Effect of artificial gravity on neurocognitive performance during head-down tilt bedrest.

This study evaluated the acute and chronic effects of intermittent and continuous Artificial Gravity (AG) on cognitive performance during 60 days of Head-down tilt bedrest (HDTBR), a well-established ground-based spaceflight analogue method. Participants were randomly assigned to three groups: intermittent AG, continuous AG, and HDTBR control group without AG exposure. Task performance and electrophysiological measures of attention and working memory were investigated during Simple and Complex tasks in the Visual and the Auditory modality. Compared to baseline, faster reaction time and better accuracy was present during HDTBR regarding the Complex tasks, however, the practice effect was diminished in the three HDTBR groups compared to an ambulatory control group. Brain potentials showed a modality-specific decrease, as P3a was decreased only in the Auditory, while P3b decreased in the Visual modality. No evidence for acute or chronic AG-related cognitive impairments during HDTBR was found.

Are head-down tilt bedrest studies capturing the true nature of spaceflight-induced cognitive changes? A review.

Although a number of studies have examined cognitive functions in space, the reasons behind the observed changes described by space research and anecdotal reports have not yet been elucidated. A potential source of cognitive changes is the cephalad fluid shift in the body caused by the lack of hydrostatic pressure under microgravity. These alterations can be modeled under terrestrial conditions using ground-based studies, such as head-down tilt bedrest (HDBR). In this review, we compare the results of the space and HDBR cognitive research. Results for baseline and in-flight/in-HDBR comparisons, and for baseline and post-flight/post-HDBR comparisons are detailed regarding sensorimotor skills, time estimation, attention, psychomotor speed, memory, executive functions, reasoning, mathematical processing, and cognitive processing of emotional stimuli. Beyond behavioral performance, results regarding brain electrical activity during simulated and real microgravity environments are also discussed. Finally, we highlight the research gaps and suggest future directions.

Persistent deterioration of visuospatial performance in spaceflight.

Although human adaptation to spaceflight has been studied for decades, little is known about its long-term effects on brain and behavior. The present study investigated visuospatial performance and associated electrophysiological responses in astronauts before, during, and after an approximately half-year long mission to the International Space Station. Here we report findings demonstrating that cognitive performance can suffer marked decrements during spaceflight. Astronauts were slower and more error-prone on orbit than on Earth, while event-related brain potentials reflected diminished attentional resources. Our study is the first to provide evidence for impaired performance during both the initial (~ 8 days) and later (~ 50 days) stages of spaceflight, without any signs of adaptation. Results indicate restricted adaptability to spaceflight conditions and calls for new research prior to deep space explorations.

Differential impact of acute hypoxia on event related potentials: impaired task-irrelevant, but preserved task-relevant processing and response inhibition.

The current study investigated how experimentally induced acute normobaric hypoxia affects attentional control functions during easy, monotonous visual sustained attention and response inhibition (modified Continuous Performance Task) and executive control tasks (number-size Stroop task). Along with behavioral efficiency, task-relevant and task-irrelevant information processing were investigated by measuring event related brain potentials (ERP) evoked by target stimuli (Target P3), task-relevant stimuli with no response needed (NoGo P3), and task-irrelevant novel stimuli (Novelty P3) during acute hypoxia exposure. Normobaric hypoxia was induced by adjusting the O2 content of the breathing mixture to obtain 80% peripheral oxygen saturation, equivalent of 5500 m above sea level. Here we report decreased Novelty P3 during acute normobaric hypoxia exposure, while Target P3 and NoGo P3, as well as behavioral efficiency remained intact. Our paper is the first to provide evidence for impaired novelty processing along with intact task-relevant information processing and response inhibition during normobaric hypoxic exposure.

Cognitive resilience after prolonged task performance: an ERP investigation.

Deleterious consequences of cognitive fatigue might be avoided if people respond with increased effort to increased demands. In this study, we hypothesized that the effects of fatigue would be more pronounced in cognitive functions reflecting compensatory effort. Given that the P3a event-related potential is sensitive to the direction and amount of attention allocated to a stimulus array, we reasoned that compensatory effort would manifest in increased P3a amplitudes. Therefore, we compared P3a before (pre-test) and after (post-test) a 2 h long cognitively demanding (fatigue group, n = 18) or undemanding task (control group, n = 18). Two auditory tasks, a three-stimulus novelty oddball and a duration discrimination two-choice response task were presented to elicit P3a. In the fatigue group, we used the multi-attribute task battery as a fatigue-inducing task. This task draws on a broad array of attentional functions and imposed considerable workload. The control group watched mood-neutral documentary films. The fatigue manipulation was effective as subjective fatigue increased significantly in the fatigue group compared to controls. Contrary to expectations, however, fatigue failed to affect P3a in the post-test phase. Similar null effects were obtained for other neurobehavioral measures (P3b and behavioral performance). Results indicate that a moderate increase in subjective fatigue does not hinder cognitive functions profoundly. The lack of objective performance loss in the present study suggests that the cognitive system can be resilient against challenges instigated by demanding task performance.

Extreme Environment Effects on Cognitive Functions: A Longitudinal Study in High Altitude in Antarctica.

This paper focuses on the impact of long-term Antarctic conditions on cognitive processes. Behavioral responses and event-related potentials were recorded during an auditory distraction task and an attention network paradigm. Participants were members of the over-wintering crew at Concordia Antarctic Research Station. Due to the reduced partial pressure of oxygen this environment caused moderate hypoxia. Beyond the hypoxia, the fluctuation of sunshine duration, isolation and confinement were the main stress factors of this environment. We compared 6 measurement periods completed during the campaign. Behavioral responses and N1/MMN (mismatch negativity), N1, N2, P3, RON (reorientation negativity) event-related potential components have been analyzed. Reaction time decreased in both tasks in response to repeated testing during the course of mission. The alerting effect increased, the inhibition effect decreased and the orienting effect did not change in the ANT task. Contrary to our expectations the N2, P3, RON components related to the attentional functions did not show any significant changes. Changes attributable to early stages of information processing were observed in the ANT task (N1 component) but not in the distraction task (N1/MMN). The reaction time decrements and the N1 amplitude reduction in ANT task could be attributed to sustained effect of practice. We conclude that the Antarctic conditions had no negative impacts on cognitive activity despite the presence of numerous stressors.

Oblique effect in visual mismatch negativity.

We investigated whether visual orientation anisotropies (known as oblique effect) exist in non-attended visual changes using event-related potentials (ERP). We recorded visual mismatch negativity (vMMN) which signals violation of sequential regularities. In the visual periphery unattended, task-irrelevant Gábor patches were displayed in an oddball sequence while subjects performed a tracking task in the central field. A moderate change (50°) in the orientation of stimuli revealed no consistent change-related components. However, we found orientation-related differences around 170 ms in occipito-temporal areas in the amplitude of the ERPs evoked by standard stimuli. In a supplementary experiment we determined the amount of orientation difference that is needed for change detection in an active, attended paradigm. Results exhibited the classical oblique effect; subjects detected 10° deviations from cardinal directions, while threshold from oblique directions was 17°. These results provide evidence that perception of change could be accomplished at significantly smaller thresholds, than what elicits vMMN. In Experiment 2 we increased the orientation change to 90°. Deviant-minus-standard difference was negative in occipito-parietal areas, between 120 and 200 ms after stimulus onset. VMMNs to changes from cardinal angles were larger and more sustained than vMMNs evoked by changes from oblique angles. Changes from cardinal orientations represent a more detectable signal for the automatic change detection system than changes from oblique angles, thus increased vMMN to these "larger" deviances might be considered a variant of the magnitude of deviance effect rarely observed in vMMN studies.

Stimulus complexity effects on the event-related potentials to task-irrelevant stimuli.

The effects of irrelevant stimuli complexity on event-related potentials were investigated in 3 conditions using both auditory and visual oddball tasks. In Conditions 1 and 2, simple standard and target stimuli were presented in series with complex, identical (Condition 1) or variable (Condition 2), task-irrelevant stimuli. In Condition 3, complex standards and targets were presented with simple, identical, task-irrelevant stimuli. In Conditions 1 and 2, but not Condition 3, the irrelevant stimuli elicited the P3a component in both auditory and visual modalities and the N2b component in the visual modality. While we found that variable, irrelevant stimuli evoked larger P3a in the auditory modality compared with identical irrelevant stimuli, we observed the opposite effect in the visual modality. These results suggest that stimuli rareness and irrelevance are not sufficient for eliciting P3a. This component is only elicited by irrelevant stimuli that are at least as complex as the task-related stimuli.