When neuroscience gets wet and hardcore: Neurocognitive markers obtained during whole-body water immersion

During the last years a growing body of literature has emerged trying to assess brain activity under extreme conditions and within extreme environments, such as human space flight research, long-term confinement as on the Concordia Station in the Antarctica or the MARS 500 project, as well as research in altered gravity conditions (e.g. parabolic flights and centrifuges). While it is of utmost importance to gain a basic understanding of neurophysiological processes during space flights and to translate these results into feasible preventive measures to preserve the astronauts´ physical and mental health, it is of further interest whether current training conditions for astronauts on earth provide realistic conditions to prepare for special tasks during actual space flight missions.

Astronauts undergo intensive training on earth to ensure a maximum of performance and safety during their missions in space. Some of the most challenging and dangerous tasks are the so called space-walks, or extra vehicular activities (EVAs), where astronauts work outside the space station. Every step during these EVAs is practiced in large swimming pools (so-called neutral buoyancy faculties, NBFs) with identical replicas of parts of the International Space Station (ISS) in order to simulate the microgravity environment. Since this is the most realistic approach to practice these EVAs on earth, it is important to investigate how water immersion affects human performance and to compare these findings with results obtained from results during microgravity. While recording EEG in microgravity has been proved to be successful using Brain Products soft- and hardware (Brümmer et al., 2011; Schneider et al., 2009; Schneider, Brümmer, Carnahan, et al., 2008a; Schneider, Brümmer, Mierau, et al., 2008b), recording EEG underwater was thought to be nearly impossible. This was until we came up with the idea to use “hardcore” equipment to obtain data under this extreme condition.

EVAs are one of the most physically and mentally challenging tasks in space (Katuntsev et al. 2004), which are practiced prior to the launch in NBFs to simulate microgravity-like conditions with identical replicas of parts of the ISS. According to professional divers and researchers at the European Space Agency (ESA), negative effects on cognitive performance and fine motor skills are already present at an immersion depth of 5 m (Dalecki et al. 2012), which results in an inverse relationship between task complexity and performance deficit. This phenomenon manifests in differences in reaction times during easy cognitive tasks, however not during more cognitive challenging tasks, which was shown in a study using a Stroop and a mental rotation task (Dalecki et al. 2013). As yet, unfortunately no study has recorded neurophysiological data in an underwater condition and identified the effects of water immersion on electrocortical activity. It is an important step to understand the effects of water immersion on cognitive processing in order to explain its relationship to the task complexity as described before. Therefore, this study aimed to determine whether electrophysiological activity of the brain can be obtained during whole-body water immersion and to investigate whether differences in cognitive processing using event related potential (ERPs) explain the inverse relationship of task complexity and decision-making.

10 male divers were recruited to participate in this study. The experimental setup consisted of an aluminum cage construction, where subjects were secured with a commercial diving jacket inside a diving pool (20m x 20m x 5m). Air supply was provided by standard scuba equipment with a prolonged hose between the regulator and the tank. A 15” LCD screen was fixed in front of the subjects’ eye level and a waterproof choice-reaction box was fixed in order to perform the experimental task underwater (WET).

A trained security diver was permanently present in order to ensure the participants´ safety and to provide task relevant instructions via waterproof sheets. As control, subjects performed the same task on land (DRY) in an identical setup in a randomized order.

The experimental task consisted of a mental arithmetic task with two different numbers or mathematical equations being presented on the left and the right side of the screen. The whole task consisted of five levels of increasing complexity, i.e. comparing two simple numbers during level one (e.g. 8 vs. 17) up until complex mathematical equations during level five (e.g. 8 x (12-4) vs. 18 – 2 x 5). The whole procedure consisted of three iterations of levels 1 – 5, where subjects were asked to decide which side shows the larger number value or result via their left and right index finger using the waterproof box.

Neurocognitive data (N200 latency and amplitude) was recorded using a modified Brain Products actiCAP with 5m shielded electrode cables. Six active electrodes were located according to the international 10/20 system over prefrontal, parietal and occipital areas (Fp1, Fp2, P1, P2, O1, O2). To prevent electrodes from incoming water and therefore from any crosstalk, a tight full-face leather mask was placed carefully over the subjects’ head with an additional bathing cap on top.

Results show a clear and reliable EEG signal (see Figure below), as can be seen from the processed raw data and the EEG frequency spectrum.

Although a slight reduction in activity during cognitive processing was seen during water immersion, neither N200 amplitude (left Figure below) nor latency (right Figure below) showed any statistical difference between the WET and DRY condition.

Therefore, this study could not show that water immersion has an impact on the N200-latency and amplitude, which might explain previously reported results. Also, unlike reported by Dalecki et al. (2013), subjects did not show a delay in their reaction times. Further studies are therefore needed in order to examine the effect of water immersion on cognitive processing and the underlying processes for the inverse relationship of task complexity and reaction times.

However, it was successfully shown that it is possible to record EEG data even under the extreme condition of whole-body water immersion following a relatively easy and feasible approach. This notion will be helpful for further investigations on human performance under extreme conditions, ranging from technical and occupational diving to the training of humans for the space flight program.

More detailed information can be obtained from the published manuscript.