Juri D. Kropotov

Independent component approach to the analysis of EEG recordings at early stages of depressive disorders

OBJECTIVE A modern approach for blind source separation of electrical activity represented by Independent Components Analysis (ICA) was used for QEEG analysis in depression. METHODS The spectral characteristics of the resting EEG in 111 adults in the early stages of depression and 526 non-depressed subjects were compared between groups of patients and healthy controls using a combination of ICA and sLORETA methods. RESULTS Comparison of the power of independent components in depressed patients and healthy controls have revealed significant differences between groups for three frequency bands: theta (4-7.5Hz), alpha (7.5-14Hz), and beta (14-20Hz) both in Eyes closed and Eyes open conditions. An increase in slow (theta and alpha) activity in depressed patients at parietal and occipital sites may reflect a decreased cortical activation in these brain regions, and a diffuse enhancement of beta power may correlate with anxiety symptoms playing an important role on the onset of depressive disorder. CONCLUSIONS ICA approach used in the present study allowed us to localize the EEG spectra differences between the two groups. SIGNIFICANCE A relatively rare approach which uses the ICA spectra for comparison of the quantitative parameters of EEG in different groups of patients/subjects allows to improve an accuracy of measurement.

Somatosensory event-related potential changes to painful stimuli during hypnotic analgesia: anterior cingulate cortex and anterior temporal cortex intracranial recordings

The present study examined neurophysiological correlates of pain and pain control by recording intracranial somatosensory event-related potentials (SERPs) to painful cutaneous stimuli in two female patients with obsessive-compulsive disorder bearing multiple intracranial electrodes during conditions of (a) attention and (b) hypnotically suggested analgesia. Intracranial electrodes were located in the anterior cingulate cortex, amygdala, temporal cortex, and parietal cortex. No changes were observed in the SERPs of the hypnotically unresponsive patient. In the hypnotically responsive patient, reduced pain perception during suggested hypnotic analgesia was accompanied by (a) a significant reduction of the positive SERP component within the range of 140-160 ms post-stimulus in the left anterior cingulate cortex (Shaltenbrandt atlas: 29.12/ -7.42/32.41), and (b) a significant enhancement of the negative SERP component within the range of 200-260 ms in the left anterior temporal cortex (Brodmann area 21). No significant changes were observed in the amygdala or the scalp-recorded Fz. The present study is the first to demonstrate the involvement of the anterior cingulate cortex and the anterior temporal cortex in the control of pain with hypnotically suggested analgesia.

Dissociating action inhibition, conflict monitoring and sensory mismatch into independent components of event related potentials in GO/NOGO task

The anterior N2 and P3 waves of event related potentials (ERPs) in the GO/NOGO paradigm in trials related to preparatory set violations in previous studies were inconsistently associated either with action inhibition or conflict monitoring operations. In the present study a paired stimulus GO/NOGO design was used in order to experimentally control the preparatory sets. Three variants of the same stimulus task manipulated sensory mismatch, action inhibition and conflict monitoring operations by varying stimulus-response associations. The anterior N2 and P3 waves were decomposed into components by means of independent component analysis (ICA). The ICA was performed on collection of 114 individual ERPs in the three experimental conditions. Three of the independent components were selectively affected by the task manipulations indicating association of these components with sensory mismatch, action inhibition and conflict monitoring operations. According to sLORETA the sensory mismatch component was generated in the left and right temporal areas, the action suppression component was generated in the supplementary motor cortex, and the conflict monitoring component was generated in the anterior cingulate cortex.

Classification of ADHD patients on the basis of independent ERP components using a machine learning system

Background In the context of sensory and cognitive-processing deficits in ADHD patients, there is considerable evidence of altered event related potentials (ERP). Most of the studies, however, were done on ADHD children. Using the independent component analysis (ICA) method, ERPs can be decomposed into functionally different components. Using the classification method of support vector machine, this study investigated whether features of independent ERP components can be used for discrimination of ADHD adults from healthy subjects. Methods Two groups of age- and sex-matched adults (74 ADHD, 74 controls) performed a visual two stimulus GO/NOGO task. ERP responses were decomposed into independent components by means of ICA. A feature selection algorithm defined a set of independent component features which was entered into a support vector machine. Results The feature set consisted of five latency measures in specific time windows, which were collected from four different independent components. The independent components involved were a novelty component, a sensory related and two executive function related components. Using a 10-fold cross-validation approach, classification accuracy was 92%. Conclusions This study was a first attempt to classify ADHD adults by means of support vector machine which indicates that classification by means of non-linear methods is feasible in the context of clinical groups. Further, independent ERP components have been shown to provide features that can be used for characterizing clinical populations.

Eeg Power Spectra at Early Stages of Depressive Disorders

In previous quantitative EEG studies of depression, mostly patients with a lifetime history of depressive disorders were reported. This study examined quantitative EEG parameters obtained in the early stages of depression in comparison with age-matched healthy controls. EEG was recorded using two different montages in eyes closed and eyes open resting states. A significant increase in spectrum power in theta (4–7.5 Hz), alpha (7.5–14 Hz), and beta (14–20 Hz) frequency bands was found in depressed patients at parietal and occipital sites, both in eyes closed and eyes open conditions. These results suggest that an increase in slow (theta and alpha) activity in the EEG pattern may reflect a decreased cortical activation in these brain regions. Enhancement of beta power may correlate with anxiety symptoms that most likely play an important role on the onset of depressive disorder.

Decomposing N2 NOGO wave of event-related potentials into independent components

Inconsistencies in previous attempts to localize the N2 wave in the GO/NOGO task led to the present investigation. The inconsistencies were probably because of heterogeneity of psychological operations involved in GO/NOGO tasks. We applied the independent component analysis to a collection of individual event-related potentials in response to GO and NOGO cues in the two stimulus visual GO/NOGO task. The selected six independent components with different topographies and time courses constituted 87% of the artifact-free signal variance. Three of them were loaded into the frontally distributed N2 wave. According to standardized low-resolution electromagnetic tomography these three independent components were generated in the supplementary motor cortex, left angular gyrus and anterior cingulate cortex.

Discriminating between ADHD adults and controls using independent ERP components and a support vector machine: a validation study

Background There are numerous event-related potential (ERP) studies in relation to attention-deficit hyperactivity disorder (ADHD), and a substantial number of ERP correlates of the disorder have been identified. However, most of the studies are limited to group differences in children. Independent component analysis (ICA) separates a set of mixed event-related potentials into a corresponding set of statistically independent source signals, which are likely to represent different functional processes. Using a support vector machine (SVM), a classification method originating from machine learning, this study aimed at investigating the use of such independent ERP components in differentiating adult ADHD patients from non-clinical controls by selecting a most informative feature set. A second aim was to validate the predictive power of the SVM classifier by means of an independent ADHD sample recruited at a different laboratory. Methods Two groups of age-matched adults (75 ADHD, 75 controls) performed a visual two stimulus go/no-go task. ERP responses were decomposed into independent components, and a selected set of independent ERP component features was used for SVM classification. Results Using a 10-fold cross-validation approach, classification accuracy was 91%. Predictive power of the SVM classifier was verified on the basis of the independent ADHD sample (17 ADHD patients), resulting in a classification accuracy of 94%. The latency and amplitude measures which in combination differentiated best between ADHD patients and non-clinical subjects primarily originated from independent components associated with inhibitory and other executive operations. Conclusions This study shows that ERPs can substantially contribute to the diagnosis of ADHD when combined with up-to-date methods.

Group Independent Component Analysis (gICA) and Current Source Density (CSD) in the study of EEG in ADHD adults

OBJECTIVE To investigate the performance of the spectral analysis of resting EEG, Current Source Density (CSD) and group independent components (gIC) in diagnosing ADHD adults. METHODS Power spectra of resting EEG, CSD and gIC (19 channels, linked ears reference, eyes open/closed) from 96 ADHD and 376 healthy adults were compared between eyes open and eyes closed conditions, and between groups of subjects. RESULTS Pattern of differences in gIC and CSD spectral power between conditions was approximately similar, whereas it was more widely spatially distributed for EEG. Size effect (Cohens d) of differences in gIC and CSD spectral power between groups of subjects was considerably greater than in the case of EEG. Significant reduction of gIC and CSD spectral power depending on conditions was found in ADHD patients. Reducing power in a wide frequency range in the fronto-central areas is a common phenomenon regardless of whether the eyes were open or closed. CONCLUSIONS Spectral power of local EEG activity isolated by gICA or CSD in the fronto-central areas may be a suitable marker for discrimination of ADHD and healthy adults. SIGNIFICANCE Spectral analysis of gIC and CSD provides better sensitivity to discriminate ADHD and healthy adults.

Working memory training with tDCS improves behavioral and neurophysiological symptoms in pilot group with post-traumatic stress disorder (PTSD) and with poor working memory

This pilot study investigated the feasibility of treating people suffering from both post-traumatic stress disorder (PTSD) and poor working memory by employing a combination of computerized working memory training and transcranial direct current stimulation (tDCS). After treatment, all four participants showed clinically significant improvements on a range of cognitive and emotional performance measures. Moreover, these improvements were accompanied by theoretically significant neurophysiological changes between pre- and post-treatment electroencephalographic (EEG) recordings. Specifically, the P3a component of participants’ event related potentials (ERP) in response to novelty stimuli, characteristically abnormal in this clinical population, shifted significantly toward database norms. So, participants’ initially slow alpha peak frequency (APF), theorized to underlie impaired cognitive processing abilities, also increased in both frequency and amplitude as a result of treatment. On the basis of these promising results, more extensive controlled studies are warranted.

Effect of Aging on ERP Components of Cognitive Control

As people age, their performance on tasks requiring cognitive control often declines. Such a decline is frequently explained as either a general or specific decline in cognitive functioning with age. In the context of hypotheses suggesting a general decline, it is often proposed that processing speed generally declines with age. A further hypothesis is that an age-related compensation mechanism is associated with a specific cognitive decline. One prominent theory is the compensation hypothesis, which proposes that deteriorated functions are compensated for by higher performing functions. In this study, we used event-related potentials (ERPs) in the context of a GO/NOGO task to examine the age-related changes observed during cognitive control in a large group of healthy subjects aged between 18 and 84 years. The main question we attempted to answer was whether we could find neurophysiological support for either a general decline in processing speed or a compensation strategy. The subjects performed a relatively demanding cued GO/NOGO task with similar omissions and reaction times across the five age groups. The ERP waves of cognitive control, such as N2, P3cue and CNV, were decomposed into latent components by means of a blind source separation method. Based on this decomposition, it was possible to more precisely delineate the different neurophysiological and psychological processes involved in cognitive control. These data support the processing speed hypothesis because the latencies of all cognitive control ERP components increased with age, by 8 ms per decade for the early components (<200 ms) and by 20 ms per decade for the late components. At the same time, the compensatory hypothesis of aging was also supported, as the amplitudes of the components localized in posterior brain areas decreased with age, while those localized in the prefrontal cortical areas increased with age in order to maintain performance on this simple task at a relatively stable level.