Issue |
Med Sci (Paris)
Volume 27, Number 1, Janvier 2011
Imagerie et cognition
|
|
---|---|---|
Page(s) | 82 - 87 | |
Section | M/S revues | |
DOI | https://doi.org/10.1051/medsci/201127182 | |
Published online | 10 February 2011 |
Imagerie fonctionnelle cérébrale appliquée à l’analyse des phénomènes douloureux
Imagerie et cognition (2)
Functionnal brain mapping of pain perception
1 Département de neurologie et Centre de la douleur, CHU, F-42055 Saint-Étienne ; Inserm U879, UCBL Lyon 1, UJM Saint-Étienne, F-42023 Saint-Étienne, France
2 Centre mémoire de ressources et de recherche, Inserm U879, CHU, 42055 Saint-Étienne, France
*
roland.peyron@univ-st-etienne.fr
Ce travail reprend les données d’imagerie fonctionnelle cérébrale appliquée à l’étude des phénomènes douloureux chez l’homme. Contre tous les préjugés qui auraient volontiers désigné le thalamus, l’aire somato-sensorielle primaire SI ou le cortex cingulaire antérieur comme des sites principaux d’intégration de la douleur chez l’homme, les phénomènes physiologiques nociceptifs concernent avant tout et de manière constante les aires somato-sensorielles secondaires et insulaires. L’enregistrement de potentiels évoqués à des stimulations laser par le biais d’électrodes implantées directement dans ces aires, mais aussi la stimulation directe de ces aires, qui induit des sensations douloureuses, sont des arguments très forts désignant ces aires comme des sites majeurs pour l’intégration de l’aspect sensoriel de la douleur et de son intensité. De même, les techniques d’imagerie fonctionnelle ont permis d’identifier le recrutement de réponses anormales, excessives, en cas de douleurs neuropathiques chroniques, en particulier dans les aires insulaires et SII, et ce de façon bilatérale. À l’inverse, les processus permettant de soulager ces douleurs impliquent l’activation des structures préfrontales médiales et cingulaires rostrales, qui fait intervenir un système inhibiteur descendant passant par la substance grise péri-acqueducale (SGPA). Les opioïdes endogènes pourraient être impliqués dans ce système inhibiteur.
Abstract
In this review, we summarize the contribution of functional imaging to the question of nociception in humans. In the beginning of the 90’s, brain areas supposed to be involved in physiological pain processes were almost exclusively the primary somatosensory area (SI), thalamus, and anterior cingulate cortex. In spite of these a priori hypotheses, the first imaging studies revealed that the main brain areas and those providing the most consistent activations in pain conditions were the insular and the SII cortices, bilaterally. This has been confirmed with other techniques such as intracerebral recordings of evoked potentials after nociceptive stimulations with laser showing a consistent response in the operculo-insular area which amplitude correlates with pain intensity. In spite of electrode implantations in other areas of the brain, only rare and inconsistent responses have been found outside the operculo-insular cortices. With electrical stimulation delivered directly in the brain, it has also been shown that stimulation in this area only - and not in other brain areas - was able to elicit a painful sensation. Thus, over the last 15 years, the operculo-insular cortex has been re-discovered as a main area of pain integration, mainly in its sensory and intensity aspects. In neuropathic pain also, these areas have been demonstrated as being abnormally recruited, bilaterally, in response to innocuous stimuli. These results suggest that plastic changes may occur in brain areas that were pre-defined for generating pain sensations. Conversely, when the brain activations concomitant to pain relief is taken into account, a large number of studies pointed out medial prefrontal and rostral cingulate areas as being associated with pain controls. Interestingly, these activations may correlate with the magnitude of pain relief, with the activation of the PAG, and, at least in some instances, with the involvement of endogenous opioids.
© 2011 médecine/sciences – Inserm / SRMS
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