Study of Cognitive and Behavioural Biases in People With Idiopathic Environmental Intolerance (IEI) Versus Healthy Controls

Symptoms that patients attribute to the environment when no environmental cause can be identified are known as "idiopathic environmental intolerance" (IEI). IEI is often associated with a major psychological and socio-professional impact. Specific diagnostic tools and evidence-based treatment programs are still lacking. As a result, IEI patients often feel left behind by physicians and public health policies.

A number of environmental agents are singled out by IEI sufferers, including chemicals (cleaning products, tobacco smoke), electromagnetic fields generated by cell phones and base stations, air conditioning and infrasound emitted by wind turbines. Patients hold one or more of these environmental agents responsible for a very wide range of chronic, non-specific physical symptoms such as diffuse pain, fatigue, dizziness, dyspnoea, hot flushes, nausea, tinnitus or palpitations, but also cognitive symptoms such as loss of memory or concentration. However, the medical examination of IEI patients shows no evidence of bodily dysfunction.

Furthermore, numerous exposure studies have shown that environmental agents did not alter the biological parameters of IEI patients, that patients could not reliably distinguish between real and fictitious exposures, and that they only presented symptoms when they thought the exposure was real, whether this was true or not. This suggests that IEI symptoms can be considered "functional", resulting from an alteration in the way the body is felt rather than from injury to the body itself. Recently, several authors including Lemogne and Pitron have proposed a cognitive model of body awareness and more specifically of functional physical symptoms.This model is part of a Bayesian understanding of brain function, which is increasingly seen as a process underlying all perceptual experiences.From this perspective, bodily experiences are the result of probabilistic calculations Two sources of information are integrated, weighted by their reliability (accuracy) with regard to the current context: the body's sensory signals on the one hand (i.e. peripheral nerve inputs) and "priors" about the body on the other (i.e. pre-existing information from previous bodily experiences, beliefs about the body, emotions, etc.). In functional physical symptoms, it has been suggested that priors override the body's sensory signals, thus skewing bodily perception.This would be the consequence of an imbalance between low-precision sensory signals on the one hand, and high-precision priors on the other.

In line with this model, Van den Bergh and Witthöft have proposed an understanding of IEI as arising from a nocebo effect.Here, we propose a research project with patients suffering from IEI to test and validate this Bayesian theoretical model of IEI, the main study C22-19, BELIEFS which is currently recruiting.

This ancillary study, C24-26 BELIEFS-VS, enables us to include a population of healthy volunteers whom we will compare with the IEI patients in the main C22-19 BELIEFS study.