  Background: Deep-sea manned submersible operation could induce mental
workload and influence neurophysiological measures. Psychophysiological
responses to submersible operation are not well known. The main aim of this
study was to investigate changes in EEG and ECG components and subjective
mental stress of pilots during submersible operation. Methods: There were 6
experienced submersible pilots who performed a 3 h submersible operation task
composed of 5 subtasks. Electroencephalogram (EEG) and electrocardiogram (ECG)
was recorded before the operation task, after 1.5 h and 2.5 h operation, and
after the task. Subjective ratings of mental stress were also conducted at
these time points. Results: HR and scores on subjective stressed scale
increased during the task compared to baseline (P<0.05). LF/HF ratio at 1.5 h
were higher than those at Baseline (P<0.05) and 2.5 h (P<0.05). Relative theta
power at the Cz site increased (P<0.01) and relative alpha power decreased
(P<0.01) at 2.5 h compared to values at Baseline. Alpha attenuation coefficient
(AAC, ratio of mean alpha power during eyes closed versus eyes open) at 2.5 h
and after the task were lower compared to baseline and 1.5 h (P<0.05 or less).
Conclusions: Submersible operation resulted in an increased HR in association
with mental stress, alterations in autonomic activity and EEG changes that
expressed variations in mental workload. Brain arousal level declined during
the later operation period.
