Effects of Augmented Reality (AR) and Transcranial Direct Current Stimulation (tDCS) on Balance and Postural Control in Chronic Stroke Survivors

Stroke remains one of the leading causes of death and long-term disability worldwide, with survivors often experiencing persistent motor and sensory impairments that significantly impact their quality of life. In 2020, it caused about 6.6 million deaths and ranked third for disability-adjusted life-years (DALYs) lost, with the burden rising fastest in low- and middle-income countries. Even after surviving a stroke, many people up to 83% continue to have problems with balance and controlling their posture. These difficulties make daily activities harder, increase the chance of falling, and lower their quality of life.

Balance and postural control are important because they help us stay steady and move safely. After a stroke, these abilities often get damaged because the brain areas that control movement and coordination are affected. People who have had a stroke may walk slower, sway more when standing, and have trouble with tasks like standing up or turning around. Balance impairments manifest as altered body weight distribution patterns, reduced weight-bearing capacity through the affected limb, and diminished postural stability, leading to increased fall risk and decreased participation in activities of daily living. In fact, only a small number of stroke survivors can walk freely without help, and many experiences falls more often than people without stroke. Stroke survivors fall more than twice as often as healthy controls, with balance impairments leading to decreased participation in activities of daily living, fear of falling, and social isolation. Augmented Reality (AR) technology has emerged as a promising intervention for stroke rehabilitation. AR systems provide immersive and interactive virtual environments that can enhance motor rehabilitation through collaborative stimulation of multiple sensory channels, including visual, auditory, and proprioceptive feedback. This multimodal approach facilitates repetitive practice with real-time feedback and encouragement, potentially enhancing rehabilitation effectiveness through increased engagement and motivation. Recent systematic reviews and meta-analyses have demonstrated that AR-based interventions can significantly improve both upper and lower limb function in stroke patients.

Studies have shown that AR training leads to improvements in obstacle avoidance, balance performance, and functional mobility compared to conventional rehabilitation alone. The technology's ability to provide personalized, adaptive training environments allows for customization based on individual patient needs and capabilities, potentially optimizing therapeutic outcomes. The integration of AR with traditional rehabilitation methods has shown particular promise, with combined approaches yielding better functional outcomes than either intervention alone.

Transcranial direct current stimulation (tDCS) represents a non-invasive neuromodulation technique that has gained considerable attention in stroke rehabilitation for its ability to modify cortical excitability and potentially enhance neuroplasticity. By delivering low-intensity electrical current through scalp electrodes, tDCS can modulate neuronal activity in targeted brain regions, with anodal stimulation typically increasing cortical excitability and cathodal stimulation having inhibitory effects. Research has demonstrated that tDCS can improve various aspects of motor function in stroke patients, including balance and postural control. Studies have shown immediate and sustained effects of tDCS on balance parameters, with improvements in weight-bearing distribution, postural stability, and functional mobility measures.

Cerebellar tDCS, in particular, has shown superior effects compared to cerebral stimulation for improving balance and gait function in chronic stroke patients. The mechanisms underlying tDCS effects involve modulation of cortical and spinal neuronal circuits involved in movement control. Meta-analyses have indicated that tDCS can provide significant benefits for balance outcomes in stroke patients, although the quality of evidence remains variable and further research is needed to optimize stimulation parameters and patient selection criteria.