Somatosensory training: a systematic review and meta-analysis with methodological considerations and clinical insights

Somatosensory training, which involves repetitive somatosensory stimulation, has been employed to enhance somatosensory performance by modulating excitability in the primary somatosensory cortex. This process, known as perceptual learning, can benefit stroke patients with somatosensory deficits. However, its effectiveness in both healthy individuals and stroke patients has not been thoroughly investigated. This systematic review and meta-analysis aimed to evaluate the effectiveness of somatosensory training in these groups. However, no eligible data on stroke patients were identified, excluding them from the analysis. In healthy participants, somatosensory training improved performance in 61.2% datasets, but this effect was observed only at the stimulated site. Additionally, it increased early somatosensory-evoked potential amplitudes in 76.9% of datasets at the stimulated site, with no effect on the non-stimulated site. Despite these moderate improvements, the risk of bias assessment revealed methodological concerns including randomization process, proper control conditions, blinding information, and missing data. The meta-analysis focused on the impact of somatosensory training on tactile two-point discrimination (TPD) in various factors, including different age groups, stimulus durations, stimulus frequencies, and stimulus types. A marked reduction in TPD threshold was observed at the stimulated finger post-training compared to pre-training, though there was a noticeable heterogeneity across studies. In contrast, no significant changes occurred at the non-stimulated fingers, and the subgroup analysis found no specific factors influencing TPD improvements. Although somatosensory training benefits healthy individuals, the variability and methodological concerns highlight the need for further high-quality research to optimize its use in treating somatosensory deficits in stroke patients.