Biomedical subjects

S Salenius

Publications and source records attributed to S Salenius.

At least 19 recordsLinked to original sources

PubMed2001

Involvement of the sensorimotor cortex in physiological force and action tremor.

Whole scalp magnetoencephalography (MEG) signals were recorded in 10 healthy subjects simultaneously with the surface electromyogram (EMG) of the contralateral forearm extensor muscles during isometric contraction and phasic movement of the wrist. In eight subjects, coherence and time domain analyses demonstrated correspondence between the MEG signal, originating near or in the hand region of the motor cortex, and the 6-12 Hz EMG recorded during isometric postural contractions. In contrast, we found little evidence for correspondence between the contralateral EMG and the MEG recorded over the Rolandic region during phasic movements. We conclude that the sensorimotor cortex is differentially involved in physiological force and action tremor at the wrist.

Adolescent↗

PubMed2001

Three-dimensional integration of brain anatomy and function to facilitate intraoperative navigation around the sensorimotor strip.

We studied 12 patients with brain tumors in the vicinity of the sensorimotor region to provide a preoperative three-dimensional visualization of the functional anatomy of the rolandic cortex. We also evaluated the role of cortex-muscle coherence analysis and anatomical landmarks in identifying the sensorimotor cortex. The functional landmarks were based on neuromagnetic recordings with a whole-scalp magnetometer, coregistred with magnetic resonance images. Evoked fields to median and tibial nerve and lip stimuli were recorded to identify hand, foot and face representations in the somatosensory cortex. Oscillatory cortical activity, coherent with surface electromyogram during isometric muscle contraction, was analyzed to reveal the hand and foot representations in the precentral motor cortex. The central sulcus was identified also by available anatomical landmarks. The source locations, calculated from the neuromagnetic data, were displayed on 3-D surface reconstructions of the individual brains, including the veins. The preoperative data were verified during awake craniotomy by cortical stimulation in 7 patients and by cortical somatosensory evoked potentials in 5 patients. Sources of somatosensory evoked fields identified correctly the postcentral gyrus in all patients. Useful corroborative information was obtained from anatomical landmarks in 11 patients and from cortex-muscle correlograms in 8 patients. The preoperative visualization of the functional anatomy of the sensorimotor strip assisted in designing the operational strategy, facilitated orientation of the neurosurgeon during the operation, and speeded up the selection of sites for intraoperative stimulation or mapping, thereby helping to prevent damage of eloquent brain areas during surgery.

Adult↗

PubMed2001

Cortical representation of sign language: comparison of deaf signers and hearing non-signers.

Numerous studies have demonstrated activation of the classical left-hemisphere language areas when native signers process sign language. More recently, specific sign language-related processing has been suggested to occur in homologous areas of the right hemisphere as well. We now show that these cortical areas are also activated in hearing non-signers during passive viewing of signs that for them are linguistically meaningless. Neuromagnetic activity was stronger in deaf signers than in hearing non-signers in the region of the right superior temporal sulcus and the left dorsal premotor cortex, probably reflecting familiarity and linguistic meaningfulness of the observed movement sequences. In contrast, the right superior parietal lobule, the mesial parieto-occipital region, and the mesial paracentral lobule were more strongly activated in hearing non-signers, apparently reflecting active visuomotor encoding of complex unfamiliar movement sequences.

Adult↗

PubMed2000

Human cortical muscle coherence is directly related to specific motor parameters.

Cortical oscillations have been the target of many recent investigations, because it has been proposed that they could function to solve the "binding" problem. In the motor cortex, oscillatory activity has been reported at a variety of frequencies between approximately 4 and approximately 60 Hz. Previous research has shown that 15-30 Hz oscillatory activity in the primary motor cortex is coherent or phase locked to activity in contralateral hand and forearm muscles during isometric contractions. However, the function of this oscillatory activity remains unclear. Is it simply an epiphenomenon or is it related to specific motor parameters? In this study, we investigated task-dependent modulation in coherence between motor cortex and hand muscles during precision grip tasks. Twelve right-handed subjects used index finger and thumb to grip two levers that were under robotic control. Each lever was fitted with a sensitive force gauge. Subjects received visual feedback of lever force levels and were instructed to keep them within target boxes throughout each trial. Surface EMGs were recorded from four hand and forearm muscles, and magnetoencephalography (MEG) was recorded using a 306 channel neuromagnetometer. All subjects showed significant levels of coherence (0.086-0.599) between MEG and muscle in the 15-30 Hz range. Coherence was significantly smaller when the task was performed under an isometric condition (levers fixed) compared with a compliant condition in which subjects moved the levers against a spring-like load. Furthermore, there was a positive, significant relationship between the level of coherence and the degree of lever compliance. These results argue in favor of coherence between cortex and muscle being related to specific parameters of hand motor function.

Adult↗

PubMed2000

Cortico-muscular synchronization during isometric muscle contraction in humans as revealed by magnetoencephalography.

Magnetoencephalographic (MEG) and electromyographic (EMG) signals were recorded from six subjects during isometric contraction of four different muscles. Cortical sources were located from the MEG signal which was averaged time-locked to the onset of motor unit potentials. A spatial filtering algorithm was used to estimate the source activity. Sources were found in the primary motor cortex (M1) contralateral to the contracted muscle. Significant coherence between rectified EMG and M1 activity was seen in the 20 Hz frequency range in all subjects. Interactions between the motor cortex and spinal motoneuron pool were investigated by separately studying the non-stationary phase and amplitude dynamics of M1 and EMG signals. Delays between M1 and EMG signals, computed from their phase difference, were found to be in agreement with conduction times from the primary motor cortex to the respective muscle. The time-dependent cortico-muscular phase synchronization was found to be correlated with the time course of both M1 and EMG signals. The findings demonstrate that the coupling between the primary motor cortex and motoneuron pool is at least partly due to phase synchronization of 20 Hz oscillations which varies over time. Furthermore, the consistent phase lag between M1 and EMG signals, compatible with conduction time between M1 and the respective muscle with the M1 activity preceding EMG activity, supports the conjecture that the motor cortex drives the motoneuron pool.

Adult↗

PubMed2000

Electrocorticogram-electromyogram coherence during isometric contraction of hand muscle in human.

OBJECTIVE: To clarify how the primary sensorimotor and supplementary motor areas are involved in the generation of the rhythmicity of electromyogram (EMG) activity during continuous muscle contraction. METHOD: We analyzed the coherence between subdurally recorded cortical electroencephalograms (EEG) and EMGs of the contralateral wrist extensor muscle during continuous isometric contraction in 8 patients with medically intractable epilepsy. RESULTS: In all subjects, a significant coherence between the primary motor area (M1) and EMG was observed at the peak frequency of 15+/-3 Hz (means+/-SD). In the primary somatosensory area (S1) of 7 subjects and the supplementary motor area proper (SMA proper) of 4 subjects, significant coherence with EMG was observed at 12+/-5 and 15+/-4 Hz, respectively. The time lags revealed by cross-correlogram were 10+/-3, 7+/-1 and 22+/-8 ms in the M1, S1 and SMA proper, respectively, with the EMG lagging in all areas. CONCLUSION: These findings suggest that the rhythmic activity in the SMA proper, as well as in the S1 and M1, is related to the generation of the rhythmicity of EMG activity.

Electromyography↗

PubMed2000

Characteristics of the human contra- versus ipsilateral SII cortex.

OBJECTIVES: In order to study the interaction between left- and right-sided stimuli on the activation of cortical somatosensory areas, we recorded somatosensory evoked magnetic fields (SEFs) from 8 healthy subjects with a 122 channel whole-scalp SQUID gradiometer. METHODS: Right and left median nerves were stimulated either alternately within the same run, with interstimulus intervals (ISIs) of 1.5 and 3 s, or separately in different runs with a 3 s ISI. In all conditions 4 cortical source areas were activated: the contralateral primary somatosensory cortex (SI), the contra- and ipsilateral secondary somatosensory cortices (SII) and the contralateral posterior parietal cortex (PPC). RESULTS: The earliest activity starting at 20 ms was generated solely in the SI cortex, whereas longer-latency activity was detected from all 4 source areas. The mean peak latencies for SII responses were 86-96 ms for contralateral and 94-97 ms for ipsilateral stimuli. However, the activation of right and left SII areas started at 61+/-3 and 62+/-3 ms to contralateral stimuli and at 66+/-2 and 63+/-2 ms to ipsilateral stimuli, suggesting a simultaneous commencing of activation of the SII areas. PPC sources were activated between 70 and 110 ms in different subjects. The 1.5 s ISI alternating stimuli elicited smaller SII responses than the 3 s ISI non-alternating stimuli, suggesting that a considerable part of the neural population in SII responds both to contra- and ipsilateral stimuli. The earliest SI responses did not differ between the two conditions. There were no significant differences in source locations of SII responses to ipsi- and contralateral stimuli in either hemisphere. Subaverages of the responses in sets of 30 responses revealed that amplitudes of the SII responses gradually attenuated during repetitive stimulation, whereas the amplitudes of the SI responses were not changed. CONCLUSIONS: The present results implicate that ipsi- and contralateral SII receive simultaneous input, and that a large part of SII neurons responds both to contra- and ipsilateral stimulation. The present data also highlight the different behavior of SI and SII cortices to repetitive stimuli.

Adult↗

PubMed1999

Task-dependent modulation of 15-30 Hz coherence between rectified EMGs from human hand and forearm muscles.

1. Recent reports have shown task-related changes in oscillatory activity in the 15-30 Hz range in the sensorimotor cortex of human subjects and monkeys during skilled hand movements. In the monkey these oscillations have been shown to be coherent with oscillatory activity in the electromyographic activity of hand and forearm muscles. 2. In this study we investigated the modulation of oscillations in the electromyogram (EMG) of human volunteers during tasks requiring precision grip of two spring-loaded levers. 3. Two tasks were investigated: in the 'hold' task, subjects were required to maintain a steady grip force (ca 2.1 N or 2.6 N) for 8 s. In the 'ramp' task, there was an initial hold period for 3 s (force ca 2.1 N) followed by a linear increase in grip force over a 2 s period. The task ended with a further steady hold for 3 s at the higher force level (ca 2.6 N). 4. Surface EMGs were recorded from five hand and forearm muscles in 12 subjects. The coherence of oscillatory activity was calculated between each muscle pair. Frequencies between 1 and 100 Hz were analysed. 5. Each subject showed a peak in the coherence spectra in the 15-30 Hz bandwidth during the hold task. This coherence was absent during the initial movement of the levers. During the ramp task the coherence in the 15-30 Hz range was also significantly reduced during the movement phase, and significantly increased during the second hold period, relative to the initial hold. 6. There was coherence between the simultaneously recorded magnetoencephalogram (MEG) and EMG during steady grip in the hold task; this coherence disappeared during the initial lever movement. Using a single equivalent current dipole source model, the coherent cortical activity was localized to the hand region of the contralateral motor cortex. This suggests that the EMG-EMG coherence was, therefore, at least in part, of cortical origin. 7. The results are discussed in terms of a possible role for synchrony in the efficient recruitment of motor units during maintained grip.

Adult↗

PubMed1999

Rhythmical corticomotor communication.

Recent non-invasive human studies show that rhythmic oscillatory activity of the motor cortex and the firing of motor units of the muscle are coherent during isometric contraction, with peak frequencies around 20 Hz or 40 Hz, depending on the contraction strength. The cortical signals precede the motor unit firing and appear to reflect modulation of the common central drive to the spinal motoneuron pool. The rhythmic modulation may form a tool for efficient driving of motor units but we express some reservations about the assumed binding and attention-related roles of the rolandic brain rhythms. The cortex-muscle coherence is of interest for understanding of cortical control of voluntary movements and the pathophysiology of various motor disorders, as well as for unravelling the functional significance of cortical rhythms.

Animals↗

PubMed1999

'Human see, human do' cortex.

Recent magnetoencephalographic (MEG) recordings support the existence of a system for matching observed and executed actions in humans and suggest that this system involves even the primary motor cortex.

Brain Mapping↗

PubMed1998

Activation of human primary motor cortex during action observation: a neuromagnetic study.

The monkey premotor cortex contains neurons that discharge during action execution and during observation of actions made by others. Transcranial magnetic stimulation experiments suggest that a similar observation/execution matching system also is present in humans. We recorded neuromagnetic oscillatory activity of the human precentral cortex from 10 healthy volunteers while (i) they had no task to perform, (ii) they were manipulating a small object, and (iii) they were observing another individual performing the same task. The left and right median nerves were stimulated alternately (interstimulus interval, 1.5 s) at intensities exceeding motor threshold, and the poststimulus rebound of the rolandic 15- to 25-Hz activity was quantified. In agreement with previous studies, the rebound was strongly suppressed bilaterally during object manipulation. Most interestingly, the rebound also was significantly diminished during action observation (31-46% of the suppression during object manipulation). Control experiments, in which subjects were instructed to observe stationary or moving stimuli, confirmed the specificity of the suppression effect. Because the recorded 15- to 25-Hz activity is known to originate mainly in the precentral motor cortex, we concluded that the human primary motor cortex is activated during observation as well as execution of motor tasks. These findings have implications for a better understanding of the machinery underlying action recognition in humans.

Animals↗

PubMed1998

Cortical correlate of the Piper rhythm in humans.

Cortical correlate of the Piper rhythm in humans. J. Neurophysiol. 80: 2911-2917, 1998. The electromyogram (EMG) of healthy humans demonstrates a tendency to rhythmic oscillations at around 40 Hz (the Piper rhythm) during strong voluntary contraction. Why motor units should discharge synchronously locked to such a high-frequency is unclear. We recorded whole scalp magnetoencephalographic (MEG) signals simultaneously with surface EMG from 10 healthy subjects. In eight subjects, coherence and time domain analyses demonstrated correspondence between the MEG signal, originating near or in the hand region of the motor cortex, and the 35- to 60-Hz EMG recorded during repeated maximal isometric contractions of the contralateral forearm extensor muscles. Three of these subjects also showed similar coherence during isometric contractions of moderate strength and slow extension movements of the wrist. In addition, coherence and time domain analyses demonstrated correspondence between the MEG signals originating near or in the foot area of the motor cortex and EMG recorded during repeated maximal isometric contractions of the contralateral tibialis anterior muscle in the 30- to 60-Hz range. Most important, the frequency at the peak of the coherence spectrum differed between forearm and leg by as much as 10 Hz in the same subject. In contrast, the peak of the coherence spectrum occurred during sustained weak contraction in the 20- to 30-Hz range similarly for both forearm and foot. The lag between EMG and MEG activity in the leg was approximately 15 ms greater than that seen in the forearm, an interval appropriate for conduction in fast pyramidal pathways. It is concluded that the Piper rhythm in muscle may be driven by a comparable oscillatory activity in the contralateral motor cortex. This cortical rhythmicity can be picked up in several types of movement and seems distinct from the 20- to 30-Hz rhythmicity recorded during weak sustained contractions.

Adult↗

PubMed1997

Modulation of human cortical rolandic rhythms during natural sensorimotor tasks.

We studied modulation of cortical neuromagnetic rhythms in association with left and right median nerve stimulation, during rest, finger movements, and passive tactile hand stimulation, in seven healthy, right-handed adults. In the rest condition, the amplitude of the rhythmic sensorimotor activity decreased immediately after the median nerve stimuli and increased above the prestimulus level within 0.4 s afterward, especially in the 7- to 25-Hz band. The rebound occurred 100-300 ms earlier for 20 (7-15)-than for 10 (15-25)-Hz activity. Suppressions and rebounds were strongest in the contralateral sensorimotor hand area for the 20-Hz, but not for the 10-Hz, activity. The maximum rebound was on average 22-34% stronger in the left than in the right hemisphere. Active exploration of objects abolished rebounds of both 10- and 20-Hz signals in the contralateral hemisphere and markedly diminished them ipsilaterally. Finger movements without touching an object and passive tactile stimulation produced a weaker effect. The sensorimotor rhythms thus show a characteristic suppression and subsequent rebound after electrical median nerve stimulation. The rebound is left-hemisphere dominant in right-handed subjects and its suppression reveals bilateral cortical activation during both motor tasks and passive tactile stimulation, especially for explorative finger movements.

Adult↗

PubMed1997

Activation of human V5 complex and rolandic regions in association with moving visual stimuli.

We recorded magnetoencephalographic responses from seven healthy humans during the presentation of stationary and rotating radial gratings. Rotations lasting 1 s evoked movement-specific sustained activity in the parieto-occipitotemporal border area, in agreement with the activation of the V5 complex specialized for the analysis of movement. The source areas of the movement-specific sustained fields were transiently active 100-130 ms after the onsets of both rotating and stationary stimuli, suggesting that movement-related cortical areas respond to any transient changes in the visual environment. Transients were evoked also in other brain areas 60-200 ms after onsets of both stimuli. Four subjects displayed additional motion-related sustained activity in the rolandic region. Sustained activity continued after the stimulus movement in several subjects during perception of the movement aftereffect. The transient activity may evoke visual attention while sustained activity of the V5 complex may be related to the conscious perception of movement.

Adult↗

PubMed1997

Involvement of primary motor cortex in motor imagery: a neuromagnetic study.

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.

Adult↗

PubMed1997

Magnetoencephalographic cortical rhythms.

We have characterized the magnetic 10- and 20-Hz rhythms recorded with a whole-scalp neuromagnetometer during different conditions. Sources of the posterior 10-Hz (alpha) rhythm clustered mainly around the parieto-occipital sulcus and, to a lesser extent, around the calcarine sulci, with several generators. Temporal Spectral Evolution (TSE) analysis, used to follow event-related changes in the different frequency bands, showed strong dampening of the alpha within 200 ms after the appearance of a visual stimulus and also during visual imagery. Suppression was often followed by a rebound above the baseline level. The rolandic mu rhythm consisted of 10- and 20-Hz components with different reactivity and source locations. The 10-Hz component seems to be mainly somatosensory in origin whereas the 20-Hz signal also receives contributions from the motor cortex, and even shows 'motorotopy' in its reactivity: the source locations depend in a somatotopical manner on the site of the moving body part. The frequency composition of the posterior spontaneous activity was disturbed in patients with small infarcts of the medial thalamus. It is shown with simulations that a surprisingly small number of synchronized cortical neurons could generate the major part of the recorded oscillatory signal. Finally, some clarifications are suggested to the terminology of brain rhythms.

Animals↗

PubMed1997

Cortical control of human motoneuron firing during isometric contraction.

We recorded whole scalp magnetoencephalographic (MEG) signals simultaneously with the surface electromyogram from upper and lower limb muscles of six healthy right-handed adults during voluntary isometric contraction. The 15- to 33-Hz MEG signals, originating from the anterior bank of the central sulcus, i.e., the primary motor cortex, were coherent with motor unit firing in all subjects and for all muscles. The coherent cortical rhythms originated in the hand motor area for upper limb muscles (1st dorsal interosseus, extensor indicis proprius, and biceps brachii) and close to the foot area for lower limb muscles (flexor hallucis brevis). The sites of origin corresponding to different upper limb muscles did not differ significantly. The cortical signals preceded motor unit firing by 12-53 ms. The lags were shortest for the biceps brachii and increased systematically with increasing corticomuscular distance. We suggest that the motor cortex drives the spinal motoneuronal pool during sustained contractions, with the observed cortical rhythmic activity influencing the timing of efferent commands. The cortical rhythms could be related to motor binding, but the rhythmic output may also serve to optimize motor cortex output during isometric contractions.

Adult↗

PubMed1996

Human cortical 40 Hz rhythm is closely related to EMG rhythmicity.

We recorded cortical neuromagnetic rhythms during self-paced index-finger movements from a subject previously reported to show prominent 40 Hz electroencephalographic activity during motor behavior. The 10 and 20 Hz components of the rolandic mu rhythm were bilaterally suppressed, whereas the contralateral 40 Hz (35-41 Hz) activity was slightly enhanced before both fast and slow movements and strongly enhanced during slow movements. The 40 Hz rhythm originated mainly in the hand motor cortex and was clearly correlated with the rhythmicity of the electromyogram from the extensor muscles, with a systematic time lag. In this subject motor preparation, and especially control of finger movements, may thus be associated with enhanced cortical rhythms near 40 Hz. The coherence of these rhythms with muscular firing patterns likely reflects communication between the sensorimotor cortex and the motor units.

Adult↗