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Introduction: The disconnection hypothesis of Alzheimer's disease (AD) is supported by growing neuroimaging and neurophysiological evidence of altered brain functional connectivity in cognitively impaired individuals. Brain functional modalities such as [18F]fluorodeoxyglucose positron-emission tomography ([18F]FDG-PET) and electroencephalography (EEG) measure different aspects of synaptic functioning, and can contribute to understanding brain connectivity disruptions in AD. Aim: This study investigated the relationship between cortical glucose metabolism and topographical EEG measures of brain functional connectivity in subjects along AD continuum. Methods: Patients diagnosed with mild cognitive impairment (MCI) and AD (n = 67), and stratified into amyloid-positive (n = 32) and negative (n = 10) groups according to cerebrospinal fluid Aß42/40 ratio, were assessed with [18F]FDG-PET and resting-state EEG recordings. EEG-based neuroimaging analysis involved standardized low-resolution electromagnetic tomography (sLORETA), which estimates functional connectivity from cortical sources of electrical activity in a 3D head model. Results: Glucose hypometabolism in temporoparietal lobes was significantly associated with altered EEG functional connectivity of the same regions of interest in clinically diagnosed MCI and AD patients and in patients with biomarker-verified AD pathology. The correlative pattern of disrupted connectivity in temporoparietal lobes, as detected by EEG sLORETA analysis, included decreased instantaneous linear connectivity in fast frequencies and increased lagged linear connectivity in slow frequencies in relation to the activity of remaining cortex. Conclusions: Topographical EEG measures of functional connectivity detect regional dysfunction of AD-vulnerable brain areas as evidenced by association and spatial overlap with the cortical glucose hypometabolism in MCI and AD patients. Impact statement The association between glucose hypometabolism, as evidenced by [18F]FDG-PET ([18F]fluorodeoxyglucose positron-emission tomography), and altered electroencephalography (EEG) functional connectivity metrics within temporoparietal lobes provides link between synaptic, neurophysiological, and metabolic impairment in mild cognitive impairment and Alzheimer's disease patients. This study reported alterations in EEG measures of both instantaneous and lagged linear connectivity across distinct frequency bands, both of which were shown to be important for inter- and intrahemispheric communication and function of memory systems in general. EEG-based imaging of brain functional connectivity has a potential to serve as a noninvasive, low-cost, and widely available alternative in assessing synaptic and network dysfunction in cognitively impaired patients.

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Electroencephalographic (EEG) signals are constantly superimposed with biological artifacts. In particular, spontaneous blinks represent a recurrent event that cannot be easily avoided. The main goal of this paper is to present a new algorithm for blink correction (ABC) that is adaptive to inter- and intra-subject variability. The whole process of designing a Brain-Computer Interface (BCI)-based EEG experiment is highlighted. From sample size determination to classification, a mixture of the standardized low-resolution electromagnetic tomography (sLORETA) for source localization and time restriction, followed by Riemannian geometry classifiers is featured. Comparison between ABC and the commonly-used Independent Component Analysis (ICA) for blinks removal shows a net amelioration with ABC. With the same pipeline using uncorrected data as a reference, ABC improves classification by 5.38% in average, whereas ICA deteriorates by -2.67%. Furthermore, while ABC accurately reconstructs blink-free data from simulated data, ICA yields a potential difference up to 200% from the original blink-free signal and an increased variance of 30.42%. Finally, ABC's major advantages are ease of visualization and understanding, low computation load favoring simple real-time implementation, and lack of spatial filtering, which allows for more flexibility during the classification step.

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The aim of this study was to investigate the changes of brain electric field induced by symptom provocation in patients with obsessive-compulsive disorder (OCD) in comparison to healthy controls in the resting state. For this purpose, EEG recordings in conditions of initial rest, clean control, symptom provocation by imaginal exposure, and final rest were used for computing spatiotemporal activity characteristics based on microstate segmentation. Within-group comparisons were significant for the symptom provocation condition: OCD showed high global field power (GFP) and transition rates into a medial frontal microstate, whereas healthy controls showed high frequency of occurrence and high percent of dwelling time for a medial occipitoparietal microstate. Between-group comparisons demonstrated significantly lower GFP and dwelling time for the medial occipitoparietal microstate in OCD in several conditions including initial rest and symptom provocation. In addition, OCD compared to healthy controls showed significant instability of the medial occipitoparietal microstate, with high preference for transitions into the medial frontal microstate. In conclusion, during rest and symptom provocation, OCD patients make preferential use of a medial frontal brain network, with concomitant reduction of use of a medial occipitoparietal network, as shown by dwelling times, explained variance, and dynamic transition rates. These findings support the idea of a possible biological marker for OCD, which might correspond to pathological hyperactivation of the frontal control network.

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BACKGROUND: Aberrant functional connectivity (FC) is increasingly implicated in the clinical phenomenology of schizophrenia. This study focused on the FC of the cortico-striatal network, which is thought to be disrupted in schizophrenia and to contribute to its clinical manifestations. METHODS: We used simultaneous resting-state functional magnetic resonance imaging (rsfMRI) and electroencephalography (EEG) recordings to investigate FC in patients with schizophrenia. The study included 20 patients with schizophrenia and 20 healthy controls (HCs). Simultaneously recorded rsfMRI and EEG data were collected with an MR-compatible amplifier, and rsfMRI data were analyzed with the CONN toolbox to calculate FC. The study focused on the caudate, which was defined as the seed. We also performed between-group comparisons of standardized low-resolution electromagnetic tomography intracortical lagged coherence for each EEG frequency band. RESULTS: Compared to HCs, patients with schizophrenia showed enhanced FC between the caudate nucleus and the posterior cingulate cortex, temporal, and occipital regions on rsfMRI. It is thus possible that HCs have negative FC between these regions, whereas patients with schizophrenia have non-negative FC. The EEG results showed no significant differences in oscillations or in FC between the groups in any frequency band in any region. CONCLUSIONS: Increased FC in the caudate may represent aberrant between-network FC resulting from the disruption of segregation between networks.

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BACKGROUND: Obsessive-compulsive disorder (OCD) is associated with cognitive dysfunction. Although there are several studies focused on the neurobiology of OCD, little is known about the biological correlates of the cognitive deficit linked to this disorder. The aim of our study was to examine the association between cognitive impairment and current source density markers in patients with OCD. METHODS: Resting-state eyes-closed electroencephalography (EEG) data were recorded in 20 patients with OCD and 15 healthy controls who were involved in the study. Cortical EEG sources were estimated by standardized low-resolution electromagnetic tomography in seven frequency bands: delta (1.5-6 Hz), theta (6.5-8 Hz), alpha-1 (8.5-10 Hz), alpha-2 (10.5-12 Hz), beta-1 (12.5-18 Hz), beta-2 (18.5-21 Hz), and beta-3 (21.5-30 Hz). Cognitive performance was measured by the Trail-Making Test (versions A and B), Stroop CW Test, and D2 Test. RESULTS: Frontal delta and theta EEG sources showed significantly higher activity in the whole group of patients with OCD (N=20) than in control subjects (N=15). Subsequent analysis revealed that this excess of low-frequency activity was present only in the subgroup of eleven patients with cognitive impairment (based on the performance in the Trail-Making Test - A). The subgroup of patients with normal cognitive functions (N=9) did not differ in cortical EEG sources from healthy controls. CONCLUSION: The present results suggest that frontal low-frequency cortical sources of resting-state EEG rhythms can distinguish groups of cognitively impaired and cognitively intact patients with OCD. Based on our results, future studies should consider whether the present methodological approach provides clinically useful information for the revelation of cognitive impairment in patients with OCD.

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Tinnitus can be distressful, and tinnitus distress has been linked to increased beta oscillatory activity in the dorsal anterior cingulate cortex (dACC). The amount of distress is linked to alpha activity in the medial temporal lobe (amygdala and parahippocampal area), as well as the subgenual (sg)ACC and insula, and the functional connectivity between the parahippocampal area and the sgACC at 10 and 11.5 Hz. The authors describe 2 patients with very severely distressing intractable tinnitus who underwent transcranial magnetic stimulation (TMS) with a double-cone coil targeting the dACC and subsequent implantation of electrodes on the dACC. One of the patients responded to the implant and one did not, even though phenomenologically they both expressed the same tinnitus loudness and distress. The responder has remained dramatically improved for more than 2 years with 6-Hz burst stimulation of the dACC. The 2 patients differed in functional connectivity between the area of the implant and a tinnitus network consisting of the parahippocampal area as well as the sgACC and insula; that is, the responder had increased functional connectivity between these areas, whereas the nonresponder had decreased functional connectivity between these areas. Only the patient with increased functional connectivity linked to the target area of repetitive TMS or implantation might transmit the stimulation current to the entire tinnitus network and thus clinically improve.

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This study investigated the response inhibition in individuals with psychopathic traits. We examined the cortical source localization of the NoGo stimuli in a Go/NoGo task by employing a standardized low-resolution electromagnetic tomography (sLORETA) using EEG. Fifteen psychopathic trait subjects and 15 control subjects performed the Go/NoGo task. The statistical analysis of P3 elicited by the NoGo stimuli indicated that the psychopathic trait group showed significantly reduced NoGo-P3 amplitudes than the control group at the frontocental area. In the Wisconsin Card Sorting Test, the psychopathic trait group showed significantly higher perseverative responses than the control group. Compared to the control group, cortical sources reduction elicited by NoGo-P3 in the psychopathic trait group was found at the left superior frontal gyrus, bilateral anterior cingulate, right precentral gyrus, and the right inferior parietal lobule. These results suggest that individuals with psychopathic traits have difficulties in inhibiting a response with reduced frontal function.

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Two types of biofeedback (BF), tomographic electroencephalogram (EEG) neurofeedback (NF) and electromyographic biofeedback (EMG-BF), both with phasic and tonic protocols, were compared for treatment effects and specificity in attention-deficit/hyperactivity disorder (ADHD). Thirteen children with ADHD trained their brain activity in the anterior cingulate cortex (ACC), and twelve trained activity of arm muscles involved in fine motor skills. In each training session, resting state 24-channel EEG and training performances were recorded. Both groups showed similar behavioral improvements and artifact reduction in selected conditions, with no significant advantages despite medium effect sizes on primary outcomes for NF. Only the EMG-BF group, however, showed clear improvement in training regulation performance, and specific motor coordination effects. The NF group tended to present individual normalization of trained frequency bands in the ACC during rest across training. The results provide evidence for some specific effects in our small sample, albeit only to a small extent.

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Previous EEG source localization studies in obsessive-compulsive disorder (OCD) reported ambiguous results. The reason probably lies in different OCD samples included in the studies - obsessive-compulsive subjects selected based on a psychopathology questionnaire (the Symptom Checklist - Revised), drug-naïve OCD cases or patients with a long-term disorder. This study was conceived as a replication of our previous research on OCD population coming to treatment in Prague Psychiatric Centre [9]. We included 50 OCD patients (8 drug-free and 42 medicated with SSRIs) and 50 healthy controls. All subjects were different from those enrolled in the previous study. Resting state EEG was analyzed in 8 frequency bands as well as with 1 Hz frequency resolution using the standardized low-resolution electromagnetic tomography (sLORETA). In OCD, sLORETA indicated low-frequency power excess at 2 and 3 Hz in the cingulate gyrus with maximal t-values in Brodmann area 24. The low-frequency activity was unrelated to the severity of clinical symptoms and illness duration but delta power in the right orbitofrontal cortex positively correlated with age of OCD onset. Our results confirm previous finding of the low-frequency excess in the cingulate gyrus in OCD and document the essential role of delta frequencies. Delta activity in the cingulate gyrus is negatively associated with reward-signalling dopamine release in the ventral striatum and increases in states connected with a need for reinforcement. Thus, delta activity could reflect a repetitive need to perform compulsive behaviour in OCD patients.

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OBJECTIVE: To review the use of deep brain stimulation (DBS) for treatment of dementia. METHODS: A PubMed literature search was conducted to identify all studies that have investigated the use of DBS for treatment of dementia. RESULTS: Three studies examined the use of DBS for dementia. One study involved fornix DBS for Alzheimer disease (AD), and two studies involved DBS of the nucleus basalis of Meynert, one to treat AD and one to treat Parkinson disease dementia. CONCLUSIONS: Evidence for the use of DBS to treat dementia is preliminary and limited. Fornix and nucleus basalis of Meynert DBS can influence activity in the pathologic neural circuits that underlie AD and Parkinson disease dementia. Further investigation into the potential clinical effects of DBS for dementia is warranted.

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Sensitivity to variations in luminance (contrast) is fundamental to perception because contrasts define the edges and textures of visual objects. Recent research has shown that contrast sensitivity, in addition to being controlled by purely stimulus-driven mechanisms, is also affected by expectations and prior knowledge about the contrast of upcoming stimuli. The ability to adjust contrast sensitivity based on expectations and prior knowledge could help to maximize the information extracted when scanning familiar visual scenes. In the present study we used the event-related potentials (ERP) technique to resolve the stages that mediate knowledge-driven aspects of contrast gain control. Using groupwise independent components analysis and multivariate partial least squares, we isolated two robust spatiotemporal patterns of electrical brain activity associated with preparation for upcoming targets whose contrast was predicted by a cue. The patterns were sensitive to the informative value of the cue. When the cues were informative, these patterns were also able to differentiate among cues that predicted low-contrast targets and cues that predicted high-contrast targets. Both patterns were localized to parts of occipitotemporal cortex, and their morphology, latency, and topography resembled P2/N2 and P3 potentials. These two patterns provide electrophysiological markers of knowledge-driven preparation for impending changes in contrast and shed new light on the manner in which top-down factors modulate sensory processing.