Using Cranial Nerve Non-invasive Neuromodulation to Improve Pain and Upper Extremity Function After a Stroke

Following a stroke, survivors experience pain in the affected upper limb (UL) and residual weakness in the UL, which impacts their quality of life and performance of activities of daily living. Exercises is a key element of any rehabilitation program and is based on the capacity of reorganization of the central nervous system (called neuroplasticity) to allow overcoming stroke deficits. In addition, it is now recognized that in the chronic phase of a stroke, motor and functional gains are still possible following various training programs, such as a strength training program. To optimize the beneficial effects of exercise and potentiate neuroplasticity, non-invasive brain stimulation (NIBS) devices are increasingly used as a complementary therapy. Among NIBS, the most widely used technique is transcranial direct current stimulation (tDCS) that modulates cortical excitability and allows for clinical and functional gains, including recovering in UL motor function and pain. However, over 50% of individuals do not respond as expected to the combination of tDCS and rehabilitation exercises. This can be due to anatomical variability between individuals and electrical current shunting. Thus, to bypass these constraints, a new technique, called cranial nerve non-invasive neuromodulation (CN-NINM), is entering stroke rehabilitation. Unlike other NIBS such as tDCS, it generates a direct flow of neural impulses via tongue stimulation. Studies have shown that priming the motor cortex with CN-NINM during a training program can promote improved balance and gait and increased activation of the motor cortex. Until now, no studies have examined the use of CN-NINM for improving UL function and pain.

Goals: 1) To assess the feasibility of using CN-NINM in chronic stroke survivors; 2) To explore the effectiveness of CN-NINM in improving motor function and reducing pain of the affected upper limb in chronic stroke survivors.

Methods: In this feasibility pilot pre/post intervention study, 12 adults at the chronic phase of a stroke (>6 months) will be recruited. Sociodemographic and stroke-related variables (e.g., age, time since stroke) will be collected to confirm participant eligibility. Prior to training, participants will undergo a clinical evaluation of their affected UL as well as an evaluation of simulated pain at the affected UL. For the latter, the effect of CN-NINM on pain will be evaluated using a tonic thermal experimental pain paradigm. For this, a thermode (hot plate) will be applied to the forearm of the participants before and after a single 20-minute application of CN-NINM. On each occasion, thermal nociceptive stimuli will be induced for 2 minutes on the participants' forearm using the thermode. Although the temperature remains constant for the entire 2 minutes, the participant will be informed that the temperature may increase, decrease, or remain stable during the procedure. The participant will then, at all times, evaluate the intensity of the pain with a visual analogue scale connected to a computer (CoVAS: visual analogue scale from 0 to 100). Afterwards, the participants will take part in a 4-week training program of their affected UL (3X/week, 60-minute duration). During each training session, the CN-NINM will be applied for 20 minutes at an intensity tailored to each participant comfort.

Inclusion criteria

• Be ≥18 years old;
• Have had a single supratentorial stroke;
• Be in a chronic stroke phase (>6 months);
• Present motor recovery in the upper limb (UL) (Fugl-Meyer Stroke Assessment [FMA] score ≥20/66);
• Have completed any rehabilitation treatment.

Exclusion criteria

• A significant spasticity at the affected upper limb (score > 3 on the modified Ashworth scale);
• A major sensory deficit at the affected upper limb (a score ≤25/34 on the Nottingham Sensory Assessment and a score <6 on the evaluation of the vibration threshold);
• A presence of hemineglect (score ≥±0. 083 on the Line Cancellation test);
• An apraxia (score >2.5 on the Alexander Test);
• The presence of a neurological disorder other than a stroke;
• Concomitant orthopaedic problem at the affected UL;
• Cognitive impairment (Mini-Cog score <2/5) and
• Any contraindication to CN-NINM.