Biomedical subjects

Rumyana Kristeva

Publications and source records attributed to Rumyana Kristeva.

7 recordsLinked to original sources

PubMed2006

Gamma-range corticomuscular coherence during dynamic force output.

The beta-range synchronization between cortical motor and muscular activity as revealed by EEG/MEG-EMG coherence has been extensively investigated for steady-state motor output. However, there is a lack of information on the modulation of the corticomuscular coherence in conjunction with dynamic force output. We addressed this question comparing the EEG-EMG coherence and the cortical motor spectral power in eight healthy subjects in a visuomotor task, in which the subjects exerted a steady-state or periodically modulated dynamic isometric force output with their right-index finger to keep a visual cursor within a target zone. In the static condition, significant coherence was confined to the beta-range. In the dynamic condition, the most distinct coherence occurred in the gamma-range and the significant beta-range coherence was strikingly reduced. The cortical motor power in the beta-range during dynamic force output was decreased, whereas the power in the gamma-range remained without significant change. We conclude that during dynamic force the corticospinal oscillation mode of the sensorimotor system shifts towards higher (principally gamma) frequencies for the rapid integration of the visual and somatosensory information required to produce the appropriate motor command.

Adult↗

PubMed2006

Oscillatory cortical activity during a motor task in a deafferented patient.

Little is known about the influence of the afferent peripheral feedback on the sensorimotor cortex activation. To answer this open question we investigated the alpha and beta band task-related spectral power decreases (TRPow) in the deafferented patient G.L. and compared the results to those of six healthy subjects. The patient has been deafferented up to the nose for 24 years but her motor fibers are unaffected and she can perform complex motor tasks under visual control. We recorded EEG (58 scalp positions) as well as the exerted force during a visuomotor task. The subjects had to maintain in precision grip an isometric force at 15% of the maximal voluntary contraction. In the patient we found a significantly higher alpha band spectral power during rest and larger alpha TRPow decreases during the motor task when compared to the healthy subjects' data. In contrast, we did not observe any significant differences between patient and controls for the beta band TRPow. The results indicate an altered functional alpha band network state in the patient, probably due to the chronic deafferentation leading to a deep 'idling' state of the contralateral sensorimotor area.

Adult↗

PubMed2006

Handwriting performance in the absence of visual control in writer's cramp patients: initial observations.

BACKGROUND: The present study was aimed at investigating the writing parameters of writer's cramp patients and control subjects during handwriting of a test sentence in the absence of visual control. METHODS: Eight right-handed patients with writer's cramp and eight healthy volunteers as age-matched control subjects participated in the study. The experimental task consisted in writing a test sentence repeatedly for fifty times on a pressure-sensitive digital board. The subject did not have visual control on his handwriting. The writing performance was stored on a PC and analyzed off-line. RESULTS: During handwriting all patients developed a typical dystonic limb posture and reported an increase in muscular tension along the experimental session. The patients were significantly slower than the controls, with lower mean vertical pressure of the pen tip on the paper and they could not reach the endmost letter of the sentence in the given time window. No other handwriting parameter differences were found between the two groups. CONCLUSION: Our findings indicate that during writing in the absence of visual feedback writer's cramp patients are slower and could not reach the endmost letter of the test sentence, but their level of automatization is not impaired and writer's cramp handwriting parameters are similar to those of the controls except for even lower vertical pressure of the pen tip on the paper, which is probably due to a changed strategy in such experimental conditions.

Adult↗

PubMed2006

Is the movement-evoked potential mandatory for movement execution? A high-resolution EEG study in a deafferented patient.

During simple self-paced index finger flexion with and without visual feedback of the finger, we compared the movement-evoked potentials of the completely deafferented patient GL with those of 7 age-matched healthy subjects. EEG was recorded from 58 scalp positions, together with the electromyogram (EMG) from the first dorsal interosseous muscle and the movement trace. We analyzed the movement parameters and the contralateral movement-evoked potential and its source. The patient performed the voluntary movements almost as well as the controls in spite of her lack of sensory information from the periphery. In contrast, the movement-evoked potential was observed only in the controls and not in the patient. These findings clearly demonstrate that the movement-evoked potential reflects cutaneous and proprioceptive feedback from the moving part of the body. They also indicate that in absence of sensory peripheral input the motor control switches from an internal "sensory feedback-driven" to a "feedforward" mode. The role of the sensory feedback in updating the internal models and of the movement-evoked potential as a possible cortical correlate of motor awareness is discussed.

Biomechanical Phenomena↗

PubMed2005

Electroencephalographic spectral power in writer's cramp patients: evidence for motor cortex malfunctioning during the cramp.

We investigated cortical activation as reflected in task-related spectral power (TRPow) changes in 8 writer's cramp patients during writing on a digital board and during isometric contraction and compared them to those of 8 age-matched healthy subjects. Scalp EEG was recorded over the contralateral primary sensorimotor area (SM1(c)), and from the ipsilateral sensorimotor area (SM1(i)). The electromyogram (EMG) was recorded from the Extensor Digitorum Communis (Extensor), Flexor Digitorum Superficialis (Flexor), and First Dorsal Interosseous (FDI) muscles. We analyzed (1) handwriting performance, (2) changes in the TRPow confined to alpha and beta band, and (3) the EMG spectral power during both tasks, writing and isometric contraction. During writing, all patients developed writer's cramp. The handwriting in writer's cramp patients was associated with significantly less reduction of the beta-range TRPow and lower frequency of the TRPow reduction compared to controls. No significant differences between patients and controls for the alpha band TRPow reduction during handwriting were observed. During writing, the patients showed higher EMG spectral power than the controls but this difference was at the border of significance. The present results indicate disorder in the motor execution system, in writer's cramp patients, associated with impaired functional beta-network state of the contra- and ipsilateral sensorimotor cortices, most probably due to inadequate modulation of the intracortical inhibition associated with writing.

Adult↗

PubMed2004

Cortico-muscular coupling in a patient with postural myoclonus.

We investigated the cortico-muscular coherence in a patient with posturally induced cortically originating negative myoclonus. We recorded simultaneously 50 channels EEG and EMG from quadriceps and biceps femoris muscles of the left upper leg. Three experimental conditions were investigated with the patient in a seated position: (i) recording during rest (Rest), (ii) recording while the patient had to hold his left leg horizontally stretched out (Postural), and (iii) recording while the patient had to hold his left leg horizontally stretched out against a vertical force (Postural against force). Coherence, phase difference and cumulant density were computed as indicators for cortico-muscular coupling. The cortical component preceding the silent period was shown by averaging and was reconstructed. During postural and postural against force conditions, the EEG over the vertex was significantly coherent with EMG, in alpha (7-15 Hz) and beta range (15-30 Hz). The strongest coherence peak was at 21 Hz. No high-frequency coherence was observed. The phase difference and the cumulant density estimate corresponded to a 32 ms time lag between motor cortex and muscles, with EEG leading. The broadening of the coherence spectrum at which the motor cortex drives the muscles together with the excessive coherence levels and the giant SEP could reflect the hyperexcitability of the sensorimotor cortex. The frequency content of the coherence may be characteristic for this type of myoclonus. The results lend support to the view that the frequency analysis may have some diagnostic potential in cortical myoclonus.

Aged↗

PubMed2003

Activation of cortical areas in music execution and imagining: a high-resolution EEG study.

Neuroimaging studies have shown that execution of a musical sequence on an instrument activates bilateral frontal opercular regions, in addition to bilateral sensorimotor and supplementary motor areas. During imagining activation of the same areas without primary sensorimotor areas was shown. We recorded EEG from 58 scalp positions to investigate the temporal sequence and the time course of activation of these areas while violin players prepared to execute, executed, prepared to imagine, or imagined a musical sequence on a violin. During the preparation for the sequence in three of seven musicians investigated the bilateral frontal opercular regions became active earlier than the motor areas and in one of them simultaneously with the motor areas. In two of the musicians a rather variable pattern of activation was observed. The frontal opercular regions were also strongly involved throughout the period of music execution or imagining. The supplementary motor area was involved in both preparation for the sequence and during execution and imagining of the sequence. The left primary sensorimotor area was involved in the preparation and termination of the musical sequence for both execution and imagining. The right sensorimotor area was strongly involved in the preparation for and during the execution of the sequence. We conclude that the bilateral frontal opercular regions are crucial in both preparation for and during music execution and imagining. They may have "mirror neurone" properties that underlie observation or imagining of one's own performance. The motor areas are differentially activated during the preparation and execution or imagining the sequence.

Adult↗