Chronic low back leads to a significant socio-economic burden. It is associated with physical and psychosocial deconditioning. Even a short "nature experience" has positive effects on the affective and cognitive factors involved in chronic pain. In the brain, the anterior cingulate cortex plays an important role in both pain and emotions. Exposure to a natural environment may decrease activation of the anterior cingulate cortex.

The main objective of this study is to evaluate the effectiveness of therapeutic horticulture on the decrease of activation of the anterior cingulate cortex in people with chronic low back pain participating in 2 sessions of 90 minutes of therapeutic horticulture and 2 sessions of 90 minutes of handiwork.

The investigators hypothesize that therapeutic horticulture may reduce the activation of the anterior cingulate cortex. The effects of therapeutic horticulture may be mediated through the double exposure to both nature and physical activity.

Non-specific low back pain is the first cause of years lived with a disability in the world. The network of biological, psychological and social contributors to chronic low back pain is complex. Within this network, physical and mental deconditioning are a key point and a privileged therapeutic target of multidisciplinary training programs.

Physical exercise improves pain and function in people with chronic low back pain. Nevertheless, its benefits decrease if it is not practiced regularly. The pleasure doing physical exercises and the possibility of integrating them into daily life are important factors of adherence. Gardening meets well the expectations of the physical treatment of chronic low back pain as it involves exercises aiming to increase spinal flexibility, strength and endurance of spine and lower limbs muscles, proprioception. Gardening is associated with the notion of pleasure and can be practiced in a group thus promoting the social bond. Moreover, therapeutic horticulture is suitable for the long term and can even be practiced in urban environment. Painful sensations are modulated by the affective and emotional state. Within the neuromatrix of pain, the cortex plays an important role in encoding pain and associated emotions. Several studies suggest an impact on several physiological parameters of an "experience of nature", even on a short time. A randomized controlled trial compared in 38 healthy volunteers, the effect of a 90-minute walk in nature (forest) and in urban setting (city), on the activation of the anterior cingulate cortex (specifically its subgenual part) assessed using variation in blood perfusion on MRI, and on rumination, assessed using a self-administered questionnaire. The authors showed that neural activation in the subgenual prefrontal cortex and rumination scores were lower in the group of healthy volunteers exposed to nature. Little is known about the impact of a "nature experience" on chronic low back pain. A non-randomized controlled study has shown that adding 7 sessions of therapeutic horticulture to a standardized pain management program improved health status, anxiety and coping strategies in patients with chronic pain.

By its nature and physical component, therapeutic horticulture could constitute a non-pharmacological accurate intervention in people with chronic low back pain, targeting both the neurobiological and physical aspects of deconditioning syndrome. Therapeutic horticulture was introduced in October 2017 in the multidisciplinary training program dedicated to chronic low back pain in our department. However, its effects have not yet been evaluated.

Inclusion Criteria:

• Adults of working-age (18 to 70 years),
• Chronic non-specific low back pain,
• Patient waiting for a short functional restoration program in the rehabilitation department,
• Failure of first-line treatment,
• Up-to-date DTP vaccination,
• Patients able to walk 2 km,
• Health insurance,
• Informed written consent.

Exclusion Criteria:

• Specific low back pain,
• Contraindication to MRI,
• Current stoppage or for more than 3 months during the last year,
• Lack of paid employment,
• Participation in another research on low back pain,
• Inability to fluently speak and/or read French language,
• Free state medical assistance
• People under tutorship or curatorship, and protected adults.