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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.

Brief targeted mindfulness interventions can help to reduce symptoms and buffer maladaptive responses to negative mood in acutely depressed patients with chronic or recurrent lifetime history.

Converging evidence suggests that a single sub-anesthetic dose of ketamine can produce strong and rapid antidepressant effects in patients that do not respond to standard treatment. Despite a considerable amount of research investigating ketamine's mechanisms of action, the exact neuronal targets conveying the antidepressant effects have not been identified yet. Preclinical studies suggest that molecular changes induced by ketamine bring forward large-scale network reconfigurations that might relate to ketamine's antidepressant properties. In this prospective two-site study we measured resting state fMRI in 24 depressed patients prior to, and 24 hours after a single sub-anesthetic dose of ketamine. We analyzed functional connectivity (FC) at baseline and after ketamine and focused our analysis on baseline FC and FC changes directly linked to symptom reduction in order to identify neuronal targets that predict individual clinical responses to ketamine. Our results show that FC increases after ketamine between right lateral prefrontal cortex (PFC) and subgenual anterior cingulate cortex (sgACC) are positively linked to treatment response. Furthermore, low baseline FC between these regions predicts treatment outcome. We conclude that PFC-sgACC connectivity may represent a promising biomarker with both predictive and explanatory power.

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