Sensory-evoked perturbational complexity in human EEG: Effects of stimulus temperature and peripheral sensitisation in nociceptive processing

The perturbational complexity index (PCI), grounded in systems dynamic and information theory, quantifies the brain’s capacity for differentiation and integration of neural activity. While it has been used to characterise consciousness states following transcranial magnetic stimulation, its responsiveness to sensory perturbations remains underexplored. Here, 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 °C, 42 °C, 60 °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 (≈ 15 °C) or hot (≈ 58 °C) stimulation. PCI scaled non-linearly with temperature, being lowest at the intermediate 42 °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, classical ERP peak measures (N2–P2 amplitude/latency) failed to explain PCI variance. These findings demonstrate that sensory-evoked PCI reflects the brain’s response to exogenous, sensory-driven perturbations, quantifying changes in neural complexity associated with both stimulus intensity, peripheral sensitisation and probabilistic manipulations. This supports its broader applicability as a measure of temporal and spatial differentiation in the domain of sensory and pain neuroscience.