Evoked Alpha Power is Reduced in Disconnected Consciousness During Sleep and Anesthesia

Darracq, Matthieu; Funk, Chadd M.; Polyakov, Daniel; Riedner, Brady A.; Gosseries, Olivia; Nieminen, Jaakko O.; Bonhomme, Vincent; Brichant, Jean François; Boly, Mélanie; Laureys, Steven; Tononi, Giulio; Sanders, Robert D.

doi:10.1038/s41598-018-34957-9

Cited by 28 publications

(25 citation statements)

References 49 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, our participant was awake during the whole session, and the EEG data show no sleeprelated signs. Latest findings from research in REM sleep and ketamine anesthesia suggest that a decrease in alpha power may be a marker for a disconnection of consciousness from sensory stimuli (Sanders et al, 2012;Darracq et al, 2018;Comsa et al, 2019). Increases in theta power have been found to be associated with cognitive control and stable attention (Cavanagh and Frank, 2014;Keller et al, 2017) as well as with decreased activity in the DMN (White et al, 2013;Hacker et al, 2017), which is related to self-processing and mind-wandering.…”

Section: Discussionmentioning

confidence: 99%

Content-Free Awareness: EEG-fcMRI Correlates of Consciousness as Such in an Expert Meditator

Winter

LeVan

Borghardt³

et al. 2020

Front. Psychol.

View full text Add to dashboard Cite

The minimal neural correlate of the conscious state, regardless of the neural activity correlated with the ever-changing contents of experience, has still not been identified. Different attempts have been made, mainly by comparing the normal waking state to seemingly unconscious states, such as deep sleep or general anesthesia. A more direct approach would be the neuroscientific investigation of conscious states that are experienced as free of any specific phenomenal content. Here we present serendipitous data on content-free awareness (CFA) during an EEG-fMRI assessment reported by an extraordinarily qualified meditator with over 50,000 h of practice. We focused on two specific cortical networks related to external and internal awareness, i.e., the dorsal attention network (DAN) and the default mode network (DMN), to explore the neural correlates of this experience. The combination of high-resolution EEG and ultrafast fMRI enabled us to analyze the dynamic aspects of fMRI connectivity informed by EEG power analysis. The neural correlates of CFA were characterized by a sharp decrease in alpha power and an increase in theta power as well as increases in functional connectivity in the DAN and decreases in the posterior DMN. We interpret these findings as correlates of a top-down-initiated attentional state excluding external sensory stimuli and internal mentation from conscious experience. We conclude that the investigation of states of CFA could provide valuable input for new methodological and conceptual approaches in the search for the minimal neural correlate of consciousness.

show abstract

Section: Discussionmentioning

confidence: 99%

Content-Free Awareness: EEG-fcMRI Correlates of Consciousness as Such in an Expert Meditator

Winter

LeVan

Borghardt³

et al. 2020

Front. Psychol.

View full text Add to dashboard Cite

show abstract

“…The oldest studies in that respect were event-related potential EEG studies (Uhl et al, 1980; Plourde and Boylan, 1991), and the fMRI or PET activation studies (Bonhomme et al, 2008). The most recent ones look into how the brain handles sensory information (Lichtner et al, 2018a,b; Nourski et al, 2018) and between-region communication (Darracq et al, 2018a), as well as the directionality of information transfer (Sanders et al, 2018), and sensory cross-modal interactions (Bekinschtein et al, 2009). Some mixed approaches exist, melting one mode of analysis with another, such as those measuring the spatio-temporal complexity of TMS-evoked cortical responses (Casali et al, 2013; Bodart et al, 2017).…”

Section: Several Ways Of Exploring the Effects Of Anesthetic Medicatimentioning

confidence: 99%

General Anesthesia: A Probe to Explore Consciousness

Bonhomme

Staquet

Montupil

et al. 2019

Front. Syst. Neurosci.

Self Cite

View full text Add to dashboard Cite

General anesthesia reversibly alters consciousness, without shutting down the brain globally. Depending on the anesthetic agent and dose, it may produce different consciousness states including a complete absence of subjective experience (unconsciousness), a conscious experience without perception of the environment (disconnected consciousness, like during dreaming), or episodes of oriented consciousness with awareness of the environment (connected consciousness). Each consciousness state may potentially be followed by explicit or implicit memories after the procedure. In this respect, anesthesia can be considered as a proxy to explore consciousness. During the recent years, progress in the exploration of brain function has allowed a better understanding of the neural correlates of consciousness, and of their alterations during anesthesia. Several changes in functional and effective between-region brain connectivity, consciousness network topology, and spatio-temporal dynamics of between-region interactions have been evidenced during anesthesia. Despite a set of effects that are common to many anesthetic agents, it is still uneasy to draw a comprehensive picture of the precise cascades during general anesthesia. Several questions remain unsolved, including the exact identification of the neural substrate of consciousness and its components, the detection of specific consciousness states in unresponsive patients and their associated memory processes, the processing of sensory information during anesthesia, the pharmacodynamic interactions between anesthetic agents, the direction-dependent hysteresis phenomenon during the transitions between consciousness states, the mechanisms of cognitive alterations that follow an anesthetic procedure, the identification of an eventual unitary mechanism of anesthesia-induced alteration of consciousness, the relationship between network effects and the biochemical or sleep-wake cycle targets of anesthetic agents, as well as the vast between-studies variations in dose and administration mode, leading to difficulties in between-studies comparisons. In this narrative review, we draw the picture of the current state of knowledge in anesthesia-induced unconsciousness, from insights gathered on propofol, halogenated vapors, ketamine, dexmedetomidine, benzodiazepines and xenon. We also describe how anesthesia can help understanding consciousness, we develop the above-mentioned unresolved questions, and propose tracks for future research.

show abstract

“…This TMS-EEG combination has been shown to be an effective discriminator of conscious levels between participants in sleep and wake conditions (Massimini et al, 2005), including periods of dreaming within rapid and non-rapid eye movement sleep (Massimini et al, 2010;Nieminen et al, 2016;Lee et al, 2019). The approach has also differentiated the effects on (un)conscious level in distinct anesthetic agents (Sarasso et al, 2015;Darracq et al, 2018). In the clinical diagnostic setting, the neural response from the TMS pulse has been quantified into the perturbational complexity index (PCI), where values above an empirically defined cutoff of 0.31 can accurately stratify patients into the same clinical categories made with behavioral assessments (Casali et al, 2013;Casarotto et al, 2016;Bodart et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Decreased Evoked Slow-Activity After tDCS in Disorders of Consciousness

Mensen

Bodart

Thibaut

et al. 2020

Front. Syst. Neurosci.

Self Cite

View full text Add to dashboard Cite

Due to life-saving medical advances, the diagnosis and treatment of disorders of consciousness (DOC) has become a more commonly occurring clinical issue. One recently developed intervention option has been non-invasive transcranial direct current stimulation. This dichotomy of patient responders may be better understood by investigating the mechanism behind the transcranial direct current stimulation (tDCS) intervention. The combination of transcranial magnetic stimulation and electroencephalography (TMS-EEG) has been an important diagnostic tool in DOC patients. We therefore examined the neural response using TMS-EEG both before and after tDCS in seven DOC patients (four diagnosed as in a minimally conscious state and three with unresponsive wakefulness syndrome). tDCS was applied over the dorsolateral prefrontal cortex, while TMS pulses were applied to the premotor cortex. None of the seven patients showed relevant behavioral change after tDCS. We did, however, find that the overall evoked slow activity was reduced following tDCS intervention. We also found a positive correlation between the strength of the slow activity and the amount of high-frequency suppression. However, there was no significant pre-post tDCS difference in high frequencies. In the resting-state EEG, we observed that both the incidence of slow waves and the positive slope of the wave were affected by tDCS. Taken together, these results suggest that the tDCS intervention can reduce the slow-wave activity component of bistability, but this may not directly affect high-frequency activity. We hypothesize that while reduced slow activity may be necessary for the recovery of neural function, especially consciousness, this alone is insufficient.

show abstract

Evoked Alpha Power is Reduced in Disconnected Consciousness During Sleep and Anesthesia

Cited by 28 publications

References 49 publications

Content-Free Awareness: EEG-fcMRI Correlates of Consciousness as Such in an Expert Meditator

Content-Free Awareness: EEG-fcMRI Correlates of Consciousness as Such in an Expert Meditator

General Anesthesia: A Probe to Explore Consciousness

Decreased Evoked Slow-Activity After tDCS in Disorders of Consciousness

Contact Info

Product

Resources

About