La contribution de l’insula au traitement de l’information : apports de l’EEG intracrânien et de l’évaluation comportementale

The role of the insular cortex in information processing has long been considered enigmatic, partly due to its deep location in the brain. However, the advent of direct electrocortical stimulation and neuroimaging approaches have shed light on its involvement in multiple of neuropsychological functions. An increasing number of studies suggest that the insular cortex plays a crucial role in processing the physical characteristics of sensory stimuli, as well as in the processing of salient information. Current theories argue that the insula would be a critical structure in the “salience network” and involved in sensory, emotional and attentional processes. However, the specific contribution of the insular cortex remains unknown, notably due to the intrinsic limitations of conventional approaches and the very low prevalence of lesions restricted to the insula, especially as little clinical evidence support these findings. Furthermore, although insular resections are becoming more frequent, the neuropsychological effects of this surgery remain unclear. Thus, the studies that make up this thesis aim to improve our understanding of the role played by the insula in the salient information processing and the neuropsychological consequences of the insular resections on sensory, emotional and attentional functions. The first two studies of this thesis assess the respective contributions of the anterior and posterior insular portions in attentional processing towards salient and relevant sensory information. The insular responses during visual and auditory oddball attentional tasks are recorded by means of intracranial EEG (iEEG) in epileptic patients undergoing invasive iEEG, with electrode contacts implanted in the insula as part of a pre-surgical evaluation of their drug-resistant seizures. The results suggest that the anterior insula participates in voluntary attentional processing around 300-500 ms following the presentation of task-relevant stimuli in both visual and auditory modality, whereas the posterior portion is involved in automatic processing occurring about 100 ms after auditory stimuli presentation, independent of task-relevant information. The next two studies examine the neuropsychological consequences of insular cortex resections on the sensory and affectivo-attentional processes, in drug-refractory epileptic patients who have undergone unilateral resection of this structure. Their performance in a revised Dot-Probe task and an emotional Stroop test, as well as their responses in a questionnaire assessing sensory behavioral patterns, were compared to a group of patients who had surgery for temporal lobe epilepsy and a group of healthy control. The results highlight alterations in sensory processing and emotional interference control following insular epilepsy surgery. In sum, the neurophysiological and behavioral data in this thesis contribute to a better understanding of the specific role of the insula in the processing of sensory, salient, emotional and attentional information. Moreover, these findings highlight the need to further develop neuropsychological tests in order to better identify functional disturbances associated with insular epilepsy and insular resection surgery.

Keyphrases: Insula, Oddball, Dot-Probe, Salience network, Attentional processing, Emotions, Interference, Intracranial EEG, Epilepsy, Emotional Stroop