Coherence between Brain Cortical Function and Neurocognitive Performance during Changed Gravity Conditions

1. Experimental Procedure

1. On ground pre-flight preparation – The subject preparation is done in a separate room at the airport. (1-2 hours before the flight)
   1. Mounting the EEG/NIRS cap
      1. Electrodes and NIR sensors are attached to the scalp using an EEG cap. This method ensures the correct position of the sensors.
      2. The size of the cap is determined by the size of the subject’s head
      3. The operator makes sure of the correct position of the cap. The Cz electrode is on the vertex (the point midway between the nasion and onion), the PO9-PO10 and the Fp1-Fp2 electrodes are horizontal, the cap is symmetric.
      4. The heart rate electrode is placed on the chest
   2. Minimization of Impedance
      1. The Brain Products actiCAP electrodes are connected to the control box.
      2. Every electrode contains LEDs, which turn red, when the impedance measurement is started.
      3. The hair is moved away from the tip of the electrode with a blunt-tipped needle.
      4. Gel is injected between the tip of the electrode and the surface of the skin.
      5. The color of the LEDs change, as the impedance decreases. The initial red color becomes yellow, the yellow becomes green, if the target impedance value is achieved.
      6. The target impedance is 25 kOhm, since the active electrodes provide good signal-to-noise ration below this value. Therefore the cap preparation is quick and convenient.
      7. The operator starts to work on the reference and ground electrodes, and repeats for all other electrodes.
2. On board pre-flight preparation
   1. Pre-measurements
      1. Subjects are placed into the experimental setup, the seat belts are fastened loosely
      2. Cables are connected, the batteries are loaded.
      3. The operator starts the EEG and NIRS module, controls the connectivity and the quality of the EEG/NIRS signal.
      4. Recording resting state EEG/NIRS. The subjects do not have any task.
      5. The recording is stopped.
      6. The subjects perform the cognitive task on the ground. The cognitive task is an attention/calculation task (http://itunes.apple.com/us/app/chalkboard-challenge/id317961833?mt=8), where subjects have to identify that side of an equation which is larger than the other in relation to speed and accuracy.
   2. Storing the equipment
      1. The operator stores the camera and the IPhones for take off.
3. In flight measurement
   1. Preparation
      1. Operator mounts the video-camera to handrail and starts recording.
      2. The iPhones are placed on the upper leg of the subjects.
      3. The operator starts the EEG and NIRS module, controls the quality of the EEG/NIRS signal, and starts the recording.
   2. Measurement
      1. The subjects perform the cognitive task during two blocks of five parabolas between parabola 11-15 and 16-20. Task will be performed in a random order in weightlessness or normal gravity. Only resting state EEG/NIRS is recorded during the first 10 parabolas. The last parabolas will be used in case of missing previous measurements (see Figure 1).
      2. The operator controls the recording, and instructs the subjects. The operator will write down all results of the cognitive tests and times.
4. On ground post-flight measurement
   1. 1. Resting state EEG/NIRS measurement is carried out.

We expect to find increased cerebral activation during weightlessness as shown before (Schneider et. al 2008+ 2009). We further expect so see increased oxygenated tissue in the frontal brain in weightlessness and lower oxygenated tissue in hypergravity. The attention task is supposed to be impaired during the whole flight compared to pre and post flight and maybe even more in weightlessness due to higher central activation and arousal in weightlessness.

2. Representative Results

Mapping the transition from the hypergravity phase to weightlessness we were able to observe increased brain cortical activity in the frontal cortex and decreased activity in the temporal and occipital cortex 2000 – 2350 ms after the onset of weightlessness (Figure 2a,b). sLORETA allowed localizing this increased frontal activation in Brodmann area 9 of the dorsolateral prefrontal cortex, which is known to be involved in executive functions with the integration of sensory and mnemonic information in the course of motor planning, organization and regulation, (Figure 3a, b). In addition, subject 2 showed an increase in Brodmann area 6, the premotor cortex, which plays a role in sensory guidance in the course of body stabilization (see Figure 3b).

Averaged over the first 10 parabolas, NIRS analysis revealed decreased oxygenated hemoglobin (HHb) concentration of both subjects in hypergravity as well as increased oxygenated hemoglobin (O2Hb) in weightlessness. For HHb hemoglobin in subject 1 we found a trend of an increase in the hypergravity phase prior to weightlessness as well as a decrease during weightlessness and the hypergravity phase after weightlessness. In this subject O2Hb was back to baseline 10 to 15 sec following the parabola. In contrast subject 2 showed a slight increase along with the decrease of O2Hb in the hypergravity phase prior to weightlessness, an increase during weightlessness and a decrease during hypergravity after weightlessness. For this subject O2Hb remained to be decreased for about 30 sec following parabola (Figure 4a,b)

The cognitive task resulted in decreased performance scores for both participants in normal gravity during the flight compared to a preflight session. Only subject 2 showed a decreased score in weightlessnes (Figure 5).

Figure 1. Parabolic flight sequence. Order of tasks and measurements during the flight; number of parabolas are indicated in grey, numbers with apostrophe indicate the length of longer breaks between parabolas.

Figure 2 Mapping view of two subjects over the timeframe of 500 ms before weightlessness (in hypergravity) until 2500 ms in weightlessness. View is from above the head; little circles indicate electrode positions, blue color decreases and yellow to red color increases of electrocortical activity in micro Volt.

Figure 3. Three LORETA views (top: from above, bottom left: from the left side, bottom right: from the back) of two subjects over the timeframe of 2000 ms until 2350 ms after onset of weightlessness. Red color indicates increased brain activity.

Figure 4. NIRS traces (red: oxygenated hemoglobin, blue: deoxygenated hemoglobin, black: gravity level) over the period of one parabola from 40 sec before the parabola in normal gravity (1G: yellow area), over the first hypergravity phase (1.8G: blue area), weightlessness (0G: red area) and the second hypergravity phase (1.8G: blue area) until 40 sec after the parabola. Gravity level is displayed inverse (decrease of trace means increase of gravity starting from 0 equal to normal gravity (1G). Data shown is an average over 10 parabolas.

Figure 5. Performance score of cognitive task of participant 1 (blue trace) and 2 (red trace) for the measurements training before flight and inflight in weightlessness (0G) and normal gravity (1G).