EEG Signal Coherence to Non-painful Thermal Stimuli

Peripheral neuropathies occur by injury to sensory afferent fibers. A common consequence of neuropathies is the loss of thermal sensitivity. In the clinic, there is a difficulty in quantifying and assessing damage to the thermal fibers (Aδ and C). Besides that, the identification of cerebral response to the stimulation of Aδ and C fibers is still a challenge, especially when it comes to the stimulation of non-painful cold and warm. Therefore, a signal processing technic—the Magnitude Squared Coherence (MSC)—allows to investigate the relationship between different electroencephalogram (EEG) frequency bands. The aim of this study was to investigate the cerebral response to non-painful thermal stimulation, in a steady-state stimulus, using coherence between hemispheres (inter-hemispheric coherence) and inside hemisphere (intra-hemispheric coherence). The peripheral thermal stimulation was performed in ten healthy male subjects, and the brain response was assessed by EEG. The contra-lateral intra-hemispheric coherence demonstrated a consistent statistical difference for cold stimuli for the gamma band in temporal lobe, compared to the spontaneous EEG. On the other hand, there was no difference for the warm stimuli.