Perturbational complexity of cortical responses to thermal pain

Abstract

While painful and non-painful thermal stimuli elicit a rich dynamical pattern of brain activity, canonical event related potentials (ERP) analyses quantify only limited aspects of this pattern. In this study, we complement the conventional ERP approach by quantifying the spatial and temporal differentiation of EEG responses to thermal stimulation using the perturbational complexity index (PCI), a complexity metric grounded in systems dynamic and information theory. Using two publicly available datasets, we computed state-transition PCI from thermal-evoked responses recorded over 32-64 scalp channels. Dataset 1 combined three stimulus intensities (10 {degrees}C, 42 {degrees}C, 60 {degrees}C) with topical application of thermosensitive TRP-channel agonists (menthol 20 %, capsaicin 1 %) or vehicle; Dataset 2 manipulated the block-wise transition probability of receiving cold ({approx} 15 {degrees}C) or hot ({approx} 58 {degrees}C) stimulation. PCI scaled non-linearly with temperature, being lowest at the intermediate 42 {degrees}C and highest at the cold and hot extremes (Datasets 1 and 2). PCI was sensitive both to peripheral sensitisation, as topical menthol and capsaicin selectively reduced PCI during cold stimulation (Dataset 1), and to changes in block-wise stimulus probability (Dataset 2). Across all analyses, canonical ERP peak measures (N2-P2 amplitude/latency) failed to account for PCI variance. These findings demonstrate that PCI reflects the brains response to exogenous, sensory-driven thermal perturbations, quantifying changes in neural complexity associated with both stimulus intensity, peripheral sensitisation and probabilistic manipulations. This supports its applicability as a measure of temporal and spatial differentiation in EEG responses relevant to pain neuroscience. SummaryThis study quantified the spatio-temporal complexity of electroencephalographic responses to thermal and pain stimuli. Complexity was sensitive to simulation temperature, chemical sensitization and probabilistic manipulations.