Neurophysiological correlates of tonic and chronic pain
Pain is a complex and highly subjective experience which subserves vital protective functions. However, in chronic pain states, pain does no longer subserve protective functions but represents a pathological condition with devastating effects on quality of life. About a fifth of an average population in the developed world suffers from chronic pain and treatment of these patients is often unsatisfactory. Recent evidence suggests that the brain plays an active role in the development of chronic pain. However, evidence on the brain mechanisms of pain largely originates from experimental studies using brief painful stimuli. Whether and how these findings translate to the main clinical problem of tonic and chronic pain is largely unknown yet. The proposed project will address this question by directly relating tonic and chronic pain to brain activity recorded by electroencephalography (EEG).
Brain network correlates of tonic and chronic pain
The project builds upon the paradigms and analyses of the previous project and extends our approach from the assessment of pain-related brain activity to the comprehensive investigation of brain connectivity, i.e., how communication in the human brain relates to ongoing pain. In patients suffering from chronic back pain and healthy human subjects, we will assess neuronal communication using recent brain connectivity measures, which overcome field spread and volume conduction limitations of traditional EEG analyses. Based on these connectivity measures we will perform timely graph theory-based network analyses of brain connectivity during ongoing tonic and chronic pain. A thorough clinical and psychological assessment will allow for relating network measures of brain connectivity to an individual’s clinical and psychological characteristics. Based on our previous findings, we hypothesize that the current intensity of ongoing experimental and clinical pain is reflected by local gamma oscillations in medial prefrontal cortex, which represents an important node in a brain network connecting at beta and/or theta frequencies. We further hypothesize that chronic pain is associated with additional global changes of brain connectivity, e.g., a reduction in small-worldness. We expect that these global network changes reflect the patient’s long-term pain-related disability rather than the current pain intensity and are therefore not observed in healthy controls. In a further step, we will use multivariate pattern analysis to test whether patterns of brain connectivity can be used to decode ongoing pain. This approach could help to establish neuronal markers of chronic pain, which might support the diagnosis and classification of chronic pain and the monitoring and optimization of pain therapy. The project, thus, promises novel insights into the brain mechanisms of pain with possible implications for the diagnosis and treatment of chronic pain.
Neurophysiological mediators of perceptual, motor and autonomic components of pain
Pain is commonly conceptualized as a perceptual phenomenon. However, the crucial protective function of pain not only depends on its perceptual component but also on appropriate motor and autonomic responses. However, how the brain translates noxious stimuli into motor and autonomic responses is far less well studied and understood than its perceptual aspects. The proposed project will comprehensively investigate how the brain translates painful stimuli into perceptual, motor and autonomic aspects of pain. We will perform a series of experiments to assess perceptual, motor and autonomic responses to painful stimuli. Brain activity will be assessed by state-of-the-art time-frequency analyses of electroencephalographic recordings. To determine which spatial-temporal-spectral features of brain activity underlie the different pain components, mediation analyses will be performed. The analysis will yield comprehensive spatial-temporal-spectral maps of brain activity translating stimulus characteristics into perceptual, motor and autonomic components of pain. The comparison of these maps will reveal component-specific and component-independent aspects of brain activity related to brief and longer-lasting pain. The results of these analyses promise to advance our understanding of the brain processes underlying different components of pain on different time scales. Understanding these processes in healthy human subjects is an important basis for studying these processes and their changes in chronic pain patients.
The projects are supported by the Deutsche Forschungsgemeinschaft and performed in collaboration with Prof. Joachim Gross from the University of Glasgow.