Experimental Pain Differentially Affects Cortical Involvement In Force And Position Control Tasks

• ¹ The University of Queensland, School of Biomedical Sciences, Australia
• ² The University of Queensland, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health , Australia
• ³ The University of Queensland, Centre for Neuromodulation, Australia
• ⁴ The University of Queensland, School of Health and Rehabilitation Sciences, Australia
• ⁵ Macquarie University, Department of Cognitive Science, ARC Centre of Excellence for Cognition and its Disorders, Australia
• ⁶ The University of Queensland, Centre for Clinical Research, Royal Brisbane & Women’s Hospital, Australia

Background: Voluntary and postural motor tasks differs in several respects, including the involvement of motor cortex output. They also differ in how they are affected by pain, which might be explained by different origins of motor output. Coherence between activities of spatially distributed motor system components enables study of communication between brain regions - cortico-cortical coherence (CCC, between electroencephalography [EEG] at different brain sites) and between the cortex (EEG) and muscles (electromyography, EMG) - corticomuscular coherence (CMC). We aimed to study whether EEG power, CCC and CMC differ in tasks matched by load, but performed with the objective to voluntarily match a force (force-control) or maintain postural alignment against an external load (position-control); and whether the effect of pain on coherence differed between tasks. Methods: Subjects (N=17) performed position- and force-control isometric knee extension in non-pain and pain states. Load (46±14 N) was matched between contractions. Hypertonic saline injection induced pain (~4/10) in the knee fat pad. A 128-channel sensor net was used for EEG. CCC was calculated between 14 electrodes (over superior parietal, sensorimotor, premotor and prefrontal cortex areas on both sides). Right knee extensor EMG was recorded. CMC was calculated between 4 left motor cortex EEG electrodes and right knee EMG. Changes in EEG power, EMG and task performance (variability of target force/knee angle) with pain were also calculated. Results: CCC (beta and gamma frequency bands) increased during pain in both tasks, but by a greater amount during force-control (P<0.05). Beta band CMC and EEG power decreased, and gamma band EEG power and force fluctuations increased during pain only during force-control (P<0.01). Conclusion: The results support observations that pain more subtly effects motor output in postural tasks, which might be explained by lesser contribution of cortical drive during these tasks.