Implicit motor imagery performance is impaired in people with chronic, but not acute, neck pain

Background: People with chronic neck pain have impaired proprioception (i.e., sense of neck position). It is unclear whether this impairment involves disruptions to the proprioceptive representation in the brain, peripheral factors, or both. Implicit motor imagery tasks, namely left/right judgements of body parts, assess the integrity of the proprioceptive represention. Previous studies evaluating left/right neck judgements in people with neck pain are conflicting. We conducted a large online study to comprehensively address whether people with neck pain have altered implicit motor imagery performance. Methods: People with and without neck pain completed online left/right neck judgement tasks followed by a left/right hand judgement task (control). Participants judged whether the person in the image had their head rotated to their left or right side (neck task) or whether the image was of a left hand or a right hand (hand task). Participants were grouped on neck pain status (no pain; <3 months-acute; >= 3 months-chronic) and pain location (none, left-sided, right-sided, bilateral). Outcomes included accuracy (primary) and response time (RT; secondary). Our hypotheses-that (i) chronic neck pain is associated with disrupted performance for neck images and (ii) the disruption is dependent on the side of usual pain, were tested with separate ANOVAs. Results: A total of 1,404 participants were recruited: 105 reported acute neck pain and 161 reported chronic neck pain. When grouped on neck pain status, people with chronic neck pain were less accurate than people without neck pain (p = 0.001) for left/right neck judgements, but those with acute neck pain did not differ from those without neck pain (p = 0.14) or with chronic neck pain (p = 0.28). Accuracy of left/right hand judgements did not differ between groups (p = 0.58). RTs did not differ between groups for any comparison. When grouped on neck pain location, people were faster and more accurate at identifying right-turning neck images than left-turning neck images, regardless of history or location of pain (p < 0.001 for both); people with no pain were more accurate and faster than people with bilateral neck pain (p = 0.001, p = 0.015) and were faster than those with left-sided neck pain (p = 0.021); people with right-sided neck pain were more accurate than people with bilateral neck pain (p = 0.018). Lastly, there was a significant interaction between neck image and side of neck pain: people with right-sided neck pain were more accurate at identifying right-sided neck turning images than people with left-sided neck pain (p = 0.008), but no different for left-sided neck turning images (p = 0.62). Conclusions: There is evidence of impaired implicit motor imagery performance in people with chronic neck pain, which may suggest disruptions to proprioceptive representation of the neck. These disruptions seem specific to the neck (performance on hand images intact) but non-specific to the exact location of neck pain.