Eyes-closed Condition Research Articles

The new wireless EEG device Mentalab Explore is a valid and reliable system for the measurement of resting state EEG spectral features

Technological advancements in neuroscience have provided many conveniences to scientists, researchers, and consumers. The emerging electroencephalography (EEG) devices are good examples for it. The objective of this study was to investigate the validity and reliability of a new wireless EEG device Mentalab Explore for resting-state EEG (rsEEG) recordings in eyes open and eyes closed conditions. Twenty-three healthy subjects were recruited for the study. The subjects visited the laboratory on two occasions. On the first day, both devices were used to record rsEEG data, and after 24 h, only the Mentalab Explore was used to record rsEEG for test–retest reliability analysis. We compared the alpha peak frequency, suppression, and mean power between the two devices. Intraclass correlation coefficient was calculated for test–retest reliability analysis. Power spectral density (PSD) was calculated using Welch method. The PSD (eyes closed p < 0.0001; eyes open p = 0.01–0.0001), alpha peak frequency (p < 0.0001), and alpha suppression (p = 0.002–0.0001) from the two EEG devices as well as the test–retest results from the Mentalab device were significantly correlated. There were no significant differences in alpha peak frequency or suppression between the clinical-grade and the new devices for O1 and O2 channels in eyes-closed condition. The two measurements completed ∼24 h apart using the Mentalab system were similar for all the variables. We showed that the consumer-grade Mentalab Explore with gel electrodes is a reliable and valid EEG recording device for rsEEG spectral features.

Effect of virtual reality training on standing balance in individuals with incomplete spinal cord injury

Recovery of balance ability during standing is one of the primary and essential aims of rehabilitative programs in individuals with incomplete spinal cord injury (iSCI). A sample of ten participants (mean age: 35.7 years, range: 25-63 years) with traumatic or non-traumatic iSCI (AIS grade C or D) and were able to stand with or without the support of an assistive device for a minimum of 2 min were recruited from the rehabilitation department of the Indian Spinal Injuries Centre, New Delhi, India. The participants received Virtual Reality (VR) based balance training for one hour, three times a week for four weeks on the Nintendo Wii gaming console. Participants were assessed three times: pre-intervention, post-intervention and follow-up assessment for the total ellipse area (TEA), total sway perimeter (TSP), sway range (anterior-posterior/medio-lateral (AP/ML)) and limits of stability (LOS). At post-intervention assessment, significant increases in comparison with pre-intervention scores was found in LOS (P=0.00), TEA with eyes open (EO) (P=0.00) and eyes closed (EC) (P=0.00), TSP with EO (P=0.00) and EC (P=0.00), sway range in AP direction (SD-AP) with EO (P=0.01) and EC (P=0.02) and sway range in ML direction (SD-ML) with EO (P=0.02) and EC (P=0.01). At follow-up assessment, a significant improvement in comparison to post intervention scores was found in TEA measured both in EO (P=0.01) and EC conditions (P=0.02), TSP measured with EO (P=0.01) and SD-ML both with EO (P=0.04) and EC (P=0.01). No significant changes were found in LOS (P=0.89), TSP measured with EC (P=0.38) and SD-AP both with EO (P=0.50) and EC (P=1). However, significant improvement was seen on comparing follow-up assessment scores with pre-intervention scores for all variables, such as LOS (P=0.00), TEA in EO (P=0.00) and EC (P=0.00), TSP with EO (P=0.00) and EC (P=0.00), SD-AP with EO (P=0.01) and EC (P=0.02) and SD-ML with EO (P=0.01) and EC (P=0.00). VR-based balance training intervention was able to elicit improvements in balance ability and maintain it during follow-up despite a small training dosage suggesting that it is a promising intervention for standing balance rehabilitation among individuals with iSCI. The VR-based balance training challenges elements of balance, which physical therapists may want to consider when designing a comprehensive rehabilitation program. Clinical Trials Registry-India: CTRI/2018/12/016814.

An orderly sequence of autonomic and neural events at transient arousal changes

Resting-state functional magnetic resonance imaging (rsfMRI) allows the study of functional brain connectivity based on spatially structured variations in neuronal activity. Proper evaluation of connectivity requires removal of non-neural contributions to the fMRI signal, in particular hemodynamic changes associated with autonomic variability. Regression analysis based on autonomic indicator signals has been used for this purpose, but may be inadequate if neuronal and autonomic activities covary. To investigate this potential co-variation, we performed rsfMRI experiments while concurrently acquiring electroencephalography (EEG) and autonomic indicator signals, including heart rate, respiratory depth, and peripheral vascular tone. We identified a recurrent and systematic spatiotemporal pattern of fMRI (named as fMRI cascade), which features brief signal reductions in salience and default-mode networks and the thalamus, followed by a biphasic global change with a sensory-motor dominance. This fMRI cascade, which was mostly observed during eyes-closed condition, was accompanied by large EEG and autonomic changes indicative of arousal modulations. Importantly, the removal of the fMRI cascade dynamics from rsfMRI diminished its correlations with various signals. These results suggest that the rsfMRI correlations with various physiological and neural signals are not independent but arise, at least partly, from the fMRI cascades and associated neural and physiological changes at arousal modulations.

Hyperconnectivity matters in early-onset Alzheimer's disease: a resting-state EEG connectivity study

ObjectivesThe aim of this study was to differentiate individuals with early-onset Alzheimer's disease (EOAD) and identify differences of functional connectivity in resting-state EEG between individuals with EOAD and late-onset AD (LOAD) in comparison with both healthy young and elderly individuals. MethodsForty EOAD and 56 LOAD patients were included along with 51 demographically matched young, and 54 elderly healthy individuals as controls to the EOAD and LOAD groups. Four minutes of resting-state EEG were recorded during the eyes-closed condition. The absolute value of imaginary coherence (ICoh) was measured for connectivity. The maximum values of ICoh were measured at delta (0.5-3.5 Hz), theta (4-7.5Hz), alpha (8-13 Hz), alpha-1 (8-10 Hz), alpha-2 (10.5-13 Hz), beta (13-30 Hz), beta-1 (13-20 Hz), and beta-2 (20.5-30 Hz) frequency bands. ResultsIndividuals with EOAD showed higher coherence values in all frequency bands than LOAD patients. Compared to young healthy controls (YHC), EOAD had increased ICoh values in theta and beta-2 bands, whereas LOAD had lower ICoh values in the alpha-1 band than elderly healthy controls (EHC). Lastly, patients with EOAD demonstrated negative moderate correlations between language domains and beta-1 ICoh values. ConclusionTo the authors’ knowledge, this is the first study evaluating coherence alterations among early-and late-onset AD patients and the diagnostic value of coherence measures. It was suggested that EOAD patients had more severe pathological changes compared with LOAD.

Relationships among postural stability, physical fitness, and shooting accuracy in Olympic female goalball players.

This study aims to examine the relationship between postural perfor-mance, physical fitness level, and shooting performance in Olympic fe-male goalball players. Eight Olympic-level goalball players (age: 20.63± 4.37 years) were recruited from the Turkish National Women's Goalball Team. Postural stability, physical fitness, and shooting performance of the players were measured. The postural stability was determined us-ing body sway measurements during parallel and single-leg stances on a force plate. The physical fitness level of the players is evaluated by curl-up, isometric push-up, trunk lift, and grip strength (dominant hand) tests. A goalball-specific shooting accuracy test was used for shooting performance. Independent sample t-test and Pearson correlation were used for statistical processing. No statistical difference was observed in body sway parameters between open eyes and closed eyes condi-tions except for the anteroposterior sway area. Some of the body sway parameters performed under different stances positively correlated with all physical fitness tests (P<0.05). There was a positive correlation between the shooting accuracy and trunk lift score (r=0.767). Right leg sway area anterior-posterior and ellipse area negatively correlated with shooting accuracy (r=-0.629 and r=-0.692 respectively). It is necessary to attach importance to the improvement of the physical fitness level specific to core strength to maintain postural stability for visually im-paired athletes. In our study, some factors affecting shooting accuracy were identified, but it is necessary not to restrict a complex structure such as shooting accuracy within certain concepts.

Abnormal Properties of Cortical Functional Brain Network in Major Depressive Disorder: Graph Theory Analysis Based on Electroencephalography-Source Estimates

Studies of scalp electroencephalography (EEG) had shown altered topological organization of functional brain networks in patients with major depressive disorder (MDD). However, most previous EEG-based network analyses were performed at sensor level, while the interpretation of obtained results was not straightforward due to volume conduction effect. To reduce the impact of this defect, the whole cortical functional brain networks of MDD patients were studied during resting state based on EEG-source estimates in this paper. First, scalp EEG signals were recorded from 19 patients with MDD and 20 normal controls under resting eyes-closed state, and cortical neural signals were estimated by using sLORETA method. Then, the correntropy coefficient of wavelet packet coefficients was performed to calculate functional connectivity (FC) matrices in four different frequency bands: δ, θ, α, β, respectively. Afterwards, topological properties of brain networks were analyzed by graph theory approaches. The results showed that the global FC strength of MDD patients was significantly higher than that of healthy subjects in α band. Also, it was found that MDD patients have abnormally increased clustering coefficient and local efficiency in both α and β bands compared to normal people. Furthermore, patients with MDD exhibited increased nodal clustering coefficients in the left lingual gryus and left precuneus in α band. In addition, β band global clustering coefficient was positively correlated with the scores of depression severity. Therefore, the findings indicated the cortical functional brain networks in MDD patients were disruptions, which suggested it would be one of potential causes of depression.

EEG-Validated Photobiomodulation Treatment of Dementia—Case Study

In this article, we perform a case study of the impact of photobiomodulation (PBM) on brain power spectrum and connectivity in an elderly person with a Self Administered Gerocognitive Exam (SAGE) score indicating probable memory and thinking disorder. First, we designed and realized the prototype of a near-infrared (NIR) device for PBM. Analysing the alpha band of the power spectrum, we found a positive long-term effect in nine out of sixteen electrodes in the eyes-open condition (OE) and in twelve out of sixteen electrodes in the eyes-closed condition (CE), while in the theta band, a positive long-term effect was found in nine out of sixteen electrodes for OE and seven out of sixteen electrodes for CE. When considering the theta-alpha ratio (TAR), the positive long-term effect is found on thirteen of sixteen electrodes for OE and on fourteen of sixteen electrodes for CE. A connectivity analysis using the imaginary component of the complex Pearson correlation coefficient (imCPCC) was also performed, and a global efficiency measure based on connectivity matrices with thresholds was calculated. The global efficiency calculated for the long-term effect was higher than before stimulation by a factor of for the OE condition and by a factor of for the CE condition. This case study suggests that PBM could have positive effects on improving desired brain activity, measured as improvement in power spectrum and connectivity measures in theta and alpha bands, for elderly people with memory and thinking disorders.

Test-retest reliability of peak location in the sensorimotor network of resting state fMRI for potential rTMS targets.

Most stroke repetitive transcranial magnetic stimulation (rTMS) studies have used hand motor hotspots as rTMS stimulation targets; in addition, recent studies demonstrated that functional magnetic resonance imaging (fMRI) task activation could be used to determine suitable targets due to its ability to reveal individualized precise and stronger functional connectivity with motor-related brain regions. However, rTMS is unlikely to elicit motor evoked potentials in the affected hemisphere, nor would activity be detected when stroke patients with severe hemiplegia perform an fMRI motor task using the affected limbs. The current study proposed that the peak voxel in the resting-state fMRI (RS-fMRI) motor network determined by independent component analysis (ICA) could be a potential stimulation target. Twenty-one healthy young subjects underwent RS-fMRI at three visits (V1 and V2 on a GE MR750 scanner and V3 on a Siemens Prisma) under eyes-open (EO) and eyes-closed (EC) conditions. Single-subject ICA with different total number of components (20, 30, and 40) were evaluated, and then the locations of peak voxels on the left and right sides of the sensorimotor network (SMN) were identified. While most ICA RS-fMRI studies have been carried out on the group level, that is, Group-ICA, the current study performed individual ICA because only the individual analysis could guide the individual target of rTMS. The intra- (test-retest) and inter-scanner reliabilities of the peak location were calculated. The use of 40 components resulted in the highest test-retest reliability of the peak location in both the left and right SMN compared with that determined when 20 and 30 components were used for both EC and EO conditions. ICA with 40 components might be another way to define a potential target in the SMN for poststroke rTMS treatment.

Resting-state EEG reveals global network deficiency in prelingually deaf children with late cochlear implantation.

There are individual differences in rehabilitation after cochlear implantation that can be explained by brain plasticity. However, from the perspective of brain networks, the effect of implantation age on brain plasticity is unclear. The present study investigated electroencephalography functional networks in the resting state, including eyes-closed and eyes-open conditions, in 31 children with early cochlear implantation, 24 children with late cochlear implantation, and 29 children with normal hearing. Resting-state functional connectivity was measured with phase lag index, and we investigated the connectivity between the sensory regions for each frequency band. Network topology was examined using minimum spanning tree to obtain the network backbone characteristics. The results showed stronger connectivity between auditory and visual regions but reduced global network efficiency in children with late cochlear implantation in the theta and alpha bands. Significant correlations were observed between functional backbone characteristics and speech perception scores in children with cochlear implantation. Collectively, these results reveal an important effect of implantation age on the extent of brain plasticity from a network perspective and indicate that characteristics of the brain network can reflect the extent of rehabilitation of children with cochlear implantation.

Effect Of Tai Chi On Resting State Alpha Power And Functional Connectivity In Older Women

Aging is associated with reduced resting state functional connectivity (rsFC). A previous study indicated that short term Tai Chi practice along with other interventions altered rsFC and was associated with improved cognitive performance in older adults; however, it is unclear what the direct effect of Tai Chi practice is on rsFC and how long-term practice affects rsFC in older adults. PURPOSE: To investigate the effects of long-term Tai Chi practice on resting state alpha %power and rsFC in older women (TCOA) compared to aged and gender matched non-practitioners (OA) and young women (YA) control by Electroencephalography (EEG). METHOD: Fifteen female participants (5 YA of age 21 ± 1.73 years, 5 OA of age 71 ± 4.53 years, and 5 TCOA of age 71.40 ± 4.34 years) were included in this study. Participants were instructed to remain with their eyes open (EO) or eyes closed (EC) in a seated position for 60 seconds while two sets of EEG signals were recorded. Clean time series of EEG were obtained after preprocessing, and 10 sub-regions of interest were selected to cluster into four regions of interest (Frontal, Central, Parietal, Occipital) for further analysis. The phase log index (PLI) of pairwise regions at the alpha band (8-12 Hz) were calculated to assess rsFC. Power spectrum density of alpha band were also calculated and standardized by total power density (%Power). Linear Mixed Effect Models (LMM) were used to assess the impact of cohort, condition, regions, and their interactions on %power and PLI. RESULTS: There were statistically significant condition effects on both alpha %power (p < 0.01) and PLI (p < 0.01). EC condition demonstrated significantly higher %power (18%) and PLI (0.07). Cohort and condition interactions were also statistically significant in %power (p < 0.01) and PLI (p < 0.05) models. Specifically, %power increased less in OA (-13%, p < 0.01) in comparison to YA and TCOA under EC condition. At the same time, TCOA demonstrated a higher PLI (0.08, p < 0.01) improvement compared to YA and OA. No statistical significance was found in regions and other pairs of interactions. CONCLUSION: Aging affects the regulation of alpha-band power at the resting state with and without visual input. Meanwhile, practicing Tai Chi may alleviate this effect in older adults by improving rsFC.

The influence of different current-intensity transcranial alternating current stimulation on the eyes-open and eyes-closed resting-state electroencephalography

Transcranial alternating current stimulation (tACS) applies a sinusoidal oscillating current to modulate intrinsic oscillatory activity. Relevant studies of tACS have indicated that tACS can increase spontaneous brain activity in the occipital area. However, few studies have compared the effects of tACS with different current intensities on spontaneous brain activity in the occipital region. In this study, 10-Hz tACS was delivered to the occipital region at different current intensities (i.e., 1 and 2 mA). We investigated the effect of the tACS on both eyes-open and eyes-closed resting-state electroencephalography (EEG). A total of 20 subjects and fifteen subjects were recruited to participate in the 1-mA tACS experiment and the 2-mA tACS experiment, respectively. Ten subjects participated in both experiments. The experimental results demonstrated that both 1-mA tACS and 2-mA tACS could increase occipital resting-state EEG activities. For the eyes-open condition, alpha activity elicited by 2-mA tACS increased significantly greater than that elicited by 1-mA tACS, while 1-mA tACS could produce greater alpha activity compared to 2 mA for the eyes-closed condition. These results suggested that the optimal current intensity might be different for the eyes-open and eyes-closed resting-state conditions, laying a foundation for the subsequent study of occipital tACS on task-state EEG activities.

Investigating the power of eyes open resting state EEG for assisting in dementia diagnosis

IntroductionThe differentiation of Lewy body dementia from other common dementia types clinically is difficult, with a considerable number of cases only being found post-mortem. Consequently, there is a clear need for inexpensive and accurate diagnostic approaches for clinical use. Electroencephalography (EEG) is one potential candidate due to its relatively low cost and non-invasive nature. Previous studies examining the use of EEG as a dementia diagnostic have focussed on the eyes closed (EC) resting state; however, eyes open (EO) EEG may also be a useful adjunct to quantitative analysis due to clinical availability.MethodsWe extracted spectral properties from EEG signals recorded under research study protocols (1024 Hz sampling rate, 10:5 EEG layout). The data stems from a total of 40 dementia patients with an average age of 74.42, 75.81 and 73.88 years for Alzheimer’s disease (AD), dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD), respectively, and 15 healthy controls (HC) with an average age of 76.93 years. We utilised k-nearest neighbour, support vector machine and logistic regression machine learning to differentiate between groups utilising spectral data from the delta, theta, high theta, alpha and beta EEG bands.ResultsWe found that the combination of EC and EO resting state EEG data significantly increased inter-group classification accuracy compared to methods not using EO data. Secondly, we observed a distinct increase in the dominant frequency variance for HC between the EO and EC state, which was not observed within any dementia subgroup. For inter-group classification, we achieved a specificity of 0.87 and sensitivity of 0.92 for HC vs dementia classification and 0.75 specificity and 0.91 sensitivity for AD vs DLB classification, with a k-nearest neighbour machine learning model which outperformed other machine learning methods.ConclusionsThe findings of our study indicate that the combination of both EC and EO quantitative EEG features improves overall classification accuracy when classifying dementia types in older age adults. In addition, we demonstrate that healthy controls display a definite change in dominant frequency variance between the EC and EO state. In future, a validation cohort should be utilised to further solidify these findings.

Frontoparietal connectivity, Sensory Features, and Anxiety in Children and Adolescents with Autism Spectrum Disorder

ObjectivesBecause atypical global neural connectivity has been documented in autistic youth, but only limited data are available regarding the association between generalized anxiety disorder (GAD), sensory features (SF), and neural connectivity between frontal and parietal brain regions, these links were investigated in a sample of male autistic children and adolescents.MethodsForty-one autistic males aged between 6 and 18 years and their mothers were recruited as volunteer participants from Queensland, Australia. Participants underwent 3 min of eyes-closed and 3 min of eyes-opened electroencephalography (EEG) under resting conditions. EEG connectivity was investigated using Granger causality between frontal and parietal regions in alpha (8–13 Hz) and beta (13–30 Hz) bands.ResultsThere was a significant (p < .01) positive correlation between SF and GAD. GAD was associated with some characteristics of SF in the sample population. Additionally, there was a significant (p < .01) inverse correlation between directional frontoparietal connectivity and SF during the eyes-closed condition, specifically in relation to avoiding stimuli and sensitivity to the environment.ConclusionsReduced frontoparietal connectivity in association with higher anxiety and SF may demonstrate reduced relaxation due to greater sensitivity to sensory input.

Immediate Effects of Single-Session Proprioceptive Neuromuscular Facilitation Exercises on the Sit-to-Stand Strategy in Patients With Chronic Lumbar Spinal Disc Disease: A Preliminary Study

ObjectiveThe purpose of this study was to measure the immediate effects of single-session proprioceptive neuromuscular facilitation exercises on the sit-to-stand (STS) task and level of pain in patients with chronic low back pain. MethodsFifty-three patients were assigned to the control and intervention groups. The total time was 30 minutes (each exercise 5 minutes). The minimum vertical ground reaction force (VGRFmin) and maximum vertical ground reaction force (VGRFmax) and time phases (Tmin – time to counterforce, Tmax – time to peak force, Ttot – time to post-peak rebound force) were measured with a Kistler force plate in eyes-open and eyes-closed conditions during the STS task. Pain level was determined on a numeric rating scale. ResultsMain effects were observed only in the intervention group: decreasing pain value (F = 25.398, P < .0001), increasing Tmin (F = 5.72, P = .0044), decreasing Tmax (F = 3.43, P = .04), and decreasing Ttot (F = 3.935, P = .02258). There was a main effect of the eyes factor on VGRFmin (F = 12.53, P < .0001) and VGRFmax (F = 7.16, P < .01). ConclusionImmediate effects of single-session proprioceptive neuromuscular facilitation exercises were observed in decreasing the level of pain. Adaptation effects were noted in the retention test. The STS task could be optimized in time phases and dynamic movements in patients with chronic low back pain.

Fractal Dimension Feature as a Signature of Severity in Disorders of Consciousness: An EEG Study.

An accurate diagnosis of the disorder of consciousness (DOC) is essential for generating tailored treatment programs. Accurately diagnosing patients with a vegetative state (VS) and patients in a minimally conscious state (MCS), however, might be very complicated, reaching a misdiagnosis of approximately 40% if clinical scales are not carefully administered and continuously repeated. To improve diagnostic accuracy for those patients, tools such as electroencephalography (EEG) might be used in the clinical setting. Many linear indices have been developed to improve the diagnosis in DOC patients, such as spectral power in different EEG frequency bands, spectral power ratios between these bands, and the difference between eyes-closed and eyes-open conditions (i.e. alpha-blocking). On the other hand, much less has been explored using nonlinear approaches. Therefore, in this work, we aim to discriminate between MCS and VS groups using a nonlinear method called Higuchi's Fractal Dimension (HFD) and show that HFD is more sensitive than linear methods based on spectral power methods. For the sake of completeness, HFD has also been tested against another nonlinear approach widely used in EEG research, the Entropy (E). To our knowledge, this is the first time that HFD has been used in EEG data at rest to discriminate between MCS and VS patients. A comparison of Bayes factors found that differences between MCS and VS were 11 times more likely to be detected using HFD than the best performing linear method tested and almost 32 times with respect to the E. Machine learning has also been tested for HFD, reaching an accuracy of 88.6% in discriminating among VS, MCS and healthy controls. Furthermore, correlation analysis showed that HFD was more robust to outliers than spectral power methods, showing a clear positive correlation between the HFD and Coma Recovery Scale-Revised (CRS-R) values. In conclusion, our work suggests that HFD could be used as a sensitive marker to discriminate between MCS and VS patients and help decrease misdiagnosis in clinical practice when combined with commonly used clinical scales.

Effects of Diabetic Neuropathy on the Postural Stability of Adults with Type 2 Diabetes Mellitus

Diabetic peripheral neuropathy (DPN) is one of the most common complications, which occurs in 50–70% of people with Type 2 diabetes mellitus (T2DM). The disease usually affects the peripheral nerves and can cause loss of sensation in the feet, leading to impaired body equilibrium during quiet stance and gait, and elevated risk of falls. A total of 38 non-insulin-dependent T2DM adults (mean age 53.21 ± 7.74 years) – 18 with DPN and 20 without DPN, and 20 age- and sex-matched controls took part in the study. The DPN group was selected with standard clinical criteria and a Bulgarian version of the Michigan neuropathy screening instrument. Postural stability was evaluated with static posturography under two visual conditions (eyes open and eyes closed) on firm and soft support. Both diabetic groups exhibited significantly higher postural instability compared with the healthy controls, as well as stronger visual dependence. While standing on firm support, subjects with DPN exhibited significantly higher postural instability than those without DPN in the closed eyes condition only, whereas when standing on soft support, their postural stability was significantly more impaired compared with the diabetic subjects without DPN in both experimental conditions (open and closed eyes). A better understanding of the changes in postural stability in persons with T2DM would contribute to early diagnostics, rehabilitation and prevention of DPN.

Body sway and movement strategies for control of postural stability in people with spinocerebellar ataxia type 3: A cross-sectional study

BackgroundPostural instability with an excessive body sway is a disabling manifestation in spinocerebellar ataxia type 3. Whether the larger body sway reflects distinct movement strategies for postural control remains uncertain. This study compared the control of postural stability of people with spinocerebellar ataxia type 3 with healthy subjects using body sway and movement strategy analyses derived from bi- and three-dimensional posturography. MethodsTwenty-three patients (7 men, 16 women, 47 ± 11 years) and 102 healthy participants (34 men, 68 women; 44 ± 22 years) underwent posturography while standing with eyes open/closed tasks. Postural stability was assessed using elliptical area and average velocity of body sway. Spatial patterns (single-, double-, or multi-centered) were derived from the number of high-density regions in the three-dimensional statokinesigram. FindingsRepeated measures two-way analysis-of-variance showed a vision-by-group interaction effect for area (F1,122 = 28.831, P < 0.001, η2 = 0.037) and velocity (F1,123 = 59.367, P < 0.001, η2 = 0.073); sway area and velocity were higher in spinocerebellar ataxia type 3 and increased under eyes-closed condition, with a higher increase in the spinocerebellar ataxia type 3. A main effect for group (F1,123 = 11.702, P < 0.001, η2 = 0.061) but not vision (F1,123 = 2.257, P = 0.136, η2 = 0.005) was found for the number of high-density regions. Spatial patterns were different between groups under trials with eyes closed (χ22,125 = 7.46, P = 0.023) but not open (χ22,125 = 2.026, P = 0.363), with a shift from single- to double- or multi-centered spatial patterns. InterpretationCompared to healthy subjects, a larger body displacement and velocity in spinocerebellar ataxia type 3, mainly under visual constraints, are not related to the predominance of either ankle or hip movement strategies.

Two mechanisms facilitate regional independence between brain regions based on an examination of alpha-band activity in healthy control adult males

BackgroundAt rest, 8 to 12 Hz alpha rhythms are the dominant rhythm in the brain, with a common peak alpha frequency (PAF = the frequency at which alpha generators show maximum power) observed across brain regions. Although a common PAF across brain regions should result in high between-region connectivity, especially connectivity measures assessing the phase-similarity between alpha generators, high inter-regional alpha connectivity has not been observed. The present study was conducted as an initial step toward identifying mechanisms that allow brain regions to maintain functional independence in the presence of a common PAF. MethodsMEG data were obtained from 16 healthy control male adults (mean age = 24 years; range 21 to 30 years). A task requiring participants to alternate between a 10 s eyes-closed condition and a 5 s eyes-open condition was used to drive parietal-occipital alpha generators, with the 10 s eyes-closed condition eliciting large-amplitude alpha activity and thus providing alpha measures with good signal-to-noise ratio for source localization. Alpha source-space measures were obtained using Vector-based Spatial-Temporal Analysis using L1-minimum-norm. In each participant, the four strongest parietal-occipital alpha generators were identified. Connectivity between sources was assessed via a measure of phase-based connectivity called inter-site phase clustering (ISPC). ResultsIntra-class correlations (ICC) showed very high similarity in the average PAF (=computed using all eyes-closed data) between the four alpha sources (ICC single measure = 0.88, p < 0.001). Despite a common average PAF, across participants, significant ISPC was often observed no more than that expected by chance. Examination of the alpha time course data indicated that low ISPC was often due to instantaneous changes in alpha phase (phase slips). ISPC analyses removing data with phase slips indicated that low ISPC was also due to slight continuous changes in the alpha frequency, with frequency drift more likely in non-significant than significant ISPC trials. ConclusionsThe present exploratory effort suggested two processes underlying the lack of observed inter-regional alpha phase coherence that may help maintain regional functional independence even in the presence of a common PAF. In particular, although the alpha generators were observed to oscillate at the same rate on average, across time each alpha generator oscillated a little slower or faster, and about every one and a half seconds an alpha generator abruptly lost the beat. Because of this, functional independence among alpha generators (and thus brain regions) was the rule rather than the exception. Studies replicating these processes that allow brain regions to maintain functional independence, using different source localization methods and in different conditions (e.g., a true resting state), are warranted. Impact statementUsing source localization to measure parietal-occipital alpha generator activity, two properties that limit between-region alpha functional connectivity are proposed. In particular, a model of alpha generator activity is offered where via transient phase slips occurring approximately every 1.5 s, as well as slight non-stationarity in the alpha frequency, brain regions retain a common alpha frequency while also maintaining regional identity and presumably functionality. Findings also suggest novel markers for use in studies examining changes in alpha activity across maturation as well as in studies examining alpha activity in patient populations where alpha abnormalities have been reported.

Postural Balance in Young Tennis Players of Varied Competition Levels.

The aim of this study was to investigate the effect of young tennis players' expertise on their postural balance (PB) under sensorial conditions with eyes open (EO) and with eyes closed (EC). Our participants were 75 healthy adolescents aged 15-18 years, divided into three groups based on their skill levels: (a) national tennis players (NAT; n = 25), regional tennis players (REG; n =25), and a control group of non-sport practitioners (CG; n = 25). We recorded center of pressure area and mean velocity on a force platform while participants stood in bipedal and unipedal stances in EO and EC conditions for all three groups. Statistical analyses showed that NAT participants swayed less than CG participants in all conditions and less than REG participants in the bipedal stance with EC and in the unipedal stance, both with EO and EC. Thus, tennis practice/experience may have improved PB in this sample, as high-level tennis players had better PB compared to novices, especially in challenging conditions.

State Changes During Resting-State (Magneto)encephalographic Studies: The Effect of Drowsiness on Spectral, Connectivity, and Network Analyses.

BackgroundA common problem in resting-state neuroimaging studies is that subjects become drowsy or fall asleep. Although this could drastically affect neurophysiological measurements, such as magnetoencephalography (MEG), its specific impact remains understudied. We aimed to systematically investigate how often drowsiness is present during resting-state MEG recordings, and how the state changes alter quantitative estimates of oscillatory activity, functional connectivity, and network topology.MethodsAbout 8-min MEG recordings of 19 healthy subjects, split into ~13-s epochs, were scored for the presence of eyes-open (EO), alert eyes-closed (A-EC), or drowsy eyes-closed (D-EC) states. After projection to source-space, results of spectral, functional connectivity, and network analyses in 6 canonical frequency bands were compared between these states on a global and regional levels. Functional connectivity was analyzed using the phase lag index (PLI) and corrected amplitude envelope correlation (AECc), and network topology was analyzed using the minimum spanning tree (MST).ResultsDrowsiness was present in >55% of all epochs that did not fulfill the AASM criteria for sleep. There were clear differences in spectral results between the states (A-EC vs. D-EC) and conditions (EO vs. A-EC). The influence of state and condition was far less pronounced for connectivity analyses, with only minimal differences between D-EC and EO in the AECc in the delta band. There were no effects of drowsiness on any of the MST measures.ConclusionsDrowsiness during eyes-closed resting-state MEG recordings is present in the majority of epochs, despite the instructions to stay awake. This has considerable influence on spectral properties, but much less so on functional connectivity and network topology. These findings are important for interpreting the results of EEG/MEG studies using spectral analyses in neurological disease, where recordings should be evaluated for the presence of drowsiness. For connectivity analyses or studies on network topology, this seems of far less importance.