Complex cognitive tasks such as mental arithmetic heavily rely on intact,
well-coordinated prefrontal cortex (PFC) function. Converging evidence
suggests that frontal midline theta (FMT) oscillations play an important role
during the execution of such PFC-dependent tasks. Additionally, it is well-
established that acute stress impairs PFC function, and recent evidence
suggests that FMT is decreased under stress. In this EEG study, we
investigated FMT oscillations during a mental arithmetic task that was carried
out in a stressful and a neutral control condition. Our results show late-
onset, sustained FMT increases during mental arithmetic. In the neutral
condition FMT started to increase earlier than in the stress condition. Direct
comparison of the conditions quantified this difference by showing stronger
FMT increases in the neutral condition in an early time window. Between-
subject correlation analysis showed that attenuated FMT under stress was
related to slowed reaction times. Our results suggest that FMT is associated
with stimulus independent mental processes during the natural and complex PFC-
dependent task of mental arithmetic, and is a possible marker for intact PFC
function that is disrupted under stress