Increase In Interhemispheric Coherence Research Articles

Evaluating interhemispheric connectivity during midline object recognition using EEG.

Functional integration between two hemispheres is crucial for perceptual binding to occur when visual stimuli are presented in the midline of the visual field. Mima and colleagues (2001) showed using EEG that midline object recognition was associated with task-related decrease in alpha band power (alpha desynchronisation) and a transient increase in interhemispheric coherence. Our objective in the current study was to replicate the results of Mima et al. and to further evaluate interhemispheric effective connectivity during midline object recognition in source space. We recruited 11 healthy adult volunteers and recorded EEG from 64 channels while they performed a midline object recognition task. Task-related power and coherence were estimated in sensor and source spaces. Further, effective connectivity was evaluated using Granger causality. While we were able to replicate the alpha desynchronisation associated with midline object recognition, we could not replicate the coherence results of Mima et al. The data-driven approach that we employed in our study localised the source of alpha desynchronisation over the left occipito-temporal region. In the alpha band, we further observed significant increase in imaginary part of coherency between bilateral occipito-temporal regions during object recognition. Finally, Granger causality analysis between the left and right occipito-temporal regions provided an insight that even though there is bidirectional interaction, the left occipito-temporal region may be crucial for integrating the information necessary for object recognition. The significance of the current study lies in using high-density EEG and applying more appropriate and robust measures of connectivity as well as statistical analysis to validate and enhance our current knowledge on the neural basis of midline object recognition.

Clinical and electrophysiological parameters of alcohol dependence and its comorbidity with affective disorders

To identify characteristics of and possible differences in clinical and electroencephalographic parameters in patients with alcohol dependence with- and without comorbid affective disorders. Ninety-five patients, including 74 with an established diagnosis of alcohol dependence and 21 with alcohol dependence and affective disorders, were examined. Duration of alcohol dependence and affective disorder (years), number of hospitalizations and suicidal attempts were analyzed as anamnestic data. Hamilton's anxiety and depression scale (HDRS), the Alcohol Use Disorders Identification Test (AUDIT), the General clinical impression scale (CGI-s) were used as psychometric tools. The study of bioelectric activity of the brain was carried out using a 16-channel encephalograph. The background electroencephalogram was recorded, the values of absolute spectral power and coherence of theta, alpha and beta rhythms were analyzed. Patients with comorbidity of alcohol dependence and affective disorders have a significantly higher risk of suicidal behavior, a greater frequency of hospitalizations, higher levels of anxiety compared with patients without affective disorders. Electrophysiological data have shown that patients with comorbidity of alcohol dependence and affective disorders have higher values of spectral power of alpha-rhythm in all parts of the cerebral cortex (except for temporal lobes) and beta-rhythm in the occipital cortex, as well as an increase in interhemispheric coherence in all frequency ranges.

Overlooking the obvious? Influence of electrolyte concentrations on seizure quality parameters in electroconvulsive therapy.

Clinical response to electroconvulsive therapy (ECT) depends on eliciting a generalized seizure. Though there are multiple ictal and other parameters to assess seizure quality, factors that influence these parameters have only been identified to a limited extend in antecedent studies (e.g., stimulus dosage, age). In the context of ECT, electrolyte concentrations have hardly been investigated so far-although hyponatremia is one well-known clinical factor to increase the risk of spontaneous seizures. In 31 patients with unipolar or bipolar depressive disorder, blood concentrations of sodium (Na), potassium (K), and calcium (Ca) were measured immediately prior to repeated sessions of maintenance ECT. Generalized linear mixed models were used to analyze the influence of Na, K, and Ca on seven seizure quality parameters: postictal suppression index (PSI), maximum sustained coherence (MSC), midictal amplitude, average seizure energy index, seizure duration (EEG/motor), and peak heart rate. Results show a statistically significant relationship between the serum sodium level and MSC: in the model, a reduction of 1mmol/l led to an increase in interhemispheric coherence of 0.678%. The further markers remained unaffected by changes in electrolyte concentrations. This finding provides first evidence that a lower blood concentration of sodium could enhance the quality of ECT-induced seizures in terms of higher interhemispheric coherence.

Wavelet Phase Coherence Estimation of EEG Signals for Neuromarketing Studies

This paper presents an Electroencephalography (EEG), Pulse Plethysmography (PPG) and Galvanic Skin Response (GSR) study for neuromarketing studies, which are related to analysis of relationship between electrodes and emotional stress across to commercial advertisement. Neuromarketing is a field of study with respect the application of neuroscience methods to analyze consumer behavior related to markets. Wavelet coherence (WC) and phase difference (PD) were used for investigating how the marketing stimuli induced the degree of information flow occurs between electrodes of EEG. Pulse rate variability (PRV) obtained from finger PPG and computed the powers in high frequency (HF), low frequency (LF). The powers in the LF and HF bands are regulated by Autonomic nervous systems (ANS) and then, Skin conductance level (SCL) computed from GSR by measuring changes in the conductivity of the skin. These electrophysiological measurements computed to evaluate emotional stress. The signals were recorded simultaneously from 30 subjects for two stages: prior to advertising stimuli (control stage) and during the advertising stimuli (experimental stage) using iMotions system in Uskudar University (Istanbul, Turkey). The WC and PD for each electrode pairs were computed for five frequency sub-bands (delta, theta, alpha, beta and gamma) of EEG. While the value of WC was generally higher in experimental stage than control stage especially in the theta, alpha and beta frequency, the value of PD was generally lower especially in gamma band. An increase of interhemispheric coherence in experimental stage occurred in the anterior frontal -temporal-parietal- area. At the same time, the LF/HF ratio and SCL were generally higher in experimental stage. We investigated whether there were statistically significant differences in WC, PD, the LF/HF ratio and SCL between the experimental and control stage. Results were demonstrated significant differences in WC and PD, LF/HF ratio between experimental stage and control stage, but there was not in SCL.

P105 Modulating inter-hemispheric coherence to influence behavior – A TMS-EEG study

Inter-hemispheric coherence (IHC) is one of the EEG parameters that measures synchronization of oscillations originating from brain regions of different hemispheres and thereby the functional connectivity between them. We know that IHC is critical for tasks such as midline object recognition that involves merging information obtained from the 2 hemispheres. In a previous study, it was observed that midline object recognition is associated with transient increase in IHC over temporo-parietal areas in the alpha frequency range (Mima et al., 2001). Whether this association is causal, remains unknown. In the current study we aimed at determining the causal association of inter-hemispheric alpha coherence to midline object recognition. Several studies have used TMS as an effective tool to entrain intrinsic brain oscillations. We interfered with the IHC by using unilateral or bilateral, synchronous or asynchronous repetitive transcranial magnetic stimulation (rTMS) pulses. Our hypothesis was that asynchronous rTMS would reduce IHC thereby impairing midline object recognition. We recruited 13 healthy subjects for the study. All subjects first participated in a screening session where the threshold intensity for blocking object recognition and the optimal coil orientation for TMS was determined. In the main experiment session, they were asked to perform the object recognition task in four blocks. During the first block, the individual alpha coherence frequency was determined by recording EEG during object recognition. During the second, third and fourth blocks rTMS was delivered in every trial with simultaneous EEG recording. Trains of 7 TMS pulses were administered over left and/or right lateral occipital gyrus at 80% of threshold intensity blocking object discrimination or 60% maximum stimulator output whichever was smaller. Our primary outcome measure for the object recognition task was d-prime or sensitivity index. Our results have not shown a significant effect of rTMS on object recognition. The EEG data is currently being analyzed to look for entrainment effects. We think that this absence of effect on behavior could be due to a ceiling effect in task performance, wrong stimulation site or sub-optimal stimulation paradigm. We are currently performing additional experiments to address the above issues.

How does a surgeon’s brain buzz? An EEG coherence study on the interaction between humans and robot

IntroductionIn humans, both primary and non-primary motor areas are involved in the control of voluntary movements. However, the dynamics of functional coupling among different motor areas have not been fully clarified yet. There is to date no research looking to the functional dynamics in the brain of surgeons working in laparoscopy compared with those trained and working in robotic surgery.Experimental proceduresWe enrolled 16 right-handed trained surgeons and assessed changes in intra- and inter-hemispheric EEG coherence with a 32-channels device during the same motor task with either a robotic or a laparoscopic approach. Estimates of auto and coherence spectra were calculated by a fast Fourier transform algorithm implemented on Matlab 5.3.ResultsWe found increase of coherence in surgeons performing laparoscopy, especially in theta and lower alpha activity, in all experimental conditions (M1 vs. SMA, S1 vs. SMA, S1 vs. pre-SMA and M1 vs. S1; p < 0.001). Conversely, an increase in inter-hemispheric coherence in upper alpha and beta band was found in surgeons using the robotic procedure (right vs. left M1, right vs. left S1, right pre-SMA vs. left M1, left pre-SMA vs. right M1; p < 0.001).DiscussionOur data provide a semi-quantitative evaluation of dynamics in functional coupling among different cortical areas in skilled surgeons performing laparoscopy or robotic surgery. These results suggest that motor and non-motor areas are differently activated and coordinated in surgeons performing the same task with different approaches. To the best of our knowledge, this is the first study that tried to assess semi-quantitative differences during the interaction between normal human brain and robotic devices.

Cerebrovascular Disease and Hippocampal Atrophy Are Differently Linked to Functional Coupling of Brain Areas: An EEG Coherence Study in MCI Subjects

The working hypothesis of paper is that the functional coupling of brain areas is combined with different neuroradiological substrates and has different clinical manifestations. 31 normal old subjects and 85 subjects with mild cognitive impairment (MCI) underwent EEG recordings and magnetic resonance imaging (MRI). Intrahemispheric and interhemispheric linear EEG coherences were computed. At first, all normal old and MCI subjects were compared. Subsequently, three subgroups of MCI were obtained based on neuroradiological substrate (subcortical cerebrovascular damage, MCI-CVD; cholinergic pathways vascular damage MCI-CHOL; and hippocampal atrophy, MCI-HIPP) and compared with a normal old sample matched for age, education and Mini-Mental State Examination score. The group of MCI subjects compared to normal old subjects shows: 1) decrease of intrahemispheric coherence in fronto-parietal regions (both right and left hemisphere); 2) increase of interhemispheric coherence on frontal regions in delta frequency; and 3) increase of interhemispheric coherence on temporal regions (from delta to alpha3 frequency bands). In the MCI subgroups, hippocampal atrophy is linked to an increase of interhemispheric coherence seen on frontal and temporal regions whereas subcortical CVD is linked to the largest decrease of coherence in fronto-parietal regions. MCI-CVD patients performed worst on Trail Making Test battery whereas MCI-HIPP patients were impaired on Rey word list delayed recall and Rey figure recall.

Cortical and thalamic coherence during spike–wave seizures in WAG/Rij rats

The study examines cortico-cortical and cortico-thalamic network synchronization at the onset of spike–wave discharges (SWD) in a genetic model of absence epilepsy, WAG/Rij rats. Coherence was measured between multiple cortical areas (intracortical), reticular and rely thalamic nuclei (intrathalamic) and between the cortex and the thalamus. SWD-related increase of coherence (5–60 Hz) was found in all investigated pairs. The highest increase of coherence was around the mean frequency of SWD (8–11.5 Hz) and in the harmonic band 16–21.5 Hz with two central maxima around 10 and 20 Hz. The frequency profile of coherence was different in different intracortical networks, therefore latter were divided into local, global and transhemispheric networks. The presumable source of SWD in the somatosensory cortex and its closest surroundings formed a minimal (local) circuit, in which occurrence of SWD was facilitated by a consistent shift of network synchrony from delta to alpha/beta frequencies. Transhemispheric coherence revealed the largest increase with an additional 16 Hz peak, suggesting a crucial involvement of the corpus callosum in the pathophysiology of absence seizures. The increase in interhemispheric coherence was largest between relatively remote somatosensory or frontal areas, supporting the assumption that SWD originate from the lateral fronto-parietal cortical area.

Visual stimulus-dependent changes in interhemispheric EEG coherence in ferrets.

In recent years, the analysis of the coherence between signals recorded from the scalp [electroencephalographic (EEG) coherence] has been used to assess the functional properties of cortico-cortical connections, both in animal models and in humans. However, the experimental validation of this technique is still scarce. Therefore we applied it to the study of the callosal connections between the visual areas of the two hemispheres, because this particular set of cortico-cortical connections can be activated in a selective way by visual stimuli. Indeed, in primary and in low-order secondary visual areas, callosal axons interconnect selectively regions, which represent a narrow portion of the visual field straddling the vertical meridian and, within these regions, neurons that prefer the same stimulus orientation. Thus only isooriented stimuli located near the vertical meridian are expected to change interhemispheric coherence by activating callosal connections. Finally, if such changes are found and are indeed mediated by callosal connections, they should disappear after transection of the corpus callosum. We perfomed experiments on seven paralyzed and anesthetized ferrets, recording their cortical activity with epidural electrodes on areas 17/18, 19, and lateral suprasylvian, during different forms of visual stimulation. As expected, we found that bilateral iso-oriented stimuli near the vertical meridian, or extending across it, caused a significant increase in interhemispheric coherence in the EEG beta-gamma band. Stimuli with different orientations, stimuli located far from the vertical meridian, as well as unilateral stimuli failed to affect interhemispheric EEG coherence. The stimulus-induced increase in coherence disappeared after surgical transection of the corpus callosum. The results suggest that the activation of cortico-cortical connections can indeed be revealed as a change in EEG coherence. The latter can therefore be validly used to investigate the functionality of cortico-cortical connections.