Table 1: Summary of Main Findings.

Topic	Research Population	Main Findings/Theory	Citation
A. Potential Explanations of Comorbidity of Depression and Pain	1. Individuals with comorbid chronic pain and depression 2. Individuals with comorbid depression, fibromyalgia, and neuropathic pain 3. a. Premenopausal women with chronic pain and depression b. Older adults c. Individuals with fibromyalgia	1. a. The source of depression in individuals with chronic pain is a predisposition to depression that results from the stress of the pain condition b. Responses of medical practitioners to individuals’ experience of chronic pain may be perceived as dismissing and serve as a stressor in the development of depression 2. a. Brain abnormalities may lead to a bidirectional relationship between chronic pain and depression b. Overstimulation of the HPA axis due to exposure to stressor(s) over a continuous period of time may impair HPA axis and influence cortisol levels, resulting in experience of pain and disruption of mood 3. An abundance of pro-inflammatory proteins may be involved in the comorbidity of pain and depression	1. a and b. Banks and Kerns [35] 2. a. Maletic and Riason [37] b1. Aguglia, Salvi, Maina, Rossetto, Aguglia [60] b2. Gracely, Ceko, Bushnell [61] 3. a. Hartman et al. [63] b. Penninx et al. [69] c. Gür, Karakoç, Nas, Denli, & Saraç [72]
B. Potential Explanations of Comorbidity of PTSD and Pain	1. Patients with accident-related chronic pain 2. Veterans with PTSD who had experienced combat versus veterans who had not 3. a. Burn victims b. Veterans c. Chronic musculoskeletal pain patients 4. No population tested 5. a. Individuals with PTSD symptomatology b. Individuals with musculoskeletal pain c. Individuals with comorbid PTSD and chronic pain 6. a. Individuals with chronic pain b. Motor vehicle accident survivors with comorbid PTSD and chronic pain or with only chronic pain	1. Anxiety enhances the perception of pain 2. Pain is processed differently among individuals with PTSD 3. Sensitivity to anxious or arousal-based stimuli can contribute to the development and maintenance of comorbid PTSD and pain 4. Anxiety sensitivity for an enhanced awareness of danger during trauma may contribute to developing comorbid PTSD and chronic pain conditions 5. a. The use of avoidant coping to deal with fearful stimuli and consequent inability to extinguish the fear maintain symptoms of PTSD b. Acute pain may develop into a chronic pain-related disability as a result of pain-related fear and avoidant behaviors c. Avoidant coping behaviors can contribute to the maintenance and development of comorbid PTSD and pain 6. a. Delayed recognition of words related to pain b. Delayed recognition of words related to both pain and trauma among individuals with PTSD and chronic pain; delayed recognition of words related only to pain among those with only chronic pain	1. Geisser, Roth, Bachman, and Eckert [86] 2. Gueze et al. [87] 3. a. Van Loey, Maas, Faber, & Taal [88] b. Jakupcak et al. [92] c. López-Martínez, Ramírez-Maestre, and Esteve [93] 4. Asmundson, Coons, Taylor, & Katz [94] 5. a. Foa, Steketee, & Rothbaum [95] b. Vlaeyen and Linton [97] c. Bosco, Gallinati, & Clark [98] 6. a. Pincus & Morley [101] b. Beck, Freeman, Shipherd, Hamblen, & Lackner [102]
C. Potential Explanation of Comorbidity of Depression, PTSD, and Pain	1. Older adults with widespread pain 2. a. and b. Male veterans c. Individuals with chronic pain as a result of an accident 3. Women with depression and women with PTSD	1. Evidence on the significance of the depression-PTSD-pain link 2. a. and b. Depression mediates the PTSD-pain link c. PTSD is directly related to depression; depression is directly related to pain magnitude and indirectly to pain intensity via its effect on disability 3. Depression, PTSD, and vulvodynia may share patho-physiological patterns and risk factors	1. Häuser, Glaesmer, Schmutzer, & Brähler [103] 2. a. Jakupcak et al. [92] b. Poundja, Fikretoglu, & Brunet [104] c. Roth, Geisser, & Bates [105] 3. Iglesias-Rios, Harlow, & Reed [106]