Leveraging meaning-induced neural dynamics to detect covert cognition via EEG during natural language listening-a case series

Abstract

At least a quarter of adult patients with severe brain injury in a disorder of consciousness may have cognitive abilities that are hidden due to motor impairment. In this case series, we developed a tool that extracted acoustic and semantic processing biomarkers from electroencephalography recorded while participants listened to a story. We tested our method on two male adolescent survivors of severe brain injury and showed evidence of acoustic and semantic processing. Our method identifies cognitive processing while obviating demands on attention, memory, and executive function. This lays a foundation for graded assessments of cognition recovery across the spectrum of covert cognition.

Keywords: cognitive function; disorder of consciousness; natural language; pediatric; temporal response function (TRF).

Figure 1

Event-related EEG markers of acoustic and semantic processing of discrete and continuous stimuli for P1 (left) and P2 (right). Top-left subplots: average auditory evoked potential recorded from channel Cz (from “click” stimuli in the case of P1, and 340 ms “beep” stimuli for P2). Top-right subplots: acoustic TRF response, estimated at channel Cz. Bottom-left subplots: average difference between responses to incongruent and congruent stimuli in the classical ‘N400' paradigm, at channel Pz. Bottom-right subplots: TRF response correlated with lexical-surprisal feature values at channel Pz. Dotted vertical lines indicate the latency of the largest negative peak (Figure 2 shows the corresponding topographic scalp maps). For discrete stimuli, time points at which event-related potentials were significantly different from zero (uncorrected p-value < 0.05) are indicated with a black horizontal line. For continuous stimuli, asterisks in legends denote the overall statistical significance level: *for p-values < 0.05 and **for p-values < 0.01. Additionally, we show the mean of the re-permuted TRFs (see Section 2.8.2) as cyan traces, and their mean ± one standard deviation as cyan-shaded regions: this is a visualization of the distribution of the TRFs under the null hypothesis that stimulus ordering does not influence the response.

Figure 2

Topographic scalp maps of the ERP and TRF responses to discrete and continuous stimuli for P1 (left) and P2 (right). Each map is computed at the time lag corresponding to the largest negative peak marked by a dotted vertical line in the corresponding panel of Figure 1. The locations of Cz and Pz are marked as white squares and triangles, respectively.