Transcranial Stimulation for Physiotherapy Optimisation - Chronic Low Back Pain (STOP-CLBP)

The main objective of this study is to investigate the effects of non-invasive brain stimulation (the so-called transcranial direct current stimulation ; tDCS) combined with an active physiotherapy program on the multidimensional impact of pain in patients with Chronic Low Back Pain (CLBP).

The secondary objectives are to compare the effects of these interventions on fear of movement, psycho-emotional state, function, functional connectivity of the left dorsolaterla prefrontal cortex (DLPFC) and erector spinae activity.

Participants will perform:

* 2 sessions including clinical assessments including questionnaires, brain activity assessment (with EEG), and back muscle activity assessment (with EMG)
* 9 interventional sessions of active physiotherapy combined with active or sham tDCS during 3 weeks (3 per week).

Investigators will compare active tDCS with sham tDCS (non active) to evaluate if active tDCS is more effective than sham tDCS.

Previous studies showed that transcranial Direct Current Stimulation (tDCS) targeting specific brain areas may offer novel treatment options in patients with chronic pain, in particular in chronic lower back pain (CLBP). Numerous tDCS trials have shown no evidence of moderate or severe adverse effects, highlighting tDCS as a safe, adequate tolerability and acceptability medical device.

However, several major limits remain before the investigators can start to design larger scale trials and more widespread clinical applications: the lack of knowledge on which brain region to target and about how neural activity is influenced by tDCS in this specific patient's population.

In consequence, the investigators do not know which setup of tDCS they can propose to CLBP patients. For instance, if the investigators manipulate brain interactions at the "wrong" tDCS setting, this may result in limited or no improvement of clinical deficits. Most existing randomized controlled trials (RCT) on tDCS treatment indeed show highly mixed effects which are likely due to incomplete understanding of tDCS-induced changes in brain and behavior. In addition, the majority of RCT have applied tDCS over the primary motor cortex (M1). Furthermore, the targeting of this brain region has recently been questioned and the dorsolateral prefrontal cortex (DLPFC) have been suggested as a valuable alternative. Knowing the mechanisms of action of tDCS based on the new rationale (i.e., tDCS targeting DLPFC) would allow us to define setup which are more likely to succeed.

The primary objective of this study is to investigate the effects of repeated sessions of tDCS combined with active physiotherapy on the multidimensional impact of pain at the end of the intervention compared to sham tDCS with active physiotherapy.

The secondary objectives are to compare the effects of these interventions on fear of movement, psycho-emotional state, function, functional connectivity of the left dorsolateral prefrontal cortex (DLPFC) and erector spinae activity.

The investigators hypothesise that tDCS combined with active physiotherapy will have a greater effect at the end of the intervention and at 3 and 6 months follow-up on all outcomes compared to sham tDCS combined with active physiotherapy.

Eligibility Criteria:
Inclusion Criteria:

* ability to give informed consent,
* ability to follow protocol instructions,
* diagnosis of Non Specific Chronic Low Back Pain ≥12 weeks,
* low back pain with or without radiation to the knee,
* average pain of the previous week ≥ 3 on the VAS (Visual Analogue Scale).
* have sufficient cognitive ability to fill in the various questionnaires (Level B2 French),

Exclusion Criteria:

* herniectomy within the last 6 months,
* lumbar spinal surgery with material (e.g. prosthesis, spondylodesis),
* sensory or motor deficit of a lower limb,
* radiant pain in the lower limb beyond the knee,
* neuropathic pain (according to the dn4 questionnaire),
* diagnosis of an inflammatory rheumatic disease (e.g. rheumatoid arthritis, spondyloarthropathy),
* diagnosis of a chronic generalized pain syndromee of fibromyalgia,
* pregnancy,
* presence of neurological or neuropsychiatric disorders,
* have epilepsy or a recent or severe head injury,
* metal implant in the skull (excluding fillings),
* presence of a pacemaker,
* unhealed wound or skin disease on the skull (electrode contact area)