PubMed Health⌕ Search

Biomedical subjects

R Kristeva-Feige

Publications and source records attributed to R Kristeva-Feige.

14 recordsLinked to original sources
PubMed2000

Lateralization of movement-related potentials and the size of corpus callosum.

Using structural MRI and whole-head EEG recordings, we analyzed the correlations between the anatomical parameters of the corpus callosum and the hemispheric distribution of the cortical movement-related potentials during right finger and shoulder movements in nine right-handed men. Statistically significant correlation was found only in finger movements. A relatively large genu and the anterior part of the truncus of the corpus callosum correlated with enhanced pre-movement EEG potential over the ipsilateral M1/S1 area. The lateralization of the movement-related potentials correlates with the size of those callosal regions which connect the homologous areas of the primary sensorimotor and frontal cortices.

Adult↗
PubMed1999

The role of higher-order motor areas in voluntary movement as revealed by high-resolution EEG and fMRI.

In the human motor cortex structural and functional differences separate motor areas related to motor output from areas essentially involved in higher-order motor control. Little is known about the function of these higher-order motor areas during simple voluntary movement. We examined a simple finger flexion movement in six healthy subjects using a novel brain-imaging approach, integrating high-resolution EEG with the individual structural and functional MRI. Electrical source reconstruction was performed in respect to the individual brain morphology from MRI. Highly converging results from EEG and fMRI were obtained for both executive and higher-order motor areas. All subjects showed activation of the primary motor area (MI) and of the frontal medial wall motor areas. Two different types of medial wall activation were observed with both methods: Four of the subjects showed an anterior type of activation, and two of the subjects a posterior type of activation. In the former, activity started in the anterior cingulate motor area (CMA) and subsequently shifted its focus to the intermediate supplementary motor area (SMA). Approximately 120 ms before the movement started, the intermediate SMA showed a drop of source strength, and simultaneously MI showed an increase of source strength. In the posterior type, activation was restricted to the posterior SMA. Further, three of the subjects investigated showed activation in the inferior parietal lobe (IPL) starting during early movement preparation. In all subjects showing activation of higher-order motor areas (anterior CMA, intermediate SMA, IPL) these areas became active before the executive motor areas (MI and posterior SMA). We suggest that the early activation of the anterior CMA and the IPL may be related to attentional functions of these areas. Further, we argue that the intermediate part of the SMA triggers the actual motor act via the release of inhibition of the primary motor area. Our results demonstrate that a noninvasive, multimodal brain imaging technique can reveal individual cortical brain activity with high temporal and spatial resolution, independent of a priori physiological assumptions.

Adult↗
PubMed1998

A comparison between electric source localisation and fMRI during somatosensory stimulation.

The present study investigates the electric source localisation of somatosensory evoked potentials (SEPs) using high-resolution EEG (61 scalp electrodes) considering the individual brain morphology as obtained from magnetic resonance images (MRI). A comparison with the activation maps in fMRI under the same somatosensory stimulation paradigm was done. The somatosensory evoked potentials (SEPs) to electrical stimulation of the right median nerve were collected from the scalp of 8 healthy right-handed subjects. The source reconstruction for the 20 ms SEP component was performed by using a single moving dipole model as a source model and a spherical three-shell model as a head model. In 6 of the subjects fMRI was performed using the same electric stimulation of the right median nerve. The source location of the 20 ms SEP component was found to be within the postcentral gyrus. The fMRI activation maps were also located in the postcentral gyrus when using the same somatosensory stimulation paradigm. The appropriateness of using high-resolution EEG and fMRI in the functional localisation of the primary somatosensory cortex is discussed.

Adult↗
PubMed1998

Estimation of the accuracy of a surface matching technique for registration of EEG and MRI data.

OBJECTIVES: We developed a method to register EEG and MRI data used for the source reconstruction of electric brain activity. METHODS: The method is based on matching of the head surfaces as obtained by 3D scanning after the EEG recording, and by segmentation of MRI data. The registration accuracy was estimated by calculating the residual error of the surface matching and its intra-individual and inter-individual variability. In addition, the test-retest reliability concerning the transformation of electrode positions was studied, to estimate how inaccuracies resulting from the 3D scanning of the head surface translate into registration uncertainty. RESULTS: For 61 measurements, performed on 20 subjects, the average root mean square of the Euclidean distances between the 3D-scanned and the MRI-derived head surfaces amounted to 3.4 mm. An inter-individual standard deviation of 0.24 mm, and an intraindividual standard deviation of 0.003-0.31 mm proved a high inter- and intra-subject stability of the surface matching technique. The variation of transformation results when studying the test-retest reliability amounted to 1.6 mm on average. The maximum error of transformation was smaller than the diameter of the electrodes. CONCLUSIONS: The findings suggest that the surface matching technique is a precise method for determination of the transformation of electrode positions and MRI data into a single co-ordinate system and can successfully be used in a routine laboratory setting.

Brain↗
PubMed1997

Reproducibility and validity of electric source localisation with high-resolution electroencephalography.

The present study investigates the reproducibility and validity of the EEG source localisation of somatosensory evoked potentials (SEPs) using high-resolution EEG (61 scalp electrodes) and a source reconstruction on the basis of the individual brain morphology as obtained from magnetic resonance images (MRIs). The somatosensory evoked potentials (SEPs) to electrical stimulation of the right median nerve were repeatedly collected from the scalp of one healthy subject in 9 replications run on 9 different days. The source reconstruction for the 19 ms SEP component was performed by using a single moving dipole model as a source model. Two different head models were used: a spherical 3 shell model and a more realistically shaped 3 compartment model computed using the boundary element method (BEM). The source locations of the 19 ms SEP component were found to be highly reproducible using both head models: the mean standard deviation of the dipole locations was found to be 2.6 mm for the 3 shell model and 4 mm for the more realistically shaped head model. By projection into the individual MRI, the dipoles resulting from either head models were found to be located within the postcentral gyrus. The electric source locations were consistent with the maximum of the task-specific changes seen in a functional magnetic resonance imaging (fMRI) experiment when using the same somatosensory stimulation protocol.

Brain Mapping↗
PubMed1997

The bereitschaftspotential paradigm in investigating voluntary movement organization in humans using magnetoencephalography (MEG).

In 1965, Kornhuber and Deecke first described the bereitschaftspotential (BP), a paradigm for investigating the organization of voluntary movement in humans, using electroencephalography (EEG). This paradigm has since been used in many studies for investigating motor control in healthy humans and patients. Over the last years, the advantages of magnetoencephalography (MEG) have been applied to the BP paradigm by a number of researchers. The main advantage of magnetoencephalography over electroencephalography is that MEG has a higher localization accuracy. This is due to the fact that the different structures of the head (brain, liquor cerebrospinalis, skull and scalp) influence the magnetic fields less than the volume current flow that causes the EEG. Additionally, the MEG is reference free, so that the localization of sources with a given precision is easier for MEG than it is for EEG. The present protocol shows in detail how the bereitschaftspotential paradigm can be applied using MEG. Some additional paradigms for investigating motor plasticity, somatosensory gating, Parkinson disease, and the efference copy theory are suggested as well.

Adult↗
PubMed1996

Neuromagnetic study of movement-related changes in rhythmic brain activity.

Neuromagnetic fields from the left cerebral hemisphere of five healthy, right-handed subjects were investigated in a typical Bereitschaftspotential paradigm consisting of self-paced voluntary movement of the right index finger. To assess movement-related spectral changes of the spontaneous magnetoencephalogram. latency-dependent short-time spectra were obtained by Fourier analysis for each single trial. The number of trials in which the spectral estimate for a certain frequency and latency deviated from reference values was then transformed into a probabilistic relative power measure. A spectral power depression around 20 Hz was observed starting about 2.5 s before movement onset, followed by elevated power in the 20-35 Hz range starting about 500 ms after movement onset. Generally, the power increase differed from the prior depression in both spectrum and topography, suggesting different generating processes rather than just a 'rebound' effect of the idling rhythm generator. The time course and topography of spectral power changes are discussed in relation to the corresponding properties of the movement-related neuromagnetic fields (readiness field, motor field, and movement-evoked field I).

Adult↗
PubMed1996

Changes in movement-related brain activity during transient deafferentation: a neuromagnetic study.

Neuromagnetic fields from the left cerebral hemisphere of three healthy, right-handed subjects were investigated preceding and during voluntary index finger movements performed every 8-15 s under two different experimental conditions: before (stage A) and during (stage B) anesthetic block of median and radial nerves at the wrist. The anesthesia caused blocking of cutaneous receptors and some of the proprioreceptors from a wide hand area, including the entire index finger. However, the index finger movements were not impaired because the muscles participating in the task were not anesthetized. The magnetic signals of the brain sources corresponding to the main components of the movement-related neuromagnetic fields (motor field, MF and movement-evoked field I, MEFI) were mapped and localized using a moving dipole model. In the three investigated subjects the MF and MEFI dipole sources were stronger (30% on average) during stage B than during stage A. No significant changes in spatial coordinates of the estimated dipole locations between stages A and B were observed. This was true for both MF and MEFI. The results show that the MEFI reflects not only proprioceptive input from the periphery but cutaneous inputs as well. In this way the results support the view that cutaneous inputs play a specific role in the cortical control of movement.

Action Potentials↗
PubMed1996

A neuromagnetic study of movement-related somatosensory gating in the human brain.

Neuromagnetic fields from the left cerebral hemisphere of five healthy, right-handed subjects were investigated under three different experimental conditions: (1) electrical stimulation of the right index finger (task S); (2) voluntary movement of the same finger (M); (3) M+S condition, consisting of voluntary movements of the right index finger triggering the electrical stimulus at the very beginning of the electromyogram. The three conditions were administered in random order every 5-8 s. In addition, the task somatosensory evoked fields (task SEFs) gathered during condition (1) were compared with control SEFs recorded at the beginning of the experiment during rest. In all subjects the overlay of somatosensory stimulation on movement provoked a decrement in brain responsiveness (gating) as determined by the amplitude of gated SEFs. The latter was found as the difference between the neuromagnetic fields during M+S condition (overlaying of movement and sensory stimulation) minus neuromagnetic fields under M condition (M only). The gating effect was found to begin approximately 30 ms after movement onset, and to last for the whole period of the ongoing movement. The theoretical locus of gating was estimated by dipole localisation of the difference between task SEFs and gated SEFS using a moving dipole model. The site of the "early" gating effect (< 40 ms) was found to be more anteriorly located than the "later" (> 40 ms) gating effect. The task SEFs were found to be larger (significant after 30 ms) than the control SEFs elicited under the basal condition. The results are discussed with respect to timing, mechanism (centrifugal and centripetal), locus and selectivity of gating. In addition, the results are discussed with regard to clinical application (measuring attentional deficits in patients with impairments of higher mental functions and measuring gating deficits in patients with disturbed sensorimotor integration.

Adult↗
PubMed1995

Neuromagnetic fields of the brain evoked by voluntary movement and electrical stimulation of the index finger.

Neuromagnetic fields from the left cerebral hemisphere of five healthy, right-handed subjects were investigated under two different experimental conditions: (1) electrical stimulation of the right index finger (task somatosensory evoked fields, task SEF's), and (2) voluntary movement of the same finger referred to as movement-related fields, (MRFs). The two conditions were, performed in random order every 5-8 s. In addition, the task SEF's were compared to control SEF's recorded at the beginning of the experiment in order to find the optimal dewar position for localizing the central sulcus. The magnetic signals of the sources corresponding to the main components of the somatosensory evoked fields (early ones at 24 ms and at 34 ms, and late ones after 50 ms) and movement-related fields (motor field, MF and movement-evoked field I-MEF I) were mapped and localized by means of a moving dipole model. In four out of five subjects the MEF I dipoles were found to be located deeper than the early task SEF dipoles. In addition, all of the task SEF's components were found to exhibit larger amplitudes than the control SEF's components. The results are discussed in respect to the ability to selectively analyze contributions of mainly proprioceptive (area 3a) and cutaneous (area 3b) areas in the primary somatosensory cortex using magnetoencephalography. An additional finding of the study was that all of the task SEF's components were found to exhibit larger amplitudes than the control SEF's components.

Adult↗
PubMed1994

A neuromagnetic study of the functional organization of the sensorimotor cortex.

Movement-related neuromagnetic fields from eight healthy human subjects were investigated in a Bereitschaftspotential paradigm. The three conditions studied were right-sided mouth, index finger and foot movement. The neuromagnetic field patterns corresponding to the motor field and the movement-evoked field I were analysed using a moving dipole model. For both components a somatotopic organization was found: the estimated dipole locations for the mouth were more lateral and those for the foot more medial than the estimated dipole positions for the index finger movement. With regard to possible clinical applications, e.g. non-invasive mapping of the sensorimotor cortex and studies of plasticity of the motor function, the present results suggest that the investigation of movement-evoked field I for the index finger condition is most likely to yield further results.

Adult↗
PubMed1993

Oscillatory brain activity during a motor task.

Changes in spectral power in neuromagnetic fields associated with a manual task requiring a high level of sensorimotor integration (SMI) were investigated by analysing spontaneous, non-invasively recorded activity during motor preparation (WAIT), task performance (SMI), and control (REST) conditions in four healthy, right-handed human subjects. Neuromagnetic fields were recorded over the left sensorimotor cortex using a 37-channel instrument. In all subjects, a prominent narrow-band motor preparation rhythm centered near 19 Hz was consistently observed during the WAIT state. During SMI, mean relative increases in 26-30 Hz activity appeared in two of the subjects, paralleling gamma band enhancement recently observed during SMI in monkeys.

Adult↗