Consciousness alteration in focal epilepsy is related to loss of signal complexity and information processing

Abstract

Alteration of awareness is a main feature of focal epileptic seizures. In this work, we studied how the information contained in EEG signals was modified during temporal lobe seizures with altered awareness by using permutation entropy (PE) as a measure of the complexity of the signal. PE estimation was performed in thirty-six seizures of sixteen patients with temporal lobe epilepsy who underwent SEEG recordings. We tested whether altered awareness (based on the Consciousness Seizure Score) was correlated with a loss of signal complexity. We estimated global changes in PE as well as regional changes to gain insight into the mechanisms associated with awareness impairment. Our results reveal a positive correlation between the decrease of entropy and the consciousness score as well as the existence of a threshold on entropy that could discriminate seizures with no alteration of awareness from seizures with profound alteration of awareness. The loss of signal complexity was diffuse, extending bilaterally and to the associative cortices, in patients with profound alteration of awareness and limited to the temporal mesial structures in patients with no alteration of awareness. Thus PE is a promising tool to discriminate between the different subgroups of awareness alteration in TLE.

Consciousness transitions during epilepsy seizures through the lens of integrated information theory

“…The reduction in signal complexity, as noted in Φ, is not unique to this metric; it is also evident in various other complexity measures. El Youssef et al 16 employed permutation entropy in their analysis of SEEG recordings. Their findings revealed a decline in signal complexity during seizures, providing insight into the manner in which the loss of signal complexity spreads within the cortex, correlating with alterations in awareness.…”

How fast does the brain recover after an epileptic seizure?

“…The average postictal period evaluated by the measure of a parameter called the PAT lasted approximately 4.5 min, but this period could extend up to an hour, indicating a potential prolonged impact on brain physiology due to altered complexity dynamics. Persistent changes in brain activity complexity may contribute to postictal cognitive deficits, as evidenced by associations with ictal (e.g., loss of awareness 8 ) and postictal deficits (e.g., transient epileptic amnesia 12 linked to postictal complexity alterations in the medial temporal regions).…”

“…Building on our previous work, 3 , 8 the parameters used in this PE study were an embedding dimension D = 3 and a time lag τ = 1. The analysis was conducted using a sliding time window of 5 sec, with an overlap of 2.5 sec.…”

“…The values of H(D) range from 0 to 1, smaller values indicating a more regular and deterministic time series, while values closer to 1 suggesting a noisier and more random time series. 7 Building on our previous work, 3,8 the parameters used in this PE study were an embedding dimension D = 3 and a time lag τ = 1. The analysis was conducted using a sliding time window of 5 sec, with an overlap of 2.5 sec.…”

Cerebral Electrometabolic Coupling in Disordered and Normal States of Consciousness

“…23 Also in other neurological conditions such as temporal lobe and absence epilepsy, during an episode of transient loss of consciousness, thalamocortical projections are implicated by increasing synchrony to pathological levels, leading to loss of differentiation and complexity needed for consciousness. [24][25][26][27] In normal conditions, the striatum inhibits the internal globus pallidus, which disinhibits the thalamus. By this disinhibition, the thalamic projections excite the frontal, temporal, parietal, and occipital cortices that project back to subcortical nuclei, closing the functional loop.…”