Table 1 -.

Assessments

Tool	Brief description
Primary outcome
Acceptability and feasibility measures scale	The scale consists of a self-assessed 5-point Likert format from 1 (Completely disagree) to 5 (Completely agree) assessing subject perceptions about the intervention (Weiner et al., 2017).
Secondary outcomes
Demographic data	This survey will age, gender, sex, race, ethnicity, education level, hand dominance, weight, height, and body mass index.
Medical history form	History of medical conditions, a list of medications currently using, allergies, history of hospitalizations or visits to an emergency room in the last year, tobacco and alcohol consumption, and emergency and primary care physician contact.
Visual Analogue Scale (VAS) for PLP	Subjects will rate their pain from 0 – indicating no pain at all, to 10 – indicating the worst pain felt. This scale is also colored, from green (at 0) to red (at 10), as a visual indicator of pain (Bolognini et al., 2013; Brodie et al., 2007; Moseley, 2006).
Visual Analogue Scale (VAS) for Residual limb pain	Any painful sensation in the stump. Subjects will rate their residual limb pain from 0 – indicating no pain at all, to 10 – indicating the worst pain felt. The scale will include colors to help in identifying the correct response (Bolognini et al., 2013).
Visual Analog Scale (VAS) for Phantom Limb Sensation	All non-painful sensations in the amputated part of the limb. Subjects will be presented with a scale starting at 0- No phantom limb sensation, to 10 – Full sensation of the amputated limb. The scale will include colors to help in identifying the correct response (Bolognini et al., 2013).
Visual Analog Scale (VAS) for Phantom Limb telescoping	Refers to the shrinking and retraction of the phantom towards the residual limb. Subjects will be presented with a scale starting at 0 - indicated that the phantom was enlarged, and 10 meant that the phantom was completely retracted into the stump, the scale will include colors to help in identifying the correct response (Bolognini et al., 2013).
Adapted Groningen Questionnaire after Arm Amputation	This questionnaire will be applied to obtain information concerning complaints that may be developed after arm amputation (Kooijman et al., 2000).
Adapted Groningen Questionnaire after Leg Amputation	This questionnaire is originally meant to obtain information concerning complaints that may be developed after arm amputation. We adapted the current arm version for lower limb amputation (Kooijman et al., 2000).
Prosthesis use questionnaire	This survey will ask for details related to the prosthesis use, including prosthesis use start date, stage of prosthesis training, use duration, usage per day, walking activity with prosthesis per day, use interruption, and prosthesis ownership.
Brief Pain Inventory (BPI) – short form	Short self-assessment questionnaire that provides information on various dimensions of pain including how pain developed, the types of pain a patient experiences, time of day pain is experienced, as well as current ways of alleviating pain (Cleeland & Ryan, 1994). It also includes the VAS Pain scale, a simple 10- point scale (0 = “no pain”, 10 = “pain as bad as you can imagine”) (Fregni et al., 2006).
Central sensitization inventory	This scale assesses symptoms that are related to central sensitization. It includes two parts: A. 25 common symptoms. B. previous diagnosis of central sensitivity syndromes (CSS) such as fibromyalgia, neck injury, temporomandibular joint disorder or migraine/tension headaches, anxiety, and depression (Neblett, 2018).
Pain and medication diary	Subjects will be asked to record the number of phantom limb episodes daily, using a pain diary. They will record the intensity of the strongest episode as well as phantom limb sensation and residual limb pain on a colored visual analog scale included in the diary, where 0 represents no pain at all and 10 represents the highest pain the patient has ever felt. Moreover, subjects will record their current medications and dosages daily in a pain medication diary, until the completion of the study. We will calculate a pain medication index to standardize the assessment (Harden et al., 2005).
Beck Depression Inventory	This self-report inventory consists of 21 multiple-choice questions and is a widely used method to classify depression severity. It assesses for the presence of several symptoms related to depression, such as irritability, hopelessness, and decreased cognitive performance. Physical symptoms such as weight loss and fatigue are also included (Santos Portilla et al., 2013; Villamar et al., 2013).
Beck Anxiety Inventory	This self-report inventory consists of 21 multiple-choice questions about how the subject has been feeling in the last week, expressed as common symptoms of anxiety (such as numbness and tingling, sweating not due to heat, and fear of the worst happening) (Beck et al., 1988).
Pain catastrophizing scale (PCS)	Pain catastrophizing is characterized by the tendency to magnify the threat value of a pain stimulus and to feel helpless in the presence of pain, as well as by a relative inability to prevent or inhibit pain-related thoughts in anticipation of, during, or following a painful event (Quartana et al., 2009). It affects how individuals experience pain, including three main characteristics: rumination, magnification, and helplessness (Vase et al., 2012; Vase et al., 2011).
The behavioral inhibition system (BIS)/ behavioral activation system (BAS) Scale	This scale is a 24-item self-report questionnaire designed to measure two motivational systems: the BIS (motivation to avoid aversive outcomes) and BAS (motivation to approach goal-oriented outcomes). Participants respond to each item using a 4-point Likert scale: 1 (very true for me), 2 (somewhat true for me), 3 (somewhat false for me), and 4 (very false for me). The scale has four subscales that were derived via factor analysis. One subscale corresponds to the BIS. Seven items contribute to this score (e.g., “Criticism or scolding hurts me quite a bit”). The remaining three subscales correspond to three components of BAS. BAS Drive measures the motivation to follow one’s goals. Four items contribute to this score. BAS Reward Responsiveness measures the sensitivity to pleasant reinforcers in the environment. Four items contribute to this score. BAS Fun Seeking measures the motivation to find novel rewards spontaneously. Five items contribute to this score (Carver & White, 1994).
Expectation for treatment scale (ETS)	The ETS is a well-validated and brief five-item scale for measuring patient expectations, with excellent test-retest properties (Barth et al., 2019).
Montreal Cognitive Assessment (MOCA)	This is a sensitive, valid, and reliable 30-point questionnaire that is used extensively in clinical and research settings to measure cognitive impairment. This instrument will be used as a brief screening of cognitive abilities. It will be used as a baseline evaluation (Freitas et al., 2012).
Pittsburgh Sleep Quality Index (PSQI)	A self-report measure of the quality and patterns of sleep in adults. It assesses 7 components of sleep quality: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medications, and daytime dysfunction over the last month. Scoring of the answers is based on a Likert scale from “0” (not during the past month) to “3” (3 or more times a week). A total sum of “5” or greater indicates a “poor” sleeper (Buysse et al., 1989).
Short version of SF-36	The short version of the SF-36 health survey is used as a measurement of quality of life. It provides a profile of functional health and well-being scores. It is also used as a psychometrical index of physical and mental health (Aldington et al., 2014; Rahimi et al., 2012; Sinha et al., 2014; Ware Jr et al., 1998).
Side Effects Questionnaire for tDCS	At each stimulation session, subjects will complete a questionnaire to evaluate potential adverse effects of tDCS (tingling, burning sensation, headache, neck pain, mood alterations) on a 4-point scale (None, mild, moderate, and severe). If any side effects are reported, the degree of relatedness to the intervention will be assessed on a 5-point scale (Villamar et al., 2013).