Two Point Discrimination

Overview

SPECIFIC AIMS Pain in both youth and adults is a complex, subjective and personal experience, and remains poorly understood. One particularly perplexing dimension of some forms of pain is the tendency of pain to spread outside of an affected body site to adjacent location, and then to unaffected body sites. Such widespread pain may reflect an altered spatial tuning of somatosensory processing, such that lateral inhibition is diminished, thereby allowing pain to spread. To date, no therapies exist which are designed specifically to diminish or even reverse the spatial spread of pain. However, training in two-point discrimination holds the potential to retune spatial aspects of somatosensory processing and may represent a novel therapy for widespread pain. Thus, the present investigation will test the following aims: Aim 1. Do youth with chronic pain have disrupted spatial tuning of somatosensory processing? Deficits in two point tactile discrimination have long been noted in adults with chronic pain, but such deficits remain poorly documented in pediatric chronic pain patients. In order to determine if such deficits exist, youth with both chronic pain and healthy youth will undergo assessment of two point discrimination thresholds. Aim 2. Does two-point discrimination training result in diminished pain and disability in youth with somatic pain? After initial characterization of tactile discrimination thresholds, youth with chronic pain will participate in multiple sessions of either two-point discrimination training or a single-point spatially-directed attentional control condition. Training will involve up to 9 additional sessions. Efficacy of training will be assessed by 1) reductions in the spatial extent of pain, 2) reductions in pain intensity and unpleasantness, and 3) reductions in pain-related disability.

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.