Golden rhythms as a theoretical framework for cross-frequency organization

While brain rhythms appear fundamental to brain function, why brain rhythms consistently organize into the small set of discrete frequency bands observed remains unknown. Here we propose that rhythms separated by factors of the golden ratio ($\phi=(1+ \sqrt{5})/2$) optimally support segregation and cross-frequency integration of information transmission in the brain. Organized by the golden ratio, pairs of transient rhythms support multiplexing by reducing interference between separate communication channels, and triplets of transient rhythms support integration of signals to establish a hierarchy of cross-frequency interactions. We illustrate this framework in simulation and apply this framework to propose four hypotheses.Comment: 8 figure

Alpha Band Resting-State EEG Connectivity Is Associated With Non-verbal Intelligence

The aim of the present study was to investigate whether EEG resting state connectivity correlates with intelligence. One-hundred and sixty five participants took part in the study. Six minutes of eyes closed EEG resting state was recorded for each participant. Graph theoretical connectivity metrics were calculated separately for two well-established synchronization measures [weighted Phase Lag Index (wPLI) and Imaginary Coherence (iMCOH)] and for sensor- and source EEG space. Non-verbal intelligence was measured with Raven’s Progressive Matrices. In line with the Neural Efficiency Hypothesis, path lengths characteristics of the brain networks (Average and Characteristic Path lengths, Diameter and Closeness Centrality) within alpha band range were significantly correlated with non-verbal intelligence for sensor space but no for source space. According to our results, variance in non-verbal intelligence measure can be mainly explained by the graph metrics built from the networks that include both weak and strong connections between the nodes

Imaging the spatial-temporal neuronal dynamics using dynamic causal modelling

Oscillatory brain activity is a ubiquitous feature of neuronal dynamics and the synchronous discharge of neurons is believed to facilitate integration both within functionally segregated brain areas and between areas engaged by the same task. There is growing interest in investigating the neural oscillatory networks in vivo. The aims of this thesis are to (1) develop an advanced method, Dynamic Causal Modelling for Induced Responses (DCM for IR), for modelling the brain network functions and (2) apply it to exploit the nonlinear coupling in the motor system during hand grips and the functional asymmetries during face perception. DCM for IR models the time-varying power over a range of frequencies of coupled electromagnetic sources. The model parameters encode coupling strength among areas and allows the differentiations between linear (within frequency) and nonlinear (between-frequency) coupling. I applied DCM for IR to show that, during hand grips, the nonlinear interactions among neuronal sources in motor system are essential while intrinsic coupling (within source) is very likely to be linear. Furthermore, the normal aging process alters both the network architecture and the frequency contents in the motor network. I then use the bilinear form of DCM for IR to model the experimental manipulations as the modulatory effects. I use MEG data to demonstrate functional asymmetries between forward and backward connections during face perception: Specifically, high (gamma) frequencies in higher cortical areas suppressed low (alpha) frequencies in lower areas. This finding provides direct evidence for functional asymmetries that is consistent with anatomical and physiological evidence from animal studies. Lastly, I generalize the bilinear form of DCM for IR to dissociate the induced responses from evoked ones in terms of their functional role. The backward modulatory effect is expressed as induced, but not evoked responses

Studies on the assessment of the adequacy of anesthesia

Several hypnosis monitoring systems based on the processed electroencephalogram (EEG) have been developed for use during general anesthesia. The assessment of the analgesic component (antinociception) of general anesthesia is an emerging field of research. This study investigated the interaction of hypnosis and antinociception, the association of several physiological variables with the degree of intraoperative nociception, and aspects of EEG Bispectral Index Scale (BIS) monitoring during general anesthesia. In addition, EEG features and heart rate (HR) responses during desflurane and sevoflurane anesthesia were compared. A propofol bolus of 0.7 mg/kg was more effective than an alfentanil bolus of 0.5 mg in preventing the recurrence of movement responses during uterine dilatation and curettage (D C) after a propofol-alfentanil induction, combined with nitrous oxide (N2O). HR and several HR variability-, frontal electromyography (fEMG)-, pulse plethysmography (PPG)-, and EEG-derived variables were associated with surgery-induced movement responses. Movers were discriminated from non-movers mostly by the post-stimulus values per se or normalized with respect to the pre-stimulus values. In logistic regression analysis, the best classification performance was achieved with the combination of normalized fEMG power and HR during D C (overall accuracy 81%, sensitivity 53%, specificity 95%), and with the combination of normalized fEMG-related response entropy, electrocardiography (ECG) R-to-R interval (RRI), and PPG dicrotic notch amplitude during sevoflurane anesthesia (overall accuracy 96%, sensitivity 90%, specificity 100%). ECG electrode impedances after alcohol swab skin pretreatment alone were higher than impedances of designated EEG electrodes. The BIS values registered with ECG electrodes were higher than those registered simultaneously with EEG electrodes. No significant difference in the time to home-readiness after isoflurane-N2O or sevoflurane-N2O anesthesia was found, when the administration of the volatile agent was guided by BIS monitoring. All other early and intermediate recovery parameters were also similar. Transient epileptiform EEG activity was detected in eight of 15 sevoflurane patients during a rapid increase in the inspired volatile concentration, and in none of the 16 desflurane patients. The observed transient EEG changes did not adversely affect the recovery of the patients. Following the rapid increase in the inhaled desflurane concentration, HR increased transiently, reaching its maximum in two minutes. In the sevoflurane group, the increase was slower and more subtle. In conclusion, desflurane may be a safer volatile agent than sevoflurane in patients with a lowered seizure threshold. The tachycardia induced by a rapid increase in the inspired desflurane concentration may present a risk for patients with heart disease. Designated EEG electrodes may be superior to ECG electrodes in EEG BIS monitoring. When the administration of isoflurane or sevoflurane is adjusted to maintain BIS values at 50-60 in healthy ambulatory surgery patients, the speed and quality of recovery are similar after both isoflurane-N2O and sevoflurane-N2O anesthesia. When anesthesia is maintained by the inhalation of N2O and bolus doses of propofol and alfentanil in healthy unparalyzed patients, movement responses may be best avoided by ensuring a relatively deep hypnotic level with propofol. HR/RRI, fEMG, and PPG dicrotic notch amplitude are potential indicators of nociception during anesthesia, but their performance needs to be validated in future studies. Combining information from different sources may improve the discrimination of the level of nociception.Useita aivosähkökäyrään (EEG) perustuvia unen syvyyden valvontamenetelmiä on kehitetty yleisanestesian aikana käytettäväksi. Kudosvaurion aiheuttamia ärsykkeitä vaimentavan yleisanestesian osan arviointimenetelmien tutkimus on alkamassa. Tässä väitöskirjatyössä tutkittiin unen syvyyden ja kudosvaurion aiheuttamien ärsykkeiden vaimennuksen vuorovaikutusta, useiden elimistön toimintaa kuvaavien muuttujien ja kudosvaurion aiheuttaman ärsytyksen suhdetta sekä EEG:n bispektraali-indeksin (BIS) käyttöä yleisanestesian valvonnassa. Lisäksi verrattiin desfluraani- ja sevofluraanianestesiaan liittyviä EEG-muutoksia ja sykevasteita. Kun anestesia oli aloitettu propofolilla, alfentaniililla ja typpioksiduulilla (N2O), propofoliannos 0.7 mg/kg esti liikevasteiden toistumista kohdun kaavinnan aikana tehokkaammin kuin alfentaniiliannos 0.5 mg. Sydämen syke ja useat sykevaihtelusta, otsalihastoiminnasta, pulssiaallon mittauksesta ja EEG:sta johdetut muuttujat olivat yhteydessä leikkauksen aiheuttamiin liikevasteisiin. Pääsääntöisesti ärsykkeen jälkeen mitatut arvot sellaisenaan tai suhteutettuna ärsykettä edeltäviin arvoihin (normalisoituna) erottelivat liikkuvat potilaat liikkumattomista potilaista. Paras luokittelu saavutettiin kohdun kaavinnan aikana yhdistämällä tieto normalisoidusta otsalihastoiminnasta ja sykkeestä (herkkyys 53%, tarkkuus 95%), ja sevofluraanianestesian aikana yhdistämällä tieto normalisoidusta (otsalihastoimintaan liittyvästä) vaste-entropiasta, sykkeestä ja pulssiaallon muodosta (herkkyys 90%, tarkkuus 100%). Kun iho valmisteltiin vain pyyhkäisemällä alkoholilla, sydänsähkökäyrän (EKG) mittaukseen tarkoitettujen elektrodien sähköinen vastus oli suurempi kuin EEG:n mittaukseen tarkoitettujen elektrodien. EKG-elektrodeilla mitatut BIS-arvot olivat korkeampia kuin samanaikaisesti EEG-elektrodeilla mitatut BIS-arvot. Kun höyrystyviä anestesia-aineita annosteltiin BIS-arvojen mukaan, toipuminen oli yhtä nopeaa isofluraani-N2O-anestesian jälkeen kuin sevofluraani-N2O-anestesian jälkeen. Kun höyrystyvän anestesia-aineen pitoisuutta nostettiin nopeasti viiden minuutin ajaksi, ohimenevää epileptistä aivosähkötoimintaa havaittiin kahdeksalla viidestätoista sevofluraanipotilaasta, mutta ei yhdelläkään kuudestatoista desfluraanipotilaasta. Havaitut ohimenevät EEG-muutokset eivät vaikuttaneet haitallisesti potilaiden toipumiseen. Desfluraanipitoisuuden nopean noston jälkeen syke kiihtyi ohimenevästi ja saavutti huippunsa kahdessa minuutissa. Sevofluraaniryhmässä sykenousu oli hitaampi ja lievempi. Tulosten perusteella voidaan todeta, että desfluraani saattaa olla sevofluraania turvallisempi anestesia-aine potilailla joiden kouristuskynnys on alentunut. Nopeaan desfluraanipitoisuuden nostoon liittyvä sykenousu voi olla haitallinen sydänsairaille potilaille. EEG-elektrodit ovat BIS-mittauksessa parempia kuin halvemmat EKG-elektrodit. Kun höyrystyvä anestesia-aine annostellaan siten että BIS-arvo pysyy välillä 50-60, toipuminen on samankaltainen sekä isofluraani-N2O- että sevofluraani-N2O-anestesian jälkeen terveillä päiväkirurgisilla potilailla. Kun anestesiaa ylläpidetään N2O:lla sekä propofoli- ja alfentaniiliannoksilla terveillä potilailla, joiden lihastoimintaa ei ole lamattu, liikevasteita estetään mahdollisesti parhaiten pitämällä uni verrattain syvänä propofolin avulla. Sydämen syke, otsalihastoiminta ja pulssiaallon muoto saattavat soveltua kudosvaurion aiheut-taman ärsytyksen valvontaan anestesian aikana, mutta lisätutkimuksia aiheesta tarvitaan. Kudosvaurion aiheuttaman ärsytyksen arviointia voidaan mahdollisesti tarkentaa yhdistämällä tietoa useista elimistön toimintaa kuvaavista muuttujista

Neural and Psychological Coordination in Social Communication and Interaction

Dynamic, naturalistic study of social interactions in humans is a small but growing literature. Emerging from this work is the theory that social interaction creates a “merged mind” between interlocutors – they come into psychological, behavioral, and neural alignment in order to better predict each other and coordinate as one social unit. However social interaction is diverse, so more work is needed to understand the specific nature of alignment between people in a variety of interactive contexts. In particular, it’s unclear how heterogeneities among members of an interaction impact their ability to align. This work aims to help address this gap by first evaluating and improving ways to collect neuroimaging data in naturalistic, social settings (Chapter 2). Then, empirical research is presented that examines how personal similarity factors impact the extent of alignment during personal disclosure interactions, where one person speaks and the other listens (Chapter 3). Finally, further empirical research investigates different types of alignment that may be present in a dyadic back-and-forth discussion in a joint decision-making paradigm. How this work contributes to a broader understanding of the ways people communicate and work together, and how this research can continue with improved methods, is discussed

Propofol-induced unresponsiveness is associated with impaired feedforward connectivity in cortical hierarchy

peer reviewedBackground: Impaired consciousness has been associated with impaired cortical signal propagation after transcranial magnetic stimulation (TMS). We hypothesised that the reduced current propagation under propofol-induced unresponsiveness is associated with changes in both feedforward and feedback connectivity across the cortical hierarchy. Methods: Eight subjects underwent left occipital TMS coupled with high-density EEG recordings during wakefulness and propofol-induced unconsciousness. Spectral analysis was applied to responses recorded from sensors overlying six hierarchical cortical sources involved in visual processing. Dynamic causal modelling (DCM) of induced time–frequency responses and evoked response potentials were used to investigate propofol's effects on connectivity between regions. Results: Sensor space analysis demonstrated that propofol reduced both induced and evoked power after TMS in occipital, parietal, and frontal electrodes. Bayesian model selection supported a DCM with hierarchical feedforward and feedback connections. DCM of induced EEG responses revealed that the primary effect of propofol was impaired feedforward responses in cross-frequency theta/alpha–gamma coupling and within frequency theta coupling (F contrast, family-wise error corrected P<0.05). An exploratory analysis (thresholded at uncorrected P<0.001) also suggested that propofol impaired feedforward and feedback beta band coupling. Post hoc analyses showed impairments in all feedforward connections and one feedback connection from parietal to occipital cortex. DCM of the evoked response potential showed impaired feedforward connectivity between left-sided occipital and parietal cortex (T contrast P=0.004, Bonferroni corrected). Conclusions: Propofol-induced loss of consciousness is associated with impaired hierarchical feedforward connectivity assessed by EEG after occipital TMS. © 2018 British Journal of AnaesthesiaARC-06/11-34