Treating Persistent Post-Concussive Symptoms with Photobiomodulation Therapy: Improvement in Cognition and Other Symptoms Both Subjectively and Objectively by ImPACT® Test.

Objective: This research evaluates the use of Photobiomodulation Therapy (PBMT) as a viable treatment modality for post-concussion symptoms secondary to a traumatic brain injury and the use of the ImPACT® test to assess improvement in cognition and symptomatology in patients treated with PBMT. Background: Several studies have detailed the ecacy of PBMT as a treatment for concussions. As there are no widely accepted imaging or laboratory modalities that document concussive injuries, monitoring improvement objectively proves dicult. ImPACT® is a computer based neurocognitive assessment meant to measure cognitive performance for concussion injuries. This study uses ImPACT® as a means to document an improvement in symptomatology for patients with post-concussion symptoms. Methods: This retrospective study reviews patient performance in the ImPACT® test in a cohort of 35 patients who are diagnosed with mild Traumatic Brain Injuries (mTBI) and experiencing post-concussive symptoms. Patient initially took the Post Injury 1 test then underwent PBMT therapy using the BIOFLEX DUO+ system three times a week for 4 weeks using approved parameters for treatment of the cervical spine soft tissue injuries. After the 4 week treatment, patients took the Post Injury 2 test and the results were compared. Results: By using PBM all the patients were improved clinically and their Post injury 2 ImPACT® test results were signicantly better compared to their Post injury 1 ImPACT® test results. Conclusion: PBMT is an effective for neurological patients with Post-Concussion symptoms and ImPACT® appropriate monitor and assess


Introduction
Brain photobiomodulation therapy (PBMT) therapy is a well-established modality for treating many medical conditions. It is currently under investigation as a treatment for several different neurological disorders. 1 This study reviews the use of PBMT in the treatment of post-concussive symptoms. We used the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT®) tool to objectively assess patients' improvement in cognition and symptoms. Traumatic brain injuries (TBI) have been labelled "a silent epidemic" by the Centers for Disease Control and Prevention (CDC). 2 This is a devastating condition, which has and continues to affect young, previously healthy people. Even worse, concussion, considered a minor TBI, can often go undiagnosed and thus untreated. An ever-growing number of professionals across Canada are working on preventing, diagnosing (the earlier the better) and treating concussion and their sequelae. Concussion, also called mild traumatic brain injury (mTBI), is an acute neurophysiological event related to traumatically induced blunt impact applied to the head and/or neck due to sudden acceleration, deceleration or rotational forces with a transient disturbance of brain function. 3,4 mTBI has often caused neurological, psychiatric and cognitive problems. Typically, patients with mTBI have suffered from headache, fatigue, dizziness, cognitive and memory impairment, depression, emotional outbursts/mood lability, impaired judgment, impulsivity, loss of executive skills, neck pain and sensitivity to environmental stimuli (light, sound, computer screens). [5][6][7][8] Although most symptoms resolve in 1 to 3 weeks, approximately 5-43% of concussed individuals have experienced persistent symptoms lasting weeks or months. 9,10 Post-concussion syndrome was a catchall term for the various persistent post-concussive symptoms and was previously accepted as a valid diagnosis. It was de ned as the persistence of physical, cognitive, emotional, and sleep symptoms beyond the usual recovery period of 7 to 21 days after a concussion. 11 Both the World Health Organization (WHO), and the Diagnostic and Statistical Manual of Mental Disorders (DSM) no longer contains a speci c entry for post-concussion syndrome. Instead, the 11 TH revision of the International Classi cation of Diseases (ICD-11) of the WHO captures persistent post-concussive symptoms under mild neurocognitive disorder, de ned as a "subjective experience of a decline from a previous level of cognitive functioning, accompanied by objective evidence of impairment in performance on one or more cognitive domains" 12 that may be attributable to several conditions, including trauma. The fth edition of the DSM likewise reclassi ed post-concussion syndrome as major or mild neurocognitive disorder due to traumatic brain injury. The diagnostic criteria has speci ed that the neurocognitive disorder must persist beyond the "acute post-injury period". 13 Background And Rationale There has been no de nitive treatment for persistent post-concussive symptoms. Previous suggested treatments focused primarily on alleviating individual symptoms and included antidepressants, antihypertensive and/or anti-epileptic agents, focused (including vestibular) rehabilitation, occupational therapy, psychotherapy and sleep therapy. 14 This has led to interest in other healing alternatives such as PBMT.

Photobiomodulation Therapy
The concept of PBMT, also called Low Level Laser Therapy, in its present form as a treatment for various disorders has been around since the 1960s. Cytochrome c oxidase (CCO) is a terminal enzyme of the electron transport chain that mediates the electron transfer from cytochrome c to molecular oxygen and therefore in uences the mitochondrial membrane potential and the consequent processes that follow such as Adenosine Triphosphate (ATP) production and the release of Nitric Oxide (NO). [15][16][17][18] Various studies has shown that pigments associated with CCO act as photoreceptors and responsive to a speci c wavelength window in the electromagnetic spectrum, concentrated speci cally within the visible red light ( 660 nm) and invisible near infrared light (NIR) wavelengths ( 810 nm). Within these wavelengths, light stimulation leads to increased production of ATP and the cascade of processes that accompanies this, from tissue repair, decreased in ammation and vasodilation. The effect of light, and PBMT speci cally, on the mitochondria and at the cellular level is the basis for the wide application of PBMT in various disorders.
All traumatic brain injuries, regardless of the severity, can cause an increase in cerebral glucose uptake, a reduction of ATP levels and prolonged cerebral metabolic rate of glucose consumption (CMRglc) depression. 19 This is accompanied by a decrease in cerebral blood ow (CBF) which can remain decreased for extended durations. Maugans et al. studied 12 children ages 11 to 15 who had a concussion secondary to a sports-related injury and showed that CBF, as measured by phase-contrast magnetic resonance angiography, was decreased relative to controls immediately after injury and that this decrease persisted beyond 30 days after injury even after symptoms resolved. 20 Neural tissues contain large amounts of mitochondrial CCO. Red and NIR photonic energy modulates reactive oxygen species, activates mitochondrial DNA replication, increases early-response genes, increases growth factor expression, induces cell proliferation, and alters nitric oxide levels. [21][22][23] Nitric oxide (released locally) increases regional cerebral blood ow. 24 Wu et al. demonstrated that a single applications of 800-810 nm NIR light within four hours of injury resulted in a considerable improvement in neurological function. 25 Many studies have shown neuroprotective effects of PBMT in many neurological disorders 26-30 and some studies showed the bene ts of red and NIR light applications in vivo in animals with experimental TBI. [31][32][33] Initial clinical studies of PBMT for persistent TBI symptoms in humans have been encouraging.
For example, Naeser et al. investigated 11 chronic TBI cases with non-penetrating brain injury and showed that these patients had signi cant improvements with PBMT. 34 Naeser et al. also reported on two patients with chronic TBI whose executive function and verbal memory were improved by midline and bilateral scalp application of red/NIR LED therapy. 35 ImPACT® (Immediate Post-Concussion Assessment and Cognitive Testing) In competitive sports, as well as in rehabilitation, pain and neurological clinics, computer-based neurocognitive testing has become a principal component in the evaluation of concussion patients. [36][37][38][39] The most recognized computer-based neurocognitive assessment tool in North America is the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT®) (ImPACT Applications Inc, Pittsburgh, Pennsylvania). 40,41 ImPACT® test has been shown to be both reliable and valid for baseline and post-concussion assessment of neurocognitive function. [42][43][44] The Meditech Rehabilitation Centre began implementing the ImPACT® test, speci cally the Post-Injury test series, as a means of objectively assessing functional cognitive and symptom improvement in patients post-concussion.
The goal of this study is to review the use of PBMT alone as a viable treatment modality for postconcussive symptoms secondary to a mTBI. Subjective reporting and objective testing with the ImPACT® test to assess improvement in cognition and symptomatology in patients.

Methodology
In this retrospective study, patient les from January to December 2018 from a single clinical site in Toronto, Ontario, Canada (Meditech Rehabilitation Centre) were reviewed after receiving independent IRB approval. Inclusion criteria included patients between the ages of 15-65 years clinically diagnosed with a qualifying mTBI within at least 3 months of the traumatic incident with persistent post-concussion symptomatology and not currently undergoing any treatment. For reference, the clinical site used the previous International Classi cation of Diseases, Tenth Revision (ICD-10) clinical criteria for Post-Concussion Syndrome de ned as a "history of TBI and the presence of three or more of the following eight symptoms: 1) headache, 2) dizziness, 3) fatigue, 4) irritability, 5) insomnia, 6) concentration or 7) memory di culty, and 8) intolerance of stress, emotion, or alcohol" 45 prior to the release of ICD-11 one year later. Patients who had any positive ndings on cranial imaging studies, a diagnosis of or a family history of neuropsychiatric co-morbidity or any additional diagnoses compounding the diagnosis of a concussion or mTBI were excluded. As well, patients were excluded if they were undergoing other types of managed therapy with the exception of over the counter pain relievers.
In total, there were 35 patients eligible for this retrospective review, who were active patients from January to December 2018. The average age for our cohort of patients was 41 years old. 49% of patients were women and 51% of patients were men. All treatment and the ImPACT® test itself, were done in a single clinical site utilizing the same Bio ex® DUO+ laser system and parameters as detailed in Table 1.
Patients are treated and tested in the same darkened room free of noise interruptions.
Following a history and physical examination, and prior to undergoing any treatment, the Post Injury Test 1 program of the Impact® test system was administered to each patient. After testing, patients underwent photobiomodulation using the Bio ex® DUO+ Laser Therapy system that uses a 180 bulb Light Emitting Diode (LED) array set followed by laser probes (Red AlGaInP Laser max power at 100mW; Infrared GaAlAs Laser max power at 200mW). Both delivery methods were applied using four arranged placements to the cervical spine and six placements to the cranial area (three placements each side), and both entailed the use of red light at 660 nm wavelength and near-infrared light at 830-840 nm wavelength. Treatment was provided three times per week on alternating days with weekends off for four weeks for a total of 12 treatments using a gradually increasing dosing scale wherein increasing power dosage and modulation is applied every week per the schedule adopted in Table 1.
At the end of the 12 weeks, all patients took a second ImPACT® test (Post Injury 2 test) and the results were compared with Post Injury 1. Clinically, all patients' conditions were improved after 12 treatments.
Statistical Analysis SPSS Version 25 was used to perform all statistical tests. These included descriptive statistics (mean, median, skewness, etc.), paired sample t-tests and Wilcoxon signed rank tests. Both parametric and nonparametric statistics were employed as the data collected, from the ImPACT® test, consisted of different data types. The Wilcoxon signed rank test has been used to compare health outcomes; speci cally, if there has been an improvement between the rst ImPACT® test and the second ImPACT® test with PBMT.
The data was rst exported from the ImPACT® system into Microsoft Excel. In Excel, the dataset was cleaned to ensure that each patient was only recorded once, and every variable is listed as test 1 (preintervention) and test 2 (post-intervention) to facilitate the statistical testing. Any extraneous and personal information that would lead to the identi cation of the patient was removed. A unique patient identi er was created.
A paired t-test was used to evaluate the changes in the sample population scores between pre-and posttreatment intervention. The Wilcoxon signed rank test was used to calculate the difference between the pre-intervention and post-intervention scores for the same participants. Importantly, the data being normally distributed is not a condition of a Wilcoxon signed rank test, even though it is for the t-test. A Wilcoxon signed rank test can be considered the nonparametric version of a paired t-test. Thus, the two statistical tests employed were complementary to one another.
As a component of the ImPACT® test, the patient ranked their symptoms on a scale of 1 to 6. This type of nonparametric hypothesis test can demonstrate that if the alternative hypothesis is correct -there are more positive differences after treatment (α = 0.05) -then the treatment was successful in helping the patient. SPSS automatically calculates the rank for the difference in scores between test 1 (preintervention) and test 2 (post-intervention) for each variable being examined. The smallest difference would receive a rank of one and the largest difference would receive n. If the difference scores were tied at any point, then they would receive the same rank regardless if it was a positive or negative difference. After each of the differences has been calculated, SPSS also attaches a positive or negative sign to each rank based on the absolute difference between test 1 and test 2.  The Wilcoxon signed rank test and the paired sample t-test were used to statistically compare between pre-intervention and post-intervention for all variables being evaluated. All statistically signi cant results have been included below.

Results
By using PBMT all the patients improved clinically and their Post injury 2 ImPACT® test results were signi cantly better, compared to their Post injury 1 ImPACT® test results.

T-test Results
The Cognitive E ciency Index (CEI) was statistically signi cant at the 95% con dence level, speci cally 0.007. Therefore, at the 95% con dence level there is improvement between the CEI calculated at the patients' pre-intervention treatment and post-intervention treatment.
Wilcoxon Signed Rank Test  Table 2 has illustrated all signi cant measures at the 95% con dence level. The symptom score presented summary information regarding the individual's self-reported symptom data. A higher score re ected a higher symptom total. 46 The mean for the second total symptom (25.49) score was less than the rst total symptom score (41.57). Colour Match in the ImPACT® system measured the reaction time in correctly matching a word with the corresponding colour ink. 46 The average colour match results improved from pre-intervention to post-intervention and thus were signi cant at the 95% con dence level. The Three Letters module of the ImPACT® test measured memory and eye-hand coordination speed. 46 In this section of the test, the patient was instructed to click backwards on numbers from 25 in a 5 by 5 grid and then shown three consonants. The patient was then instructed to click backwards from 25 again and then the patient was asked to recall the three consonants displayed just previous. This section is repeated 5 times.  Table 3 has demonstrated the positive and negative sum of ranks calculated as part of the Wilcoxon signed rank test. In all instances, the positive sums were greater than the negative sums at the 95% con dence level.

Discussion
The Centers for Disease Control and Prevention (CDC) estimated that about 2.87 million TBI-related emergency department (ED) visits, hospitalizations, and deaths occurred in 2014. 47 The current estimates of the sports-related concussions and brain injuries in the US are 1.6-3.8 million every year. 48 The annual percent change was reported by Rao et al as 9.6 (95% CI 8. Patients with a mTBI do not show any evidence of intracranial pathologies such as bleeding, subdural or epidural hematoma and/or cranial fracture on standard imaging. 50 Recent studies have shown that mTBI can cause functional neuronal disruption and structural damage in humans and animals. Due to a cerebral energy imbalance, these disruptions have the potential to manifest a wide clinical spectrum, ranging from subtle cognitive de cits only detectable on neuropsychological testing to overt neurological and behavioral symptoms. 14,51 Although full recovery is expected within three months after concussion/mTBI, there has been a small group of concussion sufferers that have experienced persistent symptoms. A number of factors can in uence the rate of recovery, including the mechanism and setting for the initial injury, age, and recurrent concussion incidents in the past. A typical mTBI patient at the Meditech Rehabilitation Centre would have had a concussion three or more months prior to initial presentation, and had already consulted a barrage of healthcare practitioners, including their family physicians, a neurologist, a physiotherapist and others, with no relief in their symptoms. All 35 patients noted improvement in their cognitive functions after PBMT.
PBMT has often been used 'off label' as a treatment modality for post-concussion symptoms secondary to TBI. Although most PBMT devices are generally classi ed and licensed as general wellness devices without public health oversight, Meditech Rehabilitation Centre uses the BIOFLEX® DUO+ system, which has Health Canada and FDA cleared treatment indications for soft tissue injuries, minor pains and to increase local blood ow. Meditech Rehabilitation Centre has been treating patients for speci c postconcussive symptoms like neck pain and stiffness for several years as a supporting regimen to traditional therapies. At Meditech Rehabilitation Centre, a number of patients have reported improvement in concussion symptoms using our BIOFLEX® DUO+ devices after traditional treatment methods proved less successful.

The Biphasic Dose Response
A major concern in the acceptance of PBMT for the treatment of neurological conditions is the use of appropriate and effective dosage. In many cases, especially in our own clinical observations, it has been found in PBMT that more light is not necessarily therapeutically better than less light in terms of energy delivery. This "biphasic dose responses (also called Arndt-Schulz law or hormesis)" shows that PBMT can simultaneously inhibit and stimulate, and the techniques and settings for consistently achieving these effects have not always been clearly stated. 52 Because of this, certain studies that utilize a static dosing mechanism in PBMT for the treatment of neurological conditions either mention no effect, or on occasion, certain uncomfortable side effects such as headaches. Being cognizant of the biphasic dose response so typical in PBMT, treatment in Meditech Rehabilitation Centre is provided in a gradually increasing dosing fashion, rst starting with a relatively mild dose with continuous light application before gradually increasing the energy density application (in Joules/cm 2) and adding pulse modulation in weekly intervals. Despite the parameters used in this study, in clinical practice the patient's response and their capacity to follow-up were taken into consideration. This gradual dosing pattern allows tissues to adjust to the treatment and absorb more photons of light as treatment progresses while maintaining depth penetration. 53 Of note, in this study, was the dual treatment modality, in which both the cervical area and parts of the cranium were treated. Most studies that have used PBMT for the treatment of neurological conditions tended to focus treatment only in the cranial area. 26,27,31,32,35,[54][55][56] The inclusion of the cervical area treatment has demonstrated that PBMT can cause vasodilation and increased local circulation and can have a potential effect on certain neurotransmitters like serotonin (5-HT) and cholinesterase levels. 57 Although most studies show that at most cranial penetration of most PBMT devices are minimal (up to 4 cm at most, based on cadaver studies), 58 including cervical treatments has been instrumental in cognitive improvement due to the effect of increased cerebral circulation. 59 The ImPACT® test with PBMT format released in 2021 and has replaced it with the Two Factor score 46 . However, given the signi cance of this measure at the 95% con dence level, we have decided to still include the CEI in the results as a report of its utility.
The CDC divides mTBI symptoms into 4 categories: Thinking/Remembering, Sleep, Emotional/Mood, and Physical. 60 Aside from the objective and rapid measurement of cognitive abilities, ImPACT® included a subjective symptom reporting scale. The ImPACT post-concussion symptom rating scale contained 22 somatic, affective, and cognitive symptoms, with each symptom being rated from 0 (none) to 6 (severe). Two values can be computed for the symptom questionnaire: total symptom score (sum of all ratings for all symptoms) and the number of symptoms endorsed as being present (regardless of the severity). Both of these values were examined for this study. The patients' symptoms decreased signi cantly at the 95% con dence level, for patients after receiving PBMT with the BIOFLEX® DUO+ system. The Wilcoxon Signed Rank tests detailed the decrease in the total symptom score. Thus, patients were experiencing less symptoms after the intervention than without it. Improvement in the objective and subjective scores of the ImPACT® test after treatment with PBMT showed that computer-based neurocognitive assessments can be considered a valuable aid in diagnosis and assessment of treatment response for mTBI patients with persistent post-concussive symptoms.

LIMITATIONS:
There were limitations to this study. Speci cally, the sample size was small, and the treatment time was limited to one month. In clinical practice, further improvement was noted beyond the one month period, and some patients had decided to continue treatment at home utilizing portable devices. Given that the consistency of use of portable devices cannot be controlled for, we decided not to include these in our study. Increasing sample sizes, extending the treatment period, and including cerebral blood ow measurement could potentially provide additional evidence of cognitive improvement utilizing PBMT.

RECOMMENDATIONS:
Our group did not initiate an ImPACT® baseline examination for this population given that they have already suffered an injury prior to their rst presentation. Doing a baseline ImPACT® test measurement under controlled conditions may have provided a better assessment of a person's cognitive state preconcussion and a better comparison of improvement with the Post Injury 1 and 2 tests. Initiating a study with the baseline measurements for certain concussion-prone population groups, i.e., hockey players, members of the armed forces, construction workers, may prove to be a valid option for a future study.

Conclusion
Concussion with persistent post-concussive symptoms is a severe health problems which has signi cant functional and economic implications for the patient, their relatives, school, employers, and organizations like the O ce of Workers' Compensation Programs (OWCP) of the United States Department of Labor and the Workplace Safety and Insurance Board (WSIB) of Ontario, Canada. Available studies using symptom based questionnaires suggested that patients with post-concussive symptoms have lower perceived levels of overall quality of life, 61,62 are less likely to immediately return to work and more likely to receive health related bene ts. 63 Patients with persistent post-concussive symptoms will need school or work-place accommodations to restrict or modify cognitive loads until recovery, which can be long, slow and frustrating for patients and severely affects their daily life endeavours. 64 Our study has shown that PBMT is an effective treatment modality for neurological rehabilitation in patients with postconcussive symptoms as assessed using the ImPACT® test, leading to improved cognitive performance and an improvement in symptomatology. PBMT should be considered one of the available options in the treatment of concussions and persistent post-concussive symptoms.

Declarations
Ethics Approval and Consent to Participate: This study is reviewed and approved by an independent Institutional Review Board (IRB) Advarra (6100 Availability of Data and Material: The datasets used and/or analysed during the current study are not publicly available due to con dentiality laws but are available from the corresponding author on reasonable request.