Residual alterations of brain electrical activity in clinically asymptomatic concussed individuals: An EEG study

ObjectiveTo examine the neural substrates underlying performance on Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) and HeadRehab Virtual Reality (VR) balance and spatial modules in a concussed and control group.MethodsThirteen controls and seven concussed participants were fitted with a Geodesic 128-channel EEG cap and completed three assessments: EEG baseline, ImPACT testing, and VR balance and spatial modules. Concussed participants completed were tested within 8 (5 ± 1) days after injury.ResultsEEG power was significantly (p < .05) decreased in the concussed group over all testing modalities. EEG coherence was significantly (p < .05) increased in the concussed group during EEG baseline and ImPACT. For VR testing, two conditions showed significant (p < .05) increases in EEG coherence between ROIs, while two different conditions showed significant (p < .05) decreases in coherence levels.ConclusionsConcussed participants passed all clinical concussion testing tools, but showed pathophysiological dysfunction when evaluating EEG variables.SignificanceConcussed participants are able to compensate and achieve normal functioning due to recruiting additional brain networks. This allows concussed participants to pass clinical tests while still displaying electrophysiological deficits and clinicians must consider this information when making return-to-play decisions.     

Evaluation of movement and brain activity

Clinical neurophysiology studies can contribute important information about the physiology of human movement and the pathophysiology and diagnosis of different movement disorders. Some techniques can be accomplished in a routine clinical neurophysiology laboratory and others require some special equipment. This review, initiating a series of articles on this topic, focuses on the methods and techniques. The methods reviewed include EMG, EEG, MEG, evoked potentials, coherence, accelerometry, posturography (balance), gait, and sleep studies. Functional MRI (fMRI) is also reviewed as a physiological method that can be used independently or together with other methods. A few applications to patients with movement disorders are discussed as examples, but the detailed applications will be the subject of other articles.     

EEG coherence studies in the normal brain and after early-onset cortical pathologies

Visual corpus callosum (CC) preferentially interconnects neurons selective for similar stimulus orientation near the representations of the vertical meridian. These properties allow studying the CC functionality with EEG coherence analysis. Iso-oriented and orthogonally-oriented gratings were presented to the two hemifields, either close to the vertical meridian or far from it. In animals with intact CC, and in man, interhemispheric coherence (ICoh) increased only with iso-oriented gratings presented near or crossing the vertical meridian. The increase was localized to occipital electrodes and was specific for the β–γ frequency band. Visual-stimulus induced changes in ICoh were studied in patients with early pathologies of the visual areas. From a girl with abnormal vision and severe bilateral lesion of the primary visual areas at 3 weeks, after premature birth at 30 weeks, we obtained no ICoh response until 9 years. In control children visual stimulation increased occipital ICoh at 6–7 years. From a young man having suffered similar lesions when he was 9 months older than the girl, no consistent increase in ICoh could be obtained. In a 14-year-old girl with congenital visual agnosia, no visible lesions, but with a temporal-occipital epileptic focus, ICoh responses were evoked both by iso-oriented, and by orthogonally-oriented gratings. In a young man with bilateral parieto-occipital microgyria extending into the calcarine sulcus, visual stimuli increased ICoh as in normal individuals, but the response was weaker. These cases are discussed in terms of development of CC connections and point to a variety of plastic changes in the cortical connectivity of children.     

Correlation between cognitive brain function and electrical brain activity in dementia of Alzheimer type

Summary Psychometric tests which assess cognitive brain function in dementia disorders are partly prone to artifacts, e.g., the experience of the investigator and the cooperation of the patient influences the results. An objective way to assess the degree of cognitive disturbance could be to measure neuronal activity represented by the electrical brain activity. The aim of the present study was to investigate how well cognitive function in dementia assessed by psychometric tests correlates with electrical brain activity (EEG). Multichannel EEG data was reduced into 3-D intracerebral equivalent dipole EEG generators allowing a more convenient statistical data management and valid physiological data interpretation. 35 patients suffering from dementia of Alzheimer type were investigated. An increase of dipole strength in the slow frequency bands, a more anterior equivalent dipole of alpha- and beta-activity, and a slowing of the EEG with increasing cognitive deterioration could be demonstrated. The results support the hypothesis that the amount of disturbance of cognitive function in dementia can be assessed by measuring the electrical activity of the brain.     

Entrainment of vastus medialis complex activity differs between genders

Introduction: That the vastus medialis oblique (VMO) is a functional unit of the vastus medialis (VM) is disputed. Delayed VMO activation predicts patellofemoral pain, which has higher rates in women. Methods: Single MUs and surface electromyogram (EMG) were collected from the VMO and VM of 9 men and 9 women. Men were tested once; women were tested during 5 menstrual phases. Coherence was assessed for motor unit (MU) firings within and between the VM and VMO using multilevel logistic models to determine statistical significance. Results: Compared with women, men have 741% (MU pairs) and 256% (MU‐EMG pairs) greater odds of common drive (0–5 Hz ) coherent oscillations. MU pairs from the VMO and the dual VM/VMO complex have 228% and 212% greater odds of coherent oscillations in the beta band (15–35 Hz ) compared with VM pairs. Conclusions: The VM and VMO are neurologically different muscles; control of the VM complex is sexually dimorphic. Muscle Nerve 53 : 633–640, 2016     

Identifying true brain interaction from EEG data using the imaginary part of coherency.

OBJECTIVE: The main obstacle in interpreting EEG/MEG data in terms of brain connectivity is the fact that because of volume conduction, the activity of a single brain source can be observed in many channels. Here, we present an approach which is insensitive to false connectivity arising from volume conduction. METHODS: We show that the (complex) coherency of non-interacting sources is necessarily real and, hence, the imaginary part of coherency provides an excellent candidate to study brain interactions. Although the usual magnitude and phase of coherency contain the same information as the real and imaginary parts, we argue that the Cartesian representation is far superior for studying brain interactions. The method is demonstrated for EEG measurements of voluntary finger movement. RESULTS: We found: (a) from 5 s before to movement onset a relatively weak interaction around 20 Hz between left and right motor areas where the contralateral side leads the ipsilateral side; and (b) approximately 2-4 s after movement, a stronger interaction also at 20 Hz in the opposite direction. CONCLUSIONS: It is possible to reliably detect brain interaction during movement from EEG data. SIGNIFICANCE: The method allows unambiguous detection of brain interaction from rhythmic EEG/MEG data.     

Preparation and performance of obstacle steps: interaction between brain and spinal neuronal activity

This study investigated the interactions of supraspinal with spinal neuronal circuits during obstacle steps by recordings of electroencephalography (EEG), reflex activity and limb muscle electromyography (EMG). Subjects walking with reduced vision on a treadmill were acoustically informed about an approaching obstacle and received feedback about task performance. Only following a task-relevant acoustic signal, spinal reflex responses, evoked by tibial nerve stimulation during mid-stance, were enhanced in proximal arm and leg flexor muscles prior to obstacle compared to normal swing, reflecting the neuronal preparation of the task. During swing over the obstacle, limb muscle EMG activity was greater than in normal swing. Both the preparation and the performance (i.e. ascending movement slope of the obstacle-crossing leg) were associated with an enhanced EEG signal mainly in the prefrontal cortex of the right hemisphere. Adaptational changes in performance, reflex activity and muscle activation during repetitive obstacle stepping were not reflected in the EEG activity, probably due to an insufficient resolution of the EEG. The observations suggest that drive from supraspinal centers initiates and maintains spinal neuronal activity underlying obstacle task preparation and performance.     

Functional significance of the ipsilateral hemisphere during movement of the affected hand after stroke

Previous fMRI observations have suggested increased task-related activation of the ipsilateral cerebral motor cortex in patients recovering from stroke. This is generally taken to infer an increased output from this area, although the functional relevance of this has been questioned. Here, we use directed EEG coherence to reveal whether there is increased informational flow from the ipsilateral motor cortex following motor stroke, and through correlation with degree of recovery, establish that this pattern of activity is associated with limited functional improvement. Unrecovered (n = 14), recovered (n = 11) patients and healthy subjects (n = 16) performed an isometric grip task with either hand that corresponded to 25% of individual maximum force, while EEG was recorded. For unrecovered stroke patients, most task-related information flow between the sensorimotor cortices in the low beta band of the EEG came from the ipsilateral (undamaged) hemisphere during grip with the affected hand. This was not the case when they gripped with their unaffected hand, when cortical activity was driven from the contralateral sensorimotor cortex. The latter pattern was also seen in recovered patients and controls. These findings suggest a functional role for the ipsilateral hemisphere in organizing movement of the impaired limb following stroke, but only in those patients that do not make a good functional recovery. Patients making a fuller recovery organize movement-related cortical activity from the hemisphere contralateral to movement.     

The implication of functional connectivity strength in predicting treatment response of major depressive disorder: A resting EEG study

Predicting treatment response in major depressive disorder (MDD) has been an important clinical issue given that the initial intent-to-treat response rate is only 50 to 60%. This study was designed to examine whether functional connectivity strengths of resting EEG could be potential biomarkers in predicting treatment response at 8 weeks of treatment. Resting state 3-min eyes-closed EEG activity was recorded at baseline and compared in 108 depressed patients. All patients were being treated with selective serotonin-reuptake inhibitors. Baseline coherence and power series correlation were compared between responders and non-responders evaluated at the 8th week by Hamilton Depression Rating Scale. Pearson correlation and receiver operating characteristic (ROC) analyses were applied to evaluate the performance of connectivity strengths in predicting/classifying treatment responses. The connectivity strengths of right fronto-temporal network at delta/theta frequencies differentiated responders and non-responders at the 8th week of treatment, such that the stronger the connectivity strengths, the poorer the treatment response. ROC analyses supported the value of these measures in classifying responders/non-responders. Our results suggest that fronto-temporal connectivity strengths could be potential biomarkers to differentiate responders and slow responders or non-responders in MDD.     

Electroencephalographic analysis of cortico-muscular coherence: reference effect, volume conduction and generator mechanism.

OBJECTIVE: To measure the synchrony between cortical and muscle oscillatory activities, the coherence estimate between EEG and EMG was computed. METHODS: The multichannel electroencephalogram (EEG) and electromyogram (EMG) of the right abductor pollicis brevis muscle were recorded in 5 normal volunteers. Various types of EEG derivation methods were systematically compared to establish a standard method to study cortico-muscular coupling. RESULTS: The use of a reference-free EEG derivation (current source density) greatly improved cortico-muscular coherence. In all subjects, EEGs over the left sensorimotor cortex were coherent with EMG (mean peak frequency: 18.7 Hz, mean highest coherence: 0.124). The time lag from cortex to muscle in 14-50 Hz was 14.3 ms. EEG source derivation revealed that both radial and tangential generators in the precentral cortex might contribute to this phenomenon. In the EEG signals using common average reference, an artifactual coherence peak over the medial frontal area was observed, which might largely be explained by volume conduction from the primary sensorimotor cortex. CONCLUSIONS: We conclude that the current source density or its approximation is preferable to estimate the cortico-muscular coherence and that the interpretation of such coherence using referenced EEGs should be taken with care.     

Prediction of treatment resistance in obsessive compulsive disorder patients based on EEG complexity as a biomarker

ObjectiveThis study aimed to identify an Electroencephalography (EEG) complexity biomarker that could predict treatment resistance in Obsessive compulsive disorder (OCD) patients. Additionally, the statistical differences between EEG complexity values in treatment-resistant and treatment-responsive patients were determined. Moreover, the existence of correlations between EEG complexity and Yale-Brown Obsessive Compulsive Scale (YBOCS) score were evaluated.MethodsEEG data for 29 treatment-resistant and 28 treatment-responsive OCD patients were retrospectively evaluated. Approximate entropy (ApEn) method was used to extract the EEG complexity from both whole EEG data and filtered EEG data, according to 4 common frequency bands, namely delta, theta, alpha, and beta. The random forests method was used to classify ApEn complexity.ResultsApEn complexity extracted from beta band EEG segments discriminated treatment-responsive and treatment-resistant OCD patients with an accuracy of 89.66% (sensitivity: 89.44%; specificity: 90.64%). Beta band EEG complexity was lower in the treatment-resistant patients and the severity of OCD, as measured by YBOCS score, was inversely correlated with complexity values.ConclusionsThe results indicate that, EEG complexity could be considered a biomarker for predicting treatment response in OCD patients.SignificanceThe prediction of treatment response in OCD patients might help clinicians devise and administer individualized treatment plans.     

Age and gender effects in EEG coherence: I. Developmental trends in normal children.

OBJECTIVE: This study investigated intra-hemispheric and inter-hemispheric EEG coherences as a function of age and gender in normal children. METHODS: Two groups of 40 boys and 40 girls, each containing 8 normal children in each 1-year band from 8 to 12 years, participated. EEG was recorded from 21 sites during an eyes-closed resting condition. Wave-shape coherence was calculated for 8 intra-hemispheric electrode pairs (4 in each hemisphere), and 8 inter-hemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. RESULTS: There was consistent evidence of coherences developing across this age range, particularly in long-range intra- and inter-hemispheric electrode pairs. Coherences were larger in the left hemisphere than the right. Coherences also appeared to develop further in males than females, across several regions and frequency bands, suggesting that females lag males in this aspect of brain development. CONCLUSIONS: EEG coherences in normal children of this age range develop systematically with age. These developmental effects vary substantially with gender, brain region and frequency bands. SIGNIFICANCE: The data reported here provide basic norms for coherence development in different brain regions in normal children.     

Anterior thalamic mediation of experimental seizures: selective EEG spectral coherence

PURPOSE: Physiological evidence has shown that the anterior thalamus (AN) and its associated efferents/afferents constitute an important propagation pathway for pentylenetetrazol (PTZ)-mediated generalized seizures in rodents. Previous work demonstrated metabolic, physical, chemical, and electrical stimulation data supporting a role for AN in the expression of PTZ seizures. We now extend these observations through examination of neuroelectric signal indicators during seizure epochs. We show that the EEG recorded from AN is highly coherent with surface cortical (CTX) EEG during the immediate preconvulsant period and during the ictal stateough. METHODS: Awake rats were continuously infused with PTZ until clonic seizures were recorded by using both subcortical AN, posterior thalamus (PT), or hippocampal (HPC) bipolar electrodes and cortical EEG. Through the signal-analysis techniques of ordinary and partial coherence, it was possible to focus selectively on signal correlations between AN and CTX (AN/CTX) by removing the effects of unaffiliated regions such as PT and HPC. RESULTS: Coherence of PT/CTX was observed to be modest, and partial coherence of PT/CTX with the effects of AN/CTX removed did not improve the signal coherence of PT/CTX (PT/CTX-AN). In contrast, AN/CTX coherence was observed to be high, with undiminished correlation when PT/CTX influence was removed (AN/CTX-PT). The most robust band of AN/CTX coherence was centered around the spike-wave clonic frequency of 1-3 Hz. Partial multiple coherence-analysis techniques were used to remove the possible signal contributions from hippocampus in addition to PT. The AN/CTX coherence remained fully preserved in the low-frequency bands. CONCLUSIONS: These data provide electrophysiologic evidence supporting the special role of the anterior thalamus in the propagation of seizure activity between subcortex and cortex.     

Interhemispheric EEG coherence after corpus callosotomy

Interhemispheric coherence analysis of scalp electroencephalograms (EEGs) in three intractable epileptic patients before and after surgical section of the anterior part of the corpus callosum was performed. Equidistant EEG periods recorded under resting conditions free of interictal epileptic activity and periods with generalized spike-and-wave discharges were investigated. Mean coherence values for five frequency EEG bands (delta, theta, alpha, beta 1 and beta 2) before and after corpus callosotomy were compared with each other and statistically evaluated. Anterior callosotomy led, in all cases, to a decrease of interhemispheric EEG coherence in most localizations, with the most profound decreases in the region corresponding to the section. These results support the hypothesis that the corpus callosum plays an important role in resting interhemispheric integration and EEG synchronization, similar to its central role in propagation of specific epileptic activity.     

The creative brain: investigation of brain activity during creative problem solving by means of EEG and FMRI

Cortical activity in the EEG alpha band has proven to be particularly sensitive to creativity-related demands, but its functional meaning in the context of creative cognition has not been clarified yet. Specifically, increases in alpha activity (i.e., alpha synchronisation) in response to creative thinking can be interpreted in different ways: As a functional correlate of cortical idling, as a sign of internal top-down activity or, more specifically, as selective inhibition of brain regions. We measured brain activity during creative thinking in two studies employing different neurophysiological measurement methods (EEG and fMRI). In both studies, participants worked on four verbal tasks differentially drawing on creative idea generation. The EEG study revealed that the generation of original ideas was associated with alpha synchronisation in frontal brain regions and with a diffuse and widespread pattern of alpha synchronisation over parietal cortical regions. The fMRI study revealed that task performance was associated with strong activation in frontal regions of the left hemisphere. In addition, we found task-specific effects in parietotemporal brain areas. The findings suggest that EEG alpha band synchronisation during creative thinking can be interpreted as a sign of active cognitive processes rather than cortical idling.     

Right parietal brain activity precedes perceptual alternation during binocular rivalry

We investigated perceptual reversals for intermittently presented stimuli during binocular rivalry and physical alternation while the ongoing EEG was recorded from 64 channels. EEG topographies immediately preceding stimulus‐onset were analyzed and two topographies doubly dissociated perceptual reversals from non‐reversals. The estimated intracranial generators associated with these topographies were stronger in right inferior parietal cortex and weaker bilaterally in the ventral stream before perceptual reversals. No such differences were found for physical alternation of the same stimuli. These results replicate and extend findings from a previous study with the Necker cube and suggest common neural mechanisms associated with perceptual reversals during binocular rivalry and ambiguous figure perception. For both types of multi‐stable stimuli, the dorsal stream is more active preceding perceptual reversals. Activity in the ventral stream, however, differed for binocular rivalry compared to ambiguous figures. The results from the two studies suggest a causal role for the right inferior parietal cortex in generating perceptual reversals regardless of the type of multi‐stable stimulus, while activity in the ventral stream appears to depend on the particular type of stimulus. Hum Brain Mapp 32:1432–1442, 2010. © 2010 Wiley‐Liss, Inc.     

Resting state EEG abnormalities in autism spectrum disorders

Autism spectrum disorders (ASD) are a group of complex and heterogeneous developmental disorders involving multiple neural system dysfunctions. In an effort to understand neurophysiological substrates, identify etiopathophysiologically distinct subgroups of patients, and track outcomes of novel treatments with translational biomarkers, EEG (electroencephalography) studies offer a promising research strategy in ASD. Resting-state EEG studies of ASD suggest a U-shaped profile of electrophysiological power alterations, with excessive power in low-frequency and high-frequency bands, abnormal functional connectivity, and enhanced power in the left hemisphere of the brain. In this review, we provide a summary of recent findings, discuss limitations in available research that may contribute to inconsistencies in the literature, and offer suggestions for future research in this area for advancing the understanding of ASD.     

Resting state connectivity in neocortical epilepsy: The epilepsy network as a patient-specific biomarker

ObjectiveLocalization related epilepsy (LRE) is increasingly accepted as a network disorder. To better understand the network specific characteristics of LRE, we defined individual epilepsy networks and compared them across patients.MethodsThe epilepsy network was defined in the slow cortical potential frequency band in 10 patients using intracranial EEG data obtained during interictal periods. Cortical regions were included in the epilepsy network if their connectivity pattern was similar to the connectivity pattern of the seizure onset electrode contact. Patients were subdivided into frontal, temporal, and posterior quadrant cohorts according to the anatomic location of seizure onset. Jaccard similarity was calculated within each cohort to assess for similarity of the epilepsy network between patients within each cohort.ResultsAll patients exhibited an epilepsy network in the slow cortical potential frequency band. The topographic distribution of this correlated network activity was found to be unique at the single subject level.ConclusionsThe epilepsy network was unique at the single patient level, even between patients with similar seizure onset locations.SignificanceWe demonstrated that the epilepsy network is patient-specific. This is in keeping with our current understanding of brain networks and identifies the patient-specific epilepsy network as a possible biomarker in LRE.     

Resting EEG and behavioural correlates of interhemispheric transfer times

Correlations between the relative speeds of left-to-right and right-to-left interhemispheric transfer times and resting quantitative electroencephalography activity were examined in order to determine if variability in interhemispheric transfer was related to individual variability in resting neural firing patterns. Resting electroencephalograph frequencies for 32 participants were regressed for 4 frequency bands at 8 different locations calculated for asymmetrical activation through subtracting the left from right average spectral power of each. Participants also completed a series of behavioural tasks that are typically localized to the right hemisphere (RH). Results indicate that the frontal medial average spectral power of the beta band is correlated with the speed of transfer such that larger resting beta values in the right as compared to left location are associated with faster right-to-left interhemispheric transfer times and that larger resting beta values in the left as compared to right location are associated with faster left-to-right interhemispheric transfer times. Furthermore, enhanced performance on tasks typically localized to the RH is correlated with slower right-to-left interhemispheric transfer times, suggesting that the dominance of one hemisphere may come at a cost to interhemispheric communication.     

Human Steady-State Visual and Auditory Evoked Potential Components During a Selective Discrimination Task

No abstract available for this article.