The normal variability in alertness we experience in daily tasks is rarely taking into account in cognitive neuroscience. Here we studied neurobehavioral dynamics of cognitive control with decreasing alertness. We used the classic Simon Task where participants hear the word "left" or "right" in the right or left ear, eliciting slower responses when the word and the side are incongruent -the conflict effect. Participants performed the task both while fully awake and while getting drowsy, allowing for the characterisation of alertness modulating cognitive control. The changes in the neural signatures of conflict from local theta oscillations to a longdistance distributed theta network suggests a reconfiguration of the underlying neural processes subserving cognitive control when affected by alertness fluctuations.

A major problem in psychology and physiology experiments is drowsiness: around a third of participants show decreased wakefulness despite being instructed to stay alert. In some non-visual experiments participants keep their eyes closed throughout the task, thus promoting the occurrence of such periods of varying alertness. These wakefulness changes contribute to systematic noise in data and measures of interest. To account for this omnipresent problem in data acquisition we defined criteria and code to allow researchers to detect and control for varying alertness in electroencephalography (EEG) experiments under eyes-closed settings. We first revise a visual-scoring method developed for detection and characterization of the sleep-onset process, and adapt the same for detection of alertness levels. Furthermore, we show the major issues preventing the practical use of this method, and overcome these issues by developing an automated method (micro-measures algorithm) based on frequency and sleep graphoelements, which are capable of detecting micro variations in alertness. The validity of the micro-measures algorithm was verified by training and testing using a dataset where participants are known to fall asleep. In addition, we tested generalisability by independent validation on another dataset. The methods developed constitute a unique tool to assess micro variations in levels of alertness and control trial-by-trial retrospectively or prospectively in every experiment performed with EEG in cognitive neuroscience under eyes-closed settings.

Mental imagery is the process through which we retrieve and recombine information from our memory to elicit the subjective impression of “seeing with the mind’s eye”. In the social domain, we imagine other individuals while recalling our encounters with them or modelling alternative social interactions in future. Many studies using imaging and neurophysiological techniques have shown several similarities in brain activity between visual imagery and visual perception, and have identified frontoparietal, occipital and temporal neural components of visual imagery. However, the neural connectivity between these regions during visual imagery of socially relevant stimuli has not been studied. Here we used electroencephalography to investigate neural connectivity and its dynamics between frontal, parietal, occipital and temporal electrodes during visual imagery of faces. We found that voluntary visual imagery of faces is associated with long-range phase synchronisation in the gamma frequency range between frontoparietal electrode pairs and between occipitoparietal electrode pairs. In contrast, no effect of imagery was observed in the connectivity between occipitotemporal electrode pairs. Gamma range synchronisation between occipitoparietal electrode pairs predicted subjective ratings of the contour definition of imagined faces. Furthermore, we found that visual imagery of faces is associated with an increase of short-range frontal synchronisation in the theta frequency range, which temporally preceded the long-range increase in the gamma synchronisation. We speculate that the local frontal synchrony in the theta frequency range might be associated with an effortful top-down mnemonic reactivation of faces. In contrast, the long-range connectivity in the gamma frequency range along the fronto-parieto-occipital axis might be related to the endogenous binding and subjective clarity of facial visual features.

Mental imagery is the process through which we retrieve and recombine information from our memory to elicit the subjective impression of “seeing with the mind’s eye”. Many studies using imaging and neurophysiological techniques have shown several similarities in brain activity between visual imagery and visual perception. However, currently the dynamics of the brain in response to socially relevant stimuli, like faces, have not been studied. Elucidating brain dynamics during visual imagery of faces may help to understand the role of internal representation of socially relevant stimuli in the brain. Here we used electroencephalography to investigate brain dynamics during visual imagery of faces. We found that internal generation of visually imagined experiences is associated with long-range phase synchronization in gamma frequency band between frontal and parietal electrodes and theta frequency band between frontal electrodes. These results suggest that fronto-parietal gamma phase synchronization may be related to the endogenous binding of facial visual features transiently sustained in memory, whereas the interhemispheric frontal-theta synchrony might be encoding the memory reactivation of face stimuli.

18Humans are remarkably capable of adapting their behaviour flexibly based on rapid situational 19 changes: a capacity termed cognitive control. Intuitively, cognitive control is thought to be affected by 20 the state of alertness, for example, when sleepy or drowsy, we feel less capable of adequately 21implementing effortful cognitive tasks. Although scientific investigations have focused on the effects 22 of sleep deprivation and circadian time, little is known about how natural fluctuations in alertness in 23 the regular awake state affect cognitive control. Here we combined a conflict task in the auditory 24 domain with neurodynamics -EEG recordings-to test how neural and behavioural markers of conflict 25processing are affected by fluctuations in arousal. Using a novel computational method, we 26 segregated alert and drowsy trials from a three hour testing session and observed that, although 27 participants were generally slower, the typical slower responses to conflicting information, compared 28to non-conflicting information, was still intact, as well as the effect of previous trials (i.e. conflict 29 adaptation). However, the behaviour was not matched by the typical neural markers of cognitive 30control -local medio-frontal theta-band power changes-, that participants showed during full alertness. 31Instead, a decrease in power of medio-frontal theta was accompanied by an increase in long-range 32 information sharing (connectivity) between brain regions in the same frequency band. The results 33show the resilience of the human cognitive control system when affected by internal fluctuations of 34 our arousal state and suggests a neural compensatory mechanism when the system is under 35physiological pressure due to diminished alertness. 36