An electroencephalography-based index of peripersonal space representation was associated with conscious vs unconscious states and may predict recovery in patients with disorders of consciousness, according to a study published in Cell Reports Medicine.

The index, derived from high-beta oscillations during an audiotactile paradigm, was present during wakefulness and dreaming but absent during dreamless sleep, and higher values were associated with better clinical outcomes at discharge.

Methods and patient population

The study combined experimental data from healthy participants with a clinical cohort of 72 patients with disorders of consciousness. Fifteen healthy participants underwent high-density electroencephalography (EEG) during wakefulness and overnight sleep using an audiotactile stimulation paradigm that varied stimulus distance (near vs far) and modality.

Consciousness during sleep was assessed using repeated awakenings, with participants reporting whether they experienced dreams or no conscious content prior to awakening.

The clinical cohort included 72 patients evaluated approximately 31 days following brain injury. Consciousness was assessed using the Coma Recovery Scale–Revised, and clinical outcomes were measured at discharge approximately 24 days later using a composite outcome index derived from multiple recovery scales.

The peripersonal space (PPS) index was calculated from spectral power differences in the high-beta range (20–30 Hz) across centroparietal electrodes, reflecting multisensory integration of near vs far stimuli.

Key findings

In healthy participants, the PPS index was present during wakefulness and localized to centroparietal regions.

During sleep, the PPS index distinguished conscious from unconscious states. Dream experiences were reported in 32% of deep sleep, 56% of intermediate sleep, and 88% of rapid eye movement sleep. The PPS index was higher during dreaming compared with no-experience sleep and was comparable to wakefulness, and was reduced during unconscious sleep.

In patients with disorders of consciousness, the PPS index correlated with Coma Recovery Scale–Revised scores (R = 0.35) and with clinical outcome at discharge (R = 0.43). Higher PPS index values were associated with better recovery.

In classification analyses, the PPS index showed a positive predictive value of 86% and specificity of 98%, compared with 67% and 89%, respectively, for behavioral assessment alone. However, sensitivity was lower, and combining both measures improved predictive performance.

In a subset of 19 patients, the PPS index correlated with forebrain mesocircuit integrity (R = 0.71) and inversely with default mode network–dorsal attention network coupling (R = −0.59).

Limitations

Clinical outcomes were assessed at discharge without long-term follow-up, limiting evaluation of longer-term recovery. The authors noted that the optimal frequency range and thresholds for the PPS index may require further refinement.

Conclusion

“These findings highlight a bedside-compatible electrophysiological marker with potential clinical utility for detecting covert consciousness and predicting outcomes in non-responsive patients,” wrote lead study author Tommaso Bertoni, of Lausanne University Hospital and University of Lausanne, and colleagues.

Disclosures: The authors reported no competing interests.

Source: Cell Reports Medicine