• Roland-Morris Disability Questionnaire score [ Time Frame: 4 months ]
  The modified RMDQ is a self-administered disability measure in cLBP patients.
• Patient-Reported Outcomes Measurement Information System (PROMIS) scores [ Time Frame: 4 months ]
  The PROMIS, funded by the NIH, is a system containing reliable, flexible, precise, and responsive assessment tools that have been widely validated in numerous samples. We will use PROMIS-29 to assess pain interferences and intensity, physical function, depression, anxiety, fatigue, and sleep in the past 7 days.
• Pain medication dose changes [ Time Frame: 4 months ]
  Pain medication dose changes as determined by a weekly-collected medication log
• Pain Catastrophizing Scale [ Time Frame: 4 months ]
  The PCS is a 15-item questionnaire used to characterize an individual's tendency to magnify the threat value of a pain experience and to feel helpless in the presence of pain.
• The Pennebaker Inventory of Limbic Languidness [ Time Frame: 4 months ]
  PILL allows individuals to rate how frequently they have experienced each of 54 common symptoms over an unspecified time period in the past using a five-point Likert scale. The PILL contains a range of physical symptoms, including some items that are pain-related (e.g., headache, back pains, sore muscles).

• Resting state functional connectivity changes of the PAG [ Time Frame: 1 month ]
  Functional connectivity changes of the periaqueductal gray while at rest.
• Resting state functional connectivity of the medial and lateral hypothalamus [ Time Frame: 1 month ]
  Functional connectivity changes of the hypothalamus while at rest.
• CBF as measured by ASL [ Time Frame: 1 month ]
  Changes in cerebral blood flow.
• Inflammation biomarkers [ Time Frame: 1 month ]
  Changes in inflammatory biomarker levels

• Other: Stimulation at Location 1
  Stimulation parameters will include 1) density wave adjusted to 20Hz with less than 1 ms pulse width, 2) intensity adjusted based on the tolerance of the patient (moderate tolerable stimulation without pain), and 3) treatment will be applied 1 time per day, 5 times per week for four weeks (on-site tVNS treatment plus self-administration at home).
• Other: Stimulation at Location 2
  Stimulation parameters will include 1) density wave adjusted to 20Hz with less than 1 ms pulse width, 2) intensity adjusted based on the tolerance of the patient (moderate tolerable stimulation without pain), and 3) treatment will be applied 1 time per day, 5 times per week for four weeks (on-site tVNS treatment plus self-administration at home).

• Experimental: Ear stimulation (Location 1)
  Intervention: Other: Stimulation at Location 1
• Experimental: Ear stimulation (Location 2)
  Intervention: Other: Stimulation at Location 2

Inclusion Criteria:

• Volunteers 18-65 years of age.
• Meet the Classification Criteria of chronic LBP (having low back pain for more than 6 months), as determined by a referring physician.
• Received stable treatment or no treatment in the past month.
• At least a 10th grade English-reading level. English can be a second language provided that the patients feel they understand all the questions used in the assessment measures.

Exclusion Criteria:

• Specific causes of back pain (e.g., epidural abscess, compression fracture, spondyloarthropathy, malignancy, cauda equina syndrome) or radicular pain, radiculopathy, or spinal canal stenosis. Complicated back problems (e.g., prior back surgery, medico-legal issues).
• Presence of headache/migraine, as well as widespread body pain such as fibromyalgia.
• The intent to undergo surgery during participation in the study.
• History of cardiac, respiratory, or nervous system disease that, in the investigator's judgment, precludes participation in the study because of a heightened potential for adverse outcomes (e.g., asthma or claustrophobia).
• Presence of any contraindications to MRI scanning (e.g., cardiac pacemaker, metal implants, fear of enclosed spaces, pregnancy, cannot lie still in fMRI scanner).
• Conditions that might confound longitudinal effects or interpretation of results (e.g. severe fibromyalgia, rheumatoid arthritis).
• Pregnant or lactating.
• Conditions making study participation difficult (e.g., paralysis, psychoses, or other severe psychological problems as per the judgment of a study investigator during Session 1).
• Active substance abuse disorders within the last 24 months (based on subject self-report).
• Use of prescription steroids for pain during the past six months.
• Presence of any other acute or chronic pain disorder.
• Any medical conditions, such as peripheral neuropathy, that could affect the results of QST.