Eye movements as indicators of awareness in prolonged disorders of consciousness: a scoping review of behavioral and neural evidence.

BACKGROUND

In prolonged disorders of consciousness (DoC), visual fixation and smooth pursuit are among the earliest signs of re-emerging awareness. Yet, because their physiology relies heavily on brainstem–cerebellar circuitry, it remains debated whether these ocular behaviors invariably reflect consciousness or, after severe brain injury, also arise from reflexive/subcortical mechanisms.

METHODS

To address this question, we conducted a PRISMA-ScR scoping review of PubMed/MEDLINE and Scopus to verify the behavioral and neural correlates of fixation and pursuit. Ocular behavior evidence was classified as cognitively mediated, not cognitively mediated or indeterminate for each study.

RESULTS

We included 24 studies spanning clinical assessment, instrumented eye‑tracking, neurophysiology, neuroimaging and brain–computer interfaces. Clinically, fixation and pursuit were the most common signs accompanying transition from unresponsive wakefulness syndrome to the minimally conscious state; still, in isolation their specificity remained undetermined. Eye-tracking improved detection and, under explicit, goal‑directed tasks, demonstrated task‑contingent responses, occasionally prompting diagnostic reclassification. Neural measures showed that task‑locked ocular behaviors frequently co‑occurred with cortical responses, whereas some studies—especially for visual fixation—found no task‑linked neural correlates.

CONCLUSIONS

Overall, fixation and pursuit are sensitive, although context‑dependent, indicators of awareness. Isolated visual signs—especially simple fixation—warrant cautious interpretation: absent convergent neural signatures may reflect either limited sensitivity to minimal consciousness or genuinely reflexive/subcortical control. Further studies are needed to quantify cognitive involvement in cases of isolated fixation or pursuit.