Improving the interpretation of ictal scalp EEG: BSS-CCA algorithm for muscle artifact removal

PURPOSE: To investigate the potential clinical relevance of a new algorithm to remove muscle artifacts in ictal scalp EEG. METHODS: Thirty-seven patients with refractory partial epilepsy with a well-defined seizure onset zone based on full presurgical evaluation, including SISCOM but excluding ictal EEG findings, were included. One ictal EEG of each patient was presented to a clinical neurophysiologist who was blinded to all other data. Ictal EEGs were first rated after band-pass filtering, then after elimination of muscle artifacts using a blind source separation-canonical correlation analysis technique (BSS-CCA). Degree of muscle artifact contamination, lateralization, localization, time and pattern of ictal EEG onset were compared between the two readings and validated against the other localizing information. RESULTS: Muscle artifacts contaminated 97% of ictal EEGs, and interfered with the interpretation in 76%, more often in extratemporal than temporal lobe seizures. BSS-CCA significantly improved the sensitivity to localize the seizure onset from 62% to 81%, and performed best in ictal EEGs with moderate to severe muscle artifact contamination. In a significant number of the contaminated EEGs, BSS-CCA also led to an earlier identification of ictal EEG changes, and recognition of ictal EEG patterns that were hidden by muscle artifact. CONCLUSIONS: Muscle artifacts interfered with the interpretation in a majority of ictal EEGs. BSS-CCA reliably removed these muscle artifacts in a user-friendly manner. BSS-CCA may have an important place in the interpretation of ictal EEGs during presurgical evaluation of patients with refractory partial epilepsy.     

Quantification of fMRI artifact reduction by a novel plaster cast head holder

In light of artifact-induced high variability of activation in fMRI repeat studies, we developed and tested a clinically useful plaster cast head holder (PCH) with improved immobilization, repositioning, and comfort. With PCH, there were considerably lower levels of translational and rotational head motion components compared to head fixation with conventional restraining straps (CRS). Rotational components cannot be fully compensated by realignment and lead to "false activations." In addition, task-correlated head motion, which highly increases the risk of artifacts, was considerably reduced with PCH, especially in a motion prone subject. Compared with PCH, head motion was 133% larger with CRS in a highly cooperative subject. With a motion prone subject, head motion range was increased by 769% (PCH: 0.9 mm, CRS: 7.8 mm), which may indicate the usefulness of PCH for restless patients. In functional activation maps, PCH alone yielded fewer residual motion artifacts than CRS + image registration. Subject tolerance of the head holder during the long measurement times of up to 2.5 hr was good, and slice orientation on different days confirmed the quality of repositioning.     

Effect of muscle-fiber velocity recovery function on motor unit action potential properties in voluntary contractions

Measurements of muscle-fiber conduction velocity during voluntary contractions have been used in the diagnosis of neuromuscular diseases. However, the velocity of propagation of action potentials depends on the interspike interval of activation due to the velocity recovery function (VRF) of muscle fibers. The comparison of muscle-fiber conduction velocity estimates between individuals may thus be influenced by differences in motor unit discharge rate. This study investigates action potential properties of motor units of the sternocleidomastoid muscle during voluntary modulation of discharge rate with the purpose of assessing the effect of the VRF on motor unit properties in voluntary contractions. Nineteen healthy men trained to control a target motor unit with feedback of surface multichannel electromyographic (EMG) signals. The subjects performed three 30-s contractions of cervical flexion/rotation modulating the discharge rate of the target motor unit from 6.6 +/- 1.6 pps to 28.0 +/- 6.4 pps. Action potential conduction velocity was correlated to instantaneous discharge rate (R = 0.38 +/- 0.21). Action potential conduction velocity, peak-to-peak amplitude, and duration varied between minimum and maximum discharge rate (P < 0.01; percent change 12.3 +/- 5.0, -11.8 +/- 9.9, and -12.9 +/- 7.3). Thus, the properties of surface motor unit action potentials vary with modulation of discharge rate. This has implications for the use of conduction velocity values measured during voluntary contractions to differentiate patient populations from healthy individuals and for the development of normative data.     

TMS-evoked long-lasting artefacts: A new adaptive algorithm for EEG signal correction

Objective

During EEG the discharge of TMS generates a long-lasting decay artefact (DA) that makes the analysis of TMS-evoked potentials (TEPs) difficult. Our aim was twofold: (1) to describe how the DA affects the recorded EEG and (2) to develop a new adaptive detrend algorithm (ADA) able to correct the DA.

Brain plasticity as a basis for recovery of function in humans

One of the factors leading to the virtual neglect of the long-term potential for functional recovery following brain damage was the eclipse of plasticity concepts during the 100 years following Broca's 1861 publication on location of function. However, in the last 30 years evidence has been accumulating that demonstrates the plasticity of the brain and thus recovery potential is a subject of practical as well as theoretical interest. "Unmasking" of relatively inactive pathways, the taking over of functional representation by undamaged brain tissue, and neuronal group selection are among the mechanisms that are being explored. Human models of recovery of function include hemispherectomy patients that have regained bilateral function, facial paralysis patients who recover function (with appropriate rehabilitation) after VII-XII cranial nerve anastomosis, and patients with muscle transpositions to re-establish lost motor functions. The role of early and late rehabilitation, with attention to psychosocial and environmental factors, appears to be critical for recovery.     

Neuroimaging of recovery of function after stroke: implications for rehabilitation

Stroke is a leading cause of morbidity and mortality in individuals. Many patients have good functional recovery after stroke. The mechanisms of recovery remain largely unknown. Neuroimaging of patients recovering from stroke may provide important insight into the mechanisms of recovery as well as assist in the development of new rehabilitation techniques. The first part of this article reviews previous neuroimaging studies that have monitored the reorganization within the motor and language areas after stroke. In the second section, a unifying theory based on John Hughlings Jackson's "Principles of Compensation" is presented as a possible theory for recovery of function. In the final portion of the article, possible implications and future applications of neuroimaging studies for rehabilitation are presented.     

ARTIST: A fully automated artifact rejection algorithm for single‐pulse TMS‐EEG data

Concurrent single‐pulse TMS‐EEG (spTMS‐EEG) is an emerging noninvasive tool for probing causal brain dynamics in humans. However, in addition to the common artifacts in standard EEG data, spTMS‐EEG data suffer from enormous stimulation‐induced artifacts, posing significant challenges to the extraction of neural information. Typically, neural signals are analyzed after a manual time‐intensive and often subjective process of artifact rejection. Here we describe a fully automated algorithm for spTMS‐EEG artifact rejection. A key step of this algorithm is to decompose the spTMS‐EEG data into statistically independent components (ICs), and then train a pattern classifier to automatically identify artifact components based on knowledge of the spatio‐temporal profile of both neural and artefactual activities. The autocleaned and hand‐cleaned data yield qualitatively similar group evoked potential waveforms. The algorithm achieves a 95% IC classification accuracy referenced to expert artifact rejection performance, and does so across a large number of spTMS‐EEG data sets (n = 90 stimulation sites), retains high accuracy across stimulation sites/subjects/populations/montages, and outperforms current automated algorithms. Moreover, the algorithm was superior to the artifact rejection performance of relatively novice individuals, who would be the likely users of spTMS‐EEG as the technique becomes more broadly disseminated. In summary, our algorithm provides an automated, fast, objective, and accurate method for cleaning spTMS‐EEG data, which can increase the utility of TMS‐EEG in both clinical and basic neuroscience settings.     

Artifact correction of the ongoing EEG using spatial filters based on artifact and brain signal topographies.

Review and analysis of continuous EEG recordings may be impeded by physiological artifacts such as blinks, eye movements, or cardiac activity. Spatial filters based on artifact and brain signal topographies can remove artifacts completely without distortion of relevant brain activity. The authors describe the basic principle of artifact correction by spatial filtering and they review different approaches to estimate artifact and brain signal topographies. The main focus is on the preselection approach, which is fast enough to be applied while paging through the segments of a digital EEG recording. Examples of real EEG segments, containing epileptic seizure activity or interictal spikes contaminated by artifacts, show that spatial filtering by preselection can be a useful tool during EEG review. Advantages and disadvantages of the different spatial filter approaches are discussed.     

Evidence for a menstrual-linked artifact in determining rates of depression

This is the first empirical report suggesting a menstrual-linked artifact in determining rates of depression. We investigated the effects of perceived menstrual cycle phase, and premenstrual and postmenstrual timing in the cycle, on scores for a self-report measure of depression that is widely used in epidemiological studies, the Center for Epidemiologic Studies Depression Scale (CES-D). The first study used a cross-sectional design and the second used a follow-up design with repeated measures across the menstrual cycle. Both studies assessed a community-based sample of regularly menstruating women. In the second study, testing was also done at 2-week intervals in men for comparison purposes. Both studies supported the hypothesis of a significant menstrual cycle-related effect on CES-D scores. The menstrual-linked effect is greater than the test-retest variability observed in men, such that women more often tend to meet the cut-off criteria for depression on the CES-D premenstrually, as compared with postmenstrually. Thus it is possible that cyclic variations in ratings on the CES-D may elevate epidemiological estimates of depression, as defined by RDC criteria, for menstruating women. Further longitudinal assessment in randomly selected samples will be needed in order to clarify whether a menstrual-linked effect is substantial and specific enough to require correction, or documentation of cycle phase, in epidemiological studies of depression.     

Cerebral reorganization as a function of linguistic recovery in children: An fMRI study

Characterizing and mapping the relationship between neuronal reorganization and functional recovery are essential to the understanding of cerebral plasticity and the dynamic processes which occur following brain damage. The neuronal mechanisms underlying linguistic recovery following left hemisphere (LH) lesions are still unknown. Using functional magnetic resonance imaging (fMRI), we investigated whether the extent of brain lateralization of linguistic functioning in specific regions of interest (ROIs) is correlated with the level of linguistic performance following recovery from acquired childhood aphasia. The study focused on a rare group of children in whom lesions occurred after normal language acquisition, but prior to complete maturation of the brain. During fMRI scanning, rhyming, comprehension and verb generation activation tasks were monitored. The imaging data were evaluated with reference to linguistic performance measured behaviorally during imaging, as well as outside the scanner. Compared with normal controls, we found greater right hemisphere (RH) lateralization in patients. However, correlations with linguistic performance showed that increased proficiency in linguistic tasks was associated with greater lateralization to the LH. These results were replicated in a longitudinal case study of a patient scanned twice, 3 years apart. Additional improvement in linguistic performance of the patient was accompanied by increasing lateralization to the LH in the anterior language region. This, however, was the result of a decreased involvement of the RH. These findings suggest that recovery is a dynamic, ongoing process, which may last for years after onset. The role of each hemisphere in the recovery process may continuously change within the chronic stage.     

Experiencing recovery: a dimensional analysis of recovery narratives

This paper applies the technique of dimensional analysis to recovery narratives in order to examine the uniqueness of the recovery process. It finds that there are four central dimensions involved in recovery: self, others, the system, and the problem. The recovery process is made up of component processes that correspond to these dimensions: recognizing the problem, transforming the self, reconciling the system, and reaching out to others. The paper concludes by suggesting how understanding these dimensions and processes may aid practice and policy.