Sustaining Aviator Performance During Extended Operational Flight
Condition: Transcranial Direct Current Stimulation
Study type: Interventional

Summary: 
      Future aviation operations are anticipated to change as advances in technology enable
      automation of more tasks. Development of new platforms under the Future Vertical Lift program
      are also anticipated to change the nature of missions as they are being designed to cover
      further distances. Longer duration flights coupled with greater automated features are
      expected to shift the role of the aviator, resulting in an increased need for attention
      maintenance, which creates potential problems related to performance. To offset the
      likelihood of performance decrements related to the need to sustain attention, we propose
      examining the use of transcranial electrical current stimulation. In the present study, we
      will evaluate whether delivery of stimulation prior to or during the task enables sustainment
      of attention and thereby reduces performance decrements as measured through primary flight
      tasks and a secondary attentional task. Further, we will evaluate whether stimulation
      enhances the ability to respond to an unexpected emergency toward the end of the flight.
    

Detailed description: 
      Volunteers will first schedule an appointment to complete informed consent, screening
      procedures and meet with study physician. After eligibility is verified, volunteers will
      complete baseline assessments. At the completion of baseline assessments volunteers will be
      scheduled for their return visits and will be given their actiwatch. Scheduling will occur
      such that there is at least 16 hours' time between baseline assessments and their first
      treatment visit, whereas treatment visits will be scheduled such that there is at least 48
      hours between visits. Stimulation will be counterbalanced with at least 48 hours between
      deliveries to allow for a washout period (Nitsche & Paulus, 2001). Scheduling will be done
      such that individual participants are always scheduled at the same time of day to control for
      any effects of circadian rhythm and individual differences.

      Visit 1: Test scheduling, informed consent, screening procedures and baseline assessments.

      During this visit, subjects will be informed that they should have 8 hours of sleep the night
      before each testing session, with a minimum of 6 accepted for participation (confirmed by an
      actiwatch and self-report). A minimum of 6 hours will be accepted to avoid potential loss of
      subjects who are not able to obtain 8 hours. However, 8 hours will be stressed to encourage
      subjects to be well rested prior to the testing days. They will also be instructed to refrain
      from taking over the counter medications which may induce drowsiness throughout the duration
      of the study, and refrain from the use of any stimulants including caffeine for a minimum of
      16 hours prior to study participation, avoid alcohol use for a minimum of 24 hours prior to
      participation, and avoid the use of nicotine for a minimum of 2 hours prior to the study.
      These are requested to obtain clean physiological recordings (e.g., Gilbert, Dibb, Plath, &
      Hiyane, 2000 [caffeine, nicotine]; Kähkӧnen, Wilenius, Nikulin, Ollikainen, & Ilmoniemi, 2003
      [alcohol]). If the participant reports use of a stimulant, medication inducing drowsiness,
      nicotine, alcohol, or the actiwatch indicates less than 6 hours of rest, the participant will
      be released from the study for that day and asked to reschedule. In the event that the
      actiwatch fails, confirmation will rely on self-report and be recorded within the study log.

      Following informed consent, subjects will complete a medical history questionnaire with a
      study physician that includes caffeine consumption habits to determine any possible side
      effects due to caffeine withdrawal. A member of the research team will measure and record the
      subject's vital signs (temperature, respiration rate, blood pressure, pulse, and oxygen
      saturation) on the medical history questionnaire. The study physician will review the medical
      history questionnaire and vital signs to make a final determination regarding eligibility. In
      addition to determining eligibility, the study physician or medical practitioner will discuss
      with the subject regular caffeine consumption habit and whether the subject is likely to
      experience any negative side effects associated with caffeine withdrawal (e.g., headache). If
      determined to be eligible by the study physician, subjects will then be enrolled in the
      study, complete the volunteer registry database form, receive the actiwatch and be provided
      verbal instructions on its use and be given a handout of participation guidelines. After
      receiving the actiwatch and guidelines, the subject will be offered the opportunity for
      stimulation familiarization. This will entail applying the stimulation at the prescribed
      intensity (2 mA) for a duration of 5 minutes, with the anode at F3 and cathode on the
      contralateral bicep (right arm). The purpose of this will be to allow the subject to
      experience what the stimulation feels like so that they know what to expect for the
      stimulation days. After stimulation has been applied, the electrodes will be removed and the
      subjects will complete the following questionnaires: demographic questionnaire,
      Morningness-Eveningness Questionnaire (MEQ) , Adult ADHD Self Report Scale (ASRS), Sleep
      Timing Questionnaire (STQ), Beck Depression Inventory (BDI), Shipley's Institute of Living
      Scale (SILS), Convergence Insufficiency Symptom Survey (CISS), Samn-Perelli Fatigue Scale,
      Short Stress State Questionnaire (SSSQ), Behavioral Inhibition / Avoidance Scales (BIS/BAS),
      Karolinska Sleepiness Scale (KSS), and Profile of Mood States - Short Form (POMS-SF). The
      subject will next complete a baseline session of the Rapid Visual Information Processing Task
      (RVIP) and Conners' Continuous Performance Task (CPT). Following completion of
      questionnaires, the electroencephalogram will be placed on the subjects and baseline
      measurements will be taken, which is a series of three computerized tasks provided by
      Advanced Brain Monitoring (ABM Tasks) which will be used for baseline, and pre- /
      post-stimulation EEG measurements. Subjects will then meet with the research pilot who will
      go over the flight tasks required of this study and escort the subject into the simulator for
      familiarization and baseline flight performance data collection. During the familiarization
      flight, the research pilot will ensure the subject is able to meet prescribed flight
      standards such as maintain specified headings, airspeeds and altitudes with minimal
      input/prompts, which will be recorded on the flight standards sheet. The baseline flight will
      consist of a scenario similar to, but not exact, as the scenarios that will be performed on
      treatment days. Baseline performance and EEG will be recorded and archived for
      analyses/interpretation. Subjects will be released at this point for the day.

      Visits 2-3: tDCS stimulation test sessions.

      Subjects will return for visit two at minimum 16 hours following their first visit. Visits
      two and three will be scheduled such that there is at least 48 hours in-between visits to
      avoid carry-over effects from stimulation application. Procedures for both visits will be the
      same. When the subject arrives, compliance with study instructions will be verified and
      recorded on the subject compliance sheet. If the subject does not comply with
      medication/stimulant/alcohol consumption instructions or the actiwatch indicates less than 6
      hours of rest, the subject will be released from the study for that day and asked to
      reschedule. In the event that the actiwatch fails, confirmation will rely on self-report and
      be recorded in the study notebook.

      Subjects will then complete the side effect questionnaire, KSS, Samn-Perelli Fatigue Scale,
      SSSQ and POMS-SF to determine whether any physical symptoms are present prior to stimulation
      (e.g., headaches) and any mood disturbances. Once questionnaires are completed, the subject's
      vital signs will be measured and recorded on the side effect questionnaire.

      Next, the subject will be prepared for completing the flight scenarios and receiving
      stimulation. First, the subject will be fitted with the EEG and pre-stimulation baseline
      recordings will be obtained while the subject completes an additional iteration of the ABM
      tasks. Next, the scalp will be marked for tDCS electrode placement using a washable marker.
      This will be done as the EEG is removed so that the EEG electrode placements can be used to
      identify placement for tDCS electrodes. Scalp cleaning will occur as needed. Once removed,
      the subject will be escorted to the simulator where the tDCS electrodes will be put in place.
      The subject will be offered the opportunity to make adjustments as needed for comfort and to
      re-familiarize with the simulator. Once comfortable, a pre-flight mission brief will be given
      by the research pilot followed by the completion of a standard pre-flight checklist. These
      are estimated to last approximately 20 minutes total. Once the brief and checklist are
      completed, the flight scenario will begin. They have been designed to require minimal inputs
      by pilots and have been previously validated as low workload. Two flight scenarios were
      designed that include the same number of maneuvers, and require the same flight parameters
      (e.g., airspeed, altitude). One flight will involve a flight from Ft. Rucker to Montgomery
      and the other flight will be reversed (Montgomery to Ft. Rucker) so the subjects do not
      repeat the exact same flight twice. Thus, subjects will fly one scenario on visit two and a
      different one on visit three, which will be counterbalanced amongst subjects.

      Timing of stimulation will differ by randomly assigning subjects to one of two groups. Group
      A will receive the active stimulation during the pre-mission brief and pre-flight checklist
      completion, for a total of 20 minutes, to evaluate whether application of stimulation at the
      start of the flight prevents the onset of degraded performance. Group B will receive the
      active stimulation at two time points, each for a duration of 10 minutes, for a total of 20
      minutes. The first delivery of stimulation would occur at 30 minutes into the flight, while
      the second administration will occur at 60 minutes into the flight. This will be done to
      evaluate whether stimulation applied during the expected timeframe of loss of vigilance
      (approximately 30 minutes into the task) will offset this loss. To clarify, stimulus timing
      is a between-groups factor. A secondary task will also be implemented to measure whether
      performance changes occur on primary or secondary task performance. The secondary task will
      consist of periodic radio calls the pilot must respond to and physical responses to a visual
      targets presented on a tablet placed within the cockpit. Each group will also experience a
      sham-stimulation condition where at each of the intervals, stimulation will be applied for
      10% of the stimulation period corresponding with their group assignments (Group A: 30s ramp
      up time, 60s stimulation, 30s ramp down time, for 2 minutes total; Group B: 2 deliveries with
      30s ramp up time and 30s ramp down time, for 1 minute total).

      At the completion of the flight the subject will be escorted out of the simulator, tDCS
      electrodes will be removed. The subject will complete the NASA TLX, side effect
      questionnaire, KSS, Samn-Perelli Fatigue Scale, SSQ, POMS-SF, and the BDI to determine
      whether any physical symptoms or sleepiness/mood changes may have occurred due to the
      stimulation. The physical side effect questionnaire and BDI will be examined immediately
      following completion to evaluate the score. If a score greater than five is obtained on the
      side effects questionnaire, the study physician will be notified and will consult with the
      subject to evaluate whether the reported symptoms are due to the stimulation and if the
      subject is safe to continue, needs to be rescheduled for another day, or needs to be removed
      from the study. After questionnaires have been completed, the EEG will be reapplied to record
      data while the participant completes one iteration of each the RVIP and CPT. Once all tasks
      are completed, the subject will complete a post-stimulation questionnaire (Appendix U) to
      evaluate whether the subject could detect differences between active and sham stimulation,
      and whether the subject thought the stimulation altered performance. Next, the subject will
      be escorted to the subject lounge. The subject will remain in the subject lounge where he
      will have access to activities (reading, TV, ping pong, etc.) for the next 8 hours. Every two
      hours after the first RVIP and CPT administration, another RVIP and CPT administration will
      be given, along with the physical side effect questionnaire, KSS, Samn-Perelli Fatigue Scale,
      SSSQ and POMS-SF. This will allow us to track the time course of the tDCS effects. After the
      final tasks and questionnaire administration, the subject will be released for the day and
      reminded to keep the actiwatch on to record any changes to sleep. As the third visit will be
      the final treatment visit, the participant will be requested to return the actiwatch at a
      time that is convenient, but at least 48 hours following the stimulation application to
      ensure measurement of at least two nights' sleep. Compensation will be contingent upon the
      return of the actiwatch device, as subjects will need to complete their 1099 tax form when
      returning the watch.

      The total length of time for a test session is approximately twelve hours. Prior to release,
      a member of the research team will check vital signs, and then the subject will meet briefly
      with the study physician to determine whether the subject can safely be cleared and released
      for the day. Table 5 presents the time required for each activity. At the end of the third
      session the subject will be reminded to return the actiwatch in at least 48 hours and to
      continue wearing it until returning. Upon return of the actiwatch, the KSS will be
      administered once more. Finally, the post-study questionnaire will be administered to
      evaluate the usability/acceptance of tDCS.
    

Intervention name(s): Active Transcranial Direct Current Stimulation (tDCS); Sham Transcranial Direct Current Stimulation (tDCS)
Intervention type(s): Device; Device
Intervention description(s): Active simulation will be applied to the right PPC. To target this region for stimulation, the anode electrode will be placed on the subject using the 10-20 EEG system as reference location (Thair et al., 2017). Stimulation intensity for all conditions will be set to 2 mA, which was chosen based on previous studies that have compared 1 mA to 2 mA and found the higher intensity produced reliable changes to performance (e.g., Moos et al., 2012). Total time of active stimulation will be the same for each group (20 minutes). Delivery times of the stimulation will vary based on Group assignment:
Group A: During pre-flight brief/checklist, for 20 minutes. Group B: First delivered at 30 minutes into flight for 10 minutes, second delivered at 60 minutes into flight for 10 minutes.; Sham simulation will be applied to the right PPC. To target this region for stimulation, the anode electrode will be placed on the subject using the 10-20 EEG system as reference location (Thair et al., 2017). Stimulation intensity for all conditions will be set to 2 mA, which was chosen based on previous studies that have compared 1 mA to 2 mA and found the higher intensity produced reliable changes to performance (e.g., Moos et al., 2012). Total time of active stimulation will be the same for each group (20 minutes). Sham stimulation will consist of active stimulation for 120s, including the ramping up to 2 mA and down to no stimulation. Delivery times of the stimulation will vary based on Group assignment:
Group A: During pre-flight brief/checklist, for 20 minutes. Group B: First delivered at 30 minutes into flight for 10 minutes, second delivered at 60 minutes into flight for 10 minutes.
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Single (Participant)
Primary purpose: Basic Science