• Clinical Pain as Assessed by a Numeric Rating Scale (NRS) for Pain [ Time Frame: week 2 ]
  The NRS total score ranges from 0 (no pain) to 100 (most intense pain imaginable).
• Clinical Pain as Assessed by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [ Time Frame: week 2 ]
  The WOMAC ranges from 0 to 96, with higher scores indicating worse osteoarthritis (OA) pain-related symptoms

• Change in clinical pain as assessed by the numeric rating scale (NRS) for pain [ Time Frame: Baseline, week 2 ]
  The NRS total score ranges from 0 (no pain) to 100 (most intense pain imaginable).
• Change in clinical pain as assessed by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [ Time Frame: Baseline, week 2 ]
  The WOMAC ranges from 0 to 96, with higher scores indicating worse OA pain-related symptoms

• Experimental Pain Sensitivity as Measured Using a Multimodal Quantitative Sensory Testing (QST) Battery - Heat Pain Threshold (HPTH) [ Time Frame: week 2 ]
  In order to measure experimental pain sensitivity, a multimodal Quantitative Sensory Testing (QST) battery will be completed: heat pain threshold (HPTH), heat pain tolerance (HPTO), pressure pain threshold (PPT), and Conditioned Pain Modulation (CPM). To assess HPTH, heat stimuli were delivered to the participant's knee using a computer-controlled TSAII NeuroSensory Analyzer. From a baseline of 32 degrees Celsius, the temperature increased by 0.5 degrees Celsius per second until the participants responded by pressing a button to stop heat stimuli. Participants were instructed to press the button when the sensation ''first becomes painful" to assess the heat pain threshold (HPTH).
• Experimental Pain Sensitivity as Measured Using a Multimodal Quantitative Sensory Testing (QST) Battery - Heat Pain Tolerance (HPTO) [ Time Frame: week 2 ]
  In order to measure experimental pain sensitivity, a multimodal Quantitative Sensory Testing (QST) battery will be completed: heat pain threshold (HPTH), heat pain tolerance (HPTO), pressure pain threshold (PPT), and Conditioned Pain Modulation (CPM). To assess HPTO, heat stimuli were delivered to the participant's knee using a computer-controlled TSAII NeuroSensory Analyzer. From a baseline of 32 degrees Celsius, the temperature increased by 0.5 degrees Celsius per second until the participants responded by pressing a button to stop heat stimuli. Participants were instructed to press the button when they ''no longer feel able to tolerate the pain" to assess their heat pain tolerance (HPTO).
• Experimental Pain Sensitivity as Measured Using a Multimodal Quantitative Sensory Testing (QST) Battery - Pressure Pain Threshold (PPT) [ Time Frame: week 2 ]
  In order to measure experimental pain sensitivity, a multimodal Quantitative Sensory Testing (QST) battery will be completed: heat pain threshold (HPTH), heat pain tolerance (HPTO), pressure pain threshold (PPT), and Conditioned Pain Modulation (CPM). To assess PPT, a handheld digital pressure algometer (Wagner, Greenwich, CT) was applied at a constant rate of 0.3 kilograms force per centimeter squared (kgf/cm^2) per second to the participant's knee. Participants were asked to notify the experimenter when the pressure sensation ''first becomes painful" to assess pressure pain threshold (PPT).
• Experimental Pain Sensitivity as Measured Using a Multimodal Quantitative Sensory Testing (QST) Battery - Conditioned Pain Modulation (CPM) [ Time Frame: week 2 ]
  In order to measure experimental pain sensitivity, a multimodal Quantitative Sensory Testing (QST) battery will be completed: heat pain threshold (HPTH), heat pain tolerance (HPTO), pressure pain threshold (PPT), and Conditioned Pain Modulation (CPM). CPM was assessed as the change in PPT on the trapezius immediately after the immersion of the contralateral hand up to the wrist in a cold-water bath (Neslab, Portsmouth, NH) at 12 degrees C for one minute. [To assess PPT, a handheld digital pressure algometer (Wagner, Greenwich, CT) was applied at a constant rate of 0.3 kilograms force per centimeter squared (kgf/cm^2) per second to the participant's trapezius. Participants were asked to notify the experimenter when the pressure sensation ''first becomes painful" to assess pressure pain threshold (PPT).]
• Psychosocial Symptoms as Measured by the Patient-Reported Outcomes Measurement Information System (PROMIS) - Anxiety Short Form [ Time Frame: week 2 ]
  The 7-item PROMIS Anxiety Short Form assesses the pure domain of anxiety in individuals age 18 and older, and each item on the measure is rated on a 5-point scale (1=never; 2=rarely; 3=sometimes; 4=often; and 5=always) with a range in score from 7 to 35 with higher scores indicating greater severity of anxiety.
• Psychosocial Symptoms as Measured by PROMIS - Depression Short Form [ Time Frame: week 2 ]
  The 8-item PROMIS Depression Short Form assesses the pure domain of depression in individuals age 18 and older, and each item on the measure is rated on a 5-point scale (1=never; 2=rarely; 3=sometimes; 4=often; and 5=always) with a range in score from 8 to 40 with higher scores indicating greater severity of depression.
• Psychosocial Symptoms as Measured by PROMIS - Sleep Disturbance Short Form [ Time Frame: week 2 ]
  The 8-item PROMIS Sleep Disturbance Short Form assesses the pure domain of sleep disturbance in individuals age 18 and older, and each item on the measure is rated on a 5-point scale (1=never; 2=rarely;3=sometimes; 4=often; and 5=always) with a range in score from 8 to 40 with higher scores indicating greater severity of sleep disturbance.
• Psychosocial Symptoms as Measured by the Pain Catastrophizing Scale (PCS) [ Time Frame: week 2 ]
  The Pain Catastrophizing Scale (PCS) consists of 13 items assessing three components of catastrophizing: rumination, magnification, and helplessness. It is measured using the 0 (not at all) to 4 (all the time) scale. Total score ranges from 0 to 52, with higher scores indicating greater pain catastrophizing.
• Number of Participants With a Significant Change in Pain-related Cortical Response on Average as Assessed by a Continuous Wave, Multichannel Functional Near-infrared Spectroscopy (fNIRS) Imaging System [ Time Frame: baseline, week 2 ]
  Pain-related cortical response will be measured using a continuous-wave, multichannel fNIRS imaging system (LIGHTNIRS, Shimadzu, Kyoto, Japan) with three semiconductor lasers at 780, 805, and 830 nm. Optical recordings will be collected during thermal pain stimulation.
• Participant Satisfaction With Treatment Using the Client Satisfaction Questionnaire (CSQ-8) [ Time Frame: week 2 ]
  The CSQ-8 comprises eight items that are summed to yield an overall score of 8-32, with higher scores indicating greater satisfaction.
• Feasibility as Measured by the Number of Participants That Completed the Full CES Protocol [ Time Frame: week 2 ]
• Feasibility as Indicated by Participant's Cranial Electrical Stimulation (CES) Experience [ Time Frame: week 2 ]
  CES experience will be measured on a 10-item scale, with each item rated 0-10 and 0 being strongly disagree and 10 being strongly agree. Total score ranges from 0 to 100, with higher scores indicating a better CES experience. Question 1. It was easy to prepare the device and accessories Question 2. The device was unnecessarily complex Question 3. The device was easy to use Question 4. I felt the video conferences with a technical person were helpful Question 5. I would imagine that most people would learn to use this device quickly Question 6. The device was cumbersome to use Question 7. I felt confident using the device Question 8. I needed to learn a lot of things before I could get going with this device Question 9. The effectiveness of the treatment increased over the course of treatment Question 10. I felt that transcranial electrical stimulation treatment benefited me
• Tolerability as Indicated by Number of Participants With Possible Side Effects of Treatment [ Time Frame: week 2 ]
  Measurement of presence and severity of possible side effects of treatment on a 0 (not at all) to 10 (highest degree) scale.If any side effects are reported, the degree of relatedness to the intervention will be assessed on a 5-point scale.

• Change in Psychosocial symptoms as measured by the Patient-Reported Outcomes Measurement Information System(PROMIS) anxiety-short form [ Time Frame: Baseline, week 2 ]
  The 7-item PROMIS Anxiety Short Form assesses the pure domain of anxiety in individuals age 18 and older, and each item on the measure is rated on a 5-point scale (1=never; 2=rarely; 3=sometimes; 4=often; and 5=always) with a range in score from 7 to 35 with higher scores indicating greater severity of anxiety.
• Change in Psychosocial symptoms as measured by the PROMIS depression-short form [ Time Frame: Baseline, week 2 ]
  The 8-item PROMIS Depression Short Form assesses the pure domain of depression in individuals age 18 and older, and each item on the measure is rated on a 5-point scale (1=never; 2=rarely; 3=sometimes; 4=often; and 5=always) with a range in score from 8 to 40 with higher scores indicating greater severity of depression.
• Change in Psychosocial symptoms as measured by the PROMIS sleep disturbance-short form scale [ Time Frame: Baseline, week 2 ]
  The 8-item PROMIS Sleep Disturbance Short Form assesses the pure domain of sleep disturbance in individuals age 18 and older, and each item on the measure is rated on a 5-point scale (1=never; 2=rarely;3=sometimes; 4=often; and 5=always) with a range in score from 8 to 40 with higher scores indicating greater severity of sleep disturbance.
• Change in Psychosocial symptoms as measured by the Pain Catastrophizing Scale (PCS) [ Time Frame: Baseline, week 2 ]
  The Pain Catastrophizing Scale (PCS) consists of 13 items assessing three components of catastrophizing: rumination, magnification, and helplessness. It is measured using the 0 (not at all) to 4 (all the time) scale. Total score ranges from 0 to 52, with higher scores indicating greater pain catastrophizing.
• Change in Experimental Pain Sensitivity as measured using a multimodal Quantitative Sensory Testing (QST) battery [ Time Frame: Baseline, week 2 ]
  In order to measure experimental pain sensitivity, a multimodal Quantitative Sensory Testing (QST) battery will be completed: heat pain sensitivity, pressure pain sensitivity, punctate mechanical pain, and Conditioned Pain Modulation (CPM).
• Change in pain related cortical response using a continuous wave, multichannel Functional near-infrared spectroscopy (fNIRS) imaging system [ Time Frame: baseline, week 2 ]
  Pain-related cortical response will be measured using a continuous-wave, multichannel fNIRS imaging system (LIGHTNIRS, Shimadzu, Kyoto, Japan) with three semiconductor lasers at 780, 805, and 830 nm. Optical recordings will be collected during thermal pain stimulation.
• Participant Satisfaction With Treatment Using the Client Satisfaction Questionnaire (CSQ-8) [ Time Frame: week 2 ]
  The CSQ-8 comprises eight items that are summed to yield an overall score of 8-32, with higher scores indicating greater satisfaction.
• Feasibility as Measured by the Number of Participants That Completed the Full CES Protocol [ Time Frame: week 2 ]
• Feasibility as Indicated by Participant's Cranial Electrical Stimulation (CES) Experience [ Time Frame: week 2 ]
  CES experience will be measured on a 10-item scale, with each item rated 0-10 and 0 being strongly disagree and 10 being strongly agree. Total score ranges from 0 to 100, with higher scores indicating a better CES experience.
• Tolerability as Indicated by Number of Participants With Possible Side Effects of Treatment [ Time Frame: week 2 ]
  Measurement of presence and severity of possible side effects of treatment on a 0 (not at all) to 10 (highest degree) scale.If any side effects are reported, the degree of relatedness to the intervention will be assessed on a 5-point scale.

• Device: Cranial Electrical Stimulation (CES)
  CES will be applied for 60 minutes per session daily for 2 weeks (Monday to Friday) via the Alpha-Stim M Electromedical Products International, Inc., Mineral Wells, TX).
  Other Name: Alpha-Stim M
• Device: Sham-CES
  For sham CES, the electrodes will be identical look and be placed in the same positions as for active stimulation, but the stimulator will not deliver electrical current.
  Other Name: Alpha-Stim M

• Experimental: Self-CES
  Intervention: Device: Cranial Electrical Stimulation (CES)
• Placebo Comparator: Sham-CES
  Intervention: Device: Sham-CES

Inclusion Criteria:

• have self-reported unilateral or bilateral knee OA pain, according to American College of Rheumatology criteria
• have had knee OA pain in the past 3 months with an average of at least 30 on a 100 Numeric Rating Scale (NRS) for pain
• can speak and read English
• have a device with internet access that can be used for secure video conferencing for real- time remote supervision
• have no plan to change medication regimens for pain throughout the trial
• are able to travel to the coordinating center
• are willing and able to provide written informed consent prior to enrollment

Exclusion Criteria:

• history of brain surgery, brain tumor, seizure,stroke, or intracranial metal implantation
• serious medical illness, such as uncontrolled hypertension (i.e., systolic blood pressure/ diastolic blood pressure ≥ 150/95 mm Hg)heart failure, or history of acute myocardial infarction
• alcohol/substance abuse
• cognitive impairment
• pregnancy or lactation
• hospitalization within the preceding year for psychiatric illness