0, additional significant local coherence maxima, clearly distinct from the coherent visual areas, occurred in the primary motor (M1) cortices of both hemispheres and in the cerebellum (posterior vermis and hemispheres). Our results highlight the time-sensitive involvement of the M1 cortices and cerebellum in the kinematic representation of observed repetitive, non-goal directed motor actions.

Social interactions fill our everyday life and put strong demands on our brain function. However, the possibilities for studying the brain basis of social interaction are still technically limited, and even modern brain imaging studies of social cognition typically monitor just one participant at a time. We present here a method to connect and synchronize two faraway neuromagnetometers. With this method, two participants at two separate sites can interact with each other through a stable real-time audio connection with minimal delay and jitter. The magnetoencephalographic (MEG) and audio recordings of both laboratories are accurately synchronized for joint offline analysis. The concept can be extended to connecting multiple MEG devices around the world. As a proof of concept of the MEG-to-MEG link, we report the results of time-sensitive recordings of cortical evoked responses to sounds delivered at laboratories separated by 5 km.

We present a novel method, corticokinematic coherence (CKC), for functional mapping of the motor cortex by computing coherence between cortical magnetoencephalographic (MEG) signals and the kinematics of voluntary movements. Ten subjects performed self-paced flexion-extensions of the right-hand fingers at about 3 Hz, with a three-axis accelerometer attached to the index finger. Cross-correlogram and coherence spectra were computed between 306 MEG channels and the accelerometer signals. In all subjects, accelerometer and coherence spectra showed peaks around 3-5 Hz and 6-10 Hz, corresponding to the movement frequencies. The coherence was statistically significant (P0.05) in all subjects, with sources at the hand area of the primary motor cortex contralateral to the movement. CKC appears to be a promising and robust method for reliable and convenient functional mapping of the human motor cortex.

The deviant tones embedded in a sequence of standard tones elicit an event-related potential (ERP) component called mismatch negativity (MMN). Because MMN is partly overlapped by other ERP components at 100–200 msec latency (N1 and P2) and its shape varies, MMN peak latency and amplitude may be ambiguous. We used the difference area between the deviant and standard ERP to evaluate the age and interstimulus interval (ISI) dependence of MMN. Sequences of standard (85%) and deviant (15%) tones were presented to 27 normal subjects (age 18–85 years) using 1 sec and 3 sec ISIs and to 6 young subjects using an additional ISI of 5 sec. With this method MMN was clearly seen in 26 out of 27 healthy subjects (96.3%). MMN area was quite stable regardless of age with 1 sec ISI. With 3 sec ISI MMN area was significantly smaller in the old than in the young subjects. This may reflect the shortening of the sensory auditory memory trace with increasing age.

We studied the electrophysiological and neuropsychological effects of acute modulation of central noradrenergic (NA) transmission using a specific alpha 2-antagonist atipamezole (ATI) in sic healthy volunteers. ATI had effects on resting EEG, auditory event-related potentials and neuropsychological tests. Quantitative EEG revealed increased total power in frontal, parietal and temporo-occipital areas without significant changes in the mean or peak frequencies. Event-related potentials showed no effects on the active attention-related processing negativity or the passive mismatch negativity, but frontally recorded mean amplitude of target-P300 was decreased. Neuropsychological tests after ATI revealed improvement in Digit Span, more errors in Word Recognition task, and no effects on Moss spatial recognition task. In healthy subjects with intact NA systems and without any attention deficit, ATI produced evident NA overactivity. ATI decreased the spontaneous thalamocortical oscillation of EEG and improved focused attention (Digit Span). It impaired, however, more divided attention (decreased mean P300 amplitude, increased errors in Word Recognition).

The influence of an extremely-low-frequency (ELF) magnetic field on the bioelectrical processes of brain and performance was studied by EEG spectral analysis, auditory-evoked potentials (AEP), reaction time (RT) and target-deletion test (TDT). Fourteen volunteers were exposed for 15 min to an intermittent (1 s on/off) 45-Hz magnetic field at 1000 A/m (1.26 mT). Each person received one real and one sham exposure. Statistically significant increases in spectral power through alpha- and beta-bands, as well as in mean frequency of the EEG spectrum were observed after magnetic field exposure. Field-dependent changes of N100 were also revealed. No changes in the amplitudes or latencies of the earlier peaks were observed. No direct effects on RT, nor on TDT performance were seen. However, practice effects on RT (decrease of RT in the course of the test-sessions) seemed to be interrupted by exposure to the magnetic field.

The influence of sinusoidal 45-Hz magnetic fields on the brain functions of 20 volunteers was investigated in a double-blind study using spectral analysis of EEG and measurements of Omega potentials and reaction time (RT). The field strength was 1,000 A/m (1.26 mT) and the duration of exposure was 1 h. Ten volunteers were exposed to a continuous field and ten received an intermittent exposure (1 s on/l s off). Each person received one real and one sham exposure. One half of the volunteers got the real exposure first and the sham treatment after at least 24 h. For the rest, the sequence was inverse. The measurements of EEG, omega potentials and RT were performed before and after each exposure. Several statistically significant changes were observed, most of them after intermittent exposure. In the EEG, an increase of alpha (7.6-13.9 Hz) activity and a decrease of delta (1.5-3.9 Hz) activity were observed. Beta waves (14.2-20 Hz) increased in the frontal derivations as did the total power in occipital derivations. The mean and peak frequencies of EEG increased mainly in the frontal derivations. No direct effects on RT were seen. Learning to perform the RT test (decrease of RT in repeated trials), however, seemed to be affected by the exposure. The persons who received real exposure first learned more slowly than those who got sham exposure first. Further experiments are necessary to confirm the findings and for understanding the mechanisms of the effects.

We used magnetoencephalography to show that the human primary somatosensory (SI) cortex is activated by mere observation of touch. Somatosensory evoked fields were measured from adult human subjects in two conditions. First, the experimenter touched the subject's right hand with her index finger (Experienced touch). In the second condition, the experimenter touched her own hand in a similar manner (Observed touch). Minimum current estimates were computed across three consecutive 300-ms time windows (0-300, 300-600 and 600-900 ms) with respect to touch onset. During 'Experienced touch', as expected, the contralateral (left) SI cortex was strongly activated in the 0-300 ms time window. In the same time window, statistically significant activity also occurred in the ipsilateral SI, although it was only 2.5% of the strength of the contralateral activation; the ipsilateral activation continued in the 300-600 ms time window. During 'Observed touch', the left SI cortex was activated during the 300-600 ms interval; the activation strength was 7.5% of that during the significantly activated period (0-300 ms) of 'Experienced touch'. The results suggest that when people observe somebody else being touched, activation of their own somatosensory circuitry may contribute to understanding of the other person's somatosensory experience.

We present a novel method, corticokinetic coher ence, for functional motor mapping by computing coherence between cortical magnetoencephalographic (MEG) signals and the kinetics of voluntary movements. Six subjects performed during an MEG recording self-paced flexion–extensions of the right-hand fingers at about 3 Hz, with a 3-axis accelerometer attached to the index finger. Cumulant density and coherence spectra were computed between the MEG and accelerometer signals.