Hand choice is an unconscious decision we make many times throughout the day, like when reaching for an item such as a cup or carrying out various tasks. This decision is shaped by information related to the target, including its position, form, and orientation. However, when the factors concerning each hand are equivalent, the chance of using either hand becomes balanced. Recent research indicates that in such uncertain scenarios, hand choices can be influenced by what we know prior to the target’s appearance. One factor that seems to affect this is prior somatosensory stimulation on one wrist, which may alter brain activity, increasing the chances of selecting the stimulated hand. This suggests an interesting link between sensory input and decisions regarding movement.
Hand choice is an unconscious decision frequently made in daily life, whether it’s reaching for an object such as a cup or performing any other task. This decision is influenced by target-related information, such as the location, shape, and orientation of the object. However, the selection probability for each hand reaches equilibrium when the target-related factors are similar for the left and right hands. Recent findings suggest that hand choice in such ambiguous situations is biased by prior information before the target presentation. One such factor is prior somatosensory stimulation on one wrist, which likely affects brain activity, enhancing the likelihood of choosing the stimulated hand. This phenomenon highlights an intriguing connection between sensory input and motor decisions.
A team of researchers led by Dr. Kento Hirayama, from Waseda University and the University of Southern California, along with Dr. Rieko Osu and Dr. Toru Takahashi from Waseda University and the Laureate Institute for Brain Research, investigated how wrist somatosensory stimulation can affect hand choice decisions. Their study shows that applying sensory stimuli to the median and ulnar nerves of the wrist tends to influence subsequent motor decisions, making it more likely for participants to use the stimulated hand when they need to choose quickly for a target. The feeling of stimulation seems to affect the brain’s motor decision-making system, guiding individuals subtly toward their stimulated hand. The outcomes of the study were published in the journal Scientific Reports on September 30, 2024.
For their experiments, the researchers had healthy participants engage in hand-choice tasks while receiving one-sided wrist somatosensory stimulation at intervals of 0, 300, or 600 milliseconds prior to the target’s appearance. The findings showed a notable trend where participants were more inclined to use the stimulated hand for targets located closer to the center, where making a choice based on target information was challenging. In areas where target information was clearer, participants generally favored the hand corresponding to the target, regardless of stimulation. These results indicate that peripheral sensory input can modify motor decisions, especially in ambiguous circumstances regarding hand selection, revealing a previously overlooked significance of somatosensory feedback in directing hand choices. Moreover, unilateral wrist electrical stimulation resulted in quicker reaction times compared to bilateral wrist stimulation and no stimulation, indicating that focused sensory input can enhance the decision-making process.
“This research could potentially open new therapeutic avenues to facilitate the use of the paretic hand, improving function in individuals with motor impairments, such as stroke survivors,” says Hirayama. “By applying controlled somatosensory stimulation, it may be possible to bias motor decisions in ways that encourage more effective use of the affected hand, which could support recovery and rehabilitation.”
Alongside its clinical significance, this study also enhances our understanding of the essential processes involved in making motor decisions. By demonstrating that the brain integrates sensory information from the body to dictate movement, this research enriches our comprehension of how the brain governs motion and reacts to external stimuli.
As neurorehabilitation advances, looking into how sensory signals can sway motor choices may lead to more personalized and effective treatment options for those with motor disabilities.
“Overall, our study lays the foundation for the development of a compact, lightweight, affordable, and easily accessible rehabilitation device that can work alongside conventional rehabilitation methods to boost motor function recovery,” concludes Hirayama.
