Biomedical subjects

Bettina Pollok

Publications and source records attributed to Bettina Pollok.

18 recordsLinked to original sources

PubMed2006

Asymmetry of interhemispheric interaction in left-handed subjects.

In right-handed subjects the execution of a simple finger-tapping task is associated with an asymmetry of interhemispheric interaction, probably suggesting that the dominant left hemisphere inhibits the right one. The present study investigated the left-handed subjects in order to elucidate whether this asymmetry is related to handedness. Nineteen healthy subjects performed unimanual left, right, and bimanual auditorily paced finger-tapping tasks while neuromagnetic activity was recorded with a 122-channel whole-head neuromagnetometer (MEG). Simultaneously, we recorded activity of the first dorsal interosseus (FDI) muscle of both hands. By using the analysis tool dynamic imaging of coherent sources (DICS), oscillatory activity at alpha as well as at beta frequency within the primary sensorimotor (S1/M1) and premotor (PMC) cortex was localized. As expected, we observed oscillatory coupling between S1/M1 and PMC contralateral to the moving hand. Furthermore, coupling between left PMC and bilateral S1/M1 occurred in each movement condition, suggesting that the left PMC modulates neural activity in bilateral primary sensorimotor cortices independent of the moving hand. Coupling between bilateral S1/M1 occurred more frequently and significantly stronger during the right hand condition. This result demonstrates the same interhemispheric coupling pattern as in right-handed subjects, suggesting that the asymmetry of this interaction is not due to hand dominance. A specialization of the left premotor cortex either for superior motor control per se or for the execution of sequential tasks might account for these results.

Adult↗

PubMed2006

Oscillatory activity reflects the excitability of the human somatosensory system.

The neuronal activity of the resting human brain is dominated by spontaneous oscillations in primary sensory and motor areas. These oscillations are thought to reflect the excitability of sensory and motor systems that can be modulated according to the actual behavioral demands. However, so far, evidence for an association between oscillatory activity and excitability has been inconsistent. Here, we used magnetoencephalography to reinvestigate the relationship between oscillatory activity and excitability in the somatosensory system on a single trial basis. Brief painful stimuli were applied to relate pain-induced suppressions of oscillatory activity to pain-induced increases in excitability. The analysis reveals a significant negative correlation between sensorimotor oscillatory activity, particularly in the alpha-band, and excitability of somatosensory cortices. Oscillatory activity outside the somatosensory system did not correlate with somatosensory excitability. These findings demonstrate that modulations of sensorimotor oscillatory activity specifically reflect modulations in excitability of the somatosensory system and thus provide direct evidence for the basic tenet of an association between oscillatory activity and cortical excitability.

Adult↗

PubMed2006

Synchronized brain network underlying postural tremor in Wilson's disease.

Common neurological manifestation of Wilson's disease (WD) is a postural tremor of the upper extremities. Recently, the primary sensorimotor cortex (S1/M1) has been shown to be involved in WD postural tremor generation. However, neuropathological changes in WD are mostly observed in subcortical structures. We therefore aimed to investigate whether S1/M1 may be functionally interconnected with other brain areas. In five WD patients, we used magnetoencephalography and surface electromyography (EMG) to record simultaneously cerebral neuronal activity and muscular activity during sustained posture of the right forearm. As demonstrated previously, the strongest coupling to tremor EMG was observed in the contralateral S1/M1. This area was taken as reference in order to identify and localize cerebro-cerebral coherence at tremor frequency and its first harmonic. The analysis revealed significant coherence within an oscillatory network including S1/M1, higher cortical motor areas (premotor cortex, PM; supplementary motor area, SMA), posterior parietal cortex (PPC) and thalamus contralateral as well as the cerebellum ipsilateral to the tremor forearm. Flow of information was mainly of bidirectional nature. Taken together, our results indicate that WD postural tremor is generated within a synchronized cerebello-thalamo-cortical network, comprising S1/M1, higher cortical motor areas (SMA, PM), and PPC.

Adult↗

PubMed2006

Coupling between cerebellar hemispheres: behavioural, anatomic, and functional data.

Although the cerebellum has been related to emotional, cognitive, and sensory processes, its outstanding significance for motor behaviour has attracted a vast variety of studies. Specifically, the role of cerebellar activity for appropriate movement timing has been investigated intensively. Behavioural studies, particularly of patients following cerebellar lesions, gave rise to the hypothesis that each hand is controlled by separate timing mechanisms most likely localized within lateral portions of each cerebellar hemisphere. Reduced timing variability during simultaneous bimanual tasks implies that both timing signals are integrated prior to movement execution, probably by information transfer between both cerebellar hemispheres. However, this raises the question for functional and anatomic fundamentals of such an integration process. The present article reviews behavioural, functional, and anatomic data to shed light on possible interactions between both cerebellar hemispheres during the execution of timed motor behaviour.

Animals↗

PubMed2005

Image-to-sound conversion: experience-induced plasticity in auditory cortex of blindfolded adults.

The ability to adapt to environmental changes is based on the impressive capacity of the central nervous system for plasticity changes. A better understanding of the requirements of neuroplasticity will help to apprehend and predict the success of sensory prostheses. To investigate neuroplastic changes associated with (1) blindfolding and (2) the use of a mobile visual-auditory substitution system, five normally sighted adults underwent weekly measurements of neuromagnetic activity using a 122-channel whole head neuromagnetometer. The substitution device converted visual images into sound patterns. During measurements subjects listened to "geometric sounds" converted from images of geometric shapes, "natural sounds" representing photographs of everyday objects, as well as to original "environmental sounds". To assess the role of visual deprivation, three individuals were blindfolded throughout a 3-week testing period. To assess the effect of extended exposure to "visual sounds", three subjects-two blindfolded, one sighted-had free use of the substitution device. Neuromagnetic responses were restricted to the auditory cortex across all measurements. Activity at 100 ms after presentation of "natural sounds", but not other auditory stimuli, showed a significant enhancement over time only in blindfolded subjects using the substitution system, indicating that the combination of visual deprivation and practice facilitated intra-modal plasticity. The fact that changes occurred only in response to "natural sounds" probably reflects the increased behavioural relevance of this category evident only for blindfolded subjects using the substitution device.

Acoustic Stimulation↗

PubMed2005

How the brain controls repetitive finger movements.

Adequate interaction with our physical and social environment requires accurate timing abilities. Since planning and control of movements is closely related to sensorimotor synchronization, the investigation of synchronization abilities may allow insights into fundamental principles of motor behaviour. The finger-tapping task has frequently been used to study the synchronization of one's own movements in relation to external events. Data from behavioural studies gave rise to the assumption that it is not the peripheral event (i.e., finger-tap or pacing signal) that is synchronized but its central representation. The neural foundations of sensorimotor synchronization have only recently been investigated and are still poorly understood. The present article reviews data from neurophysiological studies investigating sensorimotor synchronization to shed light on the neurophysiological processes associated with sensorimotor synchronization. This review focuses on studies investigating neuroelectric and neuromagnetic activity associated with simple repetitive synchronization tasks.

Brain↗

PubMed2005

Pain suppresses spontaneous brain rhythms.

The neuronal activity of the resting human brain is dominated by spontaneous oscillatory activity of primary visual, somatosensory and motor areas. These spontaneous brain rhythms are related to the functional state of a system. A higher amplitude of oscillatory activity is thought to reflect an idling state, whereas a lower amplitude is associated with activation and higher excitability of the specific system. Here, we used magnetoencephalography to investigate the effects of pain on spontaneous brain rhythms. Our results show that a focally applied brief painful stimulus globally suppresses spontaneous oscillations in somatosensory, motor and visual areas. This global suppression contrasts with the regionally specific suppressions of other modalities and shows that pain induces a widespread change in cortical function and excitability. This global change in excitability may reflect the alerting function of pain which opens the gates for processing of and reacting to stimuli of existential relevance.

Adult↗

PubMed2005

Oscillatory coupling in writing and writer's cramp.

Writing is a highly skilled and overlearned movement. In patients suffering from writer's cramp, a focal task-induced dystonia, writing is impaired or even impossible due to involuntary muscle contractions and abnormal posture, which occur as soon as the person picks up a pen or within writing a few words. The underlying pathophysiological mechanisms of this movement disorder are not fully understood up to now. The aim of the present study was to unravel the oscillatory network underlying physiological writing in healthy subjects and dystonic writing in writer's cramp patients. Using whole-head magnetoencephalography (MEG) and the analysis tool dynamic imaging of coherent sources (DICS) we studied oscillatory neural coupling during writing in eleven healthy subjects and eight patients suffering from writer's cramp. Simultaneous recording of brain activity with MEG and activity of forearm and hand muscles with surface electromyography (EMG) was performed while subjects were writing for five minutes with their dominant right hand. Applying DICS sources of strongest cerebro-muscular coherence and cerebro-cerebral coherence during writing were identified, which consistently included six brain areas in both, the control subjects and the patients: contralateral and ipsilateral sensorimotor cortex, ipsilateral cerebellum, contralateral thalamus, contralateral premotor and posterior parietal cortex. Coherence between cortical sources and muscles appeared primarily in the frequency of writing movements (3-7 Hz) while coherence between cerebral sources occurred primarily around 10 Hz (8-13 Hz). Interestingly, consistent coupling between both sensorimotor cortices was observed in patients only, whereas coupling between ipsilateral cerebellum and the contralateral posterior parietal cortex was found in control subjects only. These results are consistent with the often described bilateral pathophysiology and impaired sensorimotor integration in writer's cramp patients.

Adult↗

PubMed2005

The oscillatory network of simple repetitive bimanual movements.

Bimanual synchronization relies on the precisely coordinated interplay of both hands. It is assumed that during temporal bimanual coordination, timing signals controlling each hand might be integrated. Although a specific role of the cerebellum for this integration process has been suggested, its neural foundations are still poorly understood. Since dynamic interactions between spatially distributed neural activity are reflected in oscillatory neural coupling, the aim of the present study was to characterize the dynamic interplay between participating brain structures. More specifically, the study aimed at investigating whether any evidence for the integration of bilateral cerebellar hemispheres could be found. Seven right-handed subjects synchronized bimanual index finger-taps to a regular pacing signal. We recorded continuous neuromagnetic activity using a 122-channel whole-head neuromagnetometer and surface EMGs of the first dorsal interosseus (FDI) muscle of both hands. Coherence analysis revealed that an oscillatory network coupling at 8-12 Hz subserves task execution. The constituents are bilateral primary sensorimotor and premotor areas, posterior-parietal and primary auditory cortex, thalamus and cerebellum. Coupling occurred at different cortical and subcortical levels within and between both hemispheres. Coupling between primary sensorimotor and premotor areas was observed directly and indirectly via the thalamus. Coupling direction suggests that information was integrated within the left premotor cortex corroborating a specific role of the left premotor cortex for motor control in right-handers. Most importantly, our data indicate strong coupling between both cerebellar hemispheres substantiating the hypothesis that cerebellar signals might be integrated during task execution.

Adult↗

PubMed2004

The cerebral oscillatory network associated with auditorily paced finger movements.

Motor tasks involve neural activity in a spatially distributed network. It is assumed that coherent activity between these brain structures reflects functional connectivity. The aim of the present study was to investigate brain areas associated with a unimanual auditorily paced finger-tapping task and to characterize their dynamic interplay. We examined cerebromuscular and cerebrocerebral coupling in 10 right-handed subjects using recordings of continuous brain activity with a 122-channel whole-head neuromagnetometer while subjects performed the task with both hands consecutively. Additionally, surface EMG of the first dorsal interosseus was measured. Our data demonstrate that an oscillatory network composed of primary sensorimotor cortex, lateral as well as mesial premotor areas, the posterior parietal cortex and thalamus contralateral, and cerebellum and primary auditory cortex ipsilateral to the tapping hand subserves task execution. Connectivity between these areas and direction of coupling agree well with anatomical findings. During the right-hand condition, additional oscillatory activity in the primary sensorimotor cortex ipsilateral to the tapping hand was evident. This result suggests an asymmetric motor control in right-handers. Cerebrocerebral coupling predominantly occurs at 8-12 Hz. Therefore, our data support the hypothesis that coupling at 8-12 Hz in a cerebello-thalamic-cortical network represents a fundamental characteristic of the motor system and provides evidence for the significance of 8-12 Hz oscillations in a large scale network during the execution of simple motor tasks.

Acoustic Stimulation↗

PubMed2004

Shrinkage of somatosensory hand area in subjects with upper extremity dysmelia revealed by magnetoencephalography.

The effect of peripheral lesions on cerebral somatosensory representations is well studied for experimentally induced amputations and deafferentations acquired later in life. However, few studies have investigated the brain's capacity for plastic changes in congenital malformations. We studied somatosensory-evoked fields to electrical stimulation of the bordering fingers in 10 subjects with upper extremity dysmelia in comparison with 10 control subjects using a 122-channel whole-head magnetometer. The number of developed fingers varied between two and four in the affected subjects. We localized finger representations in the primary somatosensory cortex and calculated Euclidian distances to estimate the size of the somatosensory hand area. Euclidian distances were significantly smaller in dysmelic subjects (5.7 mm) than in control subjects (11.6 mm) and were related to the number of the developed fingers on the contralateral hand. In contrast, individual finger representations were not found to be reduced. We suggest that the shrinkage of the somatosensory hand area might be related to the congenital nature of the malformation, to the smaller anatomical hand size in the affected subjects, and/or to use-dependent effects due to impaired hand function.

Adult↗

PubMed2004

Pain facilitates tactile processing in human somatosensory cortices.

Touch and pain are intimately related modalities. Despite a substantial overlap in their cortical representations interactions between both modalities are largely unknown at the cortical level. We therefore used magnetoencephalography and selective nociceptive cutaneous laser stimulation to investigate the effects of brief painful stimuli on cortical processing of touch. Using a conditioning test stimulus paradigm, our results show that painful conditioning stimuli facilitate processing of tactile test stimuli applied 500 ms later. This facilitation applies to cortical responses later than 40 ms originating from primary (S1) and secondary (S2) somatosensory cortices but not to earlier S1 responses. By contrast, tactile conditioning stimuli yield a decrease of early as well as late responses to tactile test stimuli. Control experiments show that pain-induced facilitation of tactile processing is not restricted to the site of the painful conditioning stimulus, whereas auditory conditioning does not yield a comparable facilitation. Apart from a lack of spatial specificity, the facilitating effect of pain closely resembles attentional effects on cortical processing of tactile stimuli. Thus these findings may represent a physiological correlate of an alerting function of pain as a change in the internal state to prepare for processing signals of particular relevance.

Adult↗

PubMed2004

The role of the primary somatosensory cortex in an auditorily paced finger tapping task.

It has been suggested that a simple auditorily paced finger tapping task is associated with three tap-related neuromagnetic sources in the primary sensorimotor cortex contralateral to the tapping hand. Since a first source peaking at approximately 100 ms before tap-onset most likely represents activation of the primary motor cortex (M1) due to the motor command, a second source localized in the primary somatosensory cortex (S1) peaking around tap-onset could be due to kinesthetic feedback of the finger movement. A third source peaking at approximately 100 ms after tap-onset is also localized in the primary somatosensory cortex but inferior to the first S1 source (S1 inferior). The functional meaning of this source is still under debate. On the one hand it has been argued that S1 inferior represents the neuromagnetic correlate of tactile-kinesthetic feedback due to finger-taps and movements. On the other hand the functional meaning of this source could go beyond the sole processing of somatosensory feedback monitoring the temporal distance between tap and pacer (click) to keep the subject in time with the external event. This hypothesis is based on the observation that (1). S1 inferior seems to be coupled equally well to tap and click and (2). that this source might be triggered by the last event (i.e. tap or click). In the present study we re-examined this hypothesis by using a 122-channel whole-head neuromagnetometer. Eight healthy subjects synchronized their right index finger taps to an auditory pacing signal presented with a constant interstimulus interval of 800 ms. To test the hypothesis that the last event triggers S1 inferior we compared neuromagnetic activity following the tap as the first and the last event. In the auditorily paced finger tapping task usually the tap leads over the click (negative asynchrony). Therefore, the tap usually occurs as the first event. Since it has been shown that delivering additional feedback at the time of tap-onset results in a reduced negative asynchrony, in a second run auditory feedback was presented at tap-onset to enhance the number of positive asynchronies (i.e. the tap is the last event). Since no latency differences of S1 inferior associated with positive and negative asynchronies were found, results from the present study do not support the assumption that S1 inferior is triggered by the last event. Moreover, the amplitude of S1 inferior is significantly reduced following positive asynchronies as compared to negative asynchronies. Additionally, tap duration (i.e. the time between tap-onset and tap-offset) is significantly reduced while subjects produce positive asynchronies. Therefore, the amplitude of S1 inferior seems to be modulated by movement kinematics. This observation agrees well with the idea that activation of S1 is solely associated with the processing of somatosensory information. To conclude, our data contradict the hypothesis of an evaluation process localized in the primary somatosensory cortex and substantiate the idea that S1 inferior exclusively represents the processing of somatosensory feedback information.

Acoustic Stimulation↗

PubMed2004

Bimanual coordination: neuromagnetic and behavioral data.

It has been suggested that bimanual coordination is associated with stronger activation of the left motor cortex in right-handers. The aim of the present study was to investigate whether left motor cortex dominance constitutes a fundamental feature of bimanual coordination. We investigated neuromagnetic responses while subjects performed a bimanual tapping task using a 122-channel whole-head neuromagnetometer. Three neuromagnetic sources localized in the primary sensorimotor cortex of each hemisphere were found. Sources represent neuromagnetic correlates of the motor command and of somatosensory feedback. Since we found no differences of amplitudes or latencies of corresponding sources of both hemispheres, our data suggest that dominance of the left motor cortex is not a fundamental characteristic for bimanual coordination.

Adult↗

PubMed2004

Postural tremor in Wilson's disease: a magnetoencephalographic study.

The following study included 5 Wilson's disease (WD) patients showing a right-sided postural forearm tremor (4-6 Hz) and addressed the question of whether the primary motor cortex (M1) is involved in tremor generation. Using a 122-channel whole-head neuromagnetometer and surface electromyogram (EMG), we investigated cerebromuscular coupling. Postural tremor was observed in a sustained 45-degree posture of the right-sided forearm. Data were analyzed using dynamic imaging of coherent sources (DICS), revealing cerebromuscular coupling between EMG and cerebral activity. Coherent sources were superimposed on individual high-resolution T1-weighted magnetic resonance images (MRI). Phase lags between EMG and cerebral areas showing strongest coherence were determined by means of a Hilbert transform of both signals. In all patients, postural tremor was associated with strong coherence between tremor EMG and activity in contralateral primary sensorimotor cortex (S1/M1) at tremor or double tremor frequency. Phase lag values between S1/M1 activity and EMG revealed efferent and afferent components in the corticomuscular coupling. Taken together, our results indicate that postural tremor in WD is mediated through a pathological oscillatory drive from the primary motor cortex.

Adult↗

PubMed2003

The cerebral oscillatory network of voluntary tremor.

It has recently been shown that resting tremor in Parkinson's disease is associated with oscillatory neural coupling in an extensive cerebral network comprising a cerebello-diencephalic-cortical loop and cortical motor, somatosensory and posterior parietal areas contralateral to the tremor hand. The aim of the present study was to investigate whether this oscillatory brain network exclusively reflects a pathophysiological state in parkinsonian resting tremor or whether it constitutes a fundamental feature of physiological motor control. We investigated cerebro-muscular and cerebro-cerebral coupling in 11 healthy subjects imitating typical antagonistic parkinsonian tremor. We recorded brain activity with a 122-channel whole-head neuromagnetometer and surface EMGs of the forearm extensor. Analysis of cerebro-muscular and cerebro-cerebral coherence revealed oscillatory coupling in the same brain structures that comprise the oscillatory network of parkinsonian resting tremor. Interestingly, similar to parkinsonian resting tremor, cerebro-cerebral coherences often showed a significant peak at twice the simulated tremor frequency. The most striking differences between parkinsonian patients, as investigated in a previous study and healthy subjects imitating the antagonistic resting tremor were a reduction of the coupling between primary sensorimotor cortex and a diencephalic structure--most likely the thalamus--and an enhancement of the coupling between premotor and primary sensorimotor cortex. Our results indicate that the coupling of oscillatory activity within a cerebello-diencephalic-cortical loop constitutes a basic feature of physiological motor control. Thus, our data are consistent with the hypothesis that parkinsonian resting tremor involves oscillatory cerebro-cerebral coupling in a physiologically pre-existing network.

Adult↗

PubMed2003

Cortical activations associated with auditorily paced finger tapping.

We investigated neuromagnetic responses during an auditorily paced synchronization task using a 122-channel whole-head neuromagnetometer. Eight healthy right handed subjects were asked to synchronize left and right unilateral finger taps to a regular binaural pacing signal. Synchronization of the right hand with an auditory pacing signal is known to be associated with three tap-related neuromagnetic sources localized in the contralateral primary sensorimotor cortex. While the first source represents the neuromagnetic correlate of the motor command the second one reflects somatosensory feedback due to the finger movement. The functional meaning of the third source, which is also localized in the primary somatosensory cortex is still unclear. On the one hand this source represents a neuromagnetic correlate of somatosensory feedback due to the finger tap. On the other hand it has been suggested that the function of this source could additionally represent a cognitive process, which enables the subject to monitor the time distance between taps and clicks. The aim of the present study was to elucidate the function of this source, which would fundamentally reform the meaning of the primary somatosensory cortex in the timing of movements with respect to external events. The data of the present study demonstrate that the three sources in the contralateral sensorimotor cortex are stronger related to the tap than to the click. This result contradicts the assumption of a cognitive process localized in the primary somatosensory cortex. Thus, activation in the primary somatosensory cortex most likely represents exclusively somatosensory feedback and no further cognitive processes.

Acoustic Stimulation↗

PubMed2002

Rapid mapping of finger representations in human primary somatosensory cortex applying neuromagnetic steady-state responses.

We analyzed somatosensory evoked steady-state fields in order to localize finger representations in the hand area of the primary somatosensory cortex (S1). Using a 122-channel whole-head neuromagnetometer we recorded in six healthy subjects neuromagnetic responses to high frequency electrical stimuli delivered simultaneously to digit I, II, III and V at 22, 24, 27 and 30 Hz, respectively, and to transient stimulation of each single digit with a frequency of 3 Hz. Responses were averaged separately for each digit and were modeled by single equivalent current dipoles. Both conditions yielded the typical somatotopic finger representations within S1 hand area. Dipole locations did not differ significantly between the transient and the steady-state stimulation. Therefore, simultaneous high-frequency stimulation of the digits seems to be a reliable method for rapid and detailed mapping of the S1 hand area. This procedure has potential advantages over recording of transient responses. With simultaneous steady-state stimulation the measurement times are reduced to 2 min for mapping the whole hand area. Because of this our method probably increases spatial accuracy and permits repeated short interval recordings, e.g. in experiments studying short term plasticity.

Adult↗