Institutional Review Board Approval
All methods, including the procedures described below, received appropriate institutional review board approvals from the Committee for the Protection of Human Subjects at Sam Houston State University and the Chesapeake Institutional Review Board, Inc., for the Brain Wellness and Biofeedback Center of Washington. Signed informed consent was obtained from all participants.
Participants included 9 (8 male, 1 female) US veterans who had experienced wartime deployments in Afghanistan and/or Iraq. All had experienced service-connected TBI with the majority also having experienced some loss of consciousness (range: a few seconds to a number of minutes). While one participant reported having experienced only one concussion, the others reported having experienced multiple (typically “many” or “too many to count”) traumatic head injuries, including exposures to explosive blasts. Age (in years) ranged from 25 to 64 (M = 37.33, SD = 12.63). The duration since end of their most recent deployment to first treatment in this study ranged from 6 to 103 months, with a median of 46 months. Accordingly, many months following their return from deployment, all were experiencing persistent moderate to severe daily headaches. The majority (8) had been diagnosed to have co-morbid PTSD. Three had been diagnosed with depressive disorders. Two were not taking any prescribed medications at the time of study entry, while the remainder were taking at least one medication (range: 1–7, median 2), including acetaminophen (2 participants), antidepressants (4 participants), anti-anxiety drugs and hypnotics (3 participants), anticonvulsants (2 participants), antihistamines (2 participants), as well as statin (1 participant), alpha-blocker (1 participant), beta-blocker (1 participant), and stimulant (1 participant) drugs; one participant was using a triptan on an as needed basis, and another was taking over-the-counter supplements (e.g., biotin, melatonin, Vitamin D). They had all long stalled in terms of any improvements from pharmacologic or non-pharmacologic/psychotherapy interventions. All were treated at the Brain Wellness and Biofeedback Center of Washington (in Bethesda, Maryland, USA) in 20 individual FNS treatment sessions (except for one who moved after 17 sessions and who was doing well at the time of termination).
FNS equipment and procedures
FNS consists of a laptop computer and J&J Enterprises (Poulsbo, WA) I-300 Compact 2 (C-2) Channel EEG module with on-board feedback generating power. It uses proprietary software to link the digital brainwave recording device (C-2 module) through the computer, which then sets the parameters for the C-2 module to emit pulsed EM stimulation . The system returns a signal to the participant via conduction from the C-2 module, varying as a function of the detectable peak EEG frequency (but offset from it), thereby permitting strategic distortion of the EEG. The amount of EM stimulation was standardized with the feedback frequency being offset from the dominant EEG frequency at +20 Hertz (Hz). Pulses of EM energy operated at a duty cycle of 1 %, that is, of the maximum permissible on-time for each pulse, they were powered no more than 1 % of the time (e.g., the maximum on-time at 1 % for 1 Hz pulse was 0.01 s). Testing revealed a power level of 100 pico watts through the sensor cable (Weber Innovations, Ann Arbor, Michigan, USA).
Participants attended approximately 2–3 sessions per week. They sat comfortably with eyes closed and engaged in no specific activity. Electrodes were placed in a predetermined order over all areas of the cortex over the course of 20 sessions. Each session included a total of 4 s of EM stimulation spaced over 4 minutes. The stimulation was not immediately discernible and adverse reactions (e.g., transient increases in typical symptoms following the first few sessions) were minimal. Participants were not asked to discuss past traumas as part of the process.
Brief Pain Inventory-Headache (BPI-HA) 
The Brief Pain Inventory was modified to indicate 0–10 numerical ratings specifically for pain intensity of headaches experienced in the past week (0 = no pain, 10 = pain as bad as you can imagine), including the worst headache pain and average headache pain during that period. This was completed at the outset before any receipt of the experimental intervention (i.e., beginning of treatment with session 1) and periodically thereafter including at sessions 5, 10, 15, and 20 (end of treatment).
Posttraumatic Stress Disorder Checklist-Military version (PCL-M) [21, 22]
The PCL-M is a widely used, highly reliable, and valid measure of the 17 symptoms (each rated on a 1 = not at all bothered to 5 = extremely bothered scale) comprising the typical diagnostic criteria for PTSD. It is specifically worded to reflect trauma experienced during military service. It was administered to derive a total score of PTSD severity (which can range from 17 to 85) at the beginning of treatment, session 1, and again at sessions 5, 10, 15, and 20 (end of treatment).
A 0−10 numerical rating scale to assess extent of perceived cognitive dysfunction was completed by participants at the beginning of each of the 20 treatment sessions. “Cognitive clouding” was defined as problems with clearness of thinking, attention/concentration or memory problems; feeling “foggy,” “hazy,” or “clouded”; with 0 = no cognitive clouding and 10 = worst cognitive clouding possible.
Data analyses included beginning (session 1) to end of treatment (session 20) t-test comparisons for BPI-HA worst and average headache pain ratings, beginning to end of treatment PCL-M total scores, and first treatment session to last treatment session 0–10 numerical ratings for subjective cognitive dysfunction.