EEG FREQUENCY-TAGGING TO DETERMINE WHETHER THE CORTICAL PROCESSING OF NOCICEPTIVE AND NON-NOCICEPTIVE SOMATOSENSORY INPUT INVOLVES DISTINCT NEURONAL POPULATIONS.

Colon, Elisabeth [UCL] Legrain, Valéry [UCL] Mouraux, André [UCL]

Whether the cortical processing of nociceptive input relies on the activity of nociceptive-specific neurons or whether it relies on the activity of non-specific neuronal populations remains a matter of intense debate. Here, we address this question using EEG “frequency-tagging” of steady-state evoked potentials (SS-EPs) combined with an intermodal selective attention paradigm to test whether the cortical processing of nociceptive input relies on nociceptive-specific neuronal populations which can be selectively modulated by top-down attention. Specifically, we hypothesized that if the cortical processing of nociceptive and non-nociceptive sensory inputs involves distinct neuronal populations, selective attention would selectively enhance the SS-EPs elicited by the attended stream of sensory input. Conversely, if the cortical processing of the two sensory inputs involves the same neuronal populations, selective attention would indistinctly enhance the responses elicited by the attended and unattended streams of sensory input. Trains of nociceptive and vibrotactile stimuli (experiment 1) and trains of nociceptive and visual stimuli (experiment 2) were applied concomitantly to the same hand. A target detection task ensured that participants focused their attention on one of the two sensory modalities. We found that selectively attending to nociceptive or vibrotactile somatosensory input indistinctly enhanced nociceptive and vibrotactile somatosensory SS-EPs, whereas selectively attending to nociceptive or visual input independently enhanced the SS-EP elicited by the attended stream of sensory input. These results indicate that the processing of nociceptive input relies on neuronal populations that are also involved in processing tactile input, but distinct from the neuronal populations involved in processing visual input.