The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The continuous pain subscale assesses throbbing pain, cramping pain, gnawing pain, aching pain, heavy pain, and tender, and total score on the continuous pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The continuous pain subscale assesses throbbing pain, cramping pain, gnawing pain, aching pain, heavy pain, and tender, and total score on the continuous pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The intermittent pain subscale assesses shooting pain, stabbing pain, sharp pain, splitting pain, electric-shock pain, and piercing, and total score on the intermittent pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The intermittent pain subscale assesses shooting pain, stabbing pain, sharp pain, splitting pain, electric-shock pain, and piercing, and total score on the intermittent pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The neuropathic pain subscale assesses hot-burning pain, cold-freezing pain, pain caused by light touch, itching, tingling or 'pins and needles', and numbness, and total score on the neuropathic pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The neuropathic pain subscale assesses hot-burning pain, cold-freezing pain, pain caused by light touch, itching, tingling or 'pins and needles', and numbness, and total score on the neuropathic pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The affective description subscale assesses tiring-exhausting, sickening, fearful, and punishing-cruel, and total score on the affective description subscale ranges from 0-40, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The affective description subscale assesses tiring-exhausting, sickening, fearful, and punishing-cruel, and total score on the affective description subscale ranges from 0-40, with a higher score indicating worse pain.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess HPTH, heat stimuli were delivered to the participant's arm or 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). The temperature at which participants pressed the button to indicate the sensation ''first becomes painful" is reported.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess HPTH, heat stimuli were delivered to the participant's arm or 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). The temperature at which participants pressed the button to indicate the sensation ''first becomes painful" is reported.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess HPTO, heat stimuli were delivered to the participant's arm or 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." The temperature at which participants pressed the button to indicate they could ''no longer feel able to tolerate the pain" is reported.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess HPTO, heat stimuli were delivered to the participant's arm or 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." The temperature at which participants pressed the button to indicate they could ''no longer feel able to tolerate the pain" is reported.

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), punctate mechanical pain (PMP), 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 medial knee, lateral knee, or trapezius. Participants were asked to notify the experimenter when the pressure sensation ''first becomes painful." The pressure at which participants pressed the button to indicate that the pressure sensation ''first becomes painful" is reported.

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), punctate mechanical pain (PMP), 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 medial knee, lateral knee, or trapezius. Participants were asked to notify the experimenter when the pressure sensation ''first becomes painful." The pressure at which participants pressed the button to indicate that the pressure sensation ''first becomes painful" is reported.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess PMP, punctate mechanical pain is delivered to the patella or hand by a calibrated nylon monofilament for 10 contacts of the monofilament at one contact per second. Participants rate the pain intensity on a scale from 0 (no pain) to 100 (maximum imaginable pain).

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess PMP, punctate mechanical pain is delivered to the patella or hand by a calibrated nylon monofilament for 10 contacts of the monofilament at one contact per second. Participants rate the pain intensity on a scale from 0 (no pain) to 100 (maximum imaginable pain).

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

CPM is reported as the change in PPT before and immediately following immersion of the contralateral hand up to the wrist in a cold water bath (12 degrees Celsius) for up to 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." The pressure at which participants pressed the button to indicate that the pressure sensation ''first becomes painful" is reported.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

CPM is reported as the change in PPT before and immediately following immersion of the contralateral hand up to the wrist in a cold water bath (12 degrees Celsius) for up to 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." The pressure at which participants pressed the button to indicate that the pressure sensation ''first becomes painful" is reported.

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.

Data will be collected on participants' tDCS experience at the conclusion of tDCS treatment on a scale of 0 (strongly disagree) to 10 (strongly agree): Q1) "Overall the device was easy to use"

Data will be collected on participants' tDCS experience at the conclusion of tDCS treatment on a scale of 0 (strongly disagree) to 10 (strongly agree): Q2) "It was easy to prepare the device and accessories"

Data will be collected on participants' tDCS experience at the conclusion of tDCS treatment on a scale of 0 (strongly disagree) to 10 (strongly agree): Q3) "The effectiveness of the treatment increased over the course of treatment."

The participants will be asked in an open-ended manner whether they have experienced any side effects, and they will then be asked specifically about tingling, itching sensation, burning sensation, pain at the stimulation site, fatigue, nervousness, headache, difficulty concentrating, mood change, and changes in vision or visual perception.

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.

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.

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.

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.

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.

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.

Scores on the visual analogue scale (VAS) range from 0 (no pain) to 100 (worst pain imaginable).

The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The WOMAC is a self-administered questionnaire consisting of 3 subscales related to pain (pain subscale total score range, 0-20), stiffness (stiffness subscale total score range, 0-8), and impairments of physical function (functional impairment subscale range, 0-68), with higher scores indicating worse pain, stiffness, and impairments of physical function, respectively.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The continuous pain subscale assesses throbbing pain, cramping pain, gnawing pain, aching pain, heavy pain, and tender, and total score on the continuous pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The continuous pain subscale assesses throbbing pain, cramping pain, gnawing pain, aching pain, heavy pain, and tender, and total score on the continuous pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The intermittent pain subscale assesses shooting pain, stabbing pain, sharp pain, splitting pain, electric-shock pain, and piercing, and total score on the intermittent pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The intermittent pain subscale assesses shooting pain, stabbing pain, sharp pain, splitting pain, electric-shock pain, and piercing, and total score on the intermittent pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The neuropathic pain subscale assesses hot-burning pain, cold-freezing pain, pain caused by light touch, itching, tingling or 'pins and needles', and numbness, and total score on the neuropathic pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The neuropathic pain subscale assesses hot-burning pain, cold-freezing pain, pain caused by light touch, itching, tingling or 'pins and needles', and numbness, and total score on the neuropathic pain subscale ranges from 0-60, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The affective description subscale assesses tiring-exhausting, sickening, fearful, and punishing-cruel, and total score on the affective description subscale ranges from 0-40, with a higher score indicating worse pain.

The SF-MPQ-2 measures the quality as well as the intensity of pain. Participants complete the SF-MPQ-2 by rating the extent to which they experienced each of 22 pain descriptors in the past week using an 11-point numeric rating scale (0 = "none" to 10 = "worst possible"). The affective description subscale assesses tiring-exhausting, sickening, fearful, and punishing-cruel, and total score on the affective description subscale ranges from 0-40, with a higher score indicating worse pain.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess HPTH, heat stimuli were delivered to the participant's arm or 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). The temperature at which participants pressed the button to indicate the sensation ''first becomes painful" is reported.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess HPTH, heat stimuli were delivered to the participant's arm or 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). The temperature at which participants pressed the button to indicate the sensation ''first becomes painful" is reported.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess HPTO, heat stimuli were delivered to the participant's arm or 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." The temperature at which participants pressed the button to indicate they could ''no longer feel able to tolerate the pain" is reported.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess HPTO, heat stimuli were delivered to the participant's arm or 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." The temperature at which participants pressed the button to indicate they could ''no longer feel able to tolerate the pain" is reported.

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), punctate mechanical pain (PMP), 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 medial knee, lateral knee, or trapezius. Participants were asked to notify the experimenter when the pressure sensation ''first becomes painful." The pressure at which participants pressed the button to indicate that the pressure sensation ''first becomes painful" is reported.

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), punctate mechanical pain (PMP), 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 medial knee, lateral knee, or trapezius. Participants were asked to notify the experimenter when the pressure sensation ''first becomes painful." The pressure at which participants pressed the button to indicate that the pressure sensation ''first becomes painful" is reported.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess PMP, punctate mechanical pain is delivered to the patella or hand by a calibrated nylon monofilament for 10 contacts of the monofilament at one contact per second. Participants rate the pain intensity on a scale from 0 (no pain) to 100 (maximum imaginable pain).

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

To assess PMP, punctate mechanical pain is delivered to the patella or hand by a calibrated nylon monofilament for 10 contacts of the monofilament at one contact per second. Participants rate the pain intensity on a scale from 0 (no pain) to 100 (maximum imaginable pain).

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

CPM is reported as the change in PPT before and immediately following immersion of the contralateral hand up to the wrist in a cold water bath (12 degrees Celsius) for up to 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." The pressure at which participants pressed the button to indicate that the pressure sensation ''first becomes painful" is reported.

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), punctate mechanical pain (PMP), and Conditioned Pain Modulation (CPM).

CPM is reported as the change in PPT before and immediately following immersion of the contralateral hand up to the wrist in a cold water bath (12 degrees Celsius) for up to 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." The pressure at which participants pressed the button to indicate that the pressure sensation ''first becomes painful" is reported.

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.

Data will be collected on participants' tDCS experience at the conclusion of tDCS treatment on a scale of 0 (strongly disagree) to 10 (strongly agree): Q1) "Overall the device was easy to use"

Data will be collected on participants' tDCS experience at the conclusion of tDCS treatment on a scale of 0 (strongly disagree) to 10 (strongly agree): Q2) "It was easy to prepare the device and accessories"

Data will be collected on participants' tDCS experience at the conclusion of tDCS treatment on a scale of 0 (strongly disagree) to 10 (strongly agree): Q3) "The effectiveness of the treatment increased over the course of treatment."

The participants will be asked in an open-ended manner whether they have experienced any side effects, and they will then be asked specifically about tingling, itching sensation, burning sensation, pain at the stimulation site, fatigue, nervousness, headache, difficulty concentrating, mood change, and changes in vision or visual perception.

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.

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.

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.

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.

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.

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.