Dynamics of the perception and EEG signals triggered by tonic warm and cool stimulation

Abstract

Thermosensation is crucial for humans to probe the environment and detect threats arising from noxious heat or cold. Over the last years, EEG frequency-tagging using long-lasting periodic radiant heat stimulation has been proposed as a means to study the cortical processes underlying tonic heat perception. This approach is based on the notion that periodic modulation of a sustained stimulus can elicit synchronized periodic activity in the neuronal populations responding to the stimulus, known as a steady-state response (SSR). In this paper, we extend this approach using a contact thermode to generate both heat-and coldevoked SSRs. Furthermore, we characterize the temporal dynamics of the elicited responses, relate these dynamics to perception, and assess the effects of displacing the stimulated skin surface to gain insight on the heat-and cold-sensitive afferents conveying these responses. Two experiments were conducted in healthy volunteers. In both experiments, noxious heat and innocuous cool stimuli were applied during 75 seconds to the forearm using a Peltier-based contact thermode, with intensities varying sinusoidally at 0.2 Hz. Displacement of the thermal stimulation on the skin surface was achieved by independently controlling the Peltier elements of the thermal probe. Continuous intensity ratings to sustained heat and cold stimulation were obtained in the first experiment with 14 subjects, and the EEG was recorded in the second experiment on 15 subjects. Both contact heat and cool stimulation elicited periodic EEG responses and percepts. Compared to heat stimulation, the responses to cool stimulation had a lower magnitude and shorter latency. All responses tended to habituate along time, and this response attenuation was most pronounced for cool compared to warm stimulation, and for stimulation delivered using a fixed surface compared to a variable surface.

Human cold habituation: Physiology, timeline, and modifiers

“…Cold habituation itself involves several factors, as previously mentioned, all with varying timelines of adaptation. Habituation of cold sensation appears to be the first to occur, typically showing reduced ratings after the 1 st or 2 nd exposure [85,[107][108][109].…”

Distinct spatio-temporal and spectral brain patterns for different thermal stimuli perception

“…Similarly, such stimuli perception and processing are likely to be harbored in different regions in the brain 6 , 8 . En route to analyzing and unraveling the underlying processes within the human body that can lead to the unpleasant sensation perception, understanding intense thermal sensation, in particular, has recently gained momentum 9 – 11 . Neuroscientists have been relying on various neuroimaging techniques, including functional magnetic resonance imaging (fMRI) 12 , Positron emission tomography (PET) 13 , and invasive recordings 14 , to investigate exogenous pain processing.…”

“…Kwan et al 12 investigated in their study using fMRI the ACC’s role in sensory, motor, and cognitive functions when perceiving four thermal stimuli categorized into innocuous (cool, warm) and noxious conditions (cold, hot). However, the correlation between EEG evoked changes and different nociceptive thermal stimuli have been minimally studied 11 , 15 . Overall, EEG offers a better temporal resolution and has not been extensively studied in this context.…”

“…Overall, EEG offers a better temporal resolution and has not been extensively studied in this context. In the study by Mulders et al 11 , noxious heat and innocuous cool stimuli were applied to the forearm of healthy subjects. Particularly, they focused on both heat- and cold-evoked steady-state response.…”

Nociceptive Intra-epidermal Electric Stimulation Evokes Steady-State Responses in the Secondary Somatosensory Cortex

“…A seminal study by Mouraux et al used this approach to study pain processing by stimulating participants with blocks of nociceptive laser pulses with the hypothesis that the SSEPs elicited by this rapid thermal stimulation would result in “the activation of a network that is preferentially involved in processing nociceptive input” (Mouraux et al 2011 ). Later studies showed that it is also possible to record such a nociceptive SSEP in response to blocks of intra-epidermal electric pulses (Colon et al 2012 ) and sinusoidal ultra-slow temperature modulation of the skin (Colon et al 2017 ; Mulders et al 2020 ).…”