Background & Aims
Phantom limb pain (PLP) describes pain in a missing limb which occurs in up to 80% of individuals after amputation. The mechanisms underlying PLP remain unclear, but are believed to be a combination of multiple factors including peripheral changes, psychological factors and cortical reorganization. Brain oscillations of specific frequencies may be associated with the experience of pain, yet the causality of neural circuits in relation to PLP is not well understood. In the current study, we aimed to investigate the neural correlates and cortical oscillations of evoked (ongoing) PLP using electroencephalography (EEG). Our investigation focused on frequency ranges, including alpha (8-12Hz), beta (12-30Hz) and gamma (30-80Hz) in electrodes located above the somatosensory, motor and prefrontal cortices. EEG recordings and continuous pain ratings were carried out during evoked PLP.
Methods
We recruited a special group of amputees who could elicit phasic PLP by moving their phantom hand or leg (eight traumatic arm amputees and one traumatic leg amputee, normalized site of amputation is left). In a control condition, participants moved their phantom without eliciting PLP. During both conditions, a continuous pain rating on a visual analog scale was recorded using a trackball device. Oscillatory alpha, beta and gamma activities were recorded with a 64 channels EEG in the 10-20 system. To obtain time courses of brain activity in specific frequency ranges, EEG data were time-frequency transformed and fitted in a linear mixed model as well as OLS-regressions, taken each electrode from the regions of interest and frequency band as predictor and the individual pain rating as response variable. While considering a time lag between neurophysiological responses and behavioral pain ratings, cross correlations with time lags were computed.
Results
Activation related to evoked phantom limb pain could be located mainly to electrodes above the somatosensory cortex, demonstrating a lateralization effect with activation maxima contralateral to the site of amputation. Neurophysiological responses and behavioral pain ratings were significantly linked to each other with a time lag of one second, based on the cross-correlations (rmin= -.36 in the beta band at electrode C6, rmax=.28 in the gamma band at electrode CP4, p<.01). The results point to a role of beta-band activity (12-30Hz) as a predictor for the rated pain intensity of the evoked PLP on an individual level modeled by linear mixed models (tmax=9.13 at electrode C2, tmin= -5.31 at electrode C4, p<.01). Thereby we could observe a significant negative relationship between the intensities in the frequency bands as predictors and the rating as dependent variable in those participants, who showed a decrease of pain during the longitudinal recording.
Conclusions
The activity in the beta-band in association to the pain rating is in accordance with the literature, where it has been shown that beta-band oscillations in the prefrontal cortex are associated with contextual learning, which is highly relevant also for pain. These findings could further enhance our understanding of the underlying brain mechanisms involved in PLP. Larger sample sizes are needed to confirm and extend these findings. Based on the mechanistic, therapeutic treatment approaches modulating cortical oscillations such as transcranial alternating current stimulation, hold promise as innovative strategies for modulating and alleviating phantom limb pain.
References
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Presenting Author
Angela Serian
Poster Authors
Angela Serian
MSc
Central Institute of Mental Health Mannheim
Lead Author
Jamila Andoh
PhD
Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Germany
Lead Author
Simon Desch
Department of Experimental Psychology, Heinrich Heine University Düsseldorf, Germany
Lead Author
Michel-Pierre Coll
PhD
School of Psychology, Université Laval, Quebec City, Quebec, Canada
Lead Author
Mohsen Mosayebi-Samani
PhD
Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany
Lead Author
Hubert Neubauer
Dr. med.
BG Clinic Ludwigshafen Clinic for Hand, Plastic and Reconstructive Surgery - Severe Burn Injury Cent
Lead Author
Michael Nitsche
PhD
Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany
Lead Author
Mathieu Roy
Dept. of Psychology, McGill University, Montreal, Qc., Can., H3A 1G1
Lead Author
Herta Flor
Interdisciplinary Center for Clinical Trials, Johannes Gutenberg University Medical Center Mainz
Lead Author
Topics
- Pain Imaging