Task-related Power Research Articles

Cortical correlate of spatial presence in 2D and 3D interactive virtual reality: An EEG study

The present study is the first that examined neuronal underpinnings of spatial presence using multi-channel EEG in an interactive virtual reality (VR). We compared two VR-systems: a highly immersive Single-Wall-VR-system (three-dimensional view, large screen) and a less immersive Desktop-VR-system (two-dimensional view, small screen). Twenty-nine participants performed a spatial navigation task in a virtual maze and had to state their sensation of “being there” on a 5-point rating scale. Task-related power decrease/increase (TRPD/TRPI) in the Alpha band (8–12Hz) and coherence analyses in different frequency bands were used to analyze the EEG data. The Single-Wall-VR-system caused a more intense presence experience than the Desktop-VR-system. This increased feeling of presence in the Single-Wall-VR-condition was accompanied by an increased parietal TRPD in the Alpha band, which is associated with cortical activation. The lower presence experience in the Desktop-VR-group was accompanied by a stronger functional connectivity between frontal and parietal brain regions indicating that the communication between these two brain areas is crucial for the presence experience. Hence, we found a positive relationship between presence and parietal brain activation and a negative relationship between presence and frontal brain activation in an interactive VR-paradigm, supporting the results of passive non-interactive VR-studies.

Reactivity of alpha rhythms to eyes opening is lower in athletes than non-athletes: A high-resolution EEG study

In the present study, we tested the hypothesis that compared with non-athletes, elite athletes are characterized by a reduction of reactivity of electroencephalographic (EEG) alpha rhythms (about 8–12 Hz) to eyes opening in the condition of resting state, as a possible index of spatially selective cortical activation (i.e. “neural efficiency”). EEG data (56 channels; Eb-Neuro©) were recorded in 18 elite karate athletes and 28 non-athletes during resting state eyes-closed and eyes-open conditions. The EEG data were spatially enhanced by surface Laplacian estimation. Cortical activity was indexed by task-related power decrease (TRPD), namely the alpha power during the eyes-open referenced to the eyes-closed resting condition. Low-frequency alpha TRPD (about 8–10 Hz) was lower in the elite karate athletes than in the non-athletes in frontal (p < 0.00002), central (p < 0.008) and right occipital (p < 0.02) areas. Similarly, high-frequency alpha TRPD (about 10–12 Hz) was lower in the elite karate athletes than in the non-athletes in frontal (p < 0.00009) and central (p < 0.01) areas. These results suggest that athletes' brain is characterized by reduced cortical reactivity to eyes opening in the condition of resting state, in line with the “neural efficiency” hypothesis. The present study motivates future research evaluating the extent to which this general functional brain feature is related to heritable trait or intensive visuo-motor training of elite athletes.

Hemicraniectomy: A New Model for Human Electrophysiology with High Spatio-temporal Resolution

Human electrophysiological research is generally restricted to scalp EEG, magneto-encephalography, and intracranial electrophysiology. Here we examine a unique patient cohort that has undergone decompressive hemicraniectomy, a surgical procedure wherein a portion of the calvaria is removed for several months during which time the scalp overlies the brain without intervening bone. We quantify the differences in signals between electrodes over areas with no underlying skull and scalp EEG electrodes over the intact skull in the same subjects. Signals over the hemicraniectomy have enhanced amplitude and greater task-related power at higher frequencies (60-115 Hz) compared with signals over skull. We also provide evidence of a metric for trial-by-trial EMG/EEG coupling that is effective over the hemicraniectomy but not intact skull at frequencies >60 Hz. Taken together, these results provide evidence that the hemicraniectomy model provides a means for studying neural dynamics in humans with enhanced spatial and temporal resolution.

Temporal and spatial patterns of cortical activation during assisted lower limb movement

Human gait is a complex process in the central nervous system that results from the integrity of various mechanisms, including different cortical and subcortical structures. In the present study, we investigated cortical activity during lower limb movement using EEG. Assisted by a dynamic tilt table, all subjects performed standardized stepping movements in an upright position. Source localization of the movement-related potential in relation to spontaneous EEG showed activity in brain regions classically associated with human gait such as the primary motor cortex, the premotor cortex, the supplementary motor cortex, the cingulate cortex, the primary somatosensory cortex and the somatosensory association cortex. Further, we observed a task-related power decrease in the alpha and beta frequency band at electrodes overlying the leg motor area. A temporal activation and deactivation of the involved brain regions as well as the chronological sequence of the movement-related potential could be mapped to specific phases of the gait-like leg movement. We showed that most cortical capacity is needed for changing the direction between the flexion and extension phase. An enhanced understanding of the human gait will provide a basis to improve applications in the field of neurorehabilitation and brain-computer interfaces.

Optimized beamforming for simultaneous MEG and intracranial local field potential recordings in deep brain stimulation patients

Insight into how brain structures interact is critical for understanding the principles of functional brain architectures and may lead to better diagnosis and therapy for neuropsychiatric disorders. We recorded, simultaneously, magnetoencephalographic (MEG) signals and subcortical local field potentials (LFP) in a Parkinson's disease (PD) patient with bilateral deep brain stimulation (DBS) electrodes in the subthalamic nucleus (STN). These recordings offer a unique opportunity to characterize interactions between the subcortical structures and the neocortex. However, high-amplitude artefacts appeared in the MEG. These artefacts originated from the percutaneous extension wire, rather than from the actual DBS electrode and were locked to the heart beat. In this work, we show that MEG beamforming is capable of suppressing these artefacts and quantify the optimal regularization required. We demonstrate how beamforming makes it possible to localize cortical regions whose activity is coherent with the STN-LFP, extract artefact-free virtual electrode time-series from regions of interest and localize cortical areas exhibiting specific task-related power changes. This furnishes results that are consistent with previously reported results using artefact-free MEG data. Our findings demonstrate that physiologically meaningful information can be extracted from heavily contaminated MEG signals and pave the way for further analysis of combined MEG-LFP recordings in DBS patients.

The effects of practice distribution upon the regional oscillatory activity in visuomotor learning

BackgroundThe aim of this study was to investigate the effects of a massed compared to a distributed practice upon visuomotor learning as well as upon the regional oscillatory activity in the sensorimotor cortex.MethodsA continuous visuomotor tracking task was used to assess visuomotor learning; the underlying neuronal correlates were measured by means of EEG. The massed practice group completed a continuous training of 60 minutes, while the distributed practice group completed four 15 minutes practice blocks separated by rest intervals.ResultsWhile the massed and the distributed practice group did not differ in performance, effects of practice distribution were evident in the regional oscillatory activity. In the course of practice, the massed training group showed a higher task-related theta power and a strong task-related power decrease in the upper alpha frequency over the sensorimotor cortex compared to the distributed practice group.ConclusionsThese differences in the regional oscillatory activity indicate a higher cognitive effort and higher attention demands in the massed practice group. The results of this study support the hypothesis, that a distributed practice is superior to a massed practice in visuomotor learning.

“Neural efficiency” of athletes’ brain for upright standing: A high-resolution EEG study

“Neural efficiency” hypothesis posits that neural activity is reduced in experts. Here we tested the hypothesis that compared with non-athletes, elite athletes are characterized by a reduction of cortical activation during an engaging upright standing. EEG (56 channels; Be-plus Eb-Neuro ©) and stabilogram (RGM ©) data were simultaneously recorded in 10 elite karate, 10 elite fencing athletes, and 12 non-athletes during a simple bipodalic (standard Romberg) and a more engaging monopodalic upright standing. Balance was indexed by body “sway area”. The EEG data were spatially enhanced by surface Laplacian estimation. Cortical activity was indexed by task-related power decrease (TRPD) of EEG alpha power (8–12 Hz) during monopodalic referenced to bipodalic condition. The body “sway area” was larger during the monopodalic than bipodalic upright standing in all groups. Low-frequency alpha TRPD (about 8–10 Hz) was lower in amplitude in the karate and fencing athletes than in the non-athletes at left central, right central, middle parietal, and right parietal areas ( p < 0.01). Similarly, the amplitude of high-frequency alpha TRPD (10–12 Hz) was lower in the karate and fencing athletes than in the non-athletes at right frontal, left central, right central, and middle parietal areas ( p < 0.03). These results suggest that during monopodalic referenced to less engaging bipodalic condition, the power decrease (i.e. the desynchronization) of cortical activity at alpha rhythms is largely reduced in elite athletes than in non-athletes, in line with the “neural efficiency” hypothesis. The present study extends our understanding of the physiological mechanisms at the basis of the “neural efficiency” for engaging upright standing in elite athletes.

Frequency Domain Analysis of Human Subdural Recordings

It is possible to localize many aspects of cortical function and dysfunction without the use of direct electrical stimulation of cortex. This study explores the degree to which information can be obtained about functional cortical organization relative to epileptogenic regions through analysis of electrocorticographic recordings in the frequency domain. Information about the extent of seizure regions and the location of the normal sensory and motor homunculus and some higher language and memory related areas can be obtained through the analysis of task-related power spectrum changes and changes in lateral interelectrode coherence patterns calculated from interictal and ictal recordings.

Decreased desychronisation during self-paced movements in frequency bands involving sensorimotor integration and motor functioning in Parkinson's disease

This study examined sensorimotor integration and motor functioning in seven patients with Parkinson's disease (PD) who had mild symptoms, and seven age-matched controls. Neuro-oscillations were recorded by high-density 128-channel electroencephalography (EEG). Participants were required to perform two tasks: simple tapping of the index finger and thumb and a complex Luria finger apposition task. Both tasks were performed unimanually and bimanually. There were no significant group differences in the task-related power (TRPow) within alpha 1 (mu1) or in beta 1 frequencies (β1). In contrast, there were significant group differences in the alpha 2 (mu2) and beta 2 frequencies (β2). Patients had less desychronisation than controls at the electrodes covering the central regions of the scalp. Alpha 2 and beta 2 frequencies have been associated with task-specific sensorimotor integration and motor function, respectively. This activity difference in patients with Parkinson's disease may be due to deficits in sensorimotor integration.

EEG alpha oscillations during the performance of verbal creativity tasks: Differential effects of sex and verbal intelligence

Task-related power changes in the EEG alpha band were analyzed in 31 participants (17 males and 14 females) during performance of two verbal creativity tasks. Participants were confronted with verbal problems that are in need of explanation (insight problems) and utopian situations that will actually never happen. In both tasks they were instructed to generate as many but also as unusual, unique or original ideas as possible. To assess brain responses that come along with highly original ideas, individual responses were divided into more and less original ideas (within each participant). Creative problem solving was generally accompanied by lower levels of cortical arousal (i.e., increases in alpha power from a pre-stimulus reference to an activation interval). Additionally, more original (vs. less original) responses were associated with a stronger task-related alpha synchronization in posterior (particularly centroparietal) cortices. Task-related alpha power changes during creative problem solving were also moderated by verbal IQ and sex.

Corticocortical coupling in chronic stroke: its relevance to recovery.

The mechanisms behind motor recovery from stroke are not clearly understood. Functional imaging studies have demonstrated task-related brain activation in several motor areas, but few studies have attempted to correlate this with stroke outcome. Moreover, these studies have focused on how motor areas may individually contribute to compensation. Here, the authors investigate whether different cortical areas interact to form dynamic assemblies that may then compensate for disability. The authors investigated corticocortical coherence in 16 healthy subjects and 25 patients with chronic stroke involving one cerebral hemisphere and having varying degrees of motor recovery. Scalp EEG was recorded at rest and while right-handed subjects performed a unimanual grip task. The degree of functional recovery after stroke was assessed using a range of outcome measures. Compared with healthy subjects, hand-related asymmetries in task-related EEG-EEG coherence were increased between mesial and lateral frontal regions of the affected hemisphere, over mesial frontal regions, and over lateral frontal areas of the unaffected hemisphere when patients with stroke gripped with their affected hand. Mesial hand-related asymmetries in task-related power and coherence were negatively correlated with recovery. Increases in task-related coupling between cortical areas may dynamically compensate for brain damage after stroke. Some of this increased coupling, particularly that over mesial frontal areas, decreases as patients make a functional recovery.

Aberrant Sensorimotor Integration in Musicians' Cramp Patients

AbstractSimple tapping and complex movements (Luria finger apposition task) were performed unimanually and bimanually by two groups of professional guitarists while EEG was recorded from electrodes over the sensorimotor cortex. One group had a task-specific movement disorder (focal dystonia or musicians' cramp), while the other group did not (controls). There were no significant group interactions in the task-related power (TRPow) within the alpha range of 8-10Hz (mu1). In contrast, there was a significant group interaction within the alpha range of 10-12Hz (mu2); these latter frequencies are associated with task-specific sensorimotor integration. The significant group interaction included task (simple and complex) by hand (left, right, and both) by electrodes (10 electrodes over the sensorimotor areas). In the rest conditions, the alpha power (10-12Hz) was comparable between the groups; during movement, however, compared to the controls, patients demonstrated the greatest TRPow (10-12Hz) over all conditions. This was particularly evident when patients used their affected hand and suggests that patients with musicians' cramp have impaired task-specific sensorimotor integration.

Task-related power and coherence changes in neuromagnetic activity during visuomotor coordination.

We analyzed a set of full-head (66 channels, CTF Inc.) magnetoencephalography (MEG) data recorded when 5 subjects performed rhythmic right index-finger flexion and extension movements on the beat (synchronization) or off the beat (syncopation) with a visual metronome at 1 Hz. Neuromagnetic activities in the alpha (8-14 Hz), beta (15-30 Hz) and gamma (30-50 Hz) ranges were shown to correlate with different aspects of the task. Specifically, we found that, compared with the control condition in which subjects only looked at the visual metronome without making any movement, all the movement conditions were accompanied by a decrease of power in the alpha range (8-14 Hz) in sensorimotor channels of both hemispheres, and an increase of coherence among a subset of these channels. The same comparison showed that power changes in the beta range differentiate task conditions by exhibiting power increases for synchronization and power decreases for syncopation. Changes in the gamma range power were found to be related to the kinematics of movement trajectories (flexion versus extension). These results suggest that three important cortical oscillations play different functional roles in a visuomotor timing task.

Power changes in infant EEG frequency bands during a spatial working memory task

Developmental psychophysiologists working with infants have no commonly accepted frequency definitions of EEG waves or rhythms. The purpose of this study was to investigate the task‐related power changes in three infant EEG frequency bands during the performance of a spatial working memory task by 8‐month‐old infants. EEG data were divided into three frequency bands: 3–5 Hz, 6–9 Hz, and 10–12 Hz. Although all three frequency bands showed some level of discrimination of baseline from task and among different processing stages of cognitive activity, only the 6–9 Hz band consistently exhibited these capabilities and distinguished the correct from incorrect responses. These data may form the foundation for defining EEG frequency bands that are appropriate for use with infant research participants and for understanding the function of these frequencies during cognitive activity.

Power changes in infant EEG frequency bands during a spatial working memory task

Developmental psychophysiologists working with infants have no commonly accepted frequency definitions of EEG waves or rhythms. The purpose of this study was to investigate the task-related power changes in three infant EEG frequency bands during the performance of a spatial working memory task by 8-month-old infants. EEG data were divided into three frequency bands: 3–5 Hz, 6–9 Hz, and 10–12 Hz. Although all three frequency bands showed some level of discrimination of baseline from task and among different processing stages of cognitive activity, only the 6–9 Hz band consistently exhibited these capabilities and distinguished the correct from incorrect responses. These data may form the foundation for defining EEG frequency bands that are appropriate for use with infant research participants and for understanding the function of these frequencies during cognitive activity.

Alpha band power changes in unimanual and bimanual sequential movements, and during motor transitions

Objective: To investigate the cortical activation during execution of unimanual and bimanual synchronous and asynchronous finger sequences, as well as during transitions between those sequences. Methods: Task-related power (TRPow) analysis of multichannel surface EEG was used to examine the regional oscillatory brain activity in the lower (7.8–9.8 Hz) and upper (10.8–11.8 Hz) alpha band. Unimanual to bimanual, bimanual to unimanual, and unimanual to unimanual transitions, prompted by visual cues, were studied in 10 right handed subjects. Results: (1) Execution of unimanual and bimanual movements was accompanied by a bilateral activation over the central regions. (2) The 7.8–9.8 Hz TRPow decrease was more prominent for left and bimanual movements, suggesting sensitivity of the lower alpha band to task difficulty. (3) No difference in alpha oscillatory activity was found between bimanual synchronous and asynchronous sequences. (4) Transitions between motor sequences were invariably accompanied by a mesioparietal TRPow decrease in the lower alpha band. (5) This mesioparietal activation was contingent to the change of motor program, and could not be accounted for by the change of visual cue, or related attentional processes. Conclusion: The 7.8–9.8 Hz mesioparietal activation most likely reflects a posterior parietal motor command initiating transition between motor programs.

The influence of normal aging on the cortical processing of a simple motor task.

To assess the influence of normal aging on the cortical physiology of motor behavior. The authors studied cortical activation in eight elderly (55 to 76 years of age) and eight younger (18 to 27 years of age) healthy subjects while they performed a simple motor task. A 28-channel EEG was recorded; task-related power changes associated with repetitive, metronome-paced (1 Hz) finger movements were computed as a measure of cortical activation. Distinct, age-dependent activation patterns were expressed in four distinct frequency ranges: low-alpha (10 to 11 Hz), high-alpha (12 to 13 Hz), low-beta (16 to 17 Hz), and high-beta (22 to 23 Hz) bands. The main findings were a greater overall activation and, more specifically, a pronounced bilateral activation of sensorimotor regions in elderly subjects for both alpha bands. Additionally, in the elderly subjects there was increased activation of the mesial frontocentral cortex (supplementary motor area region) in the high-beta band, whereas younger volunteers had a prominent activation of the left lateral premotor and sensorimotor region in this frequency range. These findings demonstrate that the functional anatomy of the human motor system changes during normal aging. It appears that, for a given motor task, the aging brain recruits additional primary sensorimotor and premotor regions of both hemispheres.

Functional coupling of human cortical sensorimotor areas during bimanual skill acquisition.

Bimanual co-ordination of skilled finger movements is a high-level capability of the human motor system and virtually always requires training. Little is known about the physiological processes underlying successful bimanual performance and skill acquisition. In the present study, we used task-related coherence (TRCoh) and task-related power (TRPow) analysis of multichannel surface EEG to investigate the functional coupling and regional activation of human sensorimotor regions during bimanual skill acquisition. We focused on changes in interhemispheric coupling associated with bimanual learning. TRCoh and TRPow were estimated during the fusion of two overlearned unimanual finger-tapping sequences into one novel bimanual sequence, before and after a 30-min training period in 18 normal volunteers. Control experiments included learning and repetition of complex and simple unimanual finger sequences. The main finding was a significant increase in interhemispheric TRCoh selectively in the early learning stage (P < 0.0001). Interhemispheric TRCoh was also present during the unimanual control tasks, but with lower magnitude, even if learning was involved. Training improved bimanual sequence performance (from 58.3+/-24.1 to 83.7+/-15.3% correct sequences). After training, interhemispheric (bimanual) TRCoh decreased again, thereby approaching levels similar to those in the unimanual controls. We propose that the initial increase in TRCoh reflects changes in interhemispheric communication that are specifically related to bimanual learning and may be relayed through the corpus callosum. The present data might also offer a neurophysiological explanation for the clinical observation that patients with lesions of the corpus callosum may show deficits in the acquisition of novel bimanual tasks but not necessarily in the execution of previously learned bimanual activities.

125 Event-related desynchronization (ERD) during encoding and retrieval of semantic information

The hypothesis was tested whether event-related power shifts in the upper alpha band are specifically related to semantic memory processes. In Expt. 1 subjects had to judge whether pairs of sequentially presented words (W1-W2) were semantically congruent. In the following experiments subjects were presented the W1 words of Expt. 1 and were asked to perform a free association task in Expt. 2 and a cued recall task in Expt. 3. It is assumed that semantic memory demands dominate in Expt. 1, whereas working memory demands dominate in Expt. 3 and that Expt. 2 takes an intermediate position with respect to both types of task demands. A significant task-related power change that responds selectively to semantic processing demands was found for the upper alpha band and over the left side of the scalp. The lower alpha band, on the other hand, most likely reflects unspecific processing demands such as attention. A more general interpretation of these findings is that different cognitive processes such as semantic memory, perceptual encoding and attentional processes are reflected by band power changes in different and rather narrow frequency bands over localized regions in the brain.

Functional coupling and regional activation of human cortical motor areas during simple, internally paced and externally paced finger movements.

We studied the activation and interaction of cortical motor regions during simple, internally paced and externally paced right-hand finger extensions in healthy volunteers. We recorded EEGs from 28 scalp electrodes and analysed task-related coherence, task-related power and movement-related cortical potentials. Task-related coherence reflects inter-regional functional coupling of oscillatory neuronal activity, task-related power reflects regional oscillatory activity of neuronal assemblies and movement-related cortical potentials reflect summated potentials of apical dendrites of pyramidal cells. A combination of these three analytical techniques allows comprehensive evaluation of different aspects of information processing in neuronal assemblies. For both externally and internally paced finger extensions, movement-related regional activation was predominant over the contralateral premotor and primary sensorimotor cortex, and functional coupling occurred between the primary sensorimotor cortex of both hemispheres and between the primary sensorimotor cortex and the mesial premotor areas, probably including the supplementary motor area. The main difference between the different types of movement pacing was enhanced functional coupling of central motor areas during internally paced finger extensions, particularly inter-hemispherically between the left and right primary sensorimotor cortexes and between the contralateral primary sensorimotor cortex and the mesial premotor areas. Internally paced finger extensions were also associated with additional regional (premovement) activation over the mesial premotor areas. The maximal task-related coherence differences between internally and externally paced finger extensions occurred in the frequency range of 20-22 Hz rather than in the range of maximal task-related power differences (9-11 Hz). This suggests that important aspects of information processing in the human motor system could be based on network-like oscillatory cortical activity and might be modulated on at least two levels, which to some extent can operate independently from each other: (i) regional activation (task-related power) and (ii) inter-regional functional coupling. We propose that internal pacing of movement poses higher demands on the motor system than external pacing, and that the motor system responds not only by increasing regional activation of the mesial premotor system, including the supplementary motor area, but also by enhancing information flow between lateral and mesial premotor and sensorimotor areas of both hemispheres, even if the movements are simple and unimanual.