Claire Bradley from the Neuroapin team (CRNL) will present her final thesis work:
The first steps of cortical somatosensory and nociceptive processing in humans: anatomical generators, functional plasticity, contribution to sensory memory and modulation by cortical stimulation.
The somatosensory system participates in both non-nociceptive and nociceptive information processing, implicating common cortical areas, such as primary somatosensory and operculo-insular cortex. Important distinctions can however be drawn between the two networks’ functional organisation. In this thesis work, we model and characterise the electrical activity of the operculo-insular cortex within non-painful and nociceptive networks, using non-invasive electrophysiological recordings in humans. By using repeated stimuli, we were able to evaluate the pathway’s excitability and to examine the modalities of appearance of a very basic form of sensory memory. Validity of the modelled response to a nociceptive stimulus was evaluated by comparing it to intra-cranial recordings in epileptic patients, revealing excellent concordance. We went on to use this model to determine whether a technique of non-invasive cortical stimulation currently used to relieve neuropathic pain (motor cortex magnetic stimulation) was able to modulate acute nociceptive processing in healthy participants. We show that this intervention is not more efficacious than placebo stimulation in blocking nociception, be it at the level of conscious perception or of neuronal processing. This raises questions regarding the mechanisms of action of this technique in patients, which might implicate a modulation of pain perception at a higher level of processing. Finally, we attempted to stimulate the operculo-insular cortex directly, using three different methods. Low-frequency intra-cortical stimulation in epileptic patients revealed a decreased neuronal response at the site of stimulation, along with more labile modulations at distant sites. Subjective perception was however not systematically or consistently altered. Transcranial magnetic stimulation (TMS) of the same region in healthy participants was attempted and abandoned, due to strong unpleasantness. On the contrary, multi-polar transcranial electrical stimulation (tDCS) was very well tolerated and allowed modulation of a strong engaging pain experience, with cathodal stimulation leading to an increased pain perception. Altogether, the studies presented here show how a non-invasive approach in humans allows characterising and modulating the activity of the operculo-insular cortex. While this region might be an interesting target for future treatment of drug-resistant pain, its stimulation in patients would require further investigation of parameters and procedures.
Neurological Hospital - Amphitheater - 6th floor