l'effet placebo

[Sterd]

car il existe AUSSI des cas d'effet placebo avérés, et dont les scientifiques n'ont pas le commencement du début d'une explication

Lesquels, tu as des documents ? des infos ?

C'est pénible de discuter avec quelqu'un qui affirme sans preuves. On arrive jamais à se dégager du niveau de la discussion de bistrot.

Sterd

 

Message(s) : 0

Inscription : 27 Nov 2005, 20:51

• Message privé

Haut

[Louis]

Je parle des effets placébo avéré dans le cas des

mécanismes immunitaires

cancers

maladie de parkinson

par exemple ! Cela dit quand j'affirme que "les scientifiques n'ont pas le commencement du début d'une explication", je veux dire "une explication scientifiquement prouvée" (parce qu'ils ont des "pistes")

Cela dit, il me semble dangereux de prétendre que le fait de ne pas avoir d'explications scientifiques a tel ou tel phénoméne engendrerais forcément la croyance en des phénoménes

qui agiraient de manière immaterielle et qui sortirait du champ de l'explication scientifique!

C'est justement une (et non la moindre) des valeurs positives de l'explication scientifique : quand on ne sait pas, en science, on ne peut pas "inventer" une preuve Quand on croit, on peut toujours trouver une explication....

On dirait (mais ce n'est peut etre qu'une impression) que chez certains, on est "malade" (de façon psychosomatique, donc) quand la science ne peut pas "tout" expliquer ! Mais le jour ou la science aura "tout" expliqué, on aura plus besoin d'elle !

[canardos]

Je parle des effets placébo avéré dans le cas des

mécanismes immunitaires

cancers

maladie de parkinson

par exemple ! Cela dit quand j'affirme que "les scientifiques n'ont pas le commencement du début d'une explication", je veux dire "une explication scientifiquement prouvée" (parce qu'ils ont des "pistes")

tu parles oui, mais encore, quelles experiences, dans quelles revues, quels résultats?

parceque avant d'affirmer, il faut prouver...

alors que l'effet du stress prolongé sur la santé et sur la résistance aux maladies n'a pas seulement été mesuré, mais ses mécanismes d'action sont connus et ont fait l'objet de nombreux travaux

canardos

 

Message(s) : 18

Inscription : 23 Déc 2005, 16:16

• Message privé

Haut

[canardos]

je suis d'autant plus étonné par tes affirmations sur le fait qu'on ne comprend absolument pas le lien entre effet placebo et maladie de parkinson que la parkinson est justement une des maladies ou l'on a le mieux compris les modalités d'action de l'effet placebo qui agit par le biais d'une libération accrue de dopamine dont le déficit est à l'orgine de la maladie.

les travaux en 2001 de Jon Stoessll Directeur du Pacific Parkinson’s Research Centre à l'universitéde British Columbia sur la liaison entre l'administration d'un placebo et la production accrue de dopamine par le cerveau lui ont meme valu un award

[Louis]

un résumé ICI

Une question a deux balles : fait on des essais en double aveugle en ce qui concerne l'oncologie, l'uminologie, ou la maladie de parkinson (et dans ce cas, a quoi ça sert, puisqu'il n'y a pas d'effet placébo) ?

[canardos]

j'ai simplement dit qu'en gros on connait les mécanismes neurophysiologiques par lesquels la confiance en un traitement agit sur la maladie ou la douleur.

le texte sur lequel tu nous renvoie parle de tout autre chose, à savoir les modalités de prise en compte de l'effet placebo et de sa mesure, y compris en terme éthiques, pas du tout les mécanismes par lesquels l'effet placebo agit....

encore une fois sur quoi te fondes tu pour dire que la maniere dont l'effet placebo agit sur le cancer les défenses immunitaires et la parkinson sont totalement mysterieux....

j'ai deja répondu que ces mécanismes étaient connus pour la parkinson.

Mais c'est aussi vrai pour le cancer et les défenses immunitaires dans la mesure ou cela fait des dizaines d'années qu'on sait qu'un stress prolongé et le bouleversement durable du systeme neurovégétatif entraine un effondrement de ces défenses immunitaire. Le simple fait de ne plus stresser parce qu'on a davantage confiance dan,s un traitement, meme si cette confiance est mal fondée, rétablit donc ces défenses immunitaires au moins en partie et aide à lutter contre le cancer....

meme chose pour la douleur amplifiée par l'angoisse...le role de l'amygdale dans cette amplification est bien connu....le fait que la douleur cesse d'etre amplifiée est vécu comme une diminution....

Tes trois exemples se retournent contre toi...

vraiment évite de répondre à coté de la plaque....

[canardos]

j'en profite pour mettre en quote un article (en anglias malheureusement sur la manière dont l'effet placebo agit sur la dépression et la maladie de parkinson, en augmentant la production par le cerveau d'opiodes et de dopamine:

The Scientist ::

[center]The Biological Basis of the Placebo Effect, [/center]

Dec. 9, 2002

Imaging technologies bring empirical rigor to the study of a mysterious medical phenomenon




Image: Getty Images


The placebo effect baffles patients, confounds clinicians and frustrates drug developers. Until now, relatively little empirical evidence existed for the biological mechanisms that underlie the effect. But recently, researchers have begun approaching the challenge with methodological rigor. This new area of investigation, straddling basic and clinical realms, has evolved largely because of the novel, detailed window of observation offered by modern imaging technologies. "What we're getting," says Harvard Medical School's Ted Kaptchuk, "is good preliminary evidence that describes the hardwiring of the placebo effect--that is, the impact of symbolic treatment, and how it's mediated through the neurobiology of the brain to produce physical effects in illnesses."
Understanding the biological basis of the placebo effect has potentially wide-ranging implications. Knowing the power of placebo may help scientists and philosophers to better characterize an age-old question. "We had this Cartesian split of mind and body. It's taken us a long time to get back to having ... due respect for mind-body effects," says Linda Engel, acting director, National Center for Complementary and Alternative Medicine's division of extramural research and training. Engel co-organized a workshop on the placebo that NCCAM held in November 2000. Based in part on conclusions from this workshop, the National Institutes of Health plans several new, soon-to-be-announced grants for the coming fiscal year.1

Philosophical implications aside, understanding the biology of placebo could also help improve healthcare and help the struggling pharmaceutical industry to develop better, more effective medications. "[The placebo effect] is crushing whole areas of drug development," says Kaptchuk, an assistant professor. While clinicians like him work to maximize people's self-healing capacity, the drug industry attempts to minimize the placebo effect to demonstrate the usefulness of medications.

"[Clinicians] have looked, particularly in psychiatric disorders, for factors that might predict response to placebo to try to minimize placebo response," says Gil Block, therapeutic area medical leader for the central nervous system, pain, and infectious disease at AstraZeneca. "To date, nothing has really been clearly identified." Factors include experiment site selection, different levels of quality-care follow-up, learning effects, and the increasing incidence of patients enrolling in multiple studies, according to Block. But isolating and eliminating those factors has proven extremely difficult. Block notes, for example, that it is not unexpected to have 50% of depression trials fail, meaning the placebo responders do as well or better than those taking active antidepressant medication.

PET AND THE PLACEBO:

Positron emission tomography (PET) scans show brain activity was most pronounced in the rostral anterior cingulate cortex (rACC) during the height of opioid treatment (left image). Post hoc analysis comparing the rACC in high-placebo responders (middle image) with that in nonresponders (right image) revealed no significant differences in the heat, pain, and placebo treatments between groups. (Reprinted with permission from Science, 295:1737-40, 2002.)


PAIN AND PLACEBO

Researchers have already reported intriguing findings. For years, opioids were known to play a significant role in the placebo effect in some contexts. In 1978, scientists demonstrated that an opioid blocker called naloxone could abolish the placebo effect in a pain experiment.2 A 2001 study demonstrated that the simple interaction between patient and practitioner has measurable effects in the brain. Researchers in Italy, led by Fabrizio Benedetti, found that "open" injections of analgesics (patient-witnessed) were significantly more effective and less variable than "hidden" injections (patients were ignorant of injections).3 Furthermore, they showed that by blocking the opioids, naloxone greatly reduces this open-injection placebo effect, suggesting that the therapist-patient interaction activates the endogenous opioid systems. "We are beginning to understand what happens in the patient's brain when he or she interacts with his or her therapist," says Benedetti, a physiology professor at the University of Turin Medical School.
Earlier this year, a Swedish research group caught the relationship of pain and placebo in action using positron emission tomography (PET), and showed that placebo and opioid analgesia may have a common neural mechanism.4 Nine subjects were exposed to standardized, brief, nonharmful, painful experiences. They received either no treatment or an injection of either placebo or analgesic. Subsequent PET scans indicated activation of the rostral anterior cingulate cortex for both treatments, though analgesic did provide more pain relief.

Swedish study leader Martin Ingvar says his research is partially motivated by shortcomings in patient care and a troubled drug industry. "In spite of more and more effective medicines, patients are complaining about less and less [therapeutic] effects," says Ingvar, a cognitive neurophysiology professor. "Explaining all drug effects by pure molecular mechanisms will underexpose the effects of drugs."4

PLACEBO, PARKINSON, AND DEPRESSION

But the opioid-placebo connection, though still largely a mystery, may turn out to be more straightforward than cases of other types of placebo effects. Another study, which appeared in May, also compared brain scans of persons on placebo versus those on active medication.5 But here, investigators didn't have a specific system like the opiate system to investigate.

Researchers gave 17 severely depressed men either placebo or fluoxetine (Prozac). Scans taken at one and six weeks showed that both groups exhibited increased activity in the cortex and decreased activity in limbic regions, but only patients given fluoxetine experienced changes in brain stem, striatum, and hippocampus. "Drug is placebo plus," explains lead author Helen Mayberg, a psychiatry and neurology professor, University of Toronto. The unique brain areas activated with an active drug aren't particularly surprising, says Mayberg, since they include known binding sites for fluoxetine and serotonin, a neurotransmitter that could have a role in placebo-treated depression.

In August 2001, Parkinson disease researchers reported that the release of another neurotransmitter, dopamine, may be triggered by the placebo effect.6 Again using PET, investigators provided in vivo evidence that endogenous dopamine was released in the striata of six patients with Parkinson disease. Senior author Jon Stoessl notes that the findings indicate the importance of carefully controlling for placebo in Parkinson disease, and that dopamine release could contribute to the placebo effect in other conditions.

Of course, as with any technique, imaging studies have limitations. The depression study, for example, could not rule out the possibility that patients got well as a result of spontaneous remission rather than the placebo effect. Theoretically, suspected placebo responders might have gotten well without any medication, active or not.

The work continues. Ingvar and his colleagues are studying the underlying biology of the effect in mood disorders and so-called modern living maladies like irritable bowel syndrome. A major future goal, says Benedetti, is to understand why not all subjects respond to placebo. "[These studies] begin to say that we cannot only look at a phenomenology of people responding to imitation treatments," explains Kaptchuk. "But we can actually look at the hardwiring that possibly accounts for what we're seeing. And that's an important phenomenon."

Eugene Russo is a contributing editor.

References
1. The science of the placebo: Toward an interdisciplinary research agenda, available online at http://placebo.nih.gov.

2. J.D. Levine et al., "Mechanism of placebo analgesia," Lancet, 2:654-7, 1978.

3. M. Amanzio et al., "Response variability to analgesics: a role for non-specific activation of endogenous opioids," Pain, 90:205-15, 2001.

4. P. Petrovic et al., "Placebo and opioid analgesia - Imaging a shared neuronal network," Science, 295:1737-40, 2002.

5. S. Mayberg et al., "The functional neuroanatomy of the placebo effect," American Journal of Psychiatry, 159:728-37, 2002.

6. R. de la Fuente-Fernandez et al., "Expectation and dopamine release: Mechanism of the placebo effect in Parkinson's disease," Science, 293:1164-6, 2001.

[canardos]

je donne un lien vers certains de ces articles pour ceux que ça interesse:

il faut acrobat reader:

Placebo and Opioid Analgesia


The Functional Neuroanatomy of the Placebo Effect

Neuropharmacological Dissection of Placebo Analgesia

The neural correlates of placebo effects: a disruption account

[Louis]

Franchement, canardos, j'ai toujours du mal avec tes méthodes ! D'abord, quelque chose qui me heurte : quand un scientifique dit qu'un certain phénomène pourrait etre expliqué de telle façon tu en déduit automatiquement que le phénomène EST expliqué !
Pourtant, c'est précis, un scientifique, non ?

[canardos]

j'ai simplement dit, preuves à l'appui, qu'une grande partie des mécanismes par lesquels l'effet placebo agissait étaient deja largement connus (bien sur il reste des choses à trouver) et que l'absence de connaissance des modalités d'action de cet effet placebo ne pouvait donc plus etre l'alibi qui permettait de justifier l'efficacité de tas de pseudosciences censées agir sur l'esprit....