# Tell me what to expect: how instructions affect the pain response of patients with chronic myofascial pain with referral

## TL;DR

This study shows that expectations about pain influence how people with chronic jaw pain and healthy individuals experience and respond to pain.

## Contribution

The study demonstrates how pain expectations modulate cognitive and physiological responses differently in chronic pain patients versus healthy individuals.

## Key findings

- Pupillary diameter increased more in pain expectation conditions for both groups.
- TMD patients showed higher anxiety, somatization, and pain scores than controls.
- Pain expectations affected cognitive pain ratings in controls but not in TMD patients.

## Abstract

The aims of the study are to analyze the influence of pain and no pain
expectations on the physiological (electromyography (EMG) and pupillometry) and
cognitive (Numerical Rating Scale (NRS)) response to pain. Pain
expectation and no pain expectation situations were induced by employing
instructional videos. The induction of pain was performed by palpating the
masseter with an algometer in a sample of 2 groups: 30 healthy participants
(control group) and 30 patients (Temporomandibular disorders (TMD) group) with
chronic myofascial pain with referral in the masseter muscle (Diagnostic Criteria
for Temporomandibular Dissorders (DC/TMD)). Used a mixed design all participants
were exposed to pain and no pain conditions in the same session, but the order of
the presentation was counterbalanced across participants to control its possible
influence. A significantly larger pupillary diameter was observed in the pain
expectation relative to the no pain expectation condition in both groups. The TMD
group presented larger EMG activity and larger scores in anxiety, somatization,
catastrophizing and central sensitization than the control group. In the NRS, the
TMD group also showed a significantly higher score than the control group. The
TMD group presented similar NRS scores in the expectation condition compared to
the no pain expectation condition, while the control group presented higher
scores for pain expectation than for no pain expectation. Pain expectation
modulated the pain cognitive pain assessment and pupil diameter in controls. The
cognitive pain assessment was altered in the TMD group compared to the control
group, particularly in the no pain expectation condition, this may be due to a
negative reappraisal of pain due to past experiences, as pointed out by the
observed level of catastrophizing. Pain expectations did not influence the EMG,
significantly higher EMG activity was found in the TMD group compared to the
control group regardless of expectation type.