Browsing by Subject "electroencephalography"

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  • Cowley, Benjamin U.; Korpela, Jussi (2018)
    Existing tools for the preprocessing of EEG data provide a large choice of methods to suitably prepare and analyse a given dataset. Yet it remains a challenge for the average user to integrate methods for batch processing of the increasingly large datasets of modern research, and compare methods to choose an optimal approach across the many possible parameter configurations. Additionally, many tools still require a high degree of manual decision making for, e.g., the classification of artifacts in channels, epochs or segments. This introduces extra subjectivity, is slow, and is not reproducible. Batching and well-designed automation can help to regularize EEG preprocessing, and thus reduce human effort, subjectivity, and consequent error. The Computational Testing for Automated Preprocessing (CTAP) toolbox facilitates: (i) batch processing that is easy for experts and novices alike; (ii) testing and comparison of preprocessing methods. Here we demonstrate the application of CTAP to high-resolution EEG data in three modes of use. First, a linear processing pipeline with mostly default parameters illustrates ease-of-use for naive users. Second, a branching pipeline illustrates CTAP's support for comparison of competing methods. Third, a pipeline with built-in parameter-sweeping illustrates CTAP's capability to support data-driven method parameterization. CTAP extends the existing functions and data structure from the well-known EEGLAB toolbox, based on Matlab, and produces extensive quality control outputs. CTAP is available under MIT open-source licence from
  • Sirola, Roosa (Helsingfors universitet, 2013)
    Visual working memory (VWM) maintains information for future usage. Several studies show that the cortical oscillations in the γ-frequency band (from 30 to 120 Hz) are modulated by the VWM performance. However, less is known about the cortical sources underlying the modulation of these oscillations in VWM. To address this question, we recorded human neuronal activity with magneto- and electroencephalography (M/EEG) during a delayed-matching-to-sample VWM task with three different task conditions, within which participants were instructed to focus on different object features in turn. In addition, anatomical data was acquired with magnetic resonance imaging for source modeling purposes. We then estimated the cortical amplitude dynamics across frequencies from three to 90 Hz during the VWM retention period for these three different conditions. We found that the amplitudes of the γ –frequency band oscillations were strengthened in the occipito-temporal cortical areas during the VWM for shapes but not for color or spatial locations. These data suggest that γ –band oscillations are fundamental in VWM, especially for visual stimuli requiring perceptual feature binding. Furthermore, cortical γ –band oscillations were found to be load dependently strengthened in the frontal cortex, where the central executive and attention associated processes are believed to take place. These data support the previous hypotheses stating that γ –band oscillations contribute to the maintenance of object representations in VWM.
  • Kalevo, Laura; Miettinen, Tomi; Leino, Akseli; Kainulainen, Samu; Korkalainen, Henri; Myllymaa, Katja; Töyräs, Juha; Leppänen, Timo; Laitinen, Tiina; Myllymaa, Sami (2020)
    In response to the growing clinico-economic need for comprehensive home-based sleep testing, we recently developed a self-applicable facial electrode set with screen-printed Ag/AgCl electrodes. Our previous studies revealed that nocturnal sweating is a common problem, causing low-frequency artifacts in the measured electroencephalography (EEG) signals. As the electrode set is designed to be used without skin abrasion, not surprisingly this leads to relatively high electrode-skin impedances, significant impedance changes due to sweating and an increased risk of sweat artifacts. However, our recent electrochemical in vitro investigations revealed that the sweat artifact tolerance of an EEG electrode can be improved by utilizing an appropriate Ag/AgCl ink. Here we have investigated in vivo electrode-skin impedances and the quality of EEG signals and interference due to sweating in the population of 11 healthy volunteers. Commercial Ag and Ag/AgCl inks (Engineered Conductive Materials ECM LLC and PPG Industries Inc.) were used to test electrode sets with differently constructed ink layers. Electrode-skin impedances and EEG signals were recorded before and after exercise-induced sweating. There was extensive variation in the electrode-skin impedances between the volunteers and the electrode positions: 14.6 & x2013;200 (PPG electrodes) and 7.7 & x2013;200 (ECM electrodes). Sweating significantly decreased the impedances in most cases. The EEG signal quality was assessed by comparing average band powers from 0.5 to 2 Hz before and after sweating. Only slight differences existed between the ECM and PPG electrodes; however, the lowest band power ratio (i.e. the smallest increase in the band power due to sweating) was achieved with ECM electrodes.
  • Cowley, Benjamin; Kirjanen, Svetlana; Partanen, Juhani; Castrén, Maija (2016)
    Fragile X syndrome (FXS) is the most common cause of inherited intellectual disability and a variant of autism spectrum disorder (ASD). The FXS population is quite heterogeneous with respect to comorbidities, which implies the need for a personalized medicine approach, relying on biomarkers or endophenotypes to guide treatment. There is evidence that quantitative electroencephalography (EEG) endophenotype-guided treatments can support increased clinical benefit by considering the patient's neurophysiological profile. We describe a case series of 11 children diagnosed with FXS, aged one to 14 years, mean 4.6 years. Case data are based on longitudinal clinically-observed reports by attending physicians for comorbid symptoms including awake and asleep EEG profiles. We tabulate the comorbid EEG symptoms in this case series, and relate them to the literature on EEG endophenotypes and associated treatment options. The two most common endophenotypes in the data were diffuse slow oscillations and epileptiform EEG, which have been associated with attention and epilepsy respectively. This observation agrees with reported prevalence of comorbid behavioral symptoms for FXS. In this sample of FXS children, attention problems were found in 37% (4 of 11), and epileptic seizures in 45% (5 of 11). Attention problems were found to associate with the epilepsy endophenotype. From the synthesis of this case series and literature review, we argue that the evidence-based personalized treatment approach, exemplified by neurofeedback, could benefit FXS children by focusing on observable, specific characteristics of comorbid disease symptoms.
  • Alho, Kimmo; Zarnowiec, Katarzyna; Gorina-Careta, Natalia; Escera, Carles (2019)
    In electroencephalography (EEG) measurements, processing of periodic sounds in the ascending auditory pathway generates the frequency-following response (FFR) phase-locked to the fundamental frequency (F0) and its harmonics of a sound. We measured FFRs to the steady-state (vowel) part of syllables /ba/ and /aw/ occurring in binaural rapid streams of speech sounds as frequently repeating standard syllables or as infrequent (p = 0.2) deviant syllables among standard /wa/ syllables. Our aim was to study whether concurrent active phonological processing affects early processing of irrelevant speech sounds reflected by FFRs to these sounds. To this end, during syllable delivery, our healthy adult participants performed tasks involving written letters delivered on a computer screen in a rapid stream. The stream consisted of vowel letters written in red, infrequently occurring consonant letters written in the same color, and infrequently occurring vowel letters written in blue. In the phonological task, the participants were instructed to press a response key to the consonant letters differing phonologically but not in color from the frequently occurring red vowels, whereas in the non-phonological task, they were instructed to respond to the vowel letters written in blue differing only in color from the frequently occurring red vowels. We observed that the phonological task enhanced responses to deviant /ba/ syllables but not responses to deviant /aw/ syllables. This suggests that active phonological task performance may enhance processing of such small changes in irrelevant speech sounds as the 30-ms difference in the initial formant-transition time between the otherwise identical syllables /ba/ and /wa/ used in the present study.
  • Issakainen, Jani (Helsingin yliopisto, 2021)
    Electroencephalography (EEG) is a non-invasive neurophysiological method for evaluating brain activity by measuring electrical potential at the scalp. The electrical potentials originate mainly from postsynaptic cortical currents created by neuronal activity. It is a valuable tool for both research and clinical practice. EEG can be used e.g. to diagnose epilepsy, focal brain disorders, brain death, and coma. Intermittent photic stimulation (IPS) is an important tool in clinical EEG. Healthcare professionals use it to induce epileptic activity in patients to help diagnose their conditions. In these tests, various IPS frequencies are used with eyes-closed, eyes-open, and eye-closure conditions. IPS test is listed in clinical practice guidelines in EEG globally, and it is mainly used to diagnose photosensitive epilepsy, i.e., to detect epilepsy-related abnormal sensitivity to flickering light. Magnetoencephalography (MEG) is a non-invasive neurophysiological method in which minute magnetic fields — produced by the same postsynaptic currents as in EEG — are measured with special superconductive sensors around the head. MEG is a valuable tool for research and clinical practice with increasing world-wide utilization. The main advantages of MEG over EEG are easier source modelling and higher resolution at cortical areas. IPS has not been introduced to MEG since the IPS stimulators used in EEG are not compatible with MEG. IPS in MEG could improve the analysis of IPS and provide better tools for diagnoses. Currently, data analysis of IPS is typically limited to healthcare professionals examining the visualization of the raw data while looking for induced epileptiform activites and lateralizing them. In this thesis, an MEG-compatible IPS stimulator is introduced and alternative ways of analyzing IPS data for both MEG and EEG are showcased. Although analysis methods were applied with decent signal-to-noise ratios, further research is needed—especially to compare responses between patients with epilepsy and healthy subjects.
  • Ukai, Masayasu; Parmentier, Thomas; Cortez, Miguel A.; Fischer, Andrea; Gaitero, Luis; Lohi, Hannes; Nykamp, Stephanie; Jokinen, Tarja S.; Powers, Danielle; Sammut, Veronique; Sanders, Sean; Tai, Tricia; Wielaender, Franziska; James, Fiona (2021)
    Background Many studies of epilepsy in veterinary medicine use subjective data (eg, caregiver-derived histories) to determine seizure frequency. Conversely, in people, objective data from electroencephalography (EEG) are mainly used to diagnose epilepsy, measure seizure frequency and evaluate efficacy of antiseizure drugs. These EEG data minimize the possibility of the underreporting of seizures, a known phenomenon in human epileptology. Objective To evaluate the correlation between reported seizure frequency and EEG frequency of ictal paroxysmal discharges (PDs) and to determine whether seizure underreporting phenomenon exists in veterinary epileptology. Animals Thirty-three ambulatory video-EEG recordings in dogs showing >= 1 ictal PD, excluding dogs with status epilepticus. Methods Retrospective observational study. Ictal PDs were counted manually over the entire recording to obtain the frequency of EEG seizures. Caregiver-reported seizure frequency from the medical record was categorized into weekly, daily, hourly, and per minute seizure groupings. The Spearman rank test was used for correlation analysis. Results The coefficient value (r(s)) comparing reported seizure to EEG-confirmed ictal PD frequencies was 0.39 (95% confidence interval [CI] = 0.048-0.64, P = .03). Other r(s) values comparing history against various seizure types were: 0.36 for motor seizures and 0.37 for nonmotor (absence) seizures. Conclusions and Clinical Importance A weak correlation was found between the frequency of reported seizures from caregivers (subjective data) and ictal PDs on EEG (objective data). Subjective data may not be reliable enough to determine true seizure frequency given the discrepancy with EEG-confirmed seizure frequency. Confirmation of the seizure underreporting phenomenon in dogs by prospective study should be carried out.
  • Banville, Hubert; Albuquerque, Isabela; Hyvärinen, Aapo; Moffat, Grame; Engemann, Denis-Alexander; Gramfort, Alexandre (IEEE, 2019)
  • Miettinen, Tomi; Myllymaa, Katja; Westeren-Punnonen, Susanna; Ahlberg, Jari; Hukkanen, Taina; Töyräs, Juha; Lappalainen, Reijo; Mervaala, Esa; Sipilä, Kirsi; Myllymaa, Sami (2018)
    Using sleep laboratory polysomnography (PSG) is restricted for the diagnosis of only the most severe sleep disorders due to its low availability and high cost. Home PSG is more affordable, but applying conventional electroencephalography (EEG) electrodes increases its overall complexity and lowers the availability. Simple, self-administered single-channel EEG monitors on the other hand suffer from poor reliability. In this study, we aimed to quantify the reliability of self-administrated home PSG recordings conducted with a newly designed ambulatory electrode set (AES) that enables multichannel EEG, electrooculography, electromyography, and electrocardiography recordings. We assessed the sleep study success rate and technical quality of the recordings performed in subjects with possible sleep bruxism (SB). Thirty-two females and five males aged 39.6 +/- 11.6 years (mean +/- SD) with self-reported SB were recruited in the study. Self-administrated home PSG recordings with two AES designs were conducted (n = 19 and 21). The technical quality of the recordings was graded based on the proportion of interpretable data. Technical failure rate for AES (both designs) was 5% and SB was scorable for 96.9% of all recorded data. Only one recording failed due to mistakes in self-applying the AES. We found that the proportion of good quality self-administrated EEG recordings is significantly higher when multiple channels are used compared to using a single channel. Sleep study success rates and proportion of recordings with high quality interpretable data from EEG channels of AES were comparable to that of conventional home PSG. Self-applicable AES has potential to become a reliable tool for widely available home PSG.
  • Mannermaa, Kristiina (Helsingin yliopisto, 2017)
    Previous research has linked music training to enhanced processing of unattended auditory stimuli as indexed by such auditory event-related potential (ERP) responses as mismatch negativity (MMN) and P3a. Music training has also been linked with enhanced cognitive abilities more generally, and executive functions have been proposed to mediate this link. The current study concentrates on the processing of unattended auditory stimuli and how this relates to two aspects of executive functions: task-switching and inhibition. Sixty-seven music trained (music group) and non-trained (control group) adolescents and young adults were split into age groups, 14–16 year olds (younger) and 17–20 year olds (older), and compared in their performance on inhibition and task-switching task as well as the neural processing of unattended auditory stimuli. The ERPs were recorded in response to an oddball paradigm consisting of frequent major and infrequent minor chords. The music group demonstrated larger MMN and P3a amplitudes than the control group during the chord paradigm. The younger music group showed better performance in an inhibition task than the younger control group. However, no other differences in task performance were found between the groups. Also, no link between MMN or P3a and task performance was found. Therefore, the results of the current study are in line with the previous findings that music training is linked to enhanced early neural processing of unattended auditory stimuli. However, the results were partly in disagreement with previous reports of enhanced executive functions in musicians as a link between executive functions and music training was only observed in the younger participants, and only in regard to the inhibition task.
  • Halonen, Risto (Helsingfors universitet, 2017)
    Sleep spindles are thalamocortical oscillations that occupy the sigma band with trait-like inter-individual variability. Sleep spindles associate with reasoning abilities according to several studies, but some discrepancy exists in the strength and even direction of the associations. This may, to some extent, be due to methodological differences. The stage of brain maturation also affects spindle manifestation. In this community-based study, associations between spindle characteristics and reasoning abilities are examined in an understudied age group, adolescents. An all-night polysomnography was conducted at homes of 178 adolescents (104 girls). Working memory, visuospatial reasoning and verbal reasoning were measured in the same evening. An automatic algorithm was used to detect slow (10–13 Hz) and fast (13–16 Hz) spindles in frontal and central scalp derivations in NREM 2 sleep stage. The associations between spindle variables (density and intensity) and the cognitive test scores were analyzed with linear regression. Genders apart, the analyses were conducted first on the whole group and then separately on the Above Median (AM) and Below Median (BM) intelligence subgroups. In the analyses with all subjects, higher central fast density associated with better verbal reasoning in girls. When examining the subgroups separately, this association was not perceived in the AM group but appeared prominently in the BM group girls. No other associations were found between the spindle variables and the cognitive test scores. A positive spindle-intelligence relation is an established finding in females, but more commonly the association is typified by fluid/visuospatial reasoning and frontal brain areas. In the present study, young age may have related to the accentuated relative significance of more caudal brain regions and verbal intelligence in relation to spindles. The ongoing neural maturation and the heterogeneity of the sample may have contributed to the nature of the findings. More adolescent studies are needed to gain understanding of the matter.