Abstract
Alongside the time-locked event-related potentials (ERPs), nociceptive somatosensory inputs can induce modulations of ongoing oscillations, appeared as event-related synchronization or desynchronization (ERS/ERD) in different frequency bands. These ERD/ERS activities are suggested to reflect various aspects of pain perception, including the representation, encoding, assessment, and integration of the nociceptive sensory inputs, as well as behavioral responses to pain, even the precise details of their roles remain unclear. Previous studies investigating the functional relevance of ERD/ERS activities in pain perception were normally done by assessing their latencies, frequencies, magnitudes, and scalp distributions, which would be then correlated with subjective pain perception or stimulus intensity. Nevertheless, these temporal, spectral, and spatial profiles of stimulus induced ERD/ERS could only partly reveal the dynamics of brain oscillatory activities. Indeed, additional parameters, including but not limited to, phase, neural generator, and cross frequency couplings, should be paid attention to comprehensively and systemically evaluate the dynamics of oscillatory activities associated with pain perception and behavior. This would be crucial in exploring the psychophysiological mechanisms of neural oscillation, and in understanding the neural functions of cortical oscillations involved in pain perception and behavior. Notably, some chronic pain (e.g., neurogenic pain and complex regional pain syndrome) patients are often associated with the occurrence of abnormal synchronized oscillatory brain activities, and selectively modulating cortical oscillatory activities has been showed to be a potential therapy strategy to relieve pain with the application of neurostimulation techniques, e.g., repeated transcranial magnetic stimulation (rTMS) and transcranial alternating current stimulation (tACS). Thus, the investigation of the oscillatory activities proceeding from phenomenology to function, opens new perspectives to address questions in human pain psychophysiology and pathophysiology, thereby promoting the establishment of rational therapeutic strategy.
Highlights
Pain, affecting the well beings of millions of individuals and imposing a severe financial burden upon our societies, is a major public healthcare problem
The progress in understanding of the neural representation of pain in humans is important for basic neuroscience research, and critical to develop effective strategies for the diagnosis and management of the pathological pain conditions. This constitutes the understandings of: (1) the physiological mechanisms of the nociceptive system in healthy populations, the cortical processes underlying the perception of pain and (2) the pathophysiological mechanisms of the nociceptive system in chronic pain patients, the peripheral and central mechanisms leading to chronic pain
With the evidences showing: (1) the potential relevance of cross-frequency coupling (CFC) for understanding psychophysiological and pathological brain functions (Canolty et al, 2006; Schlee et al, 2009; Canolty and Knight, 2010; López-Azcárate et al, 2010; Miskovic et al, 2011; de Hemptinne et al, 2013) and (2) nociceptive somatosensory stimuli induced modulations of oscillations in multiple frequency bands (Schulz et al, 2011; Zhang et al, 2012; Hu et al, 2015), we believe that the oscillatory activities in different frequency bands are functioning interactively within the cortical network, and CFCs involved in pain could provide complemented information for the establishment of the cortical oscillatory bases of pain perception
Summary
Pain, affecting the well beings of millions of individuals and imposing a severe financial burden upon our societies, is a major public healthcare problem. With the evidences showing: (1) the potential relevance of CFC for understanding psychophysiological and pathological brain functions (Canolty et al, 2006; Schlee et al, 2009; Canolty and Knight, 2010; López-Azcárate et al, 2010; Miskovic et al, 2011; de Hemptinne et al, 2013) and (2) nociceptive somatosensory stimuli induced modulations of oscillations in multiple frequency bands (Schulz et al, 2011; Zhang et al, 2012; Hu et al, 2015), we believe that the oscillatory activities in different frequency bands are functioning interactively within the cortical network, and CFCs involved in pain could provide complemented information for the establishment of the cortical oscillatory bases of pain perception. With recent evidence showed that: (1) pain induced gamma oscillations over S1 covaried with objective stimulus intensity as well as subjective pain intensity (Gross et al, 2007); (2) the magnitudes of laser induced gamma band oscillations could always predict the subjective pain intensity regardless of the stimulus repetition when applying trains of three laser stimuli with constant 1 s interval (Zhang et al, 2012); and (3) tonic heat pain induced gamma oscillations could significantly predict subjective pain intensity (Peng et al, 2014; Schulz et al, 2015), we speculate that the gamma oscillation may be a candidate of the electrophysiological signatures reflecting nociceptive specific neural activities, even further investigation should be done
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