Participants with chronic back pain will complete an online prescreen. They will then be randomized to one of two different studies: a placebo vs. waitlist study or a psychotherapy vs. waitlist study, with randomization stratified on pain intensity, age, gender, and opioid use. Participants will then complete an in-person eligibility session, and eligible participants will be scheduled for the baseline assessment session. Following the baseline assessment session, participants will then be randomized to the treatment group or the waitlist group (with a ratio of 2:1 treatment:waitlist), using a computer-generated random sequence.

This scheme will result in three equally sized groups-placebo, psychotherapy, and waitlist-as the investigators will collapse data from the waitlist arms in the two studies for analyses. The investigators do not use a standard three-way randomization because the investigators do not want placebo participants to think they are in a control condition. Thus, the investigators constrain participant's expectations to either injection vs. waitlist or to psychotherapy vs. waitlist.

The placebo treatment is a subcutaneous injection of saline into the back. Participants will know that the treatment is a placebo, i.e., it is an "open label" placebo. Psychotherapy (8 sessions) will be supervised by Alan Gordon and Howard Schubiner.

Functional MRI brain imaging, self-reported clinical outcomes, and behavioral measures will be collected pre- and post-treatment. A brief follow-up survey will be sent at months 1, 2, 3, 6, and 12 after the final assessment session. These will provide longer term data about the trajectory and durability of patient improvement.

Additionally, a group of healthy controls, with no history of back pain, will complete the baseline assessment. They will serve as a comparison group to probe whether the patterns of observed brain activity is specific to CBP patients.

Inclusion Criteria:

• Participants aged 21 to 70 with CBP will be enrolled.
• CBP will be defined according to the criteria established by a recent NIH task force (Deyo et al., 2014). Pain duration must be at least 3 months, with back pain being an ongoing problem for at least half the days of the last 6 months. That is, patients can meet criteria by either reporting pain every day for the past 3 months, or by reporting pain on half or more of the days for the past 6+ months. This will be determined by asking patients: (1) How long has back pain has been an ongoing problem for you? (2) How often has low back pain been an ongoing problem for you over the past 6 months? A response of greater than 3 months to question 1 and a response of ''at least half the days in the past 6 months'' to question 2 would define CBP.
• Patients must rate pain intensity at 40/100 or greater on the Brief Pain Inventory-Short Form (BPI-SF), in keeping with inclusion criteria from previous CBP trials (Baliki et al., 2012; Cherkin et al., 2016; Hashmi et al., 2013; Seminowicz et al., 2011).
• Back pain must be elicited by our back pain device (see below).
• Participants must also be comfortable and able to communicate via email or text message, as several study measures are collected in this manner (see below).

Exclusion Criteria:

• Back pain associated with compensation or litigation issues as determined by self-report within the past year.
• Leg pain is greater than back pain. This suggests neuropathic pain, which may be less responsive to placebo or psychotherapy.
• Difficulty participating for technical/logistical issues (e.g., unable to get to assessment sessions).
• Self-reported diagnoses of schizophrenia, multiple personality disorder, or dissociative identity disorder.
• Self-reported use of intravenous drugs, due to concerns about infections and subject compliance with experimental protocols.
• Inability to undergo MRI as determined by MRI safety screen (e.g., pregnancy, metal in body, claustrophobia, using the standard screen conducted by the MRI imaging facility).
• Hypersensitive or hyposensitive to pressure pain: unable to tolerate 7kg/cm2 stimulation or reporting no pain for 4kg/cm2 stimulation; see further details below.
• Current regular use of an immunosuppressant drug, such as steroids. Such drugs interfere with immunoassay results.
• Self-reported history of metastasizing cancers-cancer of the breast, thyroid, lung, kidney, prostate or blood cancers.
• Self-reported history of stroke, brain surgery, or brain tumor.
• Self-reported diagnosis of a specific inflammatory disorder: rheumatoid arthritis, polymyalgia rheumatica, scleroderma, Lupus, or polymyositis.
• Unexplained, unintended weight loss of 20 lbs. or more in the past year.
• Cauda Equina syndrome, as screened for by self-reported inability to control bowel or bladder function.

Adverse events were collected from enrollment through completion of the post-treatment fMRI session, an average of 1.5 months after enrollment.

Adverse events were recorded when participants spontaneously reported them to study personnel.

Researchers will not know which treatment the participants will be receiving (placebo or psychotherapy).