Alteration of global workspace during loss of consciousness: A study of parietal seizures

Abstract

Summary Purpose: Loss of consciousness (LOC) in epileptic seizures has a strongly negative impact on quality of life. Recently, we showed that LOC occurring during temporal lobe seizures was correlated with a nonlinear increase of neural synchrony in associative—and particularly parietal—cortices. Whether these mechanisms might be observed in other types of seizures is unknown. This study aimed at investigating the relationship between changes in synchrony and degree of LOC during parietal lobe epilepsy (PLE), a form of epilepsy in which seizures directly involve the parietal associative cortices. Methods: Ten patients undergoing stereoelectroencephalography (SEEG) during presurgical evaluation of PLE were studied. The LOC intensity was scored using the Conscious Seizure Scale (CSS). For each studied seizure (n = 29), interdependencies between signals recorded from six brain regions were estimated as a function of time by using nonlinear regression analysis (h2 coefficient). Key Findings: Seizures were divided into three groups according to the CSS scale: group A (no LOC) with a score ≤1, group B (intermediate or partial LOC) with a score ranging from 2 to 5, and group C (maximal LOC) with a score ≥6. The majority of seizures in patients with PLE disclosed significant LOC (17/29, group C). Mean h2 values were significantly different between the three groups (p = 0.008), the maximal values of synchrony being observed in group C. In addition, a statistically significant nonlinear relationship (p = 0.0021) was found between the h2 values and the CSS scores, suggesting a threshold effect. Significance: This study indicates that excess of EEG signal synchrony within associative cortices is likely to be a crucial phenomenon associated with LOC.

Cortico-cortical evoked potentials for sites of early versus late seizure spread in stereoelectroencephalography

“…In the current literature, several semiological features have been associated with ictal network patterns. Consciousness interruption requires distant synchronization Arthuis et al (2009), Lambert et al (2012, which may imply preferential connectivity within selected frequency ranges although symptoms may alternatively require a decrease in focal synchrony Bartolomei et al (2005). Comparison of CCEP responses with additional semiological features, particularly if the moments of symptom onset are precisely characterized, may shed further light on the seizure network Bartolomei et al (2007Bartolomei et al ( , 2012Bartolomei et al ( , 2013.…”

Mapping Epileptic Activity: Sources or Networks for the Clinicians?

“…Consciousness was preserved as long as excessive synchrony was confined to the temporal lobe. Similarly, loss of consciousness in parietal seizures was associated with widespread parietal and frontal synchronization (188). The authors framed these observations into the context of the global workspace theory, in which the sustained synchronization of neuronal activity in widely distributed modules renders perceptions, memories, and intentions available to consciousness (189).…”

A master switch for consciousness?

“…Focal temporal lobe seizures with impaired consciousness exhibit decreased cerebral blood flow, slow wave activity, and enhanced synchrony in widespread regions of the frontoparietal association cortex [7–10]. Focal parietal seizures with impaired consciousness also produce abnormally enhanced long-range cortical synchrony [11]. In the case of temporal lobe seizures, there is growing evidence that seizures inhibit the crucial subcortical arousal systems, which, in turn, causes a deep sleep-like state in the cortex and impaired consciousness [12–15].…”