Affective pictures processing is reflected by an increased long-distance EEG connectivity.

Analysis of affective picture processing by means of EEG has invaded the literature. The methodology of event-related EEG coherence is one of the essential methods used to analyze functional connectivity. The aims of the present study are to find out the long range EEG connectivity changes in perception of different affective pictures and analyze gender differences in these long range connected networks. EEGs of 28 healthy subjects (14 female) were recorded at 32 locations. The participants passively viewed emotional pictures (IAPS, unpleasant, pleasant, neutral). The long-distance intra-hemispheric event-related coherence was analyzed for delta (1-3.5 Hz), theta (4-7.5 Hz), and alpha (8-13 Hz) frequency ranges for F3-T7, F4-T8, F3-TP7, F4-TP8, F3-P3, F4-P4, F3-O1, F4-O2, C3-O1, C4-O2 electrode pairs. Unpleasant pictures elicited significantly higher delta coherence values than neutral pictures (p < 0.05), over fronto-parietal, fronto-occipital, and centro-occipital electrode pairs. Furthermore, unpleasant pictures elicited higher theta coherence values than pleasant (p < 0.05) and neutral pictures (p < 0.05). The present study showed that female subjects had higher delta (p < 0.05) and theta (p < 0.05) coherence values than male subjects. This difference was observed more for emotional pictures than for neutral pictures. This study showed that the brain connectivity was higher during emotional pictures than neutral pictures. Females had higher connectivity between different parts of the brain than males during emotional processes. According to these results, we may comment that increased valence and arousal caused increased brain activity. It seems that not just single sources but functional networks were also activated during perception of emotional pictures.

Increased Beta Frequency (15-30 Hz) Oscillatory Responses in Euthymic Bipolar Patients Under Lithium Monotherapy.

The effect of lithium on neurocognition is not still fully explored. Brain oscillatory activity is altered in bipolar disorder. We aimed to assess the oscillatory responses of euthymic bipolar patients and how they are affected by lithium monotherapy. Event-related oscillations in response to visual target stimulus during an oddball paradigm in 16 euthymic drug-free and 13 euthymic lithium-treated bipolar patients were compared with 16 healthy controls. The maximum peak-to-peak amplitudes were measured for each subject's averaged beta (15-30 Hz) responses in the 0- to 300-ms time window over frontal (F3, Fz, F4), central (C3, Cz, C4), temporal (T7, T8), temporo-parietal (TP7, TP8), parietal (P3, Pz, P4), and occipital (O1, Oz, O2) areas. Patients under lithium monotherapy had significantly higher beta responses to visual target stimuli than healthy controls (P=.017) and drug-free patients (P=.015). The increase in beta response was observed at all electrode locations, however, the difference was statistically significant for the left (T7; P=.016) and right (T8; P=.031) temporal beta responses. Increased beta responses in drug-free patients and further significant increase in lithium-treated patients may be indicative of a core pathophysiological process of bipolar disorder and how it is affected by lithium. Whether the finding corresponds to lithium's corrective effect on the underlying pathology or to its neurocognitive side effect remains to be further explored. In either case, the finding is a sign that the oscillatory activity may be useful in tracking medication effect in bipolar disorder.

Best method for analysis of brain oscillations in healthy subjects and neuropsychiatric diseases.

The research related to brain oscillations and their connectivity is in a new take-off trend including the applications in neuropsychiatric diseases. What is the best strategy to learn about functional correlation of oscillations? In this report, we emphasize combined application of several analytical methods as power spectra, adaptive filtering of Event Related Potentials, inter-trial coherence and spatial coherence. These combined analysis procedure gives the most profound approach to understanding of EEG responses. Examples from healthy subjects, Alzheimer's Diseases, schizophrenia, and Bipolar Disorder are described.

Multiple gamma oscillations in the brain: a new strategy to differentiate functional correlates and P300 dynamics.

Brain oscillations in the gamma frequency band, - i.e. oscillations greater than 25 Hz - have attracted increasing attention over the last few decades in the research of sensory-cognitive processes. In the neuroscience research literature, a great number of reports aim to describe the functional correlates of oscillatory responses in the gamma frequency window. However, analysis using a broadband frequency window often leads to divergent functional interpretations and controversies. In order to provide a more exact approach, we have used a strategy by defining multiple frequency and multiple time windows according to the combined analysis of conventional power spectral windows, frequency adaptive multiple filters, and inter-trial coherence. The analysis in frequency windows of 25-30 Hz, 30-35 Hz, and 40-48 Hz enables the investigator to provide a distinction of cognitive and/or sensory responses. Moreover, according to topological differentiation and the consideration of neuroanatomic pathways, more reliable interpretations of gamma responses are reached.

Event related beta and gamma oscillatory responses during perception of affective pictures.

Several studies reveal that unpleasant pictures elicit higher beta and gamma responses than pleasant and/or neutral pictures; however, the effect of stimulation design (block or random) has not been studied before. The aim of the study is to analyze the common and distinct parameters of affective picture perception in block and random designs by means of analysis of high frequency oscillatory dynamics (beta and gamma). EEG of 22 healthy subjects was recorded at 32 locations. The participants passively viewed 120 emotional pictures (10 × 4 unpleasant, 10 × 4 pleasant, 10 × 4 neutral) in block and random designs. The phase-locking and power of event related beta (14-28 Hz) and gamma (29-48 Hz) oscillations were analyzed for two different time windows (0-200 ms/200-400 ms). Statistical analysis showed that in the 0-200 ms time window, during the block design, unpleasant stimulation elicited higher beta phase-locking and beta power than the pleasant and neutral stimulation (p<0.05). In the 200-400 ms time window, during the block design, over occipital electrodes unpleasant stimulation elicited higher gamma response power than the pleasant stimulation and neutral stimulation (p<0.05). Unpleasant stimulation did not elicit higher beta or gamma responses in the random design. The present study showed that experimental design highly influences the perception of IAPS pictures. Unpleasant stimulation elicited higher event related beta and gamma phase-locking and power only in block design but not in random design. It seems that longer blocks of aversive pictures affect the brain more than the rapid observation of these pictures.

Decrease of event-related delta oscillations in euthymic patients with bipolar disorder.

Decreased delta oscillation upon cognitive load is common in patients with Alzheimer׳s disease, mild cognitive impairment, and schizophrenia. However, there is no previous study analyzing the delta responses in euthymic medication-free patients with bipolar disorder. Participants comprised of 22 euthymic medication-free patients with DSM-IV diagnoses of bipolar disorder and 21 healthy controls who were matched to the patients for sex, age, and education. Electroencephalographic activity was recorded at 30 electrode sites using an application of an auditory oddball paradigm. The maximum peak-to-peak amplitudes for each subject׳s averaged delta response (0.5-3.5Hz) were measured. There was a significant inter-group difference in evoked and event-related delta (0.5-3.5Hz) responses. Post-hoc comparisons revealed that the event-related delta oscillatory responses of the bipolar patient group were significantly lower than those of the healthy control group over the temporo-parietal and occipital electrode sites. Euthymic bipolar patients showed reduced event-related delta oscillatory responses in comparison to healthy subjects under cognitive load. The decrease of delta oscillations may be a common phenomenon that can be observed in different neuropsychiatric disorders with cognitive dysfunction.

Evoked and event related coherence of Alzheimer patients manifest differentiation of sensory-cognitive networks.

In previous studies on Alzheimer's patients it was shown that, in frontal and parietal locations, delta and theta responses of AD patients were greatly reduced. The present study analyzed coherence functions in these highly affected frontal and parietal areas. Visual sensory and event related coherences of patients with Alzheimer type dementia (AD) were analyzed comparatively. A total of 38 mild, probable AD subjects (19 untreated, 19 treated with cholinesterase inhibitors) were compared with a group of 19 healthy controls. The sensory evoked coherence and event related target coherences were analyzed for delta (1-3.5 Hz), theta (4-7 Hz), alpha (8-13 Hz), beta (15-30 Hz) and gamma (28-48 Hz) frequency ranges for long-range intra-hemispheric (F(3)-P(3), F(4)-P(4), F(3)-T(5), F(4)-T(6), F(3)-O(1), F(4)-O(2)) electrode pairs. The healthy control group showed significantly higher values of event related coherence in "delta", "theta" and "alpha" bands in comparison to the de novo and medicated AD groups (p<0.01 for the delta, theta and alpha) upon application of a target stimuli. In contrast, almost no changes in event related coherences were observed in beta and gamma frequency bands. Furthermore, no differences were recorded between healthy and AD groups upon application of simple light stimuli. Besides this, coherence values upon application of target stimuli were higher than sensory evoked coherence in all groups and in all frequency bands (p<0.01). The cognitive networks of AD patients were highly impaired in comparison to networks activated by sensory stimulation, thus showing separate activation of sensory and cognitive networks.

A comparative analysis of sensory visual evoked oscillations with visual cognitive event related oscillations in Alzheimer's disease.

We compared visual evoked oscillatory responses of subjects with Alzheimer's disease (AD) (n=22) to healthy elderly controls (n=19) elicited by simple light stimuli. The visual evoked oscillatory responses in AD subjects without cholinergic treatment (n=11) show significant differences (df=2.38, F=4.957, P=0.012) from the controls and the AD subjects treated with a cholinesterase inhibitor (n=11). Higher theta oscillatory responses in untreated AD subjects are seen on the electrode locations over bi-parietal and right occipital regions after simple light stimuli with less, if any, cognitive load. These changes were restricted to the theta frequency range only and are related to location, frequency bands and drug effects. In our previous work we observed that visual event related oscillations elicited after the visual stimuli with a higher cognitive load, i.e. an oddball target, display lower amplitudes: between controls and AD subjects in delta frequency band without a drug effect, over the left and mid-central region. These differences between the visual evoked oscillations and the visual event related oscillations imply that there are at least two different cognitive circuits that are activated upon visual stimuli in AD patients.