Two Point Discrimination

STUDY DESIGN Prior to commencing this investigation, investigators will optimize the tactile discrimination threshold testing (i.e. as per baseline visit, below), and the training conditions, in up to ten participants (patients and/or healthy controls). This will serve as a pilot to refine operational aspects of study procedures before investigators commence the main investigation proposed herein. Following this, youth with either chronic pain (ages 10-17, n=40) or healthy youth (ages 10-17, n=20) will undergo assessments of two-point and single-point discrimination thresholds in an initial session (Aim 1). After this initial session, youth with chronic pain will participate in up to 9 additional sessions of attentional training (Aim 2). These chronic pain patients will be randomized to either two-point discrimination training (n=20) or a single-point spatially-directed attentional control condition (n=20). Participants will not be informed of which intervention they will receive (single-blind study). Psychological questionnaires will be completed in the first and last sessions in order to determine how these variables relate to tactile discrimination and response to training.

STUDY INTERVENTIONS 5.1 Two Point Discrimination Training: Two-point discrimination threshold (TPD) training may be performed 1) at spatial locations remote from pain, 2) at spatial locations adjacent to the region of pain, and/or 3) at spatial locations in the site of pain, if the participant will tolerate it. TPD is defined as the smallest distance between two points at which someone can recognize two points, and not one, touching their skin. As such this is a test of one's ability to identify separate stimulation of two discrete areas, and relies heavily on lateral inhibition. Highly precise mechanical calipers will be gently placed onto the skin and the distance between the prongs will be increased/decreased. After repeated decreases and increases in the distance between the prongs, the TPD will be deemed as the distance at which participants consistently report two points instead of one. One-point stimuli will be interleaved to serve as a control condition. Participants will be informed immediately of correct and incorrect responses as part of the discrimination training.

5.2 Control Stimulation: Participants will undergo a single-point discrimination training at the same sites as described above. Probes of different sizes will be used for this portion - a small diameter probe (~1-5 mm) and a large diameter probe (~6-50mm). The probes will be gently placed in contact with the participants' skin, and the participant will be instructed to respond if they were contacted with the small or large probe. Participants will be informed immediately of correct and incorrect responses as part of the discrimination training.

Inclusion criteria

Chronic Pain Patients:

• Somatically located chronic pain
• amplified musculoskeletal pain syndrome
• complex regional pain syndrome
• low back pain
• fibromyalgia
• other forms of chronic, widespread pain
• Male or female, 10-17 years
• High fluency in written and oral English language

Control Participants:

• Youth in good general health
• Male or female, 10-17 years
• High fluency in written and oral English language

Exclusion criteria

• Present significant mental health disorder as defined by DSM V (e.g. psychosis, bipolar disorder, major depression),
• alcohol or drug dependence
• documented developmental delays or impairments (e.g., autism, cerebral palsy, or mental retardation) of a magnitude that would interfere with adherence to study requirements or safe participation in the study
• Primary complaint of migraine or visceral (abdominal) pain, with minimal somatic involvement.