Cortical Correlates of Increased Postural Task Difficulty in Young Adults: A Combined Pupillometry and EEG Study

Abstract Objective Pupillary response reflects mental effort (or cognitive workload) during challenging cognitive and postural control conditions. EEG is more established as a non-invasive measure to assess cortical involvement of postural control. The purpose of this study was to understand the pupillary response under increasing postural task difficulty and its relationship between EEG outcomes in young adults. Methods Fifteen adults [age: 25.6 ± 2.9; sex: 10 males] completed multiple trials of standing: eyes-open, eyes-open and performing a dual-task (auditory 2-back), eyes-occluded, and eyes-occluded with a dual task. Participants stood on a force plate and wore an eye tracker and 256-channel EEG cap during the conditions. The power spectrum was analyzed for theta (4–7 Hz), alpha (8–13 Hz), and beta (13–30 Hz) frequency bands in pre-defined fronto-central of electrocortical sources. Results Increased postural task difficulty was associated with greater responses for pupillary response (p < 0.0001), fronto-central alpha power (p = 0.001), and theta/beta power ratio (p = 0.01). Greater pupillary response correlated with lower fronto-central EEG alpha power during standing eyes occluded (r=-.58, p = .04) and dual-task eyes occluded (r=-.56, p = .04). Lastly, a greater pupillary response was associated with lower CoP displacement in the anterior-posterior direction during dual-task eyes occluded (r = − .60, p = .04) Conclusion Pupillary response and fronto-central EEG outcomes appear to capture the same cortical processes that are increasingly utilized during increased postural task difficulty. In addition, these results validate pupillary response against EEG during increased postural task difficulty. In the future, pupillary response may be a potential tool to understand the underlying neurophysiological mechanisms of postural control in aging and disease populations.