Coherence and Consciousness: Study of Fronto-Parietal Gamma Synchrony in Patients with Disorders of Consciousness

Abstract

Evaluation of consciousness needs to be supported by the evidence of brain activation during external stimulation in patients with unresponsive wakefulness syndrome (UWS). Assessment of patients should include techniques that do not depend on overt motor responses and allow an objective investigation of the spontaneous patterns of brain activity. In particular, electroencephalography (EEG) coherence allows to easily measure functional relationships between pairs of neocortical regions and seems to be closely correlated with cognitive or behavioral measures. Here, we show the contribution of higher order associative cortices of patients with disorder of consciousness (N = 26) in response to simple sensory stimuli, such as visual, auditory and noxious stimulation. In all stimulus modalities an increase of short-range parietal and long-range fronto-parietal coherences in gamma frequencies were seen in the controls and minimally conscious patients. By contrast, UWS patients showed no significant modifications in the EEG patterns after stimulation. Our results suggest that UWS patients can not activate associative cortical networks, suggesting a lack of information integration. In fact, fronto-parietal circuits result to be connectively disrupted, conversely to patients that exhibit some form of consciousness. In the light of this, EEG coherence can be considered a powerful tool to quantify the involvement of cognitive processing giving information about the integrity of fronto-parietal network. This measure can represent a new neurophysiological marker of unconsciousness and help in determining an accurate diagnosis and rehabilitative intervention in each patient.

Frontal Connectivity in EEG Gamma (30–45 Hz) Respond to Spinal Cord Stimulation in Minimally Conscious State Patients

“…Gamma connectivity has been implicated relevant in subjective consciousness (Llinas et al, 1998; Singer, 1998), and gamma coherence has been shown to be a fundamental prerequisite in the aware process and the potential to participate cognitive processes (Naro et al, 2016). In addition, gamma connectivity has been identified as an important awareness-level marker in DOC patients (Cavinato et al, 2015; Naro et al, 2016). In MCS and vegetative state (VS) patients, significant differences have been demonstrated in the responses of short-range parietal and long-range fronto-parietal gamma coherences to simple sensory stimulus modalities (Cavinato et al, 2015).…”

Consciousness, awareness of insight and neural mechanisms of schizophrenia

“…In this historical context, recent studies indicate that binding of distributed information in the brain represents the basic mechanism of consciousness that manifests through neural correlates emerging in EEG specifically as fast oscillations in the γ range (40-70 Hz) (Uhlhaas et al, 2009;Lou et al, 2010;Baars et al, 2013;Cavinato et al, 2014). As might be expected, similar findings of γ oscillations were also found in the highest form of consciousness and self-awareness representing conscious recognition of one's own mental state (Jung-Beeman et al, 2004;Kounios et al, 2008;Sandkuhler and Bhattacharya, 2008).…”

Neural Correlates of Wakefulness, Sleep, and General Anesthesia

“…Magnitude squared coherence was calculated at individual frequencies in 0.5 Hz intervals from 0.5 to 155 Hz between all electrode pairs in 2 s moving windows using the ‘mscohere.m’ function in the MATLAB Signal Processing Toolbox (MathWorks Inc., Natick, MA, USA). Using the approach demonstrated in previous publications from our 28,29 and other laboratories, 30,31 the coherence values were averaged over the following frequency bands: delta (δ: 0.5-4 Hz), theta (θ: 4-10 Hz), alpha (α: 10-15 Hz), beta (β: 15-25 Hz), low gamma (γ1: 25-55 Hz), medium gamma (γ2: 85-125 Hz), and high gamma (γ3: 125-155 Hz). The mean global coherence was obtained by averaging the coherence for individual channel pairs for each animal.…”